The micro-mechanism of friction drive with ultrasonic wave was analyzed experimentally and theoretically by using a newly developed apparatus. With this apparatus, it was possible to measure the friction force at the contact interface between a rotational disk and an oscillatory pin induced by ultrasonic wave. This friction couple simulated the contact behavior of the ultrasonic wave motor. The type of pin motion (whether reciprocating or circular), its amplitude and rotational speed of disk could be controlled in this apparatus. The friction force increased with the increase of the rotational speed of disk and the decrease of the amplitude of pin motion. In the case of circular pin motion, the friction force was applied in a negative direction when the rotational speed of disk was below a critical value. The micro-mechanisms of this friction drive were analyzed theoretically by introducing a relationship between tangential coefficient and micro-displacement at the contact region, and the observed friction force as a function of the rotational speed of disk and the amplitude of pin motion was well explained by the introduced theory.
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