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Discussion on online automatic detection of LED full-color screen modules

by:Demo     2021-07-15
The color difference or brightness difference of the LED display is caused by the inadequate control of a single module in the production process, but the lack of testing in the module link or the inability to implement 100% testing will bring uncertain factors to the quality of the entire screen after assembly. This article discusses on-line automatic detection of modules, hoping to provide help for the development of the industry.

According to the inspection requirements of the display module, the original manual inspection was transformed, and the system was designed to integrate the machine vision technology into the inspection process of the LED module. The LED module was realized without changing the hardware of the LED module. The group's online, automatic, and rapid quality testing meets the testing requirements of customers and realizes the standardization of module production. It will surely have a larger application market in the field of rapid on-site testing of LED unit boards. It is not only conducive to improving the economic efficiency of the enterprise itself, but also can promote the technological progress of the industry, promote the development of China's optoelectronic industry, improve the technical level of my country's industry, reduce and replace imports, and have significant economic benefits.

Develop a set of control system software to control the display pattern of the LED display module, use the high-precision color brightness sensor probe to detect the brightness and chromaticity of the module, and then use the self-developed data acquisition and analysis software to determine the display mode Whether the brightness and chromaticity uniformity of the group is qualified, statistics and records are carried out, so as to realize the online automatic detection and industrialization of the brightness and chromaticity consistency of a large number of LED display modules.

The principle of realizing the online detection of LED full-color screen modules is that the camera (including brightness and chromaticity probes) collects the luminous signal of the LED full-color display module on site, and the software analyzes the results in real time. The camera's brightness and chromaticity calibration is realized by standard luminance and colorimeter.

(1) LED full color screen module automatic positioning detection

The LED full-color display module automatically enters the online detection system through the assembly line, and the online detection system is triggered for detection after automatic positioning. The positioning system is also responsible for supplying power to the module, and realizes the color conversion of the module under several conditions, such as plus or minus 45 degrees, 90 degrees, and so on. After the signal is stable, the detection system is triggered to test the brightness and chromaticity distribution.

(2) LED full-color screen brightness, chromaticity distribution detection and quality classification

The LED full-color screen brightness and chromaticity distribution detection system is composed of a camera and a high-precision CCD. The camera can change lenses with different focal lengths as needed. The detection system collects the image signal, realizes the positioning of the LED pixel point through the image binarization processing, the image threshold segmentation of the histogram, etc.; uses the RGB color model in the image to calculate the tristimulus value, and performs the color coordinate, color purity and correlated color temperature. Equal chromaticity parameter calculation; convert the RGB color model used in the image into XYZ and YUV color models (Y represents brightness, U and V are the two components of color), and the brightness of each pixel can be calculated conveniently and quickly value. On this basis, the statistical analysis and processing of the uniformity of the brightness and chromaticity distribution of the full screen are carried out, and the quality of the screen is classified according to the production requirements to meet the requirements of the quality consistency of the control screen.

(3) Calibration of LED full-color screen detection system

The response of the detection system composed of the camera and the high-precision CCD does not meet the requirements of the XYZ tristimulus color matching function in the chromaticity system, so the response signal must be calibrated to complete the chromaticity and brightness test requirements. The calibration of the LED full-color screen detection system is completed by a calibration system composed of a standard lamp, a standard spectrum colorimeter and a high-precision spectrometer. The standard signal generated by the calibration system is used to construct a mathematical model, and the response function of the detection system corresponding to the color matching function of the XYZ tristimulus value is established. The model contains a series of response functions under different test conditions such as different lenses and different apertures, which can be automatically called in actual tests to achieve one-time calibration and continuous use. Simplify the complexity of use and greatly improve production efficiency.

Conclusion: Through the automatic positioning control of the display screen, on-site detection and analysis of brightness uniformity, chromaticity distribution, quality judgment and classification and other key technology research and development. Improve the brightness consistency of the display screen, realize standardized testing, increase production efficiency and output, and achieve the goal of large-scale industrialization of LED full-color display screens.

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