| 摘要 |
PURPOSE:To detect the oscillating state of an ultrasonic motor without increasing its size by providing a third piezoelectric body which detects the oscillating state of progressive oscillatory waves by converting the oscillation of the oscillatory waves into electric signals and positioning the piezoelectric body to a location where a prescribed spatial phase difference is obtained on an elastic body. CONSTITUTION:An oscillation controller 14 controls the oscillation frequency of an oscillator so that voltage signals from a segment electrode for detecting oscillation can reach a peak. The voltage signals are detected by means of a detecting section 15 after unnecessary bands are removed through a band-pass filter 13 and a difference hold circuit 16 discriminates whether the voltage signals are in the increasing direction or decreasing direction with respect to the lapse of time. An oscillation control section 17 inputs the obtained information and controls the oscillator to always increase the voltage. When such an arrangement is made, the optimum frequency is always outputted from the oscillator and the rotation of the ultrasonic motor is maintained in the optimum state even when the resonance frequency between a ring-like piezoelectric body and elastic body in an ultrasonic motor is changed by disturbance. |
