High-Speed Thin Ultrasonic Spindle Motor and Its Application

In this paper, we report an ultrasonic motor capable of high-velocity revolution applicable for long continuous high operation as a microfan. This study is a response to the new challenge of developing a new field of applications for an ultrasonic motor. Ultrasonic motors using a longitudinal-flexural coupling-vibration mode of a thin plate with a vibrating piece or step-horn are considered. A stator vibrator consists of a metal plate sandwiched by two thin unipoled piezoelectric ceramic plates, the electrodes of which are not divided, and this ultrasonic motor can be driven by a single ac source. Not only the coupling between a longitudinal vibration and flexural one but also the transformation of a longitudinal vibration velocity by a vibrating piece λ/4 long and step-horn λ/2 long are used. They will be effective at making the rotary speed fast. As a result, an ultrasonic motor 0.55 mm thick rotated a shaft 1.5 mm in diameter over 8,000 rpm under conditions of an applied voltage of 30 Vp-p and an input power of only 0.16 W.