Metrics for Evaluation and Design of Large-Displacement Linear-Motion Compliant Mechanisms

This work introduces metrics for large-displacement linear-motion compliant mechanisms (LLCMs) that evaluate the performance tradeoff between displacement and off-axis stiffness. These metrics are nondimensionalized, consisting of relevant characteristics used to describe displacement, off-axis stiffness, actuation force, and size. Displacement is normalized by the footprint of the device, transverse stiffness by a new performance characteristic called virtual axial stiffness, and torsional stiffness by the characteristic torque. These metrics account for the variation of both axial and off-axis stiffness over the range of displacement. The metrics are demonstrated for several microelectromechanical systems (MEMS) that are sensitive to size because of high cost and off-axis stiffness because of function. The use of metrics in design is demonstrated in the design of an LLCM; the resulting design shows increased values for both the travel and transverse-stiffness metrics.