Model based control of a one degree of freedom workpiece manipulator for welding of nozzles

This paper presents an automatic control system for welding the root-pass in a seam joining a nozzle perpendicular onto a large diameter pipe. The system is based on the use of a geometry model of the welding seam and on inverse welding process models (i.e. models that map desired weld quality, joint shape, and equipment parameters onto appropriate welding control variables). By using these models a workpiece manipulator is controlled in such a way that an appropriate welding position (determined from the inverse process models) is obtained while welding. A robot, that is carrying the welding torch, is then positioned so that the position and orientation of the torch relatively to the seam become as specified in the inverse welding process models. The paper presents the overall concept of the system. Furthermore, algorithms for controlling the workpiece manipulator and the robot are presented.