Research On Key Technology Of Visible And Near-infrared Multi-channel Grain Color Separation Detection System

The traditional grain color selector uses the visible light waveband to detect and analyze the shape and color of the grain.However,for the heterochromatic grain with slight difference with the qualified grain surface color,as well as other impurities such as transparent glass fragments and plastics,the visible light band cannot be distinguished.It needs the infrared light to identify the internal difference.Moreover,the traditional grain color selector is mainly used for screening a certain kind or several kinds of materials in a given spectral range,and each material possesses its own specific color-sorting wavelength,so it has limitation,poor selecting effect,and high cost.The optoelectronic detection system is the core system of the whole color selector,and the optical system is a significant part of it.It is related to whether the grain can be formed a clear image on the CCD light sensor,which directly affects the color sorting accuracy of the color sorter.In this paper,based on the overall structure research and analysis of the grain color sorting detection system,according to the grain color sorting conditions,a new type of visible and near-infrared three-way grain color sorting lens is designed through the analysis and research of the optical system,the beam splitting prism system,and the optical film technology.The three-path grain-color selection lens is composed of the former group objective lens and the rear group split prism system.The whole optical system is designed by ZEMAX software.The focal length is 30 mm,F number is 2.8;the working wavelength is from 400 nm to 930nm;the modulation transfer function is greater than 0.3 at the Nyquist frequency106lp/mm;distortion is less than 1%,and the magnification difference of the three beams is less than 0.0001.A new-type light-splitting prism system structure is adopted to realize the three-path light splitting of blue-green light,red light and near-infrared light.Three irregular prisms is applied in the light-splitting prism system to reduce the size of the light path.According to the principle of total reflection,the internal space conditions of the grain color selector as well as the specifications of the CCD sensor,the prism structure is designed to realize the turning of the light path and ensure that the optical paths of the three lights are equal.Furthermore,the corresponding optical filter film is designed according to the propagation path of the light to realize the color splitting of the prism.The developed antireflection film and the spectroscopic film can meet the requirements of the spectroscopy and the environmental test from 400 nm to 930 nm.Through the test and analysis of the focal length and spectral response of the three-path light,the performance of the developed three-path grain color selection lens is evaluated.The results show that the magnification difference from the three-path light of the color selection lens meets the design requirements.Its spectral response effect is good with clear resolution,which can effectively improve the screening efficiency of the grain-color selection system.