Fully compliant bistable mechanisms with enhanced pitch stiffness

For compliant bistable mechanisms with planar configurations and exhibiting two in-plane stable states, their flexible beams are supposed to undergo in-plane bending deflections, but the out-of-plane deflections can significantly influence the kinetostatics of the mechanism, resulting in inconsistent bistable behaviors when off-axis or eccentric loads present. In this paper, we propose a novel bistable mechanism utilizing torsion-stiffness enhanced flexible beams to restrain the shuttle from out-of-plane rotation. An analytical kinetostatic model is developed for the proposed bistable mechanism. Five bistable examples are presented to demonstrate the effectiveness of the proposed bistable mechanism in suppressing unwanted motions and the correctness of the proposed kinetostatic model. The results show that the novel bistable designs are much stiffer along the out-of-plane rotation thus are more robust against off-axis or eccentric loading condition, especially when the shuttle is displaced to a position around the second equilibrium stable position (where the flexible beams are in the post-buckling states).