Extended optimum frequency tracking scheme for ultrasonic motor

This work presents a general optimum frequency tracking scheme for an ultrasonic motor, which no longer requires the amplitudes of the applied voltages to keep identical. The proposed scheme here greatly extends the application of the optimum frequency in comparison to the existing studies. The mechanical quality factor of an ultrasonic motor is initially derived to describe the loss, which further is also in proportion to the temperature rise. The optimum frequency from the loss reduction viewpoint is then obtained, at which frequency the ultrasonic motor maintains the minimum loss and subsequently the minimum temperature rise. The optimum-frequency tracking scheme is subsequently constructed. Experiments are carried out to verify the existence of the optimum frequency and the reduction of the temperature-rise under the applied voltages in the general form, whose amplitudes and phase difference are all adjustable. The results have inferred that the optimum frequency still exists even though the applied voltages are in the general form, at which frequency the temperature-rise is obviously reduced in the absence of any external cooling equipment. The optimum frequency of the ultrasonic motor now gets closer to the industrial applications, especially when the applications require the velocity adjustment in a wide range.