Bolt pretightening force measuring device and method adopting force balance method

Abstract

The invention belongs to the technical field of bolt calibration, and discloses bolt pre-tightening force measuring equipment and a bolt pre-tightening force measuring method adopting a force balance method. The bolt pretightening force measuring equipment adopting the force balance method comprises a stretching device, a vibration exciter and a vibration sensor, the stretching device comprises a stretching head and a base, the stretching head is in threaded connection with the end, stretching out of a fixing table, of a to-be-measured screw, and the base can apply acting force to the stretching head so that the stretching head can move in the direction away from the fixing table; the vibration exciter is arranged on the base, the output end of the vibration exciter abuts against the fixing table, and the vibration exciter is used for generating vibration; the vibration sensor is arranged on the stretching head and used for monitoring vibration and outputting an electric signal. According to the bolt pre-tightening force measuring equipment adopting the force balance method, the stretching driving force of the nut on the screw rod at the loosening moment is obtained by applying vibration and collecting the vibration frequency spectrum, so that the pre-tightening force of the bolt is obtained, the bolt does not need to be calibrated, and the bolt pre-tightening force measuring equipment has high practicability and convenience.

Description

Technical Field

[0001] The present invention relates to the technical field of bolt calibration, and in particular to a bolt pre-tightening force measuring device and a bolt pre-tightening force measuring method using a force balance method. Background Art

[0002] Bolted connections are a common mechanical connection method, widely used in various fields such as electricity, construction, aerospace, and transportation. In engineering practice, the safety and reliability of bolted connections are extremely important, and bolt preload is one of the key indicators for evaluating bolted connection performance. The magnitude of the preload directly affects the strength and reliability of the bolted connection. If the bolt preload is too low, the bolted connection may loosen, causing the bolts to loosen or even fall off. If the bolt preload is too high, the bolted connection may undergo plastic deformation or failure. Therefore, accurate preload is key to ensuring the quality and reliability of bolted connections.

[0003] Currently, ultrasonic measurement is often used to measure bolt preload. However, ultrasonic measurement equipment is relatively expensive and has low measurement accuracy. The bolts also need to be calibrated before measurement and are greatly affected by the surface roughness of the bolts, which causes many inconveniences in actual use.

[0004] Therefore, it is urgent to design a preload force measuring device to solve the above problems existing in the prior art. Summary of the Invention

[0005] The object of the present invention is to provide a bolt preload measurement device and a bolt preload measurement method using a force balance method, which can quickly and accurately measure the preload of a bolt or a screw.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] Bolt preload measurement equipment using the force balance method, including:

[0008] The stretching device includes a stretching head and a base, wherein the stretching head is threadedly connected to the end of the screw to be measured extending out of the fixed platform, and the base has a drive oil circuit, wherein the drive oil circuit can apply a force to the stretching head to move the stretching head in a direction away from the fixed platform;

[0009] an exciter, the exciter being disposed on the base, the output end of the exciter being in contact with the fixing platform, and the exciter being used to generate vibration;

[0010] A vibration sensor is provided on the stretching head, and is used for monitoring vibration and outputting an electrical signal.

[0011] Preferably, the base includes a cylinder body, and the cylinder body is used to abut against the fixing platform;

[0012] The cylinder body has a central cavity that passes through in a first direction, and the central cavity has a first opening and a second opening. The first opening is used for the screw to extend into. The stretching head is arranged in the central cavity and is sealed with the inner wall of the cylinder body. The driving oil circuit is arranged in the cylinder body to drive the stretching head to move along the central cavity.

[0013] Preferably, a supporting boss is provided on the inner wall of the cylinder body, and a step structure matching the supporting boss is provided on the stretching head;

[0014] Along the first direction, an oil outlet hole is provided on the end surface of the supporting boss facing the step structure, and an oil supply hole is provided on the cylinder body. One end of the driving oil circuit is connected to the outside through the oil supply hole, and the other end of the driving oil circuit is connected to the oil outlet hole.

[0015] Preferably, the base further includes a mounting portion, the mounting portion is fixedly connected to the cylinder body, and the vibrator is connected to the mounting portion.

[0016] Preferably, the stretching device further comprises a protective cover, which is fixedly connected to the cylinder body and blocks the second opening, and the stretching head is passed through the protective cover and slidably cooperates with the protective cover.

[0017] Preferably, a spring is provided between the protective cover and the stretching head, and the spring can apply an elastic force to the stretching head away from the protective cover.

[0018] Preferably, a sealing ring is provided between the protective cover and the stretching head.

[0019] As an example, when the stretching head is threadedly connected to the screw, the vibration sensor can be selected to abut against the end face of the screw, or can be selected not to contact the end face of the screw.

[0020] Preferably, the base is provided with an escape opening for screwing the nut.

[0021] The bolt preload force measurement method, using the above-mentioned bolt preload force measurement device using the force balance method, includes the following steps:

[0022] S1. Fix the screw to be measured on a fixed platform with a nut, place the base on the fixed platform, and connect the stretching head to the screw thread;

[0023] S2, turning on the vibration exciter to cause the fixed platform to vibrate;

[0024] S3, using the base to drive the stretching head to move in a direction away from the fixed platform to stretch the screw;

[0025] S4. Analyze the vibration spectrum monitored by the vibration sensor, identify the loosening moment of the nut on the screw according to the frequency response characteristics, and capture the force applied by the base to the stretching head at the loosening moment, thereby obtaining the pre-tightening force of the screw.

[0026] The beneficial effects of the present invention are:

[0027] The bolt preload measuring device using the force balance method provided by the present invention includes a stretching device, an exciter and a vibration sensor. The screw is fixed on a fixed platform. The stretching device includes a stretching head and a base. Since the stretching head is threadedly connected to the end of the screw extending out of the fixed platform, and the driving oil circuit of the base can drive the stretching head to move in a direction away from the fixed platform, the stretching head can stretch the screw under the drive of the base, so that the screw is deformed and elongated; since the exciter is provided on the base, the output end of the exciter abuts against the fixed platform, the exciter can make the fixed platform vibrate, and the vibration will be transmitted to the screw through the fixed platform, and then transmitted to the stretching head through the screw. Since the vibration sensor is provided on the stretching head, the vibration sensor It can monitor vibration and output signals, so the vibration sensor can monitor the vibration transmitted from the fixed platform and the bolt, thereby obtaining the vibration spectrum, and identifying the moment when the nut on the screw is loose through spectrum analysis, and obtaining the magnitude of the force applied by the base drive oil circuit to the tensile head at this moment, thereby obtaining the pre-tightening force of the bolt; the bolt pre-tightening force measuring device using the force balance method applies vibration to the fixed platform and the screw, and obtains the tensile driving force at the moment when the nut on the screw is loose by collecting the vibration spectrum, thereby obtaining the pre-tightening force of the bolt. It has a simple structure and is easy to operate. There is no need to calibrate the bolt before measurement, and it is not affected by the surface roughness of the screw and nut and the residual stress of the screw. It has strong practicality and convenience.

[0028] The bolt preload force measurement method provided by the present invention uses the above-mentioned bolt preload force measurement equipment using the force balance method, uses a stretching head to stretch the screw, and uses a vibration sensor to monitor the vibration frequency of the screw and the nut. Finally, by analyzing the frequency response characteristics, the driving force of the base driving oil circuit on the stretching head when the nut is loosened is obtained, thereby obtaining the preload force of the screw. The measurement method is simple and accurate, and there is no need to calibrate and preprocess the screw before measurement. It has strong practicality and convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a cross-sectional view of a bolt preload force measuring device using a force balance method provided in a specific embodiment of the present invention.

[0030] In the picture:

[0031] 100-screw;

[0032] 200-fixed table;

[0033] 300-nut;

[0034] 1-stretching device; 11-stretching head; 12-base; 121-cylinder body; 1211-center cavity; 1212-support boss; 1213-oil supply hole; 122-mounting part; 13-protective cover; 14-spring;

[0035] 2-exciter;

[0036] 3- Vibration sensor;

[0037] 4-Sealing ring. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0039] In the description of the present invention, unless otherwise expressly specified or limited, the terms "connected," "connected," and "fixed" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific circumstances.

[0040] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0041] In the description of this embodiment, terms such as "upper," "lower," "right," and "left" are used to refer to positions or locations based on those shown in the accompanying drawings. These terms are intended solely to facilitate description and simplify operation, and are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used solely for descriptive purposes and have no special meaning.

[0042] like Figure 1 As shown, the present invention provides a bolt preload measuring device using a force balance method, which includes a stretching device 1, an exciter 2 and a vibration sensor 3. The stretching device 1 includes a stretching head 11 and a base 12. The stretching head 11 is threadedly connected to the end of the screw 100 to be measured that extends out of the fixed platform 200. The base 12 has a driving oil circuit, which can apply a force to the stretching head 11 to move the stretching head 11 in a direction away from the fixed platform 200; the exciter 2 is arranged on the base 12, and the output end of the exciter 2 abuts against the fixed platform 200. The exciter 2 is used to generate vibration; the vibration sensor 3 is arranged on the stretching head 11, and the vibration sensor 3 is used to monitor vibration and output an electrical signal.

[0043] In this embodiment, since the stretching head 11 is threadedly connected to the end of the screw 100 extending out of the fixed platform 200, and the driving oil circuit of the base 12 can drive the stretching head 11 to move in a direction away from the fixed platform 200, the stretching head 11 can stretch the screw 100 under the drive of the base 12, so that the screw 100 is deformed and elongated; since the base 12 is provided with an exciter 2, the output end of the exciter 2 abuts against the fixed platform 200, and the exciter 2 can make the fixed platform 200 vibrate, and the vibration will be transmitted to the screw 100 through the fixed platform 200, and then transmitted to the stretching head 11 through the screw 100, and since the stretching head 11 is provided with a vibration sensor 3, the vibration sensor 3 can monitor the vibration and output a signal, so the vibration sensor 3 can The vibration transmitted from the fixed platform 200 and the screw 100 is monitored to obtain a vibration spectrum, and the moment when the nut 300 on the screw 100 is loosened is identified through spectrum analysis, and the magnitude of the force applied by the driving oil circuit of the base 12 to the tensile head 11 at this moment is obtained, thereby obtaining the pre-tightening force of the bolt; the bolt pre-tightening force measuring device using the force balance method applies vibration to the fixed platform 200 and the screw 100, and obtains the tensile driving force at the moment when the nut 300 on the screw 100 is loosened by collecting the vibration spectrum, thereby obtaining the pre-tightening force of the bolt. The device has a simple structure and is easy to operate. There is no need to calibrate the bolt before measurement, and it is not affected by the surface roughness of the screw 100 and the nut 300 and the residual stress of the screw 100, and has strong practicality and convenience.

[0044] Specifically, the fixed platform 200 can be a platform structure on which the equipment is fixedly installed, or it can be the box itself of the equipment with bolts, which is not limited here; the exciter 2 and the vibration sensor 3 are both commonly used devices in this field. The exciter 2 can generate an excitation force and drive the target object to generate regular vibrations through the output end; the vibration sensor 3 is a device that converts a mechanical vibration state into an electrical signal; in this embodiment, the vibration sensor 3 is connected to the computer via a data cable, and the vibration sensor 3 can convert the monitored mechanical vibration into an electrical signal and transmit it to the computer. The computer can perform spectrum analysis on the electrical signal, thereby identifying the loosening moment of the nut 300 on the screw 100 through the frequency response characteristics. This loosening moment is the moment when the tension on the screw 100 is balanced with the preload force. At this time, the preload force of the screw 100 or the bolt can be obtained by obtaining the force of the base 12 on the stretching head 11.

[0045] The specific structure of the stretching head 11 and the base 12 can be set according to actual needs, as long as the stretching head 11 can drive the screw 100 to stretch. Figure 1 As shown, the base 12 includes a cylinder body 121, which is used to abut against the fixed table 200; the cylinder body 121 has a central cavity 1211 that passes through along a first direction, and the central cavity 1211 has a first opening and a second opening, the first opening is for the screw 100 to extend into, and the stretching head 11 is arranged in the central cavity 1211 and is sealed with the inner wall of the cylinder body 121, and the driving oil circuit is arranged in the cylinder body 121 to drive the stretching head 11 to move along the central cavity 1211; since the stretching head 11 is arranged in the central cavity 1211 and moves along the central cavity 1211 under the drive of the cylinder body 121, the stability of the stretching head 11 during movement is improved, thereby ensuring the accuracy of the preload force measurement; it can be understood that the first direction is the extension direction of the central cavity 1211.

[0046] Specifically, if Figure 1As shown, a supporting boss 1212 is provided on the inner wall of the cylinder body 121, and a step structure matching the supporting boss 1212 is provided on the stretching head 11; along the first direction, an oil outlet hole is provided on the end face of the supporting boss 1212 facing the step structure, and an oil supply hole 1213 is provided on the cylinder body 121. One end of the driving oil circuit is connected to the outside through the oil supply hole 1213, and the other end of the driving oil circuit is connected to the oil outlet hole, that is, the stretching head 11 is driven by hydraulic oil, with a simple structure and easy operation; in this embodiment, the supporting boss 1212 is located in the central cavity 1211, and the supporting boss 1212 is arranged on the inner wall of the cylinder body 121; a step structure is provided on the outer peripheral surface of the stretching head 11, and the horizontal surface of the step structure can abut against the horizontal end surface of the supporting boss 1212, and the vertical surface of the step structure can abut against the vertical end surface of the supporting boss 1212, and an oil outlet hole is provided on the horizontal end surface of the supporting boss 1212. Specifically, the stretching device 1 is a hydraulic stretcher commonly used in this field. The oil supply hole 1213 is externally connected to a pressure oil pump. The staff injects hydraulic oil into the driving oil circuit through the pressure oil pump, thereby driving the stretching head 11 to move to achieve stretching of the screw 100.

[0047] like Figure 1 As shown, the base 12 also includes a mounting portion 122, which is fixedly connected to the cylinder body 121, and the vibrator 2 is connected to the mounting portion 122, so as to avoid affecting the cylinder body 121 when driving the stretching head 11; specifically, the mounting portion 122 and the cylinder body 121 are an integrated structure, the cylinder body 121 is a cylindrical structure, and the mounting portion 122 is connected to the outer wall surface of the cylinder body 121, and a mounting hole is opened on the mounting portion 122, and the vibrator 2 is installed in the mounting hole. The shape of the mounting portion 122 is not limited here.

[0048] In order to protect the central cavity 1211 and prevent external dust, debris, etc. from contaminating the central cavity 1211, Figure 1 As shown, the stretching device 1 also includes a protective cover 13, which is fixedly connected to the cylinder body 121 and blocks the second opening. The stretching head 11 is passed through the protective cover 13 and slides with the protective cover 13; specifically, the protective cover 13 is fixedly connected to the end of the cylinder body 121 corresponding to the second opening, and a through hole is provided in the center of the protective cover 13. The stretching head 11 is passed through the through hole. When the stretching head 11 stretches the screw 100, it can move relative to the protective cover 13; specifically, a sealing ring 4 is provided between the stretching head 11 and the cover 13, thereby further improving the dustproof effect of the bolt preload force measuring device using the force balance method.

[0049] like Figure 1As shown, a spring 14 is provided between the protective cover 13 and the stretching head 11. The spring 14 can apply an elastic force to the stretching head 11 away from the protective cover 13, so that after the preload force measurement of the screw 100 is completed, the stretching head 11 can automatically return to the initial screw connection position without the need for manual adjustment by the staff, thereby facilitating the next measurement.

[0050] When taking measurements, the vibration sensor 3 can monitor the vibration state of the stretching head 11, and can also monitor the vibration state of the screw 100 by directly contacting the screw 100; in order to further improve the accuracy of the measurement, when the stretching head 11 is threadedly connected to the screw 100, the vibration sensor 3 can abut against the end face of the screw 100. At this time, the vibration sensor 3 is in direct contact with the screw 100, which can improve the vibration monitoring accuracy of the vibration sensor 3 and avoid inaccurate measurement caused by the attenuation of vibration during the transmission process.

[0051] Furthermore, the base 12 is provided with a clearance opening for tightening the nut 300. This clearance opening allows a worker to tighten a loose nut 300, thereby ensuring the secure connection between the screw 100, nut 300, and mounting platform 200. Specifically, the clearance opening is provided at the end of the cylinder 121 away from the protective cover 13. After the preload force measurement is completed, the screw 100 stretches, creating a gap between the nut 300 and mounting platform 200. This clearance opening allows a worker to re-tighten the nut 300.

[0052] Specifically, if Figure 1 As shown, a sealing ring 4 is provided between the stretching head 11 and the inner wall of the cylinder body 121, and a sealing ring 4 is also provided between the step structure on the stretching head 11 and the supporting boss 1212. The sealing ring 4 can prevent the hydraulic oil from leaking to ensure the driving effect of the hydraulic oil on the stretching head 11.

[0053] In this embodiment, the installation process of the bolt preload force measuring device using the force balance method is roughly as follows: first, the staff aligns the first opening of the central cavity 1211 on the cylinder body 121 with the screw 100 on the fixed platform 200, and places the cylinder body 121 on the fixed platform 200. At this time, the screw 100 and the nut 300 on the screw 100 are both located in the central cavity 1211; then the staff screws the stretching head 11 to thread the stretching head 11 into the screw 100 until the vibration sensor 3 abuts the end face of the screw 100.

[0054] This embodiment further provides a method for measuring bolt preload force, using the above-mentioned bolt preload force measurement device using the force balance method, comprising the following steps:

[0055] S1. Fix the screw 100 to be measured on the fixed platform 200 through the nut 300, place the base 12 on the fixed platform 200, and thread the stretching head 11 to the screw 100; specifically, put the cylinder body 121 of the base 12 on the screw 100, and screw the stretching head 11 to make the stretching head 11 threadedly connected to the screw 100.

[0056] S2 . Turn on the vibration exciter 2 to make the fixing platform 200 vibrate. Specifically, the vibration of the fixing platform 200 is transmitted to the screw 100 and the nut 300 .

[0057] S3. Use the base 12 to drive the stretching head 11 to move in a direction away from the fixed platform 200 to stretch the screw 100; specifically, the cylinder body 121 of the base 12 is externally connected to a pressure oil pump. The staff starts the pressure oil pump and injects hydraulic oil into the driving oil circuit of the cylinder body 121 through the oil supply hole 1213 of the cylinder body 121. The hydraulic oil flows out through the oil outlet hole on the supporting boss 1212, thereby hydraulically driving the stretching head 11 to move to stretch the screw 100. The screw 100 will undergo elastic deformation and be elongated, and the nut 300 on the screw 100 will also be driven accordingly to separate from the fixed platform 200, thereby causing loosening.

[0058] S4. Analyze the vibration spectrum monitored by the vibration sensor 3, identify the loosening moment of the nut 300 on the screw 100 based on the frequency response characteristics, and capture the force applied by the base 12 to the stretching head 11 at the loosening moment, thereby obtaining the pre-tightening force of the screw 100; specifically, the vibration on the screw 100 will be transmitted to the stretching head 11, and the vibration sensor 3 can monitor the vibration state of the stretching head 11. The vibration sensor 3 can also monitor the vibration state of the screw 100 by direct contact with the screw 100; the vibration sensor 3 is externally connected to a computer, and the vibration sensor 3 can convert the monitored mechanical vibration into an electrical signal and transmit it to the computer to perform spectrum analysis on the electrical signal, thereby identifying the loosening moment of the nut 300 through the frequency response characteristics; the computer can also obtain the real-time output pressure value of the pressure oil pump, so that the bolt pre-tightening force measuring device using the force balance method can obtain the tensile force of the stretching head 11 on the screw 100 when the nut 300 is loose, which is the pre-tightening force of the screw 100.

[0059] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. A person skilled in the art would be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. Bolt preload measurement equipment using force balance method, characterized in that: include: A stretching device (1) comprises a stretching head (11) and a base (12), wherein the stretching head (11) is threadedly connected to the end of a screw (100) to be measured that extends out of a fixed platform (200), and the base (12) has a driving oil circuit, wherein the driving oil circuit can apply a force to the stretching head (11) so as to move the stretching head (11) in a direction away from the fixed platform (200); An exciter (2), the exciter (2) being arranged on the base (12), the output end of the exciter (2) being in contact with the fixed platform (200), and the exciter (2) being used to generate vibration; A vibration sensor (3) is provided on the stretching head (11), and the vibration sensor (3) is used to monitor vibration and output an electrical signal.

2. The bolt preload force measuring device using the force balance method according to claim 1, characterized in that: The base (12) includes a cylinder (121), and the cylinder (121) is used to abut against the fixing platform (200); The cylinder body (121) has a central cavity (1211) extending along a first direction, the central cavity (1211) has a first opening and a second opening, the first opening is used for the screw (100) to extend into, the stretching head (11) is arranged in the central cavity (1211) and is sealed with the inner wall of the cylinder body (121), and the driving oil circuit is arranged in the cylinder body (121) to drive the stretching head (11) to move along the central cavity (1211).

3. The bolt preload force measuring device using the force balance method according to claim 2, characterized in that: A supporting boss (1212) is provided on the inner wall of the cylinder body (121), and a step structure matching the supporting boss (1212) is provided on the stretching head (11); Along the first direction, an oil outlet hole is provided on the end surface of the supporting boss (1212) facing the step structure, and an oil supply hole (1213) is provided on the cylinder body (121). One end of the driving oil circuit is connected to the outside through the oil supply hole (1213), and the other end of the driving oil circuit is connected to the oil outlet hole.

4. The bolt preload force measuring device using the force balance method according to claim 2, characterized in that: The base (12) further includes a mounting portion (122), the mounting portion (122) being fixedly connected to the cylinder body (121), and the vibrator (2) being connected to the mounting portion.

5. The bolt preload force measuring device using the force balance method according to claim 2, characterized in that: The stretching device (1) further comprises a protective cover (13), wherein the protective cover (13) is fixedly connected to the cylinder body (121) and blocks the second opening; the stretching head (11) is passed through the protective cover (13) and is slidably engaged with the protective cover (13).

6. The bolt preload force measuring device using the force balance method according to claim 5, characterized in that: A spring (14) is provided between the protective cover (13) and the stretching head (11), and the spring (14) is capable of applying an elastic force to the stretching head (11) away from the protective cover (13).

7. The bolt preload force measuring device using the force balance method according to claim 5, characterized in that: A sealing ring (4) is provided between the protective cover (13) and the stretching head (11).

8. The bolt preload force measuring device using the force balance method according to claim 1, characterized in that: When the stretching head (11) is threadedly connected to the screw (100), the vibration sensor (3) can abut against the end surface of the screw (100).

9. The bolt preload force measuring device using the force balance method according to any one of claims 1 to 8, characterized in that: The base (12) is provided with an escape opening for screwing the nut (300).

10. Bolt preload force measurement method, characterized in that: Using the bolt preload force measuring device using the force balance method according to any one of claims 1 to 9 comprises the following steps: S1. Fix the screw (100) to be measured on the fixed platform (200) through the nut (300), place the base (12) on the fixed platform (200), and thread the stretching head (11) to the screw (100); S2, turning on the vibration exciter (2), causing the fixed platform (200), the screw (100), the base (12), and the nut (300) to vibrate; S3, using the base (12) to drive the stretching head (11) to move in a direction away from the fixed platform (200) to stretch the screw (100); S4. Analyze the vibration spectrum monitored by the vibration sensor (3), identify the loosening moment of the nut (300) on the screw (100) based on the frequency response characteristics, and capture the force applied by the base (12) to the stretching head (11) at the loosening moment, thereby obtaining the pre-tightening force of the screw (100).

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