| 摘要 |
PROBLEM TO BE SOLVED: To suppress the influence of an unneeded vibration mode and to stabilize its self-excitation oscillation in the self-excitation oscillation drive of an ultrasonic motor by setting the resonance point of the unneeded vibration mode higher than that of the vibration mode used for operation when the unneeded resonance point exists near the target resonance point. SOLUTION: In a drive circuit 13 of an ultrasonic motor using a Colpitts-type self-excitation oscillation circuit, two buffers 16a and 16b are connected to two electrode groups of a piezoelectric element 7. Then, a resonance circuit is composed of a vibrator that is connected to the piezoelectric element 7 and two capacitors 18 and 19, a signal from a resonance circuit is inverted and amplified by an inversion amplification circuit consisting of an inverter 15a and a resistor 14a and is returned to the resonance circuit, thus continuing oscillation. In this case, the resonance point of unneeded vibration is set higher than the resonance point of target vibration, and at the same time a circuit constant is optimized for self-excitation oscillation, thus suppressing the influence of unneeded vibration and stabilizing operation and improving efficiency. |
