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Automatic control system with a laser slit sensor was developed and applied to full automatic multi-layer GTA welding for pipe joints. The laser slit sensor was able to measure dimensions of groove of the welding section. It was also able to detect the off-positioning and the groove area which required for multi-layer welding control, and the defects on the welding surface that might be in each welding pass. The dimensions of groove with hindering blocks were able to be measured.In addition, a tracking control method that was automatically corrected by following the value off-positioning of the welding torch was established. It was shown that torch position control was able to be appropriately performed at intermittently tack welding for avoid blocks, back welding of first layer and to finish welding of multi-layer. A controlling method for amount of weld deposit was useful. Using the sensor and system, It was clarified that the sound welding joint was obtained fully automatically.

Summary To improve the automation or artificial intelligence of welding operations, it is necessary to develop high-performance sensors. Laser visual sensors are designed to recognise the configuration or detect the position of a weld by irradiating a slit light on to the welded joint, receiving the light with a CCD camera, and converting the two-dimensional information into three-dimensional information by image processing. The visual sensors for welding robots must be free from the influences of welding process disturbances, such as arc light, heat, spatter and fume. This paper describes optical component arrangements and image processing algorithms. The optical component of a sensor head helps avoid optical window contamination caused by spatter or fume. The image processor used can process image data quickly and accurately even if welding arc light illuminates the workpiece surface. The accuracy of weld position detection is within ±0.2 mm.