PURPOSE: To increase a drive efficiency of an ultrasonic motor by controlling an drive frequency setting device to output a drive frequency for the muximum drive efficiency of the ultrasonic motor or by controlling a drive voltage setting device to output a drive voltage for the muximum drive efficiency of the ultrasonic motor.
CONSTITUTION: An output frequency of a drive frequency setting device 2 corresponds to a drive frequency of an ultrasonic motor and is controlled by an output from a drive condition detector 1. A drive voltage setting device 4 supplies an output from a phase shifting device 3 to the ultrasonic motor after amplifying it to the drive voltage needed for driving the ultrasonic motor. The drive voltage setting device 4 also varies the drive voltage and changes the drive speed of the ultrasonic motor. A drive condition detector 1 watches if the ultrasonic motor is driven in an antiresonance condition and controls the drive frequency setting device 2 by its output so that the ultrasonic motor may be kept driven in an antiresonance condition.
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