Low-power coal mine wireless roof detection system and method based on vcse wavelength demodulation

Abstract

The application discloses a low-power coal mine wireless roof detection system and method based on VCSEL wavelength demodulation, and the detection system comprises a low-power wireless fiber grating demodulator, a fiber grating roof state detection sensor module and a wireless base station. The total power consumption of the low-power coal mine wireless roof state detection system is less than 500 mW when the wireless base station is not included. The detection system utilizes low-power VCSEL fiber grating wavelength demodulation technology and wireless transmission technology to realize low-power and low-cost fiber roof state detection, and solves the problems of high cost, inconvenience in construction, high power consumption and inability to display on site of the traditional fiber roof state detection system. Since the VCSEL laser does not need temperature control, the overall power consumption of the system is as low as below 500 mW, greatly improving the flexibility of the layout of a single or multiple detection points.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing / photoelectric detection technology, and in particular to a low-power wireless roof condition detection system and method for coal mines based on VCSEL fiber grating wavelength demodulation technology. Background Technology

[0002] Timely monitoring of the roof condition in coal mines and early detection of signs of potential roof instability are of great significance for preventing roof collapse accidents and ensuring safe production in coal mines.

[0003] Traditional mechanical roof condition sensors rely on manual, periodic measurements of the roof condition, resulting in significant errors and the inability to provide real-time monitoring. Electronic roof condition detection systems, on the other hand, can monitor, display, store, and upload measured roof condition data online, and are gradually replacing mechanical sensors. Due to their low power consumption and ease of establishing wireless sensor networks, electronic roof condition detection systems are widely used in coal mines. However, electronic roof condition sensors primarily operate on a potentiometer principle, converting the mechanical quantity of the relative displacement of the roof into a rotational potential quantity, which is then output as an electronic signal for detection. Because the working environment in coal mines is highly humid and dusty, prolonged exposure to this environment can cause the moving contacts of the potentiometer in electronic roof condition sensors, especially the sliding contact spring and the fixed contact resistive element, to become susceptible to moisture, oxidation, and corrosion. This can disrupt the transmission of the potential signal, leading to false alarms or no alarms, severely affecting the accuracy of roof condition detection and posing a potential hazard to coal mine safety monitoring.

[0004] In fiber optic roof condition monitoring systems, the detected roof delamination displacement and anchor bolt stress are achieved by detecting changes in the center wavelength of the FBG sensor using a Fiber Bragg Grating (FBG) demodulator. Compared to traditional electronic sensors, fiber optic sensors offer advantages such as high reliability, being non-energized, intrinsically safe, strong electromagnetic interference resistance, and ease of reuse, and have many mature applications in underground coal mines. However, in practical applications, fiber optic sensors still have the following drawbacks: 1) Long-distance fiber optic cables need to be laid on-site, posing challenges to installation and construction; 2) In harsh underground environments, falling coal or rocks can easily break the fiber optic cables; 3) Because the fiber optic sensing module is passive and non-energized, it cannot display and alarm at the monitoring site; 4) Traditional mine-use FBG demodulators typically have high power consumption, usually above 10W, requiring heavy explosion-proof protection for underground installation.

[0005] Therefore, the technical challenge that this patent aims to solve is how to overcome the shortcomings of purely electronic or purely fiber optic roof condition detection sensors while retaining their advantages. Summary of the Invention

[0006] To address the problems of the aforementioned electronic and fiber optic roof condition monitoring systems, one objective of this invention is to provide a low-power wireless roof condition monitoring system for coal mines based on Vertical-cavity surface-emitting laser (VCSEL) wavelength demodulation. The key technical problem solved is utilizing low-power VCSEL fiber grating wavelength demodulation technology to reduce the power consumption of the fiber grating demodulator, allowing it to be powered by a battery installed near the sensor, thereby significantly reducing the power consumption of the fiber optic roof condition monitoring system. The demodulated roof displacement information is transmitted wirelessly to a wireless base station via a wireless module. The wireless base station then transmits the measured data to the surface control room via an underground ring network, forming a complete fiber grating wireless roof condition monitoring system. This system utilizes the advantages of fiber gratings while overcoming the disadvantages of traditional fiber grating demodulators installed in control rooms and relying on long-distance optical cable transmission, making the fiber grating wireless roof condition monitoring system more suitable for actual field applications in coal mines.

[0007] The second objective of this invention is to provide a low-power wireless roof detection method for coal mines based on VCSEL wavelength demodulation. This detection process employs intermittent, command-wake-up, and mine lamp-wake-up modes to reduce system power consumption and improve the flexibility of querying roof status information at any time. The fiber optic roof status detection system uses a time-sharing approach between the roof status detection process and the wireless transmission process, further reducing system power consumption and meeting the requirements for wireless roof status detection in coal mines.

[0008] One of the objectives of this invention is achieved by the following technical solution: a low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation, comprising a low-power wireless fiber optic grating demodulator, a fiber optic grating roof condition detection sensor module, and a wireless base station; the total power consumption of the low-power wireless roof detection system for coal mines without the wireless base station is less than 500mW.

[0009] The low-power wireless fiber Bragg grating demodulator includes a low-power VCSEL fiber Bragg grating wavelength demodulation module, an MCU module, a wireless transceiver module, an audible and visual alarm display module, a photoelectric sensor module, a temperature and pressure detection module, and a power supply module. The MCU module is electrically connected to the low-power VCSEL fiber Bragg grating wavelength demodulation module, the wireless transceiver module, the audible and visual alarm display module, the photoelectric sensor module, the temperature and pressure detection module, and the power supply module. The low-power VCSEL fiber Bragg grating wavelength demodulation module is connected to the fiber Bragg grating top plate status detection sensor module via optical fiber or optical cable. The power supply module is used to power the low-power wireless fiber Bragg grating demodulator.

[0010] The fiber Bragg grating top plate condition detection sensing module includes a passive fiber Bragg grating top plate delamination sensing probe and a passive fiber Bragg grating anchor stress sensing probe. The sensing fiber Bragg gratings are respectively disposed within the sensing probes and connected to the low-power wireless fiber Bragg grating demodulator via optical fiber or optical cable. The passive fiber Bragg grating top plate delamination sensing probe is used to detect the delamination values ​​at deep and shallow base points; the passive fiber Bragg grating anchor stress sensing probe is used to detect the anchor stress value.

[0011] The wireless transceiver module is used to receive commands from the wireless base station to read and query the top plate status detection data, and to send the top plate status detection data to the wireless base station.

[0012] The audible and visual alarm display module is used to display relevant values ​​of the roof slab status detection on site, and to provide early warnings and alarms when the roof slab status detection values ​​are about to exceed the limit and when the limit is exceeded.

[0013] The photoelectric sensing module activates the display screen when it detects light illumination. In practical applications, when the low-power wireless fiber Bragg grating demodulator is illuminated by a miner's lamp, the display screen begins to show the measured data on-site.

[0014] The ambient temperature and pressure detection module is used to detect the ambient temperature and pressure at the current and local time, and to correct the measurement results of the fiber optic grating.

[0015] Furthermore, the low-power VCSEL fiber grating wavelength demodulation module includes a VCSEL laser, a current driving circuit, an optical fiber splitter, a photoelectric signal detector, an amplification circuit, and a data acquisition circuit; the power consumption of the low-power VCSEL fiber grating wavelength demodulation module is less than 100mW.

[0016] Furthermore, in the low-power VCSEL fiber grating wavelength demodulation module, the current driving circuit generates a sawtooth wave scanning driving current and drives the VCSEL laser to emit a beam whose scanning wavelength increases with the current. This beam is coupled into the fiber. Within each cycle of the periodic sawtooth wave scanning driving current, the range of wavelength change from short to long constitutes a wavelength scanning range, which covers the center wavelength of the fiber grating. The beam coupled into the fiber is split into 2+N output optical paths by an optical fiber splitter, where N≥1. Two of these paths correspond to the paths entering the photodetector and the built-in reference gas cell, respectively. A photoelectric reference detector converts the signal into an electrical signal; the signal is then amplified by an amplifier circuit and converted into a digital signal by a data acquisition circuit; the remaining N paths pass through N 2×1 fiber couplers, and are then transmitted via optical fibers or cables to the sensing fiber gratings installed in the fiber grating top plate state detection sensing module. After being modulated and reflected by these gratings, the light beams pass through the corresponding 2×1 fiber couplers and enter the corresponding photoelectric signal detectors, where they are converted into electrical signals. Each or / and two fiber gratings form a sensing detection unit, which is installed in the passive fiber grating anchor stress sensing probe and / or the passive fiber grating top plate delamination sensing probe. The temperature and pressure values ​​are measured using the temperature and pressure module inside the low-power VCSEL fiber grating demodulator; the MCU demodulates the change in the reflected wavelength of the fiber grating based on the acquired digital signal, the ambient temperature and pressure values ​​from the temperature and pressure module, and calculates the relative and absolute changes in the anchor stress value and the top plate delamination displacement based on the pre-calibrated wavelength-stress or displacement curve and the wavelength-temperature curve.

[0017] Furthermore, the wavelength / current coefficient of the VCSEL laser is 0.4 nm / mA, and the wavelength / temperature coefficient is 0.11 nm / ℃. By injecting a driving current of 4 mA-16 mA, an effective scanning wavelength range of 2 nm can be achieved within the range of 10-40℃, which meets the wavelength detection range requirements of the sensing fiber grating in the state detection sensing module of the fiber grating top plate.

[0018] The second objective of this invention is achieved by the following technical solution: a low-power wireless roof status detection method for coal mines based on VCSEL wavelength demodulation, wherein the detection is performed using the low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation as described above.

[0019] The low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation intermittently switches from standby to detection mode. The intermittent switching mode includes: (1) the MCU module in the low-power wireless fiber Bragg grating demodulator periodically switches the detection system from standby to detection mode at preset time intervals. After completing the detection and automatically displaying and uploading the detection data, the system automatically switches back to standby mode; (2) when the surface dispatch room issues a detection command through the ring network and wireless base station, the wireless transceiver module in the low-power wireless fiber Bragg grating demodulator receives the command to read and query the roof status detection data from the wireless base station, and the detection system switches from standby to detection mode. After completing the detection and automatically displaying and uploading the detection data, the system automatically switches back to standby mode; (3) when a miner's lamp illuminates the photoelectric sensor module in the low-power wireless fiber Bragg grating demodulator, the detection system switches from standby to detection mode. After completing the detection and automatically displaying and uploading the detection data, the system automatically switches back to standby mode. The system power consumption is minimized when the entire system enters a dormant standby state, waiting for the next wake-up switch. The time interval between system operation and hibernation / standby states can be set according to the requirements of actual applications, thereby ensuring that relevant data can be monitored in a timely manner while effectively reducing battery power consumption and extending the system's usage time after a battery replacement.

[0020] Furthermore, the detection process of the measured quantities and the wireless transmission process of these measured quantities are carried out at different time periods. Specifically, when the detection system receives a wake-up command and switches from standby to detection mode, it first activates the low-power VCSEL fiber grating wavelength demodulation module and measures the wavelengths of the sensing gratings in the passive fiber grating top plate delamination sensing probe and the passive fiber grating anchor stress sensing probe. It calculates the corresponding anchor stress value and the relative and absolute changes in the top plate delamination displacement, and displays the detected values ​​on-site through the audible and visual alarm display module. Subsequently, the detection system shuts down the low-power VCSEL fiber grating wavelength demodulation module and then activates the wireless transceiver module to transmit the measured values. The measured anchor bolt stress values ​​and relative and absolute changes in roof delamination displacement are transmitted to the wireless base station. The wireless base station then transmits the detected data to the control center via the underground ring network. Finally, the wireless transceiver module enters standby mode after transmission. If the detected value is about to exceed the limit or exceeds the limit, the audible and visual alarm display module issues a warning signal or alarm signal. Then, the wireless transceiver module is activated to transmit the measured anchor bolt stress values, relative and absolute changes in roof delamination displacement, and the warning signal or alarm signal to the wireless base station. The wireless base station then transmits the detected data to the control center via the underground ring network. The warning signal or alarm signal can only be deactivated after intervention in the control room.

[0021] Furthermore, the time interval for the detection system to wake up the low-power wireless fiber Bragg grating demodulator can be set and adjusted according to actual needs to achieve a periodic wake-up operation mode for the demodulator. For example, the time interval for the detection system to wake up the low-power wireless fiber Bragg grating demodulator can be set to wake it up once every 10 minutes.

[0022] As a further preferred option, the power module uses a 7AH dry cell battery; when the wireless base station sends a wake-up command every 10 minutes, the VCSEL fiber optic grating demodulation module completes the detection of the top plate status within 5 seconds, displays the data on-site for 30 seconds and uploads the measured data, and then automatically switches to standby mode.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation of this invention reduces the power consumption of the fiber Bragg grating demodulator by utilizing low-power VCSEL fiber Bragg grating wavelength demodulation technology. This allows the fiber Bragg grating demodulator to be powered by a battery installed near the sensor, thereby greatly reducing the power consumption of the fiber optic roof condition detection system. The demodulated roof displacement information is transmitted to a wireless base station via a wireless module using wireless transmission technology. The wireless base station then transmits the measured data to the surface control room through an underground ring network, forming a complete fiber Bragg grating wireless roof condition detection system. This detection system utilizes the advantages of fiber Bragg gratings and overcomes the disadvantages of the traditional working mode where the fiber Bragg grating demodulator is installed in the control room and relies on long-distance optical cables for data transmission. This makes the fiber Bragg grating wireless roof condition detection system more suitable for actual field applications in coal mines.

[0025] (2) This detection system adopts intermittent, command wake-up and mine lamp wake-up working modes during the detection process to reduce the system's operating power consumption. This allows the monitoring system to work stably for at least 6 months with a single battery replacement, improving the system's flexibility in querying roof status information at any time. The fiber optic roof status detection system uses a time-sharing approach between the roof status detection process and the wireless transmission process, further reducing system power consumption and meeting the needs of wireless roof status detection in coal mines. This effectively solves the problems of high cost, inconvenient construction, high power consumption, and inability to display alarms on-site in traditional fiber optic roof status detection systems. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation.

[0027] Figure 2 Schematic diagram of a single-point roof slab status detection alarm;

[0028] Figure 3 A schematic diagram of a multi-channel wireless roof panel status detection subsystem; Detailed Implementation

[0029] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0030] Example 1

[0031] like Figure 1 As shown, this embodiment provides a low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation, including a low-power wireless fiber Bragg grating demodulator, a fiber Bragg grating roof condition detection sensor module, and a wireless base station; the overall power consumption of the low-power wireless roof detection system for coal mines (excluding the wireless base station) is less than 500mW.

[0032] The low-power wireless fiber Bragg grating demodulator includes: a low-power VCSEL fiber Bragg grating wavelength demodulation module, an MCU module, a wireless transceiver module, an audible and visual alarm display module, a photoelectric sensor module, an ambient temperature and pressure detection module, and a power supply module. The MCU module is electrically connected to the low-power VCSEL fiber Bragg grating wavelength demodulation module, the wireless transceiver module, the audible and visual alarm display module, the photoelectric sensor module, the temperature and pressure detection module, and the power supply module. The low-power VCSEL fiber Bragg grating wavelength demodulation module is connected to the fiber Bragg grating top plate status detection sensor module via optical fiber or optical cable. The power supply module provides power to the low-power wireless fiber Bragg grating demodulator.

[0033] The low-power VCSEL fiber grating wavelength demodulation module includes a VCSEL laser, a laser current drive circuit, an optical fiber splitter, a photodetector, an amplifier circuit, and a data acquisition circuit. The power consumption of the low-power VCSEL fiber grating wavelength demodulation module is less than 100mW. In this application, the low-power VCSEL fiber grating wavelength demodulation module of this invention is fabricated using proprietary low-power VCSEL fiber grating wavelength demodulation technology (Chinese Patent CN202111502780.6, A Temperature-Adaptive FBG Demodulation Method and System). This temperature-adaptive FBG demodulation method uses methane gas with a relatively large absorption peak distribution range as a reference wavelength to demodulate the FBG center wavelength. Simultaneously, by selecting and matching the wavelength scanning range of the VCSEL and the FBG center wavelength, it effectively measures the change value of the FBG center wavelength without using a temperature control device, enabling the entire sensor measurement system to meet the requirements of low power consumption, low cost, and miniaturization.

[0034] The fiber Bragg grating top plate condition detection sensing module includes: a passive fiber Bragg grating anchor stress sensing probe and a passive fiber Bragg grating top plate delamination sensing probe. The passive fiber Bragg grating anchor stress sensing probe is used to detect the stress value of the anchor; the passive fiber Bragg grating top plate delamination sensing probe is used to detect the delamination values ​​of deep and shallow base points.

[0035] In the demodulator, the low-power VCSEL fiber grating wavelength demodulation module and the fiber grating top plate state detection sensing module are connected by optical fiber or optical cable. The fiber grating anchor stress sensing probe and the fiber grating top plate delamination sensing probe are respectively equipped with sensing fiber gratings, and these sensing gratings are connected to the corresponding channels of the low-power VCSEL fiber grating demodulation module by optical fiber or optical cable.

[0036] In this embodiment, within the low-power VCSEL fiber grating wavelength demodulation module, a current-driven circuit generates a sawtooth wave scanning drive current to drive the VCSEL laser to emit a beam whose scanning wavelength increases with the current. This beam is coupled into the fiber. Within each cycle of the periodic sawtooth wave scanning drive current, the range of wavelength increase from short to long constitutes a wavelength scanning range. This scanning wavelength range covers the center wavelength of the fiber grating in the fiber grating top-plate state detection sensing module. The beam coupled into the fiber is split into 2+N optical paths by an optical fiber splitter, where N≥1, and N is the number of optical paths used to connect to the fiber grating top-plate state detection sensing module. One path is used to detect the stable state of the light source's optical power. One of the paths passes through a reference gas chamber for gas absorption spectrum self-calibration; the remaining N paths are transmitted to the sensing fiber optic grating via N 2×1 fiber couplers. The beam reflected from the FBG sensor passes through N 2×1 fiber couplers and enters the photoelectric signal detector, where it is converted into an electrical signal. The electrical signal is amplified by the amplification circuit and digitized by the acquisition circuit before being sent to the MCU. The MCU demodulates the reflected wavelength of the fiber optic grating based on the acquired digital signal and the local temperature and pressure values. Based on the pre-calibrated wavelength-stress or displacement curve of the sensing fiber optic grating, the wavelength-temperature curve, and the temperature value measured by the temperature and pressure module, the MCU calculates the corresponding anchor stress value and the relative and absolute changes in the top plate delamination displacement.

[0037] The MCU in the low-power wireless fiber Bragg grating demodulator is connected to the wireless transceiver module. The wireless transceiver module receives commands to read and query roof status detection data from the underground wireless base station and sends roof status detection data to the underground wireless base station. The data is then transmitted to the surface dispatch room via the underground ring network.

[0038] The MCU in the low-power wireless fiber Bragg grating demodulator is connected to the audible and visual alarm display module. The audible and visual alarm display module displays the detected value on site and issues warning prompts and alarm signals when the detected value is about to exceed the limit and when it exceeds the limit.

[0039] The MCU in the low-power wireless fiber Bragg grating demodulator is connected to the ambient temperature and pressure detection module. By detecting the ambient temperature and pressure at the current time and place, the measurement results of the fiber Bragg grating are corrected.

[0040] As an alternative implementation, the MCU in the low-power wireless fiber optic grating demodulator is connected to the photoelectric sensor module. When the miner's lamp shines on the photoelectric sensor module, the output of the photoelectric sensor reaches a preset threshold, triggering a response switch to wake up the detection system, start detection, and display the measured data on site.

[0041] As an alternative implementation, the wavelength / current coefficient of the VCSEL laser is approximately 0.4 nm / mA, and the wavelength / temperature coefficient is approximately 0.11 nm / ℃. By injecting a drive current of 4 mA-16 mA, an effective wavelength tuning range of 2 nm can be achieved within the range of 10-40℃, which meets the wavelength detection range requirements of the sensing fiber grating in the state detection sensing module of the fiber grating top plate.

[0042] Based on the design of the above detection system, the present invention designs two specific application devices, including but not limited to the following: a single-point roof status detection alarm and a multi-channel wireless roof status detection subsystem.

[0043] like Figure 2 As shown, as an alternative implementation, the single-point roof condition detection alarm is composed of a single-point fiber Bragg grating roof condition detection sensor module and a 2-channel wireless fiber Bragg grating demodulator, forming a miniaturized single-point roof condition detection alarm for detecting the condition of a single point roof.

[0044] In each single-point roof condition detection alarm, the 2-channel wireless fiber Bragg grating demodulator uses a 1×4 fiber optic splitter, and the rest of the structure is the same as the low-power wireless fiber Bragg grating demodulator described above. Depending on the actual application requirements, each single-point fiber Bragg grating roof condition detection sensing module can be connected to two passive fiber Bragg grating anchor stress sensing probes or two passive fiber Bragg grating roof delamination sensing probes via optical fiber or optical cable.

[0045] In practical applications, within the coverage area of ​​the wireless base station signal, several single-point roof status detection alarms can be set up simultaneously. These alarms are then networked with the wireless base stations to form a wireless sensor network capable of detecting the status of several single-point roofs. The wireless base stations then transmit the detected data to the control center through the underground ring network.

[0046] like Figure 3As shown, as an optional implementation, the multi-channel wireless roof condition detection subsystem is composed of four fiber Bragg grating roof delamination sensing probes, eight fiber Bragg grating anchor stress sensing probes, and a wireless 16-channel VCSEL fiber Bragg grating wavelength demodulator, forming a multi-channel wireless roof condition detection subsystem.

[0047] The wireless 16-channel VCSEL fiber grating wavelength demodulator uses a 1×18 fiber optic splitter, with the rest of the structure being the same as the low-power wireless fiber grating demodulator described above. Each set of four detection units consists of two fiber grating anchor stress sensing probes and one fiber grating top plate delamination sensing probe. Each fiber grating anchor stress sensing probe contains one sensing fiber grating, and each fiber grating top plate delamination sensing probe contains two sensing fiber gratings. These sensing fiber gratings are connected to the 16 channels of the wireless 16-channel VCSEL fiber grating wavelength demodulator via optical fibers or cables.

[0048] In practical applications, within the coverage area of ​​the wireless base station signal, several multi-channel wireless fiber optic grating detection subsystems can be set up simultaneously. These subsystems are networked together to form a wireless sensor network with a detection capability that is many times greater than that of a single-point roof condition detection network. The wireless base station then transmits the detected data to the control center through the underground ring network.

[0049] Example 2

[0050] This embodiment, based on the low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation in Embodiment 1 above, provides a method for low-power wireless roof status detection in coal mines, including:

[0051] The low-power wireless roof condition detection system for coal mines based on VCSEL wavelength demodulation technology adopts an intermittent switching mode to switch from standby to detection mode. This intermittent switching mode includes, but is not limited to, the following three methods:

[0052] (1) The first optional intermittent switching working mode is as follows:

[0053] The MCU module in the low-power wireless fiber Bragg grating demodulator of the detection system periodically switches the detection system from standby mode to detection mode at preset time intervals. After completing detection, on-site display, and data upload, the detection system automatically switches back to standby mode. The preset time is a periodic time; the time period for the detection system to wake up the low-power wireless fiber Bragg grating demodulator can be set to once every 10 minutes. The wake-up time period can be adjusted according to the rate of change of the measured data. For example, when the data change rate is large, the wake-up time period can be reduced to once every 1 minute.

[0054] Taking the preset function of waking up the low-power wireless fiber Bragg grating demodulator every 10 minutes for detection as an example, the intermittent switching operation process of the detection system is described as follows:

[0055] Before being woken up, the low-power wireless fiber Bragg grating demodulator and the fiber Bragg grating top plate status detection sensor module are in standby mode, consuming very little power. The MCU module of the low-power wireless fiber Bragg grating demodulator wakes up the detection system every 10 minutes according to a preset schedule. When the detection system receives a wake-up command, the MCU module first starts the low-power VCSEL fiber Bragg grating wavelength demodulation module and measures the sensing grating wavelengths in the passive fiber Bragg grating top plate delamination sensing probe and the passive fiber Bragg grating anchor stress sensing probe, respectively. It calculates the corresponding anchor stress value and the relative and absolute change values ​​of the top plate delamination displacement, and displays the detected values ​​through the audible and visual alarm on-site display module. Subsequently, the detection system shuts down the low-power VCSEL fiber Bragg grating wavelength demodulation module and then starts the wireless transceiver module to send the measured anchor stress value and the relative and absolute change values ​​of the top plate delamination displacement to the wireless base station. The wireless base station then transmits the detected data to the control center through the underground ring network. Finally, the wireless transceiver module enters standby mode after transmission is completed.

[0056] If the detected value is about to exceed the limit or exceeds the limit, the audible and visual alarm display module will display and issue a warning signal (yellow light) or an alarm signal (red light) on-site. Then, the wireless transceiver module will be activated to send the measured anchor bolt stress value, the relative and absolute change value of the roof delamination displacement, and the warning signal or alarm signal data to the wireless base station. The wireless base station will then transmit the detected data to the control center through the underground ring network. The warning signal or alarm signal can only be deactivated after intervention in the control room.

[0057] In this embodiment, the power module uses a 7AH dry cell battery; the wireless base station sends a command to wake up the system every 10 minutes; the low-power VCSEL fiber grating demodulation module completes the monitoring of the top plate status detection value and data upload every 5 seconds, displays the measured data for 30 seconds on site, and then shuts down; under this working condition, the battery can support the entire detection system to work for at least 6 months.

[0058] (2) The second optional command wake-up working mode is as follows:

[0059] Before being activated, the low-power wireless fiber Bragg grating demodulator and the fiber Bragg grating roof condition detection sensor module are in standby mode, consuming very little power. When the surface control room issues a detection command via the ring network and wireless base station, the wireless transceiver module in the low-power wireless fiber Bragg grating demodulator receives a command from the wireless base station to read and query the roof condition detection data. The detection system then switches from standby mode to detection mode. The activation process is as follows: The MCU module first starts the VCSEL fiber Bragg grating wavelength demodulation module, which begins to measure the wavelengths of the sensing gratings in the passive fiber Bragg grating anchor stress sensing probe and the passive fiber Bragg grating roof delamination sensing probe, respectively. Then, it calculates the corresponding anchor stress value and the relative and absolute changes in roof delamination displacement data. The detected values ​​are then displayed on-site via the audible and visual alarm display module. Subsequently, the VCSEL fiber Bragg grating wavelength demodulation module is turned off, and the wireless transceiver module is activated to send the detected anchor stress value and the relative and absolute changes in roof delamination displacement data to the wireless base station. The wireless base station then transmits the detected data to the control center via the underground ring network. The wireless transceiver module automatically enters standby mode after sending data.

[0060] When the detected value is about to exceed the limit and exceeds the limit, a warning (yellow light) and an alarm (red light) are issued respectively; the wireless transceiver module is activated to send the measured anchor bolt stress value, the relative and absolute change value of the roof delamination displacement, and the warning or alarm signal data to the wireless base station. The wireless base station then transmits the detected data to the control center through the underground ring network; the warning or alarm signal can only be deactivated after intervention in the control room.

[0061] (3) The third optional mine lamp wake-up working mode is as follows:

[0062] When a miner's lamp shines on the photoelectric sensor module in the low-power wireless fiber Bragg grating demodulator, the MCU module wakes up the VCSEL fiber Bragg grating wavelength demodulation module, switching from standby to detection mode. The wake-up process is as follows: The MCU module first starts the VCSEL fiber Bragg grating wavelength demodulation module and measures the sensing grating wavelengths in the passive fiber Bragg grating roof delamination sensing probe and the passive fiber Bragg grating anchor stress sensing probe, respectively, calculating the corresponding anchor stress value and the relative and absolute changes in roof delamination displacement. The detected values ​​are then displayed on-site via the audible and visual alarm display module. Subsequently, the VCSEL fiber Bragg grating wavelength demodulation module is shut down, and the wireless transceiver module starts transmitting the detected anchor stress value and the relative and absolute changes in roof delamination displacement data to the wireless base station. The wireless base station then transmits the detected data to the control center via the underground ring network. After transmission is complete, the wireless transceiver module automatically switches back to standby mode.

[0063] When the detected value is about to exceed the limit and exceeds the limit, a warning (yellow light) and an alarm (red light) are issued respectively; the wireless transceiver module is activated to send the measured anchor bolt stress value, the relative and absolute change value of the roof delamination displacement, and the warning or alarm signal data to the wireless base station. The wireless base station then transmits the detected data to the control center through the underground ring network; the warning or alarm signal can only be deactivated after intervention in the control room.

[0064] Among the three intermittent switching operating modes mentioned above, the low-power VCSEL fiber grating demodulation module does not require a laser semiconductor cooling chip (TEC) and a temperature control module, thus overcoming the technical bottleneck of high power consumption in existing fiber optic roof condition detection systems and fully leveraging the outstanding advantages of VCSEL fiber grating demodulation technology, such as low power consumption and low cost. The fiber optic roof condition detection system adopts an intermittent switching operating mode, reducing system operating power consumption and improving the flexibility of the system to query roof condition information at any time. The fiber optic roof condition detection system uses a time-sharing approach for the roof condition detection process and the wireless transmission process, further reducing system power consumption and meeting the needs of wireless roof condition detection in coal mines.

[0065] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation, characterized in that, It includes a low-power wireless fiber Bragg grating demodulator, a fiber Bragg grating roof condition detection sensor module, and a wireless base station; the total power consumption of the low-power coal mine wireless roof condition detection system excluding the wireless base station is less than 500mW. The low-power wireless fiber Bragg grating demodulator includes a low-power VCSEL fiber Bragg grating wavelength demodulation module, an MCU module, a wireless transceiver module, an audible and visual alarm display module, a photoelectric sensor module, a temperature and pressure detection module, and a power supply module. The MCU module is electrically connected to the low-power VCSEL fiber Bragg grating wavelength demodulation module, the wireless transceiver module, the audible and visual alarm display module, the photoelectric sensor module, the temperature and pressure detection module, and the power supply module. The low-power VCSEL fiber Bragg grating wavelength demodulation module is connected to the fiber Bragg grating top plate status detection sensor module via optical fiber or optical cable. The power supply module is used to power the low-power wireless fiber Bragg grating demodulator. The low-power VCSEL fiber grating wavelength demodulation module includes a VCSEL laser, a current drive circuit, an optical fiber splitter, a photoelectric signal detector, an amplifier circuit, and a data acquisition circuit. The power consumption of the low-power VCSEL fiber grating wavelength demodulation module is less than 100mW; In the low-power VCSEL fiber grating wavelength demodulation module, the current driving circuit generates a sawtooth wave scanning driving current and drives the VCSEL laser to emit a beam whose scanning wavelength increases with the increase of current. This beam is coupled into the fiber. In each cycle of the periodic sawtooth wave scanning driving current, the range of change of the laser wavelength from short to long is a wavelength scanning range. The range of scanning wavelengths covers the center wavelength of the fiber grating in the fiber grating top plate status detection sensing module. The light beam coupled in the optical fiber is split into 2+N output optical paths by an optical fiber splitter, where N≥1. One path is used to detect the stable state of the light source power; another path passes through a reference gas cell for system spectral self-calibration and standardization; the remaining N paths are transmitted to sensing fiber gratings respectively; each or / and two fiber gratings form a sensing unit, which is respectively set in the passive fiber grating anchor stress sensing probe or / and the passive fiber grating top plate delamination sensing probe; After being modulated and reflected by N fiber gratings, the signal enters the photoelectric signal detector and is converted into an electrical signal; then the signal is amplified by the amplifier circuit and converted into a digital signal by the acquisition circuit; the MCU module demodulates the reflected wavelength and wavelength change of the fiber grating based on the acquired digital signal and the ambient temperature and pressure values ​​of the temperature and pressure module, and calculates the anchor stress value and the relative and absolute changes of the top plate delamination displacement based on the pre-calibrated relationship curves of the sensing fiber grating wavelength with stress or displacement and the relationship curves of wavelength with temperature. The MCU module in the low-power wireless fiber Bragg grating demodulator is connected to the wireless transceiver module. The wireless transceiver module receives commands to read and query roof status detection data from the underground wireless base station and sends roof status detection data to the underground wireless base station. The data is then transmitted to the surface dispatch room via the underground ring network.

2. The low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation as described in claim 1, characterized in that, The fiber Bragg grating top plate condition detection sensing module includes a passive fiber Bragg grating top plate delamination sensing probe and a passive fiber Bragg grating anchor stress sensing probe; the passive fiber Bragg grating top plate delamination sensing probe is used to detect the delamination values ​​at deep and shallow base points; the passive fiber Bragg grating anchor stress sensing probe is used to detect the anchor stress value.

3. The low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation as described in claim 1, characterized in that, The VCSEL laser has a wavelength / current coefficient of 0.4 nm / mA and a wavelength / temperature coefficient of 0.11 nm / ℃. By injecting a driving current of 4 mA-16 mA, an effective wavelength scanning range of 2 nm can be achieved within the range of 10-40℃, which meets the wavelength detection range of the coal mine roof condition detection sensor.

4. A low-power wireless roof condition detection method for coal mines based on VCSEL wavelength demodulation, characterized in that, The detection is performed using the low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation as described in any one of claims 1-3; The low-power wireless roof detection system for coal mines based on VCSEL wavelength demodulation adopts an intermittent switching from standby to detection mode. The intermittent switching mode includes: (1) the MCU module in the low-power wireless fiber optic grating demodulator switches the detection system from standby to detection mode at preset time intervals. After the detection system completes detection, on-site display and uploading of measured data, it automatically switches back to standby mode; (2) when the dispatch room above ground issues a detection command through the ring network and wireless base station, the wireless transceiver module in the low-power wireless fiber optic grating demodulator receives the command to read and query the roof status detection data from the wireless base station. The detection system switches from standby to detection mode. After the detection system completes detection, on-site display and uploading of measured data, it automatically switches back to standby mode; (3) when the miner's lamp shines on the photoelectric sensor module in the low-power wireless fiber optic grating demodulator, the detection system switches from standby to detection mode. After the detection system completes detection, on-site display and uploading of measured data, it automatically switches back to standby mode.

5. The low-power wireless roof status detection method for coal mines based on VCSEL wavelength demodulation as described in claim 4, characterized in that, When the detection system receives a wake-up command and switches from standby to detection mode, it first activates the low-power VCSEL fiber grating wavelength demodulation module. The passive fiber grating roof delamination sensing probe and the passive fiber grating anchor stress sensing probe then collect data on the relative and absolute changes in anchor stress and roof delamination displacement. The detected values ​​are displayed via an audible and visual alarm display module. If the detected values ​​are about to exceed limits or have already exceeded limits, the audible and visual alarm display module issues a warning signal or an alarm signal. Subsequently, the detection system shuts down the low-power VCSEL fiber grating wavelength demodulation module. Then, the on-site display and the activation of the wireless transceiver module transmit the measured anchor stress and relative and absolute changes in roof delamination displacement data to the wireless base station. The wireless base station then transmits the detected data to the control center via the underground ring network. After transmission, the wireless transceiver module enters standby mode. The warning signal or alarm signal can only be deactivated after intervention in the control room.

6. The low-power wireless roof status detection method for coal mines based on VCSEL wavelength demodulation as described in claim 4, characterized in that, The time period for the detection system to wake up the low-power wireless fiber Bragg grating demodulator can be set and adjusted according to actual needs in order to complete the operation mode of periodically waking up the demodulator for detection.

7. The low-power wireless roof status detection method for coal mines based on VCSEL wavelength demodulation as described in claim 4, characterized in that, The power module uses a 7AH dry cell battery. When the wireless base station sends a wake-up command every 10 minutes, the VCSEL fiber optic grating demodulation module completes the detection of the top plate status within 5 seconds, displays the data on-site for 30 seconds and uploads the measured data, and then automatically switches to standby mode.

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