Monolithic Geared-Mechanism Driven by a Polysilicon Surface-MicroMachined On-Chip Electrostatic Microengine

Abstract

We have previously described a practical micromachined power source: the polysilicon, surface-micromachined, electro statically-actuated microengine [l]. Here we report on three aspects of implementing the microengine. First, we discuss demonstrations of the first-generation microengine actuating geared micromechanisms including gear trains with elements having dimensions comparable to the drive gear (approximately 50 m) and a relatively large (1600-m-diameter) rotating optical shutter element. These configurations span expected operating extremes for the microengine, and address the coupling and loading issues for very-low-aspect-ratio micromechanisms which are common to the design of surface micromachined devices. Second, we report on a second generation of designs that utilize improved gear teeth design, a gear speed-reduction unit, and higher force-per-unit-area electrostatic comb drives. The speed-reduction unit produces an overall angular speed reduction of 9.63 and requires dual-level compound gears. Third, we discuss a dynamics model developed to accomplish three objectives: 1) drive inertial loads in a controlled fashion, i.e. specify and achieve a desired time dependent angular position of the drive gear, 2) minimize stress and frictional forces during operation, and 3) as a function of time, experimentally determine forces associated with the drive gear, such as load torque being applied to the drive gear due to friction.