Synthesis of Multistable Equilibrium Compliant Mechanisms.

Abstract

Whenever an engineering system operates far from its equilibrium position, the control and actuation scheme can become excessively complicated and power consuming. However, in a multistable compliant mechanism (MSCM), a passive subsystem can be integrated to afford discrete adaptability in function by providing additional equilibria thereby simplifying the actuation and control scheme. This dissertation explores the design and application of devices that exhibit multistability by exploiting compliance in design. MSCMs have the essential advantages of compliant mechanisms including reduced part-count, assembly time, wear, and increased precision, durability and reliability. However, there is no systematic method to design MSCMs and the majority of prior research is limited to design of specific types of bistable mechanisms. This is due to the fact that design of MSCMs is not intuitive and it requires enormous computational time to overcome the complexity of nonlinear behaviors. This study is motivated by the need to design MSCMs systematically without excessive computational time and complexity. The design methodology developed in this dissertation has two major components: (i) generalized methods for synthesizing bistable mechanisms and (ii) synthesis of multistable mechanisms by combining multiple bistable mechanisms. A mathematical formalism to ensure bistable behavior is first introduced. Two methods for synthesizing bistable mechanism are developed (i) by choosing “buckled” shape as initial configuration and (ii) by utilizing a reverse-lateral deformation of a clamped-pinned beam to provide bistability. Each bistable compliant mechanism works as a building block, providing either one or two additional stable states. A simplified mathematical scheme is introduced to capture essential parameters of bistable behaviors to aid in synthesis of more sophisticated multistable mechanisms. The methodology enables designers to capture design requirements mathematically, decompose the problem into feasible sub-problems, synthesize the desired MSCMs from pre-compiled combination libraries, and efficiently evaluate the designs without computationally intensive nonlinear FEA. The method also yields robust designs that are insensitive to manufacturing and other imperfections. The synthesis methodology can benefit a variety of applications including MEMS, space mechanisms, ergonomic devices, and general product design. Several novel designs and working prototypes of MSCMs are developed to demonstrate the effectiveness of the synthesis methods.