工矿自动化

Research on key technologies of mine unmanned vehicle

SUN Jiping, JIANG Ying

2022, 48(5): 1-5, 31. doi: 10.13272/j.issn.1671-251x.17947

<Abstract>(1806) <HTML> (187) <PDF>(208)

Abstract:
Mine unmanned vehicles are needed to reduce the number of coal mine underground operating personnel and to build safe, efficient, green and intelligent mines. The characteristics of mine unmanned vehicles are summarized as following points. The positions of underground operating personnel in coal mine are comprehensively identified. All mine vehicles are controlled. Mine track transportation equipment only needs one-dimensional positioning. The lighting condition is poor. The wireless transmission attenuation is large. There is no satellite signal. The electromagnetic environment is complex. The characteristics also include electrical explosion-proof, humid environment and water spray and dust. This paper analyzes the technical characteristics of mine vehicle positioning, such as ultrasonic positioning, laser position, radio positioning(including RFID, ZigBee, UWB, WiFi6, 5G), inertial navigation, simultaneous localization and mapping(SLAM), odometer and so on. This study puts forward a joint positioning method of mine vehicle, which is based on UWB and supplemented by inertial navigation, odometer and SLAM. This paper analyzes the technical characteristics of obstacle identification and distance measurement of mine unmanned vehicle, such as laser radar, millimeter wave radar, infrared camera, visible light camera, visible light binocular vision camera and so on. This study puts forward a multi-information fusion method of obstacle identification and distance measurement of mine unmanned vehicle. The method is mainly based on laser radar, supplemented by millimeter wave radar, infrared camera, visible light camera, visible light binocular vision camera and ultrasonic radar. When the road condition is complex and the automatic driving can not make decisions, the mine unmanned vehicle needs to automatically switch to the ground remote control mode. In view of the above situation, it is pointed out that the mine unmanned vehicle ground remote control technology based on 5G is the preferred scheme. However, the mine 5G wireless communication system has the problems of small wireless coverage radius and high cost. Therefore, it is suggested to study the application of WiFi7 in the mine vehicle ground remote control.

Research on the concept connotation, development goal and key technologies of data governance for smart mine

TAN Zhanglu, WANG Meijun

2022, 48(5): 6-14. doi: 10.13272/j.issn.1671-251x.2021120090

<Abstract>(918) <HTML> (154) <PDF>(162)

Abstract:
Data is the core resource to promote the development of intelligent coal mine technology, innovation of application mode and improvement of market competitiveness. Data governance is the key bottleneck for the development of smart mine from primary stage to advanced stage. However, at present, there is no consensus on the concept connotation, development goal and key technologies of data governance for smart mine. In order to solve the above problems, this paper analyzes the important position of data governance in the construction of smart mines, and defines the concept and connotation of data governance for smart mine. Data governance for smart mine is guided by the governance concept of 'precipitation, reuse, sharing and collaboration'. All departments within the coal enterprise work together with industry and government regulatory departments to formulate data standards and management specifications. The data structure and data transmission link of coal enterprises are reshaped to break through the data barriers of smart mines and ensure data quality and data security. The smart mine technology linkage and business collaboration mechanism are built to realize the process of digital-driven decision-making and flexible production. This paper discusses the development goal of data governance for smart mine from three aspects, including overall goal, development strategy and phased tasks. It is pointed out that the key point of data governance for smart mine is to solve the problem of information isolated island in the process of smart mine construction. Therefore, the data sharing and business collaboration are realized so as to make smart mine become an organic whole to promote the value enhancement of coal enterprises. Smart mine data governance needs to properly handle the five aspects relationships, including local coordination and overall coordination, physical integration and logical integration, intelligent business system and data governance platform, group-level data governance platform and mine-level data governance platform, and local processing and cloud processing. It is proposed that smart mine data governance needs to break through six key technologies, including data standard, global data modeling, data aggregation, data development, data management and data center architecture.

Research status and prospect of prognostics health management technology for mine inverter power devices

LI Hongyan, YANG Chaoxu, RONG Xiang, SHI Han, WANG Yue, LIU Bao, WANG Lei

2022, 48(5): 15-20. doi: 10.13272/j.issn.1671-251x.2022020024

<Abstract>(267) <HTML> (44) <PDF>(44)

Abstract:
Through the analysis and processing of monitoring data, the prognostics health management (PHM) technology for mine inverter power devices can extract signal characteristics, locate the open circuit fault position of power devices, predict the life of power devices and improve the safety and reliability of mine inverter. This paper introduces the principle and research status of signal characteristics extraction method in PHM technology, including coordinate transformation method, spectrum analysis method, wavelet analysis method, empirical mode decomposition method. This paper introduces the principle and research status of power device open circuit fault diagnosis method in PHM technology, including state estimation method, neural network method, support vector machine method. This paper introduces the principle and research status of power device life prediction method in PHM technology, including analytical model method, physical model method, data-driven method. The above methods are compared from five aspects, including implementation difficulty, timeliness, immunity, accuracy and data demand. The signal characteristic extraction method is single. There is open-circuit fault of multiple power devices of mine inverter. The life prediction of power devices based on data-driven method fails to consider the variable working conditions of inverter. In order to solve the above problems, the research directions of PHM technology for mine inverter power devices are proposed. The directions include signal characteristic extraction based on multi-method fusion, open-circuit fault diagnosis of multiple power devices based on intelligent algorithm, fault-tolerant control and health management, and power device life prediction under variable working conditions.

Roof stability evaluation of large section open-off cut in lower slice of slicing mining

CHAI Jing, QIAO Yu, GAO Shigang, GAO Dengyan, CHEN Sushe, LYU Qingxu, DU Wengang, HAN Zhicheng

2022, 48(5): 21-31. doi: 10.13272/j.issn.1671-251x.2021110029

<Abstract>(215) <HTML> (117) <PDF>(22)

Abstract:
In order to study the roof stability of large-section open-off cut in lower slice of slicing mining, the 14 boreholes in the top coal of the 203 open-off cut in the lower slice of 1⁻² coal seam in Huojitu Mine of Daliuta Mine is taken as the research background. The influence of the upper slice mining and the lower slice open-off cut driving on the plastic zone of the top coal of the open-off cut is analyzed by theoretical analysis, numerical simulation and field borehole peep technology. And the stability of the roof structure is evaluated by the rock mass integrity index. From the perspective of the top coal structure form, the top coal of the open-off cut is partially over-excavated or under-excavated due to the upper slicing mining. The maximum over-excavation of the open-off cut is 1.2 m, the maximum under-excavation is 0.8 m, and top-coal uneven rate is 27.7%. The result of theoretical analysis show that due to the influence of upper slice mining of the top coal of the open-off cut, the depth of plastic zone in the floor is 2.02 m. Due to the disturbance of the lower slice mining of the open-off cut, the depth of the plastic zone in the top coal is 1.50 m. Borehole peep results show that the plastic zone of the open-off cut top coal is divided into the theoretical plastic zone and the measured plastic zone according to the theoretical calculation and borehole peep respectively. Due to the influence of upper slice mining, the depth of the measured plastic zone in the floor is 1.06-2.04 m. Due to the disturbance of the lower slice mining of the open-off cut, the depth of the measured plastic zone in the top coal is 0.34-1.50 m. The measured plastic zone caused by the influence of upper slice mining on floor is 17.63% smaller than the theoretical plastic zone. The measured plastic zone of the top coal caused by the disturbance of lower slice mining of the open-off cut is 25.82% smaller than the theoretical plastic zone. The result of numerical simulation analysis shows that due to the influence of upper slice mining, the depth of plastic zone in the floor is 1-2 m. Due to the disturbance of the lower slice mining of the open-off cut, the depth of plastic zone in the top coal is 1 m. The results obtained by the above three methods are highly consistent. The stability evaluation results of the top coal in the open-off cut show that the top coal integrity index ranges from 42.9% to 87.9%. The top coal thickness is positively correlated with the integrity index and negatively correlated with the fracture development. The proportion of top coal integrity evaluation as good or above is more than 1/2, indicating that the overall structure of top coal is basically complete. The research results can provide reference for the design of top coal thickness retention standard and support scheme of large section open-off cut in lower slice of slicing mining under similar mining conditions.

Measurement method of borehole wall resistivity for coal mine gas extraction

LI Jie, LEI Zhipeng, LI Linbo, REN Ruibin, WANG Feiyu, XIANG Xueyi

2022, 48(5): 32-38. doi: 10.13272/j.issn.1671-251x.2022010025

<Abstract>(227) <HTML> (83) <PDF>(29)

Abstract:
For borehole wall state detection of horizontal directional kilometer drilling rig used for coal mine gas extraction, it is considered through analysis that the commonly used logging technologies such as gamma ray method and ultrasonic method are difficult to be applied to coal mine environment. Therefore, a seven-electrode radial resistivity measurement method is designed to measure the resistivity of borehole wall of gas extraction borehole and realize the detection of borehole wall state. The principle of seven-electrode radial resistivity measurement method is introduced. The formula of resistivity calculation is deduced. And the effects of three parameters, namely, the distance between shielding electrodes, the center distance between measuring electrodes and electrode distribution ratio, on resistivity measurement are analyzed. A three-dimensional simulation model and a two-dimensional axisymmetric simulation model are established. The models are used to study the current focusing and potential distribution around the measuring electrode under different transmit signal types and electrode distribution parameters. The results show that the penetration capability of DC and pulse signals is weak. DC and pulse signals cannot penetrate the borehole wall and cannot realize the measurement of borehole wall resistivity. The AC signal has better penetration capability and can be used for the measurement of borehole wall resistivity. The electrode distribution ratio has a significant effect on the current focusing effect. When the electrode distribution ratio is 2.5-3, the focusing effect of the emitter current is better, and a better resistivity measurement effect can be obtained. According to the above results, the transmit signal types and electrode distribution parameters are determined. The focus of emission current and potential distribution are simulated and analyzed when air, mud, rock stratum and coal seam are used as media. The results show that the seven-electrode resistivity measurement method has strong capability to distinguish the properties of the media around the electrodes. According to the simulation results, the experimental electrode is made and installed on a drill pipe to measure the resistivity of soil, air and coal particles respectively. The measured values are all within the standard reference value range. It is verified that the seven-electrode radial resistivity measurement method can realize the borehole wall resistivity measurement. This study provides an effective method for the borehole wall state detection of horizontal directional kilometer drilling rig for coal mine gas extraction.

Network hole coverage reconstruction algorithm for post-disaster coal mine Internet of things

HU Qingsong, FAN Xinge, LI He

2022, 48(5): 39-45. doi: 10.13272/j.issn.1671-251x.17885

<Abstract>(228) <HTML> (72) <PDF>(17)

Abstract:
Due to the damage of some nodes or obstacles in the post-disaster coal mine Internet of things, network hole would appear to hinder network connectivity. The existing network hole coverage algorithm does not consider the geographical environment factors after the underground disaster, and does not optimize the repaired network. Therefore, the algorithm cannot meet the reconstruction requirements of the post-disaster coal mine Internet of things. In order to solve this problem, this paper proposes a network hole coverage reconstruction algorithm with obstacles, NHCRA-O, for post-disaster coal mine Internet of things. The post-disaster coal mine Internet of things model and the node perception model are established. Delaunay triangulation is used to divide residual nodes and corner points of obstacles in the network. The node perception model is used to judge whether there is a network hole in the area. The centroid position of the Delaunay triangle is calculated. The distance between the centroid and the vertex of the Delaunay triangle is used to determine the virtual repair node position. The virtual repair node and mobile node are visualized, and the priority of both is calculated based on distance factor and energy factor. The pre-pruning operation is used to delete some calculation results to improve the convergence speed of the algorithm. According to the visual judgment result and node priority, the virtual repair node and the mobile node are matched in both directions. Therefore, the final position of the mobile node is determined and the network hole repair is completed. The node priority is calculated by fusing the residual energy factor, node connectivity and directional betweenness. The cluster head node is elected according to the priority, and other member nodes join the cluster nearby to realize network reconstruction. Matlab2016a software is used to simulate the node matching efficiency, network coverage efficiency and network time-to-live of NHCRA-O. The results show that the number of times that NHCRA-O completes the matching of mobile nodes with virtual repair nodes is 31.4% less than that of Gale-Shapley algorithm. The network coverage is higher than the C-V algorithm and the PSO algorithm, and the average moving distance of the mobile nodes is shorter. The network time-to-live reconstructed by NHCRA-O is significantly longer than that reconstructed by SEP algorithm and LEACH algorithm.

Defogging algorithm of underground coal mine image based on adaptive dual-channel prior

WANG Yuanbin, WEI Sixiong, DUAN Yu, WU Huaying

2022, 48(5): 46-51, 84. doi: 10.13272/j.issn.1671-251x.2021110053

<Abstract>(444) <HTML> (127) <PDF>(47)

Abstract:
When dark channel prior algorithm is used to deal with underground coal mine images, there are problems of image distortion, lack of details and dark light. In order to solve the above problems, a defogging algorithm of underground coal mine image based on adaptive dual-channel prior is proposed. Firstly, according to the physical model of atmospheric scattering and the special environment of underground coal mine, the dust and fog image degradation model in underground coal mine is established. Secondly, a dual-channel prior model is established by fusing the dark channel and the bright channel to optimize the transmittance. An adaptive weight coefficient is added to improve the precision of the transmittance image. And the gradient guided filtering is adopted to replace the traditional guided filtering to refine the transmittance image. Finally, combined with the mine environment, the atmospheric light value calculation method is improved. And the image is restored according to the dust and fog image degradation model. The experimental results show that the algorithm can effectively remove the fog phenomenon in the image, avoid the halo blur and over-enhancement phenomenon. Compared with dark channel prior algorithm, Retinex algorithm and Tarel algorithm, this algorithm greatly improves the image information entropy and average gradient. The algorithm enriches the detailed information of the restored image and shortens the running time.

Coal dust image segmentation method based on improved DeepLabV3+

ZUO Chunzi, WANG Zheng, ZHANG Ke, PAN Hongguang

2022, 48(5): 52-57, 64. doi: 10.13272/j.issn.1671-251x.2021120086

<Abstract>(275) <HTML> (125) <PDF>(40)

Abstract:
When the traditional semantic segmentation network is used to segment the small coal dust particles, there are some problems such as easy loss of deep information and unclear detail extraction. In order to solve this problem, a coal dust image segmentation method based on improved DeepLabV3+ is proposed. DeepLabV3+ network model is improved in three aspects. ① In the encoder, the CA-MobileNetV3 lightweight module is used to replace Xception to achieve characteristic extraction and ensure more detailed and accurate characteristic extraction. ② The atrous rate is improved in the atrous spatial pyramid pooling(ASPP) module to make it more suitable for extracting small coal dust particles. ③ A global attention up-sample(GAU) module is introduced into the decoder to weight the low-level characteristic information when the calculation amount is small. And the high-level characteristic information is used to guide the low-level characteristic information to realize characteristic fusion. The GAU module uses a global up-sampling mechanism to replace the up-sampling mechanism of the decoder. The characteristic information of the coal dust particles is not attenuated after long-distance transmission. And the method is more conducive to capture the edge detail information of the coal dust particles. The experimental results show that the recall rate of the improved DeepLabV3+ network model on the coal dust data set is 90.26%, and the accuracy is 89.23%. Compared with other network models, the improved DeepLabV3+ network model can effectively enhance the learning ability of coal dust characteristics, obtain more detailed information, greatly shorten the training time, and has better segmentation effect on small targets.

Improvement of position and posture measurement system for boom-type roadheader based on machine vision

ZHANG Xuhui, WANG Heng, SHEN Qifeng, YANG Wenjuan, ZHANG Chao

2022, 48(5): 58-64. doi: 10.13272/j.issn.1671-251x.2021100051

<Abstract>(1058) <HTML> (90) <PDF>(31)

Abstract:
In coal mine, the dust concentration is high and the illumination is low. The image acquisition quality and characteristic extraction effect are greatly affected by dust concentration. However, the camera parameters and image processing parameters cannot be adjusted adaptively according to the change of dust concentration. Therefore, it is easy to cause problems such as unstable point-line characteristic extraction and image frame loss. In order to solve the above problems, the position and posture measurement system for boom-type roadheader based on machine vision is improved. The mine-used explosion-proof industrial camera is used to collect the laser point-line images under different dust concentrations. The relationship model between the image gray value and the dust concentration level is established through the transmittance. The optimal camera parameters and image processing parameters under different dust concentration levels are obtained through experiments. A parameter adaptive adjustment algorithm is proposed, and the parameter values are adjusted adaptively according to the dust concentration levels. Therefore, the image collection quality and the stability and precision of the point-line characteristic extraction are improved. Moreover, the precision of position and posture measurement system for roadheader based on machine vision is improved. The experimental result show that the average measurement errors in X, Y and Z directions of the improved vision detection system for boom-type roadheader are 28.26 mm, 30.58 mm and 22.54 mm respectively. The number of usable images is increased from 75 to 90 after processing 100 images. These results show that the parameter adaptive adjustment algorithm can effectively improve the precision of image characteristic extraction and the data availability. The algorithm ensures the precision and stability of position and posture measurement system for boom-type roadheader based on machine vision.

Research on energy-saving optimal control method of belt conveyor in coal mine

GAO Peilin, MIAO Xin, YANG Fang

2022, 48(5): 65-71, 78. doi: 10.13272/j.issn.1671-251x.2022030057

<Abstract>(368) <HTML> (51) <PDF>(64)

Abstract:
Due to the discontinuity of coal production, the belt conveyor is often in the running state of no-load, light load and rarely full load. This causes a waste of electricity and exacerbates the wear and tear of equipment. At present, the method to solve this problem is to control the velocity of belt conveyor according to the information of coal flow. However, the current method seldom considers the connection relationship between the upstream and downstream of the coal flow between the belt conveyors, the installation position of the coal flow sensor, the detection error, the information lag and the timing sequence relationship in the process of belt velocity change. In order to solve the above problems, according to the relationship between driving power, running resistance and belt velocity of belt conveyor, the optimal energy-saving running condition and the optimal energy-saving rate of belt conveyor are obtained. According to the optimal energy-saving running conditions, the relationship between upstream and downstream connection mode of belt conveyor and material balance, rated transportation quality and rated belt velocity, the minimum belt velocity and optimal belt velocity control coefficient under the optimal energy-saving control conditions of belt conveyor are obtained. According to the installation position of the coal flow sensor, the detection error, the information lag and the time sequence relationship of the belt velocity change process, an energy-saving optimal control method of belt conveyor is proposed. According to the coal flow information of the upstream belt conveyor, this method calculates the given curve of the belt velocity change of the downstream belt conveyor under the optimal energy-saving control condition. The adjustment of the belt velocity of the downstream belt conveyor is realized according to the curve. By using the simulated energy-saving experiment platform of belt conveyor, the optimal power saving rate is tested. The results show that the optimal power saving rate of belt conveyor under the optimal energy-saving running condition is 20.9%-76.5%. However, in the actual transportation system, because the belt velocity can not be adjusted continuously, it is impossible to achieve the optimal running condition. The energy-saving optimal control method of belt conveyor is apply to the control of the No. 101 main hoisting belt conveyor in Ningtiaota Coal Mine. And the result shows that this method realizes the smooth connection of coal flow, and the power saving rate is 9.1%-43.9%. The energy saving effect is obvious.

Research on the relationship between energy dissipation and stress drop in uniaxial compression failure of coal samples

LOU Quan, WAN Xiangyun, JIA Bing, QIU Liming, SONG Yuxuan, PEGN Desheng

2022, 48(5): 72-78. doi: 10.13272/j.issn.1671-251x.2021110004

<Abstract>(242) <HTML> (131) <PDF>(13)

Abstract:
Compared with the energy dissipation of coal and rock failure, the more intuitive stress drop has certain practical significance for assisting the study of coal and rock failure characteristics and variation law of geophysical signals. And the stress drop is the macroscopic manifestation of energy dissipation. Most of the current research on energy dissipation and stress drop is only for one-sided research, without a comprehensive study on the relationship between the two. The relationship between the two is not clear, which restricts the application of the stress drop index. In order to solve the above problems, YAW−600 microcomputer controlled electro-hydraulic servo pressure testing machine is used to carry out uniaxial compression experiments on coal samples. The evolution characteristics of energy dissipation index and stress drop index in the whole process of coal sample failure under load and the relationship between them are studied and analyzed. Based on theoretical analysis, the relationship between energy dissipation index and the product of stress level and stress drop index is further studied. The results show that the energy dissipation index and stress drop index in the uniaxial compression failure process of coal sample have good response to the significant fracture of coal sample. And the indexes are in the same order of magnitude in numerical value, but they are not completely proportional. The energy dissipation rate is linearly related to the product of stress level and stress drop rate. And the energy dissipation is linearly related to the product of stress level and stress drop. The goodness of fit is 1 and 0.997 5 respectively. Compared with the energy dissipation index, the more intuitive product of stress level and stress drop index is more sensitive to the significant damage of coal samples, and has a burst characteristic. The research results clarify the relationship between energy dissipation and stress drop, and provide a certain theoretical support for the application of stress drop index. The relationship can be used for in-depth research on the coal rock failure characteristics and the variation law of geophysical signals such as acoustic emission, electromagnetic radiation and infrared radiation.

Human posture detection method in coal mine

WANG Xuan, WU Jiaqi, YANG Kang, PAN Ziheng, YANG Wei, WANG Wenqing

2022, 48(5): 79-84. doi: 10.13272/j.issn.1671-251x.17867

<Abstract>(190) <HTML> (204) <PDF>(51)

Abstract:
The posture detection of underground personnel can provide effective information for disaster warning and accident rescue. The postures of the underground personnel are complex and diverse and they are time series data. The existing human posture detection methods are difficult to process continuous related posture data. And the real-time performance is poor due to the complex algorithm and the need to configure an independent computer. In order to solve the above problems, a human posture detection method in coal mine based on improved long short term memory network(LSTM) is proposed. The pressure sensor and angle sensor are used to obtain the posture data of underground personnel, such as foot pressure, waist and leg angle, etc. The portable edge operation decision unit carried by the personnel can discriminate the posture. It can realize the real-time detection of five postures of underground personnel, such as standing, walking, bending, squatting (sitting) and lying down. In order to reduce the dimension of the original sampled data of human posture and improve the compute efficiency, LSTM is improved. The long short term memory sparse autoencoder(LSTMSA) is designed. The characteristics of the original sampled data is extracted by the sparse autoencoder(SA) to reduce the dimension, and then the human posture is detected by the LSTM. Human posture data are collected in the laboratory environment, and LSTMSA, LSTM and recursive neural network(RNN) are trained and tested respectively. The results show that under the same experimental settings and sampling data, the accuracy of LSTMSA for five kinds of human posture detection reaches more than 90%, which is close to LSTM and greater than RNN. The computing time of LSTMSA is shortened by more than 50% compared with LSTM, which meets the real-time requirements of human posture detection in coal mine.

Flexible arc suppression method for single-phase to ground fault in distribution network based on Z-type grounding transformer

SI Weibin, MA Kexiang, LEI Zhirong, DANG Changfu, SONG Guobing, YUN Baoji, LIU Bin

2022, 48(5): 85-92. doi: 10.13272/j.issn.1671-251x.2021110024

<Abstract>(238) <HTML> (41) <PDF>(18)

Abstract:
The coal mine power supply and distribution system usually adopts the neutral point non-effectively grounded method. Most of the power supply lines in this method use cable lines. The underground power supply system is complex and uses many voltage levels. When a single-phase to ground fault occurs, it is easy to form intermittent arcs at the grounding point. Moreover, the existing single-phase to ground fault arc suppression technology of the neutral point non-effectively grounded distribution network has the problem of poor arc suppression effect and difficulty in accurately measuring the parameters of the distribution network to the ground. The most common connection method of transformer winding in 10 kV substation of coal mine in China is delta connection. This mode needs to lead out neutral point and connect arc suppression coil artificially through special grounding transformer (mostly Z-type grounding transformer). In order to solve the above problems, a flexible arc suppression system for single-phase to ground fault of distribution network based on Z-type grounding transformer is designed. When the initial time of grounding fault occurs in the distribution network, the three-phase power supply electromotive force and the neutral point voltage of the power distribution network are firstly measured in real time. When the amplitude of the neutral point voltage is greater than 15% of the three-phase power supply electromotive force, it can be judged as a grounding fault. Compared with the three-phase power supply electromotive force, the phase with the smallest power supply electromotive force is the fault phase. After a single-phase to ground fault occurs, the fast switching switch corresponding to the fault phase is quickly closed. And the active inverter and the Z-type grounding transformer power conversion module are simultaneously put into operation. The Z-type grounding transformer power conversion module clamps the voltage of a neutral point in an opposite phase to be close to the electromotive force of the fault phase power supply. And the amplitude and the phase of the difference between the neutral voltage and the fault phase supply voltage are precisely compensated by the active inverter. Therefore, the control target of suppressing the voltage and the current at the fault point to zero is achieved. After a certain time delay, the fast switching switch is cut off. If the voltage of the neutral point is effectively reduced, it can be judged that the fault is a transient ground fault. And the normal operation of the power distribution network system can be restored. Otherwise, it is judged as a permanent fault. The measures to isolate the fault feeder are taken to restore the normal operation of the distribution network. The simulation results show that when the single-phase to ground fault transition resistance is 500 Ω and 3 000 Ω, the power conversion is only through the Z-type grounding transformer. The voltage and current suppression rate at the fault point reaches 79%-83%, which cannot fully achieve the effect of arc suppression. The flexible arc suppression system can effectively suppress the voltage and current at the fault point, with a suppression rate of more than 98%, realizing reliable arc suppression of single-phase to ground faults in the distribution network.

Research on security access model of coal mine safety supervision cloud data based on blockchain

TAN Liangjie, LI Yongfei, WU Qiong

2022, 48(5): 93-99. doi: 10.13272/j.issn.1671-251x.2022030023

<Abstract>(444) <HTML> (155) <PDF>(43)

Abstract:
The management and control of coal mine safety supervision cloud data is very strict, and the design of access authority should satisfy the requirements of classification and security. At present, coal mine safety supervision cloud data has the problems of unclear classification and hierarchy and weak confidentiality in the security management and contrd dimension. And the existing cloud data management and control models are difficult to meet the security requirements of coal mine safety supervision data. In order to solve the above problems, the security access model of coal mine safety supervision cloud data based on blockchain is designed, including access authority model and access control model. Based on the analysis of the access attributes and access objects of coal mine safety supervision cloud data, an access authority model based on user hierarchy and data attributes is designed. The model realizes the classification and hierarchy management and control of cloud data and dynamic generation of authority. Based on the advantages of distributed realization, full transparency and tamper-proof of blockchain, the cloud data access control model is constructed. The model realizes distributed access control, ensures the security of access control by intelligent contract, and enhances the security protection of authority information by encryption technology. The comparative analysis results shows that compared with the common role-based access control(RBAC) model and attribute-based access control(ABAC) model, the access authority model based on user hierarchy and data attributes realizes the fine-grained access authority division for the coal mine safety supervision cloud data. The user authority is intuitive, the authority rules are simple to generate. The access authority model meets the security requirements of the coal mine safety supervision cloud data. Compared with the access control model based on the third party, the access control model based on the blockchain uses the intelligent contract for access control. The model can enhance the security of the coal mine safety supervision cloud data, provide a new solution for the cloud data security problem, and meets the needs of data security access in more scenarios.

Communication system of hydraulic support electro-hydraulic controller with fault diagnosis function

SONG Danyang, SONG Jiancheng, TAO Xinya, YANG Jinheng, LU Chungui

2022, 48(5): 100-106. doi: 10.13272/j.issn.1671-251x.2021120106

<Abstract>(208) <HTML> (29) <PDF>(26)

Abstract:
There are many communication nodes, long communication distance and complex electromagnetic environment in fully mechanized working face. The existing communication system of hydraulic support electro-hydraulic controller generally lacks fault diagnosis function. In order to solve this problem, a set of communication system of hydraulic support electro-hydraulic controller with fault diagnosis and fault location function is designed by taking the ZDYZ−JK type hydraulic support electro-hydraulic controller as the research object. The system has a two-way communication network. One way adopts a bus structure to connect the main controller and all the support controllers at the same time. The other way adopts a serial structure to only connect two adjacent support controllers. The communication between the main controller and the support controller adopts a bus mode. And the communication and control between adjacent support of the support controllers under the manual mode adopts a serial mode. Therefore, the two modes do not interfere with each other. After receiving the communication signal of the main controller, the support controllers can perform fault diagnosis and record fault conditions in real time. At the same time, the support controllers can periodically send diagnosis information to the support controllers on adjacent supports. Therefore, the diagnosis result of the support controller with bus communication fault can be fed back to the main controller through the support controllers on the adjacent supports. Therefore, when the function of sending a message by the support controller fails or an error occurs, the error can be reported in time. And the report content includes the controller number information to realize the fault location. The experiment results show the following two points. ① The system works well with 121 communication nodes and the maximum communication distance of 1 040 m. And the number of nodes can be increased to 255, which meets the design requirements of 200 nodes and 1 000 m communication distance. ② The system can diagnose and accurately locate various communication faults caused by electromagnetic interference of working face, physical damage of electro-hydraulic controller, software error of electro-hydraulic controller and so on.

Research on magnetic tracking and positioning technology for automatic driving in coal mine

YANG Li

2022, 48(5): 107-111. doi: 10.13272/j.issn.1671-251x.2021110049

<Abstract>(424) <HTML> (136) <PDF>(39)

Abstract:
Most auxiliary transportation vehicles in coal mine adopt wireless positioning method, and the dynamic positioning precision is more than 3 m. This method can not meet the requirements of automatic driving vehicles positioning precision in coal mine. The response time of real-time vehicle positioning data is more than 400 ms, which cannot meet the requirements of automatic driving vehicles for real-time acquisition of positioning information. In order to solve the above problems, a magnetic tracking and positioning technology for automatic driving in coal mine is proposed. The magnetic induction antenna device is arranged at a suitable position of the automatic driving vehicle for auxiliary transportation. Several numbered passive induction magnetic nails are arranged on the vehicle driving route. When the induction antenna passes through the passive induction magnetic nails, the passive induction magnetic nails generate pulse signals under the action of the magnetic field of the induction antenna. The specific position of the pulse signal generation position within the magnetic field range of the magnetic induction antenna can be obtained in real time. The positioning information is forwarded by the magnetic induction antenna to vehicle control system through the CAN bus communication interface. According to the relative position of the center point of the magnetic induction antenna and the passive induction magnetic nail, the control system calculates the deviation position between the position of the vehicle's roadway and the center of the driving route through the batch informed tree (BIT*) algorithm. Therefore, the purpose of positioning and tracking is achieved. In order to verify the effectiveness of the magnetic tracking and positioning technology, an industrial test is carried out in Shenmu Zhangjiamao Coal Mine of Shaanxi Coal Group. Magnetic nails are arranged in a single row with equal spacing in conventional sections. According to different application requirements, the combination of 5 rows of 4 magnetic nails and 2 rows of 5 magnetic nails is used to arrange passive induction magnetic nails in mine well,roadway turn and before and after destination of vehicles route. This method realizes the millimeter-level high precision, millisecond-level low latency, and effective tracking and positioning of the automatic driving vehicle. And it enables the automatic driving vehicle to accurately drive to the destination according to the optimal path.

Design of coal mine inspection robot control system

CAI Zhihua, ZHOU Dongxu, ZHAO Minghui

2022, 48(5): 112-117. doi: 10.13272/j.issn.1671-251x.2021120034

<Abstract>(634) <HTML> (89) <PDF>(52)

Abstract:
The traditional control system of coal mine inspection robot uses bare metal program. There are problems such as poor real-time performance and easy data loss. In order to solve the above problems, a coal mine inspection robot control system based on QT and RT-Thread is designed. The system is divided into two parts according to the function, including the upper computer-human-computer interaction console and the lower computer-microcontroller. The upper computer of the inspection robot control system is developed by using QT software. The upper computer provides a human-computer interaction interface for users, completes remote control of the inspection robot, displays sensor data and alarm records, and improves the human-computer interaction performance. The lower computer of the inspection robot control system is developed by using RT-Thread real-time operating system. Through the thread scheduler, thread tasks such as sensor data acquisition, Ethernet communication, radar signal processing and indicator light alarms are scheduled in a time-slice rotation manner. The macro parallelism between multithreaded tasks in the process of robot automatic inspection is realized, and the real-time performance of the control system is improved. The circular queue data buffer is designed in the control system to solve the problem of data loss caused by the asynchronous running clock between the upper and lower computers. The kernel object semaphore is introduced to optimize the circular queue data buffer, solve the problem of resource mutual exclusion between thread tasks. Therefore, it realizes the stable and reliable data transmission between upper and lower computers for a long time. The test results show that the average delay time of thread switch is 1.08 μs, and the data loss rate is only 0.06% when the data transmission period is 100 ms. The system has high real-time performance, and the stability of thread switching process is good. The system ensures the reliability of mass data transmission.

Design of data acquisition and analysis system for deep vertical shaft

ZHAO Baiting, PANG Meng, JIA Xiaofen

2022, 48(5): 118-122. doi: 10.13272/j.issn.1671-251x.2021120088

<Abstract>(248) <HTML> (41) <PDF>(32)

Abstract:
At present, the cage guide inspection robot used for data acquisition of deep vertical shaft can only carry a small number of sensors. There is no safety protection device, so there are potential safety hazards. In addition, most of the deep vertical shaft data visualization programs use 3D GIS for rendering and display. It is difficult to transplant and has long development cycle. In order to solve the above problems, a data acquisition and analysis system for deep vertical shaft is designed. The cage guide inspection robot is improved by adding a wheel lock device to ensure the safety of the robot during operation. The cage guide inspection robot with wheel lock is used as mobile platform. The data acquisition of deep vertical shaft is realized by infrared camera, photoelectric encoder, ultrasonic ranging module and various sensors on the robot. The cloud server plus front-end visualization panel is used for data processing and display. The cloud server receives various data sent by the cage guide inspection robot and classifies and processes the data. The data of temperature and humidity sensor and the gas sensor is directly stored in the corresponding folder. The convolutional neural network (CNN) is applied to process the video data and analyze whether there are cracks or deformation in the cage guide and the shaft wall. The analysis results are stored in the corresponding folder. The front-end visual panel is lightweighted. Asynchronous JavaScript and XML (Ajax) are used to read data from the cloud server regularly. And JavaScript is used to write the host computer interface display program to improve the portability of the system. The test results show that the cage guide inspection robot with wheel lock used as the data acquisition device can improve the reliability and safety of the system. The data processing and display method of the visualization panel and cloud server reduces the memory occupied by the host computer software to less than 5 MB. The page refreshes quickly and the portability is strong.

Design of mine cascade converter with wide input voltage range

LIU Yangqing, ZHOU Yuan

2022, 48(5): 123-127. doi: 10.13272/j.issn.1671-251x.2021100013

<Abstract>(178) <HTML> (24) <PDF>(29)

Abstract:
The converter used in the power supply has problems of low voltage gain, high voltage stress of power tube, non-electrical isolation and complex control. In order to solve the above problems, a mine cascaded converter with wide input voltage range is designed to meet the requirements of AC127-1 140 V power supply voltage level of coal mine. The cascaded converter can adapt to AC70-1 400 V voltage input. The converter adopts 3-way Buck converter and LLC converter in series to improve the voltage gain of the converter. Capacitor series voltage divider is used to reduce the voltage stress of power tube. Buck converter adopts input voltage feedforward compensation to reduce the influence of input voltage fluctuation. At the same time, Buck converter improves converter stability through output voltage closed-loop PI regulation. LLC converter has the performance of input and output electrical isolation. Pulse frequency modulation technology is used to perform closed-loop PI regulation on the output voltage. Then the power tube is driven by a voltage controlled oscillator with frequency conversion to adjust the resonant frequency of the converter, thus stabilizing the output voltage. The simulation and experimental results show that when the input voltage is AC70-1 400 V, the load effect of the converter is less than 5% and the output voltage deviation is less than 5%. These results meet the requirements of MT/T 408-1995 DC stabilized power supply for coal mine.

"Three hole" in-situ test and evaluation of fault impermeability of coal seam floor

DAI Lei, DUAN Lihong

2022, 48(5): 128-132. doi: 10.13272/j.issn.1671-251x.2021110018

<Abstract>(167) <HTML> (30) <PDF>(25)

Abstract:
The double-hole method in-situ pressure permeability test technology adopts single-direction pressure permeability test without considering the direction and anisotropy of rock fissures. The results are quite different from the actual situation of multi-directional compression of complex rock strata. The 'three-hole' in-situ pressure permeability test method is adopted to conduct forward water pressure test and reverse water pressure test on F_N-6 normal fault of the second horizontal coal seam in Chengjiao Coal Mine. Three holes are arranged in a typical roadway for water injection and water pressure monitoring respectively. The first water pressure test is a forward water pressure test, and the second water pressure test is a reverse water pressure test. The point where the water pressure and pressure permeability flow volume of the water pressure monitoring hole change synchronously with the water injection pressure is taken as the initial permeability characteristic point. And the corresponding water injection pressure is determined as the initial permeability pressure. If the water injection pressure continues to increase according to the design pressure, the permeability pressure is smaller than the water injection pressure and remains stable, and the water injection flow is relatively stable, it indicates that in the original state, the in-situ rock stratum has extremely strong permeability resistance and it is an aquifuge. On the contrary, it is a diversion fissure zone. The test results of the forward water pressure test shows that the water conductivity of the upper section of the F_N-6 normal fault is extremely weak in the initial state. This section is an aquifuge. With the increase of water injection pressure, the rock mass between the water pressure hole and the water pressure monitoring hole is densely split, resulting in fissures. However, the scale and water conductivity are relatively small, and only seepage from micro fissures is dominant. During the reverse water pressure test, the number of water diversion channels is increased compared with that in the forward water pressure test. This leads to the decrease of the pressure difference between the water pressure hole and the water pressure monitoring hole. And the dominant water diversion channel is formed between the water pressure monitoring hole and the water pressure hole. The actual permeability state can be formed only when the critical permeability pressure (the critical permeability pressure of F_N-6 normal fault is 11 MPa) is exceeded.

2022 Vol. 48, No. 5

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