Abstract
In the automation of the TIG (tungsten inert gas) welding process, robots and dedicated machines have been used to place the welding torch at the correct orientation above the seam to be welded. Sensors are required to determine whether the workpiece is located correctly with respect to the welding torch, or whether distortion of the workpiece takes place due to thermal expansion during welding. The authors describe a seam tracker for following the small gap between closed butt plates. The system uses a CCD monochrome video camera with a coherent fibre-optic bundle to view the workpiece. Illumination is provided by an infrared laser diode mounted on the tracker head. The use of these components enables the tracker head to be kept extremely compact. The video signal from the camera is digitised and stored in a microcomputer which analyses the image to obtain the position and width of the gap. This information is then transferred, via a serial line, to the robot controller which then modifies the torch path to keep the welding torch over the seam throughout the welding process.