Design optimization of segment-reinforced bistable mechanisms exhibiting adjustable snapping behavior

Controlling the nonlinear bistable mechanics is crucial for the development of advanced bistable devices ranging from quantitative mass sensing to smart material/structures. However, for a large amount of pre-shaped bistable mechanisms, one or two specific bistable characteristics such as two switching forces, stroke and bistable index parameter cannot fulfill the special application requirements. Due to the complex coupling effects among different bistable mechanical properties, it is really difficult to modify one specific bistable character without affecting others by just modifying the structure parameters once the bistable configuration and boundary constraints are fixed. With the accurate mechanical analysis of MEMS bistable mechanisms, a novel optimization based method for designing specific bistable characteristic is proposed by modifying the beam local segment's geometry for optimizing the bistable index parameter and two switching forces respectively. Accordingly, five bistable compliant mechanisms are reconstructed symmetrically or asymmetrically for achieving different bistable mechanics. Also, the sharp change on the nonlinear force- displacement curve induced by the mode switching is analyzed. For experimental study, a quasi-cosine-shaped beam with reinforced local segments is manufactured by hot forming beryllium bronze sheet. The good agreement between the numerical simulation and experimental results validates the effectiveness of the optimization-based bistability design method, thus expanding the potential application range of compliant bistable mechanisms.