Adaptive Robotic Welding Using A Rapid Image Pre-Processor

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Abstract
The rapid pre-processor initially developed by NRCC and Leigh Instruments Inc. as part of the visual aid system of the space shuttle arm 1 has been adapted to perform real time seam tracking of multipass butt weld and other adaptive welding functions. The weld preparation profile is first enhanced by a projected laser target formed by a line and dots. A standard TV camera is used to observe the target image at an angle. Displacement and distorsion of the target image on a monitor are simple functions of the preparation surface distance and shape respectively. Using the video signal, the pre-processor computes in real time the area and first moments of the white level figure contained within four independent rectangular windows in the field of view of the camera. The shape, size, and position of each window can be changed dynamically for each successive image at the standard 30 images/sec rate, in order to track some target image singularities. Visual sensing and welding are done simultaneously. As an example, it is shown that thin sheet metal welding can be automated using a single window for seam tracking, gap width measurement and torch height estimation. Using a second window, measurement of sheet misalignment and their orientation in space were also achieved. The system can be used at welding speed of up to 1 m/min. Simplicity, speed and effectiveness are the main advantages of this system.

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