| 摘要 |
A microcomputer outputs a driving frequency signal to an oscillator circuit and the oscillator circuit oscillates at a driving frequency designated by the microcomputer. A switching control circuit outputs switching signals to an A-phase amplifier circuit and to a B-phase amplifier circuit at a predetermined timing. The A-phase amplifier circuit and the B-phase amplifier circuit each convert a DC voltage supplied by a voltage control circuit to an AC voltage and supply the same to two piezoelectric bodies of an ultrasonic motor. Due to the AC voltage being supplied to each of the two piezoelectric bodies, the ultrasonic motor is driven. At the start time of driving the ultrasonic motor, by gradually increasing the voltage level of the DC voltage outputted from the voltage control circuit and also gradually increasing the voltage level of a driving voltage to be supplied to the piezoelectric body of the ultrasonic motor, a stator and a rotor of the ultrasonic motor are gradually separated from each other. Further, in a case in which the voltage has been increased to a predetermined voltage level, the driving frequency is gradually lowered to increase the number of revolutions of the motor, thereby making it possible to lessen the vibration of the ultrasonic motor at the start time of driving. As a result, the generation of an audible sound can be prevented.
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