The most widely known nonlinear phenomena in Micro-electro-mechanical systems (MEMS) are probably the contact instabilities. Contact problem is an important topic in the research of micro-motors. While the micro-motor is in operation, the rotor is intended to be in electrical contact with the ground plane, and the rotor and bearing hub form a pair of contact bodies. In the paper, a mathematic model is proposed to describe the contact process and two simplified contact finite element models of the rotor, bearing and ground plane are presented to simulate the contact. The effects on the contact stress, strain and pressure are analyzed in micro-scale. The rotor-to-bearing-hub and the hemispherical-bushing-on-ground-plane configurations finite element models (FEM) are established and the implementation of the contact problem is introduced to provide the numerical solutions acted as a guide to solution of contact problems in a variable capacitance micromotor. The numerical results of the contact stress, strain and pressure and the effects of the coefficient of friction and the surface roughness of the contact pairs on contact characteristics are studied and discussed in detail. It is indicated that the nonlinear effects should not be ignored and these results must be evaluated on a relative scale to compare different design options.

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