Fundamental Study of Preload Control for Rotary Ultrasonic Motors

Abstract

In typical rotary Ultrasonic motors (USM), preload force between the stator and the rotor is carefully adjusted to offer the best compromise between maximum allowable torque and speed. The USM could then be controlled through varying the input power (voltage) to drive the motor within a certain range. However, the frictional force resulting from the fixed preload induces a high stationary torque which is not suitable for wide applications. This research studies the feasibility of employing a varying preload to control the USM. The performance of the USM was evaluated under variable static preload forces. The obtained results verify that operational range of the motor was expanded. Besides the study of static preload control, dynamic preload control was conducted by utilizing an additional linear piezo actuator. The performance under variable input voltages to the linear piezo actuator is evaluated. By employing a dynamically varying preload, the dynamic characteristics of the motor could be altered resulting in an improved system efficiency.