Quick and precise position control of ultrasonic motors with dual mode control

The ultrasonic motor (USM) is a new type motor that has many excellent performances and features which are not available in electromagnetic type motors. Therefore, it expected to be of practical use in small motor applications. The phase difference control of applied voltages seems to be most suitable for position control of this motor. However, it is difficult to carry out quick and precise position control at the same time when driving frequency is constant. In this paper, to achieve quick and precise position control, both driving frequency and phase difference of applied voltages are controlled. The effectiveness of this method is demonstrated by experiments