Experimental study of a variable-capacitance micromotor with electrostatic suspension

A variable-capacitance micromotor where the rotor is supported electrostatically in five degrees of freedom was designed, fabricated and tested in order to study the behavior of this electrostatic motor. The micromachined device is based on a glass/silicon/glass stack bonding structure, fabricated by bulk micromachining and initially operated in atmospheric environment. The analytical torque model is obtained by calculating the capacitances between different stator electrodes and the rotor. Capacitance values in the order of 10(-13) pF and torque values in the order of 10(-10) N m have been calculated from the motor geometry and attainable drive voltage. A dynamic model of the motor is proposed by further estimating the air-film damping effect in an effort to explain the experimental rotation measurements. Experimental results of starting voltage, continuous operation, switching response and electric bearing of the micromotor are presented and discussed. Preliminary measurements indicate that a rotor rotating speed of 73.3 r min(-1) can be achieved at a drive voltage of 28.3 V, equivalent to a theoretical motive torque of 517 pN m. Starting voltage results obtained from experimental measurement are in agreement with the developed dynamic model.