| 摘要 |
PURPOSE:To facilitate execution of ordinary automatic speed control within a correct allowable frequency range by a method wherein an actual resonant frequency is measured and the frequency of an ultrasonic motor is automatically controlled so as not to be out of the resonant frequency at the time of start and the allowable frequency range is variably controlled in accordance with the measured resonant frequency. CONSTITUTION:An amplitude detecting piezoelectric unit 4 which is inserted between arbitrary piezoelectric elements 1b and 1c among a plurality of piezoelectric elements 1a - 1d of which a stator 2 is composed and detects the vibrations of the adjacent piezoelectric elements 1b and 1c and outputs the amplitudes of the vibrations as a feedback signal E, a resonant frequency measuring means 7a and 7b which measures a resonant frequency from the variation characteristics of the feedback voltage E outputted from the amplitude detecting piezoelectric unit 4 following the variation of the frequency of driving signals (a) and (b) and an allowable frequency range setting means 9 which sets the allowable frequency range in accordance with the resonant frequency measured by the resonant frequency measuring means 7a and 7b are provided. In other words, the actual resonant frequency is measured and the allowable frequency range is variably controlled. With this constitution, speed control can be always performed automatically within the correct allowable frequency range. |
