A method for measuring the thickness of metal with surface covering layer with transient stable dual-state response

Abstract

The present invention provides a method for measuring the thickness of metal with a surface coating and a transient two-state response, and relates to the field of metal geometric dimension measurement. The measurement method uses pulse current excitation, and the coil magnetic flux will have positive pulse and negative pulse responses. As the metal thickness increases, the rising speed of the positive pulse response and the falling speed of the negative pulse response will gradually decrease and stabilize. Based on the above rules, a metal thickness measurement method based on the steady-state values ​​of the positive pulse and negative pulse responses of the pulse excitation response, a metal thickness measurement method combining the transient two-state of the pulse response and the transient response transition characteristic points, and a metal thickness measurement method in the stable area of ​​the dual-probe pulse response are proposed. The present invention reveals the intrinsic relationship between the transient two-state response of the magnetic flux and the metal thickness, constructs a characteristic characterization method and parameters for the metal thickness properties, and has the advantages of high measurement accuracy, small error, fast response, simplicity and convenience, etc. The advantages are particularly obvious when there is a coating on the metal surface.

Description

Technical Field

[0001] The invention relates to the field of metal geometric dimension measurement, in particular to a metal thickness measurement method with a surface covering layer and a temporary stable dual-state response method mainly used for measuring the thickness of metal with a surface covering layer. Background Art

[0002] Metal thickness measurement is a key industrial inspection technology, widely used in the production, processing, and quality control of metal materials. The development of this technology is closely tied to the high demands placed on material performance and safety in industrial production. Advances in materials science and manufacturing technology have placed higher demands on the accuracy and efficiency of metal thickness measurement. The evolution of metal thickness measurement technology has evolved from traditional mechanical measurement methods to modern non-contact measurement techniques. The application of these technologies not only improves measurement accuracy and repeatability but also expands the scope of measurement applications, enabling metal thickness measurement to adapt to diverse industrial environments and material properties. Therefore, the realization and development of metal thickness measurement is crucial.

[0003] There are various methods for measuring metal thickness, including but not limited to metallography, coulometrics, X-ray fluorescence, and ultrasonic thickness measurement. Each method has its own unique characteristics and is suitable for different applications and metal materials of varying thicknesses. Metallography uses a metallographic microscope to measure the local thickness of a metal sample's cross section. Its advantages lie in its high accuracy and reliability, but its disadvantage is that it is a destructive measurement method, requiring sample sectioning and polishing. Coulometrics is suitable for measuring the thickness of single and multi-layer metal coatings. Its advantages are high accuracy and reliability, but its disadvantages are the relatively complex operation process and the high cost of consumables, such as chemicals. X-ray fluorescence is a non-destructive measurement method with the advantages of rapid and non-destructive measurement, but its disadvantages are high cost and radiation exposure. Ultrasonic thickness measurement, based on the principle of ultrasonic pulse reflection, has the advantage of being able to accurately measure a variety of materials in production equipment, but its disadvantage is that it is easily affected by the surrounding environment. It should be noted that none of the above detection methods are applicable when the metal surface is coated or covered with a surface coating, unless the surface coating or surface coating is destroyed or removed. Therefore, it is urgent to solve the problem of online, non-destructive detection of metal thickness when there is a protective layer or shielding layer on the metal surface.

[0004] In general, the development trend of metal thickness measurement technology is towards higher precision, higher efficiency, and greater intelligence. With the continuous emergence of new technologies, metal thickness measurement technology will provide stronger support for industrial production and drive industrial production to a higher level. Summary of the Invention

[0005] In response to the above problems, the present disclosure proposes a method for measuring the thickness of metal with surface covering layer based on pulse excitation transient two-state response.

[0006] In order to solve at least one of the above technical problems, the present disclosure proposes the following technical solutions:

[0007] A method for measuring the thickness of metal with surface coatings with a transient dual-state response is proposed. In this method, pulse current is used to excite the coil magnetic flux, causing positive and negative pulse responses. As the metal thickness increases, the rising speed of the positive pulse response and the falling speed of the negative pulse response gradually decrease and stabilize, thereby achieving the measurement of the metal thickness.

[0008] In some embodiments, a method for measuring the thickness of a metal with a surface covering layer having a transient two-state response is a method for measuring the thickness of a metal based on a steady-state value of a pulse excitation response. The steady-state response of a pulse current excitation is a method for characterizing the measurement of the thickness of a metal. The steady-state value of the magnetic flux response of a pulse current excitation is an intuitive reflection of the metal thickness of the object being measured. The steady-state values ​​of different metal thicknesses in the positive pulse steady-state region decrease as the metal thickness increases, and the steady-state values ​​in the negative pulse steady-state region increase as the metal thickness increases.

[0009] In some embodiments, a method for measuring metal thickness based on a steady-state value of an impulse excitation response comprises the following steps:

[0010] Step 1-1. Determination of the steady-state value in the stationary region,

[0011] The steady-state value in the stable region of the magnetic flux response curve is used as a characteristic value to effectively measure the metal thickness. Therefore, under the action of pulse current excitation, before the next pulse arrives, the value of the magnetic flux that remains stable is recorded as the steady-state value.

[0012] Step 1-2. Steady-state value-metal thickness relationship expression,

[0013] Use the power function to fit the different metal thicknesses and the corresponding steady-state values ​​in the stable region, and finally get the relationship expression: f ( x )=A x +B, where f ( x ) represents the stable magnetic flux value in the stable region, x Represents the thickness of the metal;

[0014] Steps 1-3. Expression analysis,

[0015] The steady-state value of the positive pulse steady-state area and the stable value of the negative pulse steady-state area were quantitatively compared and analyzed with the fitting relationship curve respectively;

[0016] Steps 1-4. Accuracy assessment,

[0017] The steady-state values ​​of the positive and negative pulse plateaus of the response signal of metal aluminum of known thickness under the action of pulse signal excitation are substituted into the fitting expression respectively to obtain its response value, which is then compared with the actual metal thickness to obtain the error.

[0018] In some embodiments, a method for measuring metal thickness based on a steady-state value of an impulse excitation response comprises the following steps:

[0019] Step 1-1. Determination of the steady-state value in the stationary region,

[0020] Under the same excitation parameters and external conditions, the steady-state values ​​of the positive and negative pulse plateaus corresponding to different metal thicknesses are calculated.

[0021] Step 1-2. Steady-state value-metal thickness relationship expression,

[0022] Use the power function to fit the different metal thicknesses and the corresponding steady-state values ​​in the stable region, and finally get the relationship expression: f ( x )=A x +B, where f ( x ) represents the stable magnetic flux value in the stable region, x Represents the metal thickness. For the positive pulse response curve, A=-1.107×10 -5 , B=0.003058, for the negative pulse response curve, A=1.107×10 -5 , B=-0.003058;

[0023] Steps 1-3. Expression analysis,

[0024] The steady-state value of the positive pulse plateau gradually decreases with increasing thickness, while the steady-state value of the negative pulse plateau gradually increases with increasing thickness;

[0025] Steps 1-4. Accuracy assessment,

[0026] The steady-state values ​​of the positive and negative pulse plateaus of the response signals of aluminum metals with thicknesses of 0.08 mm and 0.44 mm under pulse signal excitation were substituted into the fitting expressions, and the values ​​were obtained as 0.076 mm and 0.4414 mm, respectively. When compared with the actual metal thickness, the errors were 3.75% and 0.32%.

[0027] In some embodiments, a method for measuring the thickness of a metal with a surface covering layer with a quasi-stable two-state response is a method for characterizing the metal thickness based on the slope of the transition characteristic points of the pulse response transient process. The pulse current excitation transient response is a unique attribute of the metal thickness measurement characterization method, which is characterized in that: the transient process of the pulse current excitation flux response contains characteristic information of the metal thickness, and the transition characteristic points are extracted based on the positive and negative pulses of the transient process. As the metal thickness increases, the slope of the transition characteristic points decreases accordingly. The slope of the transition characteristic points of the flux response transient process is adopted to effectively measure the thickness of different metals.

[0028] In some embodiments, a method for characterizing metal thickness based on the slope of a transition characteristic point of an impulse response transient process includes the following steps:

[0029] Step 2-1. Determine the transition feature points,

[0030] The transient process of pulse excitation response changes with the change of metal thickness. The slope of the transition characteristic point is used as the characteristic quantity of metal thickness measurement to ensure more accurate measurement results.

[0031] Step 2-2. Fitting the relational expression,

[0032] Use the exponential function to fit the different thicknesses of metals and the corresponding transition characteristic point slopes. The fitted relationship expression is: f ( x )=Ae Bx +Ce Dx , where f ( x ) is the slope value of the transition feature point, x Represents the thickness of the metal;

[0033] Step 2-3. Relational expression analysis,

[0034] The transition feature points extracted from the positive pulse transient process and the transition feature points extracted from the negative pulse transient process are quantitatively compared and analyzed with the fitting curves respectively;

[0035] Step 2-4. Measurement accuracy evaluation,

[0036] Select metal of known thickness, obtain the slope of the transition characteristic point based on the response curve under the action of the pulse signal excitation, and substitute it into the fitting expression to calculate the corresponding metal thickness. Compare it with the actual metal thickness to obtain the measurement error.

[0037] In some embodiments, a method for characterizing metal thickness based on the slope of a transition characteristic point of an impulse response transient process includes the following steps:

[0038] Step 2-1. Determine the transition feature points,

[0039] The maximum stable value and time through the stable area t =0 intersection point y =-k x +Φ straight line, and then intersect this straight line with the transition area of ​​each metal thickness to obtain the transition characteristic point Q corresponding to the metal of different thicknesses. Then calculate the tangent slope of this characteristic point respectively. The transition characteristic point of the negative pulse transient process is obtained in the same way.

[0040] Step 2-2. Fitting the relational expression,

[0041] Use the exponential function to fit the different thicknesses of metals and the corresponding transition characteristic point slopes. The fitted relationship expression is: f ( x )=Ae Bx +Ce Dx , where f ( x ) is the slope value of the transition feature point, x Represents the metal thickness. For the positive pulse response curve, A=1.435, B=-1.922, C=0.7115, D=-0.1446; for the negative pulse response curve, A=-13.48, B=-19.76, C=-1.578, D=-0.4752;

[0042] Step 2-3. Relational expression analysis,

[0043] By analyzing the fitting curve, the slope of the transition feature point extracted from the positive pulse transient process is basically consistent with the metal thickness fitting, while the slope of the transition feature point extracted from the negative pulse transient process is not ideal for the metal thickness fitting.

[0044] Step 2-4. Measurement accuracy evaluation,

[0045] The metal thickness is selected as 0.12mm. Based on the response curve under the excitation of the pulse signal, the slope of the transition characteristic point is obtained and substituted into the fitting expression. The metal thickness is calculated to be 0.1213mm and 0.1402mm. It is compared with the actual metal thickness to obtain the measurement error. The results show that the error value of the fitting function of the positive pulse metal thickness and the transition characteristic point slope is smaller than the fitting function of the negative pulse metal thickness and the transition characteristic point slope. Therefore, the transition characteristic point slope of the positive pulse transient process is selected to effectively measure the metal thickness.

[0046] In some embodiments, a method for measuring the thickness of a metal with a surface covering layer with a transient dual-state response is a method for measuring the thickness of a metal based on the stable value of a steady region of a dual-probe pulse response. The dual-probe pulse current excitation steady-state response is an effective way to increase the effective range of metal thickness measurement and improve accuracy. The stable value of the dual-probe pulse response also has the ability to measure metals of different thicknesses. The excitation probe is on one side of the metal, and the probe on the other side serves as the receiving end of the response signal. The stable value of the positive pulse of the magnetic flux response signal decreases significantly with the increase of the metal thickness, and the stable value of the negative pulse decreases significantly with the increase of the metal thickness.

[0047] In some embodiments, a metal thickness measurement method based on a stable value of a dual-probe pulse response stationary region is characterized by comprising the following steps:

[0048] Step 3-1. Determination of the stability value of the dual-probe stable area,

[0049] Based on the stable value of the stable area of ​​the dual-probe magnetic flux response curve as a characteristic quantity, the method of effectively measuring different metal thicknesses, controlling the pulse width, and reducing the pulse transient response time can obtain a relatively stable magnetic flux stability value;

[0050] Step 3-2. Fitting the expression of the relationship between the two probes in the stationary region,

[0051] Use the exponential function to fit the metal thickness to the corresponding stable value of the dual probe stable area. f ( x )=Ae Bx +Ce Dx , where f ( x ) is the stable value of the receiving probe in the stable area, x is the metal thickness;

[0052] Step 3-3. Analysis of the expression of the relationship between the two probe stationary regions,

[0053] The stability values ​​of the positive pulse stable area and the negative pulse stable area of ​​the dual probes were quantitatively compared and analyzed with the fitting curves.

[0054] Step 3-4. Metal thickness measurement accuracy evaluation,

[0055] The stable values ​​of the positive pulse stable area and the stable values ​​of the negative pulse stable area obtained by measuring metal aluminum of known thickness are substituted into the fitting function respectively to obtain the corresponding thickness, which is compared with the actual metal thickness to obtain the measurement error.

[0056] In some embodiments, a metal thickness measurement method based on a stable value of a dual-probe pulse response stationary region is characterized by comprising the following steps:

[0057] Step 3-1. Determination of the stability value of the dual-probe stable area,

[0058] Based on the stable value of the stable area of ​​the dual-probe magnetic flux response curve as a characteristic quantity to effectively measure different metal thicknesses, the excitation probe is placed on one side of the metal, and the probe on the other side serves as the receiving end of the response signal. The stable value of the positive pulse and negative pulse stable area corresponding to different metal thicknesses is obtained;

[0059] Step 3-2. Fitting the expression of the relationship between the two probes in the stationary region,

[0060] Use the exponential function to fit the metal thickness to the corresponding stable value of the dual probe stable area. f ( x )=Ae Bx +Ce Dx , where f ( x ) is the stable value of the receiving probe in the stable area, x is the metal thickness, positive pulse response curve, A=0.000186, B=-1.012, C=9.837×10 -5 , D=-0.3627, negative pulse response curve, A=-0.000186, B=-1.012, C=-9.837×10 -5 , D = -0.3627;

[0061] Step 3-3. Analysis of the expression of the relationship between the two probe stationary regions,

[0062] The stability value of the dual-probe positive pulse stable area gradually decreases with the increase of metal thickness, and the stability value of the negative pulse stable area gradually increases with the increase of metal thickness;

[0063] Step 3-4. Metal thickness measurement accuracy evaluation,

[0064] The stable values ​​of the positive pulse stable area and the stable values ​​of the negative pulse stable area obtained from measuring metal aluminum with a thickness of 0.3mm and 3mm were substituted into the fitting function respectively, and the obtained thicknesses were 0.3001mm and 2.98mm. They were compared with the actual metal thickness to obtain the measurement error. The results showed that both the positive pulse and negative pulse stable areas can effectively realize the measurement of metal thickness.

[0065] The above technical solution has the following advantages or beneficial effects:

[0066] The present invention provides a method for measuring the thickness of metal with a surface covering thin layer based on pulse excitation transient two-state response, which solves the contradiction between measurement accuracy and detection complexity in the prior art. Specifically,

[0067] 1) Compared with metallography, this method is non-destructive, as metallography requires sample slicing and polishing. Compared with coulometric analysis, this method is simple and highly reliable, requiring no complex operating procedures or expensive consumables such as chemicals. Compared with X-ray fluorescence, this method is fast and non-destructive, without high costs or radiation risks. Compared with ultrasonic thickness measurement, this method is less susceptible to environmental influences and is suitable for measuring the thickness of thin metal layers.

[0068] 2) The present invention provides a method for measuring metal thickness in different ranges. Different strategies are adopted for metal thickness in different measuring ranges, thereby improving measurement accuracy and saving measurement costs.

[0069] 3) When the metal surface is covered with a coating or impurities, the advantages of the metal thickness measurement method with thin surface coatings based on pulse excitation transient two-state response are particularly prominent. Other existing metal thickness measurement methods must first remove the coating and surface impurities, otherwise the measurement accuracy will be greatly reduced.

[0070] The present invention starts from the nature of eddy current changes in metals, deeply understands the intrinsic connection between pulse response and metal thickness, and explores effective feature characterization methods and parameters for describing the geometric dimensional properties of metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The present invention and its features, configurations, and advantages will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings. Like reference numerals indicate like parts throughout the drawings. The drawings are not drawn to scale, emphasis instead being placed on illustrating the subject matter of the present invention.

[0072] Figure 1 The transient positive pulse response curves of coils with different metal thicknesses in some embodiments of the present invention are shown;

[0073] Figure 2 2. Temporary stable negative pulse response curves of coils with different metal thicknesses in some embodiments of the present invention;

[0074] Figure 3 A single probe pulse excitation metal thickness measurement model in some embodiments of the present invention;

[0075] Figure 4 are the transient characteristic points of positive pulses with different metal thicknesses in Scheme 1;

[0076] Figure 5 These are the transient characteristic points of negative pulses with different metal thicknesses in Scheme 1;

[0077] Figure 6are the transient characteristic points of positive pulses with different metal thicknesses in Scheme 2;

[0078] Figure 7 These are the transient characteristic points of negative pulses with different metal thicknesses in Scheme 2;

[0079] Figure 8 A dual-probe pulse excitation metal thickness measurement model in some embodiments of the present invention;

[0080] Figure 9 1 is a pulse excitation response curve of dual probes with different metal thicknesses in some embodiments of the present invention. DETAILED DESCRIPTION

[0081] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other. It should be noted that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the exemplary implementation methods according to this application.

[0082] It should be understood that when the terms “include” and / or “comprise” are used in this specification, they specify the presence of features, steps, operations, devices, components and / or their combinations.

[0083] The terms "first", "second" and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0084] The technical solutions in the embodiments of the present invention are described below in conjunction with the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Therefore, the detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0085] The metal is stimulated by a pulse signal, and the pulse signal period T =0.2s, pulse width D =0.12s, duty cycle is 60%. The response curve has different reactions to different metal thicknesses. In the positive pulse response curve, as the metal thickness increases, the rate of increase of the magnetic flux in the rising stage will gradually decrease until it stabilizes. In the negative pulse response curve, the rate of decrease of the magnetic flux in the falling stage will gradually decrease until it stabilizes. In order to illustrate the effectiveness of this method, five kinds of metal aluminum with thicknesses of 0.1mm, 0.3mm, 0.6mm, 1mm, and 1.5mm are first selected to measure the change of their respective magnetic flux over time under the same conditions and the same time, and the magnetic flux of each metal is measured at the same time. t=0-0.0004s positive pulse response transient phase and time t = stable value when 0.25s, t = 0.08-0.0805s negative pulse response transient stage magnetic flux change and t =0.1999s. The positive pulse response curves of metals with five thicknesses are as follows: Figure 1 As shown, the negative pulse response curve is as follows Figure 2 As shown in Figure 2, both the positive pulse response curve and the negative pulse response curve show different dynamic response processes as the metal thickness changes. The differences here include the transient process of the response curve and the stable region of the response curve.

[0086] The following is a detailed introduction to the implementation of three feature extraction strategies based on the transient steady-state process of the coil flux response.

[0087] 1. Metal thickness measurement based on steady-state value of pulse excitation response

[0088] Analysis of the stable regions of the positive and negative pulse responses reveals that the curve reaches different stable values ​​after stabilizing, as the metal thickness varies. This region is called the plateau region. Therefore, selecting the stable value in the plateau region as a characteristic quantity for metal thickness measurement can effectively measure different metal thicknesses.

[0089] The specific steps of the metal thickness measurement process based on the steady-state value of the pulse excitation response are as follows: ① Set the excitation parameters and select the metal to be measured; ② Use the probe to measure the impedance value of the coil under the action of the pulse signal excitation; ③ Use the signal processing circuit to convert the impedance value at both ends of the coil into a magnetic flux value; ④ According to the magnetic flux response curve, obtain the steady-state value in the stable area; ⑤ According to the input-output fitting function, the obtained steady-state value in the stable area is input into the fitting function to solve the thickness of the metal to be measured.

[0090] like Figure 3 As shown in the figure, taking aluminum as an example, the steady-state values ​​of the magnetic flux response stable region corresponding to different metal thicknesses are calculated. Different metal thicknesses correspond to different steady-state values ​​of the positive pulse and negative pulse stable regions. The specific implementation method is as follows:

[0091] Step 1-1. Determination of the steady-state value in the stationary region

[0092] The steady-state values ​​of positive and negative pulses for different metal thicknesses are shown in Table 1.

[0093] Table 1 Metal thickness and response steady-state value

[0094]

[0095] Step 1-2. Steady-state value-metal thickness relationship expression

[0096] The power function is used to fit 20 metal thicknesses and their corresponding steady-state values ​​in the plateau region.

[0097] The relationship between metal thickness and steady-state value is established as follows:

[0098] (1)

[0099] In the formula f ( x ) is the stable magnetic flux value in the stationary region, x Represents the metal thickness.

[0100] For the positive pulse response curve, A=-1.107×10 -5 , B=0.003058;

[0101] For the negative pulse response curve, A=1.107×10 -5 , B=-0.003058.

[0102] Steps 1-3. Expression analysis

[0103] Within the metal thickness range d = 0 to 0.6 mm, there is an approximate relationship as given by formula (1). Metal thickness measurement based on the steady-state values ​​of the positive and negative pulse stationary regions of the pulse excitation response can be applied within this thickness measurement range. Therefore, when using this method for metal thickness measurement, the range of metal thickness that can be measured has certain limitations. The fitting effect of the steady-state values ​​of the positive and negative pulse stationary regions and the metal thickness was evaluated, as shown in Table 2.

[0104] Table 2 Fitting effect evaluation

[0105]

[0106] It can be seen from Table 2 that the evaluation of the fitting effect of the steady-state value in the positive pulse stable region and the steady-state value in the negative pulse stable region and the metal thickness is the same. Therefore, metal thickness measurement can be performed based on both the positive pulse and negative pulse steady-state values ​​of the response curve.

[0107] Steps 1-4. Accuracy Assessment

[0108] A metal with a thickness of 0.08 mm was selected for evaluation using the above method. The measured steady-state value of the positive pulse magnetic flux corresponding to the metal was 0.00305715252917557, and the steady-state value of the negative pulse magnetic flux was -0.00305715252917557. Substituting these into the relationship between metal thickness and steady-state value (1), the metal thickness was calculated to be 0.076 mm, and the error between this value and the actual value was 3.75%.

[0109] Similarly, a metal with a thickness of 0.44 mm was selected for evaluation using the above method. The measured steady-state value of the positive pulse magnetic flux corresponding to the metal was 0.00305311375496315; the steady-state value of the negative pulse magnetic flux was -0.00305311375496315. Substituting the relationship between the metal thickness and the steady-state value into the expression (1) is used to calculate the metal thickness to be 0.4414 mm. The error between this value and the actual value is 0.32%.

[0110] In summary, the stable values ​​of the positive pulse and negative pulse stable regions can be selected for metal thickness measurement.

[0111] 2. Metal thickness measurement based on the transient characteristic points of the impulse response transient process

[0112] (1) Implementation methods

[0113] Stable value and time based on the stable region of metal response t =0, make a line y =k x +Φ line, this line will intersect the transition area again at a point Q, and the slope of the Q point on the response curve is calculated. In order to ensure that the characteristic point can accurately reflect the change of metal thickness, two sets of solutions are designed. The first solution is to use the maximum stable value in the stable area and the time t =0, make a line y =k x +Φ line, and then intersect this line with the response curve of each metal thickness to obtain different intersection points Q, and calculate the slope of each intersection point Q with its corresponding response curve. The second solution: use the stable value of the stable area of ​​each metal thickness and time t =0, draw a line y =k x +Φ', these straight lines will intersect with their corresponding response curves to obtain their corresponding intersection points Q', and the slopes of these intersection points Q' and their corresponding response curves are calculated. Among them, when the response area is a positive pulse, the k value is -1, and when the response area is a negative pulse, the k value is 1. This is because the stable value of the stable area is related to time. t =0 is approximately a right angle, so taking 45° as the slope can better reflect the changes in the actual response curve. Below, we take metal thicknesses of 0.1mm, 0.6mm, and 1.5mm as examples to make schematic diagrams of Scheme 1 and Scheme 2. The positive and negative pulse transition characteristic points of Scheme 1 are as follows: Figure 4 and Figure 5 As shown, the positive and negative pulse transition characteristic points of Scheme 2 are respectively as follows Figure 6 and Figure 7 The above two solutions can avoid the errors caused by single data fluctuations and possible erroneous evaluations.

[0114] Therefore, the specific steps of the metal thickness measurement process based on the transition characteristic points of the pulse response transient process are as follows: ① Set the excitation parameters and select the metal to be measured; ② Use the probe to measure the impedance value of the coil under the excitation of the pulse signal; ③ Use the signal processing circuit to transform the impedance values ​​at both ends of the coil to obtain the magnetic flux; ④ According to the magnetic flux response curve, obtain the slope of the transition characteristic points of Scheme 1 and Scheme 2; ⑤ According to the input-output fitting function, the obtained characteristic point slope value is input into the fitting function to solve the measured metal thickness.

[0115] (2) Implementation process

[0116] Step 2-1. Determine transition feature points

[0117] Based on the above method, we calculated the slopes of the transition characteristic points corresponding to each metal thickness for Schemes 1 and 2. We then calculated the relationship between metal thickness and characteristic point slopes for Schemes 1 and 2. The results showed that Scheme 1 performed better than Scheme 2, so we selected Scheme 1 for further detailed analysis. We selected 20 numerical points for the study, with metal thicknesses ranging from 0 to 3 mm. Table 3 shows the slope values ​​of the positive and negative pulse transition characteristic points for the 20 metal thicknesses.

[0118] Table 3 Metal thickness and slope value of transition characteristic point

[0119]

[0120] Step 2-2. Fitting the relational expression

[0121] The power function is used to fit the 20 metal thicknesses and their corresponding characteristic point slope values.

[0122] The relationship between the fitted metal thickness and the slope value of the characteristic point is expressed as follows:

[0123] (2)

[0124] In the formula f ( x ) is the slope value of the characteristic point of scheme 1, x Represents the metal thickness.

[0125] For the positive pulse response curve, A=1.435, B=-1.922, C=0.7115, D=-0.1446;

[0126] For the negative pulse response curve, A=-13.48, B=-19.76, C=-1.578, D=-0.4752.

[0127] Step 2-3. Relational expression analysis

[0128] Analysis shows that the positive pulse fitting curve is better than the negative pulse fitting curve. Therefore, when using this method to measure metal thickness, it will be more accurate to use the positive pulse response transient process to measure metal thickness. The fitting effect evaluation data is shown in Table 4.

[0129] Table 4 Evaluation of the fitting effect of characteristic point slope and metal thickness of Scheme 1

[0130]

[0131] Step 2-4. Measurement accuracy evaluation

[0132] The above method was used to evaluate a 0.12mm thick metal. The measured positive pulse stable magnetic flux was 0.00305693421008982, with a slope of 1.8313. Substituting this into the positive pulse fitting formula (2) of Scheme 1, the metal thickness was calculated to be 0.1213mm. Therefore, the error between the actual value and the measured value is 1.08%.

[0133] Similarly, a metal with a thickness of 0.12 mm was selected for negative pulse analysis. The measured negative pulse stable magnetic flux was -0.00305693421008982, with a slope of -2.1582. Substituting this into the negative pulse fitting formula (2) of Scheme 1, the metal thickness was calculated to be 0.1402 mm. Therefore, the error between the actual value and the measured value is 16.8%.

[0134] In summary, the error value obtained by measuring the metal thickness using the transition characteristic points of the positive pulse transient process in Scheme 1 is much smaller than the error value obtained by measuring the metal thickness using the transition characteristic points of the negative pulse transient process in Scheme 1. Therefore, the positive pulse response curve can effectively measure the metal thickness.

[0135] 3. Metal thickness measurement based on dual probe pulse response stability

[0136] (1) Implementation methods

[0137] Under the action of a single probe, the greater the metal thickness, the more compact the steady-state value of the response curve is, so this method is only applicable to a small range of metal thickness. In order to solve the above problem, the original measurement is improved by adding another metal probe under the metal conductor as a signal receiving end to form a dual-probe structure, such as Figure 8 shown.

[0138] The specific steps of the metal thickness measurement process based on the stable value of the dual-probe pulse response are as follows: ① Set the excitation parameters and select the metal to be measured; ② The pulse signal is passed through one end of the probe to excite the metal, and the probe at the other end of the metal receives the impedance value of its coil; ③ Use the signal processing circuit to transform the impedance values ​​at both ends of the coil to obtain the magnetic flux; ④ According to the magnetic flux response curve, obtain the stable value of the stable area under the action of the dual probes, such as Figure 9 ⑤ According to the input-output fitting function, the stable value of the stable area under the action of the dual probes is input into the fitting function to solve the thickness of the metal being measured.

[0139] (2) Implementation process

[0140] Step 3-1. Determination of the stability value of the dual-probe stable region

[0141] The metal thickness is selected to be between d = 0 and 5 mm, and is subdivided into 20 values ​​as shown in Table 5.

[0142] Table 5 Stability value of stable area and metal thickness under the action of dual probes

[0143]

[0144] Step 3-2. Fitting the expression of the relationship between the two-probe stationary region

[0145] The power function is used to fit 20 metal thicknesses and their corresponding stable values.

[0146] The fitting function formula of the metal thickness based on the stable value of the stationary region of the dual probe response is:

[0147] (3)

[0148] Where, f ( x ) is the positive pulse stable magnetic flux value, x Represents the metal thickness.

[0149] For the positive pulse response curve, A=0.000186, B=-1.012, C=9.837×10 -5 , D = -0.3627;

[0150] For the negative pulse response curve, A=-0.000186, B=-1.012, C=-9.837×10 -5 , D=-0.3627.

[0151] Step 3-3. Analysis of the expression of the relationship between the two-probe stationary regions

[0152] For metal thicknesses between d = 0 and 5 mm, the relationship approximated by formula (3) exists. Therefore, the stability value of the negative pulse plateau region based on the dual-probe pulse excitation response can be used to measure metals with a thickness less than 5 mm. Compared to the single-probe measurement method, not only is the measurement range increased, but the displayed accuracy is also higher and the relationship is clearer. The fitting effect of the positive and negative pulse plateau region stability values ​​and metal thickness is evaluated, as shown in Table 6.

[0153] Table 6 Evaluation of the fitting effect of stable value in the stable region and metal thickness

[0154]

[0155] As shown in Table 6, the evaluation of the fitting effect of the stable value of the positive pulse steady region and the metal thickness is the same as that of the negative pulse steady region and the metal thickness, so both positive and negative pulse measurements can be selected.

[0156] Step 3-4. Metal Thickness Measurement Accuracy Evaluation

[0157] Using the above method, we selected a metal thickness of 0.3 mm and obtained a stable value of 0.00022509804 for the positive pulse magnetic flux and -0.00022509804 for the negative pulse magnetic flux. Substituting this into formula (3), we obtain a metal thickness of 0.3001 mm. Therefore, the error between the actual and measured values ​​is 0.033%.

[0158] Similarly, the metal thickness of 3mm is evaluated using the above method. The measured positive pulse magnetic flux stability value is 0.00004250299; the negative pulse magnetic flux stability value is -0.00004250299. Substituting into formula (3), the metal thickness is calculated to be 2.98mm. The error between the actual value and the measured value is 0.0067%.

[0159] In summary, the stable values ​​of the dual-probe positive pulse and negative pulse stable areas can be selected for metal thickness measurement.

[0160] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformation made by using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for measuring the thickness of metal with a surface coating with a transient two-state response, characterized in that: In this method, through pulse current excitation, the coil flux has positive pulse and negative pulse responses. As the metal thickness increases, the rising speed of the positive pulse response and the falling speed of the negative pulse response will gradually decrease and stabilize, so as to realize the measurement of the metal thickness. The metal thickness measurement method with a surface covering layer with a transient stable dual-state response is a metal thickness characterization method based on the slope of the transition characteristic points of the pulse response transient process. The pulse current excitation transient response is a unique attribute of the metal thickness measurement characterization method. The transient process of the pulse current excitation flux response contains characteristic information of the metal thickness. Based on the transition characteristic points extracted from the positive and negative pulses of the transient process, as the metal thickness increases, the slope of the transition characteristic points decreases. The slope characterization of the transition characteristic points of the flux response transient process is adopted to effectively measure different metal thicknesses. The method of characterizing metal thickness based on the slope of the transition characteristic points of the pulse response transient process specifically includes the following steps: Step 2-1. Determine the transition feature points, The maximum stable value and time through the stable area t =0 intersection point y =-k x +Φ, and then intersect this straight line with the transition area of ​​each metal thickness to obtain the transition characteristic point Q corresponding to the metal of different thicknesses. Then calculate the tangent slope of this characteristic point respectively. The transition characteristic point of the negative pulse transient process is obtained in the same way. Step 2-2. Fitting the relational expression, Use the exponential function to fit the different thicknesses of metals and the corresponding transition characteristic point slopes. The fitted relationship expression is: f ( x )=Ae Bx +Ce Dx , where f ( x ) is the slope value of the transition feature point, x Represents the thickness of the metal; Step 2-3. Relational expression analysis, The transition feature points extracted from the positive pulse transient process and the transition feature points extracted from the negative pulse transient process are quantitatively compared and analyzed with the fitting curve respectively; Step 2-4. Measurement accuracy evaluation, Select metal of known thickness, obtain the slope of the transition characteristic point based on the response curve under the action of the pulse signal excitation, and substitute it into the fitting expression to calculate the corresponding metal thickness. Compare it with the actual metal thickness to obtain the measurement error.

2. The method for measuring the thickness of metal with surface covering layer with transient stable two-state response according to claim 1, characterized in that: The method for characterizing metal thickness based on the slope of transition characteristic points of the impulse response transient process includes the following steps: Step 2-1. Determine the transition feature point. When the response area is a positive pulse, the k value is -1; when the response area is a negative pulse, the k value is 1; the stable value of the stable area is related to time. t =0 is approximately a right angle, and a slope of 45° can better reflect the changes in the actual response curve. Step 2-2. Fitting the relational expression, Use the exponential function to fit the different thicknesses of metals and the corresponding transition characteristic point slopes. The fitted relationship expression is: f ( x )=Ae Bx +Ce Dx , where f ( x ) is the slope value of the transition feature point, x Represents the metal thickness. For the positive pulse response curve, A=1.435, B=-1.922, C=0.7115, D=-0.1446; for the negative pulse response curve, A=-13.48, B=-19.76, C=-1.578, D=-0.4752; Step 2-3. Relational expression analysis; Step 2-4. Measurement accuracy evaluation, The metal thickness is selected as 0.12mm. Based on the response curve under the excitation of the pulse signal, the slope of the transition characteristic point is obtained and substituted into the fitting expression. The metal thickness is calculated to be 0.1213mm and 0.1402mm. It is compared with the actual metal thickness to obtain the measurement error. The results show that the error value of the fitting function of the positive pulse metal thickness and the transition characteristic point slope is smaller than the fitting function of the negative pulse metal thickness and the transition characteristic point slope. Therefore, the transition characteristic point slope of the positive pulse transient process is selected to effectively measure the metal thickness.

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