Adjustable speed control of ultrasonic motors by adaptive control

The driving principle of the ultrasonic motor (USM) is different from those of the electromagnetic motors and its mathematical motor model has not been developed yet. Therefore, it is difficult to control the ultrasonic motor with high performances. The traveling-wave type ultrasonic motor is suitable for variable-speed drives. In this paper, the speed control system of the traveling-wave type ultrasonic motor is designed using adaptive control theory. Because the dynamic characteristics of the ultrasonic motor are unknown and vary with time, adaptive control theory which is useful for controlling the unknown plant is applied to design the adjustable speed control of USM. The mathematical motor model of USM is derived and motor parameters are identified by the recursively least square method. Therefore, this controller can always adjust the rotor speed to speed command, precisely.>