Synthesis And Design Approaches For Compliant Multistable Mechanisms Based On Planar Linkages

A compliant multistable mechanism is capable of steadily staying at multiple distinct posi-tions without power input. Many applications including switches, valves, relays, positioners, and reconfigurable robots may benefit from multistability. Because the motion of a compli-ant multistable mechanism is always accompanied by complex nonlinear large deflections of the compliant members, it is difficult to synthesize and design a compliant mechanism with more than two stable equilibrium positions. Supported by the National Natural Science Foundation of China, this dissertation studies on the synthesis and design approaches for the compliant multistable mechanisms. The main works include:Based on a single compliant bistable mechanism and several link-slider modules, this dis-sertation presents two synthesis approaches for compliant multistable mechanisms, which utilize the bistable, the post-bistable and the reverse behaviors of the compliant bistable mechanism. Compound use of both approaches is also discussed. The equations are de-rived for calculating the motion ranges of the sliders, the distances of the stable equilibrium positions, the actuating force and the potential energy of the multistable mechanisms. The synthesis approaches are validated by several design examples and prototypes.By replacing each link-slider module in the configurations of the above compliant multi-stable mechanisms by an end-effector, a general configuration of the fully compliant mul-tistable mechanisms is obtained. The pseudo-rigid-body model method is used to derive the displacement and spring-back force formulas of the end-effectors. According to the al-lowable stress and the critical buckling load, the design parameters of the end-effector are determined. The effectiveness of the design approach is demonstrated by the successful operation of four fully compliant multistable mechanisms with four, seven and eight stable equilibrium positions.Three fully compliant multistable mechanism configurations are presented through employ-ing one end-effector and two compliant bistable mechanisms with different switching forces and different distances between the two stable equilibrium positions. The force-deflection characteristics of the two bistable mechanisms connected in series is obtained and the plot-ting approach for contour of the potential energy is provided, so as to analyze the motion of the compliant multistable mechanisms. Two examples with six stable equilibrium positions and one example with eight stable equilibrium positions are provided; the nonlinear finite element analysis results and a prototype verify the feasibility of the three configurations.The force and moment equilibrium equations and the input moment formulas are derived based on the pseudo-rigid-body model for the compliant five-bar mechanism. Three kine-matic coefficients are obtained by solving the moment equilibrium equations, and the nu-merical method for determining the position of the compliant five-bar mechanism driven by one moment is provided. By taking the compliant five-bar mechanism including two flexure hinges as an example, the solutions for the input moment equations are discussed, the condi-tions of existing three stable and three unstable equilibrium positions are obtained to design the compliant five-bar tristable mechanism, and are validated by three design examples.Finally, two design approaches based on unconstrained optimization algorithm and parti-cle swarm optimization algorithm are described to develop the compliant five-bar tristable mechanism, and two design examples are given to validate the proposed methods.In general, several novel compliant multistable mechanism configurations based on planar linkages are proposed, and the effective design approaches are presented to facilitate the design for the compliant multistable mechanisms.