A capacitive self-sensing bolt and detection method thereof

Abstract

A capacitive self-sensing bolt and a detection method thereof, wherein the structure is an integral device composed of an inward concave nut, a screw rod, a capacitive pressure element, a wireless transmission system and auxiliary components. The inward concave nut is formed by opening a cylindrical hole groove on the basis of a traditional nut, a disc buckle is installed at the bottom of the hole groove, and a small round hole is formed at the bottom of the cylindrical hole groove; the screw rod is formed by opening a cylindrical hole that runs through the entire screw rod on the basis of a traditional screw rod, corresponding to the cylindrical hole groove of the inward concave nut; the capacitive pressure element adopts a cylindrical form that matches the cylindrical hole of the screw rod; the wireless transmission system is composed of a data acquisition and storage unit, a wireless signal transmission system and a built-in power supply element, and is equipped with a backup power supply; the auxiliary components include a sealing rubber ring, a buckle, a waterproof sealant, and an insulating filler, which seal the hole groove and hole of the inward concave nut and the screw rod to ensure the normal operation of the wireless transmission system and the capacitive pressure sensor.

Description

Technical Field

[0001] The invention relates to capacitive self-sensing bolts and detection technology. Background Art

[0002] Bolt connection is a widely used connection method in the field of engineering structures. It has the advantages of easy disassembly and assembly and strong reliability. Bolts are widely used in bridge structures, rail transit, aerospace, automobile industry, special equipment, chemical pipelines, etc. However, various structural damage problems and operation and maintenance problems caused by bolt damage and loosening cannot be ignored. Especially in the aerospace field, major accidents are often caused by ignoring a small loose bolt. Bolt connection structure is the most commonly used mechanical connection method. Affected by the surface roughness, the joint surface of the two parts connected by bolts will undergo elastic deformation under external loading, so the joint surface exhibits complex mechanical properties. It is worth noting that the internal damage and external looseness of the bolts do not directly lead to the collapse of the structure in most cases, but the continuous accumulation of damage will lead to catastrophic consequences. Therefore, monitoring the looseness of bolt connections has important theoretical significance and engineering practical value.

[0003] The most primitive identification method is the manual inspection method, which can be divided into two types: visual inspection method and sound inspection method. The manual identification method is the simplest and most widely used method. Visual inspection is to observe the changes and discoloration of metal parts with the naked eye. It can also be judged whether the bolt is loose by drawing a continuous line on the nut and the connected part and observing the offset distance of the line within a certain period of time. Sound is to judge whether there is looseness or other abnormalities by knocking on the bolt connection part from the sound. For example, railway workers will find loose bolts from the abnormal sound when they hit the rails with a hammer. In fact, the loose identification method used for bolt detection at this stage is still mainly based on manual line identification. The red line and the blue line represent the marking lines drawn during the regular inspection at different time points. The obvious offset distance between the two different color lines indicates that the bolts are loose during this period of time. The advantage of this method is that it is simple and easy to understand, but its accuracy and efficiency are low. When a large number of bolts are used in the structure, the inspection amount is large, and the working status of the bolts can only be detected by surface observation, and the stress conditions inside the structure cannot be judged. In addition, the environment of most bolt joints is complex and requires inspectors to climb to a high place, so the potential safety risk is high. This patent provides a new capacitive self-sensing bolt design and its detection method, which can not only detect the working and stress status of the bolts and perform status evaluation, but also achieve self-monitoring through an internal self-sensing system and a wireless transmission system, avoiding the low accuracy and efficiency of manual detection, and reducing the risk of manual inspection of high-risk structures. The outside of the bolt adopts a P6-level waterproof seal to form an integral structure with the bolt, which has stronger impact resistance, signal anti-interference, and structural stability.

[0004] The identification and monitoring of bolt loosening is a hot issue that needs to be solved in the field of engineering structures. This problem has not been well solved since the industrial revolution. Therefore, it is urgent to propose a new capacitive self-sensing bolt design and its detection method. This paper aims to design a new bolt structure and propose an online detection and monitoring method for bolt loosening, thereby reducing the number of manual inspections, the incidence of safety accidents caused by bolts, and the cost of manual operation and maintenance. Summary of the invention

[0005] The purpose of the present invention is to provide a capacitive self-sensing bolt and a detection method thereof.

[0006] The present invention discloses a capacitive self-sensing bolt and a detection method thereof. The capacitive self-sensing bolt comprises an inner concave nut 1, a screw rod 2, and a capacitive pressure element 3. A circular hole 1-9 is opened at the bottom of the inner concave nut 1 and penetrates to the top of the screw rod 2. From top to bottom, the inner concave nut 1 comprises a chuck 1-8, a wireless transmission system 1-4, a backup power supply 1-3, a circular cover plate 1-2, and a hexagonal bolt 1-1. A cylindrical hole 2 is opened at the center of the circular cross section at the bottom of the screw rod 2 and penetrates the entire screw rod 2. -1, and the hole is no larger than 1 / 4 of the diameter of the screw rod 2, and corresponds to the circular hole groove 1-9 of the concave nut 1, and the diameter of the circular hole groove 1-9 is no larger than 1 / 2 of the cylindrical hole 2-1, the shape and size of the built-in capacitive pressure element 3-1 are consistent with the cylindrical hole 2-1, the two are connected by gluing, and spot welding is performed at the bottom of the cylindrical hole 2-1, and the threaded section 2-2 near the bottom of the cylindrical hole 2-1 is mechanically connected to the cross screw 3-2.

[0007] The capacitive self-sensing bolt detection method of the present invention comprises the following steps:

[0008] Step (1) ensuring the sealing of the bottom of the screw rod 2 and the threaded section 2-2 meeting the corresponding gap error and gap level, determining the type, specification, size, material and heat treatment process of the screw rod 2, so as to determine the conversion of the corresponding capacitor charging and discharging parameters after data transmission;

[0009] Step (2) Check the connection between the signal output line 3-1a of the capacitive piezoelectric element 3-1 and the wireless transmission system 1-4. The backup power supply 1-3 is connected to the wireless transmission system 1-4 via the wedge-shaped buckle 1-3a. The wedge-shaped buckle 1-3a is fixed and powered by a metal conductive material to ensure the stability of the internal transmission line and power supply.

[0010] Step (3) confirm that the screw rod 2 of the capacitive self-sensing bolt is in a stressed state, open the circular cover plate 1-2, turn on the backup power supply 1-3 and the wireless transmission system 1-4 inside the concave nut 1, and finally tighten the concave nut 1 through the circular cover plate 1-2 and the hexagonal bolt 1-1, and monitor the stability of the bolt signal through the acquisition terminal on site;

[0011] Step (4) Based on the material type, specification and size, material density, elastic modulus, Poisson's ratio and conductivity of the capacitive self-sensing bolt, the measurement circuit signal is calculated by formula in the background of the PC to obtain the conversion between the capacitance output and the compressive stress, and the stress limit of the bolt structure is calculated to determine the warning value of the structure, and then the detection frequency corresponding to each bolt is adjusted and the bolts are numbered and sorted;

[0012] In step (5), when the capacitive self-sensing bolt is detected, the signal-to-noise ratio of the output detection signal is not less than 3:1. The detection frequency adjusted in step (4) is used to upload the detection data to the monitoring service platform for real-time recording and storage. Different warning values ​​are set according to the type of bolt, and an alarm is issued for abnormal signals generated during the work, and the relevant maintenance personnel are notified to re-inspect and replace the corresponding bolts according to the bolt number.

[0013] The benefits of the present invention are as follows: 1. A capacitive pressure element is arranged inside the screw rod of the present invention, and the force change of the screw rod can be accurately collected under external force, and the screw rod can protect the capacitive pressure element, avoiding damage caused by external uncertain factors of the sensor. The part in contact with the external environment is sealed and fixed with a cross screw, and the circuit of the capacitive pressure element is connected inside the screw rod and the concave nut, avoiding the breakage and damage of the transmission line caused by leakage of the circuit, extending its service life, and ensuring the authenticity and effectiveness of the measurement signal;

[0014] 2. The concave nut of the present invention can ensure the stability of the wireless transmission system and the backup power supply. The concave nut is sealed by the circular cover plate in the concave nut to prevent damage to the wireless transmission system and the backup power supply caused by changes in the external environment. The circular cover plate and the concave nut have a certain rigidity to form a closed space and can resist the impact of external loads to ensure the safety of the internal structure. The wireless transmission system and the backup power supply are connected by a wedge-shaped buckle, and the wireless transmission system and the concave nut are connected by a chuck, which are interlocked, and the gaps are filled with insulating fillers, which ensure the stability of the internal structure and prevent the backup power supply from leaking and short-circuiting and damaging the wireless transmission system and the capacitive pressure element;

[0015] 3. The capacitive self-sensing bolt of the present invention forms an integral body on the outside, has a strong ability to resist external non-monitoring loads, and adopts wireless transmission to avoid the line damage problem of traditional wired transmission and the cluttered lines when arranged in large quantities. This bolt can be used under various conditions, has a wide range of applications, is easy to install, and has strong stability and data measurement effectiveness;

[0016] 4. The self-sensing principle of the capacitive self-sensing bolt of the present invention is that the external load acts on the screw rod, and the load is transmitted to the built-in capacitive pressure element through the screw rod, causing the change of the internal current of the capacitive pressure element, and the change of the current is transmitted to the wireless signal system inside the concave nut through the signal transmission line. The wireless signal system records the change of the current and transmits it to the signal acquisition terminal, and the stress state of the bolt is monitored in real time. The bolts with abnormal stress can be checked or replaced immediately to ensure the safety and stability of the structure and reduce the structural damage caused by problems such as bolt damage and loosening;

[0017] 5. The parts involved in the self-sensing bolt device of the present invention can be easily realized by using the current processing technology. After being prefabricated in the factory, they can be assembled on site, with strong processing performance and strong connectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is an overall diagram of the capacitive self-sensing bolt of the present invention. Figure 2 This is a cross-sectional view of a capacitive self-sensing bolt. Figure 3 This is a cross-sectional view of the internal equipment installation of the concave nut. Figure 4 This is the internal view of the concave nut. Figure 5 The structure diagram of the screw rod is shown in Figure 2. Figure 6 It is a schematic diagram of the structure of the capacitive pressure element. Figure 7 This is the internal details of the capacitive pressure element. Figure 8 This is the flow chart of the capacitive self-sensing bolt detection method. Fig. 9 The schematic diagram of the built-in capacitive piezoelectric element of the capacitive self-sensing bolt monitoring the bolt force change data, wherein, 1: concave nut, 1-1: hexagonal bolt, 1-2: circular cover plate, 1-3: backup power supply, 1-3a: wedge buckle, 1-4: wireless transmission system, 1-4a: L-shaped buckle, 1-5: nut barrel, 1-6: cap top thread hole, 1-7: nut bottom plate, 1-8: chuck, 1-9: circular hole. 2: screw rod, 2-1: cylindrical hole, 2-2: threaded section, 3: capacitive pressure element, 3-1: built-in capacitive pressure element, 3-1a: signal output line, 3-1b: glass layer, 3-1c: isolation diaphragm, 3-1d: sensing channel, 3-1e: measuring membrane, 3-1f: base, 3-1g: metal membrane, 3-1h, metal protective shell, 3-2: cross screw. DETAILED DESCRIPTION

[0019] The present invention discloses a capacitive self-sensing bolt and a detection method thereof. The capacitive self-sensing bolt comprises an inner concave nut 1, a screw rod 2, and a capacitive pressure element 3. A circular hole 1-9 is opened at the bottom of the inner concave nut 1 and penetrates to the top of the screw rod 2. From top to bottom, the inner concave nut 1 comprises a chuck 1-8, a wireless transmission system 1-4, a backup power supply 1-3, a circular cover plate 1-2, and a hexagonal bolt 1-1. A cylindrical hole 2 is opened at the center of the circular cross section at the bottom of the screw rod 2 and penetrates the entire screw rod 2. -1, and the hole is no larger than 1 / 4 of the diameter of the screw rod 2, and corresponds to the circular hole groove 1-9 of the concave nut 1, and the diameter of the circular hole groove 1-9 is no larger than 1 / 2 of the cylindrical hole 2-1, the shape and size of the built-in capacitive pressure element 3-1 are consistent with the cylindrical hole 2-1, the two are connected by gluing, and spot welding is performed at the bottom of the cylindrical hole 2-1, and the threaded section 2-2 near the bottom of the cylindrical hole 2-1 is mechanically connected to the cross screw 3-2.

[0020] The capacitive self-sensing bolt described above, the L-shaped buckle 1-4a at the bottom of the wireless transmission system 1-4 in the concave nut 1 corresponds to the opening of the chuck 1-8, and then is rotated and fixed, and the backup power supply 1-3 is fixed by pressing through the wedge-shaped buckle 1-3a at the bottom and the clamping hole on the upper part of the wireless transmission system 1-4 to ensure the stability of the wireless transmission system 1-4 and the backup power supply 1-3 inside the concave nut 1 to prevent them from hitting the inner wall of the concave nut 1 and causing damage, and the circular cover plate 1-2 and the top thread hole 1-6 on the concave nut 1 are connected and fixed by the hexagonal bolt 1-1.

[0021] The capacitive self-sensing bolt described above, the shape, size and length of the capacitive pressure element 3 are consistent with the cylindrical hole 2-1 of the screw rod 2, the two are connected by bonding and spot welding through the bottom of the cylindrical hole 2-1 to fix the capacitive pressure element 3-1, and finally fixed and sealed by the bottom cross screw 3-2; the capacitive pressure element 3 is composed of an outer metal protective shell 3-1h, a base 3-1f, an isolation diaphragm 3-1c, a measuring membrane 3-1e, a glass layer 3-1b, a metal film 3-1g, a sensing channel 3-1d, and a signal output line 3-1a.

[0022] In the capacitive self-sensing bolt described above, the metal protective shell 3-1h provides overall protection for the capacitive pressure element 3, the base 3-1f is used to ensure the stability of the internal structure and the validity of the output measurement value, the isolation diaphragm 3-1c is used to isolate the metal protective shell 3-1h from the internal structure and play a role in transferring the load, the metal film 3-1g is used to separate the glass layer 3-1b and the internal measuring unit, the glass layer 3-1b is used to protect the internal measuring unit and separate the external base 3-1f. When the external load changes, the force is transmitted to the sensing channel 3-1d through the isolation diaphragm 3-1c, and the compression or stretching of the sensing channel 3-1d causes the internal capacitance to change, so that the measuring membrane 3-1e at the central axis position of the structure is offset, and the change in internal capacitance causes the change in current. Finally, the current change signal is output through the signal output line 3-1a, so as to achieve the purpose of monitoring the change in bolt force.

[0023] The capacitive self-sensing bolt described above is mechanically connected by an integral capacitive pressure element 3 and the cylindrical hole 2-1 of the screw rod 2, and is fixed and sealed by a cross screw 3-2 with a sealing rubber ring. The signal output line 3-1a of the capacitive pressure element 3 passes through the circular hole groove 1-9 in the concave nut 1 corresponding to the wire hole and is connected to the wireless transmission system 1-4. The backup power supply 1-3 is fixed to the wireless transmission system 1-4 by a wedge-shaped buckle 1-3a. Finally, the concave nut 1 is sealed with a circular cover plate 1-2 and a hexagonal bolt 1-1 to ensure that the capacitive pressure element 3, the wireless transmission system 1-4 and the backup power supply 1-3 inside the integral bolt will not be damaged internally due to rain erosion and impact in the external environment.

[0024] For the capacitive self-sensing bolt described above, when an external load acts on the screw rod 2, the force is transmitted to and acts on the internal capacitive pressure element 3, and its current change is transmitted to the wireless transmission system 1-4 through the signal output line 3-1a, and the power supply is supported by the backup power supply 1-3 and the built-in power supply element of the wireless transmission system 1-4, and the data is recorded and the load change on the screw rod 2 is transmitted to the acquisition terminal.

[0025] The capacitive self-sensing bolt detection method of the present invention comprises the following steps:

[0026] Step (1) ensuring the sealing of the bottom of the screw rod 2 and the threaded section 2-2 meeting the corresponding gap error and gap level, determining the type, specification, size, material and heat treatment process of the screw rod 2, so as to determine the conversion of the corresponding capacitor charging and discharging parameters after data transmission;

[0027] Step (2) Check the connection between the signal output line 3-1a of the capacitive piezoelectric element 3-1 and the wireless transmission system 1-4. The backup power supply 1-3 is connected to the wireless transmission system 1-4 via the wedge-shaped buckle 1-3a. The wedge-shaped buckle 1-3a is fixed and powered by a metal conductive material to ensure the stability of the internal transmission line and power supply.

[0028] Step (3) confirm that the screw rod 2 of the capacitive self-sensing bolt is in a stressed state, open the circular cover plate 1-2, turn on the backup power supply 1-3 and the wireless transmission system 1-4 inside the concave nut 1, and finally tighten the concave nut 1 through the circular cover plate 1-2 and the hexagonal bolt 1-1, and monitor the stability of the bolt signal through the acquisition terminal on site;

[0029] Step (4) Based on the material type, specification and size, material density, elastic modulus, Poisson's ratio and conductivity of the capacitive self-sensing bolt, the measurement circuit signal is calculated by formula in the background of the PC to obtain the conversion between the capacitance output and the compressive stress, and the stress limit of the bolt structure is calculated to determine the warning value of the structure, and then the detection frequency corresponding to each bolt is adjusted and the bolts are numbered and sorted;

[0030] In step (5), when the capacitive self-sensing bolt is detected, the signal-to-noise ratio of the output detection signal is not less than 3:1. The detection frequency adjusted in step (4) is used to upload the detection data to the monitoring service platform for real-time recording and storage. Different warning values ​​are set according to the type of bolt, and an alarm is issued for abnormal signals generated during the work, and the relevant maintenance personnel are notified to re-inspect and replace the corresponding bolts according to the bolt number.

[0031] The technical content of the present invention is further developed in conjunction with the embodiments below. Figure 1 , Figure 2 As shown, the overall structure of the capacitive self-sensing bolt is composed of an inner concave nut 1, a screw rod 2, and a capacitive pressure element 3, wherein the inner concave nut 1 and the screw rod 2 form an integral structure, and the capacitive pressure element 3 is built into the cylindrical hole 2-1 opened in the screw rod 2.

[0032] like Figure 3 , Figure 4As shown, it is the internal structure of the concave nut 1, wherein the hexagonal bolt 1-1 and the circular cover plate 1-2 are used to seal the concave nut 1, reduce the damage to the internal structure caused by external load impact, and prevent rain erosion from causing short circuit and corrosion of the internal structural unit; wherein the wireless transmission system 1-4 is connected and fixed to the chuck 1-8 at the bottom of the nut barrel 1-5 through the L-shaped buckle at the bottom, the circular hole 1-9 is used for the wire hole through which the transmission line of the lower capacitive pressure element 3 passes, the backup power supply 1-3 is connected and fixed to the wedge-shaped card space at the top of the wireless transmission system 1-4 through the wedge-shaped buckle 1-3a at the bottom, and the gap in the nut barrel 1-5 is filled with insulating material, and the surface of the wireless transmission system 1-4 and the backup power supply 1-3 is coated with insulating paint to prevent short circuit and damage to the equipment.

[0033] like Figure 6 As shown, it is a structural diagram of the screw rod 2. A cylindrical hole 2-1 is drilled on the screw rod 2 by a drilling machine, and threading is performed on the bottom section of the cylindrical hole 2-1. The length of the threaded section 2-2 is not greater than 1 / 6 of the total length.

[0034] like Figure 6 , Figure 7 As shown, the interior of the capacitive pressure element 3 is composed of a signal output line 3-1a, a glass layer 3-1b, an isolation diaphragm 3-1c, a sensing channel 3-1d, a measuring membrane 3-1e, a base 3-1f, a metal film 3-1g, and a metal protective shell 3-1h. The size of the capacitive pressure element 3 is the same as the cylindrical hole 2-1 of the screw rod 2. The signal output line 3-1a passes through the cylindrical hole 2-1 and is connected to the wireless transmission system through the circular hole 1-9 at the bottom of the concave nut 1. The threaded section 2-2 at the bottom of the screw rod 2 is fixed and sealed with a cross screw 3-2 of the same length.

[0035] Depend on Figure 8 , Fig. 9 As shown in the figure, it is a detection flow chart and a force change diagram of the screw rod 2. First, check whether the capacitive self-sensing bolt is damaged. Then, determine the conversion relationship between the capacitor charge and discharge parameters according to the type of the bolt. Next, turn on the backup power supply 1-3 and the wireless transmission system 1-4 in the concave nut 1, number the monitored bolts, record the data through the wireless transmission system 1-4 and upload it to the acquisition terminal, and finally set the warning value according to the type of the bolt, and alarm for abnormal signals. The figure also provides the signal detected by the internal capacitive piezoelectric element 3-1 when the external load acts on the screw rod 2. The force transformation of the bolt is obtained through the corresponding conversion relationship, and the warning value is set according to the type and material of the bolt.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A capacitive self-sensing bolt, comprising an inner concave nut (1), a screw (2), and a capacitive pressure element (3), characterized in that A circular hole (1-9) is opened at the bottom of the concave nut (1) to penetrate to the top of the screw rod (2); the concave nut (1) contains a chuck (1-8), a wireless transmission system (1-4), a backup power supply (1-3), a circular cover plate (1-2) and a hexagonal bolt (1-1) from top to bottom; a cylindrical hole (2-1) is opened at the center of the circular cross section at the bottom of the screw rod (2) to penetrate the entire screw rod (2); and the cylindrical hole (2-1) is not larger than 1 / 4 of the diameter of the screw rod (2). The circular hole (1-9) corresponds to the concave nut (1), and the diameter of the circular hole (1-9) is not greater than 1 / 2 of the cylindrical hole (2-1). The shape and size of the built-in capacitive pressure element (3-1) match the cylindrical hole (2-1). The two are connected by gluing and spot welding at the bottom of the cylindrical hole (2-1). The threaded section (2-2) near the bottom of the cylindrical hole (2-1) is mechanically connected to the cross screw (3-2). The shape, size and length of the capacitive pressure element (3) match the cylindrical hole (2-1) of the screw rod (2), and the two are connected by adhesive bonding and spot welding through the bottom of the cylindrical hole (2-1) to fix the built-in capacitive pressure element (3-1), and finally fixed and sealed by the bottom cross screw (3-2); the capacitive pressure element (3) is composed of an outer metal protective shell (3-1h), a base (3-1f), an isolation diaphragm (3-1c), a measuring film (3-1e), a glass layer (3-1b), a metal film (3-1g), a sensing channel (3-1d), and a signal output line (3-1a); The metal protective shell (3-1h) provides overall protection for the capacitive pressure element (3); the base (3-1f) is used to ensure the stability of the internal structure and the validity of the output measurement value; the isolation diaphragm (3-1c) is used to isolate the metal protective shell (3-1h) from the internal structure and to transfer the load; the metal film (3-1g) is used to separate the glass layer (3-1b) and the internal measurement unit; the glass layer (3-1b) is used to protect the internal measurement unit and to separate the external base (3-1f); when the external load changes, the force is transmitted to the sensing channel (3-1d) through the isolation diaphragm (3-1c); the compression or stretching of the sensing channel (3-1d) causes the internal capacitance to change, so that the measuring film (3-1e) at the central axis position of the structure is offset; the change in internal capacitance causes the change in current; finally, the change in current is output as a signal through the signal output line (3-1a), thereby achieving the purpose of monitoring the change in bolt force.

2. The capacitive self-sensing bolt according to claim 1, characterized in that: The L-shaped buckle (1-4a) at the bottom of the wireless transmission system (1-4) in the concave nut (1) corresponds to the opening of the chuck (1-8), and then is rotated and fixed; the backup power supply (1-3) is fixed by pressing the wedge-shaped buckle (1-3a) at the bottom and the clamping hole at the top of the wireless transmission system (1-4); the circular cover plate (1-2) and the cap top thread hole (1-6) on the concave nut (1) are connected and fixed by the hexagonal bolt (1-1).

3. The capacitive self-sensing bolt according to claim 1, characterized in that: When an external load acts on the screw rod (2), the force is transmitted to and acts on the internal capacitive pressure element (3), and the current change is transmitted to the wireless transmission system (1-4) through the signal output line (3-1a), and the backup power supply (1-3) and the built-in power supply element of the wireless transmission system (1-4) are used for power supply support, and data is recorded and the load change on the screw rod (2) is transmitted to the collection terminal.

4. The capacitive self-sensing bolt detection method according to claim 1 is characterized in that: The steps are: Step (1) ensures the sealing of the bottom of the screw rod (2) and the threaded section (2-2) meets the corresponding gap error and gap level, determines the type, specification, size, material and heat treatment process of the screw rod (2), so as to determine the conversion of the corresponding capacitor charging and discharging parameters after data transmission; Step (2) checks the connection between the signal output line (3-1a) of the built-in capacitive pressure element (3-1) and the wireless transmission system (1-4), and the connection between the backup power supply (1-3) and the wireless transmission system (1-4) through the wedge-shaped buckle (1-3a), and the wedge-shaped buckle (1-3a) is fixed and powered by metal conductive material to ensure the stability of the internal transmission line and power supply; Step (3) determines that the screw rod (2) of the capacitive self-sensing bolt is in a stressed state, opens the circular cover plate (1-2), turns on the backup power supply (1-3) and the wireless transmission system (1-4) inside the concave nut (1), and finally tightens the concave nut (1) through the circular cover plate (1-2) and the hexagonal bolt (1-1), and monitors the stability of the bolt signal through the acquisition terminal on site; Step (4) Based on the material type, specification and size, material density, elastic modulus, Poisson's ratio and conductivity of the capacitive self-sensing bolt, the measurement circuit signal is calculated by formula in the background of the PC to obtain the conversion between the capacitance output and the compressive stress, and the stress limit of the bolt structure is calculated to determine the warning value of the structure, and then the detection frequency corresponding to each bolt is adjusted and the bolts are numbered and sorted; In step (5), when the capacitive self-sensing bolt is detected, the signal-to-noise ratio of the output detection signal is not less than 3:

1. The detection frequency adjusted in the fourth step is used to upload the detection data to the monitoring service platform for record storage in real time. Different warning values ​​are set according to the type of bolt, and an alarm is triggered for abnormal signals generated during work, and relevant maintenance personnel are notified to re-inspect and replace the corresponding bolts according to the bolt number.

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