Bolt pretightening force prediction method based on resonant electromagnetic sensor

Abstract

The invention discloses a bolt pre-tightening force prediction method based on a resonant electromagnetic sensor, and the method comprises the steps: firstly arranging the resonant electromagnetic sensor, and building a signal collection system; then, the bolt pre-tightening force change is converted into capacitance value change, so that the resonant frequency of the sensor antenna deviates, mutual inductance is generated between the sensor antenna and the receiving antenna, the resonant state of the receiving antenna is changed, and the network vector analyzer measures the resonant frequency of the receiving antenna to determine the pre-tightening force of the bolt. And establishing a function relationship between the resonant frequency of the sensor and the deviation of the pre-tightening force through a least square method, and finally monitoring the bolt pre-tightening force by reading the resonant frequency of the resonant electromagnetic sensor.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of bolt pre-tightening force monitoring, and more specifically relates to a bolt pre-tightening force prediction method based on a resonant electromagnetic sensor. BACKGROUND

[0002] In high-risk equipment such as tower cranes, high-strength bolts gradually attenuate the pre-tightening force due to long-term bearing of transverse alternating load, temperature fluctuation and material fatigue, thereby causing the risk of connection node loosening and even structural instability. Traditional monitoring methods rely on manual re-inspection or offline sampling inspection, which has low efficiency and poor real-time performance. Although existing online monitoring technologies introduce intelligent gaskets or wired strain gauges, the complex cable layout and external power supply requirements result in high deployment costs and maintenance difficulties, especially in rotating parts or closed scenes.

[0003] The existing bolt pre-tightening force monitoring technology has the following core defects: invasive sensors can damage the structural integrity, such as fiber Bragg grating (FBG) which needs to drill holes on the bolt axis to implant sensors, weakening the bolt bearing capacity; wired connection limits deployment flexibility, traditional piezoelectric ultrasonic, vibration analysis, etc. need external wires or power supply equipment, which is difficult to deploy in rotating parts or closed spaces for a long time. The present application provides a passive wireless resonant electromagnetic sensor, which solves the contradiction between real-time monitoring of bolt pre-tightening force and adaptability to complex working conditions through non-invasive and battery-free design. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and provide a bolt pre-tightening force prediction method based on a resonant electromagnetic sensor. By building a signal acquisition system and collecting data, the mapping relationship between pre-tightening force and resonant frequency is fitted, so as to estimate the bolt pre-tightening force in real time.

[0005] To achieve the above-mentioned purpose of the application, the bolt pre-tightening force prediction method based on the resonant electromagnetic sensor comprises the following steps:

[0006] (1) Build a signal acquisition system;

[0007] The capacitive sensing unit of the resonant electromagnetic sensor is clamped between the bolt gasket and the fastened part, the sensor antenna of the resonant electromagnetic sensor is connected with the capacitive sensing unit and externally connected with the bolt surface, the receiving antenna is connected with the vector network analyzer, and the receiving antenna is close to the sensor antenna;

[0008] (2) Measure the return loss S11 by the vector network analyzer;

[0009] (2.1) Apply different levels of pre-tightening force σi to the bolt during the measurement process i , i = 1, 2, 3, …, n, n is the number of applied pre-tightening force levels;

[0010] (2.2), based on the signal acquisition system, the full frequency band is swept by using the vector network analyzer, and the return loss S11 under different levels of pre-tightening force is obtained;

[0011] (2.3), the frequency corresponding to the minimum value of each S11 curve is recorded as the resonant frequency f of the resonant electromagnetic sensor antenna i ;

[0012] (3), the least square method is used to fit the mapping function of the resonant frequency f i and the bolt pre-tightening force sigma i ;

[0013] sigma = af + b

[0014] Wherein, sigma represents the pre-tightening force, f represents the resonant frequency, a and b are fitting coefficients;

[0015] (4), based on the signal acquisition system, the full frequency band is swept by using the vector network analyzer, and the return loss S11 is obtained;

[0016] The frequency corresponding to the minimum value in the S11 curve is the resonant frequency f, and the resonant frequency f is substituted into the mapping function, so as to estimate the bolt pre-tightening force sigma.

[0017] The purpose of the application is achieved as follows:

[0018] The bolt pre-tightening force prediction method based on the resonant electromagnetic sensor is used, the resonant electromagnetic sensor is arranged first, and the signal acquisition system is built; then the bolt pre-tightening force change is converted into the capacitance value change, and then the resonant frequency of the sensor antenna is caused to deviate, the sensor antenna and the receiving antenna produce mutual inductance, so that the resonant state of the receiving antenna is changed, the network vector analyzer measures the resonant frequency of the receiving antenna, the function relationship between the sensor resonant frequency and the pre-tightening force deviation is established by the least square method, and finally the resonant frequency of the resonant electromagnetic sensor is read, and then the bolt pre-tightening force is monitored.

[0019] Meanwhile, the bolt pre-tightening force prediction method based on the resonant electromagnetic sensor also has the following beneficial effects:

[0020] (1) Non-invasive installation: the application designs a new type of resonant electromagnetic sensor, the capacitive sensing unit of the resonant electromagnetic sensor is directly pasted on the surface of the bolt or between the gaskets, without the need of drilling, modifying the bolt or adding complex gasket structure, and the mechanical properties of the bolt are completely reserved.

[0021] (2) Wireless monitoring: the resonant frequency of the resonant electromagnetic sensor is read wirelessly through magnetic resonance coupling, and then the bolt pre-tightening force is monitored, and external excitation and wiring are eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a bolt preload prediction system based on resonant electromagnetic sensor;

[0023] Figure 2 It is a structural diagram of a resonant electromagnetic sensor;

[0024] Figure 3 It is a schematic diagram of the layout of a specific embodiment of a resonant electromagnetic sensor;

[0025] Figure 4 is the S11 curve under different preload forces;

[0026] Figure 5 It is the mapping relationship curve of resonant frequency-bolt preload. DETAILED DESCRIPTION

[0027] The following describes the specific embodiments of the present invention in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, such descriptions will be omitted here.

[0028] Example

[0029] In this embodiment, if Figure 1 As shown, the present invention provides a bolt preload prediction method based on a resonant electromagnetic sensor, comprising the following steps:

[0030] (1) Build a signal acquisition system;

[0031] In this embodiment, if Figure 2 As shown, the resonant electromagnetic sensor mainly consists of two parts: a capacitive sensing unit and a sensor antenna. The capacitive sensing unit adopts a ring structure with a hollow center to allow the bolt column to pass through the ring. The circuit is printed on the substrate through an etching process.

[0032] Table 1 Main parameters of a resonant electromagnetic sensor (mm)

[0033] [R1] [R2] [R3] θ L [[ L p1 ]]> [[ L p2 ]]> a 16 30 15 4° 63.6 19 60 0.35 g d w p1 ]]> w p2 ]]> w1 w2 w s ]]> d s ]]> 0.35 0.65 0.6 0.4 3 3 0.4 3.1

[0034] Where R1 is the inner diameter of the sensor unit, R2 is the outer diameter of the sensor unit, R3 is the outer diameter of the sensor antenna, and θ is the clearance angle of the sensor unit. p2 L p1 They represent the outer margin and center distance of the sensing unit and the sensor antenna, and the distance from the inner circle of the sensing unit to the transmission line, respectively. a is the conductor line margin, g is the conductor line width; w p1 w p2w1 w2 w s Respectively represent the sensor unit axis width, parallel conductive line width, axis base width, parallel conductive line base width and sensor antenna helical pitch; d s is the sensor antenna line distance.

[0035] like Figure 3 As shown, the capacitive sensing unit of the resonant electromagnetic sensor is sandwiched between the bolt washer and the fastener, the sensor antenna of the resonant electromagnetic sensor is connected to the capacitive sensing unit and externally positioned on the bolt surface, and the receiving antenna is connected to the vector network analyzer and close to the sensor antenna, thereby building an acquisition system;

[0036] (2) Measure the return loss S11 using a vector network analyzer;

[0037] (2.1) During the measurement process, different levels of preload σ are applied to the bolts. i , i=1,2,3,…,n, n is the number of preload levels applied;

[0038] In this embodiment, a pre-tightening force is applied to an unlocked bolt to calibrate the pre-tightening force. It is assumed that 100 levels of pre-tightening force are applied to the bolt, the bolt is made of 45# steel, and the material of the tightened part is Q235.

[0039] (2.2) Based on the signal acquisition system, a vector network analyzer is used to perform full-band frequency sweep to obtain the return loss S11 under different levels of preload;

[0040] (2.3) Record the frequency corresponding to the minimum value of each S11 curve as the resonant frequency f of the resonant electromagnetic sensor antenna i ;

[0041] In this embodiment, taking the 0 MPa curve as an example, S11 changes with frequency and has a minimum value, which appears at (-8.35 dB, 13.96 MHz). It is considered that when the stress is 0 MPa, the resonant frequency is 13.96 MHz.

[0042] In this embodiment, under partial preload conditions, the return loss S11 curves under different levels of preload are obtained as follows: Figure 4 The corresponding resonant frequencies are shown in Table 2.

[0043] σ / MPa 0 9 18 27 36 45 54 f / MHz 13.96 12.65 11.93 11.75 11.55 11.25 10.92

[0044] Table 2

[0045] (3) Fitting the resonant frequency f using the least squares method i and bolt preload σ i The mapping function of

[0046] σ = af + b

[0047] Wherein, σ represents the pretightening force; f represents the resonance frequency; a, b are fitting coefficients, and the specific calculation process is as follows:

[0048] Resonance frequencies f of n groups of data are solved respectively i And the mean value of bolt pretightening force σ i .

[0049]

[0050] Then, the coefficients a, b are solved:

[0051]

[0052] Through the data in Table 2, the mapping relationship of the resonance frequency-bolt pretightening force can be obtained, which can be expressed as: σ =-22.04586 Pa / Hz * f (MHz) + 290.47994 MPa, and the fitting curve is as shown in Figure 5 .

[0053] (4), based on the signal acquisition system built, the vector network analyzer is used for full-band sweep, and the return loss S11 is obtained;

[0054] The frequency corresponding to the minimum value in the S11 curve is recorded, that is, the resonance frequency f, and then the resonance frequency f is substituted into the mapping function, so that the bolt pretightening force σ is estimated.

[0055] In the embodiment, assuming that the measured resonance frequency is 11.00 MHz, the bolt pretightening force estimated value is:-22.04586*11.00+290.47994=47.97548 (MPa) by substituting the expression.

[0056] In summary, the method for characterizing the bolt pretightening force through electromagnetic resonance is proposed, and the non-invasive and passive wireless detection of the bolt pretightening force is realized. This is different from the conventional detection method, and the method has lower destructiveness and operation difficulty, and makes a more accurate algorithm fitting for the bolt pretightening force.

[0057] Although the above describes the specific embodiments of the present application for the purpose of facilitating the understanding of the present application by those skilled in the art, it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application defined and determined by the appended claims, and all the inventions utilizing the concept of the present application are within the scope of protection.

Claims

1. A bolt preload prediction method based on a resonant electromagnetic sensor, characterized in that: The following steps are involved: (1) Build a signal acquisition system; The capacitive sensing unit of the resonant electromagnetic sensor is sandwiched between the bolt washer and the fastener, the sensor antenna of the resonant electromagnetic sensor is connected to the capacitive sensing unit and is externally positioned on the bolt surface, and the receiving antenna is connected to the vector network analyzer and is close to the sensor antenna; (2) Measure the return loss S11 using a vector network analyzer; (2.1) During the measurement process, different levels of preload σ are applied to the bolts. i , i=1,2,3,…,n, n is the number of preload levels applied; (2.2) Based on the signal acquisition system, a vector network analyzer is used to perform full-band frequency sweep to obtain the return loss S11 under different levels of preload; (2.3) Record the frequency corresponding to the minimum value of each S11 curve as the resonant frequency f of the resonant electromagnetic sensor antenna i ; (3) Fitting the resonant frequency f using the least squares method i and bolt preload σ i The mapping function of σ=af+b Where, σ represents the preload, f represents the resonant frequency, and a and b are fitting coefficients; (4) Based on the signal acquisition system, a vector network analyzer is used to perform full-band frequency sweep to obtain the return loss S11; The frequency corresponding to the minimum value in the S11 curve is recorded as the resonant frequency f, and then the resonant frequency f is substituted into the mapping function to estimate the bolt preload σ.

2. The bolt preload prediction method based on a resonant electromagnetic sensor according to claim 1, characterized in that: The resonant electromagnetic sensor mainly consists of two parts: a capacitive sensing unit and a sensor antenna. The circuit is printed on the substrate through an etching process; Among them, the capacitive sensing unit adopts a ring structure with a hollow center so that the bolt column can pass through the ring.

3. The bolt preload prediction method based on a resonant electromagnetic sensor according to claim 1, characterized in that: The method for determining the fitting coefficients a and b is: Solve the resonant frequency f of n groups of data separately i and bolt preload σ i The mean of Next, solve for the coefficients a and b:

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