June 24, 2017
June 24, 2017
June 28, 2017
A low-cost control system experiment is presented. The plant for the control system is a modified Radio Control (RC) servo. The servo is modified by removing the controller, then brining the two motor leads, and the three potentiometer (pot) leads outside the servo case. The motor and pot are connected to an Arduino Uno R3. Inputs for auto manual selection, manual inputs, and additional pots are connected for reference and gain adjustments.
This experiment is part of an electronics course in Engineering Technology and Management (ETM). The electronics course uses the Arduino Uno R3 to teach electronics, real time programing, and with this experiment, PID control. There is no time allotted in this course for traditional frequency based or time based control system design, but this simple set up allows the student to experience many of the situations that arise in industrial control systems.
The student learns about input, output, feedback, and control. The first step for the student is to move the servo by hand and observe the feedback from the pot. The student then runs the motor and observes the direction. The student can then determine the sign of the feedback, and implement manual control.
The motor is connected to two Arduino outputs. This creates an H-bridge. Dead-band control is implemented by setting the outputs high and low for one direction, low and high for the reverse, and low and low for stop. The student sets the dead-bands to allow the servo output to follow a reference pot. At this point the student has performed his/her first control system startup and likely experienced many of the challenges of commissioning a control system.
The Arduino outputs connected to the motor are capable of Pulse Width Modulation (PWM). Proportional output is achieved by setting one output pin low, while the other is controlled using PWM. This allows proportional control of the motor in either direction. The student can now implement proportional only control. The student can turn the pot by hand and feel the control system response. This gives the student a direct kinesthetic learning experience.
Advanced learners can now add integral and derivative control. The addition of integral control forces the student to understand initialization and integral windup. The student writes the Proportional Integral Derivative (PID) control algorithm such that auto/manual transitions and gain changes are bumpless.
The addition of the control system experiment cost less than $5.00 per student, but provides the student with a realistic control system problem complete with all of the vagaries of an in-plant control system commissioning.
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