Dynamic Friction and Wear in a Planar-Contact Encapsulated Microball Bearing Using an Integrated Microturbine

The demonstration and characterization of a novel planar-contact encapsulated microball bearing using a radial in-flow microturbine are presented. Stable operation of the air-driven silicon microturbine is shown for over 1 000 000 revolutions at speeds, pressure drops, and flow rates of up to 10 000 r/min, 0.45 lbf/in2, and 3.5 slm, respectively. Incorporation of a gas thrust plenum using a novel packaging scheme has enabled comprehensive spin-down friction characterization of the encapsulated microball bearing. An empirical power-law model for dynamic friction has been developed for speeds of 250-5000 r/min and loads of 10-50 mN, corresponding to torques of 0.0625-2.5 muNldrm and friction torque constants of 2.25-5.25 x 10-4muNldrm/ r/min. The onset and effect of wear and wear debris have been studied, showing negligible wear in the load bearing surfaces for the operating conditions considered.