Experimental Verification of Nonlinear Characteristics with Hysteresis in Variable Stiffness Robotic Joint

Abstract

This paper investigates nonlinear and hysteresis characteristics of a variable stiffness robotic joint, MOD-AwAS [1], utilizing lever mechanism with moving pivot joint. In order to measure its stiffness characteristics, an experimental system with a force-torque sensor and an encoder has been developed. Through experimental works for measuring both the applied external torque and the angular displacement, the stiffness characteristics of the robotic joint was obtained about several representative stiffness sets which are decided by pivot position. It is explained that the joint has nonlinear stiffness as well as hysteresis characteristics from the experimental results. Based on that, a novel computation model of stiffness for the robotic joint was proposed, which is capable of representing both nonlinearity and hysteresis properties about most domain of joint stiffness decided by pivot position. It was verified that the proposed computation model is effective through comparison between the experimental data and the simulation result using the model.