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KR-20260066838-A - Fuel cell separator defect inspection system using pulse thermography non-destructive testing

KR20260066838AKR 20260066838 AKR20260066838 AKR 20260066838AKR-20260066838-A

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.

Inventors

  • 서현규
  • 정윤재
  • 서병연

Assignees

  • 국립공주대학교 산학협력단

Dates

Publication Date
20260512
Application Date
20241105

Claims (9)

  1. A test object (100) placed to perform non-destructive defect inspection; A heat source (200) that supplies periodic heat to a test object (100) in the form of heat pulses; An infrared camera (300) that generates a thermal image by capturing the thermal image distribution of the object to be inspected (100) formed by the thermal energy received from the heat source (200); and 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 remove noise so as to resolve temperature non-uniformity caused by the difference in distance from the heat source (200); Defect inspection system.
  2. In paragraph 1, The above control unit (400) is, When performing the temperature compensation process, Generate thermal images of defect-free test subjects and defective test subjects in advance, and Calculating at least one of an absolute temperature compensation sheet (ATC sheet) and a temperature rate compensation sheet (TRC sheet) from a thermal image of a defect-free test object, and applying at least one of the calculated ATC sheet and TRC sheet to a thermal image of a defect test object to correct non-uniform temperature effects. Defect inspection system.
  3. In paragraph 2, The above control unit (400) is, When calculating an ATC sheet from the thermal image of the defect-free test object, the temperature difference between a specific pixel in each frame of the thermal image and another pixel within a set range is reconstructed in a matrix form based on the temperature value of the specific pixel in each frame of the thermal image using the following formula (1). Defect inspection system. Equation (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.)
  4. In paragraph 2, The above control unit (400) is, When calculating the TRC sheet from the thermal image of the defect-free test object, the ratio of the temperature values of other pixels within a set range is reconstructed in a matrix form based on the temperature value of a specific pixel in each frame of the thermal image through the following formula (2). Defect inspection system. (2) (Here, the above represents an RTC with the same matrix size as the thermal image.)
  5. In paragraph 3 or 4, The above control unit (400) is, When applying 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, correction is performed through the following equations (3) and (4), respectively. Defect inspection system. (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.)
  6. In paragraph 2, The above control unit (400) is, A first removal unit (410) that removes noise by performing a temperature compensation process to eliminate temperature non-uniformity caused by the difference in distance from the flash lamp (200) within the above thermal image, and A second removal unit (420) that receives a 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. Defect inspection system.
  7. In paragraph 6, The above control unit (400) is, A third removal unit (430) that improves noise in a thermal image by calculating a signal-to-noise ratio for the extracted phase image and Further comprising a binarization performing unit (440) that receives a phase image from the third removal unit (430) and performs binarization, Defect inspection system.
  8. In Paragraph 7, The above third removal unit (430) is, When calculating the above signal-to-noise ratio (SNR), the following formula (5) is used to calculate, Defect inspection system. (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.)
  9. In paragraph 1, The above-mentioned test object is a fuel cell separator, Defect inspection system.

Description

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