Friction and wear in microfabricated harmonic side-drive motors

Abstract

Polysilicon variable-capacitance rotary harmonic side-drive micromotors and results from operational and frictional studies of these motors are described. Quantitative studies of wear under electric excitation are also reported. Voltages as low as 26 V across 1.5- mu m gaps are sufficient for operation. Frictional force estimates of 0.15 mu N at the bushings and 0.04 mu N in the bearings are obtained from measurements of stopping voltages. Extended operation of these motors to near 100 million wobble cycles at excitation frequencies of 10000 r.p.m. and 25000 r.p.m. for operational durations of 150 h and 71 h, respectively, are studied. The results indicate that bearing wear is significant and results in changes in the gear ratio of the motors by as much as 20%. Typical gear ratios are near 90 at the start of motor operation and decrease to about 70 as the bearings wear out.