Monitoring device, system and method for tunnel portal slope protection structure

Abstract

The invention relates to the technical field of online monitoring, in particular to a monitoring device and system for a tunnel portal slope protection structure. The monitoring device for the tunnel portal slope protection structure comprises a shell, two connecting rods are arranged on the shell in a sliding and penetrating mode, the ends, located in the shell, of the connecting rods are in threaded connection with first adjusting nuts and second adjusting nuts, the ends, located in the shell, of the connecting rods are sleeved with springs, and balance beams are installed at the ends, located in the shell, of the two connecting rods; a fiber grating strain gauge is installed on the balance beam, the first adjusting nut is located at the bottom of the shell, the spring is located between the first adjusting nut and the balance beam, the spring and the second adjusting nut are located on the two opposite sides of the balance beam respectively, and the monitoring device can monitor the tunnel portal slope protection structure in real time.

Description

Technical Field

[0001] The present invention relates to the technical field of online monitoring, and in particular to a monitoring device and system for a tunnel entrance slope protection structure. Background Art

[0002] The tunnel entrance slope protection structure is an important part of the overall structure of the rail transit tunnel project, including slope protection, cofferdam and retaining wall.

[0003] When the foundation is unstable during construction or as the service life increases, the tunnel entrance slope protection structure is prone to a certain degree of aging and deformation. In particular, the tunnel entrance slope protection structure built on soft soil layers will be unevenly deformed, collapsed or partially damaged under the influence of external variable loads such as foundation settlement, rain erosion, and changes in the surrounding geological environment.

[0004] In related technologies, the monitoring of the slope protection structure at the tunnel entrance adopts manual inspection and video monitoring, which requires special personnel to conduct inspections or retrieve the camera image video at the location. Without a pre-alarm mechanism, real-time monitoring cannot be achieved, and danger cannot be predicted in advance. Especially in extremely bad weather conditions, the video monitoring process has high requirements for the monitored environment, and it is necessary to ensure that the monitoring environment is dust-free or unobstructed, and the monitoring quality is greatly affected by the external environment. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a monitoring device, system and method for a tunnel entrance slope protection structure. The monitoring device for a tunnel entrance slope protection structure can perform real-time monitoring of the tunnel entrance slope protection structure; the monitoring system for a tunnel entrance slope protection structure can implement a monitoring method for a tunnel entrance slope protection structure to obtain monitoring information and issue an alarm when the tunnel entrance slope protection structure undergoes structural changes.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a monitoring device for a tunnel entrance slope protection structure, comprising: a shell, two connecting rods slidably penetrated through the shell, one end of the connecting rod located in the shell is threadedly connected with a first adjusting nut and a second adjusting nut, one end of the connecting rod located in the shell is sleeved with a spring, a balance beam is installed on one end of the two connecting rods located in the shell, a fiber grating strain gauge is installed on the balance beam, the first adjusting nut is located at the bottom of the shell, the spring is located between the first adjusting nut and the balance beam, and the spring and the second adjusting nut are respectively located on opposite sides of the balance beam.

[0008] By adopting the above technical solution, when monitoring the tunnel entrance slope protection structure, first use the embedded bolts as anchor points to fix the shell on the prefabricated installation platform, and use the positioning anchor cable to connect the anchor point to the connecting rod one-to-one. Then, first pre-tighten the first adjustment nut to make the connecting rod slide into the shell to ensure that the positioning anchor cable has a pre-tightening force. Then use the optical fiber demodulation device to connect with the fiber grating strain gauge, and pre-tighten the second adjustment nut to compress the spring to ensure that the spring has a pre-tightening force. By adjusting the spring pre-tightening force, the internal stress on the balance beam can be adjusted to a certain calibration value, and this calibration value corresponds to the wavelength value on the fiber grating strain gauge recorded by the optical fiber demodulation device in this state. This wavelength value is entered into the database of the alarm software of the monitoring terminal, and the alarm software deducts the temperature effect from the calibrated temperature coefficient of the environmental influence to obtain the real wavelength value λ0, and then sets the alarm threshold of the alarm software. The alarm software verifies the true wavelength value λ0 in real time according to the alarm threshold. When it is found that the true wavelength value λ0 cannot be read or the true wavelength value λ0 increases or decreases abnormally, the alarm mechanism is activated, thereby realizing real-time monitoring of the tunnel entrance slope protection structure.

[0009] Optionally, a connecting hole is provided on one end of the connecting rod located outside the shell.

[0010] By adopting the above technical solution, the connection hole can be easily connected to the connecting rod and the positioning anchor cable.

[0011] Optionally, a gasket is provided between the second adjusting nut and the balance beam.

[0012] By adopting the above technical solution,

[0013] Optionally, the fiber grating strain gauge is connected to an optical fiber, a penetration hole is opened on the shell, a sealing plug is installed in the penetration hole, and the optical fiber is penetrated through the sealing plug.

[0014] By adopting the above technical solution, the second adjusting nut can be prevented from loosening.

[0015] In a second aspect, the present invention provides a monitoring system for a tunnel entrance slope protection structure, comprising at least one monitoring device for a tunnel entrance slope protection structure as described in the first aspect, and also comprising a server, a fiber optic Bragg grating demodulation device and at least one user terminal; the server is respectively communicatively connected with the fiber optic Bragg grating demodulation device, the user terminal and the monitoring device.

[0016] By adopting the above technical solution, the server can obtain the true wavelength value of the fiber Bragg grating strain gauge, and determine the grating period of the fiber Bragg grating strain gauge based on the true wavelength value, and then monitor the change of the grating period in real time, and determine the change of the true wavelength value based on the change of the grating period. Finally, when the change of the true wavelength value exceeds the alarm threshold, an alarm signal is issued, thereby obtaining monitoring information and realizing an alarm when the tunnel entrance slope protection structure undergoes structural changes.

[0017] Optionally, the monitoring system for the tunnel entrance slope protection structure further includes: an optical fiber gap sensor, an optical fiber water pressure sensor, an optical fiber vibration sensor, and an optical fiber temperature sensor, which are respectively connected to the server for communication.

[0018] By adopting the above technical solutions, the optical fiber gap sensor can monitor the gap, the optical fiber water pressure sensor can monitor the water pressure, the optical fiber vibration sensor can monitor the vibration, and the optical fiber temperature sensor can monitor the temperature, thereby improving the accuracy of the monitoring system in monitoring the tunnel entrance slope protection structure.

[0019] In a third aspect, the present invention provides a monitoring method for a tunnel entrance slope protection structure, which is applied to the monitoring system for a tunnel entrance slope protection structure as described in the second aspect, and comprises the following steps:

[0020] S1: Get the real wavelength value of the fiber Bragg grating strain gauge;

[0021] S2: Determine the grating period of the fiber Bragg grating strain gauge based on the true wavelength value;

[0022] S3: monitoring a first change amount of the grating period in real time, and determining a second change amount of the real wavelength value based on the first change amount;

[0023] S4: When the second change exceeds the alarm threshold, an alarm signal is issued.

[0024] By adopting the above technical solution, the server can determine the grating period of the fiber Bragg grating strain gauge according to the real wavelength value, and then monitor the first change of the grating period in real time, and determine the second change of the real wavelength value based on the first change, and finally send out an alarm signal when the second change exceeds the alarm threshold, thereby obtaining monitoring information and issuing an alarm when the slope protection structure at the tunnel entrance undergoes structural changes.

[0025] Optionally, the calculation formula of the true wavelength value is:

[0026] λ0=λ B -λ T

[0027] Among them, λ0 represents the real wavelength value, λ B represents the Bragg wavelength of the grating, λT Represents the wavelength change of the fiber Bragg grating strain gauge under the influence of ambient temperature change;

[0028] The Bragg wavelength calculation formula of the grating is:

[0029] λ B =2nΛ

[0030] Where n represents the effective refractive index of the core mode, and Λ represents the grating period;

[0031] The wavelength variation of the fiber grating strain gauge is affected by the internal stress of the balance beam, and the internal stress of the balance beam changes according to the change of the preload force of the spring, and the preload force of the spring changes according to the tension on the positioning anchor cable applied to the connecting rod;

[0032] The formula for the change in the preload force of the spring is:

[0033] F=KΔS

[0034] Among them, F represents the preload force of the spring, K represents the elastic modulus of the spring, and ΔS represents the corresponding loosening stroke of the spring and the positioning cable.

[0035] By adopting the above technical scheme, the positioning anchor cable, connecting rod, spring, balance beam, fiber Bragg grating strain gauge, fiber Bragg grating demodulation equipment, server and user end can be connected together, so that when the positioning anchor cable is loosened due to the slope protection structure at the tunnel entrance, the change in force can be converted into a change in the grating period and displayed, thereby obtaining monitoring information and achieving the purpose of alarming when the slope protection structure at the tunnel entrance undergoes structural changes.

[0036] In summary, the present invention at least includes the following beneficial technical effects:

[0037] 1. The present invention combines the characteristics of optical fiber sensing to achieve real-time online monitoring of the tunnel entrance slope protection structure, which is not affected by environmental monitoring and can be monitored at different stages of construction and operation. During the construction stage, it can ensure the safety of interval workers and equipment, and can be connected to the intelligent interval operation management system during operation. It can transition from construction safety monitoring to later operational health monitoring, continuously realize the overall health monitoring process of the interval, and adjust the sampling frequency of monitoring data according to the stable state of the interval construction period and operation period. The complete life cycle data of the overall support structure of the interval project can be constructed.

[0038] 2. The present invention utilizes the real-time online characteristics of fiber Bragg grating sensing technology, and can transmit the deformation data collected by the fiber Bragg grating strain gauge to the server in real time through the optical cable in the form of data packets with fiber Bragg grating wavelength changes. Based on the corresponding relationship between displacement, strain, and wavelength, the deformation of the tunnel entrance slope protection structure caused by foundation settlement and stress state can be monitored in real time online, and the alarm threshold and alarm level can be set. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic cross-sectional structure diagram of a monitoring device for a tunnel entrance slope protection structure according to an embodiment of the present invention;

[0040] Figure 2 A top view of a monitoring device for a tunnel entrance slope protection structure according to an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of a monitoring system for a tunnel entrance slope protection structure according to an embodiment of the present invention;

[0042] Figure 4 A schematic diagram of another monitoring system for a tunnel entrance slope protection structure according to an embodiment of the present invention;

[0043] Figure 5 The present invention is a flowchart of a monitoring method for a tunnel entrance slope protection structure according to an embodiment of the present invention.

[0044] Explanation of the accompanying drawings: 1. Shell; 2. Fiber Bragg grating strain gauge; 3. Balance beam; 4. Connecting rod; 5. Spring; 6. First adjusting nut; 7. Second adjusting nut; 8. Connecting hole; 10. Gasket; 11. Sealing plug; 12. Server; 13. Fiber Bragg grating demodulation device; 14. User end; 15. Fiber gap sensor; 16. Fiber water pressure sensor; 17. Fiber vibration sensor; 18. Fiber temperature sensor. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] The terms used in the following embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to be used as limitations of the present invention. As used in the specification of the present invention and the appended claims, the singular expressions "one", "a kind of", "said", "above", "the" and "this" are intended to also include plural expressions, unless there is a clear contrary indication in its context. It should also be understood that the term "and / or" used in the present invention refers to and includes any or all possible combinations of one or more listed items. The term "exemplary" means "used as an example, embodiment or illustrative", and any embodiment described as "exemplary" here does not have to be interpreted as being superior to or better than other embodiments. The terms "first" and "second" are only used for descriptive purposes, and cannot be understood as implying or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" can expressly or implicitly include one or more of these features, and in the description of the embodiments of the present invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0047] An embodiment of the present invention provides a monitoring device for a tunnel entrance slope protection structure.

[0048] refer to Figure 1 and Figure 2 A monitoring device for a tunnel entrance slope protection structure includes: a housing 1, a fiber grating strain gauge 2, a balance beam 3, two connecting rods 4, two springs 5, two first adjusting nuts 6 and two second adjusting nuts 7.

[0049] The two connecting rods 4 are respectively slidably disposed on the bottom of the housing 1, and the two connecting rods 4 are arranged side by side. The two first adjusting nuts 6 are respectively threadedly connected to the two connecting rods 4, and the first adjusting nuts 6 are located at the bottom of the housing 1. The two springs 5 ​​are respectively sleeved on the two connecting rods 4, and the springs 5 ​​are located in the housing 1. The two ends of the balance beam 3 are respectively threadedly connected to the two connecting rods 4 through two second adjusting nuts 7, and the second adjusting nuts 7 and the balance beam 3 are both located in the housing 1, and the springs 5 ​​are pressed between the first adjusting nuts 6 and the balance beam 3.

[0050] A connecting hole 8 is also provided at one end of the connecting rod 4 outside the housing 1 , and the connecting hole 8 can facilitate the connection between the connecting rod 4 and the positioning anchor cable.

[0051] A gasket 10 is further provided between the second adjusting nut 7 and the balance beam 3 . The gasket 10 is sleeved on the connecting rod 4 and pressed between the second adjusting nut 7 and the balance beam 3 to prevent the second adjusting nut 7 from loosening.

[0052] The fiber grating strain gauge 2 is connected with an optical fiber, and the optical fiber is used to connect with the server 12. The housing 1 is provided with a through hole, and a sealing plug 11 is installed in the through hole. The optical fiber passes through the sealing plug 11 to ensure the sealing of the optical fiber through hole.

[0053] When monitoring the tunnel entrance slope protection structure, the housing 1 is fixed on the prefabricated installation platform with embedded bolts as anchor points, and the anchor points are connected one-to-one with the connecting rod 4 with positioning anchor cables. After that, the first adjustment nut 6 is pre-tightened first to make the connecting rod 4 slide into the housing 1 to ensure that the positioning anchor cable has a pre-tightening force. Then the optical fiber demodulation device is connected to the optical fiber Bragg grating strain gauge 2, and the second adjustment nut 7 is pre-tightened to compress the spring 5 to ensure that the spring 5 has a pre-tightening force. By adjusting the pre-tightening force of the spring 5, the internal stress on the balance beam 3 can be adjusted to a certain calibration value, which corresponds in equal proportion to the wavelength value on the optical fiber Bragg grating strain gauge 2 recorded by the optical fiber demodulation device in this state.

[0054] This wavelength value is entered into the database of the alarm software of the monitoring terminal (user terminal 14). At the same time, the alarm software deducts the temperature effect from the calibrated temperature coefficient of the environmental effect to obtain the real wavelength value λ0, and then sets the alarm threshold of the alarm software. The alarm software verifies the real wavelength value λ0 in real time according to the alarm threshold. When it is found that the real wavelength value λ0 cannot be read or the real wavelength value λ0 increases or decreases abnormally, the alarm mechanism is activated.

[0055] When the tunnel entrance slope protection structure (slope protection, cofferdam, retaining wall) collapses, settles and deforms, causing the tension on the pre-tightened positioning anchor cable to change, the positioning anchor cable will loosen, causing the connecting rod 4 to slide toward the inside of the housing 1, and the pre-tightening force of the spring 5 will change. The formula for the change in the pre-tightening force of the spring 5 is: F = KΔS, F represents the pre-tightening force of the spring 5, K represents the elastic modulus of the spring 5, and ΔS represents the corresponding loosening stroke of the spring 5 and the positioning steel cable.

[0056] Bragg wavelength λ of the grating B Determined by the following formula: B =2nΛ, n represents the effective refractive index of the core mode, and Λ represents the grating period. When the temperature, stress, strain or other physical quantities in the environment of the fiber Bragg grating strain gauge 2 change, the period of the grating or the core refractive index will change, thereby changing the wavelength of the reflected light. By measuring the change in the wavelength of the reflected light before and after the physical quantity changes, the change of the physical quantity to be measured can be obtained. Where λ0=λ B -λ T ,λ T Represents the wavelength change of the fiber Bragg grating strain gauge 2 under the influence of ambient temperature change.

[0057] As can be seen from the above, when the tension of the positioning cable changes, the preload F of the spring 5 also changes accordingly, and the corresponding real wavelength value λ0 generated on the fiber Bragg grating strain gauge 2 changes, resulting in a change in the corresponding grating period Λ. After deducting the influence of the ambient temperature, the real wavelength value λ0 and the grating period Λ are in a linear relationship. The grating period Λ can be used to determine whether the real wavelength value λ0 is abnormal, so as to determine whether the tunnel entrance slope protection structure has undergone structural changes, thereby achieving real-time monitoring of the tunnel entrance slope protection structure.

[0058] The embodiment of the present invention also provides a monitoring system for a tunnel entrance slope protection structure.

[0059] refer to Figure 3 A monitoring system for a tunnel entrance slope protection structure includes the above-mentioned monitoring device for a tunnel entrance slope protection structure, and also includes: a server 12, a fiber grating demodulation device 13 and at least one user terminal 14.

[0060] The monitoring device, the fiber Bragg grating demodulation device 13 and the user end 14 are respectively connected to the server 12 for communication. The monitoring device can be one or more, and the monitoring device is arranged at the slope protection structure at the tunnel entrance according to actual needs, and a distributed arrangement method is adopted. The fiber Bragg grating strain gauge 2 in the monitoring device is connected to the server 12 for communication through an optical fiber, and the optical fiber can be a transmission optical cable.

[0061] The user terminal 14 can be various computers and other mobile communication devices with display functions. Monitoring personnel can obtain monitoring information of the tunnel entrance slope protection structure through the user terminal 14. The user terminal 14 can alarm when the tunnel entrance slope protection structure undergoes structural changes, thereby achieving the purpose of ensuring the safety of rail transit operations.

[0062] It should be understood that the implementation process of the monitoring system can be known through the above description of the monitoring device. In order to ensure the conciseness of the specification, it will not be repeated here.

[0063] In an optional embodiment of the present application, reference Figure 4 The monitoring system for the tunnel entrance slope protection structure also includes an optical fiber gap sensor 15, an optical fiber water pressure sensor 16, an optical fiber vibration sensor 17 and an optical fiber temperature sensor 18 which are respectively connected to the server 12 for communication. The optical fiber gap sensor 15 can monitor the gap, the optical fiber water pressure sensor 16 can monitor the water pressure, the optical fiber vibration sensor 17 can monitor the vibration, and the optical fiber temperature sensor 18 can monitor the temperature, thereby improving the accuracy of the monitoring system in monitoring the tunnel entrance slope protection structure.

[0064] The embodiment of the present invention also provides a monitoring system for a tunnel entrance slope protection structure.

[0065] refer to Figure 5 , a monitoring method for a tunnel entrance slope protection structure, comprising the following steps:

[0066] S1: Get the real wavelength value of fiber Bragg grating strain gauge 2;

[0067] The server 12 obtains the real wavelength value λ0 of the fiber Bragg grating strain gauge 2 through the fiber Bragg grating demodulation device 13 .

[0068] The calculation formula of the true wavelength value λ0 is: λ0=λ B -λ T , the Bragg wavelength calculation formula of the grating is: B =2nΛ.

[0069] Among them, the fiber Bragg grating strain gauge 2 is installed on the balance beam 3, and the wavelength change of the fiber Bragg grating strain gauge 2 is affected by the internal stress of the balance beam 3. The internal stress of the balance beam 3 changes according to the change of the preload force of the spring 5, and the preload force of the spring 5 changes according to the tension on the positioning anchor cable of the connecting rod 4. The formula for the change of the preload force of the spring 5 is: F = KΔS.

[0070] S2: Determine the grating period of the fiber Bragg grating strain gauge 2 based on the true wavelength value;

[0071] The server 12 calculates the Bragg wavelength of the grating according to the formula λ B =2nΛ and the obtained true wavelength value λ0 determine the grating period Λ of the fiber Bragg grating strain gauge 2.

[0072] S3: monitoring a first change amount of the grating period in real time, and determining a second change amount of the real wavelength value based on the first change amount;

[0073] When the real wavelength value λ0 changes, the server 12 cannot directly measure the second change of the real wavelength value λ0, and the real wavelength value λ0 is linearly related to the grating period Λ. Therefore, the server 12 can reversely measure the second change of the real wavelength value λ0 through the first change of the grating period Λ.

[0074] S4: When the second change exceeds the alarm threshold, an alarm signal is issued.

[0075] When the server 12 detects that the second change amount exceeds the preset alarm threshold, the server 12 controls the user terminal 14 to send out an alarm signal, thereby realizing an alarm.

[0076] As described above, the above embodiments are only used to introduce the technical solution of the present invention in detail, but the description of the above embodiments is only used to help understand the method and core idea of ​​the present invention and should not be understood as limiting the present invention. Changes or substitutions that can be easily thought of by technicians in this technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A monitoring device for a tunnel entrance slope protection structure, characterized in that: include: A shell (1), wherein two connecting rods (4) are slidably provided on the shell (1), one end of the connecting rod (4) located in the shell (1) is threadedly connected to a first adjusting nut (6) and a second adjusting nut (7), one end of the connecting rod (4) located in the shell (1) is sleeved with a spring (5), a balance beam (3) is installed on one end of the two connecting rods (4) located in the shell (1), a fiber optic Bragg grating strain gauge (2) is installed on the balance beam (3), the first adjusting nut (7) is located at the bottom of the shell (1), the spring (5) is located between the first adjusting nut (6) and the balance beam (3), and the spring (5) and the second adjusting nut (6) are respectively located on opposite sides of the balance beam (3).

2. The monitoring device for tunnel entrance slope protection structure according to claim 1, characterized in that: A connecting hole (8) is provided on one end of the connecting rod (4) located outside the housing (1).

3. The monitoring device for tunnel entrance slope protection structure according to claim 1, characterized in that: A gasket (10) is provided between the second adjusting nut (7) and the balance beam (3).

4. The monitoring device for tunnel entrance slope protection structure according to claim 1, characterized in that: The fiber optic Bragg grating strain gauge (2) is connected to an optical fiber, a penetration hole is provided on the housing (1), a sealing plug (11) is installed in the penetration hole, and the optical fiber is penetrated through the sealing plug (11).

5. A monitoring system for a tunnel entrance slope protection structure, characterized in that: The invention comprises at least one monitoring device for a tunnel entrance slope protection structure as claimed in any one of claims 1 to 4, and also comprises a server (12), a fiber Bragg grating demodulation device (13) and at least one user terminal (14); the server (12) is respectively connected to the fiber Bragg grating demodulation device (13), the user terminal (14) and the monitoring device for communication.

6. The monitoring system for tunnel entrance slope protection structure according to claim 5, characterized in that: Also includes: An optical fiber gap sensor (15), an optical fiber water pressure sensor (16), an optical fiber vibration sensor (17), and an optical fiber temperature sensor (18) are respectively connected to the server (12) for communication.

7. A monitoring method for a tunnel entrance slope protection structure, characterized in that: The monitoring system for the tunnel entrance slope protection structure as claimed in claim 6 comprises the following steps: S1: Obtain the real wavelength value of the fiber Bragg grating strain gauge (2); S2: determining the grating period of the fiber Bragg grating strain gauge (2) based on the true wavelength value; S3: monitoring a first change amount of the grating period in real time, and determining a second change amount of the real wavelength value based on the first change amount; S4: When the second change exceeds the alarm threshold, an alarm signal is issued.

8. The monitoring method for a tunnel entrance slope protection structure according to claim 7, characterized in that: The calculation formula of the true wavelength value is: λ0=λ B -l T Among them, λ0 represents the real wavelength value, λ B represents the Bragg wavelength of the grating, λ T represents the wavelength change of the fiber Bragg grating strain gauge (2) under the influence of ambient temperature change; The Bragg wavelength calculation formula of the grating is: l B =2nΛ Where n represents the effective refractive index of the core mode, and Λ represents the grating period; The wavelength variation of the fiber grating strain gauge (2) is affected by the internal stress of the balance beam (3), the internal stress of the balance beam (3) changes according to the change of the preload force of the spring (5), and the preload force of the spring (5) changes according to the tension on the positioning anchor cable applied to the connecting rod (4); The formula for the change in the preload force of the spring (5) is: F=KΔS Wherein, F represents the preload force of the spring (5), K represents the elastic modulus of the spring (5), and ΔS represents the corresponding loosening stroke of the spring (5) and the positioning cable.

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