High-performance load-adaptive speed control for ultrasonic motors

Abstract High-performance servo-control schemes using ultrasonic motors (USMs) as new actuators have not yet been applied in practice in modern industry and office-automation systems, because the dynamic and steady-state modelling of USMs is extremely difficult from the theoretical point of view. In the first part of this paper, the rotational speed-control characteristics of a circular travelling wave motor are theoretically analysed and experimentally explored by using an experimental measuring system. In the second part, a newly-developed servo-control system using two feedback control loops based on a sensorless technique is described. This technique, using strategies for both instantaneous control and average value control, is based upon control of both the load-adaptive resonant frequency and a constant velocity. These control schemes are considered theoretically, and experimental results are demonstrated and evaluated in practice.