Optimum Efficiency Control of Traveling-Wave Ultrasonic Motor System

The operational efficiency of ultrasonic motor motion control systems is much lower than that of traditional electromagnetic motors, which badly restricts the application of ultrasonic motor in portable devices. Lower efficiency, robustness, and wear condition are the main problems of ultrasonic motor systems. This paper studies on the optimum efficiency control strategy of an ultrasonic motor system and selects the commercially used ultrasonic motor Shinsei USR60 as the experimental motor. To provide a basis for the optimum efficiency control, the control characteristic of system efficiency is studied first under speed closed-loop control condition. Then, a novel feedforward speed controller compounded with a pole-assignment controller is designed to compensate the disturbance caused by the efficiency optimization process. After that, the optimum efficiency control strategy with varying step length based on fuzzy reasoning is proposed. Experiments show that the proposed optimum control methods can greatly increase the operational efficiency of the ultrasonic motor system.