Coupled electrostatic and mechanical FEA of a micromotor

Abstract

The electrostatic forces occurring in a novel double stator axial-drive variable capacitance micromotor (VCM) are studied as a function of rotor-stator overlap, applied voltage, rotor support morphology, and rotor thickness. Analytical equations are developed using parallel plate assumptions, and results are compared with those obtained with 3D Finite Element Analysis (FEA) for tangential, axial, and radial electrostatic forces. The influence of the axial forces on the rotor deflections are studied using iterative indirect coupled field analysis, where the axial forces obtained from the electrostatic 3D FE model are iteratively applied to a structural FE model until stable rotor deflections are obtained. It was found that the axial forces, taking the rotor deflection into account, are twice as high as those obtained by analytical evaluation neglecting rotor deflections and about 70 times higher than the radial forces at a typical operating voltage of 100 V. Inclusion of bushing supports results in lower axial forces and decreases the influence of rotor tilt. Tangential forces likely to be exerted on the rotor at start-up are also examined and compared with analytical predictions. The study demonstrates that FEA provides more accurate results than analytical equations due to the geometry and field simplifications assumed in the latter. >