Bolt axial force monitoring device and monitoring method

Abstract

To provide a bolt axial force monitoring device and a monitoring method capable of detecting looseness of a bolt at a position away from a fastening part of the bolt with a simple structure.SOLUTION: The bolt axial force monitoring device includes a bolt 1 for displaying a change in axial force of the bolt 1 as a change in color on a display part 2 provided on a part of the bolt 1, a sensor part (for example, an RGB sensor 4) for detecting the change in color displayed on the display part 2, a first communication part 51 for transmitting axial force change data detected by the sensor part to a position separated from a fastening part, a power source 6 for the sensor part and the first communication part 51, a second communication part 52 provided on a position separated from the fastening part for receiving the axial force change data from the first communication part 51, a determination part 10 for determining the axial force change of the bolt 1 based on the axial force change data received by the second communication part 52, and an output part (for example, a display 11 and a storage part 12) for outputting information of the axial force change of the bolt 1 determined by the determination part 10.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a bolt axial force monitoring device and a monitoring method that are capable of detecting loosening of a bolt at a position away from the fastening point of the bolt. [Background technology]

[0002] In recent years, inspection of the tightening condition of bolts has become important from the perspective of long-term equipment maintenance. Traditionally, bolts are tightened using a torque wrench or other tool to input a specified torque value. However, the required axial force of the screw is very unstable due to friction between the screw and the bearing surface, and different axial forces are applied to each individual bolt.

[0003] For example, methods for measuring axial force that use strain gauges (including load cells), as shown in Patent Documents 1 and 2, are used for occasional measurements such as for determining basic conditions and for basic research. Furthermore, the ultrasonic method shown in Patent Document 3 involves preparing a specially processed bolt, such as by polishing the top and bottom of the threads to be parallel, attaching a sensor to the bolt head, and detecting the axial force through the response to ultrasonic waves. Ultrasonic methods are generally only suitable for standalone measurements, and can only be used, for example, for initial fastening of flange structures that are subject to external forces, or during annual inspections. Furthermore, they cannot be used on bus bars or other devices that generate electricity due to electrical noise. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2023-003388 [Patent Document 2] Japanese Patent Application Publication No. 11-118637 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-216804 Summary of the Invention [Problem to be solved by the invention]

[0005] The devices described in these prior art techniques all require many electronic components to be attached to the bolts, and are complex in structure. This type of monitoring device must be installed at fastening points where loosening of the bolts could lead to a major accident, or at high altitudes or in narrow spaces where maintenance is difficult, and must periodically monitor the axial tension of the bolts to detect loosening. Therefore, it is desirable for this type of monitoring device to have a simple structure, high detection accuracy, and low power consumption required for detecting axial tension and transmitting data to a monitoring location away from the fastening point of the bolts.

[0006] In order to solve the above-mentioned problems, an object of the present invention is to provide a bolt axial force monitoring device and monitoring method that have a simple structure and are capable of detecting bolt loosening at a position away from the bolt fastening point. [Means for solving the problem]

[0007] The bolt axial force monitoring device of the present invention has the following configuration. (1) A bolt that displays changes in the axial force of a bolt in a fastened state as a change in color on a display unit provided in a part of the bolt. (2) A sensor unit that detects a change in the color displayed on the display unit of the bolt. (3) A first communication unit that transmits data on changes in axial force detected by the sensor unit to a location away from the fastening point of the bolt. (4) A power source for the sensor unit and the communication unit. (5) A second communication unit provided at a position away from the fastening point of the bolt, for receiving data on changes in axial force from the communication unit. (6) A determination unit that determines a change in the axial force of the bolt based on the axial force change data received by the communication unit. (7) An output unit that outputs information about the change in axial force of the bolt determined by the determination unit.

[0008] The bolt axial force monitoring device of the present invention may have the following configuration. (1) The sensor unit includes an RGB sensor. (2) The sensor unit, the communication unit, and the power supply are housed in a single housing, and the housing is fixed to the bolt and / or the fastening point of the bolt so as to cover the bolt head. (3) A timer is provided to control the operation of the sensor, and the sensor is activated only when the axial force is being monitored, and data on changes in the axial force is transmitted. (4) A plurality of the bolts are provided at the fastening location, and the sensor unit, the first communication unit, and the power supply are attached to each of the plurality of bolts; The judgment unit compares the pattern of axial force change data received from the plurality of bolts with the pattern of axial force change data of the plurality of bolts stored in advance in a memory unit, and judges whether or not the fastening state of the fastening points using the plurality of bolts is acceptable. (5) The sensor unit is a camera that captures the color displayed on the display unit of the bolt.

[0009] The bolt axial tension monitoring method of the present invention includes the following steps. (1) A step of attaching a sensor unit to a bolt that displays a change in axial force of a bolt in a fastened state as a change in color on a display unit provided on a part of the bolt, and that detects a change in color displayed on the display unit of the bolt. (2) A step of transmitting data on the change in axial force detected by the sensor unit to a position away from the fastening point of the bolt. (3) receiving data on changes in axial force at a position away from the fastening point of the bolt; (4) A step of determining a change in the axial force of the bolt based on the received data on the change in axial force. (5) A step of outputting information on the change in axial force of the bolt determined in the determining step. [Effects of the Invention]

[0010] According to the present invention, looseness of a bolt can be detected at a position away from the fastening point of the bolt with a simple structure. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view showing an example of a bolt according to the first embodiment. [Figure 2] FIG. 3 is a functional block diagram showing a detection unit provided in the first embodiment. [Figure 3] FIG. 2 is a cross-sectional view schematically showing the structure of the detection unit according to the first embodiment. [Figure 4] 1 is a block diagram showing the overall configuration of a bolt axial force monitoring device according to a first embodiment. [Figure 5] FIG. 10 is a block diagram showing a bolt axial force monitoring device according to a second embodiment. [Figure 6] FIG. 10 is a block diagram showing a bolt axial force monitoring device according to a third embodiment. [Figure 7] FIG. 10 is a cross-sectional view showing another embodiment of the detection unit of the present invention. [Figure 8] FIG. 10 is a cross-sectional view showing still another embodiment of the detection unit of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] [1. First embodiment] [1-1. Configuration of the first embodiment] [1-1-1. Bolt attachment part] As shown in Figure 1, the bolt axial force monitoring device of this embodiment can use, as a monitored object, a bolt 1 in a tightened state that shows changes in axial force as a color change in a window-type display unit 2 provided in a part of the bolt 1. As an example, this bolt 1 can be a well-known bolt 1 provided by the applicant, called the DTI System (registered trademark) or SmartBolt (registered trademark), which changes color in response to changes in axial force.

[0013] As shown in Figure 1, this bolt 1 uses an indicator embedded inside it that changes color on the display 2 according to the axial force of the bolt 1. Specifically, as the axial force changes, the color changes from red in Figure 1(a), which indicates a state where the axial force is zero, to black in Figure 1(c), which indicates a state where the appropriate axial force has been obtained, as the axial force increases, allowing the tightening state to be visually confirmed. This makes it easy to determine whether the bolt 1 is loose or overtightened, contributing to more efficient maintenance and improved safety.

[0014] The bolt 1 of the present invention is not limited to the SmartBolt (registered trademark) provided by the applicant, and other bolts 1 can be used as long as they have an indicator 2 that changes color depending on the axial force. For example, bolts 1 described in U.S. Patent Nos. 3,987,699, 490,413, 7,958,614, U.S. Patent Publication No. 20090092457, etc. can be used.

[0015] As shown in FIG. 3 , in the bolt axial tension monitoring device of this embodiment, a detection unit U is detachably attached to the head of the bolt 1 to detect a change in color of the display unit 2 of the bolt 1 shown in FIG. 1 . The detection unit U includes a waterproof housing 3, and each of the components according to this embodiment is housed within this housing 3. The housing 3 can be equipped with multiple attachment means to easily and securely attach the detection unit U to the head of the bolt 1. For example, the housing 3 can be equipped with a fitting portion formed to match the shape of the head of the bolt 1, a strong magnet such as a neodymium magnet, or even a fixing structure using screws attached to the bottom of the housing 3. Furthermore, depending on the structure of the installation location, it is also possible to form a flange on the bottom of the housing 3 and screw the flange to the surface of the structure F to fix the housing 3 so that it covers the head of the bolt 1.

[0016] This configuration allows the detection unit U to be stably attached even when the size and shape of the bolt 1, installation location restrictions, or environments with vibration or impact are present. Furthermore, the detection unit U is detachable, facilitating on-site maintenance, inspection, and replacement, contributing to improved work efficiency and a longer lifespan for the device. Additionally, the housing 3 is designed to cover the head of the bolt 1, preventing direct sunlight and dust from entering the display unit 2, ensuring the visibility of the display unit 2 and improving the stability of detection accuracy. The material and shape of the housing 3 can be selected or processed as needed depending on the on-site environment (indoors / outdoors, humidity, temperature, etc.), and can be designed to meet required performance requirements such as light-blocking, waterproofing, dustproofing, and heat resistance.

[0017] 2 and 3, the housing 3 of the detection unit U contains a sensor unit that detects changes in the color displayed on the display unit 2 of the bolt 1, a first communication unit 51 that transmits data on changes in axial force detected by the sensor unit to a location away from the fastening point of the bolt 1, and a power supply 6 for the sensor unit and first communication unit 51. Furthermore, if the color change in the display unit 2 cannot be confirmed with natural light alone, such as when the material of the housing 3 is opaque, when the bolt 1 to be monitored is installed indoors, or when monitoring is required at night, it is preferable to provide an LED 7 inside the housing 3 as a light-emitting unit for confirming the color of the display unit 2.

[0018] In this embodiment, an RGB sensor 4 is used as the sensor unit. The RGB sensor 4 detects the three basic colors of red, green, and blue to identify the color of an object. The RGB sensor 4 measures the intensity of these basic colors and combines them to reproduce a wide range of colors. Typically, an LED 7 is used to illuminate the display unit 2 of the bolt 1, and the reflected light is detected by the RGB sensor 4. This allows the RGB sensor 4 to recognize the color displayed on the display unit 2.

[0019] In addition to the RGB sensor 4, the following can be used as the sensor section, but the RGB sensor 4 is preferred, especially when monitoring small diameter bolts 1 or a large number of bolts 1, as it has a simple configuration and can be made compact. (1) CMOS sensor CMOS (Complementary Metal-Oxide-Semiconductor) sensors detect color by placing an RGB filter on each pixel. (2) CCD sensor It detects color using a CCD (Charge-Coupled LED7 Device) RGB filter, and is characterized by high sensitivity and low noise. (3) Spectral sensor To obtain more detailed color information, light of multiple wavelengths is detected. (4) Photodiode array Multiple photodiodes are arranged, each with a different color filter attached, to detect color.

[0020] Short-range wireless communication technology such as Bluetooth (registered trademark) can be used for the first communication unit 51 and the second communication unit 52 (described later). Bluetooth has low power consumption and is suitable for battery operation, and Bluetooth Low Energy (BLE) in particular is extremely energy-efficient. Its communication range is approximately 10 to 100 meters, and it can connect multiple devices simultaneously, making it suitable for monitoring multiple bolts 1 simultaneously. Furthermore, it has data encryption and device authentication functions, providing high security. Therefore, it is suitable for arranging the second communication unit 52, determination unit 10, memory unit 12, etc., which are installed outside the fastening point, in a variety of devices such as smartphones, tablets, PCs, and smartwatches.

[0021] The first communication unit 51 can also be other power-saving wireless communication types such as those described below, or wired communication using a signal line. Note that, in Figures 4 to 6, signal lines are shown to clarify the connection between the first communication unit 51 and the second communication unit 52, but this does not mean that communication in the present invention is limited to wired communication. (1) 2.4GHz RF (Radio Frequency) (2) Wi-Fi (2.4GHz or 5GHz) (3) Zigbee (registered trademark) (4) Z-Wave (registered trademark) (5) LoRa (Long Range) (registered trademark) (6) ANT+ (registered trademark) (7) NFC (Near Field Communication) (registered trademark)

[0022] In this embodiment, a button battery, dry cell battery, lithium ion battery, or rechargeable battery equipped with a solar panel built into the housing 3 can be used as the power source 6 for the sensor unit, the LED 7, and the first communication unit 51. Note that in the case of wired communication, instead of a battery, it is also possible to use a power supply line together with a signal line.

[0023] A timer 8 that manages the operation of the RGB sensor 4 is provided inside the housing 3. This timer 8 turns on the power supply 6 to the RGB sensor 4, LED 7, and communication unit 5 only when monitoring the axial force. In other words, the power consumption of the timer 8 alone is significantly smaller than that of other devices, so by turning on the power supply 6 to each device at regular intervals set in the timer 8, the axial force of the bolt 1 can be monitored periodically and over a long period of time with little power.

[0024] [1-1-2. Location away from fastening point] As shown in Figure 4, a server 9 that monitors changes in the axial force of the bolt 1 is provided at a position away from the fastening point of the bolt 1. This server 9 is equipped with a second communication unit 52 that receives axial force change data from a first communication unit 51 provided inside the housing 3 on the bolt 1 side, a determination unit 10 that determines the change in the axial force of the bolt 1 based on the axial force change data received by the second communication unit 52, and an output unit that outputs information on the change in the axial force of the bolt 1 determined by the determination unit 10. The determination unit 10 determines the change in the axial force from the received change data itself or by performing a predetermined calculation on the change data.

[0025] If necessary, the server 9 may be provided with an input unit 13 such as a keyboard or touch panel for receiving commands from the user. If the interface with the user is provided only in a terminal 14 (described later), the server 9 may be provided with only a second communication unit 52 and a determination unit 10.

[0026] The second communication unit 52 receives data from the first communication unit 51 provided inside the housing 3, and has a function corresponding to the type of the first communication unit 51. The determination unit 10 detects data relating to a change in color shown on the display unit 2 detected by the RGB sensor 4, for example, a change from black, which indicates an appropriate fastening force, to red, which indicates loosening, and determines that loosening has occurred in the monitored bolt 1. The output unit includes a memory unit 12 that stores the determination result and a display 11 that displays it.

[0027] A terminal 14 such as a personal computer or tablet is connected to the server 9 via a network N. Depending on the monitoring content desired by the user, the terminal 14 is provided with a display means such as a display 11 or a printer, a memory unit 12 for storing the judgment results, and an output unit for the judgment results such as an alarm device.

[0028] It is also possible to send data from the first communication unit 51 directly to a terminal 14 such as a personal computer or a tablet, instead of the server 9 connected to the network N. In that case, the terminal 14 is provided with a second communication unit 52, a determination unit 10, an output unit, etc.

[0029] [1-2. Operation of the First Embodiment] In this embodiment, when a bolt is fastened to a structure F, if the bolt 1 is tightened with an appropriate axial force, a color (e.g., black) indicating the appropriate axial force is displayed on the display unit 2 according to the axial force applied to the bolt 1.

[0030] To monitor the axial force of the bolt 1 fastened to the structure F in this way, a housing 3 with a built-in sensor unit and the like is attached to the head of the bolt 1 in a fastened state. The monitoring device of this embodiment has a built-in timer 8, so when a preset monitoring time arrives, the timer 8 turns on the power supply 6 to devices such as the RGB sensor 4, LED 7, and first communication unit 51 inside the housing 3. The LED 7 then illuminates the display unit 2, and the reflected light reaches the RGB sensor 4, which then detects the color shown on the display unit 2.

[0031] Data relating to the color detected by the RGB sensor 4 is transmitted to the server 9 via the first communication unit 51 and the network N, and a determination unit 10 in the server 9 determines whether the color indicates that the axial force applied to the bolt 1 is normal (for example, black), or whether the color indicates that the axial force has decreased and the tightening torque of the bolt 1 is insufficient (for example, red). The determination unit 10 outputs this determination result to an output unit such as a display 11 or memory unit 12 provided therein, and also transmits it via the network N to a terminal 14 connected to the server 9. Note that if only the determination unit 10 is provided in the server 9, the server 9 does not output the determination result itself, but transmits only the determination result to the terminal 14.

[0032] The terminal 14 that receives the judgment result outputs the judgment result to its own output unit such as display 11 or memory unit 12, and the user can read this judgment result to know whether the bolt 1 being monitored is tightened with an appropriate axial force.

[0033] [1-3. Effects of the First Embodiment] The effects of the monitoring device of this embodiment are as follows.

[0034] (1) By using a bolt 1 that displays changes in axial force with color and detecting the color change with an RGB sensor 4, loosening of the bolt 1 can be detected more accurately and easily than conventional technologies that use ultrasonic sensors, etc.

[0035] (2) The detection results of the RGB sensor 4 are transmitted wirelessly or by wire to a server 9 or terminal 14 installed at a location away from the fastening point of the bolt 1, so there is no need for the user to go to the fastening point of the bolt 1 to inspect the axial force of each bolt 1. Therefore, it is easy to monitor bolts 1 installed at high places or in narrow places.

[0036] (3) Because the RGB sensor 4, LED 7, power supply 6, and other devices that detect color changes are housed within a single housing 3, color changes in the monitored bolt 1 can be detected simply by attaching the housing 3 to the head of the bolt 1. This makes it significantly easier to install monitoring equipment on the bolt 1 than with conventional technology. In addition, by fixing the housing 3 to the head of the bolt 1 or the fastening point by means of screws or other means, the housing 3 will not fall off the bolt 1.

[0037] (4) By covering the head of the bolt 1 with the housing 3, corrosion resistance and heat resistance (prevention of thermal changes) are achieved, and disturbances such as sunlight can be prevented when detecting color changes in the display unit 2 using a light source such as an LED 7.

[0038] (5) By incorporating a timer 8 into the housing 3, the timer 8 can manage the activation of the RGB sensor 4, LED 7, etc. that detect changes, and by activating each device only when measurement is required, extreme power saving is possible, making it possible to continue monitoring for a long period of time such that the bolt 1 may loosen.

[0039] [2. Second Embodiment] 5 shows a second embodiment of the present invention. In the second embodiment, when a plurality of bolts 1 are installed in a fastening location having a certain range, a detection unit U with a built-in sensor is installed in each of the plurality of bolts 1.

[0040] Generally, in bridge piers, wind power generator frames, and other buildings, large structural members F are fastened together with a large number of bolts 1, but these bolts 1 do not loosen at the same time. Furthermore, the standard for determining whether a decrease in the fastening strength between structural members F exceeds the allowable range varies depending on the position and number of bolts 1 that have loosened among the multiple bolts 1. Therefore, in the second embodiment, a detection unit U containing various devices such as sensors is attached to each of the multiple bolts 1, and color change data from the multiple bolts 1 is transmitted to a server 9 or a determination unit 10 of a terminal 14.

[0041] On the other hand, the server 9 and the terminal 14 are provided with a memory unit 12 for storing data that serves as the judgment criteria, and data regarding the position of each bolt 1 at the fastening point of the structure F, the required axial force, and even data regarding the pattern of bolts 1 that have loosened, which serves as the criteria for issuing an alarm, are stored in advance.

[0042] In the second embodiment, the judgment unit 10 not only detects looseness of each bolt 1, but also compares the pattern of axial force change data received from the plurality of bolts 1 with the pattern of axial force change data of the plurality of bolts 1 stored in advance in the memory unit 12 to judge whether the fastening state of the fastening point using the plurality of bolts 1 is acceptable. As a result, the user can monitor not only the status of the individual bolts 1 provided at the fastening point, but also the joint strength of the entire structure F, allowing for easy and accurate maintenance management of the structure F.

[0043] In particular, in the second embodiment, by assigning a unique ID to the detection unit U attached to each bolt 1, it becomes possible to show detailed location information of the bolt 1 that has loosened on the display. Furthermore, when loosening is detected, an LED provided in the detection unit U can be illuminated, making it easy to find the bolt 1 in question even at an actual construction site. In this way, when this embodiment is applied to a large number of bolts 1, it becomes possible for a worker to easily find the location of a detected "loose bolt" at a site where bolts 1 are being tightened.

[0044] 3. Third Embodiment The third embodiment shown in Figure 6 uses a camera as the sensor provided in the detection unit U. The camera can detect color changes in the display 2 of a single bolt 1, like the RGB sensor 4 in the first embodiment, but in the third embodiment, the camera is placed in a location where it can simultaneously photograph multiple bolts 1, so that the color changes in the displays of multiple bolts 1 are simultaneously photographed by a single camera.

[0045] As in the second embodiment, the judgment unit 10 of the third embodiment compares patterns of axial force change data of multiple bolts 1 stored in advance in the memory unit 12 to judge whether the fastening state of the fastening points using multiple bolts 1 is acceptable or not.

[0046] The third embodiment having such a configuration has the advantage of facilitating installation of the monitoring device, since multiple bolts 1 can be monitored with one camera without attaching a detection unit U to each individual bolt 1. Furthermore, by capturing the color changes of multiple bolts 1 as a pattern as in the second embodiment, it becomes possible to monitor the joint strength of the entire structure F, allowing for easy and accurate maintenance and management of the structure F.

[0047] 4. Other Embodiments The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining the multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, the following embodiments are also included in the present invention.

[0048] (1) As the sensor unit, various types of sensors that can detect color changes can be used in addition to the RGB sensor and camera described in the embodiment. For example, color sensors based on the L*a*b* color system or the XYZ color system can also be used.

[0049] (2) When multiple bolts are monitored simultaneously, as in the second and third embodiments, it is possible to vary the content and strength of the warning given to the user depending on the number and position of the bolts that have changed color and the pattern. For example, it is possible to issue a warning even if only one bolt is detected, or to issue a warning only when a specific pattern change occurs.

[0050] (3) When detecting the axial force of multiple bolts, multiple sensors that detect color changes of multiple bolts can be built into one housing. If the positions and spacing of multiple bolts are known in advance, the configuration can be simplified by sharing the housing, power supply, LED, etc. for multiple bolts.

[0051] (4) If the housing is made transparent or a light window is provided so that natural light or light from surrounding lighting can be irradiated onto the display unit 2 of the bolt 1, it is not necessary to provide a lighting means such as an LED.

[0052] (5) The structure shown in FIG. 7 can be used to secure the detection unit to the bolt. That is, in FIG. 7, housing 3 of the detection unit is made of a cylindrical member, and the components constituting the detection unit, as shown in FIG. 2, are housed inside in a sealed state. A male thread 3a is provided on the outer periphery of the upper part of housing 3. A weather-resistant protective cap 20 is attached to the outer periphery of housing 3. A female thread 20a is provided on the inner periphery of protective cap 20, and by inserting housing 3 into protective cap 20 and rotating it, the male thread 3a and female thread 20a are screwed together, and housing 3 is secured to the inside of protective cap 20. The lower part of the protective cap 20 protrudes beyond the lower end of the housing 3, and a space is provided inside the lower part of the protective cap 20 to fit the head of the bolt 1. The lower edge of the protective cap 20 is located on the same plane as the underside of the head of the bolt 1.

[0053] A seal cap 21 made of a material such as rubber or flexible plastic is provided on the lower edge of the protective cap 20 and the underside of the head of the bolt 1. The seal cap 21 has a bolt insertion hole 21a in its center, and the shaft of the bolt 1 protruding from the center of the protective cap 20 is inserted into this insertion hole 21a. The seal cap 21 closes the gap between the protective cap 20 and the head of the bolt 1. The seal cap 21 also functions to seal the gap between the bolt 1 and the structure F tightened by the bolt 1, as well as the gap between the structure F and the protective cap 20. A female thread may be provided on the inner periphery of the insertion hole 21a of the seal cap 21. In this case, by screwing the seal cap 21 onto the shaft of the bolt 1, the seal cap 21 can be brought into close contact with the lower edge of the protective cap 20 and the underside of the head of the bolt 1. In this case, by providing a nut portion 21b integrally with the surface of the seal cap 21 opposite the head of the bolt 1 so as to surround the insertion hole 21a, the seal cap 21 can be easily rotated using a wrench.

[0054] The insertion hole 21b may be a simple through-hole without a female thread. In this case, by making the inner diameter of the insertion hole 21b equal to or slightly smaller than the shaft of the bolt 1, the shaft of the bolt 1 can be press-fitted into the insertion hole 21b while maintaining airtightness. The seal cap 21 and the protective cap 20 are preferably fixed together with an adhesive, which not only ensures that the seal cap 21 and the protective cap 20 are fixed together reliably, but also ensures that they are tightly sealed.

[0055] (6) The shape of the seal cap 21 shown in Fig. 8 can also be used. This seal cap 21 partially fits over the head of the bolt 1 and covers the entire bolt head. A flange 21c is provided at the bottom of the seal cap 21, and by using a flexible material such as rubber, it is possible to fill the gap between the bolt 1 and the structure F and seal it. [Explanation of symbols]

[0056] 1...Bolt 2...Display section 3. Housing 3a...male thread 4...RGB sensor 51...First Communications Department 52...Second Communications Department 6…Power supply 7...LED 8...Timer 9...Server 10…Judgment section 11...Display 12...Storage section 13...Input section 14...Terminal 15...Camera 20...Protective cap 20a...female thread 21...Seal cap 21a...insertion hole 21b...Nut part 21c...flange U: Detection unit N...Network F...Structure

Claims

1. a bolt that displays a change in axial force of the bolt in a fastened state as a change in color on a display unit provided in a part of the bolt; a sensor unit that detects a change in the color displayed on the display unit of the bolt; a first communication unit that transmits data on changes in axial force detected by the sensor unit to a position away from the fastening point of the bolt; a power source for the sensor unit and the first communication unit; a second communication unit provided at a position away from the fastening point of the bolt and configured to receive axial force change data from the first communication unit; a determination unit that determines a change in the axial tension of the bolt based on the axial tension change data received by the second communication unit; A bolt axial force monitoring device comprising an output unit that outputs information on the change in axial force of the bolt determined by the determination unit.

2. The bolt axial tension monitoring device according to claim 1 , wherein the sensor unit includes an RGB sensor.

3. 3. The bolt axial force monitoring device according to claim 2, wherein the sensor unit, the first communication unit, and the power supply are housed in a single housing, and the housing is fixed to the bolt and / or the fastening point of the bolt so as to cover the head of the bolt.

4. 4. A bolt axial force monitoring device according to claim 3, further comprising a timer for controlling the operation of said sensor unit, said sensor unit being activated only when monitoring the axial force and transmitting data on changes in the axial force.

5. a plurality of the bolts are provided at the fastening location, and the sensor unit, the first communication unit, and the power supply are attached to each of the plurality of bolts; 4. A bolt axial force monitoring device according to claim 1, wherein the determination unit compares a pattern of axial force change data received from the plurality of bolts with a pattern of axial force change data of the plurality of bolts stored in advance in a storage unit to determine whether or not the fastening state of the fastening points using the plurality of bolts is acceptable.

6. The bolt axial tension monitoring device according to any one of claims 1 to 4, wherein the sensor unit is a camera that photographs the color displayed on the display unit of the bolt.

7. The bolt axial tension monitoring device according to claim 5, wherein the sensor unit is a camera that photographs the color displayed on the display unit of the bolt.

8. a step of displaying a change in axial force of a bolt in a fastened state as a change in color on a display unit provided on a part of the bolt, and attaching a sensor unit to the bolt to detect the change in color displayed on the display unit of the bolt; a step of transmitting data on the change in axial force detected by the sensor unit to a position away from the fastening point of the bolt; receiving data on changes in the axial force at a position away from the fastening point of the bolt; A step of determining a change in the axial tension of the bolt based on the received data on the change in the axial tension; a step of outputting information on the change in axial force of the bolt determined in the determining step; A bolt axial force monitoring method comprising:

9. a housing that houses the sensor unit and the first communication unit; a protective cap covering the housing and the head of the bolt; a seal cap that encloses the head of the bolt and the protective cap and has an insertion hole for the shank of the bolt; 3. The bolt axial force monitoring device according to claim 1, further comprising:

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