Minimizing Under-Constraint in Folded Beams to Achieve Optimal Bearing Performance in Diaphragm Flexures

Abstract Diaphragm flexures are widely used in various precision applications to generate guided motion along the out-of-plane directions and provide load bearing along the in-plane directions. The traditional Asymmetric Simple Beam (ASB) diaphragm flexure suffers from large parasitic rotation about the out-of-plane translation direction. The Asymmetric Folded Beam (AFB) design eliminates or minimizes the parasitic rotation seen in the ASB design and offers desirably low out-of-plane stiffness. However, its in-plane stiffness is undesirably low and exhibits a steep drop with increasing the out-of-plane displacement due to the under-constraint of the unsupported ends of the folded beams. This paper proposes a novel diaphragm flexure design, referred to as the Sandwich Asymmetric Folded Beam with Parallelogram Flexure Module in-plane interconnect (SAFB-PFM), that minimizes the under-constraint of the folded beams in the AFB design, thereby achieving a substantial improvement in the in-plane stiffness without compromising the out-of-plane stiffness. This novel design comprises a sandwich arrangement of two identical AFB diaphragm flexures spaced apart along the out-of-plane direction, with out-of-plane interconnects between the two corresponding diaphragms, the two corresponding frames, and every pair of the corresponding unsupported ends of the folded beams and an in-plane interconnect between the unsupported ends of each AFB layer. The optimal bearing performance of the SAFB-PFM design (i.e., high in-plane stiffness and low out-of-plane stiffness) is demonstrated via nonlinear finite element analysis (FEA) followed by several physical design observations. Additionally, FEA-based modal analysis is utilized to highlight the improved dynamic performance of the sandwich design compared to the single-layer AFB design.