A cylindrical shaped micro ultrasonic motor utilizing PZT thin film (1.4 mm in diameter and 5.0 mm long stator transducer)

A cylindrical micro ultrasonic motor utilizing PZT thin film was fabricated and successfully operated on. The dimensions of a stator transducer were 1 .4 mm in outer diameter, 1.2 mm in inner diameter, and 5.0 mm in length. Th is volume is 17% compared to our previous motor (2.4 mm in diameter and 10 mm long stator transducer). To deposit a PZT thin film, a hydrothermal method was adopted. In this stud y, we developed an "improved nucleation process", and succeeded in improvin g the performance of the deposited PZT thin film. The thickness of a PZT th in film was 12 mu m, and the d(31) factor was -25 pC/N. The resonance frequency of the stator transducer was 227 kHz and the vibrat ion amplitude was 58 nm(p-p) at 4.0 Vp-p driving voltage. The rotor was dri ven by frictional force and the revolving direction was reversible. The max imum revolution speed was 680 rpm and the maximum torque was 0.67 mu N m. T he experimental conditions were 20 Vp-p and 5.3 mN pre-load. These results were investigated using an equivalent circuit from the point of a scale law. The performances of smaller ultrasonic motors were discusse d. The output torque of the motor with 0.1 mm diameter was estimated at 27 nN m. (C) 2000 Elsevier Science S.A. All rights reserved.