Research On Dimension Measurement Method Of Plane Parts Based On Level Set

Vision measurement technology has the advantages of non-contact, high precision, fast, easy to implement automation and intelligence, etc., and it has been widely used in many areas in recent years. This thesis studies the key technologies of large-size planar vision measurement system (PVMS), which includes hardware selection, camera distortion model, planar parts thickness error compensation model, sub-pixel edge detection, system error compensation and other issues. The main contents are as follows:(1) A method of the level sets with comer constraint for detecting the sub-pixel edgeIn vision measurement, at the curve intersection or the angular point, the gray value distribution is irregular because of the integration effects of CCD or the different reflection characteristics of object and background. The detection results of the traditional sub-pixel method will deviate from the real edge. In this paper, level sets sub-pixel detection with comer constraint is proposed to improve the accuracy of sub-pixel edge detection at the inflection point.(2) Camera distortion correction and thickness compensation modelsThe linear model and the nonlinear model of the camera are studied. According to the theory of camera imaging model, the camera calibration algorithm with plane constraint is used to solve the camera distortion parameters. Based on the principle of the plane vision measuring system, the thickness error compensation method is presented, and the error caused by the thickness of the edge of the object is compensated.(3) PVMS system constructionThe dimension measurement system of planar parts is set up to realize the measurement of the metal plate. The accuracy of the level set sub-pixel edge location, the high precision camera calibration method and the system error compensation method are studied in the back light source illumination environment.Experiments show that the proposed method in this paper can effectively improve the detection accuracy of the system, so that the measurement relative error of planar parts is less than 0.05%. The research of this paper provides an effective method to measure the size of large size plate.