Performance comparison of PI and adaptive controller for adjustable speed drives of ultrasonic motors

The ultrasonic motor (USM) is new type motor that is driven by ultrasonic vibration of piezoelectric element, and has many excellent performances and features. In the paper, the authors investigate the fundamental characteristics of USMs and point out the problems for controlling the speed of them. In order to solve these problems, two speed control systems, based on PI control (proportional and integral) and adaptive control, are discussed. From the experimental results, the authors compare their control performances. Because the speed characteristics of the ultrasonic motor vary with time, adaptive control with an identifier and the ability to detect characteristics variation of USMs is suitable for an adjustable speed control system