A bolt loosening detection method based on spectrum ratio coefficient method and a bolt loosening degree detection method

Abstract

The present application relates to a bolt loosening detection method based on a spectral ratio coefficient method and a bolt loosening degree detection method, comprising the following steps: obtaining a reference amplitude-frequency curve of a healthy structure, obtaining non-healthy amplitude-frequency curves under different bolt loosening degrees, obtaining amplitude-frequency ratio curves of the non-healthy amplitude-frequency curves and the reference amplitude-frequency curve under different bolt loosening degrees, and establishing a fitting linear equation between the bolt loosening degree and the average value of the amplitude-frequency ratio absolute value curves. The present application uses the characteristic that bolt loosening can cause the stiffness of a structure connection to decrease and thus cause the characteristic frequency to shift, uses the amplitude-frequency ratio absolute value curve of a healthy bolt connection structure as a reference, and uses the average value of the amplitude-frequency ratio absolute value curves under different loosening degrees as a bolt loosening degree detection index to identify the loosening state of the bolt, and the detection of the early loosening state of the bolt is more sensitive, thus providing a more intuitive and convenient bolt loosening detection method for a bolt connection structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fault diagnosis, in particular to a bolt loosening detection method based on a frequency spectrum ratio coefficient method and a bolt loosening degree detection method. BACKGROUND

[0002] Bolt connection structure has the advantages of low cost, easy installation and disassembly, strong bearing capacity, etc. Due to these advantages, bolt connection is widely used in civil engineering, machinery, aerospace and other fields. However, due to the harsh working conditions faced by bolt connection, it may be subjected to vibration and impact caused by long-term alternating load, resulting in fatigue, bolt connection structure loosening or even falling off, which may cause damage to buildings or equipment. Therefore, in engineering structures, if the loosening state of bolt connection cannot be detected in time and appropriate measures are not taken, not only the cost of mechanical equipment operation and maintenance will be increased, but also the structure may be damaged, causing serious safety accidents.

[0003] Although there are many bolt loosening detection methods based on vibration signals at present, they all have certain limitations, such as the need to install sensors on each bolt to measure the vibration signal; the early bolt loosening detection effect is not good. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a bolt loosening detection method based on a frequency spectrum ratio coefficient method and a bolt loosening degree detection method, which overcomes the limitations of existing detection methods and makes it more intuitive and convenient to detect bolt loosening through vibration signals.

[0005] To achieve the above purpose, the present application adopts the following technical solution: a bolt loosening detection method based on a frequency spectrum ratio coefficient method, comprising the following steps:

[0006] Step S1: obtaining the vibration data of a healthy structure under a known sweep excitation when the bolt is not loosened, and simultaneously obtaining the frequency change curve of the sweep excitation signal and the vibration signal of the structure response through the data acquisition system during measurement;

[0007] Step S2: taking the frequency change curve of the sweep excitation signal as the input parameter of the chirp Fourier transform CFT, and calculating the amplitude-frequency curve of different frequency orders of the structure response vibration signal;

[0008] Step S3: observing the amplitude-frequency curves of different frequency orders, selecting the amplitude-frequency curve of a specific order that can reflect the resonance frequency of the structure; repeating steps S1 and S2 to calculate multiple sets of amplitude-frequency curves of the healthy structure under the same parameters, and then calculating the average amplitude-frequency curve of the multiple sets of amplitude-frequency curves as the reference amplitude-frequency curve of the healthy structure;

[0009] Step S4: When the structural bolts become loose during the operation of the structure, the same sweep frequency excitation is applied to the unhealthy structure, and the frequency variation curve of the sweep frequency excitation signal and the vibration signal of the structural response are obtained through the data acquisition system.

[0010] Step S5: using the frequency variation curve of the swept frequency excitation signal as an input parameter of the frequency modulated Fourier transform (CFT) to obtain the amplitude-frequency curve of the selected frequency order of the vibration signal of the unhealthy structure response;

[0011] Step S6: Calculate the ratio curve of the amplitude-frequency curve of the selected frequency order of the vibration signal of the unhealthy structure and the reference amplitude-frequency curve of the healthy structure, and then calculate the average value of the amplitude-frequency ratio curve within the fixed frequency range;

[0012] Step S7: The loosening of the bolts of the structure can be monitored in real time by changing the average value of the amplitude-frequency ratio curve within a fixed frequency range.

[0013] The present invention also provides a method for detecting the degree of bolt loosening based on a spectrum ratio coefficient method, comprising the following steps:

[0014] Step S1: obtaining a reference amplitude-frequency curve of vibration data of a healthy structure under a known swept frequency excitation when the bolts are not loosened;

[0015] Step S2: obtaining unhealthy amplitude-frequency curves of vibration data of known swept frequency excitation under different degrees of bolt looseness, i.e., different torques;

[0016] Step S3: First, all amplitude-frequency curves are translated upward by 5 units as a whole. Then, the amplitude-frequency ratio curves of the unhealthy amplitude-frequency curves and the reference amplitude-frequency curves of the vibration data of the known swept frequency excitation under different bolt looseness degrees are obtained. The amplitude-frequency ratio curves within the fixed frequency range [f1, f2] are extracted. The obtained amplitude-frequency ratio curves are translated downward by 1 unit as a whole and their absolute values ​​are taken. Finally, the average value of the absolute value curves of the amplitude-frequency ratio under different bolt looseness degrees is obtained. The average value of the absolute value curves of the amplitude-frequency ratio under different bolt looseness degrees corresponding to the torque xN·m is

[0017]

[0018] Where A[x(i)] is the absolute value of the amplitude-frequency ratio curve at point i within the fixed frequency range [f1, f2] under the working condition of the bolt torque of x N·m; A[x health (i)] is the absolute value curve amplitude of the amplitude-frequency ratio at point i within the fixed frequency range [f1, f2] corresponding to the healthy bolted connection structure;

[0019] Step S4: Using the torque of the bolt as the abscissa and the average value of the absolute value curve of the amplitude-frequency ratio within a fixed frequency range as the ordinate, a linear fitting is performed on the average value of the torque-absolute value curve of the amplitude-frequency ratio to establish a linear fitting equation between the degree of bolt loosening and the average value of the absolute value curve of the amplitude-frequency ratio;

[0020] Step S5: Under any condition of bolt looseness, the average value of the absolute value curve of the amplitude-frequency ratio is obtained, and then the average value is substituted into the linear fitting equation to obtain the looseness degree of the bolt.

[0021] In a preferred embodiment, in step S6, if the bolts are not loose, the structure is in a healthy state, the resonant frequency peak of the structure does not shift, and the amplitude of the amplitude-frequency ratio curve in this state is substantially stable at approximately 1. At this time, the average value of the amplitude-frequency ratio curve within a fixed frequency range is approximately 1. If the bolts are loose, the structure is in an unhealthy state, and structural parameters such as the stiffness of the structure will change, causing the resonant frequency peak of the structure to shift. In this state, the amplitude of the amplitude-frequency ratio curve will oscillate near the resonant peak, and the oscillation range is proportional to the resonant frequency shift. The average value of the amplitude-frequency ratio curve within the fixed frequency range will change with the degree of shift in the resonant frequency peak.

[0022] In a preferred embodiment, in step S7, the loosening of the bolts causes the stiffness of the structure to decrease, and the resonant frequency peak will also decrease, that is, the coordinate of the resonant frequency peak shifts to the left. Therefore, the average value of the amplitude-frequency ratio curve within the fixed frequency range will increase as the resonant frequency peak shifts to the left.

[0023] In a preferred embodiment, all the amplitude-frequency curves are shifted upward by 5 units as a whole, so that the ratio curve is smoother and better reflects the influence of the shift of the resonance frequency peak on the change of the ratio.

[0024] In a preferred embodiment, the amplitude-frequency ratio curve is shifted downward by 1 unit as a whole and its absolute value is taken, which can enhance the change trend of the amplitude-frequency ratio curve and further highlight the effect of the left shift of the resonance frequency peak on the bolt looseness detection index.

[0025] In a preferred embodiment, the fixed frequency range is a frequency band with a smooth single resonance peak, so that the leftward shift of the resonance frequency peak coordinate can be better reflected by the increase in the average value of the amplitude-frequency ratio curve.

[0026] Compared with existing technologies, the present invention has the following advantages: It provides a method for detecting bolt loosening based on the spectrum ratio coefficient method. This method reduces the number of acceleration sensors required for detection, enabling detection of the looseness of any bolt connection in a structure using only a single sensor. By obtaining the amplitude-frequency curve of a healthy bolt connection structure and using it as a reference amplitude-frequency curve, it is possible to detect not only whether a bolt is loose but also the degree of looseness. The method is particularly sensitive to detecting early-stage loosening of bolts, providing a novel looseness detection method for bolted connection structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of a bolt loosening detection device according to an example of the present invention.

[0028] Figure 2 Schematic diagram of the results of the present invention. Figure 2 (a) is the original time domain signal diagram; Figure 2 (b) is the servo motor speed frequency change curve; Figure 2 (c) Four sets of amplitude-frequency curves of healthy structures; Figure 2 (d) is the baseline amplitude-frequency curve of the healthy structure; Figure 2 (e) is the baseline amplitude-frequency curve of a healthy structure within a fixed frequency range; Figure 2 (f) is the linear fitting diagram between the bolt torque and the average value of the absolute value curve of the amplitude-frequency ratio.

[0029] Figure 3 It is a specific flow chart of bolt looseness detection of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0032] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form, and it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0036] The following is a specific application example to verify the effectiveness of the present invention in engineering applications:

[0037] Step S1: Figures 1-3 As shown, the servo motor is bolted to the vibration isolation platform. A torque wrench is used to ensure the bolts are tight, allowing the motor shaft to rotate horizontally. The accelerometer is fixed to the horizontal surface on top of the servo motor, preventing relative slip between the accelerometer and the motor. The corresponding parameters are set in the acquisition software to ensure that the vertical vibration signal of the servo motor structure, which is fixed with the bolted structure, is accurately and clearly displayed on the signal acquisition system interface.

[0038] Step S2: Use a torque wrench to loosen any bolt to a specified torque according to the working condition. Here, the tightening torque of 25 N·m is used as the working condition of a healthy connection structure. First, the corresponding data of the healthy structure is measured experimentally.

[0039] Step S3: Use the USBDAQ device to output the analog voltage of the specified change curve to the analog voltage input terminal of the servo motor drive controller, and connect the voltage sensor to the analog voltage output port of the USBDAQ device for measurement. Through analog voltage control, the servo motor rotates according to the specified law, and continues for 9 speed change cycles. The voltage change curve obtained by the signal acquisition system and the synchronously measured vibration data are imported into the signal processing system, such as Figure 2 (a) is shown. Substituting the analog voltage control gain multiple into the obtained servo motor speed frequency change curve, as shown in Figure 2 (b) is shown. Using CFT (Frequency Modulated Fourier Transform), the amplitude-frequency curve of the swept frequency excitation in the uniformly rising stage of the vibration frequency in each cycle of the healthy structure is obtained. Then, the 10-fold frequency spectrum that can better reflect the structural resonance frequency is selected. The amplitude-frequency curves of the four cycles are shown as follows: Figure 2 (c) is shown. Then the average amplitude-frequency curve of multiple periodic amplitude-frequency curves is obtained, as shown in Figure 2As shown in (d), the fixed frequency range is set to the 420-490 Hz frequency band with a smooth single resonance peak, and the average amplitude-frequency curve within the fixed frequency range corresponding to the healthy structural condition is obtained.

[0040] Step S4: Divide the working conditions from 25 N·m to 1 N·m into 13 conditions with an interval of 2 units, plus the no-bolt working condition for a total of 14 working conditions. Use a torque wrench to loosen the bolts according to the working conditions to the specified torque corresponding to each working condition. Then repeat step S3 under each working condition to obtain the average amplitude-frequency curve within the fixed frequency range corresponding to each loosening working condition. Shift all the average amplitude-frequency curves upward by 5 units as a whole. The average amplitude-frequency curve within the fixed frequency range of the healthy bolt connection structure (i.e., the tightening state corresponds to a tightening torque of 25 N·m) is used as the reference amplitude-frequency curve, as shown in Figure 4. Figure 2 As shown in (e), the average amplitude-frequency curves of 14 working conditions are substituted and compared with the amplitude-frequency curves of the healthy bolt connection structure.

[0041] Step S5: Obtain the amplitude-frequency ratio curve for each working condition, shift the amplitude-frequency ratio curve of the healthy bolt connection structure and each working condition downward by 1 unit and take the absolute value, calculate the average value of the amplitude-frequency ratio absolute value curve under different bolt connection looseness degrees, and use the average value of the amplitude-frequency ratio absolute value curve as the bolt looseness detection index. Substitute the average value of the amplitude-frequency ratio absolute value curve of the 14 working conditions in the order of increasing bolt torque, and establish a linear fitting equation between the bolt torque and the average value of the amplitude-frequency ratio absolute value curve, as shown in the following figure: Figure 2 As shown in (f), it can be clearly observed that with the decrease of the bolt connection torque, the average value of the absolute value curve of the amplitude-frequency ratio basically shows a linear upward trend, and the change of the average value of the absolute value curve of the amplitude-frequency ratio is also more obvious in the early stage of loosening (i.e., the bolt connection torque decreases slightly).

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A bolt loosening detection method based on spectrum ratio coefficient method, characterized in that: The following steps are involved: Step S1: Acquire vibration data of a healthy structure under a known swept frequency excitation with the bolts intact. During the measurement, a frequency variation curve of the swept frequency excitation signal and a vibration signal of the structural response are simultaneously obtained through a data acquisition system. Step S2: Using the frequency variation curve of the swept frequency excitation signal as the input parameter of the frequency modulated Fourier transform (CFT) to obtain the amplitude-frequency curves of different frequency orders of the structural response vibration signal; Step S3: Observe the amplitude-frequency curves of different frequency orders and select an amplitude-frequency curve of a specific order that can reflect the structural resonant frequency; repeat steps S1 and S2 under the same parameters to obtain multiple sets of amplitude-frequency curves of healthy structures, and then obtain the average amplitude-frequency curve of the multiple sets of amplitude-frequency curves as the baseline amplitude-frequency curve of the healthy structure; Step S4: When the structural bolts become loose during the operation of the structure, the same sweep frequency excitation is applied to the unhealthy structure, and the frequency variation curve of the sweep frequency excitation signal and the vibration signal of the structural response are obtained through the data acquisition system. Step S5: using the frequency variation curve of the swept frequency excitation signal as an input parameter of the frequency modulated Fourier transform (CFT) to obtain the amplitude-frequency curve of the selected frequency order of the vibration signal of the unhealthy structure response; Step S6: Calculate the ratio curve of the amplitude-frequency curve of the selected frequency order of the vibration signal of the unhealthy structure and the reference amplitude-frequency curve of the healthy structure, and then calculate the average value of the amplitude-frequency ratio curve within the fixed frequency range; Step S7: The loosening of the bolts of the structure can be monitored in real time by changing the average value of the amplitude-frequency ratio curve within a fixed frequency range.

2. The bolt loosening detection method based on the spectrum ratio coefficient method according to claim 1 is characterized in that: In step S6, when the bolts are not loose, the structure is in a healthy state, the resonant frequency peak of the structure does not shift, and the amplitude of the amplitude-frequency ratio curve in this state is stable at about 1. At this time, the average value of the amplitude-frequency ratio curve in the fixed frequency range is about 1; when the bolts are loose, the structure is in an unhealthy state, the stiffness of the structure will change, and the resonant frequency peak of the structure will shift. The amplitude of the amplitude-frequency ratio curve in this state will oscillate near the resonant peak, and the oscillation range is proportional to the resonant frequency shift; the average value of the amplitude-frequency ratio curve in the fixed frequency range will change with the degree of shift of the resonant frequency peak.

3. The bolt loosening detection method based on the spectrum ratio coefficient method according to claim 1 is characterized in that: In step S7, the loosening of the bolts causes the stiffness of the structure to decrease, and the resonance frequency peak will also decrease, that is, the coordinate of the resonance frequency peak moves to the left. Therefore, the average value of the amplitude-frequency ratio curve within the fixed frequency range will increase as the resonance frequency peak moves to the left.

4. A method for detecting the degree of bolt looseness based on the spectrum ratio coefficient method, characterized in that: The following steps are involved: Step S1: obtaining a reference amplitude-frequency curve of vibration data of a healthy structure under a known swept frequency excitation when the bolts are not loosened; Step S2: obtaining unhealthy amplitude-frequency curves of vibration data of known swept frequency excitation under different degrees of bolt looseness, i.e., different torques; Step S3: First, all amplitude-frequency curves are translated upward by 5 units, and then the amplitude-frequency ratio curve of the unhealthy amplitude-frequency curve and the reference amplitude-frequency curve of the vibration data of the known sweep frequency excitation under different bolt looseness degrees is obtained, and the fixed frequency range is Extract the amplitude-frequency ratio curve within the bolt connection, translate the obtained amplitude-frequency ratio curve downward by 1 unit and take its absolute value. Finally, calculate the average value of the absolute value curve of the amplitude-frequency ratio under different degrees of bolt connection looseness. The torque x N corresponding to different degrees of bolt connection looseness is The average value of the absolute value curve of the amplitude-frequency ratio under m is ,in, The bolt torque is x N Fixed frequency range under working conditions of m The absolute value of the amplitude-frequency ratio curve at point i; is a fixed frequency range corresponding to a healthy bolt connection structure The absolute value of the amplitude-frequency ratio curve at point i; Step S4: Using the torque of the bolt as the abscissa and the average value of the absolute value curve of the amplitude-frequency ratio within a fixed frequency range as the ordinate, a linear fitting is performed on the average value of the torque-absolute value curve of the amplitude-frequency ratio to establish a linear fitting equation between the degree of bolt loosening and the average value of the absolute value curve of the amplitude-frequency ratio; Step S5: Under any condition of bolt looseness, the average value of the absolute value curve of the amplitude-frequency ratio is obtained, and then the average value is substituted into the linear fitting equation to obtain the looseness degree of the bolt.

5. The method for detecting the degree of bolt looseness based on the spectrum ratio coefficient method according to claim 4 is characterized in that: All the amplitude-frequency curves are shifted upward by 5 units as a whole, so that the ratio curve is smoother and better reflects the influence of the shift of the resonance frequency peak on the change of the ratio.

6. The method for detecting bolt looseness based on spectrum ratio coefficient method according to claim 4, characterized in that: The amplitude-frequency ratio curve is shifted downward by 1 unit as a whole and its absolute value is taken, which can enhance the change trend of the amplitude-frequency ratio curve and further highlight the influence of the left shift of the resonance frequency peak on the bolt looseness detection index.

7. The method for detecting bolt looseness based on spectrum ratio coefficient method according to claim 4, characterized in that: The fixed frequency range, that is, the frequency band with a smooth single resonance peak is selected as the fixed frequency range, so that the leftward shift of the resonance frequency peak coordinate can be better reflected by the increase in the average value of the amplitude-frequency ratio curve.

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