Bolt Unit

Abstract

The present invention provides a bolt unit comprising: a bolt body portion having a threaded portion formed at one end and the other end connected to a bolt head portion; a nut portion screw-coupled to the threaded portion of the bolt body portion; a gauge pin installed inside the bolt body portion along the longitudinal direction of the bolt body portion; an elongation gap formed on the bolt head portion side inside the bolt body portion to provide a space in which the gauge pin can be extended; a sensing portion provided in the bolt head portion to detect displacement of the gauge pin within the elongation gap; a battery portion provided on the outside of the bolt head portion to supply power to the sensing portion; and a lamp portion provided in the battery portion to light up according to the degree of extension measured by the sensing portion.

Description

Technology Field

[0001] The present invention relates to a smart bolt unit capable of monitoring the fastening status of a bolt in real time and measuring the bolt load, and a bolt unit system including the same. More specifically, it relates to an intelligent bolt unit and a bolt unit system capable of accurately determining the fastening force by embedding a gauge pin and a sensing unit inside the bolt to measure the elongation of the bolt, and remotely monitoring via wireless communication. Background Technology

[0002] Bolt connections are the most basic and important fastening method across industries.

[0003] In particular, for large structures such as offshore wind power structures, bridges, plant facilities, aircraft, and railway vehicles, the fastening condition of bolts is directly linked to the overall safety of the structure. If bolts fail to maintain proper fastening force, structural loosening, increased vibration, and fatigue failure may occur, potentially leading to serious accidents.

[0004] Traditionally, methods used to verify bolt tightening force have included torque measurement using a torque wrench, tensile force measurement using a tensile tester, and ultrasonic testing. However, these methods have the following limitations.

[0005] First, the torque method is sensitive to changes in the coefficient of friction, which can result in a large discrepancy with the actual clamping force. Since about 90% of the torque is consumed by friction and only about 10% is converted into the actual clamping force, even a slight change in the coefficient of friction can cause a significant difference in the actual clamping force.

[0006] Furthermore, all existing measurement methods require skilled technicians to visit the site in person to install equipment and perform measurements. This leads to issues such as high labor costs, safety risks, and difficult access. Inspection costs and risks are particularly high when dealing with offshore structures or work at heights.

[0007] Furthermore, one-time measurements cannot continuously monitor changes in fastening force over time or loosening phenomena caused by vibration or temperature changes. There is a risk that abnormal conditions occurring between regular inspections may not be detected early, potentially leading to accidents.

[0008] Therefore, there is an urgent need to develop a smart bolt system that can determine fastening force with high accuracy by directly measuring the elongation of the bolt through the embedded sensor, monitor remotely in real time via wireless communication, operate for a long period without battery replacement, and is easy to install and maintain. Prior art literature

[0009] Registered Patent No. 10-1670358 The problem to be solved

[0010] The present invention is an invention devised to solve the problems of the aforementioned prior art, and aims to provide a smart bolt unit capable of determining accurate fastening force by directly measuring the elongation of the bolt by embedding a gauge pin and a high-precision displacement sensor inside the bolt.

[0011] In addition, the present invention aims to provide a bolt unit that enables long-distance wireless data transmission by utilizing wireless communication technology and allows the fastening status to be checked immediately on-site through an LED indicator.

[0012] In addition, the present invention aims to provide a bolt unit system capable of managing multiple bolt units in an integrated manner and rapidly identifying bolts that have problems.

[0013] The problems of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0014] To achieve the above-mentioned objective, the present invention provides a bolt unit comprising: a bolt body portion having a threaded portion formed at one end and the other end connected to a bolt head portion; a nut portion screw-coupled to the threaded portion of the bolt body portion; a gauge pin installed inside the bolt body portion along the longitudinal direction of the bolt body portion; an elongation gap formed on the bolt head portion side inside the bolt body portion to provide a space in which the gauge pin can be extended; a sensing portion provided on the bolt head portion to detect displacement of the gauge pin within the elongation gap; a battery portion provided on the outside of the bolt head portion to supply power to the sensing portion; and a lamp portion provided on the battery portion to light up according to the degree of elongation measured by the sensing portion.

[0015] Here, the sensing unit is configured in a linear variable differential transformer (LVDT) manner and can detect displacement in micrometer units.

[0016] Meanwhile, the present invention provides a bolt unit system comprising: a plurality of bolt units; a thermal imaging camera unit for photographing the bolt units; a second control unit for detecting abnormal bolts by analyzing a thermal image received from the thermal imaging camera unit; and a communication unit connected to the second control unit for transmitting measurement data and analysis results to a cloud server. Effects of the invention

[0017] The bolt unit and bolt unit system according to one embodiment of the present invention configured as described above provide the following effects.

[0018] First, by embedding a gauge pin and a high-precision sensing unit inside the bolt to directly measure the actual elongation of the bolt, it has the effect of enabling much more accurate measurement of fastening force compared to the torque method.

[0019] Second, the LED lamp unit allows for immediate visual inspection of the bolt tightening status on-site, enabling rapid verification without the need for separate measuring equipment or power supply units.

[0020] Third, by utilizing wireless communication technology, long-distance data transmission within a range of several kilometers is possible, and remote real-time monitoring is enabled by transmitting data to the cloud via a gateway. This allows for continuous monitoring of bolt conditions without on-site visits, effectively significantly reducing maintenance costs and safety risks.

[0021] Fourth, the bolt unit system equipped with a thermal imaging analysis function using a camera unit can quickly identify the heating status of the heating part among multiple bolts and identify abnormal bolts at an early stage. This has the effect of enabling efficient predictive maintenance even in large-scale structures.

[0022] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims. Brief explanation of the drawing

[0023] FIG. 1 is a perspective view of a bolt unit according to one embodiment of the present invention; FIG. 2 is a cross-sectional view of FIG. 1 above; FIG. 3 is a cross-sectional view of a bolt unit according to another embodiment of the present invention; FIG. 4 is a perspective view of a bolt unit according to another embodiment of the present invention; FIG. 5 is a cross-sectional view of FIG. 4 above; and FIG. 6 is a block diagram showing the connection relationships between the main components of a bolt unit system according to another embodiment of the present invention. Specific details for implementing the invention

[0024] A preferred embodiment of the present invention, in which the purpose of one embodiment of the present invention can be specifically realized, will be described in detail below with reference to the attached drawings. In describing this embodiment, the same names and reference numerals are used for identical components, and additional explanations thereof will be omitted.

[0025] FIG. 1 is a perspective view of a bolt unit according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view of FIG. 1.

[0026] The bolt unit (100) according to the present embodiment includes a bolt body part (110), a bolt head part (112), a gauge pin (124), a sensing part (132), a battery part (152), a lamp part (158), and a nut part (180).

[0027] The bolt body (110) is provided with a threaded portion (111) at one end so that a nut portion (180) can be screw-coupled. Here, the bolt body (110) is preferably formed of a high-strength alloy steel material and has the same strength grade as a conventional bolt.

[0028] In addition, the above-mentioned threaded portion (111) is machined according to standard metric or inch thread specifications and can be manufactured in various sizes from M10 to M100 or larger depending on the use and size of the bolt.

[0029] A gauge pin (124) is installed on the bolt head portion (112) side of the bolt body portion (110) in a manner that crosses the interior of the bolt body portion (110). The gauge pin (124) is installed in the longitudinal direction along the central axis of the bolt body portion (110), with one end fixed to the lower end of the bolt body portion (110) and the other end extending to the elongation gap (118) formed adjacent to the bolt head portion (112).

[0030] The operating principle of the gauge pin (124) is as follows. When the bolt is tightened by the nut portion (180), an axial tensile force is applied to the bolt body portion (110).

[0031] At this time, the bolt undergoes slight elongation in the longitudinal direction depending on the fastening state, deformation of the structure, or temperature changes; this elongation is generally in the range of tens of micrometers to hundreds of micrometers. The elongation (ΔL) of the bolt is proportional to the tensile force (F) according to Hooke's Law and is expressed by the following equation.

[0032] ΔL = (F × L) / (A × E)

[0033] Here, L is the effective length of the bolt, A is the cross-sectional area of ​​the bolt, and E is the elastic modulus of the material. Since the gauge pin (124) is fixed to the bottom of the bolt body (110), the gauge pin (124) moves together with the bolt when it elongates. However, since the bolt head (112) is relatively fixed, the free end of the gauge pin (124) moves within the elongation gap (118) by the amount of elongation of the bolt. By detecting this minute displacement by the sensing unit (132), the tensile force of the bolt can be accurately measured.

[0034] That is, the elongation gap (118) is an internal cavity that provides sufficient space for the gauge pin (124) to move freely as the bolt elongates. The depth of the elongation gap (118) is designed to be greater than the maximum expected elongation of the bolt so that the gauge pin (124) does not touch the top of the elongation gap (118) even when the bolt is tightened to near the yield strength. Generally, the depth of the elongation gap (118) is designed to be in the range of 1 to 5 mm.

[0035] Meanwhile, a sensing unit (132) is provided in the battery unit (152), and the sensing unit (132) measures the degree of elongation of the gauge pin (124) extending into the elongation gap (118).

[0036] The above sensing unit (132) is composed of a high-precision displacement sensor and is configured to accurately detect minute movements of the gauge pin (124).

[0037] The above sensing unit (132) may adopt a linear variable differential transformer (LVDT) method or a magnetic displacement sensor method.

[0038] In the case of the LVDT method, a ferromagnetic core is attached to the gauge pin (124), and a primary coil and two secondary coils are arranged on the inner wall of the irrigation gap (118). When an alternating current is applied to the primary coil, a magnetic field is formed, and the difference in voltage induced in the two secondary coils changes depending on the position of the ferromagnetic core. By measuring this voltage difference, the exact position of the gauge pin (124) can be determined. The LVDT method has the advantages of being non-contact, having no wear, very high measurement accuracy, and excellent stability against temperature changes.

[0039] In the case of the magnetic displacement sensor method, a permanent magnet is attached to the end of the gauge pin (124), and a Hall effect sensor or a magnetoresistive sensor is placed on the inner wall of the elongation gap (118). The strength of the magnetic field detected by the sensor changes according to the change in the position of the permanent magnet, thereby measuring the displacement of the gauge pin (124). The magnetic sensor method has the advantages of a simple structure, easy miniaturization, and low power consumption.

[0040] The above-mentioned sensing unit may be applied in various other known forms.

[0041] The sensing unit (132) measures the displacement of the gauge pin (124) in real time and converts it into an electrical signal. This electrical signal is transmitted to the control unit (170), converted into digital data, and converted into an actual bolt load (tensile force) using the calibration data.

[0042] The above sensing unit (132) has high resolution capable of detecting displacement in micrometer units.

[0043] The elongation degree data measured by the sensing unit (132) is transmitted to a separately provided control unit, and the control unit can analyze it to determine the state of the bolt's fastening force. If the fastening force is within a set standard range, it is determined to be in a normal state, and if it is outside the standard range, a separately provided lamp unit (158) is controlled to display a visual signal.

[0044] Specifically, the fastening force status of the bolt can be classified as follows.

[0045] If the elongation amount of the gauge pin (124) is within the range of 60 to 100% of the design standard value, it is determined to be in a normal fastening state; if it is within the range of 40 to 60%, it is determined to be in a state of caution regarding reduced fastening force; and if it is less than 40%, it is determined to be in a state of risk of insufficient fastening force. Additionally, if the elongation amount exceeds 100% of the design standard value, it is determined to be in an over-fastening state; and if it exceeds 120%, it is determined to be in a state of risk where the bolt reaches the yield point and permanent deformation may occur.

[0046] The lamp unit (158) is configured to light up according to the degree of elongation measured by the sensing unit (132). The lamp unit (158) is preferably composed of a high-brightness LED and positioned so as to be exposed on the outer surface of the bolt head unit (112) so that it can be visually identified from a distance of 20m or more. Additionally, the lamp unit (158) is preferably configured to use a multi-color LED so that it flashes in different colors depending on the fastening state of the bolt.

[0047] The display method of the above lamp unit (158) can be as follows.

[0048] For example, when the bolt load is in the normal range (60~100%), it flashes green to indicate that it is in a normal state, and when the bolt load drops to the range of 40~60% of the reference value, it flashes yellow to indicate that caution is required.

[0049] In addition, if the bolt load drops below 40%, it flashes red to warn of a dangerous condition requiring immediate re-tightening. If the bolt load is excessively high and approaches or exceeds the yield point, it remains lit in red to indicate an over-tightened state, warning that the bolt may be permanently deformed and unusable.

[0050] The lamp (158) is normally turned off to minimize power consumption, but it may be set to automatically turn on when a user brings a wireless activation device (e.g., a portable reader) near the bolt head (112). Alternatively, it may be set to flash periodically for a short period of time so that the status can be checked from a distance. It may also be set to automatically start flashing to provide a visual warning when the bolt status reaches a warning or danger level.

[0051] The battery unit (152) supplies power to the sensing unit (132), the control unit (170), and the lamp unit (158). The battery unit (152) is mounted on the upper outer side of the bolt head unit (112) and uses a lithium primary battery or a lithium secondary battery.

[0052] The battery unit (152) can be configured to be used for a long period of time through an ultra-low power design. The sensing unit (132) normally stands in sleep mode, wakes up only at a set measurement cycle (e.g., every hour) to measure the amount of growth, and then switches back to sleep mode. The wireless communication unit also transmits data for a short time only immediately after the measurement is completed and remains off for the rest of the time. Through this power management technique, the battery unit (152) can be used without replacement as much as possible.

[0053] The method of use of the bolt unit (100) configured as described above is as follows. First, the bolt body (110) is inserted into the fastening hole of the structure, and the nut part (180) is attached from the opposite side. The nut part (180) is tightened using a torque wrench or a hydraulic fastening device to reach the design fastening force. During this process, the bolt load can be monitored in real time through a tablet or smartphone application. When the load value measured by the sensing part (132) reaches the design standard range, the fastening is stopped. When the fastening is completed, the lamp part (158) flashes green to confirm that it has been properly fastened.

[0054] After fastening, the bolt unit (100) is periodically automatically measured for deformation according to the deformation of the structure or temperature, and the measurement data can be wirelessly transmitted to a gateway and stored on a cloud server. Additionally, the user can check the status of the bolt anytime and anywhere through a web browser or mobile app. If the bolt load exceeds the set range, the system automatically sends a warning message, and the lamp unit (158) flashes red so that the abnormality can be immediately identified on-site.

[0055] Meanwhile, the bolt body (110) and the bolt head (112) may be made of different colors, or the bolt body (110) may be coated with luminous paint so that it is easy to identify the state in which the bolt body (110) is exposed after being partially loosened and joined to the structure.

[0057] FIG. 3 is a cross-sectional view of a bolt unit according to another embodiment of the present invention.

[0058] The bolt unit according to the present embodiment also includes a bolt body part (110), a bolt head part (112), a gauge pin (124), a sensing part (132), a battery part (152), a lamp part (158), and a nut part (180). Since these configurations are identical to the embodiments of FIGS. 1 and FIG. 2 described above, a redundant description is omitted.

[0059] A feature of the present embodiment is that an elastic absorbing member (172) is provided inside the bolt body portion (110). The elastic absorbing member (172) is inserted into the internal space of the bolt body portion (110) and is formed of an elastic material such as silicone rubber, EPDM (Ethylene Propylene Diene Monomer) rubber, urethane foam, or shape memory alloy.

[0060] The operating principle and effect of the elastic absorbing member (172) are as follows. When a strong external impact is applied to a structure in which a bolt unit (100) according to this embodiment is installed, the impact energy is transferred to the bolt, and a very large stress may be generated instantaneously.

[0061] If such impact stress is repeated, the accumulation of fatigue in the bolt accelerates, shortening its lifespan, and in the worst case, may lead to cracking or fracture.

[0062] The above elastic absorbing member (172) significantly reduces the stress transmitted to the bolt body (110) by absorbing and dispersing such impact energy through elastic deformation.

[0063] Specifically, when an impact is applied, the elastic absorbing member (172) undergoes compressive deformation, storing part of the impact energy as elastic energy and dissipating part of it as thermal energy through internal friction. This allows the peak stress transmitted to the bolt to be reduced to a significant level.

[0064] In addition, when the impact is removed, the elastic absorbing member (172) is restored to its original shape and can continue to perform the repetitive shock absorption function.

[0065] Furthermore, the elastic absorbing member (172) also serves to alleviate thermal stress caused by rapid temperature changes. For example, in marine structures or structures in extreme climate regions, there are large daily temperature fluctuations or seasonal temperature changes. When the temperature rises, the bolt and the structure undergo thermal expansion, and when the temperature falls, they contract. If the coefficients of thermal expansion of the bolt and the structure differ, additional thermal stress is generated in the bolt during temperature changes, causing the fastening force to fluctuate. The elastic absorbing member (172) absorbs this difference in thermal expansion through elastic deformation to alleviate thermal stress and allows the fastening force to be maintained more stably.

[0066] A shape memory alloy may also be used as an elastic absorption member (172). In this case, a phase change of the material occurs depending on the temperature, and the elastic modulus changes within a specific temperature range.

[0067] By utilizing this, the effect of automatically compensating for bolt tightening force in response to temperature changes can be achieved. For example, at low temperatures, the shape memory alloy softens into the martensite state to absorb shrinkage stress, and at high temperatures, it hardens into the austenite state to limit expansion stress, thereby maintaining a constant tightening force across the entire temperature range.

[0068] The bolt unit (100) according to the present embodiment is particularly useful in environments with a lot of shock or vibration, such as railway rail fastening, bridge structures, offshore platforms, wind towers, and heavy equipment. Through the elastic absorbing member (172), the fatigue life of the bolt can be extended by 2 to 3 times, and stable fastening force can be maintained even with rapid temperature changes.

[0069] FIG. 4 is a perspective view of a bolt unit according to another embodiment of the present invention, and FIG. 5 is a cross-sectional view of FIG. 4.

[0070] The bolt unit according to the present embodiment also includes a bolt body part (110), a bolt head part (112), a gauge pin (124), a sensing part (132), a battery part (152), a lamp part (158), and a nut part (180). Since these basic configurations are the same as those described in the previous embodiments, a detailed description is omitted.

[0071] The feature of this embodiment is that a pair of washer parts (161) are fastened between the nut part (180) and the bolt head part (112), and a cushioning part (165) is fastened between the pair of washer parts (161).

[0072] The above pair of washer parts (161) consists of an upper washer and a lower washer, and is manufactured in the form of a general flat washer or a spring washer. The washer parts (161) are formed of high-strength steel and serve to evenly distribute the load of the bolt onto the surface of the structure.

[0073] The buffer section (165) is sandwiched between a pair of washer sections (161). The buffer section (165) has a sealed chamber structure containing fluid inside. The buffer section (165) consists of an upper metal plate, a lower metal plate, and a fluid chamber between them.

[0074] The fluid contained within the buffer section (165) is a high-viscosity fluid such as silicone oil, glycerin, or viscoelastic gel. When such a fluid is subjected to a compressive load, its internal pressure increases, and energy is dissipated by the viscous resistance of the fluid. Additionally, a fine orifice or channel is formed within the buffer section (165), allowing the fluid to move slowly through it.

[0075] The operating principle and effect of the buffer (165) are as follows.

[0076] When vibration or impact is applied to a structure where a bolt is fastened, a relative micro-movement occurs between the bolt head portion (112) and the nut portion (180). As this micro-movement is repeated, the nut portion (180) gradually loosens, and the fastening force decreases. The damping portion (165) effectively absorbs and dampens this micro-movement, thereby preventing the nut from loosening.

[0077] Such a buffer (165) is particularly effective for structures that are continuously exposed to strong vibrations and shocks, such as offshore wind turbines, bridges, railways, and construction heavy equipment. For example, the bolts connecting the tower and foundation structure of an offshore wind turbine are subjected to continuous vibrations caused by wind and waves. In such an environment, applying the buffer (165) can significantly reduce the frequency of maintenance due to bolt loosening.

[0078] The bolt unit (100) according to the present embodiment provides excellent fastening force retention performance in a vibration environment, and can significantly extend the periodic inspection and re-fastening cycle, thereby drastically reducing maintenance costs.

[0079] Meanwhile, according to the present embodiment, a heating element (155) is provided on the outside of the battery unit (152). The heating element (155) is arranged to surround the battery unit (152) and generates heat to optimally maintain the performance of the battery and sensor in a low-temperature environment.

[0081] FIG. 6 is a block diagram showing the connection relationships between the main components of a bolt unit system according to another embodiment of the present invention.

[0082] The bolt unit applied in this embodiment is equipped with a control unit (170) and is electrically connected to the sensing unit (132), lamp unit (158), and heating unit (155). The control unit (170) may be composed of an integrated circuit including a microcontroller (MCU), an analog-to-digital converter (ADC), a memory, a wireless communication module, etc.

[0083] And, the control unit (170) receives a displacement signal of the gauge pin (124) from the sensing unit (132), converts it into digital data, and applies the calibration data to convert it into an actual bolt load.

[0084] In addition, the calculated bolt load is compared with a set threshold value to determine a state such as normal, caution, or danger, and the color and flashing pattern of the lamp unit (158) are controlled according to the determined state. Also, in a low-temperature environment, if the temperature drops below a set value, the heating unit (155) is activated to maintain an appropriate temperature.

[0085] The control unit (170) can store measurement data in memory and transmit it to an external gateway via a wireless communication module. The transmitted data includes information such as a bolt ID, measurement time, load value, temperature, remaining battery level, and status. The control unit (170) performs a power management function to minimize power consumption by switching most circuits to sleep mode during times when there is no measurement or communication.

[0086] The bolt unit system of the present embodiment further includes a configuration for integrated management of a plurality of bolt units (100). It comprises a camera unit (194) for measuring the heating unit (155), a second control unit (192) electrically connected to the camera unit (194), and a communication unit (196) electrically connected to the second control unit (192).

[0087] The above camera unit (194) is composed of a thermal imaging camera and photographs a structure in which a plurality of bolt units (100) are installed. When the heating unit (155) is operating or a malfunction occurs in the bolt, causing frictional heat to be generated, the temperature of the corresponding area rises. The camera unit (194) acquires this temperature distribution as a thermal image and transmits it to the second control unit (192).

[0088] The above camera unit (194) may be configured as a fixed type or a mobile type (drone-mounted type). The fixed type is permanently installed at an appropriate location on the structure and periodically takes thermal images. The drone-mounted type allows an operator to control a drone to tour the structure and take pictures, or to set an autonomous flight path to take pictures automatically. The drone-mounted type is particularly useful for inspecting high areas or large structures that are difficult to access.

[0089] The second control unit (192) analyzes the thermal image received from the camera unit (194). It identifies each bolt location using an image processing algorithm and measures the temperature of the corresponding location. That is, it is configured to automatically detect abnormal bolts based on the temperature difference between normal bolts and abnormal bolts. For example, bolts whose temperature is 5°C or higher or lower than that of surrounding bolts are classified as abnormal candidates.

[0090] The second control unit (192) evaluates the condition of the bolts by combining the thermal image analysis results and load data received wirelessly from each bolt unit (100). Bolts that appear as high temperatures in the thermal image and are simultaneously detected as abnormalities in the load data are classified as high-priority inspection targets. Through this multi-sensor fusion method, the accuracy of the diagnosis can be increased and false detections can be minimized.

[0091] The communication unit (196) is electrically connected to the second control unit (192) to transmit data to the outside. The communication unit (196) can be connected to the Internet using LTE, 5G, Wi-Fi, or a satellite communication module, and can be configured to transmit measurement data, thermal images, analysis results, warning messages, etc. to a cloud server.

[0092] On the cloud server, collected data is stored in a database and visualized through a web-based dashboard, allowing users to check the status of all vaults in real time via a web browser or mobile app.

[0093] In other words, the location of each bolt, current load, load change trend, temperature, and status (normal / caution / danger) can be displayed, and the status of the bolts can be displayed in color on the 3D model of the structure so that the overall situation can be grasped at a glance.

[0094] Furthermore, the cloud server can be configured to analyze long-term accumulated data to learn the load change patterns of each bolt, utilize machine learning algorithms to learn normal patterns, and detect abnormal patterns deviating from them at an early stage. For example, if the load on a specific bolt shows a continuously decreasing trend, it can generate a warning in advance, even if it has not yet reached a danger level, enabling preventive measures to be taken.

[0095] The cloud system can be configured to automatically generate alerts when predefined conditions are met, for example, if the bolt load exceeds a set range, if the rate of load change over the past 24 hours exceeds a threshold, if abnormal temperatures are detected in thermal images, or if the battery level drops below a certain threshold. Alerts can be immediately delivered to the responsible person via various methods, such as email, SMS, and mobile app push notifications.

[0096] Meanwhile, in this embodiment, the bolt head portion (112) may be made of a material that facilitates light reflection, and a lighting portion that irradiates light between the structure to which the bolt is fastened and the bolt head portion (110), and a sensing portion that detects light reflected after being supplied from the lighting portion when the bolt head portion (112) is exposed may be additionally provided to enable detection of the bolt loosening state, etc.

[0097] Preferred embodiments according to the present invention have been described above, and it is obvious to those skilled in the art that, in addition to the embodiments described above, the present invention may be embodied in other specific forms without departing from the spirit or scope thereof. Therefore, the embodiments described above should be regarded as illustrative rather than restrictive, and accordingly, the present invention is not limited to the description above but may be modified within the scope of the appended claims and their equivalents. Explanation of the symbols

[0098] 100: Bolt unit 110: Bolt body 111: Screw thread 112: Bolt head 118: Elongation Gap 124: Gauge pin 132: Sensing unit 152: Battery section 158: Lamp section 180: Nut part

Claims

Claim 1 A bolt body portion having a threaded portion formed at one end and the other end connected to a bolt head portion; a nut portion screw-coupled to the threaded portion of the bolt body portion; a gauge pin installed inside the bolt body portion along the longitudinal direction of the bolt body portion, with one end fixed to the lower end of the bolt body portion and the other end extending toward the bolt head portion as a free end; an elongation gap formed inside the bolt body portion on the bolt head portion side, providing a space for the free end of the gauge pin to extend; a sensing portion provided in the bolt head portion to detect displacement of the gauge pin within the elongation gap; an elastic absorbing member inserted inside the bolt body portion to absorb stress on the bolt body portion caused by external shock and vibration; and a battery portion provided on the outside of the bolt head portion to supply power to the sensing portion. A voltage unit comprising: a lamp unit provided in the battery unit to light up in a plurality of colors according to the degree of elongation measured by the sensing unit; wherein the lamp unit flashes green when the elongation amount of the gauge pin is in the range of 60 to 100% of the design reference value, flashes yellow when it is in the range of 40 to 60%, and flashes red when it is less than 40%. Claim 2 In claim 1, the sensing unit is configured as a linear variable differential transformer (LVDT) to detect displacement in micrometer units, a voltage unit. Claim 3 delete

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