Abstract: A driving apparatus for an ultrasonic motor which generates a driving force by using a piezoelectric member, wherein an oscillation frequency fd is varied so as to follow a driving frequency fm which is particular to a mechanical resonance frequency fro when the mechanical resonance frequency fro varies by influence of environment. For this purpose, current and voltage detectors are provided for respectively detecting the current corresponding to the mechanical vibration of the piezoelectric member and the voltage impressed on the piezoelectric member. The phase difference between the detected current and voltage is detected, and this phase difference is used to drive a variable frequency oscillator so as to maintain the phase difference constant. The output of the variable frequency oscillator is then used to drive the driving circuit for the piezoelectric member of the ultrasonic motor.

Abstract: In a driving circuit for a piezoelectric ultrasonic motor (23) supplying driving signal from an astable oscillator (51), which comprises an oscillation IC (49), a capacitor (48) and charge-discharge resistors (45, 46, 47), is controlled by controlling leakage current through a leakage resistor (47) to a point E, through controlling of the voltage of the point E by a temperature-dependent voltage producing circuit 52.

Abstract: In a driving apparatus for an ultrasonic motor, which motor has a stator comprising a pair of piezoelectric members for generating travelling mechanical vibrations, the driving apparatus has an oscillator, a phase shift circuit, and delay circuits. By deferring phases of two control signals for two switching devices, there is no fear of dangerous simultaneous turn-ons of the switching devices.

Abstract: An overcurrent protection apparatus for a DC motor which can be used with a speed control system of a DC motor to prevent an overcurrent condition arising when the DC motor is run with a heavy load or locked by an overload from burning or overheating windings of the motor. The apparatus is constructed using at least one integrated circuit and includes a current mirror circuit for detecting an overcurrent and for cutting off the supply current of the DC motor. A timing circuit prevents overcurrents lasting only a short time from triggering the apparatus to shut down the motor. Once the apparatus is triggered to shut off the motor, the motor will remain off for an indefinite period of time until the apparatus is reset.