Simulation And Detection Of The Aesthetic Defects Of Polarizer

As a usual polarizing optical component, the polarizer has a wide range of applications. It is one of the key materials of the LCD(liquid crystal display). The aesthetic defects of polarizer have a straight and serious impact on the quality of liquid crystal panel. Visual inspection by humans is of really large labor intensity, and the inspection accuracy is also apt to be influenced by the subjective facts of inspectors, such as the tiredness and the resolution ability of individual eyes. Furthermore, the speed of manual inspection is hard to improve. Hence, an automated non-destructive detection technology for such defects with high accuracy and speed is highly important for the relevant industries.Some slight and transparent defects can hardly imaging and be characterized under conventional illumination. In order to inspect these special defects, a new and automated inspection method based on machine vision was investigated, which employed the structured-light illumination to enhance the defects imaging. So the subsequent image processing is straight and simple because of the enhancement. The detection accuracy and speed therefore were improved. Specific research work as followed: 1? Simulation of the imaging enhancement.The transparent defects are modeled as micro-lens for the first time. The simulation of the imaging system based on was established in Trace Pro to investigate the mechanism of the imaging enhancement. The simulation demonstrated that the transparent defects can imaging in the captured images as “black spots in bright stripes " or " bright spot in black stripes” under the structure light illumination. Comparing to the conventional illumination, the contrast increases at least 7.8 times. When the defects appear at the edge of the stripes, the contrast is the best and reach to 14.6 times. 2? Simulation of imaging ruleThe impact of the image distance, depth of defect and refractive index difference on the defect imaging was studied. The simulation results of the imaging rule with the image distance variation are consistent with the experimental results. The imaging variations resulted from the defect depth and the image distance are similar, it revealed that the equivalent focal length of a defect is determined by its depth. The best image distance is decreasing with the defect depth rising. This would reveal a new method for estimating the defects depths. Simulation results show that the refractive index difference between the inner transparent defect and adjacent region is about 10-3 order of magnitude. 3? Image processing algorithm.A template difference method was studied, it scans the defect and the template four times during a period, respectively, the subtraction between each pair of the images was calculated, and then the four subtractions were combined to a final image with satisfied contrast. The threshold segmentation was applied to the final image for identification and abstraction of the defects. The detection speed reaches to 9.5s/piece on an ordinary PC with an accuracy of 99%. 4?Detection system.A detection system for the aesthetic defects of polarizer was designed according to the simulation results. It consists of the structured a light source, an industrial camera, an environmental isolating apparatus and a computer. A rich set of experimental results illustrate that this system can extremely enhance the imaging of the defects.