Graphic Coding and Decoding Methods Using Relative Coordinates

Abstract

There are many processes in PCB production. In order to facilitate management and problem tracing, PCB monitoring is required in each production process. The production process of PCB is very different from that of common products. Barcode, QR code or electronic label can be pasted on common products, but not on PCB. Because corrosive chemical solution is used in many PCB production processes. In order to solve this problem, a coding method based on relative coordinates and a graphic decoding method combining Hough transform and projection transformation are proposed. This method takes into account that the most commonly used NC drilling machine in PCB manufacturing enterprises. The graphic coding method uses the relative coordinates of holes drilled on the PCB. The relative coordinates of the holes centers represent the encoding information. The image decoding method uses the Hough transform and the projection transformation. First, the captured image is transformed by Hough transform, and the center coordinates of the image are detected. Secondly, the image is projective transformed by the centers of the most lateral four holes as the feature points. The distortion image is transformed into a regular image. Then, the image decoding is realized by calculating the relative coordinates of the centers. The practicability of the method and the correctness of the algorithm are verified by experiments. This method has been used in the PCB production line of an enterprise.