Modeling of contact with projections on rotor surfaces for ultrasonic traveling wave motors

Abstract

In this paper, we present a model of a contact interface with projections on the surface of the rotor of a traveling wave ultrasonic motor. The projections are introduced to enlarge the actual contact area between the stator and the rotor. The friction force is assumed to be proportional to the relative velocity between the rotor and the stator, which is different from the traditional model of using the Coulomb friction law. The relation between the preload and the output torque is computed. There is a certain preload that would result in a maximum output torque. This optimal preload, which gives the highest output torque, is larger when the projection density is higher.