| 摘要 |
PROBLEM TO BE SOLVED: To make a resonance frequency applied to a vibrating body follow up the actual resonance frequency of the vibrating body when the actual resonance frequency varies by feeding a residual frequency generated by the residual vibration of the vibrating body back to a PLL control means. SOLUTION: When a duty ratio control circuit 12 does not apply a resonance frequency to a driving circuit 13, an ultrasonic motor 15 slightly vibrates owing to residual vibration caused by inertia. This residual vibration generates an electromotive force. A resistance 14 is provided so as to accelerate a flow of a current generated by this electromotive force and a sufficient current is supplied to a current monitor 15 and then shifted (delayed) in phase and converted into a voltage at the same time. Then the generated voltage is fed as actual resonance frequency information back to a PLL control circuit 11 through a zero-cross comparator 17. Consequently, the actual resonance frequency of the residual vibration can accurately be obtained from the electromotive force, and a sufficient signal can be obtained as the feedback signal of the PLL control circuit 11. |
