Real Time Trajectory Generation in Robotic Shielded Metal Arc Welding

Abstract. The Shielded Metal Arc Welding (SMAW) is a typical manual process with many dangerous application for the welder (pipe hot tapping, underwater welding, etc.). The process robotization seems to be great for safety associated with the improvement of weld quality and repeatability. This work presents a methodology developed for real time trajectory generation for the robotic SMAW. In this methodology, while the electrode is melted the robot makes the diving movement, keeping the electric arc length constant. The trajectory is generated in real-time as a function of melting rate and independent of the welding speed, given by the welding parameters. The proposed methodology uses a variable Tool Center Point (TCP) model where the covered electrode is considered a prismatic joint, whose displacement is determined by the melting rate. The homogeneous transform matrix relating the last manipulator joint and the TCP is then recalculated at each control sampling period. With this methodology, the TCP will always be located at the tip of the electrode (melting front), allowing to program the welding speed independently of the electrode diving speed. This methodology also allows the user to program the weld bead geometry over the joint without caring about the diving movement, which is automatically done by the robot during the welding. This paper also shows some results obtained with the process robotization as welds made on plate and on tubes (linear and circular TCP trajectories).