| Color difference is one of the important indexes to evaluate the quality of fabric products.With the increasing production level of textile industry in China,the detection of color difference of fabrics often lags behind the production in the process of mass production of fabrics,resulting in many unqualified products.In order to improve the efficiency and accuracy of fabric color and color difference measurement,the research of fabric color difference online measurement system is of great significance.In this thesis,an online measurement system of fabric color difference was designed based on the principle of photoelectric integral color measurement and combined with digital sensing technology,then the measurement data of the system was calibrated by constructing a color calibration matrix,which realized the measurement of fabric color tristimulus value and color difference.The main research contents of this thesis are as follows:(1)The basic color measurement theories of chromaticity were compared and summarized.This thesis introduced the basic concepts of color and color difference,presented the composition of CIE standard color space and uniform color space,and determined the standard color space and numerical calculation method on which color and color difference measurement was based.(2)The online measurement system of fabric color difference was studied and designed.The system was mainly composed of optical structure,hardware circuit and software program.The optical structure of color measurements,such as illumination geometry condition,illumination light source and observation field,were studied and analyzed,in order to ensure that color light signal was accurately transmitted to the sensitive surface of AS73211 color sensor.The bottom communication connection between STM32 and AS73211 color sensor was completed through the design of STM32 main control circuit and AS73211 color sensor working circuit,which laid the foundation for subsequent data acquisition and transmission.The main control program of STM32 was designed to realize the data acquisition of AS73211 color sensor and the serial data transmission between the AS73211 color sensor and the host computer.The interface of the host computer was designed with MATLAB GUI for realizing the processing,display,storage of color data and the control of the working state of the system.(3)Calibrated the output data of the AS73211 color sensor.The color measurement system utilizing spectrophotometer was built.The standard reference of the sample color tristimulus value was obtained by measuring and calculating.The color calibration matrix was calculated by using the standard reference value and the ADC value of the sensor output according to the calibration formula,then this matrix multiply by the ADC value of the sensor output to achieve the calibrated color tristimulus value data.The calibration results showed that the calibrated data was very close to the standard reference value data,which indicated that the calibration matrix could be used for the subsequent color measurement of the system.(4)The online measurement of fabric color difference was completed.Taking the special color card of textile fabric as the measured object,the stability,repeatability,reproducibility and indication error of the test system were tested according to the verification regulation of photoelectric integral colorimeter.Meanwhile,the dynamic measurement and distance change influence test were carried out.After testing,the indexes of the system accorded with the first level standard of the verification regulation of color difference meter.On this basis,the color difference of the sample was tested online,and the color difference ?ELab*between the measurement results and the standard value was kept below 0.5,which indicated that the system could realize the accurate measurement of the color tristimulus value and could be applied to the online detection of fabric color difference. |
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