Stiffness Analysis of a Variable Stiffness Joint Using a Leaf Spring

A variable stiffness joint using a leaf spring is designed to ensure physical safety. The joint stiffness is often controlled by changing the effective length of the leaf spring. The stiffness model based on the small-deformation theory cannot solve large deflection problems of the leaf spring caused by larger joint deflected angles. The elliptic integral solution is considered to be the most accurate method for analyzing large deflections of beams. In this paper, a stiffness analysis model based on the elliptic integral solution is proposed. The joint stiffness property is analyzed. The simulation results show the joint stiffness is nonmonotonic and strong nonlinear. A stiffness simplified model is presented by nonlinear curve fitting for application simplicity. The experiment is carried out to verify the stiffness property and the stiffness analysis model.