Design of Ultrasonic Motor for Driving Spherical Surface

This paper presents a new ultrasonic motor, which uses two sets of actuator in order to control the direction of the thrust within the tangential plane at the contact point of the actuator and the rotor. The drive unit consists of four piezoelectric stack actuators arranged in a pyramid shape. Circular vibration at the apex generates a thrust when a rotor is pressed against the apex. The direction of the thrust within the tangent plane of the rotor is controlled by the amplitude and phase differences among the four actuators. This enables a spherical drive if a spherical surfaced rotor is used. Experiments have verified that the direction of the thrust was controllable by the ratio between the two drive signals, as predicted by the theoretical analysis.