Design and nonlinear spatial analysis of compliant anti-buckling universal joints

Abstract

Compliant universal joints have been widely used in many applications such as precision transmission mechanisms and continuum robots. However, their nonlinear spatial analysis in terms of load-displacement relations is less investigated in the compliant mechanisms community, which are needed to show the physical insight into constraint behavior of the universal joint. In addition, the design of existing compliant universal joints is not robust to withstand buckling under applied compression loads. This paper aims to address these problems and starts from presenting a novel anti-buckling universal joint consisting of two inversion-based symmetric cross-spring pivots (IS-CSPs). Two nonlinear spatial models of the IS-CSP and of anti-buckling universal joint are proposed, resorting to two single-sheet closed-form kinetostatic models as the first step, respectively. Then center shifts, primary rotations, and load-dependent stiffness are parametrically studied under different loading conditions over a load and displacement range of practical interest, namely, point loads, cable-force actuations, and varying loading positions. The modeling results of these performance characteristics are shown to be accurate using nonlinear finite element analysis. In addition, preliminary experimental tests are carried out to investigate the manufacturability of the prototype and verify the nonlinear spatial models. Finally, this paper presents and models two new bi-directional anti-buckling universal joints, each with two IS-CSPs and two non-inversion-based symmetric cross-spring pivots (NIS-CSPs).