Speed control of ultrasonic motors by discrete time variable structure control

Ultrasonic motors (USM) have many useful features as servomotors. In this paper, the authors propose a speed control system for travelling wave type USM using variable structure control based on adaptive control theory. They construct the control system which includes a variable structure self-tuning regulator connecting an integrator. Then, steady-state speed error is reduced when heavy load torque is applied to the motor. In the proposed speed control system, high-performance adjustable speed control is maintained even if parameter values are not sufficiently identified. The effectiveness and validity of the proposed controller are demonstrated by experiments.