|关键词||大口径光学元件 表面瑕疵检测 振动测量 显微视觉|
|英文摘要||With the need of large scale equipment manufacturing and strategic scientific research, large aperture optical elements are widely used in various large optical systems, such as large telescope lens, ICF laser driver system, satellite wide viewing angle observation camera and optical imaging missile guidance systems. Due to the application of large aperture optical elements, very small defects in the surface of the optical elements will have a great impact on the entire optical system. So it is of great significance to detect the surface defects of large aperture optical elements accurately and objectively. There are many flexible structures in the industrial field. These flexible structures are prone to vibration, which leads to the damage of the whole structure. So it is significant to measure the vibration of flexible structures. At present, the method of detection and measurement based on vision is widely used in the field of industry. Many researchers have proposed a variety of systems and the corresponding algorithms for surface defect detection and vibration measurement. But there are still problems to be solved in practical application. This dissertation focuses on the research on the surface defects detection of large aperture optics and the vibration measurement of flexible structure based on microscopic vision. The main work and contributions are as follow:|
(1) A surface flaw detection system for large aperture optical elements is designed, which combines the dark-field imaging system (DFIS) and the bright-field imaging system (BFIS). A line-scan camera with line source is used in the DFIS to the rapid scanning of the defect. An array camera with a coaxial light source is used in the BFIS, which carries on the further accurate detection and the measurement to the flaw. The final flaw detection results are obtained by fusing the detection data under bright and dark field. The detection system is designed in detail from three aspects: the image acquisition subsystem, the motion subsystem and the software subsystem. The experiments show that the proposed system’s performance is greatly improved compared with the existing detection systems’ in the three aspects of adaptability, efficiency and accuracy of detection.
(2) Due to its own characteristics of large aperture optical elements, the line-scan camera is easy to out of focus in the process of scanning. In this work, the method of scanning path planning of line scan camera is presented for dark field image acquisition of the large aperture optical elements and aspheric. Aiming at the problem of dark field image stitching, an image stitching algorithm based on SURF features is designed to achieve a fast stitching of dark field scanning image. For the display of large image data, a display method based on image pyramid is presented to achieve efficient and rapid display of dark field images. For dark field scattering effect of defect size, the method based on the fusion of bright and dark field is proposed to realize the accurate measurement of the defect size. Experiments on the above methods have been carried out. The results show that the method is accurate and effective.
(3) To solve the problems of nanometer depth of scratch detection and full length detection, this dissertation proposes an algorithm combining the coarse and fine scratches detection. A line segment detection algorithm based on Gabor filter is designed to detect the fine scratch. And the scratch location connection method based on LSD algorithm is used to realize fine detection. Experiments show that the algorithm can accurately detect various types of scratches on the surface of optical elements in the low signal-to-noise ratio and edge blur. In this dissertation, the defect target segmentation algorithm based on the characteristics of Kitter is proposed to realize the accurate segmentation of the defects in the middle and low contrast of the bright field image. The accurate classification method based on Gist feature for scratch and pollution is designed to classify damage and pollution defects. The texture features under bright field are used to accurately distinguish dust and pits.
(4) Aiming at the vibration measurement of the flexible micro target, a vibration measurement system based on microscopic vision is set up. The image Jacobian matrix is calibrated by the active motion. In this dissertation, two kinds of image feature extraction methods are proposed based on two cases, i.e., circular ring marker and no marker. The vibration of flexible object is measured accurately by using the image Jacobian matrix. Experiments verify the effectiveness of the proposed methods.
Finally, the results of the research are summarized, and the future work is analyzed and prospected.
|陶显. 基于显微视觉的表面瑕疵检测与振动测量研究[D]. 北京. 中国科学院研究生院,2016.|