Robot End-Effector Virtual Force Tracking Impedance Control for Contactless Cutting Operations

This research aims to utilize a robot manipulator for metal cutting using a laser or plasma arc method by maintaining a constant distance (as small as 1mm) from the physical cutting surface. Sometimes, the position control bandwidth in practice is constrained by certain factors which limit its use in tightly bound motion. Therefore, this study proposes the robot end-effector’s virtual force-tracking impedance control for motion stabilization by assuming a virtual surface with defined stiffness near the actual surface. Subsequently, the interaction force between the virtual surface and robot end-effector is then regulated to achieve the desired compliance. The selection of impedance dynamic parameters indirectly influences impedance control performance. Therefore, the closed-loop system with linear dynamics is constructed and utilized in particle swarm optimization (PSO) for desired parameter offline tuning. Because of linear dynamics, the tuned parameters may not be accurate. Subsequently, this uncertainty is compensated using the sliding mode control (SMC)-based impedance control. SMC is a nonlinear control that ensures finite time stability by compensating the perturbation effect. Finally, the simulations and experiment results validate that a stabilized motion and force tracking is achieved using the proposed impedance control while maintaining the constant distance near the real surface.