An ultrasonic motor using an injection-molded plastic rotor and its application to motor-driven potentiometers

Ultrasonic motors, used as compact servomotors for precision positioning, have many advantages over electromagnetic motors. However, they have a complicated structure and require a complicated drive circuit, which makes them costly. This study has realized a low-cost ultrasonic motor for application to low-cost products. The first application target was as the motor of a high-voltage focus adjustment potentiometer in a CRT monitor. A motor was fabricated and operated successfully. For the basic type of ultrasonic motors, a piezoelectric revolving resonator (PRR)-type motor was adopted because it simplifies the structure. In addition, the rotor of the main component was produced using injection-molded plastics. This ensured stable generation of the torque, low cost, and good mass productivity. The diameter of the outer rotor was 24 mm and the motor achieved a large holding torque of 150 gf-cm, and a low drive voltage of between 5 and 10 V. An inclined contact coil brush was developed for the motor-driven potentiometer. The coil brush realized stable multipoint contact with a very light load of 10 gf-cm. The rotor and the brush holder were formed integrally, which provided a compact structure. This paper describes structural design of the ultrasonic motor and the motor-driven potentiometer, their operation, and experimental results. (C) 2000 Scripta Technica.