Study on the stiffness property of a variable stiffness joint using a leaf spring

Abstract

Variable stiffness joints designed to ensure physical safety or adjust stiffness actively have attracted much attention in recent years. Springs are used in the internal kinematic structures of variable stiffness joints to achieve the compliance. In this paper, the stiffness property of a variable stiffness joint using a leaf spring is studied on the basis of geometric nonlinearity associated with large deflections of leaf springs. A new end structure is used in the variable stiffness joint to exert the external force on the leaf spring. Based on the elliptic integral solution to large deflection problems of cantilever beams, the effects of different end exertion force structures and geometric nonlinearity of leaf springs on the stiffness property are analyzed when the deflected angle of the joint is larger. It is found that the end exertion force structure and large deflection of leaf springs have a great impact on the changes of the joint stiffness during the joint deflection. A new variable stiffness joint using two leaf springs is proposed to meet different application requirements by changing the end exertion force structure. The experiment of the proposed joint is carried out to verify the validity of the stiffness analysis results.