Ability Enlargement of Ultrasonic Motor Utilizing Two-Parameters-PWM Control

Abstract

Ultrasonic Motor (USM) has the capability of maintaining the torque continuously against an environment even under the switch-off. This characteristic is well-known as self-sustaining one and, thus, USM can produce “lock state”. “free state” can be also generated by switching CW and CCW commands periodically with the same time interval. In this paper, we newly propose Two-Parameters-PWM Control, in which OFF period is included between CW and CCW commands. This control contributes to changing the apparent friction between rotor and stator. For example, setting a large OFF period makes the friction increase, and as a result, the rotor becomes difficult to slip against an external torque. As an extreme case, the lock state can be generated.