Research On Defects Detection Technology Of Optical Surface By Scattering And Scanning Method

Combining with the geometrical characteristic of the spherical optical element, this paper uses LED to irradiate optical element surface and the microscopic imaging system captures the image by receiving the scattering light from defects. In the image, bright defects are showed in black background. Through the loop scanning, the defects image of the whole elements surface can be captured. The relation of real size and imaging size of defects are determined by the antitheses and standard system. The resolution of detecting system is approximately a micrometer, and the image and experimental results are very good.Firstly, the characteristics and harm of defects are reviewed. In most time, the detections of defects use the scattering of defects. Then the scattering of optical surface with defects are discussed, and three main scatterings on surface and their affection on the defects scattering images are analyzed.Secondly, the model of defect detection system has been set up, including illumination system, microscopic imaging system, scanning system. Based on detection target, the parameters of lens, CCD camera and scanning device are calculated. The image of scratch influenced by the angle of LED is researched. The scanning method is designed which can detection the whole surface. Then the experimental platform is built to capture the defects images. Because of the small filed of view, the image mosaic algorithm is founded to solve the problem. In order to improve the automatic of image processing, the GUI image processing interface is programmed by using matlab which can improve preprocessing automatic effectively.Finally, the defects of image after mosaic is segmented and marked,20 defects samples are selected,and the geometrical data are calculated, such as area, perimeter, roundness and elongation. The true size of defects is measured by polarization microscope. This paper the relationship between true size and pixel size is got by using the groups of data.In this paper, the research is trial and exploration on scanning method and image mosaic algorithm. It is useful for the automatic defects detection about the spherical optical element in the future.