Compact ultrasonic rotary motors

This paper reviews recent developments of compact ultrasonic rotary motors using piezoelectric resonant vibrations. Following the historical background, three ultrasonic motors recently developed are introduced; windmill, PZT tube and metal tube types. Driving principles and motor characteristics are described in comparison with the conventional ultrasonic motors. Motors with 1.5 mm in diameter and 0.1 mNm in torque have been actually developed.