Evidence for pre-sliding tangential deflections in MEMS friction

We have developed a new inchworm actuator, consisting of a plate and two frictional clamps, which utilizes leveraged bending for improved amplitude control. Here we investigate its friction characteristics. We measure its average slip per cycle as a function of friction load and independently measure the clamp friction coefficients. A model is developed that takes into account the electromechanics of the actuation plate, boundary conditions and clamp friction. We find that the model does not satisfactorily describe the operation of the actuator. We attribute this to pre-sliding tangential deflections and devise a test whose results are consistent with this phenomenon. This suggests that stable pre-sliding deflections control the behavior of nanometer-scale slip events in MEMS.