Characteristics of traveling wave ultrasonic motor under atmosphere and vacuum cycle condition

Under atmosphere and vacuum cycle condition, characteristics of a disc-type traveling wave ultrasonic motor (TWUSM) are tested, variations of rotation speed with time and load are also obtained. Two vacuum conditions used are low vacuum of 2 Pa and high vacuum of 5 × 10⁻³ Pa. The lower the environment pressure is, the smaller the rotation speed of TWUSM. And load characteristics of TWUSM in vacuum are poorer than that in atmosphere. Then, using polyfluortetraethylene (PTFE) composite and p-hydroxybenzoic acid polymer (Ekonol) composite as friction materials, load characteristics of TWUSM are compared. As a result, the load characteristics of Ekonol composite are better than the former one, which can hold bigger torque with higher speed. Both principle of ultrasonic motor and knowledge of tribology are applied to analyze the reason that stall torque of TWUSM in vacuum is smaller than in atmosphere.