An extended stiffness model for 7 Dofs collaborative robots using the virtual joint method

Abstract

In order to improve the stiffness modeling accuracy, an extended stiffness modeling and identification method of a 7 degrees of freedom(Dofs) collaborative robot is introduced in this paper. Unlike the traditional stiffness model which is assumed that each actuated joint is presented by a single one-dimensional virtual spring, the compliance of links, bearings and other structural components are considered and equivalent to two virtual joints in this method. These two additional virtual joints are orthogonal to the rotation axis of actuated joints. Including the equivalent virtual joint of joint torsional stiffness, each actuated joint of the robot has three virtual joints eventually. The method extends the traditional virtual joint method(VJM) and opens new prospects in terms of the stiffness optimal synthesis. Meanwhile, the accuracy of stiffness modeling is improved. Based on a 7 Dofs collaborative robot SHIR5, the static compliance simulations are performed to identify the elastic parameters of the robot, and the results show that more precise Cartesian stiffness characteristics are obtained from the extended stiffness model. Finally, the influence of compliance of links, bearings and other structural components on the stiffness model of the robot are analyzed.