An ultrasonic micromotor using a bending cylindrical transducer based on PZT thin film

Ultrasonic motors have a good high-torque performance. In particular, it seems that cylinder-type ultrasonic motors are superior to disk- or ring-type ones in the sense of high-torque application. For miniaturization of the motor size, a simple structure of an ultrasonic transducer becomes effective. This paper presents an ultrasonic micromotor using a bending cylindrical transducer based on a lead zirconate titanate (PZT) thin film on the side wall of a small tube. The transducer of the ultrasonic motor consists of a short cylindrical titanium pipe, PZT thin film and electrodes. The titanium pipe is introduced as a base material on which to deposit the PZT thin film by a hydrothermal method. The thickness of the film is about 9 mu m. The electrodes are divided into four parts in a circumferential direction to excite degenerate bending vibration modes with two r.f. driving electrical sources. A rotor loaded on the transducer turns in the intended direction. The maximum revolution speed is 295 rpm.