ME2142E Feedback and Control Lab -Speed Position Control of a DC Motor

7/23/2019 ME2142E Feedback and Control Lab -Speed Position Control of a DC Motor

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LIN SHAODUN A0066078X

Lab Group 6B

Date 18th

Feb 2011


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TABLE OF CONTENTS

EXPERIMENTAL DATA TABLE 1, 2, 3, 4, 5, 6 2

GRAPH 1 TACHO OUTPUT VS. MOTOR SPEED 4

GRAPH 2 MOTOR SPEED VS .INPUT VOLTAGE FOR BRAKE 0, 2, 4 4

GRAPH

3A SPEED VS.BRAKE(3 GAINS, OPE N-LOO P) 5

GRAPH 4B SPEED VS. BRAKE(3 GAINS,CLOSED-LOO P) 5

DISCUSSION 6

APPENDIX OSCIALLOSCOPE WAVEFORMS 9


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EXPERIMENTAL DATA

Table 1: TACHO-GENERATOR CHARACTERISTICS

Speed (rpm) 400 800 1200 1600 2000Tacho Output (volts ) 1.19 2.30 3.50 4.66 5.87

Do with speed feedback. (To make speed easily controlled) Speed range is 400 rpm to 2000 rpm in increments of approximately 400 rpm. Gain =0.1

Table 2a: Brake Setting = 0 (No feedback) Gain=0.1

MOTOR CHARACTERISTICS SPEED vs. INPUT

Speed (rpm) 400 800 1200 1600 2000

Volt (mV) 31.43 70.03 109.92 149.54 190.42

Speed range is 400 rpm to 2000 rpm in increments of approximately 400 rpm.Table 2b: Brake Setting = 2 (No feedback) Gain=0.1


Speed (rpm) 400 800 1200 1600 2000

Volt (mV) 32.89 72.68 114.63 155.68 196.67

Speed range is 400 rpm to 2000 rpm in increments of approximately 400 rpm.Table 2c: Brake Setting = 4 (No feedback) Gain=0.1


Speed (rpm) 400 800 1200 1600 2000

Volt (mV) 42.07 93.27 145.34 201.04 228.75

Speed range is 400 rpm to 2000 rpm in increments of approximately 400 rpm.Table 3: OPEN-LOOP LOAD-SPEED CHARACTERISTICS (No Feedback)

Brake Setting 0 2 4 6 8 10

Speed (Gain=0.02) 1000 950 780 660 560 480

Speed (Gain=0.05) 1000 970 780 680 550 500

Speed (Gain=0.10) 1000 960 770 660 550 490

For each gain setting, start with speed of about 1000 rpm at zero brake scale setting.


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Table 4: CLOSED-LOOP LOAD-SPEED CHARACTERISTICS (With Speed Feedback)

Brake Setting 0 2 4 6 8 10

Speed (Gain=0.02) 1000 980 860 760 680 610

Speed (Gain=0.05)1000 980 900 830 760 700

Speed (Gain=0.10) 1000 980 930 880 840 790

For each gain setting, start with speed of about 1000 rpm at zero brake scale setting.Table 5: CLOSED-LOOP LOAD-SPEED TRANSIENT RESPONSE (With Speed Feedback)

Brake

Setting

Brake=5 Brake=10

Overshoot %Settling

Time, mSRise Time,

mSOvershoot %

SettlingTime, mS

Rise Time,mS

Gain=0.02 0 112 92 0 88 68

Gain=0.05 0 76 68 0 64 52

Gain=0.10 0 68 60 0 56 48

Settling Time: within 5% of steady state value. Rise Time: Time to reach steady state value at the first instance.

Table 6: CLOSED-LOOP LOAD-SPEED TRANSIENT RESPONSE (With Position Feedback)

Brake

Setting

With Speed Feedback Without Speed Feedback

Overshoot % SettlingTime, mS Rise Time,mS Overshoot % SettlingTime, mS Rise Time,mS

Gain=0.02 0 770 650 0 520 450

Gain=0.05 0 540 480 0 250 230

Gain=0.10 0 510 440 11.6% 150 140

Settling Time: within 5% of steady state value. Rise Time: Time to reach steady state value at the first instance.


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GRAPH - 1 TACHO OUTPUT VS. MOTOR SPEED

GRAPH - 2 MOTOR SPEED VS. INPUT VOLTAGE FOR BRAKE 0, 2, 4

Note: when Brake Setting = 4, highest motor speed only can achieve 1670 rpm.

y = 0.0029x - 0.0120R = 0.9998

1.0

2.0

3.0

4.0

5.0

6.0

400 800 1,200 1,600 2,000

TachoOutput(Volts)

Motor Speed (rpm)

Tacho Output vs. Motor Speed

Tacho Output

0

50

100

150

200

250

400 800 1,200 1,600 2,000

InputVoltatge(mV)

Motor Speed (rpm)

Motor Speed vs. Input Voltage for Brake 0, 2, 4

Brake Setting = 0Brake Setting = 2

Brake Setting = 4


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GRAPH 3A SPEED VS. BRAKE (3 GAINS, OPEN-LOOP)

GRAPH 3B SPEED VS. BRAKE (3 GAINS, CLOSED-LOOP)

400

600

800

1000

1200

0 2 4 6 8 10

Speed(rpm)

Brake Settings

Speed vs. BRAKE (3 gains, Open-Loop)

Gain=0.02

Gain=0.05

Gain=0.1

400

600

800

1000

1200

0 2 4 6 8 10

Speed(rpm)

Brake Settings

Speed vs. BRAKE (3 gains, Closed-Loop)

Gain=0.02

Gain=0.05

Gain=0.1


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DISCUSSION

1. Discuss the differences in open-loop and closed loop control in achieving a speedcontrol system and the effects of the loop gain and load on the output speed.

Graph 3a is the result from open-loop speed control system, it shows:1) The desired motor speed output is solely controlled by potentiometer input.2) The desired motor speed can be achieved if there is not load or disturbance, but

the speed output will drop significantly if there is a disturbance (in this case,

the magnetic brake), and the amount of speed reduction is proportional to the

magnitude of disturbance (Magnetic brake angle).

3) Different Gain setting of Op. Amp is totally ineffective against disturbance.The characteristic of open-loop controller is that it does not use feedback to determine

if its output has achieved the desired goal of the input. This means that the system

does not observe the output of the processes that it is controlling; hence an open-loopsystem cannot compensate any disturbances.

From above block diagram of open-loop control system we can see that the loop gain

has not effect to the Op. Amp as the speed feedback from Tachometer is physically

disconnected, hence the system will not compensate any disturbance.

Graph 3b is the result from closed-loop speed control system, it shows:

1) The motor speed output is still proportional to disturbance, but amount ofspeed drop is not so severe compare with open-loop system.

2) Difference Gain setting of Op. Amp affects the final speed output, higher thegain setting, lesser the system is affected by disturbance.

In a closed-loop control system, a sensor monitors the system output (the motor speed)

and feeds the data to a controller which adjusts the controller as necessary to maintain

the desired system output.

From above block diagram of closedloop control system, it shows higher loop gain

helps system endure higher disturbance. During the experiment, if it is possible to

increase the loop gain, let say to 0.8, the motor output will be maintained at 1000 rpm

even at maximum magnetic brake angle setting.

Brake

Op.AmpE

Servo Amp+

-

Motor Tachometer

Brake

Op.AmpE Servo Amp+

-

Motor Tachometer-

+

Gain


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2. Discuss the effect of loop gain and brake scale settings on the transient response ofthe closed-loop speed control system.

When plot the loop gain vs. transient response, the graph looks like this:

From above graph we can observe the following facts:

1) Higher disturbance results in lower settling and rise time.2) Higher loop gain setting also helps to reduce settling and rise time.

All these can be explained by the block diagram and the transfer function of the

closed-loop speed control system model.

The speed feedback control system is a first order system which transfer function is:()() Smaller the time constant , faster the system will response. As we know:

Obviously this equation indicates Kd

, hence increase Kdwill reduce systemresponse time.

As for disturbance TL , the transfer function between output is:()() Which means when KL is constant, increase TL also causes reduce, hence system will

response faster.

40

60

80

100

120

0.02 0.04 0.06 0.08 0.10

TransientRespone(mS)

Gain Settings

Gain vs. Transient RespondBrake=5, Settling Time

Brake=5, Rise Time

Brake=10, Settling Time

Brake=10, Rise Time

Brake TL

Kp

E +-

-

+

Kd

TL


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Alternately, when the disturbance TL is higher, the error feedbacks to Op.Amp will be

higher, which results in higher output to compensate the error and bring system back

to original state, hence the response time will be shorter.

3. Discuss the effect of loop gain and velocity feedback on the transient response of theclosed-loop speed control system.

When plot the loop gain vs. transient response, the graph looks like this:

Result from Table 6 shows:1) With speed and position feedback, the Settling and Rise time of control system

is longer than those without speed feedback, and the difference is even more

obvious at higher loop gain setting.

2) When without speed feedback, control system could overshoot at higher loopgain setting. ( Please refer to Appendix, page 11)

The transfer function of speed and position feedback control system is:

()()

From above equation, if without speed feedback, the system nature frequency will the

higher, and the damping ratio will be smaller, hence faster settling time is observed.

With higher loop gain setting, same phenomena will be observed.

100

200

300

400

500

600

700

800

0.02 0.04 0.06 0.08 0.10

TransientResp

one(mS)

Gain Settings

Gain vs. Transient Respond

With Speed and Position Feedback , settling time

With Speed and Position Feedback , Rise time

Without Speed and Position Feedback ,Settling time

Without Speed and Position Feedback , Rise time


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APPENDIX - OSCIALLOSCOPE WAVEFORMS

Brake 5 Gain 0.02 with Speed feedback Brake 5 Gain 0.05 with Speed feedback

Brake 5 Gain 0.1 with Speed feedback

Brake 10 Gain 0.02 with Speed feedback Brake 10 Gain 0.05 with Speed feedback


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Brake 10 Gain 0.1 with Speed feedback

Brake 5 Gain 0.02 with

Position S eed feedback


Position S eed feedback


Position/S eed feedback


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Documents

ME2142E Feedback and Control Lab -Speed Position Control of a DC Motor