Research On3D Measurement For High Temperature Long-shaft Heavy Forging Based On CCD Image

Long-shaft Heavy Forging is the foundation of large components manufacturing ofimportant equipment. Large axial dimensions shaft are forged by free forging method. But itis difficult to control precision dimensions of forgings. The large machining allowance is keep.At present, manual measurement method is used in most of forging firms in order obtain thesize of forging. Measurement Method based on CCD image is a fast, non-contact, multi-parameters and high accuracy measurement. It is the current hot topics and trends of the study.The large radiation of high temperature forgings causes many key technologies, such as imageacquisition, features, image matching,3D reconstruction. Some key technology will beresearched on CCD image measurement of long shaft forgings in this article. The maincontents and results of the study are as follows:(1) For large number of hot radiation and large range of the temperature in formingprocess of high temperature forging, the relationship among radiant exitance and wavelengthand temperature are analysed., an automatic exposure model is studied based on the basecolor grey of image. The stability single grey value of grey image can be obtained by thismethod. Features of noise in images are analysed. Characteristic of the medium value filterand Gaussian filter are researched. First pepper noise is eliminated with medium value filterand random noise is reducing with Gaussian filter by combination filter algorithm. The PSNRvalue of images decreased obviously.(2) In order to obtain forging target from images, law of three basic color grey in imageare analysed, image regional features and edge features is respectively analyzed. Thecorrelation between basic color grey in different temperature zone is found. The dynamicrelative threshold from the red and blue grey ration is used to recognize target and background.The grey change law in the forging edge of temperature forging image is studied. Edgetemperature field of high temperature forging is simulated by using ANSYS software. It isfound that the average grey value of high temperature area can be as edge segmentationthreshold. A sub-pixel interpolation algorithm is studied. It can be effective improvesegmentation precision for far distance collection forging image.(3) The theory and method of stereo vision measurement is analyzed. A measurementsystem layout mode of up and down camera is designed for measurement of axis class forging.The vertical epipolar line stereo vision measurement system is modeled. A big calibrationboard is made for big scene measurement. Intrinsic parameters matrix of two CCD cameras are obtained by calibration. By calculating space location of two cameras, the spacetranslation and rotating in external parameters matrix of up and down camera is obtainedrelationship. The epipolar line constraints equation is formulated. The stereo images arerectified by using equation. The experiment results show that this model is feasible.(4) In order to realize features match problem of high temperature forging image, theshape change characteristics and internal features of the image are analyzed. A featureextraction method based on section line is studied. The extremum points in grey distributioncurve are be as features points. A sparse features matrix is established. By Euclidean distanceand epipolar line constraints, sparse feature points in the section line from stereo images arematched. A match matrix and disparity matrix of features points are obtained by this method.(5)3D reconstruction and measurement of high temperature forging are the goal of thisarticle. Fitting method of space discrete point on section line and the forging center line arestudied.3D model reconstruction of forging and coordinate system conversion algorithm arestudied. The experiment results from forging workshop show that3D model could bereconstructed from high temperature forging image without structure light or laser ranginginstrument such as auxiliary devices. The measurement precision and speed can meet thedemand of actual production. Measurement system device and measurement software aredesigned and developed. It realize real-time monitor the dimension of forging and analyzedifference between the reconstruction model and theoretical model of forgings.