Method for evaluating crossed fibers in a fiber bundle

Abstract

This technology provides an evaluation method for crossing fibers in a fiber bundle. [Solution] The method of the present disclosure comprises: (a) acquiring a luminance image of a fiber bundle; (b) generating a two-dimensional power spectrum image by performing a two-dimensional FFT analysis on the luminance image data; (c) generating a modified power spectrum image by performing a masking process on the two-dimensional power spectrum image to remove a mask region corresponding to a luminance image component whose intersection angle with respect to the horizontal direction of the luminance image is less than or equal to an angle threshold; and (d) generating a modified luminance image by performing an inverse FFT analysis on the modified power spectrum image.

Description

Technical Field

[0001] The present disclosure relates to a method for evaluating cross fibers in a fiber bundle.

Background Art

[0002] Patent Document 1 discloses a method for evaluating the generation of fiber fly in a fiber bundle. This method includes a step of acquiring a luminance image of the fiber, a step of converting the luminance image into a power spectrum image using Fourier transform processing, a step of generating a masking image by masking a rectangular region showing a frequency component corresponding to the fiber direction of the fiber with respect to the power spectrum image, a step of inversely converting the masking image into a masking luminance image using inverse Fourier transform, and a step of binarizing the masking luminance image.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above prior art, although it is possible to evaluate the fiber fly protruding from the fiber bundle, there is a problem that it is impossible to evaluate the cross fibers that are twisted or crossed in the fiber bundle. Therefore, a technique for evaluating cross fibers in a fiber bundle is desired.

Means for Solving the Problems

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to the embodiment of the present disclosure, a method for evaluating crossing fibers in a fiber bundle is provided. This method comprises: (a) acquiring a luminance image of the fiber bundle; (b) generating a two-dimensional power spectrum image by performing a two-dimensional FFT analysis on the luminance image data; (c) generating a modified power spectrum image by performing a masking process on the two-dimensional power spectrum image to remove a mask region corresponding to a luminance image component whose crossing angle with respect to the horizontal direction of the luminance image is less than or equal to an angle threshold; and (d) generating a modified luminance image by performing an inverse FFT analysis on the modified power spectrum image. This method allows for the generation of a modified luminance image containing only luminance image components where the intersection angle is greater than the angle threshold, thus enabling easy evaluation of intersecting fibers in a fiber bundle. (2) The above method may further include (e) a step of determining the number of pixels in the corrected brightness image that are equal to or greater than the brightness threshold as a cross fiber index value indicating the amount of cross fibers. This method allows us to evaluate the amount of interwoven fibers. (3) In the above method, the mask region may be defined by two isosceles triangles formed by two straight lines that intersect diagonally and symmetrically at the center of the two-dimensional power spectral image. This method allows for the removal of power spectra from luminance image components whose intersection angle is below an angular threshold. (4) In the above method, when the angle threshold is A and the ratio of the width to the height of the brightness image is 1:R, the vertex angle θ of the isosceles triangle may be 2 × arctan(sin(A) / (R × cos(A))). This method allows for easy determination of the shape of the mask region. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing the configuration of the fiber bundle evaluation system in the embodiment. [Figure 2] A flowchart illustrating the processing procedure for evaluating fiber bundles in an embodiment. [Figure 3] An explanatory diagram showing the processing details for evaluating fiber bundles in the embodiment. [Figure 4] An explanatory diagram showing how to set the mask area. [Modes for carrying out the invention]

[0008] Figure 1 is a schematic diagram showing the configuration of a fiber bundle evaluation system in an embodiment. This fiber bundle evaluation system includes a fiber bundle evaluation device 100 for evaluating fiber bundles FB. In this embodiment, the fiber bundles FB are used to form a reinforcing layer of a high-pressure tank 40. That is, the fiber bundles FB are wound around the liner of the high-pressure tank 40 by a filament winding device 10 to form a reinforcing layer of the liner. The fiber bundle evaluation device 100 is positioned on the transport path of the fiber bundles FB and performs an evaluation of the fiber bundles FB before they are wound onto the high-pressure tank 40.

[0009] The fiber bundle FB is, for example, carbon fiber reinforced plastic (CARBON FIBER REINFORCED PLASTICS) in which carbon fibers are impregnated with a heat-reinforced resin such as epoxy resin. The fiber bundle FB is fed out from the bobbin 11 and wound onto the high-pressure tank 40. Multiple conveyor rollers 12 and 13 are arranged along the conveying path of the fiber bundle FB until it is wound onto the high-pressure tank 40.

[0010] The fiber bundle evaluation device 100 comprises an imaging unit 110 and an evaluation execution unit 120. The imaging unit 110 captures a luminance image of the fiber bundle FB. A luminance image means an image that represents the luminance or brightness for each pixel. As the imaging unit 110, for example, a microscope or camera that captures multi-gradation images in gray or color can be used. As a microscope, for example, a scanning electron microscope (SEM) can be used. Microscopes such as scanning electron microscopes are preferred because they have high resolution that can identify thin fibers one by one. The evaluation execution unit 120 is equipped with a CPU, memory, etc., and realizes the function of performing a process to evaluate the fiber bundle FB from the luminance image of the fiber bundle FB by executing a pre-stored computer program. However, some or all of the functions of the evaluation execution unit 120 may be realized by hardware circuits.

[0011] Figure 2 is a flowchart showing the processing procedure for fiber bundle evaluation in the embodiment, and Figure 3 is an explanatory diagram showing the processing content of fiber bundle evaluation in the embodiment. In step S10, the imaging unit 110 acquires a brightness image IM0 of the fiber bundle FB by imaging the fiber bundle FB.

[0012] In step S20, the evaluation execution unit 120 generates a two-dimensional power spectrum image PS0 by performing a two-dimensional FFT (Fast Fourier Transform) analysis on the luminance image IM0. The two-dimensional power spectrum image PS0 is an image obtained by transforming the luminance distribution in the luminance image IM0 into a frequency space. The horizontal axis of the two-dimensional power spectrum image PS0 represents the horizontal frequency Fh in the luminance image IM0, and the vertical axis of the two-dimensional power spectrum image PS0 represents the vertical frequency Fv in the luminance image IM0. At the center of the two-dimensional power spectrum image PS0, both the vertical and horizontal frequencies Fh and Fv are zero, and the frequency increases from low to high as you move from the center towards the edges. The pixels in the two-dimensional power spectrum image PS0 indicate that the brighter the pixel, the larger its frequency component, and the darker the pixel, the smaller its frequency component.

[0013] In step S30, the evaluation execution unit 120 generates a modified power spectrum image PS1 by performing a masking process on the two-dimensional power spectrum image PS0 to remove the mask region MR. The mask region MR is a region corresponding to the luminance image component whose intersection angle with respect to the horizontal direction of the luminance image IM0 is less than or equal to an angle threshold.

[0014] Figure 4 is an explanatory diagram illustrating the method for setting the mask region MR. It shows an ideal luminance image IMa and a modified power spectrum image PSa, which is the same luminance image but with the mask region MR applied to its two-dimensional power spectrum image. The mask region MR is shown as a hatched area.

[0015] An ideal luminance image (IMa) is an image in which multiple fibers with slightly different inclinations are arranged regularly. Specifically, multiple fibers with intersection angles with respect to the horizontal ranging from -20 degrees to +20 degrees, differing by 1 degree each, are arranged regularly. The mask region (MR) is defined by two isosceles triangles TR1 and TR2 formed by two diagonally intersecting straight lines L1 and L2 in a symmetrical manner at the center CP of the two-dimensional power spectral image.

[0016] When the angle threshold is A and the aspect ratio (ratio of width to height) of the luminance image IMa is 1:R, the vertex angle θ of the isosceles triangles TR1 and TR2 is given by the following equation. θ=2×arctan(sin(A) / (R×cos(A))) …(q1)

[0017] By removing the power spectral values ​​in this mask region MR and setting them to zero, luminance image components whose intersection angle with the horizontal direction of the luminance image IMa is less than or equal to the angular threshold A can be removed. Furthermore, the shape of the mask region MR can be easily determined.

[0018] In step S40, the evaluation execution unit 120 generates a corrected luminance image IM1 by performing inverse FFT analysis on the corrected power spectrum image PS1. The corrected luminance image IM1 includes only luminance image components whose crossing angle is greater than the angle threshold A. Therefore, by using this corrected luminance image IM1, the crossing fibers in the fiber bundle FB can be easily evaluated.

[0019] In step S30, two mask regions MR may be set using two different values as the angle threshold A, and a corrected power spectrum image representing the difference between the results of removing the two mask regions MR from the two-dimensional power spectrum image may be generated. In this way, as a result of the inverse FFT analysis in step S40, only luminance image components having an angle between the two angle thresholds A can be extracted.

[0020] In step S50, the evaluation execution unit 120 performs noise removal on the corrected luminance image IM1 to create a corrected luminance image IM1c after noise removal. However, step S50 may be omitted.

[0021] In step S60, the evaluation execution unit 120 obtains a crossing fiber index value indicating the amount of crossing fibers from the corrected luminance image IM1c. As the crossing fiber index value, for example, the number of pixels having a luminance value equal to or higher than a luminance threshold included in the corrected luminance image IM1c can be used. The luminance threshold is set in advance experimentally or empirically. In this way, the amount of crossing fibers in the fiber bundle FB can be evaluated.

[0022] Note that, as the crossing fiber index value, other values different from the number of pixels having a luminance value equal to or higher than the luminance threshold may be used. For example, performing a Hough transform on the corrected luminance image IM1c to detect one or more straight lines, and using the histogram of the slopes of those straight lines as the crossing fiber index value may be acceptable.

[0023] As described above, in this embodiment, a masking process is performed on a two-dimensional power spectral image to remove mask regions corresponding to luminance image components whose intersection angle with respect to the horizontal direction of the luminance image is less than or equal to the angle threshold A. Inverse FFT analysis is then performed on the resulting modified power spectral image. As a result, a modified luminance image can be generated that contains only luminance image components whose intersection angle is greater than the angle threshold A, making it easy to evaluate the intersecting fibers in the fiber bundle FB.

[0024] Other forms: This disclosure is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit. For example, this disclosure can also be implemented in the following forms (aspects). The technical features in the embodiments described above that correspond to the technical features in each of the forms described below can be replaced or combined as appropriate in order to solve some or all of the problems of this disclosure, or to achieve some or all of the effects of this disclosure. Furthermore, if such technical features are not described as essential in this specification, they can be deleted as appropriate.

[0025] This disclosure can also be implemented in various forms other than a method for evaluating crossed fibers in a fiber bundle. For example, it can be implemented in the form of an evaluation device or fiber bundle evaluation system for evaluating crossed fibers in a fiber bundle, a computer program that performs the process of evaluating crossed fibers in a fiber bundle, or a non-transitory storage medium on which the computer program is recorded. [Explanation of Symbols]

[0026] 10…Filament winding device, 11…Bobbin, 12…Conveyor roller, 40…High-pressure tank, 100…Fiber bundle evaluation device, 110…Imaging unit, 120…Evaluation execution unit

Claims

1. A method for evaluating crossing fibers in a fiber bundle, (a) A step of acquiring a brightness image of the fiber bundle, (b) A step of generating a two-dimensional power spectrum image by performing a two-dimensional FFT analysis on the luminance image, (c) A step of generating a modified power spectral image by performing a masking process on the two-dimensional power spectral image to remove mask regions corresponding to luminance image components whose intersection angle with respect to the horizontal direction of the luminance image is less than or equal to an angle threshold, (d) A step of generating a corrected luminance image by performing inverse FFT analysis on the corrected power spectrum image, A method for providing this.

2. The method according to claim 1, further, (e) A step of determining the number of pixels in the corrected brightness image that are equal to or greater than the brightness threshold as a cross fiber index value indicating the amount of cross fibers, A method that includes this.

3. The method according to claim 1, The mask region is defined by two isosceles triangles formed by two straight lines that intersect diagonally and symmetrically at the center of the two-dimensional power spectral image, in this method.

4. The method according to claim 3, When the angle threshold is A and the ratio of the width to the height of the brightness image is 1:R, The vertex angle θ of the aforementioned isosceles triangle is given by 2 × arctan(sin(A) / (R × cos(A))).

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