A study on high-efficiency drive of ultrasonic motors

Ultrasonic motors possess many advantages, such as high torgue, low speed. compact size, and no magnetic field generation; however, there are several technical problems to be solved. Improvement of efficiency is important fro m a low power drive view point. The purpose of this work is to achieve maxi mum efficient drive of ultrasonic motor. Firstly, this paper shows characte ristics based on efficiency of ultrasonic motor and proposes a search metho d of maximum efficiency point. Furthermore, this paper presents a speed con trol method of the motor by PWM control of DC source combined with drive fr equency control in order to realize maximum efficient drive.