Stability Improvement Of Light Pen Vision Coordinate Measuring System

The light pen portable coordinate measuring system with CCD cameras is a new type of 3D coordinate measurement, which combines contact measurement with computer vision measurement. The measuring system has the advantages of the kind of measurement technology, especially giving a good solution about how to measure the “deep hole or hidden hole”. The laboratory has invented a light pen portable coordinate measuring system based on the probe detection technology in traditional coordinate measurement, which makes the focus of visual inspection from measured object to light pen. This measuring system has lots of advantages such as light and portable, large measuring range, light weight, simple establishment and operation. However, the accuracy of the system is still inferior to the international advanced level. Especially the accuracy of the positioning stability of the control points is poor in the system. In this thesis, some improved algorithms are described in detail from the following several aspects. Main contents of this dissertation are as follows:1. The stability accuracy research of the center positioning of the optical control circle. After pixel edge detection on the control circle, take a method to get the sub-pixel edge which is based on the theory of Polynomial interpolation. The stability accuracy of the center positioning precision is improved.2. The influence factors research of the z axis' s measurement accuracy. Many experiments' results showed that z axis' s measurement accuracy is one order of magnitude lower than the x axis and y axis. There is a guess that the range of the plane before and after the light pen is close. By many experimental results, it is proved different distance between the two planes affects the measurement accuracy of z axis.3. A new method of camera calibration was put forward. A database was established based on the corresponding relation between the ideal image coordinates and actual image coordinates. In the process of measuring the coordinates of image positioning in the database to search to find matching points or through the adjacent point interpolation compensation for the actual image plane coordinates4. Based on the previous research, a new object function is established according to the actual situation to estimating the center position of probe tip. We optimize the measurement process combined average theory to make the convergence speed faster.