The objective of this lab is to design a PID motor controller. The desired speed is received from a user interface (either a keypad or the SCI). You should use a variable-speed DC motor, paying careful attention to the voltage and current specifications of the motor. Attach onto the motor shaft a circular disk, and paint contrast lines in a circular pattern around the disk. Mount a reflectance optical sensor, such as the QRB1113 or QRB1134, pointing toward the disk, and interface it so that there is a digital squarewave with a frequency related to the speed of the shaft. Build the state estimator that measures shaft speed in real time. The first experimental measurement is to determine the current required to spin the motor at full speed. The next step is to design a PWM actuator so the software can control the delivered power to the motor. Measure the inductance of the motor (L) and the turn-off time (Δt) of the PWM switch. Use these parameters to mathematically determine the back EMF (V = L • ΔI/Δt) that occurs when the motor is turned off. Make sure the snubber diode can handle this voltage. Use the PWM in open-loop fashion and the state estimator to generate a DC response curve like that shown in Figure 13.24. Furthermore, you should measure a process reaction curve similar to that shown in Figure 13.14. Use the Ziegler and Nichol equations to design the initial PID controller, and implement it using fixed-point math. Run through an experimental fine-tuning, choosing PID parameters that minimize both controller error and response time.
Figure 13.24
