| 摘要 |
PURPOSE:To obtain a rotational force which requires a low power-consumption power and is needed when driving an ultrasonic motor. CONSTITUTION:In the initial state of drive, the duty ratio of the output pulse of a pulse width modulator 47 is set so that a target maximum speed can be reached by the output power of a DC-DC converter 48 when not loaded. Then, when a load increases, a drive frequency decreases and rotational force increases. When the power supplied from the converter 48 is smaller than the power required for driving, a motor stops before a required rotational force is reached, the DC voltage value obtained from the rotational speed signal becomes smaller than a voltage value which is a reference for judgment outside a region which can be driven, the output of the comparator 45 is set to a high level, the oscillation frequency of a voltage-controlled oscillator 22 is shifted to a higher frequency than the resonance frequency of a vibration body before restarting, and the duty ratio of the output pulse of a pulse width modulator 47 is increased with a certain ratio, and power supplied from the converter 48 also increases. |
