Real-Time Trajectory Compensation in Robotic Friction Stir Welding Using State Estimators

This brief demonstrates a method of real-time motion control for robotic friction stir welding (FSW). For some manufacturing processes, the lack of stiffness of industrial manipulators can cause a lack of precision and is, thus, problematic. During the processes that require significant forces, this error becomes the primary source of defects. This brief provides significant improvements using digital estimators. A compensator based on a discrete-time nonlinear observer and two other compensators that use only motor current and position measurements are proposed to compensate for the tracking error due to the deflection of the robot. Simulations and experiments on an industrial robot show the effectiveness of the three proposed compensators, which successfully attenuate the dynamic error in the case of a 2-D FSW process. Our adapted compensators provide accurate performance (similar to 90% error reduction) for a robotized FSW welding setup.