A rotating pulsed eddy current probe structure and detection method for reducing the influence of lift-off fluctuations

Abstract

The application discloses a rotating pulse eddy current probe structure and a detection method for reducing the influence of lift-off fluctuation, belongs to the technical field of electromagnetic nondestructive detection, and comprises the following steps: S1, establishing a simplified structure, establishing an induced voltage signal △U ; according to △U , an integral formula is established; S2, the actual maximum lift-off of the probe and the minimum value of the angle between the probe coils are combined with the axial distance between the excitation coil and the receiving coil of the probe D , the integral actual value of the formula is solved, the integral actual value is not changed according to the principle, and the corresponding coil angle of different lift-offs is calculated; S3, the different lift-offs and the corresponding coil angles are subjected to curve fitting; and S4, the fitting curve is used to verify the correctness of the lift-off effect. The method and the probe structure can change the coil angle at different lift-offs to reduce the lift-off effect.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic nondestructive testing technology, specifically to a rotating pulse eddy current probe structure and testing method for reducing the influence of lift-off fluctuations. Background Technology

[0002] Pulsed eddy current testing is a novel detection method developed based on eddy current testing. Due to variations in coating thickness, irregular shape, or vibrations in the scanning device connecting the probe to the test object, the pulsed eddy current probe may be in a fluctuating state, meaning the lift-off distance between the probe and the test piece surface will continuously change, thus affecting the detection signal and reducing detection accuracy. Therefore, suppressing the effects of lift-off is a key focus in pulsed eddy current testing research.

[0003] Designing and optimizing pulsed eddy current probes is one of the main ways to reduce the lift-off effect. Previous studies have shown that non-coaxial Tx-Rx (excitation-receiver) probes can reduce the lift-off effect by optimizing the spacing between the excitation and receiving coils; however, the signal amplitude decreases as the spacing between the excitation and receiving coils increases. How to ensure a certain signal amplitude while reducing the lift-off effect remains a challenge. Summary of the Invention

[0004] The present invention provides a rotating pulse eddy current probe structure and detection method for reducing the impact of lift-off fluctuations. It can change the coil angle during lift-off, thereby reducing the lift-off effect.

[0005] To achieve the above objectives, the present invention provides a rotating pulsed eddy current detection method for reducing the influence of lift-off fluctuations, comprising the following steps: S1: placing the pulsed eddy current probe on a flat plate specimen, establishing a simplified structure, and establishing an induced voltage signal based on the simplified structure. △U The expression; according to △U The relevant parameters affecting the lift-off effect in the expression are used to establish an integral formula;

[0006] The integral formula is: (1)

[0007] J 0( x ) represents the zeroth-order Bessel function; e -2αlo This is the lift-off coefficient; i The included angle is the angle between the receiving coil and the horizontal plane. i The angle is acute; the axial distance between the excitation coil and the receiving coil is... D ; l o For removal;

[0008] S2: Substitute the actual maximum lift-off of the probe and the minimum angle between the probe coils into equation (1), and then combine this with the axial distance between the probe's excitation coil and receiving coil. D Together, we can find the actual value of the integral of equation (1), and calculate the coil angle corresponding to different lift-offs based on the principle that the actual value of the integral remains unchanged.

[0009] S3: Perform curve fitting on the different lift-offs and corresponding coil angles in S2;

[0010] S4: Using the curve fitted in S3, obtain different lift-offs and corresponding coil angles, and verify the correctness of reducing the lift-off effect using different lift-offs and coil angles.

[0011] Furthermore, in step S1, the simplified structure has three layers, from bottom to top: air, flat specimen, and probe lift-off; the pulsed eddy current probe is located above the simplified structure.

[0012] With the axis of symmetry of the excitation coil as z Axis, with z A cylindrical coordinate system is established with the intersection of the axis and the point where the probe is lifted off the upper surface as the origin. r , i , z );

[0013] Induced voltage signal △U It can be represented as:

[0014]

[0015] in, R'' 4,3 ( α () represents the generalized reflection coefficient of the three-layer structure. e -2αlo The lift-off coefficient, S'' ( α ) represents the coil coefficient of the pulsed eddy current probe. J 0( x ) and J 1( x () denote the zeroth and first-order Bessel functions, respectively. i The included angle of the coil, oh and I ( oh These represent the angular frequency and the amplitude of the harmonic excitation current, respectively. j It is the imaginary unit. m 0 is the permeability of free space. m r2 It is the relative permeability. s 2 is the electrical conductivity of the metal plate; n , r 1, r 2,l These are the number of coil turns, inner diameter, outer diameter, and height, respectively, with the subscripts T and R representing the excitation coil and the receiving coil, respectively.

[0016] This involves constructing an integral equation, based on a simplified structure and the corresponding cylindrical coordinate system, to build the induced voltage signal. △U .

[0017] Furthermore, in step S3, the curve is fitted using a quadratic polynomial.

[0018] The fit is relatively accurate and can more clearly reflect the relevant patterns.

[0019] Furthermore, maximum lift l omax =10 mm, corresponding to the minimum angle of the probe coil. i min = 0°; Set the axial distance between the excitation coil and the receiving coil. D= 10mm, the outer diameter of both the excitation coil and the receiving coil is 5mm;

[0020] Or, maximum lift l omax =10 mm, corresponding to the minimum angle of the probe coil. i min = 0°; Set the axial distance between the excitation coil and the receiving coil. D= The outer diameter of the excitation coil is 5mm; the outer diameter of the receiving coil is 12mm.

[0021] Two different placement methods for the excitation coil or the receiving coil: the excitation coil may be inside the receiving coil or the excitation coil may be outside the receiving coil. Both cases were demonstrated in Example 1, showing that both cases reduce the lift-off effect.

[0022] Furthermore, a rotating pulsed eddy current probe structure for reducing the impact of lift-off fluctuations includes a housing, a receiving cavity within the housing, and an excitation coil assembly and a receiving coil assembly within the receiving cavity;

[0023] The excitation coil assembly includes:

[0024] The excitation coil frame is fixed to the inner wall of the receiving cavity;

[0025] The excitation coil is wound on the excitation coil frame, with its central axis set vertically.

[0026] The receiving coil assembly includes:

[0027] The support is fixed to the inner wall of the receiving cavity;

[0028] The mounting frame is rotatably connected to the bracket by a rotating shaft; the axis of the rotating shaft is set horizontally, that is, along the X direction.

[0029] The receiving coil frame is fixed on the mounting frame;

[0030] The receiving coil is wound on the receiving coil frame. Let the central axis of the receiving coil be a. Then the plane that a always lies on during the rotation is plane P. The X direction is always perpendicular to plane P.

[0031] It also includes a drive assembly for rotating the mounting frame and changing the coil angle; the excitation coil is inside or outside the receiving coil; and it also includes an excitation coil connector and a receiving coil connector that are respectively connected to the excitation coil and the receiving coil.

[0032] Furthermore, the driving component includes:

[0033] The probe is movably mounted on the inner wall of the receiving cavity and can move vertically.

[0034] The limiting spring and the limiting plate are located above the probe and are fixed to the inner wall of the receiving cavity. One end of the limiting spring is fixedly connected to the limiting plate and the other end is fixedly connected to the upper end of the probe. The limiting spring is always in a compressed state.

[0035] The slider is fixedly connected to the probe.

[0036] The rack is vertically positioned and fixedly connected to the slider.

[0037] The transmission rod is rotatably connected to the receiving cavity. One end is fixed with a transmission gear, which coincides with the axis of the transmission rod and meshes with a rack. The other end is fixed with a driving bevel gear, which coincides with the axis of the transmission rod. The axis of the transmission rod is set horizontally and perpendicular to the X direction.

[0038] The driven rod is rotatably connected to the inner wall of the receiving cavity, and its axis is set vertically.

[0039] The driven bevel gear is fixed on the driven rod, coincides with the axis of the driven rod, and meshes with the driving bevel gear;

[0040] A cam used to rotate the mounting frame is horizontally positioned with its outer edge abutting against the mounting frame; it is detachably connected to the driven rod.

[0041] The spring used to reset the mounting frame is always in a compressed state, with one end fixedly connected to the bracket and the other end fixedly connected to the surface wall of the mounting frame; the cam and the spring are located on opposite sides of the surface wall of the mounting frame.

[0042] Beneficial effects:

[0043] This method, after determining the probe, maintains the axial distance between the excitation coil and the receiving coil at a certain value. D By changing the coil angle correspondingly when changing the lift-off, the integral in equation (1) remains unchanged, thereby reducing the lift-off effect. Attached Figure Description

[0044] Figure 1 This is a schematic diagram showing the pulsed eddy current probe positioned above a three-layer structure.

[0045] Figure 2 The quadratic polynomial fitting curve of the lift-off and coil angle;

[0046] Figure 3 To determine the detection signal Δ of probe 1 when lifted at 0 and 10 mm without changing the coil angle, U ;

[0047] Figure 4 For different lo and i The detection signal △ of the lower probe 1 U ;

[0048] Figure 5 The detection signal Δ of probe 1 at 10 mm and 0 mm lift-off points. U ;

[0049] Figure 6 The detection signal Δ of the 10mm thick flat plate probe 1 U ;

[0050] Figure 7 The detection signal △ for the aluminum plate U ;

[0051] Figure 8 The detection signal △ of probe 2 U ;

[0052] Figure 9 A schematic diagram of a pulsed eddy current probe structure that can reduce the impact of lift-off fluctuations;

[0053] Figure 10 This is a schematic diagram of the overall structure of the outer shell.

[0054] Reference numerals: 10, Excitation coil assembly; 101, Excitation coil frame; 102, Excitation coil;

[0055] 20. Receiver coil assembly; 201. Mounting frame; 401. Bracket; 202. Receiver coil frame; 203. Receiver coil; 402. Excitation coil connector; 403. Receiver coil connector;

[0056] 30. Drive assembly; 301. Limiting plate; 302. Probe; 303. Slider; 304. Rack; 305. Limiting spring; Transmission rod; 306. Transmission gear; 307. Transmission rod; 308. Driving bevel gear; 309. Driven bevel gear; 310. Driven rod; 311. Spring; 312. Cam. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0058] A method for detecting rotating pulsed eddy currents to reduce the impact of lift-off fluctuations includes the following steps:

[0059] S1: Place the pulsed eddy current probe on the flat specimen, establish a simplified structure, and establish the induced voltage signal based on the simplified structure. △U The expression; according to △U Establish the integral formula using the relevant parameters in the expression;

[0060] Specifically, the placed flat plate specimen is considered as a simplified three-layer structure, viewed from bottom to top. The first layer is air, the second layer is the flat plate specimen, and its thickness is...

[0061] c The third layer is for probe removal. l o The pulsed eddy current probe, consisting of an excitation coil and a receiving coil, is located in the fourth layer of a three-layer structure, and the axial distance between the excitation coil and the receiving coil is... D .

[0062] D The value of can simulate two cases: the excitation coil is located inside the receiving coil and the excitation coil is located outside the receiving coil. Figure 1 The diagram shows the case where the excitation coil is located outside the receiving coil. Considering that the excitation current is a circular current, a cylindrical coordinate system is chosen for ease of calculation. r , i , z );set up z The axis coincides with the axis of symmetry of the excitation coil, and the origin of the coordinate system is ( O The point is located on the upper surface of the three-layer structure.

[0063] When the excitation current is a square wave signal, according to the Fourier transform, the square wave excitation can be regarded as a superposition of a series of harmonic excitations. Therefore, by adding the signals of each harmonic and performing an inverse discrete Fourier transform on the result, the time-domain induced voltage signal of the pulsed eddy current can be obtained. For each harmonic component, the induced voltage signal of the receiving coil... △U It can be represented as:

[0064]

[0065] in, R'' 4,3 ( α () represents the generalized reflection coefficient of the three-layer structure. e -2αlo The lift-off coefficient, S'' ( α ) represents the coil coefficient of the pulsed eddy current probe. J 0( x ) and J 1( x () denote the zeroth and first-order Bessel functions, respectively. i The coil angle (the angle between the receiving coil and the horizontal plane) I, included angle i (acute angle) oh and I ( oh These represent the angular frequency and the amplitude of the harmonic excitation current, respectively. j It is the imaginary unit. m 0 is the permeability of free space. m r2 It is the relative permeability. s 2 is the electrical conductivity of the metal plate. n , r 1, r 2, l These are the number of coil turns, inner diameter, outer diameter, and height, respectively, with the subscripts T and R representing the excitation coil and the receiving coil, respectively.

[0066] From equation (1), we can see that △ U Mainly composed of R" 4,3 ( α ), S" ( α )and e -2αlo × J 0( αD )× cosθ These three decisions. Among them, R" 4,3 ( α It is only related to parameters such as the material of the specimen. S" ( αIt depends only on the coil parameters (number of turns, inner diameter, outer diameter, and coil height). Therefore, R" 4,3 ( α )and S" ( α It will not be taken away. l o Changes occur when the parameters of the specimen and coil (number of turns, inner diameter, outer diameter, and height) are determined. R" 4,3 ( α )and S" ( α ) will also be determined at this time. △ U The expression can only take the value of... e -2αlo × J 0( αD )× cosθ Related to the coil spacing. D After fixing, change the coil angle. I, make e -2αlo × J 0( αD )× cosθ The value of Δ does not change with lift-off, at which point Δ U This will remain unchanged, thus eliminating the effects of lifting.

[0067] To find the appropriate coil angle i and the included angle of the coil i The corresponding lift-off l o Therefore, in this embodiment, the integral shown in equation (6) (referred to as in this scheme) is used. l o – i To solve the above problem, we only need to integrate the points (i.e., as long as...). l o and i When changes occur, maintain lo–θ If the integral value remains unchanged, then it is considered that e -2αlo × J 0( αD ) × cosθ It remains unchanged.

[0068]

[0069] S2: Utilize the actual maximum lift. l omax Minimum value of the angle between the coil and the coil i min Combined with known D， Find lo–θ The actual value of the integral, and then based on lo–θ Integrate the actual value and calculate the coil angle corresponding to different lift-off conditions.

[0070] Specifically, since the maximum lift-off of the probe during the detection process can be estimated, and the minimum coil angle is known (typically 0°), these two values ​​can be used to determine... lo–θ The integral value of . Then it can be defined as:

[0071]

[0072] in, l omax yes l o The maximum value, i min yes i The minimum value.

[0073] In practice, when using probe 1 (whose parameters are shown in Table 1) to inspect the rail, the lift-off of probe 1 fluctuates between 0 and 10 mm. l omax =10 mm, minimum coil angle i min = 0°. Then, according to the parameters of probe 1 in Table 1, fix the coil spacing. D = r 2T + r 2R =2 r 2 = 10 mm. (The rest of the text appears to be incomplete and requires further context.) l omax and i min and D Substituting 10mm into equation (7), the result is calculated. Int ( l omax ， i min The value is 28.2. Then, based on the obtained... Int ( l omax ,the min ) Calculations differ l o Down i The values ​​are shown in Table 2. According to Table 2, adjusting the coil angle under different lift-off conditions can reduce the lift-off effect.

[0074] Table 1. Parameters of the excitation coil or receiving coil in probe 1

[0075]

[0076] Table 2. Probe 1 at different lift levels l o Below, the corresponding coil angle i value

[0077]

[0078] S3: Based on the coil angle corresponding to different lift-off conditions in S2, a quadratic polynomial is used to fit the relationship between lift-off and coil angle.

[0079] Specifically, based on the data in Table 2, the fitted curves are shown below. Figure 2 The expression for the fitted curve is: i = -0.79 l o 2 +1.89 l o + 61.71.

[0080] The coil angle of the probe 1 can be adjusted in real time according to the change of lift-off, so as to reduce the influence of the lift-off effect and improve the detection accuracy.

[0081] S4: Use the fitted curve from S3 to obtain different lift-offs and corresponding coil angles, and use different lift-offs and coil angles to verify the correctness of reducing the lift-off effect.

[0082] To demonstrate that probe 1 with an optimized coil angle can reduce the lift-off effect, relevant verifications were conducted. Probe 1 was designed using the data in Table 1, and the following tests were performed using probe 1. Figure 3 To detect the signal of a 20 mm thick ferromagnetic metal plate under 0 mm and 10 mm lift without changing the coil angle;

[0083] Figure 4 and Figure 5 For in different l o and corresponding i Below, the detection signal is obtained by using probe 1 to measure the signal on a 20 mm thick ferromagnetic metal plate. Figure 4 The detection signals shown are based on those listed in Table 2. l o and i Obtained. To highlight signal differences, from Figure 4 Two signals under maximum and minimum lift-off conditions were extracted, and the results are as follows: Figure 5 .

[0084] Will Figure 3 and Figure 5 A comparison shows that, Figure 5 The signal difference in the middle is less than Figure 3The signal differences are more pronounced in the latter half of the signal. This indicates that, according to lo–θ Integral adjustment coil angle i This can reduce the lift-off effect.

[0085] From equation (7), we can see that lo–θ Points only with l omax and i min and D Related to, among them D Depending on the outer diameter of the coil, it means... lo–θ The integration is unaffected by other parameters of the specimen and probe (number of turns, inner diameter, height). Therefore, the probe performance is analyzed under conditions of different specimen thicknesses, different materials, and different probe parameters.

[0086] To demonstrate that the optimized coil angle can be used for testing flat plates of other thicknesses (i.e., unaffected by different specimen thicknesses), a 10 mm thick ferromagnetic metal flat plate was designed, and its detection signal is as follows: Figure 6 As shown. Figure 6 The results show that the detection signal difference of probe 1 is small at 0 mm and 10 mm lift-off, indicating that the optimized coil angle in Table 2 can be used to reduce the lift-off effect of a 10 mm thick ferromagnetic metal plate. (Comparison) Figure 4 and Figure 6 This indicates that it can be used to reduce the lift-off effect of metal plates of different thicknesses.

[0087] To demonstrate that the optimized coil angle can be used to test flat plates made of other materials (i.e., unaffected by different material specimens), a 20 mm thick aluminum plate was used. Figure 7 The signal obtained by using probe 1 to detect the aluminum plate. Figure 7 This indicates that probe 1 in this method can be used to reduce the lift-off effect of the aluminum plate. (Comparison) Figure 4 and Figure 7 This indicates that probe 1 can also be made of other materials.

[0088] Furthermore, to demonstrate the relationship between the change in lift-off and coil angle and the coil spacing... D Regarding this, probe 2 was designed, with excitation coil parameters identical to those of probe 1, and receiving coil parameters as shown in Table 3. Assuming the distance between the excitation and receiving coils is 5mm, the excitation coil is placed inside the receiving coil. According to... l o – i Integral calculation yields Int ( l omax ,the min = 30.6, then calculate the coil angle corresponding to different lift-off conditions based on this value. i The results are shown in Table 4. Based on the data in Table 4, a quadratic polynomial was used to fit the relationship between the lift-off and the coil angle. The fitted expression is as follows: i = -0.82 l o 2 +1.07 l o + 74.43. Figure 8 The detection signal obtained by probe 2 based on the lift-off and coil angle changes in Table 4. Figure 8 This indicates that the signal from probe 2 is almost unaffected by the lift-off effect, compared to... Figure 7 and Figure 8 This demonstrates the relationship between the coil angle and the coil spacing as the coil is lifted. D Related. By Figure 4 and Figure 8 It can be seen that the structure of this scheme is effective for probe structures in both cases where the excitation coil is located inside the receiving coil and where the excitation coil is located outside the receiving coil.

[0089] Table 3. Probe 2 parameters

[0090]

[0091] Table 4. Coil angle values ​​for probe 2 at different lift-off conditions

[0092]

[0093] It should be noted that although the relationship between the coil angle and lift-off is related to the coil spacing D, once the probe is replaced, as long as the coil spacing is fixed, the relationship will change. D And learned l omax and i min The value of can also be obtained from equation (7). lo–θ integral Int ( l omax ,the min The value of is obtained, and then the coil angle under different lift-off conditions is calculated based on this value. The relationship between lift-off and coil angle is then fitted based on the obtained data. Based on the fitted relationship, the purpose of reducing the lift-off effect in different application scenarios can be achieved. Example 2

[0094] See Figure 9 A rotating pulsed eddy current probe structure that reduces the influence of lift-off fluctuations can be used to fabricate probe 1 in Example 1.

[0095] The probe structure includes a housing (see...) Figure 10(The outer frame 407 and the cover plate 408 are connected as a whole by bolts. The outer shell is a rectangular frame with a receiving cavity in it. The receiving cavity contains an excitation coil assembly 10, a receiving coil assembly 20 and a driving assembly 30.)

[0096] Excitation coil assembly 10 includes:

[0097] Excitation coil frame 101 is fixed to the inner wall of the receiving cavity;

[0098] The excitation coil 102 is wound around the excitation coil frame 101. The central axis of the excitation coil 102 is set vertically.

[0099] The receiving coil assembly 20 includes:

[0100] Support 401 is fixed to the inner wall of the receiving cavity;

[0101] Mounting frame 201 is rotatably connected to bracket 401 via a rotating shaft; assuming the axis of the rotating shaft is horizontal, i.e. Figure 9 In the X direction;

[0102] The receiving coil frame 202 is fixed on the mounting frame 201 and rotates with the mounting frame 201.

[0103] The receiving coil 203 is wound around the receiving coil frame 202 and rotates with the mounting frame 201. Let the central axis of the receiving coil 203 be a, then the plane that a always lies on during the rotation is plane P, and the X direction is always perpendicular to plane P.

[0104] In this embodiment, the excitation coil 102 is located outside the receiving coil 203, and the two are not nested together.

[0105] The cover plate is connected to an excitation coil connector 402 and a receiving coil connector 403, which are respectively connected to the excitation coil 102 and the receiving coil 203. The excitation coil connector 402 is used to generate an excitation signal for the excitation coil 102, and the receiving coil connector 403 is used to receive the induced signal.

[0106] Driver component 30 includes:

[0107] The probe 302 is set vertically along its axis and is movably locked onto the inner wall of the receiving cavity. The probe 302 can move vertically. A probe protective shell 405 is fixed on the inner wall of the receiving cavity and wraps around the probe 302. The lower end of the probe 302 extends out of the receiving cavity and abuts against the upper surface wall of the object to be tested.

[0108] The limiting spring 305 and the limiting plate 301 are located above the probe 302 and are fixed to the inner wall of the receiving cavity. One end of the limiting spring 305 is fixedly connected to the limiting plate 301, and the other end is fixedly connected to the upper end of the probe 302. The limiting spring 305 is always in a compressed state.

[0109] The slider 303 and probe 302 are fixedly connected to the slider 303 via a probe bracket; the slider 303 moves as the probe 302 moves.

[0110] The rack 304 is fixed on the slider 303 and is arranged vertically.

[0111] The transmission rod 307 has a horizontal axis and the axis of the transmission rod 307 is perpendicular to the X direction. The transmission rod 307 is rotatably connected to the inner wall of the receiving cavity by the limiting frame 406. The limiting frame 406 is fixed to the inner wall of the receiving cavity, and the transmission rod 307 can rotate relative to the limiting frame 406.

[0112] The transmission gear 306 is aligned with the axis of the transmission rod 307, fixed on the transmission rod 307, and meshes with the rack 304.

[0113] The active bevel gear 308 coincides with the axis of the transmission rod 307 and is fixed on the transmission rod 307. The active bevel gear 308 and the transmission gear 306 are located at the two ends of the transmission rod 307, respectively.

[0114] Driven rod 310 is rotatably connected to the inner wall of the receiving cavity, and its axis is set vertically;

[0115] The driven bevel gear 309 coincides with the axis of the driven rod 310, is fixed on the driven rod 310, and meshes with the driving bevel gear 308.

[0116] Cam 312, detachably connected to driven rod 310, is horizontally positioned. The outer circumferential wall of cam 312 abuts against one side surface wall of mounting frame 201. Cam 312 and excitation coil assembly 10 are located on the same side of mounting frame 201. Probe 302 rotates mounting frame 201 sequentially via slider 303, rack 304, transmission rod 307, driven rod 310, and cam 312, thereby adjusting the coil angle. i Change;

[0117] Spring 311 is fixedly connected at one end to bracket 401 and at the other end to the surface wall of mounting frame 201. Cam 312 and spring 311 are located on opposite sides of the surface wall of mounting frame 201. Spring 311 is always in a compressed state to push mounting frame 201 to rotate. When cam 312 does not generate a force to rotate the mounting frame, the elastic force of spring 311 is used to reset mounting frame 201.

[0118] Except for the spring 311, the excitation coil 101, and the receiving coil 203, all other components in this design are made of non-conductive materials.

[0119] Change the coil angle i The process is as follows:

[0120] The lower end of the probe 302 is in contact with the surface of the object being measured. When the probe 302 detects a change in lifting, the probe 302 will move accordingly under the elastic force of the limit spring 305; the slider 303 also moves with the movement of the probe 302.

[0121] Since the slider 303 meshes with the transmission gear 306 through the rack 304, and the transmission rod 307 is rotatably connected to the receiving cavity, the vertical movement of the slider 303 will drive the transmission gear 306 to rotate, the transmission gear 306 will then cause the transmission rod 307 to rotate, and in turn the active bevel gear 308 will rotate.

[0122] Since the active bevel gear 308 meshes with the driven bevel gear 309, the active bevel gear 307 drives the driven bevel gear 309 to rotate, which in turn causes the driven rod 310 to rotate.

[0123] Rotation of the driven rod 310 causes the cam 312 to rotate in the horizontal plane. Since the outer circumferential wall of the cam 312 abuts against the mounting frame 201, when the cam 312 rotates, the mounting frame 201 will rotate around the axis of rotation (X direction), resulting in an increase in the coil angle. i The outer edge of cam 312 is ground according to the actual situation, corresponding to the coil angle in embodiment 1. i The fitting curve of the quadratic term is set so that the coil angle can be adjusted. i The data in Table 2 of Example 1 are satisfied. Example 3

[0124] The difference from Embodiment 2 is that in this embodiment, a rotating pulsed eddy current probe structure for reducing the impact of lift-off fluctuations has an excitation coil located inside the receiving coil, which can be used to fabricate probe 2 in Embodiment 1; that is, the receiving coil is sleeved on the excitation coil. The other structures are completely identical to Embodiment 2.

[0125] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for detecting rotating pulsed eddy currents to reduce the influence of lift-off fluctuations, characterized in that, Includes the following steps: S1: Place the pulsed eddy current probe on the flat specimen, establish a simplified structure, and establish the induced voltage signal based on the simplified structure. △U The expression; according to △U The relevant parameters affecting the lift-off effect in the expression are used to establish an integral formula; The integral formula is: ； J 0( x ) represents the zeroth-order Bessel function; e -2αlo This is the lift-off coefficient; θ The included angle is the angle between the receiving coil and the horizontal plane. θ The angle is acute; the axial distance between the excitation coil and the receiving coil is... D ; l o For removal; In step S1, the simplified structure has three layers, from bottom to top: air, flat specimen, and probe lifting; the pulsed eddy current probe is located above the simplified structure. With the axis of symmetry of the excitation coil as z Axis, with z A cylindrical coordinate system is established with the intersection of the axis and the point where the probe is lifted off the upper surface as the origin. r , θ , z ); S2: Substitute the actual maximum lift-off of the probe and the minimum angle between the probe coils into equation (1), and then combine this with the axial distance between the probe's excitation coil and receiving coil. D Together, we can find the actual value of the integral of equation (1), and calculate the coil angle corresponding to different lift-offs based on the principle that the actual value of the integral remains unchanged. S3: Perform curve fitting on the different lift-offs and corresponding coil angles in S2; S4: Using the curve fitted in S3, obtain different lift-offs and corresponding coil angles, and verify the correctness of reducing the lift-off effect using different lift-offs and coil angles.

2. The rotating pulse eddy current detection method for reducing the influence of lift-off fluctuations according to claim 1, characterized in that, Induced voltage signal △U It can be represented as: ； ； ； ； ； in, R'' 4,3 ( α () represents the generalized reflection coefficient of the three-layer structure. e -2αlo The lift-off coefficient, S'' ( α ) represents the coil coefficient of the pulsed eddy current probe. J 0( x ) and J 1( x () denote the zeroth and first-order Bessel functions, respectively. θ The included angle of the coil, ω and I ( ω These represent the angular frequency and the amplitude of the harmonic excitation current, respectively. j It is the imaginary unit. μ 0 is the permeability of free space. μ r2 It is the relative permeability. σ 2 is the electrical conductivity of the metal plate; n , r 1, r 2, l These are the number of coil turns, inner diameter, outer diameter, and height, respectively, with the subscripts T and R representing the excitation coil and the receiving coil, respectively.

3. The rotating pulse eddy current detection method for reducing the influence of lift-off fluctuations according to claim 1, characterized in that, In step S3, a quadratic polynomial is used to fit the curve.

4. The rotating pulse eddy current detection method for reducing the influence of lift-off fluctuations according to claim 1, characterized in that, In step S2, maximum lift l omax =10 mm, corresponding to the minimum angle of the probe coil. θ min = 0°; Set the axial distance between the excitation coil and the receiving coil. D= 10mm, the outer diameter of both the excitation coil and the receiving coil is 5mm; Or, maximum lift l omax =10 mm, corresponding to the minimum angle of the probe coil. θ min = 0°; Set the axial distance between the excitation coil and the receiving coil. D= The outer diameter of the excitation coil is 5mm; the outer diameter of the receiving coil is 12mm.

5. A rotating pulse eddy current probe structure for reducing the influence of lift-off fluctuations, used in the rotating pulse eddy current detection method for reducing the influence of lift-off fluctuations as described in any one of claims 1-4, characterized in that, The system includes a housing, which contains a receiving cavity, and the receiving cavity contains an excitation coil assembly and a receiving coil assembly. The excitation coil assembly includes: The excitation coil frame is fixed to the inner wall of the receiving cavity; The excitation coil is wound on the excitation coil frame, with its central axis set vertically. The receiving coil assembly includes: The support is fixed to the inner wall of the receiving cavity; The mounting frame is rotatably connected to the bracket by a rotating shaft; the axis of the rotating shaft is set horizontally, that is, along the X direction. The receiving coil frame is fixed on the mounting frame; The receiving coil is wound on the receiving coil frame. Let the central axis of the receiving coil be a. Then the plane that a always lies on during the rotation is plane P. The X direction is always perpendicular to plane P. It also includes a drive assembly for rotating the mounting frame and changing the coil angle; the excitation coil is inside or outside the receiving coil; and it also includes an excitation coil connector and a receiving coil connector that are respectively connected to the excitation coil and the receiving coil.

6. The rotating pulse eddy current probe structure for reducing the influence of lift-off fluctuations according to claim 5, characterized in that, The driving component includes: The probe is movably mounted on the inner wall of the receiving cavity and can move vertically. The limiting spring and the limiting plate are located above the probe and are fixed to the inner wall of the receiving cavity. One end of the limiting spring is fixedly connected to the limiting plate and the other end is fixedly connected to the upper end of the probe. The limiting spring is always in a compressed state. The slider is fixedly connected to the probe. The rack is vertically positioned and fixedly connected to the slider. The transmission rod is rotatably connected to the receiving cavity. One end is fixed with a transmission gear, which coincides with the axis of the transmission rod and meshes with a rack. The other end is fixed with a driving bevel gear, which coincides with the axis of the transmission rod. The axis of the transmission rod is set horizontally and perpendicular to the X direction. The driven rod is rotatably connected to the inner wall of the receiving cavity, and its axis is set vertically. The driven bevel gear is fixed on the driven rod, coincides with the axis of the driven rod, and meshes with the driving bevel gear; A cam used to rotate the mounting frame is horizontally positioned with its outer edge abutting against the mounting frame; it is detachably connected to the driven rod. The spring used to reset the mounting frame is always in a compressed state, with one end fixedly connected to the bracket and the other end fixedly connected to the surface wall of the mounting frame; the cam and the spring are located on opposite sides of the surface wall of the mounting frame.

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