A simple stiffness equation for a variable stiffness joint using a leaf spring

Abstract

Variable stiffness joints using leaf springs have been developed to improve human-robot safety by stiffness variation, in which joint stiffness is often controlled by changing the effective length of the leaf spring. The nonlinearity of the leaf spring caused by large deflection complicates the calculation of the joint stiffness during the joint deflection. Many methods available to solve large deflection problems are limited by complex calculation process in application. A simple stiffness equation for a variable stiffness joint using a leaf spring is presented in this paper on the basis of the elliptic integral solution (EIS) and the small deformation assumption. Compared with the stiffness model based on the EIS, the prediction error of the simple stiffness equation is within ±20%, which is much smaller than that of the stiffness model based on the small deformation assumption. The simple stiffness equation is proved more practical in the experiment, which can be used straightforward to improve the efficiency and the accuracy of the stiffness calculation.