38
1 WB2414-Mechatronic System Design 2013-2014 1 Delft University of Technology Mechatronic system design Mechatronic system design wb24142013/2014 Course part 5 Prof.ir. R.H.Munnig Schmidt Mechatronic System Design Motion control WB2414-Mechatronic System Design 2013-2014 2 Delft University of Technology Lecture outline: What did you learn about PID ‐ motion control so far? Introduction to motion control Feedforward control of piezoelectric scanner PD – feedback control of CDplayer Sensitivity Stability and Robustness PID ‐ feedback control of massspring system PID ‐ feedback control of magnetic bearing How to deal with difficult plants having multiple eigenmodes

Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

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Page 1: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

1

WB2414-Mechatronic System Design 2013-2014 1DelftUniversity ofTechnology

Mechatronic system design

Mechatronic system design wb2414‐20132014

Course part 5

Profir RHMunnig SchmidtMechatronic System Design

Motion control

WB2414-Mechatronic System Design 2013-2014 2DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

2

WB2414-Mechatronic System Design 2013-2014 3DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 4DelftUniversity ofTechnology

Motion Control

bull Control the trajectory of a machine

bull Position control

bull Velocity control (eg scanning)

bull Path planning

bull Disturbance rejection (vibrations from environment imperfections of the guidance system hellip)

3

WB2414-Mechatronic System Design 2013-2014 5DelftUniversity ofTechnology

A walk around the control loop

Plant G(s)

sensorAD

DAFeedbackPre‐filter

Feedforward

Guidancesignal r

-

Input disturbance

Output disturbance

Processdisturbance

Sensor disturbance

Output

EnergyInformation

WB2414-Mechatronic System Design 2013-2014 6DelftUniversity ofTechnology

The plant is the process that needs to be controlled

The successive order is fixed

4

WB2414-Mechatronic System Design 2013-2014 7DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 8DelftUniversity ofTechnology

A walk around the control loop Feedforward control

bull requires no sensorbull predictable (if reference is known)

(faster than pure feedback)bull cannot introduce instabilitybull no feeding back of sensor noise

bull plant has to be stablebull no compensation of model uncertaintiesbull can only compensate for distur‐bances that are known (measured)

5

WB2414-Mechatronic System Design 2013-2014 9DelftUniversity ofTechnology

Feedforward control of a piezoelectric scanning unit

Stefan Kuiper TUDTNO

WB2414-Mechatronic System Design 2013-2014 10DelftUniversity ofTechnology

Model-based open-loop feedforward control of the piezo scanner

Plant transfer function

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

Problem is low damped first eigenmode

6

WB2414-Mechatronic System Design 2013-2014 11DelftUniversity ofTechnology

Model based open-loop feedforward control of the piezo scanner

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

2 2f 1 1

ff ff f21

2( ) ( ) ( )

s sC s G s C s C

Plant transfer function

Compensate dynamics by feedforward controller (pole‐zero cancellation)

Such a controller is unfortunately not realisable (infinite gain at infinite frequencies)

WB2414-Mechatronic System Design 2013-2014 12DelftUniversity ofTechnology

In practice it can only be used to increase the damping

2 2 2 2f 1 1 f 1 1

ff ff2 2 21 1 1

2 2( ) ( )

2middot1middot

s s s sC s C s

s s

Add a well damped ζ=1 second order transfer function

And with an additional first order low pass filter against noise

Which combines into

2 2

f 1 1ff 2 2

1 1 1

2( )

( ) 2

s sC s

s s s

2 2f f 1 1

tff ff 2 2 2 2f 1 1 1 1 1

f2 2

1 1 1

( 2 )( ) ( ) ( )

( 2 ) ( ) 2

( ) 2

C s sG s G s C s

s s s s s

C

s s s

7

WB2414-Mechatronic System Design 2013-2014 13DelftUniversity ofTechnology

Resulting response

f

t ff ff 2 21 1 1

( ) ( ) ( )( ) 2

CG s G s C s

s s s

WB2414-Mechatronic System Design 2013-2014 14DelftUniversity ofTechnology

Triangular scanning movement

Withoutpole-zerocancellation

Withpole-zerocancellation

8

WB2414-Mechatronic System Design 2013-2014 15DelftUniversity ofTechnology

Second method input shapingWithout

With

WB2414-Mechatronic System Design 2013-2014 16DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

9

WB2414-Mechatronic System Design 2013-2014 17DelftUniversity ofTechnology

A walk around the control loop Feedback control

bull sensor requiredbull slower than FF (error has to occur first) bull (sensor) noise is also fed backbull can introduce instability

(also of open‐loop stable systems)

bull can stabilize unstable systemsbull can suppress disturbancesbull can handle uncertainties

Plant

G(s)Feedback

Cfb (s)Pre‐Filter

F(s) _

e ur y

Measurement

M(s)

rf

Input disturbance

Output disturbance

Process disturbance

x

Sensor disturbance

v

WB2414-Mechatronic System Design 2013-2014 18DelftUniversity ofTechnology

Active stiffness by feedback in a CD player (from Dynamics lecture)

bull200 μm radial vibrations at 25 Hz

bullMass lens 10 10‐3 kg

bullMax radial error 02 μm

6r

0 6r

r0

2 2 5r 0

1middot10

ˆ 200 10 25 800

0

2

2 10

4 25 Nm

xf f Hz

kf k mf

m

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 2: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

2

WB2414-Mechatronic System Design 2013-2014 3DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 4DelftUniversity ofTechnology

Motion Control

bull Control the trajectory of a machine

bull Position control

bull Velocity control (eg scanning)

bull Path planning

bull Disturbance rejection (vibrations from environment imperfections of the guidance system hellip)

3

WB2414-Mechatronic System Design 2013-2014 5DelftUniversity ofTechnology

A walk around the control loop

Plant G(s)

sensorAD

DAFeedbackPre‐filter

Feedforward

Guidancesignal r

-

Input disturbance

Output disturbance

Processdisturbance

Sensor disturbance

Output

EnergyInformation

WB2414-Mechatronic System Design 2013-2014 6DelftUniversity ofTechnology

The plant is the process that needs to be controlled

The successive order is fixed

4

WB2414-Mechatronic System Design 2013-2014 7DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 8DelftUniversity ofTechnology

A walk around the control loop Feedforward control

bull requires no sensorbull predictable (if reference is known)

(faster than pure feedback)bull cannot introduce instabilitybull no feeding back of sensor noise

bull plant has to be stablebull no compensation of model uncertaintiesbull can only compensate for distur‐bances that are known (measured)

5

WB2414-Mechatronic System Design 2013-2014 9DelftUniversity ofTechnology

Feedforward control of a piezoelectric scanning unit

Stefan Kuiper TUDTNO

WB2414-Mechatronic System Design 2013-2014 10DelftUniversity ofTechnology

Model-based open-loop feedforward control of the piezo scanner

Plant transfer function

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

Problem is low damped first eigenmode

6

WB2414-Mechatronic System Design 2013-2014 11DelftUniversity ofTechnology

Model based open-loop feedforward control of the piezo scanner

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

2 2f 1 1

ff ff f21

2( ) ( ) ( )

s sC s G s C s C

Plant transfer function

Compensate dynamics by feedforward controller (pole‐zero cancellation)

Such a controller is unfortunately not realisable (infinite gain at infinite frequencies)

WB2414-Mechatronic System Design 2013-2014 12DelftUniversity ofTechnology

In practice it can only be used to increase the damping

2 2 2 2f 1 1 f 1 1

ff ff2 2 21 1 1

2 2( ) ( )

2middot1middot

s s s sC s C s

s s

Add a well damped ζ=1 second order transfer function

And with an additional first order low pass filter against noise

Which combines into

2 2

f 1 1ff 2 2

1 1 1

2( )

( ) 2

s sC s

s s s

2 2f f 1 1

tff ff 2 2 2 2f 1 1 1 1 1

f2 2

1 1 1

( 2 )( ) ( ) ( )

( 2 ) ( ) 2

( ) 2

C s sG s G s C s

s s s s s

C

s s s

7

WB2414-Mechatronic System Design 2013-2014 13DelftUniversity ofTechnology

Resulting response

f

t ff ff 2 21 1 1

( ) ( ) ( )( ) 2

CG s G s C s

s s s

WB2414-Mechatronic System Design 2013-2014 14DelftUniversity ofTechnology

Triangular scanning movement

Withoutpole-zerocancellation

Withpole-zerocancellation

8

WB2414-Mechatronic System Design 2013-2014 15DelftUniversity ofTechnology

Second method input shapingWithout

With

WB2414-Mechatronic System Design 2013-2014 16DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

9

WB2414-Mechatronic System Design 2013-2014 17DelftUniversity ofTechnology

A walk around the control loop Feedback control

bull sensor requiredbull slower than FF (error has to occur first) bull (sensor) noise is also fed backbull can introduce instability

(also of open‐loop stable systems)

bull can stabilize unstable systemsbull can suppress disturbancesbull can handle uncertainties

Plant

G(s)Feedback

Cfb (s)Pre‐Filter

F(s) _

e ur y

Measurement

M(s)

rf

Input disturbance

Output disturbance

Process disturbance

x

Sensor disturbance

v

WB2414-Mechatronic System Design 2013-2014 18DelftUniversity ofTechnology

Active stiffness by feedback in a CD player (from Dynamics lecture)

bull200 μm radial vibrations at 25 Hz

bullMass lens 10 10‐3 kg

bullMax radial error 02 μm

6r

0 6r

r0

2 2 5r 0

1middot10

ˆ 200 10 25 800

0

2

2 10

4 25 Nm

xf f Hz

kf k mf

m

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 3: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

3

WB2414-Mechatronic System Design 2013-2014 5DelftUniversity ofTechnology

A walk around the control loop

Plant G(s)

sensorAD

DAFeedbackPre‐filter

Feedforward

Guidancesignal r

-

Input disturbance

Output disturbance

Processdisturbance

Sensor disturbance

Output

EnergyInformation

WB2414-Mechatronic System Design 2013-2014 6DelftUniversity ofTechnology

The plant is the process that needs to be controlled

The successive order is fixed

4

WB2414-Mechatronic System Design 2013-2014 7DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 8DelftUniversity ofTechnology

A walk around the control loop Feedforward control

bull requires no sensorbull predictable (if reference is known)

(faster than pure feedback)bull cannot introduce instabilitybull no feeding back of sensor noise

bull plant has to be stablebull no compensation of model uncertaintiesbull can only compensate for distur‐bances that are known (measured)

5

WB2414-Mechatronic System Design 2013-2014 9DelftUniversity ofTechnology

Feedforward control of a piezoelectric scanning unit

Stefan Kuiper TUDTNO

WB2414-Mechatronic System Design 2013-2014 10DelftUniversity ofTechnology

Model-based open-loop feedforward control of the piezo scanner

Plant transfer function

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

Problem is low damped first eigenmode

6

WB2414-Mechatronic System Design 2013-2014 11DelftUniversity ofTechnology

Model based open-loop feedforward control of the piezo scanner

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

2 2f 1 1

ff ff f21

2( ) ( ) ( )

s sC s G s C s C

Plant transfer function

Compensate dynamics by feedforward controller (pole‐zero cancellation)

Such a controller is unfortunately not realisable (infinite gain at infinite frequencies)

WB2414-Mechatronic System Design 2013-2014 12DelftUniversity ofTechnology

In practice it can only be used to increase the damping

2 2 2 2f 1 1 f 1 1

ff ff2 2 21 1 1

2 2( ) ( )

2middot1middot

s s s sC s C s

s s

Add a well damped ζ=1 second order transfer function

And with an additional first order low pass filter against noise

Which combines into

2 2

f 1 1ff 2 2

1 1 1

2( )

( ) 2

s sC s

s s s

2 2f f 1 1

tff ff 2 2 2 2f 1 1 1 1 1

f2 2

1 1 1

( 2 )( ) ( ) ( )

( 2 ) ( ) 2

( ) 2

C s sG s G s C s

s s s s s

C

s s s

7

WB2414-Mechatronic System Design 2013-2014 13DelftUniversity ofTechnology

Resulting response

f

t ff ff 2 21 1 1

( ) ( ) ( )( ) 2

CG s G s C s

s s s

WB2414-Mechatronic System Design 2013-2014 14DelftUniversity ofTechnology

Triangular scanning movement

Withoutpole-zerocancellation

Withpole-zerocancellation

8

WB2414-Mechatronic System Design 2013-2014 15DelftUniversity ofTechnology

Second method input shapingWithout

With

WB2414-Mechatronic System Design 2013-2014 16DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

9

WB2414-Mechatronic System Design 2013-2014 17DelftUniversity ofTechnology

A walk around the control loop Feedback control

bull sensor requiredbull slower than FF (error has to occur first) bull (sensor) noise is also fed backbull can introduce instability

(also of open‐loop stable systems)

bull can stabilize unstable systemsbull can suppress disturbancesbull can handle uncertainties

Plant

G(s)Feedback

Cfb (s)Pre‐Filter

F(s) _

e ur y

Measurement

M(s)

rf

Input disturbance

Output disturbance

Process disturbance

x

Sensor disturbance

v

WB2414-Mechatronic System Design 2013-2014 18DelftUniversity ofTechnology

Active stiffness by feedback in a CD player (from Dynamics lecture)

bull200 μm radial vibrations at 25 Hz

bullMass lens 10 10‐3 kg

bullMax radial error 02 μm

6r

0 6r

r0

2 2 5r 0

1middot10

ˆ 200 10 25 800

0

2

2 10

4 25 Nm

xf f Hz

kf k mf

m

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 4: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

4

WB2414-Mechatronic System Design 2013-2014 7DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 8DelftUniversity ofTechnology

A walk around the control loop Feedforward control

bull requires no sensorbull predictable (if reference is known)

(faster than pure feedback)bull cannot introduce instabilitybull no feeding back of sensor noise

bull plant has to be stablebull no compensation of model uncertaintiesbull can only compensate for distur‐bances that are known (measured)

5

WB2414-Mechatronic System Design 2013-2014 9DelftUniversity ofTechnology

Feedforward control of a piezoelectric scanning unit

Stefan Kuiper TUDTNO

WB2414-Mechatronic System Design 2013-2014 10DelftUniversity ofTechnology

Model-based open-loop feedforward control of the piezo scanner

Plant transfer function

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

Problem is low damped first eigenmode

6

WB2414-Mechatronic System Design 2013-2014 11DelftUniversity ofTechnology

Model based open-loop feedforward control of the piezo scanner

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

2 2f 1 1

ff ff f21

2( ) ( ) ( )

s sC s G s C s C

Plant transfer function

Compensate dynamics by feedforward controller (pole‐zero cancellation)

Such a controller is unfortunately not realisable (infinite gain at infinite frequencies)

WB2414-Mechatronic System Design 2013-2014 12DelftUniversity ofTechnology

In practice it can only be used to increase the damping

2 2 2 2f 1 1 f 1 1

ff ff2 2 21 1 1

2 2( ) ( )

2middot1middot

s s s sC s C s

s s

Add a well damped ζ=1 second order transfer function

And with an additional first order low pass filter against noise

Which combines into

2 2

f 1 1ff 2 2

1 1 1

2( )

( ) 2

s sC s

s s s

2 2f f 1 1

tff ff 2 2 2 2f 1 1 1 1 1

f2 2

1 1 1

( 2 )( ) ( ) ( )

( 2 ) ( ) 2

( ) 2

C s sG s G s C s

s s s s s

C

s s s

7

WB2414-Mechatronic System Design 2013-2014 13DelftUniversity ofTechnology

Resulting response

f

t ff ff 2 21 1 1

( ) ( ) ( )( ) 2

CG s G s C s

s s s

WB2414-Mechatronic System Design 2013-2014 14DelftUniversity ofTechnology

Triangular scanning movement

Withoutpole-zerocancellation

Withpole-zerocancellation

8

WB2414-Mechatronic System Design 2013-2014 15DelftUniversity ofTechnology

Second method input shapingWithout

With

WB2414-Mechatronic System Design 2013-2014 16DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

9

WB2414-Mechatronic System Design 2013-2014 17DelftUniversity ofTechnology

A walk around the control loop Feedback control

bull sensor requiredbull slower than FF (error has to occur first) bull (sensor) noise is also fed backbull can introduce instability

(also of open‐loop stable systems)

bull can stabilize unstable systemsbull can suppress disturbancesbull can handle uncertainties

Plant

G(s)Feedback

Cfb (s)Pre‐Filter

F(s) _

e ur y

Measurement

M(s)

rf

Input disturbance

Output disturbance

Process disturbance

x

Sensor disturbance

v

WB2414-Mechatronic System Design 2013-2014 18DelftUniversity ofTechnology

Active stiffness by feedback in a CD player (from Dynamics lecture)

bull200 μm radial vibrations at 25 Hz

bullMass lens 10 10‐3 kg

bullMax radial error 02 μm

6r

0 6r

r0

2 2 5r 0

1middot10

ˆ 200 10 25 800

0

2

2 10

4 25 Nm

xf f Hz

kf k mf

m

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 5: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

5

WB2414-Mechatronic System Design 2013-2014 9DelftUniversity ofTechnology

Feedforward control of a piezoelectric scanning unit

Stefan Kuiper TUDTNO

WB2414-Mechatronic System Design 2013-2014 10DelftUniversity ofTechnology

Model-based open-loop feedforward control of the piezo scanner

Plant transfer function

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

Problem is low damped first eigenmode

6

WB2414-Mechatronic System Design 2013-2014 11DelftUniversity ofTechnology

Model based open-loop feedforward control of the piezo scanner

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

2 2f 1 1

ff ff f21

2( ) ( ) ( )

s sC s G s C s C

Plant transfer function

Compensate dynamics by feedforward controller (pole‐zero cancellation)

Such a controller is unfortunately not realisable (infinite gain at infinite frequencies)

WB2414-Mechatronic System Design 2013-2014 12DelftUniversity ofTechnology

In practice it can only be used to increase the damping

2 2 2 2f 1 1 f 1 1

ff ff2 2 21 1 1

2 2( ) ( )

2middot1middot

s s s sC s C s

s s

Add a well damped ζ=1 second order transfer function

And with an additional first order low pass filter against noise

Which combines into

2 2

f 1 1ff 2 2

1 1 1

2( )

( ) 2

s sC s

s s s

2 2f f 1 1

tff ff 2 2 2 2f 1 1 1 1 1

f2 2

1 1 1

( 2 )( ) ( ) ( )

( 2 ) ( ) 2

( ) 2

C s sG s G s C s

s s s s s

C

s s s

7

WB2414-Mechatronic System Design 2013-2014 13DelftUniversity ofTechnology

Resulting response

f

t ff ff 2 21 1 1

( ) ( ) ( )( ) 2

CG s G s C s

s s s

WB2414-Mechatronic System Design 2013-2014 14DelftUniversity ofTechnology

Triangular scanning movement

Withoutpole-zerocancellation

Withpole-zerocancellation

8

WB2414-Mechatronic System Design 2013-2014 15DelftUniversity ofTechnology

Second method input shapingWithout

With

WB2414-Mechatronic System Design 2013-2014 16DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

9

WB2414-Mechatronic System Design 2013-2014 17DelftUniversity ofTechnology

A walk around the control loop Feedback control

bull sensor requiredbull slower than FF (error has to occur first) bull (sensor) noise is also fed backbull can introduce instability

(also of open‐loop stable systems)

bull can stabilize unstable systemsbull can suppress disturbancesbull can handle uncertainties

Plant

G(s)Feedback

Cfb (s)Pre‐Filter

F(s) _

e ur y

Measurement

M(s)

rf

Input disturbance

Output disturbance

Process disturbance

x

Sensor disturbance

v

WB2414-Mechatronic System Design 2013-2014 18DelftUniversity ofTechnology

Active stiffness by feedback in a CD player (from Dynamics lecture)

bull200 μm radial vibrations at 25 Hz

bullMass lens 10 10‐3 kg

bullMax radial error 02 μm

6r

0 6r

r0

2 2 5r 0

1middot10

ˆ 200 10 25 800

0

2

2 10

4 25 Nm

xf f Hz

kf k mf

m

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 6: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

6

WB2414-Mechatronic System Design 2013-2014 11DelftUniversity ofTechnology

Model based open-loop feedforward control of the piezo scanner

2f f 1

2 2 2f 1 1

f21 1

( ) 2

2 1

C CG s

s s s s

2 2f 1 1

ff ff f21

2( ) ( ) ( )

s sC s G s C s C

Plant transfer function

Compensate dynamics by feedforward controller (pole‐zero cancellation)

Such a controller is unfortunately not realisable (infinite gain at infinite frequencies)

WB2414-Mechatronic System Design 2013-2014 12DelftUniversity ofTechnology

In practice it can only be used to increase the damping

2 2 2 2f 1 1 f 1 1

ff ff2 2 21 1 1

2 2( ) ( )

2middot1middot

s s s sC s C s

s s

Add a well damped ζ=1 second order transfer function

And with an additional first order low pass filter against noise

Which combines into

2 2

f 1 1ff 2 2

1 1 1

2( )

( ) 2

s sC s

s s s

2 2f f 1 1

tff ff 2 2 2 2f 1 1 1 1 1

f2 2

1 1 1

( 2 )( ) ( ) ( )

( 2 ) ( ) 2

( ) 2

C s sG s G s C s

s s s s s

C

s s s

7

WB2414-Mechatronic System Design 2013-2014 13DelftUniversity ofTechnology

Resulting response

f

t ff ff 2 21 1 1

( ) ( ) ( )( ) 2

CG s G s C s

s s s

WB2414-Mechatronic System Design 2013-2014 14DelftUniversity ofTechnology

Triangular scanning movement

Withoutpole-zerocancellation

Withpole-zerocancellation

8

WB2414-Mechatronic System Design 2013-2014 15DelftUniversity ofTechnology

Second method input shapingWithout

With

WB2414-Mechatronic System Design 2013-2014 16DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

9

WB2414-Mechatronic System Design 2013-2014 17DelftUniversity ofTechnology

A walk around the control loop Feedback control

bull sensor requiredbull slower than FF (error has to occur first) bull (sensor) noise is also fed backbull can introduce instability

(also of open‐loop stable systems)

bull can stabilize unstable systemsbull can suppress disturbancesbull can handle uncertainties

Plant

G(s)Feedback

Cfb (s)Pre‐Filter

F(s) _

e ur y

Measurement

M(s)

rf

Input disturbance

Output disturbance

Process disturbance

x

Sensor disturbance

v

WB2414-Mechatronic System Design 2013-2014 18DelftUniversity ofTechnology

Active stiffness by feedback in a CD player (from Dynamics lecture)

bull200 μm radial vibrations at 25 Hz

bullMass lens 10 10‐3 kg

bullMax radial error 02 μm

6r

0 6r

r0

2 2 5r 0

1middot10

ˆ 200 10 25 800

0

2

2 10

4 25 Nm

xf f Hz

kf k mf

m

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 7: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

7

WB2414-Mechatronic System Design 2013-2014 13DelftUniversity ofTechnology

Resulting response

f

t ff ff 2 21 1 1

( ) ( ) ( )( ) 2

CG s G s C s

s s s

WB2414-Mechatronic System Design 2013-2014 14DelftUniversity ofTechnology

Triangular scanning movement

Withoutpole-zerocancellation

Withpole-zerocancellation

8

WB2414-Mechatronic System Design 2013-2014 15DelftUniversity ofTechnology

Second method input shapingWithout

With

WB2414-Mechatronic System Design 2013-2014 16DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

9

WB2414-Mechatronic System Design 2013-2014 17DelftUniversity ofTechnology

A walk around the control loop Feedback control

bull sensor requiredbull slower than FF (error has to occur first) bull (sensor) noise is also fed backbull can introduce instability

(also of open‐loop stable systems)

bull can stabilize unstable systemsbull can suppress disturbancesbull can handle uncertainties

Plant

G(s)Feedback

Cfb (s)Pre‐Filter

F(s) _

e ur y

Measurement

M(s)

rf

Input disturbance

Output disturbance

Process disturbance

x

Sensor disturbance

v

WB2414-Mechatronic System Design 2013-2014 18DelftUniversity ofTechnology

Active stiffness by feedback in a CD player (from Dynamics lecture)

bull200 μm radial vibrations at 25 Hz

bullMass lens 10 10‐3 kg

bullMax radial error 02 μm

6r

0 6r

r0

2 2 5r 0

1middot10

ˆ 200 10 25 800

0

2

2 10

4 25 Nm

xf f Hz

kf k mf

m

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 8: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

8

WB2414-Mechatronic System Design 2013-2014 15DelftUniversity ofTechnology

Second method input shapingWithout

With

WB2414-Mechatronic System Design 2013-2014 16DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

9

WB2414-Mechatronic System Design 2013-2014 17DelftUniversity ofTechnology

A walk around the control loop Feedback control

bull sensor requiredbull slower than FF (error has to occur first) bull (sensor) noise is also fed backbull can introduce instability

(also of open‐loop stable systems)

bull can stabilize unstable systemsbull can suppress disturbancesbull can handle uncertainties

Plant

G(s)Feedback

Cfb (s)Pre‐Filter

F(s) _

e ur y

Measurement

M(s)

rf

Input disturbance

Output disturbance

Process disturbance

x

Sensor disturbance

v

WB2414-Mechatronic System Design 2013-2014 18DelftUniversity ofTechnology

Active stiffness by feedback in a CD player (from Dynamics lecture)

bull200 μm radial vibrations at 25 Hz

bullMass lens 10 10‐3 kg

bullMax radial error 02 μm

6r

0 6r

r0

2 2 5r 0

1middot10

ˆ 200 10 25 800

0

2

2 10

4 25 Nm

xf f Hz

kf k mf

m

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 9: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

9

WB2414-Mechatronic System Design 2013-2014 17DelftUniversity ofTechnology

A walk around the control loop Feedback control

bull sensor requiredbull slower than FF (error has to occur first) bull (sensor) noise is also fed backbull can introduce instability

(also of open‐loop stable systems)

bull can stabilize unstable systemsbull can suppress disturbancesbull can handle uncertainties

Plant

G(s)Feedback

Cfb (s)Pre‐Filter

F(s) _

e ur y

Measurement

M(s)

rf

Input disturbance

Output disturbance

Process disturbance

x

Sensor disturbance

v

WB2414-Mechatronic System Design 2013-2014 18DelftUniversity ofTechnology

Active stiffness by feedback in a CD player (from Dynamics lecture)

bull200 μm radial vibrations at 25 Hz

bullMass lens 10 10‐3 kg

bullMax radial error 02 μm

6r

0 6r

r0

2 2 5r 0

1middot10

ˆ 200 10 25 800

0

2

2 10

4 25 Nm

xf f Hz

kf k mf

m

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 10: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

10

WB2414-Mechatronic System Design 2013-2014 19DelftUniversity ofTechnology

Virtual stiffness

bull Measure position

bull Actuate with force proportional and opposite to the deviation (feedback)

bull Gives virtual spring stiffness

p r m a p ct r r F k G G G G G

r p tr

F

k k G

WB2414-Mechatronic System Design 2013-2014 20DelftUniversity ofTechnology

Servo position control

2

2 2

1 10 kg

1 100( )

( ) 1

m

G sms s

M s

For the example

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 11: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

11

WB2414-Mechatronic System Design 2013-2014 21DelftUniversity ofTechnology

adding a P-gain (controller) hellip

CD‐player example control of lens positionm = 10 g

Is this system stable

5fb p

7

p fb p 2 2

( ) ( ) 25 10

1 25 10( ) ( ) ( ) ( )

pC s C s k

L s G s C s M s kms s

Open loop gain

2 2

1 100

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 22DelftUniversity ofTechnology

hellip closing the loop with P-controller

pp 2

2p2

p 0

( ) 1 1( )

( ) 1 1 1

L sT s

mL s sk

p 30

0 0

5 10

1800 Hz

2

k

m

f

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

Unity-gaincrossoverfrequency

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 12: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

12

WB2414-Mechatronic System Design 2013-2014 23DelftUniversity ofTechnology

We need some damping (PD-control)

fb pd p d

p dpd pd 2

( ) ( )

( ) ( ) ( )

C s C s k k s

k k sL s G s C s

ms

pd p d 0 dpd 22

pd p d 0 p20 0

2 1( ) 2

( ) ( ) 1

2 1

jL s k k s k

T sL s ms k k s k

j

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 24DelftUniversity ofTechnology

Look better at the graph

Increased unity-gain crossover frequency Reduced

slope at high frequencies

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 13: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

13

WB2414-Mechatronic System Design 2013-2014 25DelftUniversity ofTechnology

PD-control behaves like ldquotransmissibilityrdquo andcannot be made in reality (not proper)

Reduced reduction of high frequencies by continuous D‐actionInfinite gain at infinite frequency

WB2414-Mechatronic System Design 2013-2014 26DelftUniversity ofTechnology

The D-action must be terminated at high frequencies and kp must be reduced

dpd p d p p d p

p d

( ) (1 ) (1 ) (1 )k s

C s k k s k s k s kk

pd dpdt 2

0 t

1( )

1

k sL s

ms s

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 14: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

14

WB2414-Mechatronic System Design 2013-2014 27DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

hellip closing the loop with tamed PD-controller

pd dpdt 2

0 t

1( )

1

k sL s

ms s

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

WB2414-Mechatronic System Design 2013-2014 28DelftUniversity ofTechnology

CD‐player example control of lens positionm = 10 g

Closed-loop step response of PD-controlled mass

Plant

G(s)

Feedback

Cfb (s)

Measurement

M(s)

e

u Output

disturbance

r y

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 15: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

15

WB2414-Mechatronic System Design 2013-2014 29DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants

WB2414-Mechatronic System Design 2013-2014 30DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

Feedback Loop Sensitivity Functions

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 16: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

16

WB2414-Mechatronic System Design 2013-2014 31DelftUniversity ofTechnology

Response to reference Complementary sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

u x x y GC

d n r r GC

Complementary sensitivity function T(s)

1 1 11

1 1 1

1 1 1

G GC GCFx d n r

GC GC GCG GCF

y d n rGC GC GCGC C CF

u d n rGC GC GC

WB2414-Mechatronic System Design 2013-2014 32DelftUniversity ofTechnology

1 1 11

1 1 1

1 1 1

G GC FCGx d n r

GC GC GCG FCG

y d n rGC GC GCGC C FC

u d n rGC GC GC

Output disturbance rejection sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

If F(s) = 1

1

1

y

n GC

Sensitivity function T(s)

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 17: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

17

WB2414-Mechatronic System Design 2013-2014 33DelftUniversity ofTechnology

Relation of the two sensitivity functions

fb

fb fb

( ) ( ) 1( ) ( ) ( ) 1 ( )

1 ( ) ( ) 1 ( ) ( )

G s C sT s T s S s S s

G s C s G s C s

|T|

w

Complementary sensitivity

gain=1|S|

w

Sensitivity

Plant G(s)

Feedback Cfb (s)

Pre‐FilterF(s) _

Process disturbance d

Output disturbancen

e u v xr yrf

WB2414-Mechatronic System Design 2013-2014 34DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 18: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

18

WB2414-Mechatronic System Design 2013-2014 35DelftUniversity ofTechnology

Stability and robustness

bull When is a (closed‐loop) system stable

bull A system is asymptotically stable if and only if all poles are in the left half of

the complex plane

bull When is a system robustbull Robustness of a feedback controlled system means that the closed‐loop

system can accept (some) model uncertainties (parameter variations)

bull Both properties are investigated with the Bode and Nyquist plot

WB2414-Mechatronic System Design 2013-2014 36DelftUniversity ofTechnology

Loop-Shaping design for stability and robustness

Shape the frequency response of the open‐loop system such thatbull high gain (gtgt1) at low frequencybull low gain (ltlt1) at high frequencybull less than 180 degree phase lag in crossover region (unity‐gain)

Robustnessbull Gain margin GMbull Phase margin PM

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 19: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

19

WB2414-Mechatronic System Design 2013-2014 37DelftUniversity ofTechnology

It happens around the unity-gain cross-over frequency

Stability Is the unity‐gain crossing of the magnitude plot at a frequency with less than 180ordm phase lag

Robustnessbull Gain margin GMbull Phase margin PM

WB2414-Mechatronic System Design 2013-2014 38DelftUniversity ofTechnology

Nyquist Plot of open-loop transfer L(s)

bull Stability The ‐1 point must be

passed at the left side when increasing the frequency

bull Robustnessbull Gain margin (GM) how much the gain can be increased until instabilitybull Phase margin (PM) how much the phase lag can be increased until instability

The circle that is just passed at the left gives the peak value of the resonance after closing the loop

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 20: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

20

WB2414-Mechatronic System Design 2013-2014 39DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 40DelftUniversity ofTechnology

The plant an undamped mass-spring system

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 21: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

21

WB2414-Mechatronic System Design 2013-2014 41DelftUniversity ofTechnology

Specifications of closed loop system

bull Bandwidth of 100 Hz (unity‐gain cross‐over frequency)

bull So far beyond the natural frequency on the mass line

bull Asymptotically stable all poles in the left half plane

bull Sufficiently damped (is requirement)

bull Specification max Q = 13 (+3dB)

bull Zero steady‐state error (0 Hz)

WB2414-Mechatronic System Design 2013-2014 42DelftUniversity ofTechnology

P-control

bull Lift the response to unity gain 100 Hz =gt kp~105

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 22: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

22

WB2414-Mechatronic System Design 2013-2014 43DelftUniversity ofTechnology

D-control for damping

bull reduce the phase lag 100Hz

bull Donrsquot forget to reduce kp

WB2414-Mechatronic System Design 2013-2014 44DelftUniversity ofTechnology

I-control for infinite gain at 0 Hz

bull Sensitivity =fb

1( )

1 ( ) ( )S s

G s C s

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 23: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

23

WB2414-Mechatronic System Design 2013-2014 45DelftUniversity ofTechnology

PID-control in math

p i d

ip d

ipid p d

ipid p d

0

d ( ) ( ) ( ) ( )d

d

( ) ( )

( )( )

( )

( )( )

( )

t e tu t k e t k e k

t

ku s e s k k s

s

ku sC s k k s

e s s

kuC k j jk

e

WB2414-Mechatronic System Design 2013-2014 46DelftUniversity ofTechnology

The bode plot of the designed PID controller

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 24: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

24

WB2414-Mechatronic System Design 2013-2014 47DelftUniversity ofTechnology

Open-loop controller and plant

WB2414-Mechatronic System Design 2013-2014 48DelftUniversity ofTechnology

Nyquist plot

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 25: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

25

WB2414-Mechatronic System Design 2013-2014 49DelftUniversity ofTechnology

Closed loop total system

WB2414-Mechatronic System Design 2013-2014 50DelftUniversity ofTechnology

Increased sensitivity for disturbances above f0 on a linear scale

Waterbed effect due to Bode sensitivity integralEquals zero for system with 2 more poles than zeros 0

ln ( ) dS

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 26: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

26

WB2414-Mechatronic System Design 2013-2014 51DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

WB2414-Mechatronic System Design 2013-2014 52DelftUniversity ofTechnology

Magnetic bearings are often based on the variable reluctance actuator

I

F

n

xdx

g

ys

wF

gA gA

ymmover

stator

Force based on energy balanceEnergy stored in magnetic field

2

g 0

g 4

AnIF

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 27: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

27

WB2414-Mechatronic System Design 2013-2014 53DelftUniversity ofTechnology

Balancing and linearisation with two variable reluctance actuators

2 1

2 2 2 2 2g 0 g 0 g 02 1 2 1

2 2g2 g1 g2 g14 4 4

F F F

A A n AnI nI I I

2 2 2g 0 2 1

2g4

n A I IF

g1 g2 gIn the mid-position l l l

2 a 1 aWith and I I I I I I

2 22 2g 0 g 0a a a

2 2g g

2a g 0

2g

4

4 4

n A n AI I I I I IF

I n AF

I

C2C1

I1

x

F

F1 F2I2

dx

g2g1

What is the force toposition relation at a certain current level

WB2414-Mechatronic System Design 2013-2014 54DelftUniversity ofTechnology

Flux in a balanced reluctance actuator depends on the current direction

Sharing the flux paths by reversing the current in one of the coils

C2C1

I1

C2C1

I1

I2

I2

F F

dx dx

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 28: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

28

WB2414-Mechatronic System Design 2013-2014 55DelftUniversity ofTechnology

Inserting a permanent magnet in a double reluctance actuator

Creating the common mode flux with a permanent magnet

C2C1

I1PM

I2

C2C1

F

PMI2

Elastic hinge

I1

x xF

N N

dx dx

WB2414-Mechatronic System Design 2013-2014 56DelftUniversity ofTechnology

Hybrid actuator (right position) Permanent magnet biased reluctance actuator

movement

All PM flux passes through coil 1

Coil 1 Coil 2

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 29: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

29

WB2414-Mechatronic System Design 2013-2014 57DelftUniversity ofTechnology

Two ultimate positions

movement movement

Ratio of PM flux through the coils depends on the position of the mover

WB2414-Mechatronic System Design 2013-2014 58DelftUniversity ofTechnology

Superposition of the PM and current induced magnetic flux

Large dΦdxHigh forceShort stroke

Coil 1 Coil 2

F

Flux increase Flux decrease

I2

nn

I1

xAg

N

dx

g2g1

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 30: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

30

WB2414-Mechatronic System Design 2013-2014 59DelftUniversity ofTechnology

Hybrid actuator in Magnetic bearings

Discuss the 4 coordinatedirection bearing control

WB2414-Mechatronic System Design 2013-2014 60DelftUniversity ofTechnology

Control of a magnetic bearing

bull Bodeplot of negative stiffness

2 2n

n

2 4

1 1

10000 Nm

01

( )

( )1

k

middot10

g

1

01

t

t

Cms ms

k

m

C

xs

F k k

x

F

2n

n 316

0 ms

ks

m

k

Poles

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 31: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

31

WB2414-Mechatronic System Design 2013-2014 61DelftUniversity ofTechnology

Shifting the pole to the left (root-locus)

For robustnesskp gt 2 kn

After closing the loop

WB2414-Mechatronic System Design 2013-2014 62DelftUniversity ofTechnology

Bode plot of P(I)D-controlledmagnetic bearing

p 2n

pn

2 2

n n

plant+P

1

12

1

)

1

(

Cms

s kk

kk

k km m

s s

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 32: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

32

WB2414-Mechatronic System Design 2013-2014 63DelftUniversity ofTechnology

Nyquist explains what happens

WB2414-Mechatronic System Design 2013-2014 64DelftUniversity ofTechnology

Lecture outline

bull What did you learn about PID ‐motion control so far

bull Introduction to motion control

bull Feedforward control of piezoelectric scanner

bull PD ndash feedback control of CD‐player

bull Sensitivity

bull Stability and Robustness

bull PID ‐ feedback control of mass‐spring system

bull PID ‐ feedback control of magnetic bearing

bull How to deal with difficult plants having multiple eigenmodes

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 33: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

33

WB2414-Mechatronic System Design 2013-2014 65DelftUniversity ofTechnology

4 types of responses

WB2414-Mechatronic System Design 2013-2014 66DelftUniversity ofTechnology

Type I -2 slope zero pair pole pair -2 slope

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 34: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

34

WB2414-Mechatronic System Design 2013-2014 67DelftUniversity ofTechnology

Type II -2 slope pole pair zero pair -2 slope

WB2414-Mechatronic System Design 2013-2014 68DelftUniversity ofTechnology

Type III -2 slope pole pair -4 slope

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 35: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

35

WB2414-Mechatronic System Design 2013-2014 69DelftUniversity ofTechnology

Type IV -2 slope pole pair -2 slope

WB2414-Mechatronic System Design 2013-2014 70DelftUniversity ofTechnology

non-collocated measuring at non-rigid body

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 36: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

36

WB2414-Mechatronic System Design 2013-2014 71DelftUniversity ofTechnology

Bode and Nyquist with PID control open loop of sheet 48

WB2414-Mechatronic System Design 2013-2014 72DelftUniversity ofTechnology

Pole-zero cancellation (notching) But donrsquot overdo it

Risk of frequency drift

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 37: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

37

WB2414-Mechatronic System Design 2013-2014 73DelftUniversity ofTechnology

Adding a low-pass filter (a pole)

WB2414-Mechatronic System Design 2013-2014 74DelftUniversity ofTechnology

Only Nyquist gives the real answer on stability

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency

Page 38: Lecture 5 motion control for handouts - TU Delft OCW · 2016. 2. 23. · 5 Delft WB2414-Mechatronic System Design 2013-2014 9 University of Technology Feedforward control of a piezoelectric

38

WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology

Optimisation with LPF corner frequency