SPEED SERVO

• Picture of the frontpanel of the simulator
• What is needed to run the the simulator? Read to get most recent information!
• Tips for using the simulator.
• The simulator: speedservo.exe (click to download). The simulator runs immediately after the download by clicking Open in the download window. Alternatively, you can first save a copy of the exe-file on any directory (folder) on your PC and then run the exe-file, which starts the simulator.

Description of the simulated system

A speed control system - i.e. a speed servo -- is simulated. The motor is the DC motor Electro-Craft S-19-3AT which is an armature controlled, voltage controlled DC motor.

A mathematical model of the motor is given here. The speed is measured using a tachometer. The tachometer  gain and the other motor parameters can be adjusted from the front panel of the simulator. Note: The simulator shall have tachometer constant equal to 14 V/krpm, not 0.134 V/krpm as indicated on the existing simulator front panel.

Aim

The aim of this simulator is to get a better understanding of how a speed control system works dynamically.

Motivation

DC motors are used in many servo systems. Compared to other electro motors DC motors are easy to model mathematically, and, hence, easy to simulate.

Tasks

In the tasks below is assumed - unless otherwise stated - that the process (motor) is in its normal or nominal operating point, defined as follows:

• The speed S is 1000 rpm (revolutions per minute), which is used as a nominal speed setpoint.
• The load torque T_L is 0.

The values of the motor parameters are shown here (the parameters can be adjusted from the front panel).

Unless other information is given, it is assumed that the simulator runs while you do the tasks.

1. Control using constant control signal. Set the controller in manual mode.
   1. Find the nominal control signal u₀ experimentally (on the simulator) which bringd the process to the nominal operating point.
   2. Change the load torque (disturbance) from 0 to 5 Nm. What is the steady-state control error?

    

2. Tuning a PID control: In the subsequent tasks the motor speed is controlled by a PID controller (unless otherwise stated). Adjust the controller using the Ziegler-Nichols' closed loop method.
   
   

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   If you have not done Task 2, you can use the following PID settings in the following tasks:

   Kp = 0.4, Ti = 0.005s, Td = 0.001s

    

3. Steady state setpoint tracking and disturbance (load torque) compensation: First, let the the load torque be zero and the speed setpoint 1000rpm.
   1. How large is the steady state control error?
   2. Adjust the setpoint as a step from 1000rpm to 1500rpm. What is the control error?
   3. Change the load torque as a step frm 0 to 5Nm. What is the steady state control error? Is there an improvement from task 1b?

    

4. Tracking a setpoint ramp: Let the load torque be constant. Let the setpoint be a ramp of slope 1000rpm/s. What is the steady state control error (as read off from the front panel of the simulator)?

    

5. Control using a P controller:
   1. Find a proper value of the controller gain.
   2. Are the static setpoint tracking and disturbance tracking perfect with a P controller? (Simulate!)

   
   

6. The stability of the control system at parameter changes: Let the setpoint be 1000 rpm and the load torque 0 Nm. Observe what happen to the control system stability at the parameter changes described below. In each task/experimentyou can excite the control system via a small step in the setpoint. The experiments should be performed independently, i.e. the parameter values should be reset to default values once each of the experiments is finished.
   1. The control gain is increased (much).
   2. The integral time is decreased (much).
   3. The derivative time is increased (much).
   4. The intertia of the load is increased (much) and (thereafter) reduced (much).
   5. The tachometer gain (measurment gain) is increased  (much).

[KYBSIM] [TechTeach]

Updated February 7, 2005. Developed by Finn Haugen. E-mail: finn@techteach.no.