Study Of Laser Scanning Imaging And Weld Defects Extraction Base On Computed Radiography

Computed radiography, commonly referred to as CR, is an advanced digital imaging technology in which the conventional x-ray screen-film combination, in one case, is replaced with a reusable imaging plate coated with a photostimulable storage phosphor. The great advantages of the IP compared to conventional film are, a) the wide dynamic range, b) the high spatial resolution, c) the large detection area, d) the high detective efficiency, and e) reusability. Therefore, it is widely used in medical diagnosis, and has been used in the oil, natural gas, electricity engineering and aviation in recent years.Laser scanner of CR is a core and key component of CR system, one of the most important applications of of CR system is weld defects detection. The design of laser scanner of CR is very complex. At present, all laser scanner of CR need to be imported in our country. Research and design of CR system is very important to the development of laser scanning imaging technique. Supported by National Scientific and Technical Supporting Programs which funded by Ministry of Science& Technology of China During the 11th Five-year Plan, this paper has focused on the design of laser scanner for computed radiography and study of defects extraction of X-ray weld images. The main content of the dissertation are listed as follows:1. The new collectivity design scheme for laser scanner of CR was proposed. A new high-performance laser scanning system was designed. In view of difference in performances of scanning methods, a scanning arm was designed which was composed by pentagonal prism and scanning object lens. To cooperate with scanning arm, a circular imaging plate transport mechanism was designed. Scanning arm can receive stimulation fluorescence as a receiving device, too.2. According to the requirement of collectivity design scheme, we have properly selected key components. Optical system and mechanical structure were designed according to the scheme. Based to the design scheme of imaging plate transmission mechanism, the sensors were selected and arranged legitimately and the control program of system was realized.3. A defects extraction algorithm of X-ray weld image based on Imaging Plate is proposed. At first, a wavelet adaptive denoising method based genetic algorithm is proposed to reduce the noise of image. Then, aiming at two types of images in detection, two algorithms of contrast enhancement according to the differences of contrast are proposed:a wavelet image fusion approach to contrast enhancement and a multiscale morphological approach to local contrast enhancement. Finally, background be simulated, and defect region were extracted successfully using arithmetic of digital subtraction, iterative threshold segmentation method accomplished defect extraction. The simulation results indicated that the methods can achieve automatic extraction of defect region, which lays a good foundation for flaw feature parameter extraction and choice4. The experimental results demonstrate the feasibility and efficiency of the optical system. Data obtained here provide useful experimental evidence for the design of the optical system. The chief factors which affect the system spatial resolution of laser scanner have been discussed, such as motor rotation speed, environmental temperature, spherical aberration of scanning objective, et al.. Simulation results show it can meet the performance requirements of optical systems.5. Dynamic simulation of mechanical structure was processed in this paper with the finite element software of Ansys.Effect of scanning speed on mechanical structure was analyzed when the rotating parts has existed eccentricity. The resonant frequency and critical speed were calculated. Results showed that the rotating speed should be far away from the natural frequencies of different orders of the structure, or it would cause the resonance, the laser scanner of computed radiography might not work normally.6. The spatial resolution of laser scanner was measured and the results showed that it can meet requirements of industrial inspection.Experiments were carried out to verity the performance of laser scanner and the results indicated that the images have good visual effect.