Method for detecting and inspection apparatus for membrane electrode assembly

Abstract

The present invention relates to a detection method and an inspection apparatus for a membrane electrode assembly. The inspection method for a membrane electrode assembly includes a first process of acquiring an X-ray transmission image of the membrane electrode assembly, a second process of identifying a brightness reduction region having a lower brightness than that of a surrounding region in the X-ray transmission image acquired in the first process, a third process of correcting the brightness of the brightness reduction region identified in the second process according to a planar size of the brightness reduction region based on a correlation between a planar size of a foreign matter in the membrane electrode assembly and a brightness change due to diffraction of X-rays, and a fourth process of calculating a thickness of the foreign matter in the membrane electrode assembly based on the brightness corrected in the third process.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an inspection method and an inspection apparatus for a membrane electrode assembly. BACKGROUND

[0002] Regarding an inspection method for a membrane electrode assembly for a fuel cell, for example, the technology disclosed in Japanese Unexamined Patent Application Publication No. 2017-162745 (JP 2017-162745 A) notes the fact that X-rays are absorbed by catalyst particles included in an electrolyte membrane, and calculates a load amount of the catalyst particles in the electrolyte membrane based on X-ray transmittance calculated from a difference between an X-ray emission intensity and a detection intensity. SUMMARY

[0003] At the time of manufacture, a foreign matter having an X-ray absorption ability, such as an Fe particle, can be mixed into a membrane electrode assembly. The present disclosure provides an inspection method and an inspection apparatus for a membrane electrode assembly that are able to detect the size of such a foreign matter with high precision using X-rays.

[0004] The present disclosure can be implemented in the following aspects.

[0005] According to a first aspect of the present disclosure, an inspection method for a membrane electrode assembly is provided. The inspection method includes a first process that acquires an X-ray transmission image of the membrane electrode assembly, a second process that identifies a luminance reduction region having a lower luminance than that of a surrounding region in the X-ray transmission image acquired in the first process, a third process that corrects the luminance of the luminance reduction region identified in the second process according to a planar size of the luminance reduction region based on a correlation between a planar size of a foreign matter in the membrane electrode assembly and a luminance change due to diffraction of X-rays, and a fourth process that calculates a thickness of the foreign matter in the membrane electrode assembly based on the luminance corrected in the third process. According to this aspect, by correcting the influence of the diffraction of X-rays on the luminance of the X-ray transmission image, the thickness of the foreign matter can be calculated with high precision as the size of the foreign matter in the membrane electrode assembly.

[0006] The above aspect can further include a fifth process that calculates a three-dimensional size of the foreign matter based on the thickness calculated in the fourth process and the planar size of the luminance reduction region. According to this aspect, the three-dimensional size of the foreign matter can be calculated with high precision as the size of the foreign matter in the membrane electrode assembly.

[0007] The above aspect can further include a sixth process that performs quality judgment processing for judging whether the membrane electrode assembly is defective or non-defective by comparing the three-dimensional size of the foreign matter calculated in the fifth process with a defect judgment threshold value set in advance.

[0008] In addition to the above aspects as the inspection method of the membrane-electrode assembly, the present disclosure can be implemented in various aspects such as, for example, an inspection device for a membrane-electrode assembly and an inspection system.

[0009] Another aspect of the present disclosure provides an inspection device of a membrane-electrode assembly. The inspection device of the membrane-electrode assembly includes an acquisition unit configured to acquire an X-ray transmission image of the membrane-electrode assembly, and a processing unit configured to identify a brightness reduction region having a lower brightness than a surrounding region in the X-ray transmission image, correct the brightness of the brightness reduction region according to a planar size of the brightness reduction region based on a correlation between a planar size of a foreign matter in the membrane-electrode assembly and a brightness change due to diffraction of X-rays, and calculate a thickness of the foreign matter in the membrane-electrode assembly based on the corrected brightness.

[0010] In the above aspect, the processing unit can be configured to calculate a three-dimensional size of the foreign matter based on the thickness calculated by the processing unit and the planar size of the brightness reduction region.

[0011] In the above aspect, the processing unit can be configured to perform quality determination processing for determining whether the membrane-electrode assembly is defective or non-defective by comparing the three-dimensional size of the foreign matter with a pre-set defect determination threshold. BRIEF DESCRIPTION OF DRAWINGS

[0012] Features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

[0013] Figure 1 is a diagram of an inspection system for inspecting a membrane-electrode assembly;

[0014] Figure 2 is a process diagram illustrating a method for inspecting a membrane-electrode assembly;

[0015] Figure 3 is an enlarged schematic view of a portion of an X-ray transmission image;

[0016] Figure 4 is a diagram illustrating a relationship between a planar size of a foreign matter and a brightness reduction amount;

[0017] Figure 5 is a diagram illustrating a relationship between a thickness of a foreign matter and a brightness reduction amount; and

[0018] Figure 6 is a diagram for describing effects of an embodiment. DETAILED DESCRIPTION

[0019] A. First Embodiment

[0020] Figure 1 is a diagrammatic view of an inspection system 100 for inspecting a membrane electrode assembly. In the present embodiment, the inspection system 100 includes an X-ray source 10, a detection camera 20, a stage 30, and an inspection device 40. A membrane electrode assembly 50 is placed on the stage 30. Figure 1 The X, Y, and Z directions orthogonal to each other are shown. The Z direction is the thickness direction of the membrane electrode assembly 50. The Y direction is the conveyance direction of the stage 30. The X direction is a direction orthogonal to the Y direction and the Z direction. The X direction and the Y direction are the planar directions of the membrane electrode assembly 50, and are horizontal directions in the present embodiment.

[0021] The X-ray source 10 emits X-rays toward the membrane electrode assembly 50 placed on the stage 30. In the present embodiment, the stage 30 is provided with an opening 60. The X-ray source 10 irradiates the membrane electrode assembly 50 with X-rays from below through the opening 60. For the X-ray source 10, a water-cooled or air-cooled X-ray tube can be used, for example, the tube voltage can be 15 kV to 50 kV, and the tube current can be 0.1 mA to 35 mA.

[0022] The detection camera 20 is disposed to face the X-ray source 10 with the stage 30 interposed therebetween. In the present embodiment, the detection camera 20 is disposed above the stage 30 to face downward. The detection camera 20 has a predetermined pixel resolution and a brightness resolution, and images the membrane electrode assembly 50 irradiated with X-rays to generate an X-ray transmission image. The foreign matter detected by the detection camera 20 is a foreign matter having an X-ray absorption ability, and is, for example, an iron-based foreign matter such as iron or stainless steel in the present embodiment. As the detection camera 20, a linear image sensor or a planar image sensor of a charge-coupled device (CCD) type or a complementary metal-oxide semiconductor (CMOS) type can be used. The image sensor can be a time delay integration (TDI) type sensor. The positional relationship between the detection camera 20 and the X-ray source 10 can be reversed in the up-down direction.

[0023] In the present application, the "brightness" in the X-ray transmission image has the same meaning as the "signal intensity". Specifically, the brightness of each pixel represents the signal intensity of the X-rays transmitted through the membrane electrode assembly 50, and indicates that the higher the brightness, the higher the signal intensity of the X-rays transmitted through the membrane electrode assembly 50. Any foreign matter having an X-ray absorption ability present in the membrane electrode assembly 50 will absorb X-rays, so the signal intensity of the X-rays transmitted through the membrane electrode assembly 50 will be weakened, and the brightness will be reduced. As a result, the area in which a foreign matter is present in the X-ray transmission image appears as a dark region.

[0024] The stage 30 is configured to be movable in a horizontal direction between the X-ray source 10 and the detection camera 20. The stage 30 includes a fixing jig, which is omitted from the drawing, for fixing the membrane electrode assembly 50 on the stage 30. The stage 30 is transported and moved in the horizontal direction by a moving device, such as a linear actuator, a belt conveyor, or the like, which is omitted from the drawing. A plurality of stages 30 can be prepared, and a plurality of membrane electrode assemblies 50 can be continuously inspected by sequentially moving the stages 30 between the X-ray source 10 and the detection camera 20.

[0025] The inspection device 40 is constituted by a computer including a central processing unit (CPU) and a storage device, and controls the X-ray source 10, the detection camera 20, and the stage 30. The inspection device 40 includes an acquisition unit 41 that acquires the X-ray transmission image taken by the detection camera 20, and a processing unit 42 that calculates the size of the foreign matter in the membrane electrode assembly 50 on the basis of the X-ray transmission image acquired by the acquisition unit 41. The acquisition unit 41 and the processing unit 42 are functional units realized by the CPU provided in the inspection device 40 executing a program stored in the storage device. Note that the acquisition unit 41 and the processing unit 42 can be configured as a circuit.

[0026] The membrane electrode assembly 50 is a member in which a catalyst electrode layer is formed on both faces of an electrolyte membrane. The electrolyte membrane is a solid polymer membrane formed of, for example, a fluorinated sulfonic acid polymer. The catalyst electrode layer is constituted of, for example, catalyst-supported carbon on which catalyst particles such as platinum are supported and an electrolyte resin. In the present embodiment, a gas diffusion layer constituted of carbon paper, carbon nonwoven fabric, or the like is provided on one or both faces of the membrane electrode assembly 50, and the inspection is performed in a state where a resin frame member is fixed around the membrane electrode assembly 50 by an adhesive. After the inspection, a pair of gas separators is provided so as to sandwich the membrane electrode assembly 50 from which no foreign matter is detected and the frame member, thereby completing a fuel cell. Note that the inspection of the membrane electrode assembly 50 can be performed in a state where the frame member and the gas diffusion layer are not provided on the membrane electrode assembly 50.

[0027] Figure 2 is a process chart showing a method of the inspection of the membrane electrode assembly performed in the inspection device 40. First, in step S10, the inspection device 40 controls the X-ray source 10, the detection camera 20, and the stage 30 to irradiate the membrane electrode assembly 50 with X-rays, and the acquisition unit 41 acquires the X-ray transmission image. The process of step S10 is also referred to as a first process.

[0028] In step S20, the processing unit 42 of the inspection device 40 identifies the reduced-brightness region from the X-ray transmission image acquired in step S10. The process of step S20 is also referred to as a second process.

[0029] Figure 3 is a schematic view of a portion of the X-ray transmission image. The processing unit 42 identifies a region in which the luminance is lower than that of the surrounding region in the X-ray transmission image as a luminance reduction region BA. Specifically, in the present embodiment, a set of pixels in which the luminance value is darker than that of the surrounding pixels by 10 times or more is identified as the luminance reduction region BA. In Figure 3 , the luminance reduction region BA is surrounded by a thick line. The processing unit 42 identifies the amount of luminance reduction of the pixel CP at the center of the luminance reduction region BA as the amount of luminance reduction of the luminance reduction region BA. The amount of luminance reduction refers to the amount of luminance reduction from the maximum luminance of the X-ray transmission image, and indicates the X-ray attenuation amount. The greater the amount of luminance reduction, the smaller the luminance value, and the smaller the amount of luminance reduction, the greater the luminance value.

[0030] In Figure 2 step S30, the processing unit 42 corrects the amount of luminance reduction of the luminance reduction region based on the planar size of the luminance reduction region identified in step S20. In the present embodiment, the planar size is the area of the luminance reduction region BA.

[0031] Figure 4 is an explanatory diagram showing the relationship between the planar size of a foreign object and the amount of luminance reduction. Figure 4 The horizontal axis of the graph shown is the planar size of a foreign object, and the vertical axis is the amount of luminance reduction. As is well known, X-rays, like light, have the characteristic of bending around to the rear of an obstacle. Therefore, when a foreign object is present in the membrane electrode assembly 50, X-rays are diffracted to the rear of the foreign object (upper side in Figure 4 ) and affect the amount of luminance reduction in the luminance reduction region. The size of the effect varies depending on the planar size of the foreign object. Specifically, as Figure 4 shown, when the planar size of the foreign object is very small, the amount of X-rays that bend around to the rear of the foreign object is large, and therefore the amount of luminance reduction is small. On the other hand, when the planar size of the foreign object is very large, the amount of X-rays that bend around to the rear of the foreign object is small relative to the planar size of the foreign object, and therefore the amount of luminance reduction becomes large. However, the diffraction of X-rays occurs at the edges of the foreign object, so when the planar size of the foreign object increases beyond a certain degree, the diffraction of X-rays does not affect the amount of luminance reduction at the center of the foreign object. Due to this phenomenon, within a range in which the planar size of the foreign object is smaller than a predetermined value (threshold value), the smaller the planar size of the foreign object becomes, the smaller the amount of luminance reduction becomes relative to the planar size of the foreign object, and within a range in which the planar size is not smaller than the threshold value, the amount of luminance reduction becomes constant regardless of the planar size of the foreign object, as Figure 4 shown. Note that when the planar size of the foreign object is within the range of sizes assumed in the present embodiment (diameter not greater than about 1 millimeter (mm)), the correlation between the planar size of the foreign object and the amount of luminance reduction does not change even when the thickness of the foreign object is different.

[0032] In step S30, the processing unit 42 is based on Figure 4 The correlation between the planar size of the foreign object and the brightness change is corrected until the brightness reduction in the brightness reduction region BA is the original brightness reduction amount after eliminating the influence of X-ray diffraction. Specifically, when the planar size of the brightness reduction region BA is less than a threshold, the smaller the planar size, the larger the correction amount used to increase the brightness reduction. Furthermore, when the planar size of the brightness reduction region BA is not less than the threshold, the processing unit 42 does not perform correction. The relationship between the planar size of the foreign object and the brightness change can be preset as a function or mapping through simulation and experimentation. The processing unit 42 can perform the above correction by using such a function or mapping. The process of step S30 is also referred to as the third process.

[0033] exist Figure 2 In step S40, the processing unit 42 calculates the thickness of the foreign object present in the brightness reduction region BA based on the corrected brightness reduction amount.

[0034] Figure 5 This is an explanatory diagram showing the relationship between the thickness of the foreign object and the amount of brightness reduction. Figure 5 The graph shown has the horizontal axis representing the thickness of the foreign object and the vertical axis representing the reduction in brightness. The more X-rays a foreign object with X-ray absorption capacity absorbs, the greater its thickness. Therefore, the greater the thickness of the foreign object, the greater the reduction in brightness. Figure 5 As shown. Processing unit 42 uses a function or mapping predetermined by simulation or experiment to determine the relationship between the thickness of the foreign object and the amount of brightness reduction, and calculates the thickness of the foreign object corresponding to the amount of brightness reduction based on the amount of brightness reduction corrected in step S30. The process in step S40 is also called the fourth process.

[0035] exist Figure 2 In step S50, processing unit 42 calculates the three-dimensional dimensions of the foreign object based on the thickness and planar dimensions of the brightness reduction region BA obtained in step S40. In this embodiment, the surface area of ​​the foreign object is calculated in step S50. Specifically, the brightness reduction regions BA on the top and bottom are identified in step S20, and the thickness obtained in step S40 is used as the height to calculate the surface area of ​​the columnar shape. The process of step S50 is also referred to as the fifth process.

[0036] In step S60, the processing unit 42 performs quality determination processing for determining whether the membrane-electrode assembly 50 is defective or non-defective by comparing the three-dimensional size of the foreign matter calculated in step S50 with a pre-set defect determination threshold. When the three-dimensional size of the foreign matter calculated in step S50 is not smaller than the defect determination threshold, the processing unit 42 determines that the membrane-electrode assembly 50 is defective, and when it is found that the three-dimensional size of the foreign matter is smaller than the defect determination threshold in step S50, determines that the membrane-electrode assembly 50 is non-defective. Note that when a plurality of brightness reduction regions BA are recognized in step S20, the processing from the above-described steps S30 to S60 is performed for all the brightness reduction regions BA, and when even one of the brightness reduction regions is determined to be defective, the membrane-electrode assembly 50 is determined to be defective. Further, when no brightness reduction region is recognized in the membrane-electrode assembly 50 in step S20, the processing from step S30 to step S50 is skipped, and in step S60, it is determined that the membrane-electrode assembly 50 is non-defective. The inspection device 40 can output the determination result of the quality determination processing through an output device such as a display device connected to the inspection device 40.

[0037] When the quality determination of whether the membrane-electrode assembly 50 is defective or non-defective is performed in the inspection system 100 as described above, the membrane-electrode assembly 50 determined to be non-defective is used for manufacturing a fuel cell. Figure 2 The illustrated process illustrates the inspection process of one membrane-electrode assembly 50. Therefore, by repeatedly performing the process of the above-described steps S10 to S60, the membrane-electrode assemblies 50 can be continuously inspected.

[0038] According to the inspection method of the membrane-electrode assembly 50 in the above-described embodiment, by correcting the influence of the diffraction of the X-rays on the brightness of the X-ray transmission image, the size of the foreign matter in the membrane-electrode assembly 50, particularly the thickness of the foreign matter, can be calculated with high accuracy. Further, in the embodiment, the thickness of the foreign matter is calculated based on the corrected brightness reduction amount, and the three-dimensional size of the foreign matter is calculated based on the thickness and the planar size of the brightness reduction region, and thus the three-dimensional size of the foreign matter in the membrane-electrode assembly 50 can be calculated with high accuracy.

[0039] Further, in the embodiment, since the foreign matter can be detected using only the X-ray transmission image, the inspection can be easily performed without using other methods such as component analysis like fluorescent X-ray analysis and the like. Therefore, the cycle time required for the inspection of the membrane-electrode assembly 50 is shortened, and a fuel cell can be efficiently manufactured.

[0040] Figure 6 is a diagram for describing the effects of the embodiment. In Figure 6In the graph shown, the horizontal axis represents the measured value of the three-dimensional size of the foreign matter, and the vertical axis represents the value of the three-dimensional size of the foreign matter calculated by the above-described inspection. The value calculated by the above-described inspection method will be referred to as an "estimated value" hereinafter. The measured value is calculated by analyzing a three-dimensional computed tomography (CT) image of the foreign matter. In Figure 6 In the above-described embodiment, the region in which the foreign matter data whose brightness reduction amount has been corrected in step S30 of the above-described inspection method falls within the 3σ range is denoted by "R1", and the region in which the foreign matter data that has not been corrected falls within the 3σ range is denoted by "R2". These regions are regions that are statistically obtained by calculating the measured value and the estimated value for thirty foreign matter samples having various shapes.

[0041] As Figure 6 shown in the above-described embodiment, when the brightness reduction amount is corrected based on the planar size of the foreign matter in step S30 of the inspection method, the measured value of the foreign matter size and the estimated value thereof have a stronger correlation than when the brightness reduction amount is not corrected. That is, by correcting the brightness reduction amount, the three-dimensional size of the foreign matter can be estimated with high accuracy. As a result, the defect determination threshold value for the quality determination of whether the membrane electrode assembly 50 is defective or non-defective does not need to be set with a large margin, and thus the defect determination threshold value can be set to a large value. Therefore, it is possible to determine that a part of the membrane electrode assembly 50 that is determined to be defective without correction (the membrane electrode assembly 50 whose estimated size of the foreign matter corresponds to the hatched part in Figure 6 ), is non-defective, and it is possible to improve the yield of the membrane electrode assembly 50.

[0042] B. Other Embodiments

[0043] B-1

[0044] In the above-described embodiment, the quality determination of whether the membrane electrode assembly 50 is defective or non-defective is performed based on the three-dimensional size of the foreign matter. In contrast, the quality determination of whether the membrane electrode assembly 50 is defective or non-defective can be performed based on the thickness of the foreign matter. In this case, step S50 of the inspection method shown in Figure 2 is omitted, and in step S60, the quality determination of whether the membrane electrode assembly 50 is defective or non-defective is performed by comparing the thickness of the foreign matter with a predetermined quality determination threshold value.

[0045] B-2

[0046] In the above-described embodiment, the processing unit 42 identifies the brightness reduction amount of the pixel at the center of the brightness reduction region BA as the brightness reduction amount in the brightness reduction region BA. In contrast, the processing unit 42 can identify the maximum brightness reduction amount in the brightness reduction region BA as the brightness reduction amount in the brightness reduction region BA.

[0047] B-3

[0048] In the above-described embodiment, the processing unit 42 obtains the area of the luminance reduction region BA as the planar dimension of the luminance reduction region BA. Conversely, the processing unit 42 can obtain the maximum dimension of the luminance reduction region BA in the planar direction or the larger dimension of the dimensions in the X and Y directions as the planar dimension of the luminance reduction region BA.

[0049] B-4

[0050] In the above-described embodiment, the processing unit 42 obtains the surface area of the foreign matter as the three-dimensional dimension of the foreign matter. Conversely, the processing unit 42 can obtain the volume of the foreign matter by multiplying the thickness obtained in step S40 and the planar dimension of the luminance reduction region BA as the three-dimensional dimension of the foreign matter. Figure 2

[0051] B-5

[0052] In the above-described embodiment, the processing unit 42 corrects the amount of luminance reduction of the luminance reduction region BA. Conversely, the processing unit 42 can correct the luminance value of the luminance reduction region BA. Both the amount of luminance reduction and the luminance value are indicators of luminance, and thus it can be said that both correction of the amount of luminance reduction and correction of the luminance value correct the luminance. Note, however, that the amount of luminance reduction is small when the luminance value is large, and the amount of luminance reduction is large when the luminance value is small. Therefore, when the luminance value is corrected in step S30, Figure 2 the planar dimension of the luminance reduction region BA is smaller than the threshold value, the smaller the planar dimension, the larger the amount of correction for reducing the luminance value that the processing unit 42 sets.

[0053] The present disclosure is not limited to the above-described embodiments, and can be implemented in various configurations without departing from the scope thereof. For example, in order to solve some or all of the problems described above, or in order to achieve some or all of the effects described above, the technical features in the embodiments corresponding to the technical features in each of the modes described in the summary section can be appropriately replaced or combined. When a technical feature is not described as indispensable in this specification, such a technical feature can be appropriately omitted.​

Claims

1. A method for inspecting a membrane electrode assembly, the method being characterized by comprising: The first process involves acquiring an X-ray transmission image of the membrane electrode assembly; The second process identifies a brightness reduction region in the X-ray transmission image acquired in the first process that has a brightness lower than the surrounding region. The third process is based on the correlation between the planar dimensions of the foreign matter in the membrane electrode assembly and the brightness change caused by X-ray diffraction, and corrects the brightness of the brightness-reduced region identified in the second process according to the planar dimensions of the brightness-reduced region. as well as The fourth process determines the thickness of the foreign matter in the membrane electrode assembly based on the brightness corrected in the third process.

2. The inspection method according to claim 1, characterized in that... It also includes a fifth process, which determines the three-dimensional dimensions of the foreign object based on the thickness and planar dimensions of the brightness reduction region obtained in the fourth process.

3. The inspection method according to claim 2, characterized in that... It also includes a sixth process, which performs a quality assessment process to determine whether the membrane electrode assembly is defective or not by comparing the three-dimensional dimensions of the foreign object obtained in the fifth process with a pre-set defect assessment threshold.

4. An inspection apparatus for a membrane electrode assembly, characterized in that it comprises: An acquisition unit configured to acquire an X-ray transmission image of the membrane electrode assembly; and Processing unit, the processing unit is configured to In the X-ray transmission image, identify regions of reduced brightness that are less bright than the surrounding area. Based on the correlation between the planar dimensions of foreign matter in the membrane electrode assembly and the brightness change caused by X-ray diffraction, the brightness of the brightness-reduced region is corrected according to the planar dimensions of the brightness-reduced region. The thickness of the foreign matter in the membrane electrode assembly is determined based on the corrected brightness.

5. The inspection device according to claim 4, characterized in that, The processing unit is configured to determine the three-dimensional dimensions of the foreign object based on the thickness determined by the processing unit and the planar dimensions of the brightness reduction region.

6. The inspection device according to claim 5, characterized in that, The processing unit is configured to perform a quality assessment process to determine whether the membrane electrode assembly is defective or not by comparing the three-dimensional dimensions of the foreign object with a pre-set defect assessment threshold.

Images