ROLLING FRICTION IN A LINEAR MICROACTUATOR

In order to design a precise and repeatable microelectromechanical system, friction and wear must be minimized in the surfaces of the microstructure. Rolling bearings are known to exhibit lower friction over sliding contact bearings in precision macromechanical systems. Rolling friction can be characterized on a microscale to facilitate the design of precision microelectromechanical systems. We have designed a test specimen utilizing stainless steel microballs (285 mum in diameter) in contact with silicon micromachined v-groove surfaces (310 mum wide, 163 mum deep, 10 000 mum long). Different thin films are deposited on the surface of the silicon v grooves and their frictional properties are investigated experimentally. We have shown that at zero applied normal force, the adhesion is dominant and as the applied normal force is increased, the friction coefficient reaches an asymptotic value below 0.01. The measured frictional forces represent the total resistance at the onset of rolling motion for the bearing which is generated at all the contacting surfaces. The measured values for the coefficient of friction will allow designers to select optimum lubricant surfaces to be used in microroller bearings using microballs and silicon micromachined V-groove surfaces.