Robust multi-stage hybrid vision/force control of industrial robots

This paper presents a novel multi-stage method for robust hybrid vision/force control of industrial robots, subject to model uncertainties. It aims to improve the performance of the three phases of the control process: a) free-motion using the image-based visual servoing (IBVS) before the interaction with the workpiece; b) the moment that the end-effector touches the workpiece; and c) hybrid vision/force control during the interaction with the workpiece. First, the camera motion is decomposed into transitional and angular movements. Then, utilizing a switching method, the rotational and translational movements of the camera are controlled in the first two stages, respectively. In the last stage, hybrid vision/force control is activated. For each stage, super-twisting sliding mode controller (STSMC) is utilized. Employing STSMC results in robustness against uncertainties while addressing the chattering problem. A variable-gain sliding surface is also proposed to address the instability and convergence speed issues of the traditional switch IBVS. The experimental results demonstrate the effectiveness and superiority of the proposed multi-stage method compared to other traditional approaches.