Robust Seam Tracking Algorithm Based On Majority Voting Logic

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Abstract
A general purpose algorithm for visually guiding a robot to automatically follow a seam is presented. The algorithm was designed for automated welding applications but may be used for other seam tracking problems such as the inspection of machined part edges. The algorithm is particularly useful in its ability to work on low contrast seam images and is robust enough to ignore higher contrast scratches and markings near the seam, allowing for the use of conventional illumination techniques. The seam tracker works by continuously measuring an offset from a nominal position. The offset can be stored to modify a coarsely pretaught robot path or can be used as an input to a real time trajectory control loop. The seam position is computed using a matched edge filter and a majority voting scheme based on features measured from the current image frame as well as from past image frames. The success of this algorithm is based on several generally valid assumptions and rules. One such assumption is that the seam is nearly vertical in the image or can be made vertical by rotating the image data by an angle based on a pretaught robot path or by using results from previous image frames. By assuming that the seam width and position is smoothly varying, these parameters can be fed back from previous image frames to maintain tracking. An implementation of this algorithm for a real time weld seam tracking application is discussed.

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