| 摘要 |
PURPOSE:To improve efficiency, and to stabilize the driving the title motor by inputting AC voltage into two regions in a piezoelectric body, measuring the phase difference of the voltage of two electrodes obtained by polarizing the electrodes not polarized and varying applied frequency so as to keep the phase difference constant. CONSTITUTION:An annular-shaped piezoelectric body 12 for an ultrasonic motor is composed of a polarized electrode 60 mounted on the electrode A51 side of an electrode 43 not polarized on the rear, an electrode 61 formed in the same manner, etc. The phase of output voltage from both electrodes 60, 61 is compared, and a phase comparator 70 outputting voltage corresponding to the phase difference and a voltage-frequency converter 71 generating the AC voltage of frequency corresponding to output voltage from the phase comparator 70 are provided. Consequently, when the resonance frequency of the piezoelectric body 12 is changed, output voltage from the phase comparator 70 is fluctuated, and the generating frequency of the voltage-frequency converter 71 is altered so as to coincide with the varying resonance frequency of the piezoelectric body 12. Accordingly, drive frequency and resonance frequency agree with each other at all times. |
