At present, there are difficulties in the management of underground personnel in coal mines. It is difficult for managers to grasp the dynamic distribution and operation of underground personnel in time. Once an accident occurs, there is a lack of reliable information for the rescue of underground personnel, and the efficiency of rescue and relief and safety rescue is low. The introduction and application of the underground personnel positioning system in the coal mine, the electronic tags worn by the staff transmit their location information to the monitoring center through the underground monitoring node, and master everyone’s underground location and activity track in real time, which will play a positive role in the safety production of the coal mine and reduce casualties to a certain extent. Usually, the uploaded location information can also be used as staff attendance records.

1. RFID Technology

1.1 RFID development

RFID is a new non-contact automatic identification technology rising in the 1990s. It uses wireless transmission mode for two-way data communication, so as to achieve the purpose of automatic identification and exchange of information. In recent years, automatic recognition technology has been rapidly popularized and popularized, and there are a variety of automatic recognition methods: bar code is a widely used and cheap automatic recognition technology, but the amount of bar code information is small and can not be rewritten; IC card with contact row is the most common structure of electronic data carrier, but in many cases, the connection of mechanical contact is unreliable; RF ID can realize the real automatic management of items, and its advantages are very obvious: it has a large amount of stored information, and each product has a unique ID number; No light source is needed for reading and writing, and data can be read through external materials; Long service life, able to work in harsh environment; It can be easily embedded or attached to products of different shapes and types; The reading distance is longer, and data can be written and accessed to realize the dynamic change of label content; It can process multiple tags at the same time; The data access of the tag is password protected, with higher security; The object to which the RF ID tag is attached can be tracked and located.

1.2 composition of RFID system

RFID system is mainly composed of tag, reader, antenna, etc. generally, it also needs the support of other software and hardware.

1) Reader writer. The reader can be simplified into two basic functional modules: high frequency interface module (transmitter and receiver) and control unit. The reader / writer reads the information in the electronic tag and then sends the information to the ground monitoring center.

2) Passive electronic tag. The electronic tag consists of a coupling element and an ASIC (IC). Passive electronic tag, that is, the electronic tag without its own power supply, is powered by the high-frequency field sent by the reader. The analog front end cooperates with the demodulator to absorb current from the electronic tag antenna, charge the capacitor after rectification, and then supply power to the electronic tag after voltage stabilization.

2. Can bus technology

Can is a serial communication bus defined by ISO. It was first used in the automotive industry in the late 1980s. It has high bit rate, high anti electromagnetic interference, high reliability, and can detect any errors. Can is an ideal solution when microcontrollers need to communicate with each other or when microcontrollers and remote peripheral devices need to communicate with each other. It has been widely used in various control systems.

Can adopts new technology and unique design, which has outstanding reliability, real-time and flexibility compared with RS485. Can has the network characteristics of multiple master nodes, high bus utilization, fast data transmission speed, good scalability, long communication distance, and repeater communication distance can reach tens of kilometers. It has a reliable error handling and error detection mechanism. The failure of individual nodes does not affect the operation of the whole communication network, and has good real-time performance. In addition, the two-way communication of can makes up for the defect of RS485 half duplex communication. It can not only upload the position information, but also modify the information of a underground monitoring contact in real time when necessary. It can be seen from the comparison that the RS – 485 network has no comparability in other performance aspects except that the hardware cost and development difficulty are slightly superior to the can – bus network. Today, when the product update speed is particularly fast, if the product launch time, the later maintenance of the product and the difficulty of software development are calculated together, the hardware cost advantage of RS – 485 is not very obvious. Therefore, it is a more thorough scheme to replace RS – 485 bus with CAN bus.

3. Design of underground personnel positioning system in coal mine

3.1 basic composition of positioning system

The system consists of two parts of equipment, i.e. downhole equipment and downhole equipment. The well equipment is mainly composed of monitoring center (including server) and shared network terminal; Underground equipment takes can bus as the main transmission path, develops corresponding underground personnel monitoring nodes, and connects with the monitoring center with antenna, electronic tag, transmission medium and repeater R, so as to realize the positioning and safety management of underground operators. The system network structure is shown in Figure 1.

Application of electronic tag in monitoring and positioning of underground personnel in coal mine

3.2 working principle of positioning system

The positioning system mainly realizes the safety monitoring of underground personnel and equipment. Monitoring nodes shall be installed at the intersection of tunnel and working face, and the personnel entering the well shall wear the belt with electronic label or the safety helmet with electronic label as required. The RF ID reader transmits a signal to the electronic tag through a fixed frequency RF carrier. The electronic tag (worn by the staff) is activated after entering the antenna working area of the reader, and transmits the RF signal containing personal information through the transceiver module in the card; The reader / writer antenna receives the RF signal from the electronic tag. After processing, it extracts the personal information and sends it to the well monitoring center through the Fieldbus to record the real-time information such as the passing place, time and activity track of the underground staff. It can also automatically generate the report data of attendance statistics and management, so as to improve the management efficiency.

3.3 core component of positioning system – RF ID monitoring node

1) Hardware design of RF ID monitoring node. The monitoring node is composed of reader / writer, microcontroller (MCU) and can node. The RF chip used in the reader is ri – stu – 650a. It has the advantages of strong anti-interference ability, high communication rate, low power consumption and stable performance. Considering the cost and other problems, the working frequency of RF ID is 915MHz. The test shows that it can meet the functional requirements of the system in terms of transmission distance and data reliability. The SP I serial interface is used for communication between the reader and the microcontroller 89C51. The CAN node is composed of three parts: independent can controller SJA1000, can driver 82C250 and high-speed optocoupler 6n137, as shown in Figure 2. In order to enhance the anti-interference ability of CAN nodes, SJA1000 is not directly connected with 82C250, but is connected with 82C250 through high-speed optocoupler 6n137, which well realizes the electrical isolation between can nodes on the bus.

Application of electronic tag in monitoring and positioning of underground personnel in coal mine

2) RFID monitoring node software design. The single chip microcomputer software design of the monitoring node uses C51 and assembly language mixed programming, including reset module, anti-collision module, read-write module and communication module. Its flow chart is shown in Figure 3. When the tag is verified to be legal, the reader / writer will officially read / write the tag data. After information processing, it will be uploaded to the ground monitoring center by the CAN bus. When the tag is verified as illegal, the reader / writer will turn to the direct reset response state and wait for the next read / write operation to start.

3.4 main functions realized by the system

1) Attendance management function. Through the special management software of the operation platform, classify and count the downhole personnel’s downhole times, downhole residence time and other information, which is convenient for assessment, and realize the staff’s attendance statistics management function and the printing of relevant reports.

2) Security function. According to the historical data information stored in the database, the system can quickly know the distribution of underground personnel and important equipment. In case of mine disaster, it can locate and search the trapped personnel on site for effective rescue.

Application of electronic tag in monitoring and positioning of underground personnel in coal mine

3) Production scheduling function. By calling the data in the database, we can query the distribution of underground personnel and quickly allocate personnel according to needs, so as to realize the optimal allocation of underground limited resources and achieve twice the result with half the effort.

4. Conclusion

Coal mine safety is the eternal theme of coal mine production. Personnel monitoring and positioning is one of the important guarantees to realize coal mine safety production. Therefore, this paper investigates and analyzes the coal mine personnel attendance management system, studies the current positioning technology, and puts forward a coal mine personnel positioning system with RF ID as the core and can – bus communication network as the link. After experimental verification, the expected purpose is achieved. The system greatly meets the needs of real-time mastering the dynamic distribution and safety management of coal mine personnel, and can realize the attendance management function and quickly guide the rescue work of coal mine sudden accidents.

Responsible editor: GT

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