Patent ID: 7573180

Claim:
An ultrasonic motor which, by applying two-phase driving AC voltages to an ultrasonic vibrator, simultaneously produces a longitudinal vibration mode and a flexural vibration mode in the ultrasonic vibrator, giving rise to a substantially elliptical vibration at an output end of the ultrasonic vibrator to move the ultrasonic vibrator and a driven body that is in contact with the ultrasonic vibrator relative to each other, the ultrasonic motor comprising: a control unit configured to detect a vibration detection signal corresponding to the longitudinal vibration mode, to detect a phase difference between the vibration detection signal and any one of the driving AC voltages, to set a driving frequency such that the phase difference becomes a prescribed value, and to apply each driving AC voltage with the set driving frequency to the ultrasonic vibrator; wherein the ultrasonic vibrator includes a piezoelectric layered body in which a plurality of piezoelectric elements are laminated; at least one of the piezoelectric elements includes an internal electrode for vibration detection disposed in a region where positive electrical charges or negative electrical charges are generated in the longitudinal vibration mode and where positive electrical charges and negative electrical charges in substantially the same amount as that of the positive electrical charges are generated in the flexural vibration mode; and the control unit detects the vibration detection signal on the basis of electrical signals from the internal electrode for vibration detection.