Research of a Spherical Motor with Three-Degree-of-Freedom Driven by Ultrasonic Linear Actuators

Abstract

To realize an actuator with many degrees of freedom which moves like a human wrist, a spherical motor with three-degree-of-freedom is tried, the spherical body of which is driven by ultrasonic linear actuators, and consequently, the spherical motor has no limitation on the position of its rotational axis in principle, and can rotate around an arbitrary spatial axis at an arbitrary speed. The spherical body of the motor is a steel bearing ball of 76.2mm in diameter. The six ultrasonic linear actuators are placed at every sixty degrees on the horizontal outer circumference of the ball; a pair of two actuators lying symmetrically regarding the center of the ball induce a rotational torque. In an experiment the ball rotated around the vertical z-axis at 15rpm, and also rotated around other spatial axes adjusting the outputs of the three pairs of actuator.