Field Calibration Method Of Camera For Measuring The Dimensions Of Large Forging

With the development of national economy, huge mechanical and electronic equipments, such as rotors in nuclear power plants, crankshafts in huge marine engines and decks on submarines etc. require a great amount of large forgings. In the forging process of large forging, obtaining accurate online dimensions of large forgings betimes will help to economize material and energy, improves quality of products and productivity. To get the accurate online dimensions of large forgings binocular stereo vision measurement method was proposed. This method is a non-touch measuring method which is time-saving, flexible, accurate, and has wide measuring scope. In the binocular stereo vision measurement system, validity of the calibration plays an important role in accuracy and effectiveness of the measuring results, and calibration of cameras is a pivotal technology of constructing the measuring system. Not only the accuracy of the calibration should be considered, but also the efficiency and applicability should be taken into account. The dissertation focuses on field calibration of the cameras which are used in binocular stereo vision measurement system. And it contains four parts which are as follows.1. A general and systemic introduction of dimension measuring system of large forging was given. Division of the system was achieved according to its functions, and subsystems were obtained.2. Research on theories of camera-calibration and investigations on common methods for camera-calibration was carried out. Principium of camera-calibration method in stereovision systems and pertinent research home and abroad was presented in detail. A new calibration method of CCD camera with projected targets technique which is based on active vision was suggested according to the intrinsic characteristics of dimension measuring system of large forging and the environment it works in. The intrinsic parameters of CCD camera can be obtained by capturing the projected targets during orthogonal movements of camera, and recognizing the feature points of targets, while the extrinsic parameters of CCD camera is measured by detecting the distance between the feature points of targets with the electronic theodolite. 3. Combined with Stereo vision system, calibration was carried out with the camera-calibration method proposed in the paper in the field of forging large parts. Measurements of a cylinder parts machined and a forging part were taken respectively. By comparing the results probable sources of error were found out and improvement was made. Results of comparison between calibration board and field calibration show that the method proposed in the paper is more accurate. And constructive discussions were achieved by analyzing the experimental results.