Comparing controllers with the ball in a tube experiment

The control objective for the "ball in a tube" is to regulate the speed of a fan blowing air into a tube so as to keep a small ball suspended at some predetermined level in the tube. This is a difficult control problem due to the nonlinear effects on the ball and the complex physics governing its behavior. There is also a significant time delay in the system response. Here we use this device to experimentally compare a conventional PID controller and several types of fuzzy controllers under changing conditions: restricted airflow change of setpoint, and change of ball. The results show significant differences in the performance characteristics of the controllers. Overall the Fuzzy PID and Fuzzy PI controllers performed the best. The conventional PID controller too was stable but displayed a much slower response time. The Fuzzy P and Fuzzy PD controllers showed relatively poor performance.