Seam tracking of large pipe structures for an agile robotic welding system mounted on scaffold structures

This paper proposes a seam tracking technique for an agile robotic system for automated welding of large pipe structures at elevated heights. The welding system is designed to adapt to the scaffold structure which is generally erected around large workpieces. Large intersecting pipe structures are selected as the welding target because of their complex curved seams and wide applications in jackup oil rig manufacturing. A pipe localization method using only two profile scans is proposed to effectively localize the pipe and compute the initial location of the weld seam. The initial weld seam is then refined by a correction procedure to minimize the kinematic errors caused by base compliance, sensor measurement and system calibration. Subsequently, the seam is tracked to maintain a constant weld speed. Experimental results in a laboratory simulated environment show the feasibility of both the proposed seam tracking method and the concept of the agile robotic welding system for such applications. The precision of the mean tracking error for this system was found to be within 0.14 mm and 0.06 mm of the tool x and z axis respectively.