Design and Analysis of Leaf Beam Single-Translation Constraint Compliant Modules and the Resulting Spherical Joints

A wire beam is a single-translation constraint along its axial direction. It offers many applications in compliant mechanisms such as being a transmitting/decoupling element connected to a linear actuator, and being a fundamental constitutive element to design complex compliant joints and mechanisms. It is desired to find alternative leaf beam single-translation constraint to equal a wire beam, in order to improve the manufacturability and robustness to external loading. In this paper, we propose and model a new single-translation constraint compliant module, I-shape leaf beam design, to compare with a corresponding L-shape leaf beam design reported in the literature. Two spherical (S) joints using three I-shape leaf beams and three L-shape leaf beams, respectively, are then analytically modelled and analysed. Three key geometric parameters are adopted to thoroughly assess four performance indices of each S joint including stiffness ratio, rotation radius error, coupling motion and parasitic motion. It shows that the I-shape leaf beam based S joint performance indices are generally 10 times better than those of the L-shape leaf beam based S joint. For each S joint, the optimal parameters are found under the given conditions. Finally, experimental tests are carried out for a fabricated S joint prototype using the I-shape leaf beams, the results from which verify the accuracy of the proposed analytical model and the fabrication feasibility.