On-Line Identification and Control of Part-Preparation and Fixturing Errors in Arc Welding

Sensing elements need to be incorporated in robotic welding systems to enable the robot to perceive and adapt to on-line variations occurring in the welding process. In this work, infrared thermal imaging techniques have been used to track variations produced by inadequate control during the joint preparation and fixturing stages. Variations in two joint parameters, gap and position, were studied. Changes in these parameters were found to have peculiar effects on the surface temperature distributions. The observed effects were used to develop quantitative error signals. These error signals were then used to measure the joint gaps and joint-torch offsets in real-time. The joint torch offset error signal was successfully used to control an initial error in joint position during real-time welding.