Research On The System Of Workpiece Positioning In Laser Marking Based On Machine Vision

Laser marking is widely used in laser processing field, and the positioning of the workpiece is a most crucial step in the processing of laser marking. With the development of production, using fixed jig to locate the workpiece is not only costly, but also not conducive to the multi-workpiece location, and the positioning error is not stable which caused by human. So, a vision positioning technology was be introduced into Laser Marking System, using the advantages of visual positioning technology to achieve fast, stable and accurate positioning of the workpiece, and improve productivity.Firstly, a brief introduction about the development of laser marking and machine vision technology has been given. Secondly, considering the practical problems of workpiece positioning in the processing of laser marking, the commonly used algorithms in machine vision have been studied, such as image segmentation, binary morphological image filtering, image edge detection and so on. Considering the high complexity and cumbersome process operations of traditional calibration algorithm and the the positioning of workpiece in laser marking is carried out within a two-dimensional plane, a camera calibration method based on a single plane perspective transformation has been proposed, and a polynomial distortion correction algorithm has been introduced to correct the image distoration. In order to obtain the coordinates and azimuth angle of workpiece in the laser marking system, the center of the workpiece contour has been used to determine its position, and the hough transformation has been used to detect accurate straight lines in the outline of workpiece combined with least squares method, so the azimuth angle of the workpiece can be obtained from the angle of the straight line.According to the actual application requirements, we choose the right hardware to build hardware system. Using Microsoft foundation class library to design software system interface,and inorder to improve the response speed of the software interface, multi-threading technology is used.For the data exchange between the location software and marking system software, activex controls provided by the company of Germany SamLight are used.After the completion of the hardware and software of the system, experiment has been set up. The experimental results show that the calibration algorithm for this system can achieve a high precision, and the average calibration error in direction of x-axis and y-axis is less than 0.1mm, the maximum calibration error is less than 0.1mm. Positioning and marking for the workpiece on the marking platform, experiments show that the system is capable of positioning the workpiece accurattly and stablely.Finaly, this paper gives a depth analysis of positioning error from the image processing accuracy, which laid a foundation for future work.