Spatial and thermal measurements using thermography CCD during HF soldering of metallic tubes

High frequency soldering allows high production speed, contactless heating and good quality of the weld. The speed limit of soldering is principally imposed by a good drive of the metal in the profiling machine. To control a HF soldering process, the authors propose a new method and approach which consists in controlling the temperature with a thermal image acquisition system developed in their laboratory. Their computer vision, described in this paper, is based on CCD thermography. This technology brings many advantages and tools in the measurement of thermal and spatial parameters. In fact, high spatial (800/spl times/600 pixels) and temporal resolutions, good relative thermal resolution (10/spl deg/C in the range of 800 to 2000/spl deg/C), linearity of calibration curves and large temperature measurement range are the main advantages of their system. They especially developed some specific image processing (line subpixel detection) used to measure spatial parameters: soldering angle, tube axis, shift between borders of the metal sheet along transversal cross section. All these parameters controlled in real time, allow to inform the welder operator about process drift. Actually, this machine is used to control the process and not to supervise it. Some information measured during HF soldering help them to analyse and understand all the occurring process drift.