Characteristics of ultrasonic motors driven in a vacuum

Ultrasonic motors are driven by the frictional force between a rotor and a stator, and therefore, the contact surfaces are affected by ambient atmosphere. One example of severe driving conditions is a vacuum. First, friction materials, carbon fiber reinforced plastics and carbon metal, which have already been used for ultrasonic motors driven under atmospheric pressure conditions were tried out under two different vacuum pressures. Ceramic materials such as Al2O3, Si3N4 and SiC, have recently been tried out under two different vacuum pressures. The characteristics of motor, friction and wear such as rotor speed, maximum torque, friction coefficient and wear height, were measured and the feasibility of using the ultrasonic motor in vacuum was discussed.