Bolt looseness detection device and method

Abstract

The invention provides a bolt looseness detection device, and belongs to the technical field of bolt looseness detection, the device comprises a first permanent magnet, a second permanent magnet and a TMR sensor chip, the second permanent magnet is fixed on a shell through a cantilever beam and directly faces the first permanent magnet, the TMR sensor chip is fixed on the shell, and when the first permanent magnet moves relative to the second permanent magnet, the TMR sensor chip is fixed on the shell. The magnetic field where the TMR sensor chip is located changes; the invention further provides a bolt looseness detection method. According to the magnetic induction principle, non-contact detection on whether the bolt is loosened or not is achieved, the device is simple in structure, low in cost and convenient to install, a wireless passive working mode is adopted, external power supply is not needed, and long-term stable operation can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bolt loosening detection, in particular to a bolt loosening detection device and method. BACKGROUND

[0002] Bolt connection is one of the main connection methods for angle steel connection of power transmission towers. However, power transmission towers are usually located outdoors, and the natural environment of power transmission towers is complex and changeable, which causes the stress state of power transmission lines to change frequently. With the joint action of long-term wind vibration, conductor dancing and temperature fluctuation and other factors, the bolt connection part is prone to looseness. Bolt loosening not only reduces the structural stiffness of the power transmission tower, but also may even cause instability of the tower over a long period of time. Therefore, regular inspection of bolts and timely tightening when loosening are becoming a routine maintenance work that cannot be ignored. However, this work requires a large amount of manual resources, and the labor intensity of workers is large, especially in the complex natural environment, the related problems are more and more concerned, and it is urgent to find a more efficient and convenient solution.

[0003] In order to effectively solve this problem, using a sensing node to monitor the bolt loosening in real time has become an important technical means. Specifically, the existing monitoring methods include the following: (1) contact monitoring by installing a pressure or grating sensing unit on the nut, which can realize real-time monitoring at multiple points and obtain the loosening state of the bolt; but the installation of such sensors requires disassembly of the nut, punching or welding of the bolt and other modifications, which not only damages the original bolt structure, but also is time-consuming and labor-intensive; in addition, the sensor of this method usually needs long-time continuous measurement, and its high energy consumption makes the power supply system extremely complex, resulting in a large device size and affecting the convenience of installation; (2) using ultrasonic detection technology, which can provide high measurement accuracy and effectively detect bolt loosening, but the equipment is expensive and cannot support multi-point real-time monitoring, which limits its application in large-scale detection; (3) using computer vision technology and image processing technology for non-contact bolt monitoring, which avoids physical damage to the bolt structure and does not require direct contact during measurement, but this method usually needs to mark on the bolt or install a special device, and is easily disturbed by light environment, cannot be monitored all day long, and in addition, requires complex supporting equipment.

[0004] Therefore, the existing monitoring method faces many challenges, mainly focusing on high cost, large equipment size, difficult installation, and difficulty in long-term stable operation. In order to be widely applied to the daily maintenance work of the transmission tower, it is urgent to develop a more efficient, low-cost, easy-to-install and all-weather working bolt loosening detection technology to meet the monitoring needs of the transmission line in complex environment and ensure the stability and safety of the transmission equipment.

[0005] The mechanism of tunnel magnetoresistance (TMR) effect is closely related to spin-dependent tunneling effect. Specifically, TMR effect occurs in a base magnetic tunnel junction with a three-layer structure of ferromagnetic layer / non-magnetic insulating layer / ferromagnetic layer, which is usually referred to as "sandwich" structure. In the saturated magnetization state, the magnetization directions of the two ferromagnetic layers are usually in consistent parallel arrangement. However, the coercivities of the two ferromagnetic layers are generally different, which means that their magnetization directions do not flip at the same time during external magnetic field or magnetization reversal process. When performing reverse magnetization operation, the ferromagnetic layer with lower coercivity will flip its magnetization first, causing the magnetization directions of the two ferromagnetic layers to change from parallel to antiparallel. In this structure, electrons are transmitted from one ferromagnetic layer to another ferromagnetic layer through the tunneling effect of the non-magnetic insulating layer, and the size of the tunneling current is closely related to the magnetization directions of the two ferromagnetic layers. When the magnetization directions of the two ferromagnetic layers are parallel, most of the electrons in the majority spin band will enter the empty state of the majority spin band in the other ferromagnetic layer, while the electrons in the minority spin band will enter the empty state of the minority spin band, and the overall tunneling current is large. On the contrary, when the magnetization directions of the two ferromagnetic layers become antiparallel, the situation has fundamentally changed. In this state, the electrons in the majority spin band will enter the empty state of the minority spin band in the other ferromagnetic layer, and the electrons in the minority spin band will enter the empty state of the majority spin band in the other ferromagnetic layer. This spin mismatch state causes the tunneling current to decrease significantly. Therefore, TMR effect is essentially caused by the change of tunneling conductance due to the magnetization direction of the two ferromagnetic layers. When the magnetization directions are parallel, the tunneling conductance is high, and when the magnetization directions are antiparallel, the tunneling conductance is low.

[0006] The key of TMR effect is that the magnetization direction of two ferromagnetic layers can be changed by the regulation of external magnetic field, thereby causing the change of tunneling conductance, and further showing the change of tunneling magnetoresistance. Specifically, by applying an external magnetic field, the magnetization direction of the ferromagnetic layer will change, and when the magnetization direction of the two ferromagnetic layers changes from parallel to antiparallel, the tunneling current decreases, resulting in an increase in resistance, which is the TMR effect. Compared with traditional Hall effect or anisotropic magnetoresistance (AMR) sensors, the tunnel structure design of TMR sensors has a significant advantage in terms of magnetic resistance change. TMR sensors can provide higher magnetic resistance change rate in a weak magnetic field change environment, so they have higher output resolution. This makes TMR sensors particularly suitable for application scenarios sensitive to magnetic field changes, such as magnetic field disturbances caused by small structural displacement. In such applications, TMR sensors can provide more accurate detection and high-resolution response. In addition, another important advantage of TMR effect is that it provides the possibility for miniaturization and low-power design of sensors. Since TMR sensors have higher sensitivity and greater magnetic resistance change rate, they can work effectively under smaller volume and lower power consumption conditions. This makes TMR technology not only suitable for precision measurement and detection tasks, but also expected to play a key role in low-power, high-performance sensor modules, promoting the development of intelligent sensors and miniaturization technology.

[0007] A kind of can perceive fastener nut loosening of intelligent fastener and online monitoring system of Chinese invention patent application for publication No.CN110273909A discloses a kind of can perceive fastener nut loosening of intelligent fastener, including fastener body, the fixed part of fastener body is connected with the connecting piece, and its threaded portion is screwed with nut, nut is provided with fixed cover, the inner cavity of fixed cover is provided with angle detection device for detecting the relative rotation angle of nut and fastener body, angle detection device includes TMR tunnel magnetoresistance sensor assembly or GMR magnetic field sensor assembly arranged in fixed cover to detect the relative rotation angle of nut and fastener body, its main disadvantage is that angle calculation needs to be carried out according to different bolt pitch, nut position, and the size of fixed cover needs to be adjusted according to the size after bolt and nut fastening, workload is large, and calculation is complex. SUMMARY

[0008] The technical problem to be solved by the present application is how to solve the problems of high cost, large equipment size, difficult installation and long-term stable operation of existing bolt loosening detection technology.

[0009] The application solves the above technical problems through the following technical scheme: a bolt loosening detection device, which comprises a first permanent magnet, a second permanent magnet and a TMR sensor chip, the second permanent magnet is fixed on a shell through a cantilever beam and faces the first permanent magnet, and the TMR sensor chip is fixed on the shell; when the first permanent magnet moves relative to the second permanent magnet, the magnetic field in which the TMR sensor chip is located changes.

[0010] In the application, the first permanent magnet is placed on a bolt to be detected, the second permanent magnet is fixed on a shell through a cantilever beam, when the bolt loosens, the first permanent magnet moves relative to the second permanent magnet, the second permanent magnet drives the cantilever beam to change in vibration frequency due to the change of the magnetic field, and the vibration is transmitted to the TMR sensor chip through the shell, at the same time, the magnetic field in which the TMR sensor chip is located changes, the TMR sensor chip is saturated magnetized due to the magnetic field, when the magnetic field changes, the magnetic sensitive resistance of the TMR sensor chip changes, the output voltage of the TMR sensor chip changes, and the loosening of the bolt can be determined by detecting the output voltage. The application realizes non-contact detection of whether the bolt loosens or not by using the magnetic induction principle, effectively reduces the modification process of the bolt, has simple device structure, low cost and convenient installation; the wireless passive working mode is adopted, external power supply is not needed, the service life limit and maintenance difficulty of the traditional battery power supply mode are avoided, and the reliability and durability of long-term operation of the device are improved.

[0011] Preferably, the cantilever beam is a single cantilever beam, a double cantilever beam or a ring-shaped cantilever beam.

[0012] Compared with the single cantilever beam structure, the double cantilever beam structure has higher frequency stability and vibration suppression ability in dynamic response, which helps to improve the identification accuracy of magnetic field disturbance, and is especially suitable for complex outdoor application scenes such as high wind speed and strong electromagnetic interference; the ring-shaped cantilever structure has multidirectional response ability, can capture magnetic field disturbance in different directions, and thus improves the detection sensitivity and direction resolution. The structure is especially suitable for complex structures with asymmetric vibration sources or uneven spatial magnetic field distribution, and effectively enhances the response ability and discrimination accuracy of the sensor to the slight loosening state.

[0013] Preferably, the first permanent magnet is fixed on the nut of the bolt to be detected, the second permanent magnet is bonded on the cantilever beam, and the two ends of the cantilever beam are respectively fixed on the two side walls of the shell.

[0014] The bolt loosening detection device of the application has simple structure, does not depend on additional cable wiring for installation, can be quickly installed on the surface of the bolt through structural glue or magnetic attraction, greatly reduces the difficulty of manual deployment, and is convenient for wide promotion.

[0015] Preferably, the device further comprises a first metal plug and a solder pad, the TMR sensor chip is fixed at one end of the first metal plug through the solder pad, and the other end of the first metal plug is fixed on the shell through the solder pad after penetrating through the shell.

[0016] Preferably, the device further comprises a protective shell and a second metal plug, one end of the second metal plug is fixed on the solder pad outside the shell, and the other end of the second metal plug is fixed on the protective shell through the solder pad after penetrating through the protective shell.

[0017] Preferably, the device further comprises a detection circuit, a signal processing circuit and a wireless gateway, the input end of the detection circuit is connected to the TMR sensor chip for detecting the output voltage of the TMR sensor chip, the input end of the signal processing circuit is connected to the output end of the detection circuit for filtering, amplifying and compressing the output voltage to obtain a processed signal, and the input end of the wireless gateway is connected to the output end of the signal processing circuit for outputting a high level or a low level after comparing the processed signal with a set threshold.

[0018] The application also provides a bolt loosening detection method, which adopts the bolt loosening detection device, and the method comprises the following steps: placing the first permanent magnet on the nut of the bolt to be detected, determining the installation position of the shell according to the distance between the nut and the screw cap, so that the second permanent magnet faces the first permanent magnet; setting a detection range, detecting the output voltage of the TMR sensor chip, and comparing the output voltage with a set threshold, so as to determine whether the bolt is loosened when the output voltage is less than the set threshold.

[0019] The application adopts a logic level system similar to TTL (transistor-transistor logic), and when the output of the wireless gateway changes from a high level to a low level, it indicates that the bolt is loosened, which can accurately detect whether the nut and the first permanent magnet are within the detection range of the TMR sensor, so as to realize accurate monitoring of the positions of the nut and the first permanent magnet.

[0020] Preferably, the detection range is set by moving the first permanent magnet, detecting the output voltage of the TMR sensor chip through the detection circuit, and when the output voltage is equal to the set threshold, the distance between the first permanent magnet and the second permanent magnet is the detection range.

[0021] Preferably, when the nut rotates to drive the first permanent magnet to move and be located in the detection range, the TMR sensor chip has a saturation magnetization phenomenon, the tunneling current increases, the detection circuit detects the output voltage of the TMR sensor chip, the output voltage is processed by the signal processing circuit, and the processed signal is output, the processed signal is greater than the set threshold value, the wireless gateway outputs a high level, and it is judged that the bolt is not loose; when the nut rotates to drive the first permanent magnet to move and leave the detection range, the saturation magnetization state of the TMR sensor chip disappears, the tunneling current decreases, the detection circuit detects the output voltage of the TMR sensor chip, the output voltage is processed by the signal processing circuit, and the processed signal is output, the processed signal is less than the set threshold value, the wireless gateway outputs a low level, and it is judged that the bolt is loose.

[0022] Preferably, the minimum loosening angle of the bolt is:

[0023] wherein, the set threshold value is, all are proportional constants, is the initial resistance of the TMR sensor chip, is the initial magnetic field intensity.

[0024] The magnetic induction switch has the characteristics of rapid response and low cost, the magnetic induction switch does not need to contact the detected object, can convert the received signal into a switch quantity electric signal through the magnetic induction method, provide the control system, can achieve the purpose of evaluating the bolt loosening of the power transmission tower, and solves the problem of low artificial detection efficiency in the existing evaluation method. Compared with the traditional monitoring system based on stress and strain or image processing, the bolt loosening state is indirectly represented by using the magnetic signal, the dependence on external light, power stability and structural modification is significantly reduced. At the same time, the magnetic induction path is clear, the response logic is simple, the subsequent signal acquisition and discrimination algorithm are modularized, the system integration and engineering adaptability are improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a front view of the bolt loosening detection device provided by the embodiment 1 of the application; Figure 2 is a sectional view of the bolt loosening detection device provided by the embodiment 1 of the application; Figure 3 is a side view of the bolt loosening detection device provided by the embodiment 1 of the application; Figure 4 is a working principle diagram of the bolt loosening detection device provided by the embodiment 1 of the application; Figure 5 ​​This is a schematic diagram of the cantilever beam in the bolt loosening detection device provided in Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of a cantilever beam with another structure in the bolt loosening detection device provided in Embodiment 1 of the present invention; Figure 7 This is a schematic diagram of a cantilever beam with another structure in the bolt loosening detection device provided in Embodiment 1 of the present invention; Figure 8 This is a schematic diagram of the TMR sensor in the bolt loosening detection device provided in Embodiment 1 of the present invention; Figure 9 This is a schematic diagram of the installation of the TMR sensor chip in the bolt loosening detection device provided in Embodiment 1 of the present invention; Figure 10 This is a side view of the TMR sensor in the bolt loosening detection device provided in Embodiment 1 of the present invention; In the diagram: 10 First permanent magnet, 20 TMR sensor, 21 Second permanent magnet, 22 Cantilever beam, 23 TMR sensor chip, 24 Housing, 31 First metal plug, 32 Solder pad, 33 Second metal plug, 40 Protective shell, 100 Bolt to be tested, 101 Nut, 102 Screw, 1021 Nut, 1022 Screw rod, 50 Detection circuit, 60 Signal processing circuit, 70 Wireless gateway. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] Example 1 like Figure 1 As shown, this embodiment provides a bolt loosening detection device for detecting whether bolts have become loose. See [link to relevant documentation]. Figure 2 and Figure 3 The bolt 100 to be tested includes a nut 101 and a screw 102. The nut 101 is threaded onto the threaded shank 1022 of the screw 102. When the bolt is used to connect the angle steel of the transmission tower, the end of the threaded shank 1022 away from the nut 1021 passes through the angle steel, and then the nut 101 is threaded onto the threaded shank 1022. Tightening the nut 101 achieves a fixed connection to the angle steel. The bolt 100 to be tested may include, but is not limited to, M10, M12, M16, M18, and M20.

[0028] The device comprises a first permanent magnet 10, a second permanent magnet 21, a TMR sensor chip 23, a first metal plug 31, a pad 32, a second metal plug 33, and a protective shell 40. The first permanent magnet 10 is fixed on the nut 101 of the bolt 100 to be detected by magnetic force or structural adhesive. The second permanent magnet 21, the cantilever beam 22, the TMR sensor chip 23, and the shell 24 constitute a TMR sensor 20. The model of the TMR sensor chip 23 can be MagnTek MT6835. Specifically, the second permanent magnet 21 is fixed on the cantilever beam 22 and faces the first permanent magnet 10. The second permanent magnet 21 is bonded on the cantilever beam 22 by glue, and the two ends of the cantilever beam 22 are fixed on the two inner side walls of the shell 24. The TMR sensor chip 23 is fixed on one end of the first metal plug 31 through the pad 32, and the other end of the first metal plug 31 is fixed on the shell 24 through the pad 32 after passing through the shell 24. The shell 24 is fixed and connected to the inner side wall of the protective shell 40 through the second metal plug 33 and the pad 32. One end of the second metal plug 33 is fixed on the pad 32 outside the shell 24, and the other end of the second metal plug 33 is fixed on the protective shell 40 through the pad 32 after passing through the protective shell 40.

[0029] The selection of the first permanent magnet 10 and the second permanent magnet 21 needs to consider the matching of magnetic field strength and size. Preferably, they are made of rare earth high magnetic energy level materials (such as neodymium iron boron) to ensure that sufficient magnetic field strength is provided in a small volume to trigger the response of the TMR sensor chip, and have good temperature resistance and corrosion resistance characteristics, suitable for outdoor long-term use requirements.

[0030] The first metal plug 31 and the pad 32, and the second metal plug 33 and the pad 32 are respectively connected by conductive glue to enhance the overall signal stability and anti-interference ability, suitable for long-period, low-maintenance remote monitoring application scenarios. To ensure the reliability and repeatability of the sensor response, the relative position between the cantilever beam 22 and the shell 24 needs to be kept stable during installation to avoid error drift caused by stress concentration or shell micro-deformation. In addition, a flexible buffer layer can be added at the installation position to play a dual role of shock isolation and temperature compensation, suitable for typical working environments of large day-night temperature difference and frequent structure micro-vibration of power transmission towers. In the actual assembly process, the protective shell 40 can be made of insulating materials with dustproof and corrosion-resistant properties to adapt to outdoor high-humidity and high-temperature difference environments.

[0031] The second permanent magnet 21, the cantilever beam 22, and the TMR sensor chip 23 constitute a magnetic sensing element. During the installation of the TMR sensor 20, the second permanent magnet 21 is aligned with the first permanent magnet 10 to ensure that the magnetic sensing element and the end face of the nut are in the same axial plane, avoiding magnetic deviation caused by installation tilt. Simultaneously, the solder pad connection area requires the use of highly reliable solder and a protective coating to enhance oxidation and electrochemical corrosion resistance, ensuring the stability of signal output during long-term operation.

[0032] Cantilever beam 22 can be a single cantilever beam, a double cantilever beam, or a cantilever beam with a ring, such as... Figure 5 As shown, the cantilever beam 22 is a single cantilever beam, with the second permanent magnet 21 bonded to the middle position of the cantilever beam 22, and the two ends of the cantilever beam 22 fixed to the two inner sidewalls of the housing 24, respectively. Figure 6 As shown, the cantilever beam 22 is a double cantilever beam, which can be considered as two parallel single cantilever beams. The second permanent magnet 21 is bonded to the middle position of the cantilever beam 22. Compared with the single cantilever beam structure, the double cantilever beam structure exhibits higher frequency stability and vibration suppression capability in dynamic response, which helps to improve the accuracy of magnetic field disturbance recognition. It is particularly suitable for complex outdoor application scenarios such as high wind speed and strong electromagnetic interference. This structure can also achieve an optimized balance between sensitivity and anti-interference capability by adjusting the distance between the two arms.

[0033] like Figure 7 As shown, the cantilever beam 22 is a ring-shaped cantilever beam with a ring structure in the middle, and the second permanent magnet 21 is bonded to the ring structure. The ring-shaped cantilever structure has multi-directional response capability, which can capture magnetic field disturbances in different directions, thereby improving detection sensitivity and directional resolution. This structure is particularly suitable for complex structures with asymmetric vibration sources or uneven spatial magnetic field distribution, effectively enhancing the sensor's response capability and discrimination accuracy to minor loosening conditions.

[0034] See Figure 4 When the bolt loosens, the position of the nut 101 on the screw 1022 changes, causing the first permanent magnet 10 to move. The first permanent magnet 10 moves relative to the second permanent magnet 21, and the change in the magnetic field of the second permanent magnet 21 causes a change in the vibration frequency of the cantilever beam 22. Since the cantilever beam 22 is connected to the housing 24, this causes a change in the vibration frequency of the housing 24, which in turn causes a change in the magnetic field of the TMR sensor chip 23. This affects the magnetoresistance in the TMR sensor chip 23. The resistance of the external resistor changes due to the influence of the changing magnetic field, causing a change in the current in the circuit, which in turn affects the resistance of the external resistor. The voltage across the terminals changes, and the external resistor... The voltage at both ends of the TMR sensor chip 23 is the output voltage of the TMR sensor chip 23. The input end of the detection circuit 50 is connected to the TMR sensor chip 23, used to detect the output voltage of the TMR sensor chip 23. The input end of the signal processing circuit 60 is connected to the output end of the detection circuit 50, used to filter, amplify and compress the output voltage, and obtain the processed signal. The input end of the wireless gateway 70 is connected to the output end of the signal processing circuit 60, used to compare the processed signal with the set threshold value and output high or low level. When the wireless gateway signal changes from high level to low level, it means that the bolt has been loosened.

[0035] The signal processing circuit 60 includes a filter unit, an amplifier unit and a compression unit. The TMR signal is often affected by noise, especially high-frequency noise. Therefore, a low-pass filter can be used to smooth the signal and remove these noises. The transfer function of the filter is wherein is the time constant of the filter. Through filtering, the noise component of the signal is weakened, thereby improving the stability and accuracy of the signal. Secondly, since the output signal of the TMR sensor may be weak, it is usually necessary to enhance the signal through a gain amplifier to improve the amplitude of the signal, so that it is easier to be detected by the system. The gain factor G makes the processed signal (1) The dynamic range compression technique can be used to limit the change amplitude of the signal within a reasonable range, avoiding misjudgment caused by excessive amplification of the signal. The formula for dynamic range compression is wherein, is the compression factor, which controls the strength of compression. In order to remove the noise in the signal, the Fourier transform denoising method can be used. By converting the signal to the frequency domain, the unnecessary noise component is removed by using a frequency domain filter to obtain the denoised signal. The Fourier transform denoising formula is wherein, is the Fourier transform of the signal.

[0036] ​​The application sets a detection range, which can be set according to the required detection accuracy. The detection range is set by moving the first permanent magnet 10, detecting the output voltage of the TMR sensor chip 23 through the detection circuit, and when the output voltage is equal to the set threshold value, the distance between the first permanent magnet 10 and the second permanent magnet 21 at this time is the detection range. When the position of the nut 101 and the first permanent magnet 10 changes and is located within the detection range, the wireless gateway 70 will always output a high level, indicating that the nut 101 is not loose, and when the position of the nut 101 and the first permanent magnet 10 changes and leaves the detection range, the wireless gateway 70 will output a low level, indicating that the nut 101 is loose.

[0037] The application adopts a logic level system similar to TTL (Transistor-Transistor Logic). When the nut 101 and the first permanent magnet 10 enter the detection range of the TMR sensor 20 during rotation, a series of physical and electrical changes will occur. The TMR sensor chip 23 will undergo saturation magnetization due to the action of the magnetic field. This saturation magnetization will cause changes in the electronic structure inside the TMR sensor chip 23. The magnetically sensitive resistance of the TMR sensor 20 becomes smaller, causing the tunneling current to increase significantly. As the tunneling current increases, the current flowing through the external resistance increases, and the voltage across the external resistance increases. The detection circuit detects the voltage across the external resistance as the output voltage of the TMR sensor chip 23 . When the nut 101 and the first permanent magnet 10 are within the detection range of the TMR sensor 20, the output voltage is greater than the set threshold value , and the wireless gateway outputs a high level. When the nut 101 and the first permanent magnet 10 leave the detection range of the TMR sensor 20, the output voltage is less than the set threshold value , and the wireless gateway outputs a low level, indicating that the nut is loose. The application can accurately detect whether the nut 101 and the first permanent magnet 10 are within the detection range of the TMR sensor 20 by detecting when the wireless gateway output changes from high to low, indicating that the bolt is loose, thereby achieving accurate monitoring of the position of the nut 101 and the first permanent magnet 10.

[0038] The relationship between the magnetically sensitive resistance of the TMR sensor 20 and the magnetic field strength B is: (2) where, R0 is the initial resistance, k is the proportionality constant.

[0039] magnetic field strength B Rotation angle with nut 101 There is a linear relationship between them, and the relationship is as follows: (3) in, The initial magnetic field strength is given.

[0040] Therefore, magnetic field changes for: (4) Magnetic field changes This will cause a change in the magnetoresistance of the TMR sensor 20. for: (5) The output voltage of the TMR sensor chip 23 With changes in magnetoresistance Proportional: (6) in, Output voltage With changes in magnetoresistance The proportionality constant.

[0041] If the nut becomes loose and is just at the critical point of the detection range, the output voltage of the TMR sensor chip 23 will... equal to the set threshold At this time, the rotation angle of nut 101 Minimum loosening angle to be detected : (7) This formula determines the minimum angle of nut loosening based on changes in resistance and signal. Different detection accuracies can be achieved by adjusting parameters to meet different detection requirements.

[0042] See Figure 2 and Figure 3 A coordinate system is established for bolt loosening detection, ignoring the size of the permanent magnet, with the center of the second permanent magnet 21 as the origin. The line connecting the second permanent magnet 21 and the first permanent magnet 10 when they are directly opposite each other is the X-direction. The first permanent magnet 10 is located in the positive direction of the X-axis. The direction in which the nut 101 moves away from the nut 1021 on the screw 1022 is the positive direction of the Z-axis. Ignoring the movement distance of the first permanent magnet 10 in the Y-direction, the coordinates of the first permanent magnet 10 can be expressed as follows: ,in The distance between the first permanent magnet 10 and the second permanent magnet 21 in the X direction is [missing information]. For the distance of the first permanent magnet 10 and the second permanent magnet 21 in the Z direction, the first permanent magnet 10 and the second permanent magnet 21 are regarded as a point respectively, the connecting line vector of the two points is , the distance between the center of the first permanent magnet 10 and the center of the second permanent magnet 21 is , the magnetic moment of the second permanent magnet 21 is , the magnetic moment of the second permanent magnet 21 The angle between the horizontal projection of the connecting line of the center points of the first permanent magnet 10 and the second permanent magnet 21 is , the magnetic moment of the first permanent magnet 10 is , the magnetic moment of the first permanent magnet 10 The angle between the horizontal projection of the connecting line of the center points of the first permanent magnet 10 and the second permanent magnet 21 is , the magnetic moment of the second permanent magnet 21 The size of , the magnetic moment of the first permanent magnet 10 The size of : (8) (9) Wherein, The residual magnetism of the magnet, The volume of the second permanent magnet 21, The volume of the first permanent magnet 10, The vacuum permeability, the potential energy of the magnetic coupling pole interaction Is: (10) (11) (12) (13) Substitute formula (12) and formula (13) into formula (10) to obtain: (14) Since the force is the negative gradient of potential energy:

[0043] Therefore, the force in the horizontal direction (X direction) is:

[0044] The force in the vertical direction (Z direction) is:

[0045] The angle between the magnetic moment of the first magnet 10 and the magnetic moment of the second magnet 21 is , less than or equal to 180 degrees, when , ; when , ; according to the second-order system vibration equation, the deflection function of the cantilever beam under the driving of the permanent magnet can be obtained as:

[0046] By the Lagrange multiplier method, the peak current corresponding to different and horizontal distance d can be calculated, so as to indirectly determine the number of rotations. In actual situation, the current size corresponding to different positions and angles can be collected first, and then the number of rotations of the loose bolt is inferred reversely. By increasing the cantilever beam, the detection of the number of rotations of the loose bolt can be increased on the basis of fine detection of the magnetic field change, so as to realize the detection of the entire number of rotations of the loose bolt.

[0047] The first permanent magnet 10 is placed on the bolt to be detected, the second permanent magnet 21 is fixed on the shell 24 through the cantilever beam 22, when the bolt is loose, the first permanent magnet 10 moves relative to the second permanent magnet 21, the second permanent magnet 21 drives the cantilever beam 22 to change in vibration frequency due to the change of the magnetic field, and transmits the vibration to the TMR sensor chip 23 through the shell 24, at the same time, the magnetic field where the TMR sensor chip 23 is located changes, the TMR sensor chip 23 will be saturated magnetization due to the magnetic field, when the magnetic field changes, the magnetic sensitive resistance of the TMR sensor chip 23 changes, so that the output voltage of the TMR sensor chip 23 changes, and the bolt loosening can be judged by detecting the output voltage. The application realizes non-contact detection of bolt loosening or not by using the magnetic induction principle, effectively reduces the modification process of the bolt, adopts wireless passive working mode, does not need external power supply, avoids the service life limitation and maintenance problem of the traditional battery power supply mode, and improves the reliability and durability of the device.

[0048] The magnetic induction switch has the characteristics of rapid response and low cost, and the magnetic induction switch does not need to contact the detected object, can convert the received signal into a switch quantity electric signal through the magnetic induction method, provide the control system, and can achieve the purpose of evaluating the bolt loosening of the power transmission tower. Compared with the traditional monitoring system based on stress and strain or image processing mode, the application indirectly represents the bolt loosening state by using the magnetic signal, significantly reduces the dependence on external light, power stability and structural modification. At the same time, the magnetic induction path is clear, the response logic is simple, the subsequent signal acquisition and discrimination algorithm modular design are facilitated, and the system integration and engineering adaptability are improved.

[0049] In addition, the bolt loosening detection device of the present application has simple structure, and installation does not depend on extra cable wiring. The device can be quickly installed on the bolt surface through structural glue, buckle type or magnetic attraction, greatly reducing the difficulty of manual deployment and facilitating wide promotion. The device of the present application can be combined with an integrated antenna or a low-power communication module. The system can be expanded into a remote wireless monitoring node to realize the functions of regular collection and remote early warning upload of the bolt state.

[0050] Embodiment 2 The present embodiment provides a bolt loosening detection method using the bolt loosening detection device of embodiment 1. The method comprises the following steps: Step 1: Place the first permanent magnet 10 on the nut 101 of the bolt 100 to be detected. According to the distance between the nut 101 and the screw cap 1021 of the screw 102, determine the installation position of the shell 24 so that the second permanent magnet 21 is directly opposite the first permanent magnet 10. Step 2: Set the detection range, detect the output voltage of the TMR sensor chip 23, compare the output voltage with the set threshold value, and when the output voltage is less than the set threshold value, judge that the bolt is loose.

[0051] The setting method of the detection range is: moving the first permanent magnet 10, detecting the output voltage of the TMR sensor chip 23 through the detection circuit, and when the output voltage is equal to the set threshold value, the distance between the first permanent magnet 10 and the second permanent magnet 21 at this time is the detection range.

[0052] In step 2, when the nut 101 rotates to drive the first permanent magnet 10 to move and be located in the detection range, the TMR sensor chip 23 has a saturated magnetization phenomenon, the tunneling current increases, the detection circuit detects the output voltage of the TMR sensor chip 23, the output voltage is processed by the signal processing circuit, and the processed signal is output. The processed signal is greater than the set threshold value, the wireless gateway outputs high level, and it is judged that the bolt is not loose; when the nut 101 rotates to drive the first permanent magnet 10 to move and leave the detection range, the saturated magnetization state of the TMR sensor chip 23 disappears, the tunneling current decreases, the detection circuit detects the output voltage of the TMR sensor chip 23, the output voltage is processed by the signal processing circuit, and the processed signal is output. The processed signal is less than the set threshold value, the wireless gateway outputs low level, and it is judged that the bolt is loose.

[0053] The minimum loosening angle of the bolt is:

[0054] wherein, is the set threshold value, , are proportional constants, is the initial resistance of the TMR sensor chip,​ is the initial magnetic field strength.

[0055] The above embodiments are only used to illustrate the technical solutions of the present application, but not intended to limit the present application; even though the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still make modifications to the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A bolt loosening detection device, characterized in that: The device includes a first permanent magnet (10), a second permanent magnet (21), and a TMR sensor chip (23). The second permanent magnet (21) is fixed to the housing (24) by a cantilever beam (22) and faces the first permanent magnet (10). The TMR sensor chip (23) is fixed to the housing (24). When the first permanent magnet (10) moves relative to the second permanent magnet (21), the magnetic field of the TMR sensor chip (23) changes.

2. The bolt loosening detection device according to claim 1, characterized in that: The cantilever beam (22) is a single cantilever beam, a double cantilever beam, or a cantilever beam with a ring.

3. The bolt loosening detection device according to claim 1, characterized in that: The first permanent magnet (10) is fixed on the nut (101) of the bolt (100) to be tested, and the second permanent magnet (21) is bonded to the cantilever beam (22). The two ends of the cantilever beam (22) are respectively fixed on the two side walls of the shell (24).

4. The bolt loosening detection device according to claim 1, characterized in that: The device also includes a first metal plug (31) and a pad (32). The TMR sensor chip (23) is fixed to one end of the first metal plug (31) by the pad (32), and the other end of the first metal plug (31) passes through the housing (24) and is fixed to the housing (24) by the pad (32).

5. The bolt loosening detection device according to claim 4, characterized in that: The device also includes a protective shell (40) and a second metal plug (33). One end of the second metal plug (33) is fixed to a pad (32) on the outside of the shell (24), and the other end of the second metal plug (33) passes through the protective shell (40) and is fixed to the protective shell (40) by the pad (32).

6. The bolt loosening detection device according to claim 1, characterized in that: The device also includes a detection circuit (50), a signal processing circuit (60), and a wireless gateway (70). The input of the detection circuit (50) is connected to the TMR sensor chip (23) to detect the output voltage of the TMR sensor chip (23). The input of the signal processing circuit (60) is connected to the output of the detection circuit (50) to filter, amplify, and compress the output voltage to obtain the processed signal. The input of the wireless gateway (70) is connected to the output of the signal processing circuit (60) to compare the processed signal with a set threshold and output a high level or a low level.

7. A bolt loosening detection method, using the bolt loosening detection device according to any one of claims 1-6, characterized in that: The methods include: Place the first permanent magnet (10) on the nut (101) of the bolt (100) to be tested. Determine the installation position of the housing (24) based on the distance between the nut (101) and the nut (1021) of the screw (102), so that the second permanent magnet (21) is directly opposite the first permanent magnet (10). Set the detection range, detect the output voltage of the TMR sensor chip (23), compare the output voltage with the set threshold, and determine that the bolt is loose when the output voltage is less than the set threshold.

8. The bolt loosening detection method according to claim 7, characterized in that: The detection range is set as follows: the first permanent magnet (10) is moved, and the output voltage of the TMR sensor chip (23) is detected by the detection circuit. When the output voltage is equal to the set threshold, the distance between the first permanent magnet (10) and the second permanent magnet (21) is the detection range.

9. The bolt loosening detection method according to claim 7, characterized in that: When the nut (101) rotates and drives the first permanent magnet (10) to move and be within the detection range, the TMR sensor chip (23) becomes saturated magnetized, the tunneling current increases, the detection circuit detects the output voltage of the TMR sensor chip (23), the output voltage is processed by the signal processing circuit and outputs the processed signal, the processed signal is greater than the set threshold, the wireless gateway outputs a high level, and it is determined that the bolt has not loosened; when the nut (101) rotates and drives the first permanent magnet (10) to move and leave the detection range, the saturated magnetization state of the TMR sensor chip (23) disappears, the tunneling current decreases, the detection circuit detects the output voltage of the TMR sensor chip (23), the output voltage is processed by the signal processing circuit and outputs the processed signal, the processed signal is less than the set threshold, the wireless gateway outputs a low level, and it is determined that the bolt has loosened.

10. The bolt loosening detection method according to claim 7, characterized in that: Minimum loosening angle of bolts for: in, To set a threshold, , All are proportionality constants. This is the initial resistance of the TMR sensor chip. The initial magnetic field strength is given.

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