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# lab4 - Laboratory Assignment 5 Digital Velocity and...

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Laboratory Assignment 5 Digital Velocity and Position control of a D.C. motor 2.737 Mechatronics Dept. of Mechanical Engineering Massachusetts Institute of Technology Cambridge, MA-02139 1 Topics Motor modeling Proportional, PI velocity control Implementation of Anti-Windup Proportional position control Lead-Lag compensation Velocity minor loop / Position major loop 2 Equipment PC 486 with ATMIO-16 card Oscilloscope Function generator D.C. motor Power amplifier Protoboard 1

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3 Introduction In this laboratory, digital control of a D.C. motor will be studied. Each station is equipped with a D.C. motor (with an integral tachometer to measure angular velocity), a single turn potentiometer to measure angular position and a power amplifier to drive the motor. First, we will develop a model for the motor. This model will then be used to perform velocity and position control experiments on the motor. For the purpose of this lab, controller design will be done using continuous time methods. Discrete time controllers will be obtained from these by using either backward difference or ZOH equivalents. Initial experiments will focus on velocity control. A proportional controller will be implemented first. Resulting steady state errors are observed and the effect of increasing gain on steady state error is seen. This is followed by implementation of a PI controller to remove steady state errors in response to a step input. Problems with integral windup are observed and an anti-windup scheme is implemented. Next, step and frequency response specifications are met by designing a controller in Matlab and implementing it. Next, position control of a D.C. motor will be studied. Initially, a proportional controller will be implemented. The effect of increased gain on servo stiffness is observed. Lead-Lag compensators are designed using Matlab and implemented on the actual hardware and the performance studied. Finally, a velocity minor loop/position major loop controller will be implemented. Proportional gains for both loops are selected based on frequency domain criteria. Note that the structure of the controller is much like that in state feedback control with velocity and position as state variables. 4 D.C. Motor model Each station has a D.C. motor and a power amplifier. Please follow a few precautions before powering up your setup. The power supply to the power amplifier is from the same Tektronix supply that you used in lab 4. Make sure that the power supply is operated in series as in lab 4 and that the current limit on both supplies (both positive and negative) is set to the maximum. Also, the voltage rails to the power amplifier should not exceed 17 volts. A good practice would be to turn the master voltage knob all the way to zero before switching the power supply on and then slowly bring it up to 15 volts. Note that as in lab 4, exceeding the voltage rails specified could damage the power amplifier. Please exercise caution.
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