Enhancing Robot End-Effector Trajectory Tracking Using Virtual Force-Tracking Impedance Control

Abstract

This article presents an extended Cartesian space robot control framework that features a virtual force tracking impedance control to enhance the end-effector trajectory tracking performance. Initially, the concept of a virtual surface is introduced, which is assumed to be at some constant distance from the desired end-effector trajectory. This virtual surface generates a virtual contact force when interacting with the torque-controlled robot end-effector. The interaction is then manipulated using an impedance control model to track a constant desired force. If the robot end-effector deviates from the desired trajectory, the constant force-tracking impedance control generates a compliance trajectory that regulates the end-effector movements, constraining it to the desired trajectory. For robust force tracking, impedance parameters are optimally tuned using a closed-loop dynamic model incorporating both robot and impedance dynamics. Additionally, super twisting sliding mode control (STSMC) is integrated to overcome uncertainties and the impact of robot dynamics on force-tracking performance. Experimental validation confirms the theoretical claims of the proposed approach. It demonstrates that force-tracking impedance control improves the end-effector trajectory tracking by quickly reacting to the dynamic trajectories compared to position control only and effectively maintains it on the desired trajectories.