Topology optimization of efficient and strong hybrid compliant mechanisms using a mixed mesh of beams and flexure hinges with strength control

This paper presents a new topology optimization technique for the design of compliant mechanisms that are efficient in transferring motion, force, or energy while being sufficiently strong to resist yield or fatigue failure. Generally, flexure hinges are efficient in transferring motion, force, or energy but are weak in resisting yield or fatigue failure while slender beams are relatively inefficient but strong. Thus, our philosophy is that a compliant mechanism may benefit from the above complimentary properties of flexure hinges and slender beams if they are connected and sized in a rational way. This requires a design approach with both flexure hinges and beams as constructional elements, and the design approach should include criteria on both efficiency and strength. Therefore, in the proposed technique, a mixed mesh of flexure hinges and beams was employed to discretize the design domain, and their connectivity, locations, and sizes were simultaneously determined to fulfill both the so-called stiffness-flexibility criterion (for efficiency) and a newly proposed input stroke criterion (for strength). The input stroke of a compliant mechanism, defined per the von-Mises yield criterion, is inversely proportional to the maximum stress per input displacement and represents the mechanism's maximum input displacement before yield failure. Both theoretical explorations and design examples demonstrate that the strength of compliant mechanisms can be significantly improved without compromising the efficiency, and trade-off designs that are better balanced between strength and efficiency can be obtained.