Approach to speed control using temperature characteristics of ultrasonic motor

Ultrasonic motors have some special unique features, such as high-torque under low-speed operation, compact size, and no electromagnetic noise. Ultrasonic motors would be expected to apply an element of the artificial muscle. The driving principle of the ultrasonic motor is based on friction force between a rotor and a stator. Therefore, it is difficult to drive the ultrasonic motor at a constant speed, because the generation of heat by friction changes the friction force. In this study, we proposed speed controllers of the ultrasonic motor, considering the temperature rise of the ultrasonic motor. From the results, these methods were proved the most effective for the speed control of the ultrasonic motor in experiments.