Fuel cell separator defect inspection system using pulse thermography non-destructive testing

Abstract

The present invention relates to a fuel cell separator plate defect inspection system through pulse thermal imaging non-destructive inspection, and more specifically, to a fuel cell separator plate defect inspection system through pulse thermal imaging non-destructive inspection capable of detecting back surface defects of a fuel cell separator plate that are difficult to identify with the naked eye. To this end, the present invention comprises: a test object positioned to perform non-destructive defect inspection; a heat source that supplies periodic heat to the test object in the form of a heat pulse; an infrared camera that captures the thermal image distribution of the test object formed by the thermal energy received from the heat source to generate a thermal image; and a control unit that receives the thermal image generated from the infrared camera and performs noise removal to generate a noise-removed thermal image, wherein the noise is removed by performing a temperature compensation process to resolve temperature non-uniformity caused by the difference in distance from the heat source. This project (result) is the result of the Phase 3 Leading University for Industry-Academic Cooperation (LINC 3.0) project, which was funded by the Ministry of Education and the National Research Foundation of Korea.

Description

Technology Field

[0001] The present invention relates to a fuel cell separator plate defect inspection system through pulse thermal imaging non-destructive inspection, and more specifically, to a fuel cell separator plate defect inspection system through pulse thermal imaging non-destructive inspection capable of detecting back surface defects of a fuel cell separator plate that are difficult to identify with the naked eye. Background Technology

[0003] Fuel cells are a core component of hydrogen electric vehicles that continuously and directly converts the chemical energy of fuel into electrical energy through a chemical reaction in a cell. Because they are not subject to the limitations of the Carnot cycle, they can achieve higher efficiency than other power generation methods and are a pollution-free power generation method that does not emit NOx and SOx.

[0004] These fuel cells differ in their applications and characteristics depending on the operating electrolyte; this study focuses on PEMFCs (Polymer Electrolyte Membrane Fuel Cells). A PEMFC stack is generally composed of hundreds of unit cells, which consist of membrane electrode assemblies (MEAs), gas diffusion layers (GDLs), and separators (bipolar plates), playing a crucial role in generating electricity.

[0005] In particular, among the above unit cell components, the separator is one of the main components of the stack, isolating each stacked membrane electrode assembly as a power generation unit, is positioned between the membrane electrode assemblies, and each side of the separator faces the anode and cathode sides of the adjacent membrane electrode assembly.

[0006] In addition, hydrogen, a fuel gas, is supplied to the anode side and oxygen, a reaction gas, is supplied to the cathode side through the gas flow field, inducing a chemical reaction in the battery to generate electrical energy, water, and heat, and the gas flow field acts to discharge the generated water.

[0007] Here, when humid air is introduced into the flow field of the fuel cell separator, water generated during an excessive reaction causes a flooding phenomenon in which reaction gases (hydrogen, oxygen) block the flow field. This increases the pressure inside the flow field of the separator, and the increased pressure creates defects in the separator.

[0008] In addition, since metal separators form the flow channels through multi-stage forming processes (stamping, pressing), defects may occur in the flow channel sections during this process. In a fuel cell stack, each flow channel must maintain airtightness; if this airtightness is compromised due to cracks in the separator, the reaction surface of the membrane electrode assembly becomes contaminated by the cooling water, leading to critical damage to the fuel cell's performance and destruction of its structural stability due to fuel loss of hydrogen and oxygen.

[0009] Accordingly, since disassembling an operating hydrogen fuel cell (PEMFC) to identify microcracks and reassembling it can reduce the fuel cell's lifespan, defects in the separator plates must be inspected through non-destructive testing; however, conventional non-destructive testing technologies have primarily utilized visual inspection (VT), leak testing, and light source inspection methods.

[0010] However, in the case of visual and light source inspections, only surface defects can be inspected, and in the case of leak inspections, only fluid leakage can be inspected.

[0011] Therefore, there is a need to improve the method for detecting defects in separator plates of hydrogen vehicle fuel cell stacks by utilizing pulsed thermal imaging techniques among non-contact infrared thermal imaging non-destructive inspection technologies. Prior art literature

[0013] Korean Patent Publication No. 10-2023-0152307 (Publication Date: Nov. 03, 2023) The problem to be solved

[0014] The present invention was devised to solve the above problems and aims to provide a fuel cell separator plate defect inspection system through pulse thermal imaging non-destructive inspection capable of detecting defects on the back side of a fuel cell separator plate that are difficult to identify with the naked eye. means of solving the problem

[0016] The present invention has the following features to solve the above problem.

[0017] The present invention comprises: a test object positioned to perform non-destructive defect inspection; a heat source that supplies periodic heat to the test object in the form of a heat pulse; an infrared camera that captures the thermal image distribution of the test object formed by the thermal energy received from the heat source to generate a thermal image; and a control unit that receives the thermal image generated from the infrared camera and performs noise removal to generate a noise-removed thermal image, wherein the control unit performs a temperature compensation process to remove noise so as to resolve temperature non-uniformity caused by the difference in distance from the heat source.

[0018] Here, when performing a temperature compensation process, the control unit generates a thermal image of a defect-free test object and a thermal image of a defective test object in advance, calculates at least one of an absolute temperature compensation sheet (ATC sheet) and a temperature rate compensation sheet (TRC sheet) from the thermal image of the defect-free test object, and applies at least one of the calculated ATC sheet and TRC sheet to the thermal image of the defective test object to correct non-uniform temperature effects.

[0019] In addition, the control unit, when calculating the ATC sheet from the thermal image of the defect-free test object, reconstructs the difference in temperature values ​​between other pixels within a set range and a specific pixel in each frame of the thermal image in the form of a matrix based on the temperature value of the specific pixel in each frame of the thermal image through the following equation (1).

[0020] Equation (1)

[0021] Here, the above is the temperature value matrix data of the nth thermal image, is the temperature value of a specific pixel in each thermal image, represents an ATC with the same matrix size as the thermal image.

[0022] In addition, when the control unit calculates the TRC sheet from the thermal image of the defect-free test object, it reconstructs the ratio of the temperature values ​​of other pixels within a set range based on the temperature value of a specific pixel in each frame of the thermal image into a matrix form using the following equation (2).

[0023] (2)

[0024] Here, the above represents an RTC with the same matrix size as the thermal image.

[0025] In addition, the control unit performs correction through the following equations (3) and (4), respectively, when applying at least one of the calculated ATC sheet and TRC sheet to the thermal image of the defective test object to correct the non-uniform temperature effect.

[0026] (3)

[0027] (4) ⊙

[0028] Here, the above represents a thermal image acquired from the above-mentioned defective test object, and is a thermal image with ATC applied, represents a thermal image with TRC applied.

[0029] In addition, the control unit includes a first removal unit that removes noise by performing a temperature compensation process to eliminate temperature non-uniformity caused by the difference in distance from the heat source within the thermal image, and a second removal unit that removes second-order noise by receiving the thermal image from which first-order noise has been removed from the first removal unit, performing a Discrete Fourier Transform (DFT), extracting a phase image according to the Discrete Fourier Transform, and determining an optimal frequency having a maximum phase difference according to frequency to create an image.

[0030] In addition, the control unit further includes a third removal unit that improves noise in the thermal image by calculating a signal-to-noise ratio for the extracted phase image, and a binarization performing unit that receives the phase image from the third removal unit and performs binarization.

[0031] In addition, the third removal unit calculates the signal-to-noise ratio (SNR) using the following equation (5).

[0032] (5)

[0033] Here, Ps is the signal of the defective part of the test object, and Pn is the signal of the sound part within the set range of the test object.

[0034] In addition, the above-mentioned test object may be a fuel cell separator. Effects of the invention

[0036] According to the present invention, through temperature compensation of the thermal pulse image, there is an effect of more accurately detecting defects on the back side of a fuel cell separator that are difficult to identify with the naked eye. Brief explanation of the drawing

[0038] FIG. 1 is a diagram showing the schematic configuration of a defect inspection system according to an embodiment of the present invention. FIG. 2 is a drawing showing the internal configuration of a control unit according to an embodiment of the present invention. FIG. 3 is a drawing showing a defect-free test object (SP1, FIG. 3 (a)) and two defective test objects (SP2 and SP3, FIG. 3 (b) and (c)) prepared in a first removal unit according to an embodiment of the present invention. FIG. 4 is a diagram showing a thermal image of temperature and phase for which temperature compensation through an ATC sheet was not performed for SP2 and SP3 in the first removal section according to an embodiment of the present invention. FIG. 5 is a diagram showing a thermal image of temperature and phase in which temperature compensation through an ATC sheet is performed for SP2(a) and SP3(b) in the first removal section according to an embodiment of the present invention. FIG. 6 is a diagram showing a phase image that has been binarized by a binarization performing unit according to an embodiment of the present invention. FIG. 7 is a drawing showing a thermal image generated using a test object as a fuel cell separator plate according to another example of the present invention. FIG. 8 is a diagram showing a thermal image (b) in which temperature compensation through an ATC sheet is performed on a thermal image (a) according to FIG. 7. Figure 9 is a diagram showing the determination of an optimal frequency representing the maximum phase difference according to frequency in the second removal unit and the derivation of a phase image of the corresponding frequency. Specific details for implementing the invention

[0039] Embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In the drawings, parts unrelated to the explanation have been omitted to clearly explain the invention, and the same reference numerals are used for identical or similar components throughout the specification. Furthermore, specific descriptions of widely known prior art are omitted.

[0040] Throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0041] FIG. 1 is a diagram showing the schematic configuration of a defect inspection system according to an embodiment of the present invention, FIG. 2 is a diagram showing the internal configuration of a control unit according to an embodiment of the present invention, and FIG. 3 is a diagram showing a defect-free test object (SP1, FIG. 3 (a)) and two defective test objects (SP2 and SP3, FIG. 3 (b) and (c)) prepared in a first removal unit according to an embodiment of the present invention.

[0042] In addition, FIG. 4 is a diagram showing a thermal image of temperature and phase in which temperature compensation through an ATC sheet is not performed for SP2 and SP3 in the first removal unit according to an embodiment of the present invention, FIG. 5 is a diagram showing a thermal image of temperature and phase in which temperature compensation through an ATC sheet is performed for SP2(a) and SP3(b) in the first removal unit according to an embodiment of the present invention, FIG. 6 is a diagram showing a phase image (a) in which temperature compensation through an ATC sheet is not performed, and a phase image (b) in which temperature compensation through an ATC sheet is performed, while binarization is performed by a binarization unit according to an embodiment of the present invention.

[0043] In addition, FIG. 7 is a drawing showing a thermal image generated using a test object as a fuel cell separator plate according to another example of the present invention, FIG. 8 is a drawing showing a thermal image (b) in which temperature compensation is performed through an ATC sheet on the thermal image (a) according to FIG. 7, and FIG. 9 is a drawing showing the determination of an optimal frequency representing the maximum phase difference according to frequency in the second removal unit and the derivation of a phase image of the corresponding frequency.

[0044] Referring to the drawings, a defect inspection system (1000) according to one embodiment of the present invention comprises: a test object (100) arranged to perform non-destructive defect inspection; a heat source (200) that supplies periodic heat to the test object (100) in the form of a heat pulse; an infrared camera (300) that captures the thermal image distribution of the test object (100) formed by the thermal energy received from the heat source (200) to generate a thermal image; and a control unit (400) that receives the thermal image generated from the infrared camera (300), performs noise removal to generate a noise-removed thermal image, and performs a temperature compensation process to remove noise so that temperature non-uniformity caused by the difference in distance from the heat source (200) is resolved.

[0045] Here, the test object (100) may be a fuel cell separator according to an example of the present invention, and may also be another object for detecting internal defects through non-destructive testing.

[0046] In addition, the heat source (200) is configured to supply periodic heat to the object under inspection (100) in the form of heat pulses, and according to one example of the present invention, a flash lamp may be applied as such a heat source (200).

[0047] In addition, it goes without saying that a power supply unit for supplying electric energy to the heat source (200), that is, the flash lamp, is further provided.

[0048] Meanwhile, the infrared camera (300) is configured to generate a thermal image by capturing the thermal image distribution of the fuel cell separator plate, which is the object to be inspected (100). This infrared camera (300) can continuously capture images in real time to generate thermal images in frame units.

[0049] In addition, the control unit (400) is configured to receive a thermal image from the infrared camera (300) and directly determine whether there is a defect in the object to be inspected (100), or to provide a noise-removed thermal image so that the user can make a determination. This control unit (400) includes a first removal unit (410) that removes first-order noise by performing a temperature compensation process to resolve temperature non-uniformity caused by the difference in distance from the heat source (200) from the received thermal image; a second removal unit (420) that removes second-order noise by receiving the thermal image from which first-order noise has been removed from the first removal unit (410), performing a Discrete Fourier Transform (DFT), extracting a phase image according to the Discrete Fourier Transform, and determining an optimal frequency having a maximum phase difference according to frequency to create an image; a third removal unit (430) that improves the noise of the thermal image by calculating a signal-to-noise ratio on the extracted phase image; and a third removal unit (430) that receives the phase image from the third removal unit (430) and performs binarization It consists of a binary conversion execution unit (440) that performs the binary conversion.

[0050] As described above, a defect determination unit may be further provided to analyze and determine whether there is a defect in the object to be inspected (100) through a phase image that has been binarized by the binarization execution unit (440), and such a defect determination unit may be configured to make a determination using a deep learning model such as a CNN.

[0051] Meanwhile, the first removal unit (410) performs a temperature compensation process to resolve temperature non-uniformity caused by the difference in distance from the heat source (200) from the received thermal image. When performing this temperature compensation process, a thermal image of a defect-free test object and a thermal image of a defect test object are generated in advance.

[0052] FIG. 3 shows an example of a defect-free test specimen (SP1) (a) and examples of defective test specimens (SP2, SP3) ((b) and (c)). The test specimen is an example of a containment steel plate made of SS 275 material with a thickness of 6 mm and dimensions of 300 mm in width and 300 mm in length.

[0053] Figure 3(b) shows a total of 12 artificial defects processed considering three types of thinning defects with apparent area sizes of 20×20, 30×30, and 40×40 in width (mm)×height (mm) under four thinning depth conditions of 10%, 30%, 50%, and 70% relative to thickness, and configured to allow verification of the influence of the apparent area for each thinning depth.

[0054] Also, (c) of FIG. 3 is all 40 × A total of 9 artificial defects with a thickness of 10% to 90% were fabricated on the same apparent area of ​​40, and the configuration was designed to quantitatively verify the LIT inspection performance according to the thickness of the CLP.

[0055] Accordingly, the first removal unit (410) can calculate at least one of an absolute temperature compensation sheet (ATC sheet) and a temperature rate compensation sheet (TRC sheet) from the thermal image of the defect-free test object, and apply at least one of the calculated ATC sheet and TRC sheet to the thermal image of the defect test object to correct the non-uniform temperature effect.

[0056] To this end, the first removal unit (410) reconstructs the temperature difference between other pixels within a set range and the temperature value of a specific pixel in each frame of the thermal image in the form of a matrix using the following formula (1) when calculating the ATC sheet from the thermal image of the defect-free test object.

[0057] Equation (1)

[0058] Here, the above is the temperature value matrix data of the nth thermal image, is the temperature value of a specific pixel in each thermal image, represents an ATC with the same matrix size as the thermal image.

[0059] In addition, when the first removal unit (410) calculates the TRC sheet from the thermal image of the defect-free test object, it reconstructs the ratio of the temperature values ​​of other pixels within a set range based on the temperature value of a specific pixel in each frame of the thermal image in the form of a matrix using the following formula (2).

[0060] (2)

[0061] Here, the above represents an RTC with the same matrix size as the thermal image.

[0062] Accordingly, the first removal unit (410) applies at least one of the calculated ATC sheet and TRC sheet to the thermal image of the defective test object to correct the uneven temperature effect, and performs correction through the following equations (3) and (4), respectively.

[0063] (3)

[0064] (4) ⊙

[0065] Here, the above represents a thermal image acquired from the above-mentioned defective test object, and is a thermal image with ATC applied, represents a thermal image with TRC applied.

[0066] Accordingly, the second removal unit (420) receives a thermal image from the first removal unit (410) from which the first noise has been removed, performs a Discrete Fourier Transform (DFT), extracts a phase image based on the Discrete Fourier Transform, and removes the second noise by determining and imaging an optimal frequency having the maximum phase difference according to frequency as shown in FIG. 9, thereby further improving the defect detection performance.

[0067] In addition, the third removal unit (430) is provided to improve the noise of the thermal image by calculating the signal-to-noise ratio of the phase image extracted through the second removal unit (420), and the third removal unit (430) calculates the signal-to-noise ratio (SNR) using the following equation (5).

[0068] (5)

[0069] Here, Ps is the signal of the defective part of the test object, and Pn is the signal of the sound part within the set range of the test object. This SNR is a suitable factor for comparing and evaluating defect detection capability and uncertainty; it is calculated as the ratio of the intensity of the defective part (Ps) to the sound part (Pn) and is expressed in decibels (dB).

[0070] Meanwhile, the binarization execution unit (440) receives a phase image from the third removal unit (430) and performs binarization. As shown in FIG. 6, it can be seen that when temperature compensation is performed through an ATC sheet, much more accurate defect detection is possible than when it is not.

[0071] FIGS. 3 to 6 illustrate the process of performing noise removal in a thermal image using a containment steel plate as a test object, while FIGS. 7 to 9 illustrate the process of performing temperature compensation through an ATC sheet in a thermal image using a fuel cell separator plate as a test object and extracting a phase image according to the optimal frequency.

[0072] In this way, according to the defect inspection system (1000) of the present invention, it is possible to implement a defect inspection system having a higher detection capability.

[0074] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the specific embodiments described above. That is, those skilled in the art to which the present invention pertains can make numerous changes and modifications to the present invention without departing from the spirit and scope of the appended claims, and all such appropriate changes and modifications should be deemed to fall within the scope of the present invention as equivalents. Explanation of the symbols

[0076] 100 : Blood sample 200 : Heat source 300: Infrared camera 400 : Control unit 410: 1st Removal Section 420 : 2nd removal section 430 : 3rd Removal Section 440 : Binarization Executor 1000 : Defect Inspection System

Claims

Claim 1 A test object (100) placed to perform non-destructive defect inspection; a heat source (200) that supplies periodic heat to the test object (100) in the form of heat pulses; and an infrared camera (300) that captures a thermal image distribution of the test object (100) formed by the thermal energy received from the heat source (200) to generate a thermal image. A defect inspection system comprising: a control unit (400) that receives a thermal image generated from the infrared camera (300), performs noise removal to generate a thermal image with noise removed, and performs a temperature compensation process to eliminate noise so as to resolve temperature non-uniformity caused by the difference in distance from the heat source (200); wherein, when performing the temperature compensation process, the control unit (400) generates a thermal image of a defect-free test object and a thermal image of a defect test object in advance, calculates at least one of an absolute temperature compensation sheet (ATC sheet) and a temperature rate compensation sheet (TRC sheet) from the thermal image of the defect-free test object, and applies at least one of the calculated ATC sheet and TRC sheet to the thermal image of the defect test object to correct the non-uniform temperature effect. Claim 2 delete Claim 3 A defect inspection system according to claim 1, wherein the control unit (400) reconstructs the difference in temperature values ​​between other pixels within a set range and a specific pixel in each frame of the thermal image in a matrix form based on the temperature value of the specific pixel in the thermal image when calculating an ATC sheet from the thermal image of the defect-free object to be inspected, using the following formula (1). Formula (1) (Here, the above is the temperature value matrix data of the nth thermal image, is the temperature value of a specific pixel in each thermal image, represents an ATC with the same matrix size as the thermal image.) Claim 4 A defect inspection system according to claim 1, wherein the control unit (400), when calculating a TRC sheet from a thermal image of a defect-free object to be inspected, reconstructs the ratio of temperature values ​​of other pixels within a set range based on the temperature value of a specific pixel in each frame of the thermal image in a matrix form using the following equation (2). Equation (2) (Here, the above represents an RTC with the same matrix size as the thermal image.) Claim 5 A defect inspection system according to claim 3 or 4, wherein the control unit (400) performs correction through the following equations (3) and (4), respectively, when correcting non-uniform temperature effects by applying at least one of the calculated ATC sheet and TRC sheet to the thermal image of the defective object to be inspected. Equation (3) (4) ⊙ (Here, the above represents a thermal image acquired from the above-mentioned defective test object, and is a thermal image with ATC applied, represents a thermal image with TRC applied.) Claim 6 A defect inspection system according to claim 1, wherein the control unit (400) comprises a first removal unit (410) that removes noise by performing a temperature compensation process to resolve temperature non-uniformity caused by the difference in distance from the flash lamp (200) within the thermal image, and a second removal unit (420) that receives the thermal image from which first-order noise has been removed from the first removal unit (410), performs a Discrete Fourier Transform (DFT), extracts a phase image according to the Discrete Fourier Transform, and removes second-order noise by determining an optimal frequency having a maximum phase difference according to frequency and imaging it. Claim 7 In claim 6, the control unit (400) further comprises a third removal unit (430) that calculates a signal-to-noise ratio for the extracted phase image to improve the noise of the thermal image, and a binarization performing unit (440) that receives the phase image from the third removal unit (430) and performs binarization, a defect inspection system. Claim 8 In claim 7, the third removal unit (430) is a defect inspection system that calculates the signal-to-noise ratio (SNR) using the following formula (5). Formula (5) (Here, Ps is the signal of the defective part of the test object, and Pn is the signal of the sound part within the set range of the test object.) Claim 9 In paragraph 1, the above-mentioned test object is a fuel cell separator plate, a defect inspection system.

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