Study Of The Two-Light Pen-Camera Type3D-Coordinate Measuring System

A novel light-pen is designed based on the two-light pen-camera type3D-coordinate measuring system. The model of binocular stereoscopic vision isestablished and the cameras are calibrated accurately. When the tip of the Pen is placed onan object, both cameras obtain images which contain eight LEDs light sources in the LightPen, and the coordinates in the center of the images are gained by method of barycenter.After that,3D coordinates of eight LEDs of the right camera are calculated by the cameramodel after being matched. Finally,3D coordinate of the tip of the Pen is achieved byusing the linear relationship between the2D coordinate system containing eight LEDs andthe3D coordinate system of the right camera. The system has features of simple structure,low cost and easy operation, and so on. Experimental results prove that the system has ahigh accuracy and is tailored to the detectable needs of the great size work piece. Themain and creative work in the paper consists of the following aspects:1. An appropriate light-pen is designed taking the size of camera field, the clarity ofthe graph and etc to these standard fixed points into account.2. Finish the calibration of camera using the non-coplanar RAC(Radial AlignmentConstraint) calibration method combining with the analysis of the system transformationmodel which aberration error compensated.3. Get the coordinates of the feature point using barycenter method. In order toadvance the accuracy of coordinates, specific threshold is used during calculation processto eliminate irrespective background value and aberration error is compensated.4. Ascertain the three-coordination of the standard fixed points using the binocularstereo matching principle which comminutes with geometric transformation amongdifferent three-coordination system.5. Ascertain the three-coordination of the measured points between the measuredpoints and the standard fixed points.The innovation of this paper is that a novel light-pen is designed and a stereomatching algorithm is proposed. Meanwhile,3D coordinate of the tip of the Pen isachieved by using the linear relationship between the2D coordinate system containingeight LEDs and the3D coordinate system of the left camera.