Circuit and method of driving an ultrasonic motor to method for driving an ultrasonic motor

A method of driving an ultrasonic motor having a stator, a piezoelectric element carried by the stator, the piezoelectric element that is divided into two portions, a rotor that is rotatably mounted on the stator such that the rotor is driven by applying drive signals of different phases to the two portions of the piezoelectric element, and a monitor electrode for outputting a monitor signal indicative of the vibration of the rotor, the method comprising the steps of:

• setting a start drive frequency higher than a resonant frequency of the motor;
• setting a target frequency for the drive signals that is lower than the resonant frequency of the motor;
• sweeping the frequency of the drive signals from the start frequency to the target frequency;
• detecting abnormal vibrations of the rotor occurring during sweeping of the drive frequency based on the monitor signal, wherein in the event that an abnormal vibration is detected, the target frequency is reset to equal the actual drive frequency at the time the abnormal vibration was detected, and the actual drive frequency is reset to a reset start frequency that is higher than the reset target frequency;
• and
• repeating the drive frequency sweeping step.