| 摘要 |
PROBLEM TO BE SOLVED: To detect a weak audible signal included in a feedback signal without any influence of a disturbance, by providing a difference between amplitude level of a drive frequency signal of an ultrasonic motor included in a feedback signal from a piezoelectric element and amplitude level of an audible signal. SOLUTION: A rotary sensor 46 outputs a pulse signal with a cycle corresponding to rotating speed of a rotor to a microcomputer 32. An oscillation circuit 34 is connected to one output terminal, while one input terminal of a switching control circuit 36 is connected to the other output terminal. The output terminal of the oscillation circuit 34 is connected to the other input terminal of the switching control circuit 36. The oscillation circuit 34 oscillates with an oscillation frequency in response to a signal from the microcomputer 32. The switching control circuit 36 switches a drive pulse according to the oscillation frequency from the oscillation circuit 34, and at the same time outputs the pulse to A/B phase amplification circuits 42 and 44. A drive frequency signal in a feedback signal and an audible signal are detected and outputted. |
