Friction drive of an SAW motor. Part III: modeling.

A 2-layer modeling method of friction drive of a surface acoustic wave motor is proposed. The surface layer accounts for the previously proposed point-contact friction drive model, which was generalized to correspond spatially to the underlying layer that is comprised of a 3-D elasticity field. A method to determine stiffness through the use of analytical solutions of 3-D contact problems bridges the 2 layers. Because the determined stiffness expresses the accuracy of the results regarding either layer, the validity of the results concerning the stiffness and the resulting stress field was evaluated by comparison with the results of finite element analysis. Furthermore, we executed numerical simulations by using the friction drive model, which were compared with the measured displacements of the frictional surface of the slider. The simulation accurately represented the normal displacement of the frictional surface; the modeling procedure in the normal direction was found to be reliable. However, because the friction coefficient drastically changes the tangential displacement, we could not discuss the reliability of the modeling procedure in the tangential direction. A thorough discussion of the friction drive would thus require further investigation of the friction phenomena.