Studies On CT Online Inspection Technology Of Steel Tube From Three Projections

The online inspection technology is needed for the purpose of correcting the possible errors in the manufacture of steel tube, which plays an important role for its quality assurance. However, most of the existing inspection technology is of singal function, and can not inspect the steel tube online. In order to meet the requirements of steel tube inspection, the paper aims to develop a comprehensive system that can inspect the steel tube online by doing studies on CT image reconstruction technique from three projections. Therefore, the research has some theoretical significance and application prospects.A projection data collection system having no mechanical scanning motion in which both the sources and detector arrays are stationary is used to save time in the process of CT inspection. It can acquire three projections of the same section quickly even though the steel tube moves in the manufacture. Furthermore, the simulation platform is built based on the CT system of the laboratory of nuclear technology and application in Tsinghua University. Then the simulation model of steel tube section and the calculation method of projections are confirmed for further studies.The results of simulation experiments indicate that either the analytical algorithms or the iterative algorithms can reconstruct the steel tube section from three projections. Therefore, the characteristicses of steel tube section, including the section shape and the distribution of pixel value, are used to modify the iterative algorithms. The experiment results show that the section can be reconstructed from three projections with the modified methods. And it is found that the MEEM algorithm is superior to several other modified iterative algorithms for the image reconstruction of steel tube section. Besides, the IMPEEM algorithm is proposed so as to improve the performance of image reconstruction. It can save the reconstruction time and improve the inspection precision by means of substituting the EEM algorithm with PEEM algorithm and adopting some reconstruction skills.The method of rotating polar coordinates is a technique of image reconstruction, which can save the reconstruction time by reducing the computation complexity. The experiment results indicate that the steel tube section can be reconstructed from few projections with the method of rotating polar coordinates. Moreover, the performance and applicable scope of the method are analyzed by comparing with the method of rectangular cocordinates. Then a reconstruction algorithm of discrete tomography is introduced and its potential applications are discussed.The calculation method of the spatial resolution of CT system is discussed based on the analysis of its major effect factors. Then the reconstruction parameters of the inspection system are optimized according to the accuracy requirement of steel tube. The results of Monte Carlo simulation show that the optimization can improve the results significantly. At last, the inspection precision and reconstruction time are studied and the process of choosing proper reconstruction parameters is introuduced, which are useful for the system design.