Research On The Technology And System Of Portable Light Pen Coordinate Measurement System

Measurement equipments can be divided into three categories. First one is contacting measurement equipments which contain coordinate measuring machine and artificial measuring arm, their measuring precision is very high, but they can hardly satisfy the complex production requirements. The second is structure-light measuring machines which represent non-contacting measuring equipments, and they are credited with fast speed, but they can't be used to position single point and have light discontinuity situations. The last one is Light Pen Measuring System (LPMS) which is more flexible, and its structure is much easier and has no light discontinuity situations. So it performs well in measuring hiding points and deep holes that light can hardly reach and it provides a new way for assembling and detection. At present, the demand of the LPMS is increasing very fast. However there is only one company called Matrix that has developed the light-pen measuring system and its price is too expensive. So this paper makes researches on the key technology of the LPMS to develop our own system which has independent intellectual property rights.The right choice and proper use of the LPMS's hard device will improve the whole performance of this system.This paper makes a deep research of the hardware device on many aspects. It contains the feature and error source of CCD and Lens, the effect of circle marks' material and the effect of different CCD cameras' interface on the precision. Experimental prototype is successfully built.It is an effective way to use filter to reduce noise of the LPMS's images. By studying the features of the LPMS's images and different kinds of filters, the Gaussian smoothing filter with linear and rotational symmetry is chose.This filter can remarkably reduce the noise and guarantee the accuracy of edges of circle marks.Regional threshold segmentation of the LPMS's images is the first step to track the marks. On the base of research on different threshold segmentation technology a mathematical morphological pseudo top-hat algorithm is employed to compensate the non-uniformity of LPMS's digital image's background light, and realize accurate threshold segmentation in circle mark areas. After the feature of marks' areas is studied, criteria based on integration of shape and area is proposed to realize accurate regional recognition and extraction.The extracting precision of positioning the center of marks is guaranteed by the center of the marks. A least-squares fitting algorithm which take gradient amplitude as a weighting factor is proposed to fitting the marks' centers. And this algorithm is proved to be accurate and robust by experiments.Camera calibration is one of the most important steps in photogrammetry. This paper designs a circle-mark calibration board and realizes the automated coding technology of calibration marks. So automation level of the calibration process is increased. On the base of Zhang's flexible calibration method, 3-order radial distortion and 2-order tangential distortion mathematic mold is under consideration, so the precision of camera calibration will be improved.Calibration of LPMS's structure parameters is the key step before measurement. This paper uses bound adjustment to obtain the marks' coordinates, and single point multi-posture self-calibration method is proposed. Then the LPMS' parameters can be accurately calibrated. The precision of this method is authenticated by experiments. The realistic display of measurement data is mean. This paper proposes the realistic display of three-dimensional point cloud algorithm based on reflected light. This algorithm takes the normal vector of micro tangent plane as the normal vector of the point and the light source and texture will be defined by OpenGL. Finally each point can get realistic display.Finally a complete LPMS technology is completed by the research of above and the LPMS is developed. And this technology is proved to be feasible and robust by applications.