High Bandwidth Force Control for Robotic Friction Stir Welding

Due to their flexibility and cost efficiency, industrial robots are increasingly being used for manufacturing processes. One such process is friction stir welding, which places high demands on the manipulator due to the high process forces and force gradients involved. The high compliance of industrial robots compared to traditional machine tools necessitates the implementation of force control for robotic friction stir welding. This paper presents an approach to increasing the bandwidth during force control of robotic friction stir welding. To achieve this, an industrial robot is controlled through an open control architecture, which offers the possibility to employ advanced force control structures. An admittance controller with inner velocity loop and a parallel force controller are compared to the state-of-the-art external force controller and validated in a digital twin of the robot. The most promising structure of the admittance controller is then implemented and validated on the test system, demonstrating an increase in accuracy and efficiency.