Impact dynamics of rough and surface protected MEMS gears

The paper provides an analysis of dynamics of micro-gear pairs, typically used in an assortment of micro-electromechanical system (MEMS) devices. It includes a mathematical hierarchical model of the impact dynamics of meshing gear teeth. It comprises the nanoscopic effect of asperity tips' adhesion for relatively rough surfaces on a microscopic level (overall contact domain). The analysis is extended to the depletion of long chain molecule self-assembled molecules (SAM) in impact behaviour of meshing gear-teeth pairs. The analyses show that for the usual high operating speeds of MEMS gears, due to high impact velocities, the role of asperity tips' adhesion is quite insignificant. However, the same is not true for lower impact velocities, which would occur under start-up, run-up to normal operating speeds or during deccelerative motions. The paper proposes a novel spectral-based approach to predict the degradation of the protective SAM layer between meshing teeth, while the mechanism is in continual relative motion. (C) 2008 Elsevier Ltd. All rights reserved.