Detecting and Tracking of Welding Line in Visual Plasma Robotic Welding

Abstract

The formation of stable back beads in joining of the thick materials is important in order to achieve high quality welded metal joints. Since plasma welding employs the high welding current density, it is suitable for the thick materials. Keyhole in the plasma welding depends on the pilot gas and the welding current. The voltage behavior depends on the keyhole situation. If the torch is moved away from the welding line in conventional GMA welding, the welding voltage and the welding current are changed due to variations of the arc length. But, the welding voltage does not change with the arc length in the plasma welding, since the welding voltage depends on the situation of the keyhole. The authors tried to observe the weld pool on top side by using a CCD camera. The timing of the shutter in the CCD camera is investigated to take clear image of the weld pool. As a result, the clear images of the weld pool were taken when the welding current was reduced to 30A and an interference filter of 950nm was attached to the CCD camera. The weld pool shape was changed with the torch position in the groove. The image processing method was developed to detect the top of the weld pool. The torch position was estimated by processing the weld pool images. The digital control was designed to trace the welding line. The performance of the controller was verified by carrying out the tracking experiments.