Compliant bistable mechanisms,devices with two distinct stable equilibrium positions,are used in a variety of applications,such as switches,clasps,and valves.Many kinds of compliant bistable mechanisms were proposed and studied during the past decade.Among them,tension-based compliant bistable mechanisms,that incorporate tension pivots as their flexible members,feature in short travel distance and low power consuming.So far,the design of this kind of bistable mechanisms is done using finite element method through trial and error,thus is time-consuming.By treating the tension pivots as fixed-guided segments and their elongation as a spring,we developed a novel three degree-of-freedom (3-DOF) pseudo-rigid-body model (PRBM) for this kind of bistable mechanisms.The principle of virtual work is used to derive the force-deflection relationship of the PRBM model.The comparison between the PRBM results and the experimental results of the force-deflection characteristics shows that the PRBM can predict not only the bistable behavior of the tension-based bistable mechanisms,but also their soft spring-like post-bistable behavior and the spring-like force-deflection characteristics when pulling in the reverse direction from the as-fabricated position,which is called reverse behavior.The 3-DOF PRBM can be used to design and identify tension-based bistable mechanisms.Using the PRBM instead of the trial-and-error method can greatly reduce the development time of this kind of bistable mechanisms.
A compliant metamorphic mechanism attributes to a new type of metamorphic mechanisms evolved from rigid metamorphic mechanisms. The structural characteristics and representations of a compliant metamorphic mechanism are different from its rigid counterparts, so does the structural synthesis method. In order to carry out its structural synthesis, a constraint graph representation for topological structure of compliant metamorphic mechanisms is introduced, which can not only represent the structure of a compliant metamorphic mechanism, but also describe the characteristics of its links and kinematic pairs. An adjacency matrix representation of the link relationships in a compliant metamorphic mechanism is presented according to the constraint graph. Then, a method for structural synthesis of compliant metamorphic mechanisms is proposed based on the adjacency matrix operations. The operation rules and the operation procedures of adjacency matrices are described through synthesis of the initial configurations composed of s+1 links from an s-link mechanism (the final configuration). The method is demonstrated by synthesizing all the possible four-link compliant metamorphic mechanisms that can transform into a three-link mechanism through combining two of its links. Sixty-five adjacency matrices are obtained in the synthesis, each of which corresponds to a compliant metamorphic mechanism having four links. Therefore, the effectiveness of the method is validated by a specific compliant metamorphic mechanism corresponding to one of the sixty-five adjacency matrices. The structural synthesis method is put into practice as a fully compliant metamorphic hand is presented based on the synthesis results. The synthesis method has the advantages of simple operation rules, clear geometric meanings, ease of programming with matrix operation, and provides an effective method for structural synthesis of compliant metamorphic mechanisms and can be used in the design of new compliant metamorphic mechanisms.
