A Collaborative Control Method of Forging Force for Double‑Sided Friction Stir Welding Based on Reference Admittance Model

Abstract In the aerospace industry, double-sided friction stir welding has gradually become a crucial solid-state welding technology for rocket manufacturing. During the welding process, the welding equipment on both sides may encounter complex conditions involving unsynchronized collaborative movements. The resulting bending stress and destructive vibration affect workpiece processing quality. Therefore, this study proposes an adaptive admittance-based dual-robot collaborative forging force control method for double-sided friction stir welding. Specifically, the following steps are required: First, we analyzed the mechanism model of the hybrid robot and indirectly estimated the forging force value of friction stir welding using the Jacobian matrix of the hybrid robot. Second, an adaptive variable admittance controller was designed based on the reference admittance model with ideal stiffness. Subsequently, an adaptive variable admittance controller was applied to the dual-machine hybrid robot. By adjusting the welding trajectory and correcting the position error, the forging force was corrected, allowing adaptive tracking control of the forging force in complex environments. Finally, we conducted double-sided friction stir welding experiments to compare and verify the effectiveness of the adaptive tracking control algorithm for the forging force.