The purpose of this research is to develop the tools necessary to create tristable compliant mechanisms; the work presents the creation of models and concepts for design and a demonstration of the feasibility of the designs through the fabrication of tristable compliant mechanism prototypes on the macro scale. Prior methods to achieve tristable mechanisms rely on detents, friction, or power input; disadvantages to these methods include a high number of parts, the necessity for lubrication, and wear. A compliant tristable mechanism accomplishes tristability through strain energy storage. These mechanisms would be preferable because of increased performance and cost savings due to a reduction in part count and assembly costs. Finite element analysis and the pseudo-rigid-body model are used to design tristable compliant mechanisms. The mechanisms are initially designed by considering symmetrical or nearly symmetrical mechanisms which achieve a stable position if moved in either direction from the initial (fabrication) position, thus resulting in a total of three stable positions. The mechanisms are fabricated and tested in both partially and fully compliant forms, and efforts to miniaturize the mechanism are discussed. The basic mechanism design is used as a starting point for optimization-based design to achieve tailored stable positions or neutrally stable behavior. An alternative to fabrication methods commonly used in compliant mechanisms research is introduced. This method integrates torsion springs made of formed wire into compliant mechanisms, allowing the desired force, stiffness, and motion to be achieved from a single piece of formed wire. Two ways of integrating torsion springs are fabricated and modeled, using either helical coil torsion springs or torsion bars. Because the mechanisms are more complex than ordinary springs, simplified models are presented which represent the wireform mechanisms as four-bar mechanisms using the pseudo-rigid-body model. The method is demonstrated through the design of mechanically tristable mechanisms. The validity of the simplified models is discussed by comparison to finite element models and experimental measurements. Finally, fatigue testing and analysis is presented.



College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering



Date Submitted


Document Type





tristable, multistable, optimization, compliant mechanisms, BYU