A Near Infrared Optimal Wavelength Imaging Method for Detection of Foreign materials

摘要

The objective of this research was to develop an optimal wavelength imaging system for detecting foreign materials in the NIR (near infrared) region from 750 nm to 2500 nm. This method is based on the principle that different fibers have different spectral absorptions and reflectance characteristic. When submitted to a source of illumination at different wavelength, foreign materials present different reflectance values in comparison to those from cotton fibers. For simultaneously discriminating several types of foreign materials from cotton, the optimal wavelength evaluation function for describing the cotton/foreign materials absorption discrimination was set up. Through the Fourier transform spectrometer experiment, the optimal wavelength for these detected foreign materials was determined and accordingly an optimal wavelength imaging system was developed. The wavelength selection experiment showed that the 940 nm wavelength was the most appropriate for detection of a wide range of foreign materials in cotton, and the 940 nm wavelength imaging system gave the clear image features of these foreign materials. The result suggests that use of NIR optimal wavelength imaging technique is a feasible and effective method to detect foreign materials in cotton, which are currently difficult for sorting.