An Optimum-Frequency Tracking Scheme for Ultrasonic Motor

This paper presents a high-efficiency optimum frequency tracking scheme with the ability to control the velocity for the ultrasonic motor. Prior to developing the scheme, characteristics of the ultrasonic motor being excited at the optimum frequency are analyzed, based on the mechanical quality factor of the ultrasonic motor. Then, the amplitudes and frequency of the input voltages are applied to stabilize the velocity and track the newly-discovered optimum frequency, at which frequency the motor maintains the minimum power consumption. The proposed scheme is implemented based on the quarter-phase three-level switching circuit. Experiments are carried out to verify the existence of the optimum frequency and the merit of the proposed scheme under load over a range of working frequencies. The results obtained have demonstrated that the proposed scheme is superior to the existing resonance and antiresonance frequency tracking approaches, in terms of tracking the preset reference velocity and maximizing the efficiency.