An optical sensing system for seam tracking and weld pool control in gas metal arc welding of steel pipe

A visual sensing system was developed for automatic gas metal arc welding (GMAW) of the root pass of steel pipe. The system consisted of a vision sensor that consisted of a charge-coupled device (CCD) camera and lenses, a frame grabber, image processing algorithms, and a computer controller. A specially designed five-axis manipulator was used to position the welding torch and to provide the vision sensor with automatic access to view the welding position. During the root pass welding, an image of the weld pool and its vicinity was captured using the camera without interference of the intensive arc light by viewing at the instance of a short-circuit of the welding power. The captured image was then processed to recognize the weld pool shape. For seam tracking, the manipulator was used to adjust the torch position based upon the pool image to the groove center. The measured gap size was used to determine the appropriate welding conditions to obtain sound penetration. The welding speed was chosen using fuzzy logic with the knowledge of a skilled welder and measured gap. The automatic welding equipment demonstrated that both welding conditions and torch position could be appropriately controlled to obtain a sound weldment and a good seam tracking capability.