Adaptive PID control of a stepper motor driving a flexible rotor

Stepping motors are widely used in robotics and in the numerical control of machine tools to perform high precision positioning operations. The classical closed-loop control of the stepper motor can not respond properly to the system variations unless adaptive technique is used. In this paper, the feasibility of fuzzy gain scheduling control for stepping motor driving flexible rotor has been investigated and illustrated by numerical simulation. The proposed control was concerned with the permanent magnet step motor (PMSM) with mechanical variations such as stiffness of rotor and load inertia. A mathematical model for the PMSM was derived and the gains of a conventional PID control were presented. The data base required in learning process of the fuzzy logic gain scheduling mechanism was obtained from the mathematical model. It was found that the stable value for the integral gain is half the value of the proportional gain. The fuzzy systems for scheduling the derivative gain and the proportional gain are presented. The conducted simulation showed that the fuzzy system is able to adapt the controller gains to track the desired load and speed response. Fuzzy PID performance is much better than the conventional PID control scheme. Fuzzy self-tuning controller demonstrates a very fast response and little overshoot.