Ultrasonic Rotary Motor Using Longitudinal and Bending Multimode Vibrator with Mode Coupling Caused by External Additional Asymmetry

The present paper deals with the ultrasonic rotary motor using a longitudinal and bending multimode vibrator constructed so that the mode coupling is caused by external additional asymmetry. It is well known that on a rectangular piezoelectric plate vibrator with its two corners cut diagonally or a parallelogram-shaped piezoelectric plate vibrator, the first longitudinal and second bending vibration modes are coupled under a certain dimensional condition. The motor mentioned above is to use this phenomenon; that is, a one-channel drive, reversible rotary motor can be achieved. From results of measurement and calculation of such a trial vibrator, it was found that there were two new resonance vibration modes in the neighborhood of degenerate resonance frequencies of original longitudinal and bending vibrations; hence, the directions of rotor revolution were different at both new modes when the mode-coupled vibrator was used to construct an ultrasonic rotary motor. The trial motor has proven that a simple ultrasonic motor could be easily constructed and it was suitable for light-load use because of its small contact area to the rotor.