Light Pen Binocular Vision Measurement System

With the development of manufacturing technology of large mechanical equipment, the need of precise measuring of large-size workpiece is increasing. However, the accuracy of equipment and technology is insufficient for large-size measurement. Based on the study of three-coordinate measuring apparatus with large measurement range, a light-pen dual-cameras 3D coordinate vision measurement system has been devised for this purpose. The system offers a new means for large-size workpiece ordinary measuring and presents characteristics such as simple operation, large measurement range.The measuring principle of Light-pen vision measurement system, method of calibrating camera aberration error, extraction of LED spot center coordinates is discussed in detail. The main work are as follows:1. In the light-pen vision measurement system, LED used as the pointolite of lightpen is studied. Influence of LED on the imaging quality of light spot is discussed. To analyze the LED glare, experiment is conducted on different LED which has distinct photochromic properties, luminous intensity and structure.2. Based on the principle of perspective transformation, dual cameras mathematical model has been established. To fulfill the fast measurement requirement, a kind of camera calibration methods is developed, which is capable of high accuracy measurement. To test the scheme, Camera calibration experiment with Zhang algorithm is carried out.3. The Seven-point measuring structure of lightpen which is for dual-cameras 3D coordinate vision measurement system is proposed.4. The obtention method of LED spot center coordinates is the main factor affecting the measuring stability and accuracy. The dissertation adopts advanced Otsu algorithm to make image preprocessing as well as Canny algorithm to recognize and extract image contour edge point. Through this way, contour tracking and point serialization are achieved. Furthermore elliptical profile of spot centrepoint sub-pixel extraction method based on Gaussian quadrics fitting is given.In this paper, the structure of seven-point measurement lightpen is proposed. The seven-point structure minimizes deviation and improves the robustness. Moreover, tracking and serialization methods of image contour edge and extraction method of elliptical profile spot centrepoint sub-pixel based on Gaussian quadrics fitting, whose reliability are proved by experiment, are discussed.