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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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
38
WB2414-Mechatronic System Design 2013-2014 75DelftUniversity ofTechnology
Optimisation with LPF corner frequency