| 摘要 |
PROBLEM TO BE SOLVED: To extend the interval between detection's of audible noise and to prevent the occurrence of audible noise in driving an ultrasonic motor by quickly increasing a driving frequency and afterward by decreasing it slowly when audible noise is detected from feedback signals. SOLUTION: If audible noise is detected from the feedback signals outputted from a piezoelectric element 26 provided on the elastic material of an ultrasonic motor 10 in the steady-state drive of the ultrasonic motor 10, a microcomputer 32 increases a driving frequency sharply by a given amount. Then, the driving frequency is lowered by an audible noise controlling means at a given decreasing speed lower than a given increasing speed so that it is restored to the driving frequency of a steady-state period. This enables the driving frequency to quickly move away from the frequency range which causes audible noise to occur. Therefore, it is possible to prevent production of audible noise in driving the ultrasonic motor 10. |
