Currently, coal mines generally face difficulties in managing personnel entering the mine. Managers struggle to promptly grasp the dynamic distribution and operational status of underground personnel. In the event of an accident, reliable information is lacking for rescue efforts, resulting in low efficiency in disaster relief and safety operations. Introducing and utilizing a coal mine personnel positioning system, where workers wear electronic tags that transmit their location information to the monitoring center via underground monitoring nodes, allows for real-time tracking of each person's location and activity trajectory underground. This will positively impact coal mine safety production and reduce casualties to some extent. The uploaded location information can also be used for worker attendance records. 1. Radio Frequency Identification (RFID) Technology 1.1 RFID Development RFID is a new type of non-contact automatic identification technology that emerged in the 1990s. It utilizes wireless transmission for two-way data communication to achieve automatic identification and information exchange. In recent years, automatic identification technology has been rapidly popularized and promoted, and there are various automatic identification methods: barcodes are a widely used and inexpensive automatic identification technology, but barcodes have a small amount of information and cannot be rewritten; IC cards with contact strips are the most common structure of electronic data carriers, but in many cases, the connection of mechanical contacts is unreliable; RFID, however, can achieve true automated management of items, and its advantages are very obvious: large storage capacity, each product has a unique ID number; reading and writing do not require a light source, and data can be read through external materials; long service life, and can work in harsh environments; can be easily embedded or attached to products of different shapes and types; longer reading distance, can write and retrieve data, and realize dynamic changes in the content of the tag; can process multiple tags simultaneously; tag data access is password protected, and the security is higher; it can track and locate the object to which the RFID tag is attached. 1.2 Composition of RFID System An RFID system mainly consists of tags, readers, antennas, etc., and generally requires the support of other hardware and software. 1) Reader. The reader/writer can be simplified into two basic functional modules: a high-frequency interface module (transmitter and receiver) and a control unit. The reader/writer reads the information from the electronic tag and then sends the information to the ground monitoring center. 2) Passive electronic tags. Electronic tags consist of coupling elements and ASICs (ICs). Passive electronic tags, i.e., electronic tags without their own power supply, are powered by the high-frequency field emitted by the reader/writer. The analog front end, in conjunction with the demodulator, absorbs current from the electronic tag antenna, rectifies it to charge the capacitor, and then supplies power to the electronic tag after voltage regulation. 2 CAN bus technology CAN is a serial communication bus defined by ISO, initially used in the automotive industry in the late 1980s. It has high bit rate, high resistance to electromagnetic interference, high reliability, and can detect any errors. CAN is an ideal solution for communication between microcontrollers or between microcontrollers and remote peripheral devices, and is widely used in various control systems. CAN adopts new technologies and unique designs, and compared with RS485, it has outstanding reliability, real-time performance, and flexibility. CAN has the network characteristics of multiple master nodes, high bus utilization, fast data transmission speed, good scalability, long communication distance (tens of kilometers with repeaters), reliable error handling and detection mechanisms (the failure of individual nodes does not affect the operation of the entire communication network), and good real-time performance. Furthermore, CAN's bidirectional communication compensates for the shortcomings of RS485's half-duplex communication, enabling not only the uploading of location information but also real-time modification of information at a specific monitoring point underground when needed. Comparatively, RS-485 networks, apart from slight advantages in hardware cost and development difficulty, are incomparable to CAN-bus networks in other performance aspects. In today's rapidly evolving product landscape, considering factors such as product launch time and the difficulty of developing post-launch maintenance software, the hardware cost advantage of RS-485 becomes less significant. Therefore, replacing RS-485 with CAN bus is a more thorough solution. 3. Design of Underground Personnel Positioning System in Coal Mines 3.1 Basic Composition of the Positioning System The system consists of two parts: equipment above ground and equipment underground. The surface equipment mainly consists of a monitoring center (including a server) and shared network terminals; the underground equipment uses the CAN bus as the main transmission path, and develops corresponding underground personnel monitoring nodes for coal mines. These nodes, along with antennas, electronic tags, transmission media, repeaters, etc., are connected to the monitoring center to achieve the positioning and safety management of underground workers. The system network structure is shown in Figure 1. [IMG=Positioning System Network Structure Diagram]/uploadpic/THESIS/2007/11/2007111912284675738E.jpg[/IMG] Figure 1 Positioning System Network Structure Diagram 3.2 Working Principle of the Positioning System The positioning system mainly realizes the safety monitoring of underground personnel and equipment. Monitoring nodes are installed at the intersections of tunnels and working faces. Workers entering the mine wear belts with electronic tags installed as required, or wear safety helmets with electronic tags installed. The RFID reader transmits signals to the electronic tag via a fixed-frequency radio frequency carrier. The electronic tag (worn by the staff) is activated when it enters the reader's antenna working area, transmitting the radio frequency signal carrying personal information via the card's transceiver module. The reader's antenna receives the radio frequency signal from the electronic tag, processes it, extracts the personal information, and sends it to the surface monitoring center via fieldbus. This records real-time information such as the location, time, and activity trajectory of the underground staff, and can automatically generate reports on attendance statistics and management, improving management efficiency. 3.3 Core Component of the Positioning System—RFID Monitoring Node 1) RFID Monitoring Node Hardware Design. The monitoring node consists of a reader, a microcontroller (MCU), and a CAN node. The RFID chip used in the reader design is the RI-STU-650A, which has advantages such as strong anti-interference capability, high communication speed, low power consumption, and stable performance. Considering cost and other factors, the RFID operating frequency is 915MHz. Testing has proven that it meets the system's functional requirements in terms of transmission distance and data reliability. The reader communicates with the 89C51 microcontroller via an SPI serial interface. The CAN node consists of three parts: an independent CAN controller SJA1000, a CAN driver 82C250, and a high-speed optocoupler 6N137, as shown in Figure 2. To enhance the anti-interference capability of the CAN node, the SJA1000 is not directly connected to the 82C250, but rather through the high-speed optocoupler 6N137, thus effectively achieving electrical isolation between the CAN nodes on the bus. [IMG=Internal Functional Module Diagram of Monitoring Node]/uploadpic/THESIS/2007/11/2007111912302373019U.jpg[/IMG] Figure 2 Internal Functional Module Diagram of Monitoring Node 2) RFID Monitoring Node Software Design. The microcontroller software design of the monitoring node uses a mixed programming of C51 and assembly language, including a reset module, anti-collision module, read/write module, and communication module. Its flowchart is shown in Figure 3. When a tag is verified as valid, the reader officially reads/writes the tag data. After information processing, the data is uploaded to the ground monitoring center via the CAN bus. When a tag is verified as invalid, the reader switches to a direct reset response state, waiting for the next read/write operation to begin. 3.4 Main Functions Implemented by the System 1) Attendance Management Function. The system uses dedicated management software on the operating platform to classify and statistically analyze information such as the number of times personnel go down into the mine and the time spent underground, facilitating performance evaluation and enabling attendance statistics management and the printing of relevant reports. 2) Safety Assurance Function. Based on historical data stored in the database, the system can quickly determine the distribution of personnel and important equipment underground. In the event of a mine disaster, it can locate and search for trapped personnel, facilitating effective rescue. [IMG=RFID Monitoring Node Software Flowchart]/uploadpic/THESIS/2007/11/20071119123155321028.jpg[/IMG] Figure 3 RFID Monitoring Node Software Flowchart 3) Production Scheduling Function. By calling data from the database, the distribution of personnel underground can be queried, and personnel can be quickly allocated as needed, achieving optimal allocation of limited underground resources and achieving twice the result with half the effort. 4 Conclusion Coal mine safety is an eternal theme in coal mine production, and personnel monitoring and positioning are one of the important guarantees for achieving safe production in coal mines. Therefore, this paper investigates and analyzes the coal mine personnel attendance management system, studies the current positioning technology, and proposes a coal mine underground personnel positioning system with RFID as the core and CAN-bus communication network as the link. After experimental verification, the expected purpose has been achieved. The system greatly meets the needs of real-time monitoring of the dynamic distribution of personnel entering the coal mine and safety management, and can realize attendance management functions and quickly guide the rescue work of sudden accidents in the mine.