| 摘要 |
PURPOSE:To follow the output frequency of a VCO by a method wherein the rotation and stop of an ultrasonic motor is detected by a rotation and/or stopping detecting means while a reference voltage for rectifying a current for monitoring of the motor is controlled variably. CONSTITUTION:The current of the piezo-electric element of an ultrasonic motor 1 is monitored by a current monitoring means 2 and the wave form of the current is rectified and amplified to effect the feed-back of it. In this case, the rotation and/or stopping of the motor 1 is detected by a rotation and/or stopping detecting means 6. A reference voltage for the above-described rectification and amplification is controlled variably by the output signal through a reference voltage control means 7. According to this method, a reference voltage for rectifying and amplifying the wave form of the current of the motor 1 can be controlled automatically so as to be optimum even when the motor 1 is stopped by the change of a resonance frequency due to the change of the heat generation of the motor 1, an ambient temperature, the abutting force of a moving body, the magnitude of an impressing signal and the like. Accordingly, the output frequency of a VCO can be followed and the motor 1 can be driven again. |
