A New Class of Single-DoF Compliant Mechanisms with Optimal Bearing Characteristics

Abstract This paper introduces a new class of single-Degree of Freedom (DoF) compliant mechanisms that exhibit optimal bearing characteristics, defined by low stiffness in the out-of-plane motion direction, high stiffness in the in-plane bearing directions, and zero parasitic motion in the in-plane bearing directions. This new class features multi-layer arrangements of two thin, planar compliant mechanisms (referred to as diaphragm flexures) separated in the out-of-plane direction and strategically interconnected at several critical locations. Optimal bearing performance is not achievable in traditional single-layer diaphragm flexures. The only prior multi-layer design based on folded flexure beams, despite exhibiting optimal bearing characteristics, suffers from two major limitations: structural complexity and poor bearing stiffness in the in-plane rotational bearing direction. To address these limitations, this work presents a novel synergistic integration of two design innovations: 1) a new single-layer diaphragm flexure comprising nested flexure beams instead of conventional folded flexure beams, and 2) two distinct multi-layer architectures between a pair of nested beam diaphragm flexures, each incorporating a carefully designed combination of compliant and rigid elements, and specifically tailored to overcome one of the fundamental limitations associated with the previous folded beam multi-layer design. Analytical models are derived for the bearing direction and motion direction stiffness of the proposed multi-layer designs that closely match Finite Element Analysis (FEA) predictions, and the optimal bearing performance of these designs is demonstrated and thoroughly discussed.