Non-sampling and sample-preparation cross-belt coal quality online detection LIBS (Laser-induced Breakdown Spectroscopy) spectrum system

Abstract

The invention discloses a sampling-free sample preparation cross-belt coal quality online detection LIBS (laser-induced breakdown spectroscopy) spectrum system which comprises a belt conveying system and an optical detection system, and a laser range finder is arranged on a branch conveying belt; and the laser range finder is used for detecting and recording the height of the coal in the detection area on the branch conveying belt. An optical detection system based on the LIBS technology is directly erected on the coal conveying belt, the problems that the speed of the conveying belt is high and real-time sampling detection cannot be achieved are solved, rapid and real-time cross-belt coal quality quantitative analysis with high sampling rate is achieved, and the detection accuracy is improved for the problem that the spectral stability is affected by the height change of coal on the belt. And the focal length of the LIBS detection system is quickly adjusted through the height of the sample in the detection area recorded by the laser range finder, so that the stability of the spectrum is improved.

Description

Technical Field

[0001] The invention relates to the technical field of coal detection, and in particular to a LIBS spectroscopy system for online detection of coal quality across a belt without sampling. Background Art

[0002] At present, high-precision LIBS detection systems for coal ores require sampling and cake pressing. High-precision LIBS (laser induced breakdown spectroscopy) detection systems for coal ores usually require sampling and sample preparation. This is because LIBS technology has requirements for the particle size and shape of the sample, and the sample needs to be prepared into a form suitable for analysis.

[0003] In high-precision LIBS detection systems such as coal and ore, the sampling process is the process of collecting representative samples. Common sampling methods include drilling sampling, sampling, batch sampling, etc. When sampling, care should be taken to avoid the mixing of impurities and to maintain the representativeness of the sample.

[0004] The sample preparation process is to process the collected samples according to certain standards to make them suitable for LIBS analysis. The sample preparation process usually includes sample crushing, preparing into a uniform powder sample, and undergoing appropriate pretreatment, such as drying, grinding, etc., to obtain accurate and reliable LIBS analysis results.

[0005] In addition, for samples that require a cake pressing process, the powder samples need to be pressed into solid round or square pieces, which can improve the optical quality of the samples and ensure the accuracy and repeatability of LIBS analysis.

[0006] In the existing online detection technology (Chinese patent CN102661935A), a flat and uniform layer of powdered material is obtained by belt transmission and baffles. The device structure solves the problem of uniform distribution of the powdered material surface and the problem of unstable distance from the material surface to the lens, which is conducive to continuous laser excitation. The RSD value of the generated laser-induced plasma spectrum signal intensity fully meets industrial needs, but it does not have the ability to detect uneven coal piles.

[0007] Therefore, it is necessary to provide a LIBS spectroscopy system for online detection of coal quality across belts without sampling to solve the above technical problems. Summary of the invention

[0008] The present invention overcomes the shortcomings of the prior art and provides a LIBS spectrum system for online detection of coal quality across a belt without sampling.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is: a LIBS spectroscopy system for online detection of coal quality across belts without sampling and preparation, comprising: a belt transmission system and an optical detection system;

[0010] The belt conveyor system comprises: a main conveyor belt, a secondary crusher, a storage bin and a branch conveyor belt arranged in sequence;

[0011] The optical detection system is mounted on the branch conveyor belt;

[0012] The branch conveyor belt is provided with a laser rangefinder, and the horizontal distance between the laser rangefinder and the optical detection system is 50-100 cm; the laser rangefinder is used to detect and record the height of the coal in the detection area on the branch conveyor belt;

[0013] The optical detection system comprises: a substrate, and a laser emission component, an automatic focusing component and a spectrum analysis component arranged on the substrate;

[0014] The laser emission assembly is used to emit pulsed laser, and includes: a laser, a 45-degree reflector, a beam expander lens and a dichroic mirror arranged in sequence;

[0015] The automatic focusing assembly focuses the laser beam emitted by the laser emitting assembly onto the coal based on the height of the coal above the detection area;

[0016] The spectrum analysis component is used to receive the plasma radiation signal generated by the interaction between the pulse laser and the coal material, obtain its spectrum and analyze the coal quality.

[0017] In a preferred embodiment of the present invention, the main conveyor belt is used to transport large pieces of coal, and part of the coal is taken from the main conveyor belt and transported to the secondary crusher for crushing, and the particle size of the crushed coal is 10-15 mm;

[0018] The storage bin is arranged at the discharge port below the secondary crusher to receive the crushed coal. The coal falls through the discharge port of the storage bin or is transferred to the branch conveyor belt and is transported forward at a fixed speed, passing through the laser rangefinder and the lower end of the optical detection system in turn.

[0019] In a preferred embodiment of the present invention, the optical detection system further includes a detection position determination module, which determines the position and height of the coal for optical detection based on the height data of the coal on the branch conveyor belt continuously monitored by the laser rangefinder.

[0020] In a preferred embodiment of the present invention, the method for determining the coal material detection position comprises the following steps:

[0021] Use a laser rangefinder to continuously monitor the height data of the coal on the branch conveyor belt to obtain a large number of continuous height data points;

[0022] Analyze the difference in coal height between adjacent height data points and select the points with the smallest difference as the predetermined detection points;

[0023] A length of coal is divided into N sampling intervals, each sampling interval has several predetermined detection points, and a predetermined detection point is selected in each sampling interval as a coal detection position to obtain N coal detection positions.

[0024] In a preferred embodiment of the present invention, the method for selecting the predetermined detection point is specifically as follows:

[0025] Calculate the height difference Δh between adjacent height data points i,j = | h i -h j | , where h i and h j are the heights of the i-th and j-th height data points respectively;

[0026] Set the height difference threshold Δh according to the particle size of the coal i,j , filter out all Δh according to the threshold i,j The consecutive height data point pairs that are less than the threshold;

[0027] The midpoint of each pair of consecutive height data points is selected as the predetermined detection point.

[0028] In a preferred embodiment of the present invention, the determination of N detection positions first satisfies the minimum frequency of height changes and further satisfies the minimum height difference between adjacent detection positions. The specific screening process includes:

[0029] For each detection position k, calculate its height change frequency F k The height change frequency refers to the number of times the height change exceeds the set threshold ε in the continuous measurement data. The specific calculation process is:

[0030]

[0031] Where I is an exponential function, which takes the value of 1 when the condition is met, otherwise it takes the value of 0; h k,i is the i-th predetermined detection point of the k-th detection position; ε is the set height change threshold;

[0032] Select F k The smallest predetermined detection point is used as a candidate detection position;

[0033] For each candidate detection position k, calculate the height difference Δh between it and the adjacent detection position k :

[0034] Δh k = | h k+1 -h k| + | h k -h k-1

[0035] Among them, h k is the height of the kth detection position, h k+1 and h k-1 are the heights of the k+1th and k-1th candidate detection positions respectively;

[0036] Among the candidate detection positions with the least frequency of height changes in a sampling interval, select Δh k The smallest candidate detection position is taken as the final detection position, and finally N detection positions are obtained.

[0037] In a preferred embodiment of the present invention, the optical detection system is mounted on the branch conveyor belt by a three-dimensional four-corner support frame, the lower end of the three-dimensional four-corner support frame is welded and fixed to the ground, and pulleys are provided on both sides of the base plate of the optical detection system for sliding left and right on the three-dimensional four-corner support frame.

[0038] In a preferred embodiment of the present invention, the automatic focusing assembly includes: a concave plane reflector, an automatic focusing displacement stage, and a convex plane reflector disposed on the automatic focusing displacement stage.

[0039] In a preferred embodiment of the present invention, the spectral analysis component includes: a focusing lens, an optical fiber and a spectrometer.

[0040] In a preferred embodiment of the present invention, the spectral analysis component further includes a prediction model for analyzing the water content, ash content, sulfur content, calorific value, as-received lower calorific value and dry basis higher calorific value of the coal sample;

[0041] Establishing the prediction model and quantitative analysis process includes the following steps:

[0042] S21. Collect several groups of coal samples from different trains on the main conveyor belt, and collect spectra of these groups of samples on the branch conveyor belt at the same time. Collect 500-700 groups of spectra for each sample. Then, dry and grind the collected groups of coal samples, and use chemical titration method to obtain true values, including analytical water content, ash content, sulfur content, calorific value, as-received low calorific value and dry basis high calorific value of coal.

[0043] S22. Use Matlab programming to clean, screen and preprocess several groups of coal sample data, use the Laida criterion to remove abnormal spectra, use the window translation smoothing method to remove spectral background, use the channel spectral intensity area normalization to reduce the fluctuation of spectral signals, use wavelet transform to remove spectral noise, use peak finding, non-peak zeroing, peak drift correction and missing peak filling methods to eliminate the matrix effect and instrument error that lead to spectral peak drift and peak intensity loss, use the spectral lines and corresponding true values ​​of several groups of coal sample data after preprocessing as the input variables of the model, use partial least squares regression analysis to establish a prediction model for several groups of coal sample spectral lines and true values, and obtain the coefficient matrix and error terms of the model;

[0044] S23. Perform the same data preprocessing on the spectral data of the coal sample collected online, and bring it into the prediction model to predict the analytical water content, ash content, sulfur content, calorific value, received basis lower calorific value and dry basis higher calorific value of the coal.

[0045] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0046] (1) The present invention provides a LIBS spectroscopy system for online detection of coal quality across a belt without sampling and preparation. An optical detection system based on LIBS technology is directly mounted on the coal conveyor belt, thereby solving the problem that the conveyor belt is fast and cannot be sampled and detected in real time. Rapid and real-time quantitative analysis of coal quality across the belt with a high sampling rate is achieved. In view of the problem that the height of coal on the belt changes and thus affects the spectral stability, a laser rangefinder is arranged in front of the detection system. The rangefinder has the functions of identifying the presence or absence of samples and identifying and recording the sample height in the detection area. The focal length of the LIBS detection system can be quickly adjusted by recording the height, thereby improving the stability of the spectrum.

[0047] (2) The present invention determines N detection positions within a length through a method for determining the coal detection position. These detection positions not only have the least frequency of height changes, but also have the smallest height difference between adjacent detection positions. In other words, the frequency and scale of focal length adjustment are reduced, thereby reducing the adverse effects of focal length adjustment. This is because the adjustment of the focal length changes the optical path length of the laser beam from the concave plane reflector to the convex plane reflector and then back to the detection area. Due to changes in the curvature and position of optical elements (such as reflectors), the degree of diffusion (i.e., the divergence angle) of the laser beam during propagation will be affected. If the focal length is not adjusted properly, the laser beam may diverge significantly before reaching the surface of the coal pile, resulting in a larger light spot and a lower energy density, thereby affecting the interaction effect between the laser and the coal and the accuracy of the spectral analysis.

[0048] (3) The present invention uses a method for determining the coal detection position to obtain the optical detection position and the corresponding coal height. The automatic focusing displacement stage automatically adjusts the distance between the convex plane reflector and the concave plane reflector according to the optical detection position and the corresponding coal height, thereby adjusting the focal length of the concave plane reflector to achieve automatic focusing of the optical detection system, ensuring that the focus is always on the sample, improving the stability of the spectrum, and solving the problem of the change in coal height on the branch transmission belt affecting the stability of the spectrum. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0050] Figure 1 It is a structural schematic diagram of a preferred embodiment of the present invention;

[0051] Figure 2 is a light path diagram of a preferred embodiment of the present invention;

[0052] Figure 3 is a diagram of a method for determining a coal material detection position according to a preferred embodiment of the present invention;

[0053] In the figure: 1. main conveyor belt; 2. secondary crusher; 3. storage bin; 4. branch conveyor belt; 5. shell; 6. laser rangefinder; 7. vacuum cleaner; 8. three-dimensional four-corner support frame; 9. pulley; 10. spectrometer; 11. industrial computer; 12. display; 13. laser cooling device; 14. substrate; 15. laser; 16. 45-degree reflector; 17. beam expander lens; 18. dichroic mirror; 19. automatic focusing stage; 20. concave plane reflector; 21. convex plane reflector; 22. focusing lens; 23. optical fiber. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0056] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the scope of protection of the present application.

[0057] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0058] like Figure 1 As shown, the present invention provides a LIBS spectroscopy system for online detection of coal quality across a belt without sampling, including: a belt transmission system and an optical detection system.

[0059] The belt conveyor system includes: a main conveyor belt, a secondary crusher, a storage bin and a branch conveyor belt arranged in sequence. The main conveyor belt is used to transport large pieces of coal. Part of the coal is taken from the main conveyor belt and transported to the secondary crusher for crushing. The coal particle size after crushing is 10-15mm, and the coal particle size is preferably 13mm.

[0060] Furthermore, a storage bin can be designed at the discharge port below the secondary crusher to receive the crushed coal, or the crushed coal can be transferred to the storage bin by other methods. The storage bin is set on the branch conveyor belt, and the coal falls / is transferred to the branch conveyor belt through the discharge port of the storage bin and is transported forward at a fixed speed, passing through the laser rangefinder and the lower end of the optical detection system in turn.

[0061] In this embodiment, the branch transmission belt is provided with a housing for protection, the belt transmission device comprises a transmission belt and a motor for driving the belt to move, the transmission belt circulates through two rollers, and the speed of the branch transmission belt is 1 m / s.

[0062] The optical detection system is mounted on the branch conveyor belt. Specifically, the optical detection system is mounted on the branch conveyor belt by a three-dimensional four-corner support frame, wherein the lower end of the three-dimensional four-corner support frame is welded and fixed to the ground, and pulleys are installed on both sides of the base plate of the optical detection system to slide left and right on the three-dimensional four-corner support frame to adjust the position of the optical detection system, that is, to adjust the distance between the laser rangefinder and the optical detection system. The three-dimensional four-corner support frame is 135 cm long, 110 cm wide, and 120 cm high.

[0063] A laser rangefinder is provided on the branch conveyor belt, and the horizontal distance between the laser rangefinder and the optical detection system is 50-100cm. The laser rangefinder is in front and the optical detection system is in the back, and the position where the laser rangefinder detects the height of the coal is consistent with the position where the optical detection system obtains the coal spectrum. The laser rangefinder is used to detect and record the height of the coal in the detection area on the branch conveyor belt. Specifically, the laser rangefinder calculates the distance to the target object based on the round-trip time by emitting laser pulses and receiving the reflected laser. According to the initial distance between the laser rangefinder and the upper surface of the branch conveyor belt, the difference between the initial distance and the distance to the target object is calculated to obtain the height of the coal.

[0064] Furthermore, the method for determining the coal material detection position includes the following steps:

[0065] S11. Use a laser rangefinder to continuously monitor the height data of the coal material on the branch conveyor belt to obtain a large number of continuous height data points.

[0066] S12, analyzing the difference in coal height between adjacent height data points, and selecting several points with the smallest difference as predetermined detection points. Specifically:

[0067] Calculate the height difference Δh between adjacent height data points i,j = | h i -h j | , where h i and h j are the heights of the i-th and j-th height data points respectively;

[0068] Set the height difference threshold Δh according to the particle size of the coal i,j <2mm, filter out all Δh according to the threshold i,j The continuous height data point pairs that are less than the threshold value; in the specific implementation, it is adjusted as needed;

[0069] Furthermore, the midpoint of each pair of consecutive height data points is selected as the predetermined detection point. For example, there are three consecutive height data points h i-1 、hi和 h i+1 If both satisfy the condition that the height difference is less than the threshold, then h can be selected i As a scheduled inspection point.

[0070] The relative flatness of the coal at the predetermined detection point selected in this step can reduce the distribution and height changes of the coal caused by vibration during the coal transportation process and improve the laser focusing accuracy in coal quality detection.

[0071] S13, dividing a length of coal into N sampling intervals, each sampling interval having several predetermined detection points, selecting a predetermined detection point in each sampling interval as a coal detection position, and obtaining N coal detection positions.

[0072] Furthermore, the determination of the N detection positions first satisfies the minimum frequency of height changes and further satisfies the minimum height difference between adjacent detection positions. The specific screening process includes:

[0073] For each detection position k, calculate its height change frequency F k The height change frequency refers to the number of times the height change exceeds the set threshold ε in the continuous measurement data. The specific calculation process is:

[0074]

[0075] Where I is an exponential function, which takes the value of 1 when the condition is met, otherwise it takes the value of 0; h k,i is the i-th predetermined detection point of the k-th detection position; ε is the set height change threshold;

[0076] Further, select F k The smallest predetermined detection point is used as a candidate detection position;

[0077] For each candidate detection position k, calculate the height difference Δh between it and the adjacent detection position k :

[0078] Δh k = | h k+1 -h k | + | h k -h k-1 |

[0079] Among them, h k is the height of the kth detection position, h k+1 and h k-1 are the heights of the k+1th and k-1th candidate detection positions respectively;

[0080] Among the candidate detection positions with the least frequency of height changes in a sampling interval, select Δh k The smallest candidate detection position is used as the final detection position, and finally N detection positions are obtained. These detection positions not only have the least frequency of height changes, but also the smallest height difference between adjacent detection positions, that is, when performing optical detection, the height change of each position change is the smallest, so as to reduce the frequency of focal length adjustment during optical detection and the accuracy of detection height.

[0081] The present invention determines N detection positions within a length through a method for determining the detection position of coal material. These detection positions not only have the least frequency of height changes, but also have the smallest height difference between adjacent detection positions, that is, the frequency and scale of focal length adjustment are reduced, and the adverse effects of focal length adjustment are reduced. This is because the adjustment of the focal length changes the optical path length of the laser beam from the concave plane reflector to the convex plane reflector and then back to the detection area. Due to changes in the curvature and position of optical elements (such as reflectors), the degree of diffusion (i.e., the divergence angle) of the laser beam during propagation will be affected. If the focal length is not adjusted properly, the laser beam may have diverged significantly before reaching the surface of the coal pile, resulting in an increase in the light spot and a decrease in energy density, thereby affecting the interaction effect between the laser and the coal material and the accuracy of the spectral analysis.

[0082] The optical detection system includes: a substrate, and a laser emission component, an automatic focusing component and a spectrum analysis component arranged on the substrate; the substrate is fixed on a three-dimensional four-corner support frame, and the substrate is 60 cm long and 50 cm wide. The laser emission component is used to emit pulsed lasers, and includes: a laser, a 45-degree reflector, a beam expander lens and a dichroic mirror arranged in sequence. The operation mode of the laser emission component is: the laser emits pulsed lasers horizontally, passes through a 45-degree emission mirror, changes the pulsed laser path to vertically downward, and reflects to the beam expander lens to expand the pulsed laser beam, and the expanded beam is projected out through the dichroic mirror.

[0083] The automatic focusing component focuses the laser beam emitted by the laser emitting component onto the coal based on the height of the coal in the detection area. The automatic focusing component includes: a concave plane reflector, an automatic focusing displacement stage, and a convex plane reflector arranged on the automatic focusing displacement stage.

[0084] It is worth noting that when no focusing is performed, the light beam passing through the dichroic mirror is transmitted to the convex plane reflector, and the light beam is reflected to the concave plane reflector by the convex plane reflector, and then focused on the coal material in the detection area.

[0085] The spectrum analysis component is used to receive the plasma radiation signal generated by the interaction between the pulsed laser and the coal material, obtain its spectrum and analyze it. The spectrum analysis component includes: a focusing lens, an optical fiber and a spectrometer. The spectrum acquisition process is as follows: the pulsed laser interacts with the coal sample, and the plasma radiation signal generated is reflected by the concave plane reflector and collected on the convex plane reflector, and then reflected by the convex plane reflector to the dichroic mirror. The dichroic mirror reflects the radiation signal below the wavelength of 920nm to the focusing lens, and the plasma radiation signal is focused on the collection optical fiber port through the focusing lens, and the spectrum is acquired by the spectrometer for analysis.

[0086] The specific steps of the present invention for optically detecting the coal on the branch conveyor belt are as follows: a laser emits a pulsed laser with a wavelength of 1064nm, passes through a 45-degree reflector, and reflects the light beam to a beam expander lens, the diameter of the light beam passing through the beam expander lens is 14.5mm, the light beam after expansion is transmitted to a convex plane reflector with a diameter of 15mm through a dichroic mirror, and the light beam is reflected to a concave plane reflector with a diameter of 100mm and a center hole diameter of 15mm through the convex plane reflector, and the light beam passing through the concave plane reflector is focused on the coal in the detection area, the focused high-energy short-pulse laser interacts with the coal sample to generate high-temperature and high-pressure laser plasma composed of free electrons, ions and atoms, the plasma radiation signal is reflected by the concave plane reflector and collected on the convex plane reflector, and then reflected by the convex plane reflector to the dichroic mirror, the dichroic mirror reflects the radiation signal below the wavelength of 920nm to the focusing lens, the plasma radiation signal is focused at the collecting optical fiber port through the focusing lens, and the spectrum is acquired by the spectrometer for analysis.

[0087] Furthermore, the present invention uses a method for determining the coal detection position to obtain the optical detection position and the corresponding coal height. The automatic focusing displacement stage automatically adjusts the distance between the convex plane reflector and the concave plane reflector according to the optical detection position and the corresponding coal height, thereby adjusting the focal length of the concave plane reflector to achieve automatic focusing of the optical detection system, ensuring that the focus is always on the sample, improving the stability of the spectrum, and solving the problem of changes in coal height on the branch transmission belt affecting the stability of the spectrum.

[0088] It is worth noting that the response time of the laser rangefinder is in microseconds, the optical path signal transmission time is in microseconds, the response time of the automatic focusing stage is in microseconds, and the overall signal transmission delay is in microseconds. Through system software programming, the automatic focusing stage can quickly and automatically adjust the focal length according to the sample height recorded and detected by the laser rangefinder.

[0089] Furthermore, the optical detection system also includes a detection position determination module, which executes the above-mentioned coal detection position determination method, and determines the coal position and height for optical detection based on the height data of the coal on the branch conveyor belt continuously monitored by the laser rangefinder.

[0090] Furthermore, the optical detection system is also provided with additional components, including: a laser cooling device, an industrial computer, a display and a vacuum cleaner. Among them, the vacuum cleaner is installed near the laser focus point. In order to solve the problem that dust affects the spectral stability during sampling, a vacuum cleaner device is installed near the laser focus point to remove dust in real time, thereby improving the stability of the spectrum.

[0091] In this embodiment, in order to obtain accurate coal sample analysis indicators such as water content, ash content, sulfur content, calorific value, as-received low calorific value and dry basis high calorific value, a prediction model and a quantitative analysis process are further established, including the following steps:

[0092] S21. First, 50 groups of coal samples from different trains are collected on the main conveyor belt, and at the same time, the spectra of these 50 groups of samples are collected on the branch conveyor belt. 600 groups of spectra are collected for each sample. Then, the 50 groups of coal samples collected are dried and ground, and then the true value is obtained by chemical titration method, including the analytical water content, ash content, sulfur content, calorific value, received basis low calorific value and dry basis high calorific value of the coal.

[0093] S22. Matlab programming was used to clean, screen and preprocess 50 groups of coal sample data. The abnormal spectra were eliminated using the Laida criterion, the spectral background was removed using the window translation smoothing method, the channel spectral intensity area was normalized to reduce the fluctuation of the spectral signal, the spectral noise was removed using wavelet transform, peak finding, non-peak zeroing, peak drift correction and missing peak completion methods were used to eliminate the spectral peak drift and peak intensity missing caused by the matrix effect and instrument error. The spectral lines and corresponding true values ​​of the 50 groups of coal sample data after preprocessing were used as the input variables of the model, and the partial least squares regression analysis was used to establish a prediction model for the 50 groups of coal sample spectral lines and true values, and the coefficient matrix and error terms of the model were obtained.

[0094] S23. Perform the same data preprocessing on the spectral data of the coal sample collected online, and bring it into the prediction model to predict the analytical water content, ash content, sulfur content, calorific value, received basis lower calorific value and dry basis higher calorific value of the coal.

[0095] The present invention discloses a LIBS spectral system for online detection of coal quality across a belt without sampling and preparation. An optical detection system based on LIBS technology is directly set up on the coal conveyor belt, so as to solve the problem that the conveyor belt has a high speed and cannot be sampled and detected in real time, and realizes rapid and real-time quantitative analysis of coal quality across the belt with a high sampling rate. In view of the problem that the height change of coal on the belt affects the spectral stability, a laser rangefinder is arranged in front of the detection system. The rangefinder has the functions of identifying the presence or absence of samples and identifying and recording the height of samples in the detection area. The focal length of the LIBS detection system can be quickly adjusted according to the recorded height, thereby improving the stability of the spectrum.

[0096] Since the belt is constantly moving at a certain speed, there is a certain distance between the laser rangefinder and the optical detection system, ensuring that the same position of the sample is detected and analyzed, improving the accuracy and precision of the detection results. Establish a fast and high-precision universal algorithm model, develop a software system with intelligent learning and big data statistics functions, build an intelligent instrument that can self-learn, realize high-frequency data processing and high-accuracy and high-precision quantitative analysis of coal quality, and finally realize online rapid detection of coal quality on the belt. Traditional sampling detection methods have problems such as cumbersome sampling, long detection cycle, and large human intervention. The laser excitation of the cross-belt coal quality online detection system based on LIBS technology can reach 20Hz / s, with a high sampling rate, no sampling, real-time online detection of coal quality on the belt, and simultaneous acquisition of multiple parameters of coal quality, with accuracy and precision reaching the dynamic national standard detection range.

[0097] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A LIBS spectroscopy system for online detection of coal quality across belts without sampling, comprising: Belt conveyor system and optical detection system, characterized by: The belt conveyor system comprises: a main conveyor belt, a secondary crusher, a storage bin and a branch conveyor belt arranged in sequence; The optical detection system is mounted on the branch conveyor belt; The branch conveyor belt is provided with a laser rangefinder, and the horizontal distance between the laser rangefinder and the optical detection system is 50-100 cm; the laser rangefinder is used to detect and record the height of the coal in the detection area on the branch conveyor belt; The optical detection system comprises: a substrate, and a laser emission component, an automatic focusing component and a spectrum analysis component arranged on the substrate; The laser emission assembly is used to emit pulsed laser, and includes: a laser, a 45-degree reflector, a beam expander lens and a dichroic mirror arranged in sequence; The automatic focusing assembly focuses the laser beam emitted by the laser emitting assembly onto the coal based on the height of the coal above the detection area; The spectrum analysis component is used to receive the plasma radiation signal generated by the interaction between the pulse laser and the coal material, obtain its spectrum and analyze the coal quality.

2. The LIBS spectroscopy system for online detection of coal quality across belts without sampling according to claim 1 is characterized in that: The main conveyor belt is used to transport large pieces of coal. Part of the coal is taken from the main conveyor belt and transported to the secondary crusher for crushing. The particle size of the crushed coal is 10-15 mm. The storage bin is arranged at the discharge port below the secondary crusher to receive the crushed coal. The coal falls through the discharge port of the storage bin or is transferred to the branch conveyor belt and is transported forward at a fixed speed, passing through the laser rangefinder and the lower end of the optical detection system in turn.

3. The LIBS spectroscopy system for online detection of coal quality across belts without sampling according to claim 1 is characterized in that: The optical detection system also includes a detection position determination module, which determines the position and height of the coal for optical detection based on the height data of the coal on the branch conveyor belt continuously monitored by the laser rangefinder.

4. The LIBS spectroscopy system for online detection of coal quality across belts without sampling according to claim 3 is characterized in that: The method for determining the coal material detection position comprises the following steps: Use a laser rangefinder to continuously monitor the height data of the coal on the branch conveyor belt to obtain a large number of continuous height data points; Analyze the difference in coal height between adjacent height data points and select the points with the smallest difference as the predetermined detection points; A length of coal is divided into N sampling intervals, each sampling interval has several predetermined detection points, and a predetermined detection point is selected in each sampling interval as a coal detection position to obtain N coal detection positions.

5. The LIBS spectroscopy system for online detection of coal quality across belts without sampling and preparation according to claim 4 is characterized in that: The method for selecting the predetermined detection point is specifically as follows: Calculate the height difference Δh between adjacent height data points i,j = | h i -h j | , where h i and h j are the heights of the i-th and j-th height data points respectively; Set the height difference threshold Δh according to the particle size of the coal i,j , filter out all Δh according to the threshold i,j The consecutive height data point pairs that are less than the threshold; The midpoint of each pair of consecutive height data points is selected as the predetermined detection point.

6. The LIBS spectroscopy system for online detection of coal quality across belts without sampling according to claim 4 is characterized in that: The determination of N detection positions first meets the requirement of minimum height change frequency and minimum height difference between adjacent detection positions. The specific screening process includes: For each detection position k, calculate its height change frequency F k The height change frequency refers to the number of times the height change exceeds the set threshold ε in the continuous measurement data. The specific calculation process is: Where I is an exponential function, which takes the value of 1 when the condition is met, otherwise it takes the value of 0; h k,i is the i-th predetermined detection point of the k-th detection position; ε is the set height change threshold; Select F k The smallest predetermined detection point is used as a candidate detection position; For each candidate detection position k, calculate the height difference Δh between it and the adjacent detection position k : Δh k = | h k+1 -h k | + \ h k -h k-1 | Among them, h k is the height of the kth detection position, h k+1 and h k-1 are the heights of the k+1th and k-1th candidate detection positions respectively; Among the candidate detection positions with the least frequency of height changes in a sampling interval, select Δh k The smallest candidate detection position is taken as the final detection position, and finally N detection positions are obtained.

7. The LIBS spectroscopy system for online detection of coal quality across belts without sampling according to claim 1 is characterized by: The optical detection system is erected on the branch conveyor belt by a three-dimensional four-corner support frame, the lower end of the three-dimensional four-corner support frame is welded and fixed to the ground, and pulleys are arranged on both sides of the base plate of the optical detection system for sliding left and right on the three-dimensional four-corner support frame.

8. The LIBS spectroscopy system for online detection of coal quality across belts without sampling according to claim 1 is characterized by: The automatic focusing assembly comprises: a concave plane reflecting mirror, an automatic focusing displacement stage, and a convex plane reflecting mirror arranged on the automatic focusing displacement stage.

9. The LIBS spectroscopy system for online detection of coal quality across belts without sampling according to claim 1 is characterized in that: The spectrum analysis component includes: a focusing lens, an optical fiber and a spectrometer.

10. The LIBS spectroscopy system for online detection of coal quality across belts without sampling and preparation according to claim 1 is characterized in that: The spectral analysis component also includes a prediction model for analyzing the water content, ash content, sulfur content, calorific value, as-received lower calorific value and dry basis higher calorific value of the coal sample; Establishing the prediction model and quantitative analysis process includes the following steps: S21. Collect several groups of coal samples from different trains on the main conveyor belt, and collect spectra of these groups of samples on the branch conveyor belt at the same time. Collect 500-700 groups of spectra for each sample. Then, dry and grind the collected groups of coal samples, and use chemical titration method to obtain true values, including analytical water content, ash content, sulfur content, calorific value, as-received low calorific value and dry basis high calorific value of coal. S22. Use Matlab programming to clean, screen and preprocess several groups of coal sample data, use the Laida criterion to remove abnormal spectra, use the window translation smoothing method to remove spectral background, use the channel spectral intensity area normalization to reduce the fluctuation of spectral signals, use wavelet transform to remove spectral noise, use peak finding, non-peak zeroing, peak drift correction and missing peak filling methods to eliminate the matrix effect and instrument error that lead to spectral peak drift and peak intensity loss, use the spectral lines and corresponding true values ​​of several groups of coal sample data after preprocessing as the input variables of the model, use partial least squares regression analysis to establish a prediction model for several groups of coal sample spectral lines and true values, and obtain the coefficient matrix and error terms of the model; S23. Perform the same data preprocessing on the spectral data of the coal sample collected online, and bring it into the prediction model to predict the analytical water content, ash content, sulfur content, calorific value, received basis lower calorific value and dry basis higher calorific value of the coal.

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