| The wear estimation of the friction materials used for rotary type wave traveling ultrasonic motors is strongly required to predict life of ultrasonic motors from a design point of view. However, the wear evaluation of friction is not constant. The wear loss is proportional to the pre-pressure and sliding distance between stator and rotor of ultrasonic motors. In this paper, ultrasonic vibration of stator surface points at the contact region of stator and rotor in ultrasonic motor is resolved into horizontal and vertical vibration. The horizontal vibration produces friction driving force and vertical vibration affects horizontal driving effect. The role of vertical ultrasonic vibration of stator surface point in ultrasonic motors is equivalent to the role of ultrasonic vibration being perpendicular to sliding direction in common sliding test. The pre-pressure with the ultrasonic vibration is less than the normal pro-pressure because of the effect of ultrasonic vibration. The sliding distance between stator and rotor of ultrasonic motors is proportional to the stator/rotor speed and ultrasonic motors' running time. The life of ultrasonic motor can be estimated by our proposed expression that was proved by life-test of ultrasonic motor. |