Topology optimization of bistable mechanisms with maximized differences between switching forces in forward and backward direction

A small bistable mechanism with a strong robustness to external disturbances is eagerly desired in many practical applications. The difference between the switching forces in forward and backward directions is a critical parameter influencing the robustness. However, the difference decreases with the size of bistable mechanisms. This study designs robust bistable mechanisms with maximized differences between the reaction forces at the desired critical points using topology optimization. The reaction forces are obtained by finite element analysis (FEA). Geometric constraints of the minimum length scale in topology optimization are employed to reduce the requirement on fabrication. An additive hyperelasticity technique is utilized to ensure the convergence of the nonlinear finite element problems. An approximate expression of the sensitivity is deduced to obtain the derivatives from ANSYS. The experimental studies indicate that the optimized mechanism is more stable than the conventional mechanisms based on inclined straight beams or preshaped curved beams. (C) 2019 Elsevier Ltd. All rights reserved.