AN EXPERIMENTAL-TECHNIQUE AND A MODEL FOR STUDYING THE OPERATION OF HARMONIC SIDE-DRIVE MICROMOTORS

This paper studies the operation of harmonic side-drive micromotors through gear ratio measurements and modeling of the micromotor dynamics. A simple experiment in which the wobble micromotor gear ratio is measured as a function of excitation voltage and pattern is used to characterize micromotor operation. This experiment in conjunction with the micromotor dynamic model presented can be used to study friction at the micromotor bearing and bushing contacts by fitting the model to the experiment. The model is based on a detailed analysis of the electrostatic and friction forces acting on the bearing and bushing contacts. In particular, the model accounts for sliding and rolling of the rotor on the bearing, and sliding of the rotor on the bushing. The model can be used in conjunction with the experiment to estimate the bearing coefficient of friction and the bushing friction force. For micromotor operation in nitrogen gas, a polysilicon on polysilicon coefficient of friction of 0.36-0.4 is estimated. The bushing frictional force is found to consist of a constant term and a term that depends on the square of the excitation voltage.