Magnetostatic MEMS relays for the miniaturization of brushless DC motor controllers

Abstract

Magnetostatic MEMS relays which are capable of commutating the field windings of a DC brushless motor are presented. The commutation system based on these relays is less than 10% the mass and volume of the electronics it replaces, it eliminates all but two wires from the wiring harness, it requires no external control and it dissipates less than 1/1000 th the total motor power. Closure forces greater than 5 millinewton are generated in the relays providing four-wire contact resistance readings of less than 35 milliohms. Utilizing gold-to-gold contacts, hot switching of currents greater than 1 amp has been demonstrated. For lifetimes greater than 10 million cycles (greater than 50 hours of continuous motor operation), switched currents should be limited to less than 120 milliamp. At signal levels of less than 1 milliamp, no failure is seen after greater than half a billion cycles. No contact bounce is seen during make or break. Motor commutation in vacuum down to 5 microtorr and from room temperature down to -30° C has been demonstrated.