Research On The Key Technology Of The Light Pen Based On Binocular Stereo Vision

The light pen measurement system has a characteristic of portable schleping,high flexibility, non blackout interference etc. The light pen measurement technologyhas a veryapplication needs in the large aircraft manufacturing, automobilemanufacturing, electric power equipment manufacturing,engineering machinerymanufacturing, shipbuilding and other industries and fields.Light pen measuringsystem is monopolized by the foreign, and the domestic related technology research isstill in its infancy. Therefore, the systematic study of light pen measuring keytechnologies has an important theoretical significance and practical value.Based on the measurement principle and hardware structure of the measuringsystem of the light pen,9-point light pen structure is designed, and carbon fibermaterial is selected as a light pen making materials. The characteristics of the LEDlight source point and are analysed in comparison, so the light reflection coded pointsare selected as the light pen mark point type, and the coding theory is given. The typeof camera and lens is selected according the lens and CCD chip parameters. The typeof image acquisition card is confirmed according the characteristics of the camera.According to the characteristics of the light pen image, the projection ellipse ofthe light pen mark points is extracted by the image processing of filtering andsegmentation. The coordinates of the edge of the ellipses are extracted by the Cannyedge extraction operator, and the coefficient of the elliptic equations as well as thecoordinates of the center of the ellipse and the length of axis is geted using theweighted least-squares ellipse fitting method. Edge model is established and the edgemodel parameters are solved with the ellipse target gradation characteristics and thecoordinates of the center of the ellipse is corrected to sub-pixel. The light penmeasuring image encoding flag area is extracted according to the ellipse parameters.According to the principle of central projection, the the camcorder ideal model is established, and the correspondence relationship between the coordinates of the two-dimensional coordinates in the image and the three-dimensional corresponding spacecoordinates is derived. The camera ideal model is modified to get the camera actualimaging model by increasing the camera radial distortion and tangential distortionmodel. The plane calibration template is designed with circular mark points andautomatic identification method of template landmarks is given. The camera iscalibrated by the two-step calibration method based on the planar calibration template.Calculation method of the three-dimensional space coordinates is studied. Stereoimage pair’s match is achieved with coding theory. The relative position of the9codedpoints in the coordinate system of the light pen is calibrated with the principle ofbinocular stereo vision. The light pen probe is calibrated according to the principle ofthe same position. The world coordinates of the under test point on the space object isobtained using the conversion relationship between coordinate systems of thebinocular vision and the world coordinate system, and the coordinate measuringfunction of this system is realized.A system interface is written with the function of image acquisition, imageprocessing, camera calibration, the three-dimensional coordinate’s solver, data fittingetc. The three-dimensional coordinates measuring function of the system is verified bythe actual measurement experiment.