| 摘要 |
PURPOSE:To prevent lowering of driving efficiency by detecting phase current flowing through a piezoelectric body thereby detecting the driving state of a motor. CONSTITUTION:Driving frequency of a ultrasonic motor is determined by the phase difference between the phase current flowing through the stator electrodes 1-1, 1-2 and a voltage to be applied on a piezoelectric body. Phase current is detected through a detecting resistor 12 and an active bandpass filter 2 separates only the basic wave component of the driving frequency. Detected current waveform is converted through a comparator 3 into logic level pulses, and a phase comparator 4 compares the phase of the driving voltage and the current. Oscillation frequency of a voltage control oscillator 6 is determined such that a predetermined phase difference is achieved. |
