Design and Simulation of an Active Electrostatic Bearing for MEMS Micromotors

A new electrode design for a rotary micromotor where the ring-shaped rotor is suspended electrostatically in five degrees of freedom is presented in this paper with an aim to simplify the stator structure, capacitive sensing and electrostatic actuation. A glass-silicon-glass sandwich structure is utilized in this electrostatic micromotor which is fabricated by bulk silicon micromachining. The dynamics of the rotor for axial motion, translation in the z-direction and rotation about two in-plane axes, is derived and decoupled in an effort to achieve stable levitation of the rotor. Performance of the closed-loop levitation control system, based on the decoupled model, is simulated and presented in order to study the behavior of these electrostatic levitated bearings and further optimize the structure parameters. Simulation results demonstrate the superiority of the proposed three-electrode group design over traditional four-electrode group system in position sensing and overload capacity.