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

Abstract

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. This 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 study, we developed an “improved nucleation process”, and succeeded in improving the performance of the deposited PZT thin film. The thickness of a PZT thin film was 12 μm, and the d 31 factor was −25 pC/N. The resonance frequency of the stator transducer was 227 kHz and the vibration amplitude was 58 nm p–p at 4.0 V p–p driving voltage. The rotor was driven by frictional force and the revolving direction was reversible. The maximum revolution speed was 680 rpm and the maximum torque was 0.67 μN m. The experimental conditions were 20 V p–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 discussed. The output torque of the motor with 0.1 mm diameter was estimated at 27 nN m.