Study Of The Key Technologies Of Online 3D Vision Measurement System For Large-Scale Equipments

With the rapid development of science and technology, the aviation, spaceflight, war and civil industries ask online three-dimensional measurement for the large-scale equipments for more high demand. To meet these demands, the technologies and equipments for three-dimension coordinate on-line measurement have increased dramatically in the past few years. The vision coordinates measurement technology is a rising 3D spatial coordinate measurement technology based on computer vision technology and coordinates measurement technology, it fits to the modern production which needs measurement technology that holds higher measurement precision and larger measurement scale from a bran-new coordinates measurement idea.The subject"study of the key technologies of online 3D vision measurement system for large-scale equipments"is to study a large-scale stereo vision coordinate measurement system project based on optical probe with the function of measurement and calibration to meet three-dimensional online measurement for large-scale equipments. During the measurement process, the calibration parameters are calculated to judge whether the system is exceed the error bound. If there is something wrong then it alarms to make sure the system is under the control. For this system, we must solve some key technologies, such as precision calibration the camera intrinsic parameters, the extrinsic parameters online calibration of two cameras, and stereo vision measurement modeling, etc.Based on the coordinate measurement principle of stereo vision measurement system, using the location restriction of optical features on the optical probe and their spatial coordinates calculated with their image coordinates, this paper puts forward the Levenberg-Marquardt iterated stance estimation method based on unit quaternions to obtain the transformation between the two coordinate systems. The measured point coordinate is computed using the known location relationship of style and features. The online calibration of the style is carried out with the length restriction between the style and the origin of probe coordinate system.To solve the reconstruction problem of the stereo vision measurement in general case, the paper presents a method of stereo vision reconstruction by minimizing the projection distance based on the common perpendicular constraint. The method not only minimizes the distances of the space point to the two projection rays, but also minimizes the distances between the two images point of space point and the measurement images point, and lowers the effects of the distances from the spatial point to the two cameras. The experiment result shows this method is better than the other common methods.To the camera intrinsic parameters calibration, this paper presents a valid camera calibration method based on high precision virtual stereo calibration pattern, which is carried out by minimizing the distances from all the 3D space points to the corresponding optical rays generated by their projections image points and the center of camera. It consists of linear optimization parameter estimation and nonlinear refinement. The proposed technique not only overcomes the shortcomings of the machining and calibration of large stereo calibration pattern and lower precision of plane pattern, but also improves the measurement precision by using the same features in measurement and calibration to insure the consistency of the features. By optimizing the distances from all the 3D space points to the corresponding optical rays, the method assures the spatial distance error is minimal, and enhances the calibration precision. Because of consisting of linear optimization parameter estimation and nonlinear refinement, the calibration process can quickly and availably converge to the totally optimization.To solve the problem of on-line extrinsic parameters calibration of large-scale stereo vision measurement system, this paper presents a calibration method with two points based on the developed optical bar with special frame. By moving the optical bar over the measurement volume, the relative orientation and position of two cameras can be quickly determined with epipolar constraint of the stereo cameras catching features and the distance between the feature points on the optical probe. The experiment result proves that the calibration method proposed is flexible, valid, can obtain high calibration accuracy and good results in the application, and applies to the online calibration of the stereo vision measurement system.The general experiment of the measurement system approves the theory is valid, the algorithm is feasible, the system is of high precision and can satisfy the demand of the large-scale three dimension geometry measurement, and has good application.