Extremum seeking control of preload-controllable ultrasonic motor

Abstract:
Ultrasonic motors (USM) are electormechanical trasnducers with superior features in terms of compactness, weight, energy density, and power output. However, an optimum USM control strategy is still to be found. Their working principle is based upon exciting a traveling wave at the stator surface where frictional forces can be transferred to the rotor through sufficient preload. Under a constant preload force, common control strategies are based upon controlling the traveling wave amplitude through controlling the driving signal voltage amplitude, frequency, or phase difference. Yet, we propose dynamic preload control to expand the output power range with optimum efficiency. To maximize efficiency, Extremum seeking control (ESC) is applied to track optimum driving state, Adjusting a single control variable would limit the motor’s driving efficiency and its output power range.Thus, we propose Extremum Seeking Control (ESC) as an efficiency optimization technique and preload control for an extended output power control range.