| Most of those LED light source now in the market are made by the traditional dispensing process production line, there exist two main problems: uneven LED phosphor coating and silicone resin would being muddy because of its heat-labile factor, this results in LED’s low luminous efficiency, poor spatial uniformity and short life. In recent years, many countries have competed to develop new planar coating packaging technology. Professor Haibo Rao proposed "phosphor self-adaptive planar phosphor coating technique", in which phosphors mixed with phosphor photosensitive polymers exposed by the blue-violet light of the LED chip itself, as to match the phosphor layer with the light intensity, and then remove the exposured silicone resin by plasma stripping. This coating method completely solved two problems above. Many foreign manufacturers have developed their own mature LED planar coating packaging production line, but this kind of production line is still in blank stage in China, therefore, developing the LED light production line which based on the LED self-adaptive planar phosphor coating process is of great significance to China’s LED industry.This thesis focus on the design and implementation of the hardware and software of "phosphor coating quality visual inspection system" —one of process of the production line above. The system aims to detect dispensing integrity to ensure the proper function of follow-up processes, at the same time, to reduce useless processing towards unqualified products. In the production line, LED chips transit on the conveyor belt by fixed in special moulds. The main content of this thesis are as follows:(1)Automatical identify of coated phosphor color of LED, and determine its coating quality;(2)According to the actual situation of the production line, complete the hardware of image capture system: Capture images for four branch production lines using a camera; make the system coordinate with the other processing machines.This paper determined the quality of the individual LED by comparing the area of phosphor-coated part in each LED reflector cup to the standard coating area using image processing method; at same time, by positioning and calculating the chrominance of each LED Center, we can judge its phosphor color. This process used adaptive binarization, edge detection, Hough transform and HSV-based color image segmentation image processing method, ect.Eventually, it achieved the initial requirements of the system, the percent of correct judging of phosphor color was 100%, the correct rate of coating quality detecting was 100%, tests based on 40 experimental samples.The production line was made of four parallel branch production lines, the system controls the stepper motor to make linear guide which fixed one camera move to complete image acquisition of LED on four parallel branch lines. After Final tests, its positioning error rate is small than 0.1%, and it was with good stability and advanced anti-jam capabilities.At present, almost all LED light qulity test was arranged at the end of production line, with the method of observing light spot, it’s a great deal of waste of human resouse, and it’s not acuurate and efficient as well, it influents the yield of LED. I believe "LED phosphor coating quality visual inspection system" that this paper proposed would have broad applications in the increasing LED planar coating production lines in the future. |
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