The modern factory is no longer a simple production and processing site. It is a complex area including office areas, production and development, special operations, warehouses, restaurant logistics, parking lots and other places. Accidents such as fire and explosion in chemical plants, mechanical damage from machinery factories, falling from high places on construction sites, and dust explosions in production workshops are frequent in the world, most of which are caused by unsafe behavior or unsafe conditions. Therefore, safe production is the foundation of the factory's survival. At the same time, the diversity of factory personnel makes managers need to spend more energy and time, but the final result is not ideal.
Due to the current Time Difference Of Arrival (TDOA) [1] technology, the theory is clear, the positioning method is optimized, the positioning accuracy is high, and the ultra-wideband UWB[2] used has strong pulse penetration capability, signal fidelity and fast rate. In this paper, this paper proposes a design scheme of factory personnel security positioning system based on the positioning technology, combined with the analysis and summary of the safety hazards of modern factories, and designs the security and security positioning system for the above-mentioned unsafe problems. The entire security positioning system has been designed through system structure design [3], anti-control function design [4], and operation process, which not only complements the traditional video surveillance, but also improves the management of the entire plant personnel and machinery. effectiveness.
1 TDOA positioning technologyThe TDOA positioning is simple to understand the time difference of arrival, that is, the time difference between the UWB (Ultra Wideband) ultra-wideband pulse signal transmitted by the mobile station to the two base stations (Base Station). The system only needs to synchronize the clock between the base stations to avoid the error caused by the clock instability caused by moving the target to be tested. TDOA positioning technology only needs to obtain the time difference instead of the absolute time point, the time error is small, and the positioning accuracy is high. The Time Of Arrival (TOA) positioning technology requires the base station to maintain strict time synchronization with the mobile target, a requirement that is difficult to achieve in most cases.
1.1 TDOA positioning principleTDOA positioning technology is an important foundation of security positioning systems. The principle of TDOA positioning is derived from the hyperbolic characteristic, that is, the distance difference from any point on the hyperbola to the two focal points is equal. Figure 1 shows the two-parallel hyperbola, where L1, L2, and L3 are moving the target to be tested to the base station 1 respectively. Distance between (BS1), base station 2 (BS2), and base station 3 (BS3).
Assume that the coordinates of the moving target are (x, y, z), and the coordinates of the nth base station are known to be (xn, yn, zn). Here, the first base station is used as the clock reference base station, and the three-dimensional can be derived. Stereospace mathematical equations:
Solve three-dimensional space mathematical equations:
The Gauss-Markov theorem shows that when the variances of the error vector components are the same, the error localization accuracy is the best.
2 Security positioning system designIn the design process of security positioning system, according to the characteristics of TDOA positioning technology [6], this paper systematically and clearly presents the main body of the system through three parts: system structure design, prevention and control function design and operation flow design.
2.1 Structural designThe security positioning system and the existing security system will not conflict with each other, and have the auxiliary function and enhance the original security effect. With this aim, the schematic diagram of the positioning security system shown in Figure 2 is designed. The whole positioning system consists of three parts: pulse signal receiving and processing, wireless network coverage system and terminal control display system (if there is a need for functional integration, the terminal The control display system and the control room terminal warning and control system can be combined into one).
There are three ways to build and process pulse signals: presence location, one-dimensional positioning, two-dimensional and three-dimensional positioning. As can be seen from FIG. 2, the existence of the location can be completed by one micro base station, and two micro base stations are required for one-dimensional positioning, and three or more micro base stations are required for two-dimensional and three-dimensional positioning. The pulse signal receiving and processing process is that the electronic tag is responsible for issuing a specific coded signal, and the micro base station receives the signal and decodes and calculates the distance between the two. The wireless network coverage system mainly uses the existing power line system of the factory to install a communication modem to connect to the broadband for wireless network coverage, and the micro base station transmits and exchanges data information with the system through the wireless network. The wireless local area network signal formed by the existing power line is stable. The transmission speed is fast and the traditional complicated network wiring is avoided, and the efficiency is saved and the cost is saved. The terminal control display system obtains the data information transmitted by the micro base station through the network, that is, the distance between each electronic tag and the micro base station, and then the system obtains the coordinates of the moving target to be tested by writing a good MATLAB algorithm.
2.2 Anti-control function designTDOA positioning technology is the basic and important part of the security positioning system. However, for various safety hazards in the factory, it is necessary to use TDOA positioning technology and machine vision technology to design the function in a targeted manner. Figure 3 shows the precise positioning. And unsafe condition monitoring system, involving machine vision inspection personnel access, real-time virtual warning line, electronic warning wall and alarm device.
The positioning of factory employees and outsiders requires the configuration of electronic work card labels. The system calculates the coordinates of the corresponding personnel or machinery through real-time pulse signals from the electronic work cards to achieve positioning. Due to the large space in some workshops, the rotating pan/tilt camera is used to replace the traditional all-round control camera, and the positioning system is used to control the pan/tilt rotation camera. The whole workshop is equivalent to a three-dimensional coordinate system. The human and the machine are coordinate points. The dangerous space in the workshop and the special operation area are divided into virtual space with hierarchical authority, such as high-pressure dangerous area and warehouse heavy land. Once the personnel enters, the setting is set. The identification information is recognized in the grid, and an alarm is generated immediately when a non-special operation worker or an outside authorized person enters, and the camera recording information of the imaging device in the interval is defined.
In addition to personnel positioning, the system is also equipped with unsafe condition monitoring, such as special job requirements for employees, helmets and insulated gloves, which are analyzed and processed by the camera in the terminal control system and early warning system. Figure 4 shows the control. Room terminal warning and control system. In terms of visual algorithms, the system adds more advanced neural networks, machine learning, big data processing and other techniques to deal with various unsafe conditions.
The electronic tag (the ultra-wideband pulse uses the transient benign avalanche effect of the switching transistor) transmits a specific encoded pulse signal, the micro base station receives the pulse time, determines the distance between the electronic tag and the base station by the time difference, and calculates the moving target coordinate using the TDOA positioning principle. The security positioning system performs identification and monitoring according to the divided space, analyzes and processes the unsafe state of the non-professional workers in the dangerous area, and finally issues a warning through the terminal control system and saves the real-time status information. The entire system is automated, and the administrator can view the information records at any time. The workflow is shown in Figure 5.
The personnel security positioning system is based on TDOA positioning technology, and performs algorithm writing, software production and system function design. Under the premise of complete equipment installation, the error of the distance measurement between the electronic tag and the micro base station is controlled within 0.1 m; the coordinates of the personnel obtained by the TDOA positioning algorithm are controlled within 0.2 m; the virtual warning line and the electronic warning wall The space is divided correctly, and the position information of personnel and machinery is accurately exchanged; in the aspect of camera linkage, the coordinate information can control the camera pan/tilt rotation; the video information can be timely feedback feedback information under the processing of the system machine vision algorithm; using the display record function The manager can query the position and track information of the personnel at any time, call up the real-time camera picture, and count the attendance. Three sets of experiments were carried out using the existing experimental conditions. The experimental results and error analysis are shown in Table 1.
The factory security positioning system based on TDOA positioning technology proposed in this paper is a low-cost, low-energy, high-efficiency and high-reliability auxiliary system for modern monitoring systems. The main features include:
(1) Adopting the latest and most practical TDOA positioning technology, it can jump out of the clock error problem and achieve the purpose of improving accuracy. This technique takes advantage of the hyperbolic properties and solves the matrix with least squares to get the most accurate coordinates.
(2) Solving the problem of large-scale, complex and difficult to manage orderly management of large-scale modern factory personnel. In this design, the factory personnel divide the space according to the type of work and the work area. The system can quickly record the attendance and attendance status of the personnel, and can also record the movement track in the factory.
(3) Completed the integration assistance with the video surveillance system of the modern factory. The system can input the name or number of the worker to view the coordinates of the worker anytime and anywhere, and call the camera in the coordinate area to view the situation of the coordinate area, realizing real-time monitoring and camera linkage.
(4) Using neural networks, machine learning, big data processing and other technologies to deal with unsafe conditions and improve system early warning capabilities.
(5) Complementing the deficiencies in modern video surveillance systems, providing a reliable and efficient design basis for large factories and industries with significant security needs.
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