工矿自动化

Improvement of vision measurement system for cutting head position of boom-type roadheader

ZHANG Xuhui, XIE Nan, ZHANG Chao, YANG Wenjuan, ZHANG Kaixin, ZHOU Chuang

2021, 47(7): 1-7. doi: 10.13272/j.issn.1671-251x.2021010057

<Abstract>(72) <HTML> (12) <PDF>(13)

Abstract:
In the vision measurement system for cutting head position of cantilever roadheader based on infrared LED characteristics, the stability of external calibration and the accuracy of infrared LED spot center extraction have an important influence on the cutting head position detection accuracy. The existing external parameter calibration method relies on experience to swing the cutting arm to the center position (unknown), and the calibration results have large fluctuations. In order to solve the above problem, a multi-point fixed external parameter calibration method is proposed. This method controls the cutting arm of the roadheader to swing to the four known limit positions of upper left corner, upper right corner, lower left corner and lower right corner respectively, and collects the target images. The method calculates the value of the external parameter matrix, which can improve the stability of the external parameter calibration effectively. The existing gray-scale centroid method uses the grayscale value of the pixel as the weight to calculate the spot centroid. And the accuracy can only reach the pixel level, which only roughly meets the practical application requirements. In order to solve this problem, a sub-pixel edge detection algorithm is proposed to improve the spot center extraction method. Firstly, the gray-scale centroid method is used for coarse extraction of the spot center. Secondly, the sub-pixel level edge detection algorithm is used to find the sub-pixel level edge coordinates. Finally, the least squares method is used to fit the spot center to achieve accurate extraction of the spot center. The experimental results show that the improved spot center extraction method reduces the maximum measurement error of the target LED lamp spacing from 3.2 mm to 1 mm, which improves the detection accuracy. The external parameter matrix obtained by the multi-point fixed external parameter calibration method is relatively stable, the maximum variation of displacement in the translation matrix is 15 mm, and the maximum variation of angle in the rotation matrix is 1°. Before the improvement of the vision measurement system, the measurement error of the cutting head swing angle was within ［-1.2°,1.7°］. After the improvement, the error of the horizontal swing angle of the cutting head is within ［-0.5°,0.5°］ and the error of the vertical swing angle is within ［-0.6°,0.6°］. The results show that the improved method improves the detection accuracy of the cutting head swing angle effectively.

Fault diagnosis method of shearer planetary gear transmission systemunder variable speed conditions

MAO Qinghua, ZHANG Yongqiang, ZHAO Xiaoyong, ZHANG Xuhui, FAN Hongwei, ZHANG Fei

2021, 47(7): 8-13. doi: 10.13272/j.issn.1671-251x.17779

<Abstract>(118) <HTML> (13) <PDF>(7)

Abstract:
When the shearer cuts the coal seam, the planetary gear transmission system of the traction unit is in a variable speed working condition, and the structure of the planetary gear transmission system is complicated. This leads to a variety of modulation phenomena of vibration signals, which affects the extraction of fault characteristics of the planetary gear transmission system. In order to solve the above problems, a fault diagnosis method of shearer planetary gear transmission system based on envelope order spectrum analysis is proposed by combining order analysis technique with envelope spectrum. Firstly, the method performs Hilbert envelope analysis on the non-stationary time-domain vibration signal of the planetary gear transmission system. Secondly, the method performs computed order tracking on the non-stationary time-domain envelope signal, converts it into equal angle angular domain signal. Finally, the method performs the fast Fourier transform on the equal angle angular domain signal to obtain the envelope order spectrum of the signal. The simulation analysis of this method and the fault diagnosis test of planetary gear transmission system under variable speed conditions based on the comprehensive test bed for power transmission fault diagnosis are carried out. The results show that it is difficult for the order analysis to extract the characteristic order for the vibration modulation signal under variable speed conditions. However, the envelope order spectrum analysis method can extract the characteristic order effectively and realize the accurate fault diagnosis of planetary gear transmission system.

Double inertial navigation shearer positioning method based on adaptive Kalman filter

YANG Jinheng, SONG Danyang, TIAN Muqin, SONG Jiancheng, XU Chunyu

2021, 47(7): 14-20. doi: 10.13272/j.issn.1671-251x.2021030113

<Abstract>(94) <HTML> (7) <PDF>(9)

Abstract:
The shearer positioning method based on inertial navigation has inherent defects such as error accumulation, attitude angle and position drift. Although the introduction of error compensation technology and multi-sensor combination positioning technology can reduce the error to a certain extent, the effect is limited. In order to solve the above problems, a dual inertial navigation shearer positioning method based on adaptive Kalman filtering is proposed. The acceleration and attitude angle of the 2 inertial navigation systems installed on shearer are collected synchronously in real time, the position of the inertial navigation system is used as the state quantity, and the distance and angle between the inertial navigation systems are used as observed quantities. The dual inertial navigation positioning model is established to overcome the shortcomings of accumulated single inertial navigation positioning errors. However, the large difference in the output of the dual inertial navigation system can lead to sudden changes in the state of the dual inertial navigation positioning model and reduce the accuracy of the positioning model. Therefore, the adaptive Kalman filtering algorithm is used to evaluate whether the dual inertial navigation positioning model has sudden changes in the state by calculating the residual-based chi-square test value. And the covariance matrix of the process noise is dynamically adjusted by using a three-segment fuzzy discriminant function to reduce the impact of sudden changes in the state on the positioning accuracy. The simulation and experimental results show that the adaptive Kalman filter has stronger anti-interference ability than the extended Kalman filter, and reduces the estimation error effectively when the state changes suddenly. The positioning error of the dual inertial guidance shearer positioning method based on adaptive Kalman filter is reduced in all directions than that of the single inertial guidance shearer positioning method.

Distributed real time prediction model of shearer operating state data

ZHANG Jianrang, LIU Ruiqing, LI Xuewen, WANG Zhipeng, SHI Zhendong

2021, 47(7): 21-28. doi: 10.13272/j.issn.1671-251x.2020110032

<Abstract>(64) <HTML> (8) <PDF>(7)

Abstract:
In order to solve the problem that a large amount of shearer operating state data cannot be processed in time, the distributed real-time prediction model of shearer operating state data based on Storm is proposed. Combined with the actual operating state data of the shearer, the Hadoop distributed storage database is used to simulate the real-time data flow of the operating state of the shearer. The Storm distributed real-time big data processing framework is used to process a large number of time series data of the operating state of the shearer. And Gate Recurrent Unit (GRU) is adopted as the prediction model to achieve real-time prediction of shearer operating state data. Combined with the threshold setting of various data, the model can realize fault warning. Taking the data of MG400930-WD electric traction shearer in fully mechanized working face as an example, eight kinds of monitoring data are used as experimental data to train and test the prediction model. The data include cutting part motor current, cutting part motor temperature, traction part motor current, traction part motor speed, height adjustment pump working pressure, height adjustment pump working speed, cooling water pressure and inverter current. The results show that the prediction model converges quickly, and the goodness of fit is above 0.9. Except for the cooling water pressure, the early warning accuracy rate of the remaining data is above 95%. The processing speed is fast and the whole early warning process is about 10 s in total, which can meet the application requirements.

Construction of intelligent maintenance knowledge base for shearer based on knowledge graph

WANG Yan, CAO Xiangang, ZHANG Xuhui, FAN Hongwei, DUAN Yong, HUO Xiaoquan

2021, 47(7): 29-36.. doi: 10.13272/j.issn.1671-251x.17786

<Abstract>(94) <HTML> (9) <PDF>(12)

Abstract:
In order to meet the requirement for precise location of fault sources at the meta-component level of shearers and improve mining efficiency and safety controllability of fully mechanized working faces, knowledge graph technology is introduced into the process of dynamic modeling, formal storage and intelligent interaction of shear fault maintenance knowledge. An intelligent maintenance knowledge base of shear based on knowledge graph is constructed. From the aspects of the shearer hardware topology, fault maintenance, sensor monitoring, related terms and naming structures are standardized. The entities, relationships and attributes of the shearer intelligent maintenance knowledge graph are defined and extracted, and a hardware topology sub-network diagram is established,which contains 5 types of entities, including whole machine, component, sub-component, element and part. And a fault maintenance sub-network diagram is established, which contains 5 types of entities, including fault type, location, phenomenon, cause and solution. A sensing monitoring sub-network diagram is established, which contains 2 types of entities, including sensor and monitoring location.Through the process of entity disambiguation and common reference resolution, 3 sub-network diagrams, including hardware topology, fault maintenance and sensor monitoring, are merged to form a network diagram of intelligent maintenance knowledge of coal shearers. And the interaction relationship between network nodes is formally described to express intelligent maintenance knowledge. Using Neo4j, Py2neo and other technologies, a prototype system of intelligent maintenance knowledge base of shearer that can realize dynamic interaction is built, and the functions of fault information retrieval and technical guidance are realized initially.

Longitudinal tear detection of belt conveyor based on multi linear lasers

XU Hui, LIU Lijing, SHEN Ke, ZOU Sheng

2021, 47(7): 37-44. doi: 10.13272/j.issn.1671-251x.17681

<Abstract>(140) <HTML> (14) <PDF>(12)

Abstract:
The underground coal mine environment is dim, humid and dusty, and the collected video images are blurred, which makes it difficult to identify the longitudinal tear of the conveyor belt. The existing research results only focus on whether there is longitudinal tear, without involving the location of tear damage and trend tracking. This paper proposes a method for longitudinal tearing detection of belt conveyors based on multi-channel linear laser. This method uses a mine intrinsically safe structured light emitter to project multiple linear lasers onto the surface of the conveyor belt, and uses a mine intrinsically safe industrial camera to take linear laser stripe images. By extracting the center line of the laser stripe and analyzing its characteristics, this method determines whether there is longitudinal tear damage in a single frame image. When there is damage, this method can search for damage boundary points and calculate damage width and depth characteristic values. The method fuses multi-frame image detection results and speed sensor values to calculate the complete longitudinal tear damage length, average width and average depth. By detecting the position of the marker on the conveyor belt, the method can locate the longitudinal position of the tear damage and locate the lateral position by finding the bit width ratio of the starting point of the damage on the conveyor belt. And the damage trend tracking is realized based on the longitudinal position. The method is tested by setting the conveyor belt longitudinal tear damage length to 0.73, 0.95 m, the average width to 0.01 m, the average depth to 0.008 m, and the sampling rate to 25 frames/s. The results show that the method can accurately detect whether the belt conveyor has longitudinal tears, the average error of damage length calculation is 0.06 m, the average error of damage average width and average depth calculation is 0.001 m, and the error of longitudinal positioning is less than 0.1 m. It can determine the development trend of longitudinal tears accurately.

Mine belt conveyor roller operation condition monitoring system

JIANG Kuosheng, MAO Zhongyuan, XIE Youhao, BIAN Shijun, ZHOU Yuanyuan, GUO Shuai, HU Kun

2021, 47(7): 45-49. doi: 10.13272/j.issn.1671-251x.2021040100

<Abstract>(119) <HTML> (8) <PDF>(16)

Abstract:
The belt conveyor roller fault monitoring based on manual inspection and vibration signal diagnosis cannot guarantee high reliability and real-time performance. Therefore, power line carrier communication is used to transmit belt conveyor roller operation data. The traditional power line carrier communication is intrusive and requires regular battery replacement. In order to solve the above problems, a mine belt conveyor roller operation condition monitoring system based on self-powered and non-intrusive power line carrier communication is proposed. The system consists of transmitter, receiver and 127 V lighting power line. The transmitter is installed at the belt conveyor rollers, and FPGA is used as the core controller to collect and modulate the audio signals that generated during the operation of the rollers into high-frequency signals. The high-frequency signal is coupled into the lighting power line through an inductive coupler so as to realize non-intrusive power line carrier communication. The receiver is installed in the ground control room to realize the decoupling, demodulation, and restoration of the signal in the lighting power line. Pearson correlation coefficient analysis is performed on the collected original audio signal and the restored audio signal. After confirming the accuracy of the restored audio signal, the cepstral analysis is performed so as to judge the fault of the rollers. The experimental results show that the system can accurately diagnose the fault of belt conveyor rollers.

Design of energy harvester for self-checking roller in belt conveyor

SUN Liang, ZHOU Gongbo, WANG Wei, HE Zhenzhi, LI Tingting

2021, 47(7): 50-56. doi: 10.13272/j.issn.1671-251x.17792

<Abstract>(52) <HTML> (7) <PDF>(6)

Abstract:
The belt conveyor self-checking roller installs wireless sensor nodes inside the roller to collect and wirelessly transmit temperature and vibration signals, which provides a new idea for the health checking of coal mine belt conveyor rollers. In order to solve the energy supply problem of the wireless sensor nodes in the closed roller, an energy harvester based on the Halbach permanent magnet array is designed. This paper introduces the structural design of the energy harvester, and analyzes the energy supply requirements based on the actual energy consumption of the wireless sensor nodes and the efficiency of the energy management circuit. COMSOL Multiphysics 5.5 is used for finite element analysis of the energy harvester to verify that Halbach permanent magnet array has obvious advantages over conventional permanent magnet array when used in small rotating body energy harvesters. The effect of air gap thickness, permanent magnet thickness and rotor speed on the power generation performance of the energy harvester is analyzed. And it is concluded that the induced voltage of the energy harvester can be increased effectively by reducing the air gap thickness, increasing the permanent magnet thickness and increasing the rotor speed. Based on the analysis of energy supply demand, installation space requirement and finite element analysis, the parameters of the energy harvester are optimized, and a prototype is built for testing. The results show that at 5 r/s rotor speed, the effective value of the induced voltage of the energy harvester is 4.77 V, the maximum power is 171.33 mW, and the power density is 6.78 mW/cm3, which meets the energy consumption requirements (165.722 mW) of wireless sensor nodes.

Remote fault diagnosis system of fully mechanized mining equipment group based on cloud platform

LI Xu, WU Xuefei, TIAN Ye, DONG Bo, DANG Enhui

2021, 47(7): 57-62. doi: 10.13272/j.issn.1671-251x.17794

<Abstract>(72) <HTML> (9) <PDF>(15)

Abstract:
The currently developed remote fault diagnosis systems for fully mechanized mining equipment are mostly for single-machine equipment such as coal shearers, scraper conveyors and belt conveyors, and for expert remote guidance and maintenance systems based on video or virtual reality. However, there is few research on equipment group fault diagnosis systems that integrates cloud platform, remote fault diagnosis and expert remote guidance and maintenance. In order to solve the above problem, a remote fault diagnosis system of fully mechanized mining equipment group based on cloud platform is designed. Firstly, the method collects the state monitoring information of shearer, hydraulic support, scraper conveyor, transfer machine, emulsion pump station, belt conveyor and power supply system of fully mechanized working face through sensors. Secondly, the state monitoring information of fully mechanized mining equipment group is transmitted to the ground server through the underground ring network of the coal mine. The ground server performs intelligent fault diagnosis analysis, data storage, and alarm query on the received information. Finally, the state monitoring information of fully mechanized mining equipment group of the ground server is transmitted to the cloud server in a unified format through the MQTT protocol for data processing and format conversion. And the converted data is transmitted to the mobile terminal by 4G/5G network and transmitted to the PC terminal by the MQTT protocol. Therefore, the method can realize the visualization, fault query, fault alarm and timely push of fault warning information of the state monitoring of fully mechanized mining equipment group. With visual video monitoring as the medium, when the fully mechanized mining equipment fails, the video information can be transferred to the corresponding expert in real time. The expert can remotely guide the coal workers for remote maintenance through the video information. The system has been tested in the fully mechanized working face of Huangling Coal Mine in Shaanxi. The results show that the system realizes the remote fault diagnosis of fully mechanized mining equipment group. The system realizes the real-time push of the state monitoring and fault warning information of fully mechanized mining equipment group through the mobile phone platform. Moreover, the system reduces the fault rate and the number of unplanned shutdowns of fully mechanized mining equipment group and improves the production efficiency by about 30%.

Research on rolling bearing fault diagnosis under strong noise background and variable speed working conditio

GONG Tao, YANG Jianhua, SHAN Zhen, LIU Houguang

2021, 47(7): 63-71. doi: 10.13272/j.issn.1671-251x.17757

<Abstract>(90) <HTML> (15) <PDF>(18)

Abstract:
The working environment of coal mine mechanical equipment is harsh, the background noise is strong, and the early fault characteristic information of the bearing is weak. Therefore, it is difficult to extract the information reflecting the fault state from the vibration signal measured by the sensor. Moreover, the coal mine mechanical equipment work in high speed, shock and other working conditions, which are typical non-stationary working conditions. The unstable excitation and complex working conditions directly lead to the difficulty of extracting the bearing fault characteristic signal. In order to solve the above problems, a rolling bearing fault diagnosis method based on computed order analysis and adaptive stochastic resonance is proposed in the background of the working conditions of mine hoisting equipment. Firstly, the method simulates the typical variable speed working conditions in the operation of mine hoist, constructs the fault simulation signals and collects the experimental signals of bearing vibration. Secondly, by collecting synchronous time-domain key-phase signal at equal angles, the non-stationary vibration signal of the bearing is resampled into a stationary signal by using computed order analysis. Thirdly, the stationary signal is decomposed into a number of intrinsic mode function (IMF) components by using the variational mode decomposition (VMD) method, and the bearing fault type is judged by the bearing fault order. Finally, the adaptive stochastic resonance method is used to enhance the bearing fault characteristic order so as to achieve the extraction and enhancement of fault characteristics for fault diagnosis. The simulation and experimental results prove the effectiveness of the method. And the method is compared with the maximum correlation kurtosis deconvolution (MCKD) method. The results show that although the MCKD method can also observe the fault characteristic order, but the characteristic order is only 0.001 96 higher than the amplitude of the surrounding interference order, which is lower than the results of the proposed method, indicating the superiority of the proposed method.

Research progress of low-power carbon monoxide sensors

WANG Haibo

2021, 47(7): 72-78. doi: 10.13272/j.issn.1671-251x.17755

<Abstract>(83) <HTML> (8) <PDF>(21)

Abstract:
Low-power carbon monoxide sensor is an important guarantee for safe coal mining and a key foundation for distributed wireless sensing technology. In this paper, the working principle of low-power carbon monoxide sensor is described, and the latest research progress of electrochemical and semiconductor carbon monoxide sensor is introduced. This paper analyzes their advantages and disadvantages and proposes the development direction and prospects of low-power carbon monoxide sensor. ① The electrochemical carbon monoxide sensor is mainly composed of electrodes and electrolyte. There are two-electrode structure and three-electrode structure. The two-electrode electrochemical carbon monoxide sensor has no reference electrode. It has a simple structure and is easy to be designed and manufactured. The sensor has a low cost and is suitable for the monitoring of low-concentration carbon monoxide. The three-electrode electrochemical carbon monoxide sensor introduces a reference electrode with a larger range and higher accuracy, but the cost is high. The electrochemical carbon monoxide sensor has a short response time and has the prospect of distributed wireless sensing applications. The research focus is on the preparation of platinum-carbon composite electrodes. However, the electrochemical carbon monoxide sensor still uses liquid solvent, which has the risk of liquid leakage. Moreover, it is difficult to realize micro-miniaturization. The future development trend is to avoid the use of liquid solvents, to study all solid-state electrochemical carbon monoxide sensors, and to control the porosity to shorten the response and recovery time. On the other hand, the trend is to find cheap and efficient electrode materials to reduce sensor costs. In addition, manufacturing micro-miniaturized electrochemical carbon monoxide sensor is also an important part of future work. ② The semiconductor carbon monoxide sensor can be divided into non-micro-heating plate type and micro-heating plate type. The non-micro-heating plate type carbon monoxide sensor uses a ceramic tube substrate or an alumina plate substrate. Due to the large heater size, severe heat conduction and high power consumption with usually above 100 mW, it is difficult to be used in distributed wireless sensing occasions. The micro-heating plate type carbon monoxide sensor has low thermal quality, which can greatly reduce the operating power consumption of the heater. It is also compatible with integrated circuit process. A system-on-chip carbon monoxide sensor can be obtained, which reduces the power consumption of peripheral circuits and is suitable for IoT applications. The micro-heating plate type carbon monoxide sensor is smaller than solid electrolyte electrochemical carbon monoxide sensor, and has the advantages of low cost, high sensitivity and easy on-chip integration. However, it is easily affected by humidity and the baseline is easy to drift. The future research direction is to improve the modification of sensitive materials, optimize the packaging process, and use intelligent algorithms to self-calibrate the baseline. It is proposed to use zeolite to modify sensitive materials to reduce the impact of humidity on the sensor, or use a water-repellent membrane such as polytetrafluoroethylene in the packaging process. The intelligent algorithm can use a combination of support vector machines and artificial neural networks or artificial intelligence algorithms. In the future, it is hoped that high-efficiency edge computing can be achieved to improve the efficiency and accuracy.

Current status and development trend of research on intelligent maintenance of coal mine electromechanical equipment

LIU Yuanyua

2021, 47(7): 79-84. doi: 10.13272/j.issn.1671-251x.17753

<Abstract>(249) <HTML> (7) <PDF>(28)

Abstract:
The intelligent maintenance of coal mine electromechanical equipment is an important part of the construction of intelligent mines. The research status of intelligent fault diagnosis and predictive maintenance of coal mine electromechanical equipment is summarized from four aspects, coal mine electromechanical equipment fault mechanism, equipment condition monitoring, signal analysis and processing, and fault diagnosis and prediction algorithm. ① Equipment fault mechanism research is mainly for different equipment, which uses different methods to establish equipment fault analysis models and applies incentives to the models to obtain dynamic response to equipment fault so as to provide a basis for subsequent fault diagnosis. ② Equipment condition monitoring research has established a relatively complete condition monitoring system for coal mine electromechanical equipment, which can obtain equipment parameters accurately and timely and provide data support for equipment fault diagnosis. ③ Signal analysis and processing research not only uses traditional time domain, frequency domain and time-frequency domain analysis methods, but also combines multiple methods for signal processing and characteristic extraction, which improves the efficiency of signal processing and the reliability of processing results. ④ Fault diagnosis and prediction algorithms mainly use artificial neural networks, including machine learning, deep learning and other intelligent algorithms to establish equipment fault diagnosis and prediction models so as to achieve intelligent diagnosis and prediction of faults. It is pointed out the problems of intelligent maintenance research of coal mine electromechanical equipment are as follows. ① The study of equipment fault mechanism lacks the study of fault mechanism under multiple fault compound state. And more research is needed on the chain reaction caused by the fault of a certain part of the equipment. ② The fault data obtained in the simulated environment cannot fully reflect the actual operating conditions of the equipment, and it is necessary to continuously collect on-site monitoring data for a long time, preferably the whole life cycle data of the equipment. ③ At present, there is few research using the combined algorithm, and the research object is more limited to a certain part or component of the equipment. Finally, the development trend of intelligent maintenance of coal mine electromechanical equipment is proposed as follows. ① It is suggested to study the application of intelligent sensors with higher sensitivity to monitor equipment, combine the methods such as random resonance and blind source separation to extract weak characteristic signals from strong noise to identify early equipment faults in a timely manner, thus realizing predictive maintenance. ② The use of independent diagnosis method can no longer meet the diagnosis needs of actual equipment. The diagnosis and prediction based on multiple sensor information fusion technology can identify all faults in the equipment accurately and effectively. ③ It is proposed to use the migration learning algorithm as a 'bridge' to establish the correlation between simulation, test data and field data, and provide data support and guarantee for solving the problem of the difference between simulation and test conditions and field conditions.

Research on the safety of 5G electromagnetic wave radiation energy in coal mine

LIU Xiaoyang, MA Xinyan, LIU Kun, WANG Wenqing, TIAN Zijian, DENG Zhigang, LIU Jing, WANG Di

2021, 47(7): 85-91. doi: 10.13272/j.issn.1671-251x.2020090050

<Abstract>(105) <HTML> (12) <PDF>(17)

Abstract:
The electromagnetic wave energy emitted by wireless radio frequency equipment in coal mines is coupled into the energy storage elements on the metal structure. And once the metal structure has a breakpoint and an on-off contact occurs, the discharge spark generated by the accumulated electromagnetic wave energy may cause a gas explosion. 5G uses large-scale multiple-input multiple-output (MIMO) technology, which has the problem of power superposition between multiple transmitting antennas, increasing the possibility of igniting the gas. In order to solve the above problem, the coupling process of electromagnetic wave radiation energy and metal structure is analyzed, and the conditions for the discharge spark to ignite the gas when the metal load is in resonance are obtained. It is found that if the energy released by the discharge spark exceeds 0.28 mJ in 100 μs, the gas can be ignited. The ray tracing method is used to establish a roadway electromagnetic wave energy propagation model. The electromagnetic simulation software Wireless insite is applied to simulate single-antenna and multi-antenna radio frequency equipment in the 5G frequency band. The results show that electromagnetic wave energy propagates in the form of radiation. The electromagnetic wave energy emitted by single-antenna radio frequency equipment with operating frequencies above 700 MHz is intrinsically safe, and the minimum safe distance between 4T4R (4 transmitting and 4 receiving) multi-antenna radio frequency equipment and metal structures is 0.25 m.

Distance measurement between bus equipment based on RS485 data frame timing

BAI Sizhong

2021, 47(7): 92-97. doi: 10.13272/j.issn.1671-251x.2020120025

<Abstract>(38) <HTML> (6) <PDF>(7)

Abstract:
There are a large number of online equipment working in underground coal mines that do not have positioning function and the equipment installed with wireless positioning are susceptible to electromagnetic interference, resulting in low positioning accuracy. In order to solve the above problems, a distance measurement method between bus equipment based on RS485 data frame timing is proposed by combining the time domain reflectometry method of cable fault location and wireless single-sided-two-way-ranging time of flight method. The method uses the communication cable as a carrier to measure the distance between master and slave computers by using the flight time of communication data between a pair of master and slave computers. And the equipment along the bus measure the distance between themselves and slave computers by monitoring the data so as to realize the distance measurement between all equipment on the bus. Moreover, the one-dimensional distribution of equipment can be calculated based on the measurement results of 2 different reference slave computers. The factors affecting the distance measurement accuracy are analyzed from four aspects, clock frequency, master-slave computer clock deviation, circuit time delay and electromagnetic wave propagation speed. And the corresponding measures are proposed to improve the measurement accuracy. The method uses one mine intrinsically safe display as master computer and eight mine sensors as slave computers to establish the test platform so as to measure the distance between the bus equipment. The results show that this method does not need to change the hardware and only updates the software to measure the distance between all equipment on the RS485 bus, and a one-dimensional distribution with the master computer as the origin can be established. The distance measurement error within 5 km of the cable length does not exceed ±1.5 m, and the measurement result is not affected by transmission loss and electromagnetic interference.

Hydraulic cutting cooperative pressure relief and permeability enhancement technology in low permeability outburst coal seam

DU Jinlei, ZHANG Minbo, ZHANG Dianji, ZHANG Dangyu, ZHANG Zhen, CUI Li, WANG Zichao, LI Chunxin, ZHANG Fujian

2021, 47(7): 98-105. doi: 10.13272/j.issn.1671-251x.17698

<Abstract>(67) <HTML> (9) <PDF>(6)

Abstract:
The effect of a single hydraulic cutting is not very ideal for thick coal seam with low permeability or coal seam with gangue to increase the permeability and release the pressure. In order to solve the above problem, taking the 21212 working face of Dongpang Coal Mine of Jizhong Energy Co. as an example, this paper proposes hydraulic cutting cooperative pressure relief and penetration enhancement technology in the upper and lower coal seam. According to the specific structure of coal seam, the hydraulic cutting construction is carried out once in the upper and once in the lower coal seam. The fractures generated by the 2 slots in the upper and lower coal seam continue to crack, expand and extend, resulting in the full development of coal fissures between the hydraulic cutting holes, forming a three-dimensional fissure network connected with each other. The network generates cooperative pressure relief and penetration enhancement effects, and expands the effective extraction radius. In order to arrange the test hole spacing of hydraulic cutting more reasonably, FLAC 3D software is used to establish a physical model of hydraulic cutting cooperative pressure relief. The hydraulic cutting water pressure is 30 MPa. One coal output is 4.5 m3 (cutting width is 0.3 m, seam depth is 1.57 m, double cutting in the upper and lower coal seams). Another coal output is 6 m3 (cutting width is 0.3 m, seam depth is 1.78 m, double cutting in the upper and lower coal seams). The theoretical effective extraction radii of these two types of coal rock are 4.5 m and 4.8 m respectively. In order to determine the effect of hydraulic cutting, the extraction effect of test hole S1 with coal output of 4.5 m3 and test hole S2 with coal output of 6 m3 and non-cutting extraction hole. The results show that the average volume fraction of gas extraction in the non-cutting extraction hole is 22.38% and the average pure volume of gas extraction is 0.206 m3/min. The average volume fraction of gas extraction in the cutting extraction test hole S1 is 75.73% and the average pure volume of gas extraction is 0.382 m3/min. The average volume fraction of gas extraction in the cutting extraction test hole S2 is 86.91%, and the average pure volume of gas extraction is 0.454 9 m3/min. Compared with the hole without cutting, after adopting hydraulic cutting to increase permeability, the permeability of coal seam is greatly improved. The gas extraction volume fraction is increased by about 4 times, the gas extraction volume is increased by about 2 times, and the gas extraction effect is good. According to the actual measured effective extraction radius of gas pressure drop method, the relationship between the effective extraction radius and extraction time of the coal output of 4.5 m3 and 6 m3 hydraulic cutting can be obtained. When the extraction time is 30 d, 60 d, 120 d and 180 d, the effective extraction radii of the 4.5 m3 hydraulic cutting process are 4.9 m, 5.5 m, 6.1 m and 6.5 m. And the effective extraction radii of the 6 m3 hydraulic cutting are 5.1 m, 5.6 m, 6.3 m and 6.7 m. After comprehensive consideration, the construction parameters of hydraulic cutting technology suitable for Dongpang Coal Mine are finally obtained. The coal output is 4.5 m3, the extraction time is 60 days, the effective extraction radius is 5.5 m, and the hole spacing is 7.7 m.

Study on gas extraction from parabolic high level drilling during the initial mining period of fully mechanized caving face

LIU Qingbao, CHEN Long, GONG Xuanping, YU Rui, CHENG Xiaoyu, DING Jianxun

2021, 47(7): 106-114. doi: 10.13272/j.issn.1671-251x.17699

<Abstract>(59) <HTML> (7) <PDF>(7)

Abstract:
The gas extraction effect during the initial pressure on the working face by using conventional high-level directional long drilling is poor. In order to solve the above problem, taking the project background of 12309 fully mechanized caving face of Wangjialing Mine of China Coal Huajin Group Co., Ltd. as an example, the paper analyzes the overburden rock structure and fracture development law of the coal seam roof in the fully mechanized caving face during the initial mining period by physical similar simulation and numerical calculation. During the initial mining period, the height of fractures is low and the number of fractures is small in the coal seam roof. With the advancement of working face, the roof fractures gradually develop, the height and range of fractures increase with the increase of advancement distance. The maximum height of the fractures is about 28 m, and the pressure step distance of the working face is about 50 m. During the initial mining period, the gas concentration and emission volume of the working face are relatively large. Along the working face tendency, the gas concentration gradually increases from 20 to 150 supports. Along the working face direction, the gas concentration gradually increases from 300 mm of the coal wall to the rear scraper conveyor. The gas emission volume of the goaf mining area accounts for more than 50% of the gas emission volume of the working face, and the gas emission volume as a whole is on an upward trend with obvious phase characteristics. According to the actual situation of the site and the gas emission characteristics, overburden rock structure and fracture evolution law of the fully mechanized caving face during the initial mining period, the trajectory of the conventional high-level directional drilling during the initial mining period is optimized, and the parabolic high-level directional drilling gas extraction method during the initial mining period is proposed. The final hole of the borehole is designed in the coal seam, which is directly connected with the goaf mining area and used for low level gas extraction in the mining area during the initial mining period of the working face. It solves the problem of high level of conventional high-level long borehole during the initial mining period. The field application results show that compared with the conventional high-level directional drilling, the use of parabolic high-level directional drilling can extract the low level gas in the goaf mining area effectively before the initial pressure of the basic roof of the working face. The average pure volume of gas extraction increases by about 37%, and the maximum gas volume fraction in the upper corner and return air flow is less than 0.80%. The result has achieved the expected effect of gas extraction.

Tensile strength test of coal and rock with different coal structure

HUANG Kai, WU Jiwen, ZHAI Xiaorong, BI Yaosha

2021, 47(7): 115-119. doi: 10.13272/j.issn.1671-251x.2020120057

<Abstract>(73) <HTML> (8) <PDF>(9)

Abstract:
Coal and rock, as a special sedimentary rock, mostly undergoes multiple phases of tectonic movements after its formation, resulting in the diversity of coal structures. Therefore, it is difficult to directly use a certain method to test the tensile strength of coal and rock with different coal structures. In order to obtain the tensile strength of coal and rock with different coal structures, taking No.10 of Suntuan Coal Mine of Huaibei Mining (Group) Co., Ltd. as an example, the Brazilian splitting test and the point load test are conducted on coal and rock with different coal structures. The results show the following three points. ① The average tensile strengths of primary structure coal and fractured coal measured by Brazilian splitting test are 1.174 and 0.710 MPa respectively. The average point load strengths of primary structure coal, fractured coal, crushed coal and mylonite coal measured by point load test are 0.368, 0.248, 0.112 and 0.041 MPa respectively. ② The point load strength and tensile strength of coal have a good linear correlation. The point load strength and tensile strength test results are linearly fitted to obtain the conversion equation between the point load strength and the tensile strength. According to the equation, the calculated average tensile strengths of crushed coal and mylonite coal are 0.345 and 0.126 MPa respectively. ③ From primary structure coal to fractured coal, crushed coal and cinder coal, the tensile strength of coal rock decreases significantly with the increase of the damage degree of coal structure, and the decline tends to increase gradually.

Combustion characteristics experiments of coal with different moisture content

GAO Pengyong, SHI Biming, ZHANG Leilin, XUE Chuang, ZHONG Zhen, LIU Yi

2021, 47(7): 120-124. doi: 10.13272/j.issn.1671-251x.2021030017

<Abstract>(136) <HTML> (6) <PDF>(6)

Abstract:
In order to study the effect of moisture content on the combustion characteristics of coal, taking the bituminous coal from Zhujixi Coal Mine as the research object, the method uses cone calorimeter to test the parameters of ignition time, heat release rate, total heat release, smoke generation rate, total smoke release and CO generation rate of coal samples with different moisture content and analyzes the combustion efficiency of coal samples. The experimental results show the following points. ① The ignition time of coal samples decreases first and then increases with the increase of moisture content. The order of moisture content of coal samples corresponding to ignition time from long to short is 17.82%>13.82%>1.82%>5.82%>9.82%. The peak heat release rate of the coal sample decreases first, then increases and then decreases with the increase of water content. The order of moisture content of coal samples corresponding to peak heat release rate from large to small is 9.82%>1.82%>5.82%>13.82%>17.82%. The total heat release, smoke generation rate, and total smoke release of coal samples decrease first, then increase and then decrease with the increase of water content. The order of the moisture content of coal samples corresponding to the total heat release, smoke generation rate, and total smoke release from large to small is 1.82%>9.82%>5.82%>13.82%>17.82%. In the late stage of combustion process, the coal sample with 5.82% moisture content has the lowest CO generation rate, and the coal sample with 17.82% moisture content has the highest CO generation rate. The high moisture content will increase the CO yield. The order of the moisture content of coal samples corresponding to the combustion efficiency from high to low is 9.82%>5.82%>1.82%>13.82%>17.82%. ② Appropriate moisture content can improve the combustion performance of coal. It is suggested to choose the coal with moisture content of 5.82% to 9.82% so as to shorten the coal ignition time, reduce the smoke generation rate, total smoke release and CO generation rate, and improve the heat release rate and combustion efficiency.

Positioning system of fully mechanized working face based on UWB and laser ranging

NIU Yonggang, DOU Xueli, YIN Peng, LI Jingsheng, LUAN Liangliang, LAN Xiang

2021, 47(7): 125-129. doi: 10.13272/j.issn.1671-251x.17732

<Abstract>(209) <HTML> (9) <PDF>(17)

Abstract:
Traditional wireless positioning technology has low accuracy, and UWB positioning technology can achieve centimeter-level high-precision positioning to meet the accuracy requirements of the fully mechanized working face positioning systems. However, the existing researches ignore the impact of position change of the base station installed on the hydraulic support on the positioning effect. In order to solve the above problems, laser ranging technology is applied to the mine environment and a positioning system of fully mechanized working face based on UWB and laser ranging is designed. The positioning base station is installed on the hydraulic support, and the position of the base station changes when the position of the hydraulic support changes. The mine intrinsically safe laser ranging sensor is used to measure the distance between the positioning base stations. The external antenna of the positioning base station transmits fixed-power UWB wireless signals. The positioning base station communicates with the positioning identification card worn on the personnel or installed on the equipment, and determines the positioning information of the moving target through the time-of-flight ranging method. The positioning base station uploads the positioning information data to the ground data center through the mine ring network. The system test is carried out on the E2308 working face of Gaohe Coal Mine, and the result show that the positioning accuracy of the system reaches 0.193 m and the positioning accuracy is high. Moreover, the system base station position calibration accuracy is about 0.011 m, which solves the problem of base station position calibration effectively.

Mine uniqueness detection device based on 433 MHz wireless communication and iris recognitio

ZHANG Wei, FU Yuan, LIU Xin

2021, 47(7): 130-134. doi: 10.13272/j.issn.1671-251x.17769

<Abstract>(103) <HTML> (7) <PDF>(9)

Abstract:
The entrance of the underground personnel in coal mine should be equipped with a device to detect whether the identification card is working properly and uniquely. There are problems in the use of uniqueness detection technology based on palm prints and fingerprints, facial images, gait and other biological characteristics to detect the person carrying this card. The recognition accuracy is low due to the impact of the environment. The existing mine uniqueness detection device is interfered by the identification card outside the detection area, and the detection effect is not ideal when the person carries multiple identification card, carries wrong identification card, and does not carry the identification card. In order to solve the above problems, a mine uniqueness detection device based on 433 MHz wireless communication and iris recognition is designed. Firstly, by adjusting the transmission power of the directional antenna, real-time configuration of the detection area is realized. The 433 MHz wireless communication module configures the detection area identifier to the identification cards in the detection area through the directional antenna. The card reader base station reads the message data of the identification cards, and detects whether the detection area identifier of the message data is equal to the configured detection area identifier. In order to eliminate the interference of identification cards outside the area, the number of identification cards in the detection area is detected, and the detection results are written into the result table of the intermediate database. Secondly, the iris information of the personnel to be inspected is collected, and the identification card information of the personnel is queried by identifying the iris information. Finally, by judging whether the identification card information queried according to the iris information matches with the result table information of the intermediate database, the uniqueness detection of the identification card is realized. The test results show that the detection accuracy of the device is 100% for the cases of carrying multiple identification cards, carrying wrong identification cards, not carrying identification cards and carrying right identification cards. The average detection time does not exceed 2 s.

2021 Vol. 47, No. 7

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