Introduction of planar compliant joints designed for combined bending and axial loading conditions in lamina emergent mechanisms

This work introduces three joints to allow motion in lamina emergent mechanisms (LEMs) that were designed to have minimal parasitic motion under tension, compression, and a combination of tension and compression loadings. Closed-form models of the joints were developed and combined with optimization algorithms for maximum flexibility in bending and then modeled using finite element analysis (FEA). The FEA results were used to predict the stiffnesses of the joints in bending, tension, and compression. As a baseline, Lamina Emergent Torsional (LET) joints were designed to match the bending stiffness of each of the joints, so that the tensile-compressive performance could be compared. The joints demonstrate improved off-axis stiffness in tensile and/or compressive stiffness, at the cost of limited bending flexibility compared to the LET joint and requiring more material area. The resulting joints provide a broad set of capabilities that can be used by designers in lamina emergent mechanism design.