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Circuitry for driving an ultrasonic motor in which a rotor is driven by travelling waves generated by a piezoelectric effect, which circuitry includes a pulse generator for generating pulses applied to the ultrasonic motor for driving the same, a driving pulse width changing circuit for changing the

Circuitry for driving an ultrasonic motor in which a rotor is driven by travelling waves generated by a piezoelectric effect, which circuitry includes a pulse generator for generating pulses applied to the ultrasonic motor for driving the same, a driving pulse width changing circuit for changing the width of the driving pulse to change the rotational speed of the motor, a feed-back piezoelectric element provided on the motor for generating a feed-back signal in response to the rotational speed of motor, and a driving frequency automatic tracking circuit responsive to the feed back signal from the motor for generating a voltage signal to control the pulse generator.

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Circuitry for driving an ultrasonic motor in which a movable member which is in a frictional contact relationship with the surface of an elastic member is forcedly moved by applying an alternating voltage to a piezoelectric element secured to said elastic member to generate travelling vibration wave

Circuitry for driving an ultrasonic motor in which a movable member which is in a frictional contact relationship with the surface of an elastic member is forcedly moved by applying an alternating voltage to a piezoelectric element secured to said elastic member to generate travelling vibration waves upon the surface of the elastic member, comprising; a voltage controlled oscillator for generating rectangular waves having a frequency 4n times (where n is an integer) greater than that of said applied alternating voltage; a distributor for separating said rectangular waves into four phase pulse wave (f0, f1, f2 and f3 wherein f0 and f1; f2 and f3 are 180°out-of-phase with each other, f0 and f2, f1 and f3 being 90°out-of-phase with each other); a saw-tooth-wave generator for generating saw-tooth-wave signals which are in synchronization with said rectangular waves; a pulse width modulating comparator for comparing the level of said saw-tooth-wave signals with that of a reference voltage; a reference voltage adjusting means for changing said reference voltage in response to an external operation; a driving pulse width changing circuit for changing the width of said four phase pulses in response to the output from said pulse width modulating comparator; an output circuit which combines 180°out-of-phase pulses f0 with f1; f2 with f3, the pulse width of which have been changed by said driving pulse width changing circuit and amplifies the combined pulses to apply them to said piezoelectric element as two 90°out-of-phase alternating voltages; a feed-back piezoelectric element secured to said elastic member for generating a feed back signal developed due to the piezoelectric effect on driving of the ultrasonic motor; and a driving frequency automatic tracking circuit responsive to said feed back signal for outputting to said voltage controlled oscillator a voltage signal representative of a difference between an optimum driving frequency and a current driving frequency.