Research on coal-rock interface distribution perception based on near-infrared spectra

Near-infrared reflectance spectra can distinguish coal and rock based on the difference of reflectance spectra characteristics caused by different intrinsic material attributes of coal and rock. This method has high identification accuracy and good real-time performance. But it has not been used for identification of coal-rock interface position distribution. According to the demand for self-determination of the coal-rock interface in the subsequent cutting cycle of shearer memory cutting, the precise distribution sensing technology of coal-rock interface based on near-infrared reflectance spectra technology is studied. A coal-rock interface platform is built by using gas coal and carbonaceous shale cutting block samples. A spectrum detector integrated with optical fiber collimator and tungsten halogen light source is designed and installed on the shearer's body. The near-infrared (1 000-2 500 nm) backward reflectance spectra curves of coal and rock near the coal-rock interface are measured at three walking velocities of the shearer (0, 3, 7 m/s) and four scanning angular velocities of the spectrum detector (3, 4, 5, 6 °/s). For all the reflectance spectra collected by the spectrum detector in each scanning track on the coal wall, the unsupervised identification of coal-rock reflection spectra is carried out based on cosine distance fuzzy C-means clustering (CFCM) in the differential characteristic wave bands of 2 150-2 250 nm. According to the detection results of each position on each scanning trajectory, the theoretical detection position of the coal-rock interface point is determined based on the height difference weighting method and scanning trajectory equation. The research result shows that under each movement state of the shearer and the spectrum detector, the near-infrared reflectance spectra in the backward direction of gas coal and carbonaceous shale collected by the integrated optical fiber collimator tungsten halogen light source spectrum detector have obvious differential absorption valley bands around 1400, 1900, 2200 nm. The reflectance spectra curves of coal and rock all show a downward trend with the increase of the detection incident angle. With the increase of the scanning angular velocities of the spectrum detectors under the same walking velocity of the shearer, and with the increase of the walking velocity of the shearer under the same scanning angular velocity of the spectrum detector, the reflectance spectra curves of coal and rock tend to be flat as a whole. Based on CFCM, height difference weighting method and coal wall scanning trajectory equation, rapid and precise detection of coal-rock interface points under the movement of the shearer and spectrum detector can be realized. Among them, the root mean square error of the detection results of coal-rock interface points under three scanning angular velocities of spectrum detectors 3, 4, 5 °/s is not more than 1.5 cm. The research provides a reference for the application of near-infrared reflectance spectra technology to the precise and efficient perception of coal-rock interface distribution.