Multi-Objective Optimization of a Compact Compliant Rotational Bistable Mechanism with a Large Angular Stroke Using Chained Beam Constraint Modeling

Bistable mechanisms can maintain two distinct stable equilibrium states without continuous energy input. Although translational bistable mechanisms have attracted considerable research attention, rotational bistable mechanisms (RBMs) remain relatively underexplored, and a systematic optimization-based framework for designing RBMs subject to specific constraints is still lacking. This paper proposes an automated optimization framework that integrates the chained beam constraint model (CBCM) with the Non-dominated Sorting Genetic Algorithm II (NSGA-II). The accuracy and computational efficiency of CBCM in large-deflection analysis enable NSGA-II to efficiently explore the design space and identify Pareto-optimal solutions. The proposed framework produced a compact RBM with an outer diameter of 50 mm and a rotational stroke of up to 90°. Experimental validation showed that the fabricated mechanism reached its second stable equilibrium position at approximately 87°. These results demonstrate the feasibility of designing compact RBMs with large angular strokes. In addition, a parametric study was conducted to evaluate the effect of beam width on the agreement between CBCM and finite element analysis (FEA), thereby clarifying the applicability and limitations of CBCM for RBM design.