Patent ID: 12196690

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A structure information acquisition apparatus according to an embodiment of the present invention and a structure information acquisition method using the same will be described below with reference to the drawings. First, as a base of the description, a configuration example of an object from which information is to be acquired will be described.

(Object)

A hydrogen tank for a fuel cell vehicle is used as an object1in the present embodiment. The object1has a liner portion11made of a resin and carbon fibers (that is, anisotropic materials)12wound around the outer periphery of the liner portion11(seeFIG.1).

The liner portion11has a cylindrical shape with both ends closed so that hydrogen can be stored inside. Both ends of the liner portion11are spherical to avoid stress concentration. However, both ends of the liner portion11may have flat surfaces. Also, the liner portion11is not limited to a cylindrical shape, and may have another appropriate shape such as an ellipsoidal shape and a spherical shape.

The carbon fibers12have a hoop-winding (that is, a hoop-layer)121, a high-angle helical winding (that is, a high-angle helical layer)122, and a low-angle helical winding (that is, a low-angle helical layer)123, each being wound around the liner portion11in a layer. As a result, a part of the carbon fibers12is wound in a hoop-winding, and the other parts are wound in different winding directions. Here, the hoop-winding is a fiber wound in a direction substantially perpendicular to a central shaft of the liner portion11. The high-angle helical winding is a fiber wound in an oblique direction with respect to the central shaft of the liner portion11. The low-angle helical winding is a fiber obliquely wound at an angle lower (that is, at an angle closer to parallel to the central shaft of the liner portion11) than that of the high-angle helical winding. Note that, inFIG.1, the ends of the fibers in the respective layers are separated from the liner portion11for easy understanding, but in an actual hydrogen tank, the fibers are tightly wound around the liner portion11(See, for example, Japanese Patent Laid-Open No. 2015-214087).

Further, with reference toFIG.2, a cross-sectional structure of the object1will be described.FIG.2schematically shows the structure for easy understanding, and the dimensional ratio is not accurate. As shown inFIG.2, the hoop-winding121, the high-angle helical winding122, and the low-angle helical winding123are arranged in layers. Note that the stacking order of these layers is not limited to the example inFIG.2. Due to the structure described above, the object1of the present embodiment has fibers that are each a long anisotropic material curved in an arc shape.

(Structure Information Acquisition Apparatus of the Present Embodiment)

Next, the structure information acquisition apparatus according to the present embodiment will be described with reference toFIGS.3to5.

This apparatus mainly has a phase-contrast X-ray optical system2for acquiring a scattering image of the object1and a processing unit3(seeFIG.3). Further, the apparatus has a control unit4, an output unit5and a support mechanism6(seeFIG.3). Note that the shape of the object1shown inFIG.3is different from that shown inFIG.1in that both ends are flat, and the central shaft13protrudes outward from both end surfaces. However, the basic configuration is the same as the example ofFIG.1.

(Phase-Contrast X-Ray Optical System)

The phase-contrast X-ray optical system2has a grating unit21, a radiation source22for irradiating the grating unit21and the object1with X-rays, and a detection unit23for detecting X-rays having passed through the grating unit21and the object1.

The grating unit21has a G0 grating211, a G1 grating212, and a G2 grating213for constituting a Talbot-Lau interferometer. Further, this grating unit21has a grating drive unit214for driving the G1 grating212to perform what is called a fringe scanning method. The G0 grating211is an absorption grating through which X-rays, from the radiation source22generating non-coherent X-rays, penetrate to equivalently generate a plurality of coherent point light sources. In other words, the G0 grating211can be said to be substantially a part of the radiation source. In this example, the periodic direction of the gratings of the G0 to G2 gratings211to213are the direction perpendicular to the axis of the object1(seeFIG.5described later), but can also be the direction parallel to the axis of the object1. The grating drive unit214can use an appropriate drive mechanism capable of driving the grating by predetermined steps at required timing, such as a ball screw, linear motor, piezo element, or electrostatic actuator.

The radiation source22is used for generating X-rays of required intensity and irradiating the grating unit21and the object1with them. The radiation source22can use a source that generates non-coherent X-rays in the case of a Talbot-Lau interferometer configuration. In a case in which the G0 grating is omitted, a radiation source is used which generates X-rays phases of which are spatially aligned (that is, coherent) to the extent necessary for practical use (for example, a minute point light source, etc.). In the present embodiment, the direction of X-rays from the radiation source22to the object1is along the tangential direction of the curved carbon fibers12. This point will be further described later.

The detection unit23has a plurality of pixels (not shown) capable of providing practically sufficient resolution, and can acquire, with these pixels, an intensity distribution image of X-rays that have passed through the grating unit21and the object1. The intensity distribution image acquired by the detection unit23is sent to the processing unit3.

Since the phase-contrast X-ray optical system2used in the present embodiment may be basically the same as that conventionally used, further detailed description is omitted (reference: International Publication No. WO 2004/058070, Pfeiffer F, Weitkamp T, Bunk O, David C, Phase retrieval and differential phase-contrast imaging with low-brilliance X-ray sources. Nat. Phys. 2 (2006) 258-261).

(Processing Unit)

The processing unit3has: a scattering image generation unit31for obtaining a scattering image based on the intensity distribution image of the X-rays obtained by the detection unit23of the phase-contrast X-ray optical system2; and an extraction unit32for extracting structure information of the carbon fibers12from the obtained scattering image (seeFIG.4).

Operation of the scattering image generation unit31and the extraction unit32will be described later. The processing unit3is specifically implemented by a combination of computer hardware and software.

(Control Unit)

The control unit4controls the drive amount (i.e., movement amount or movement angle) and drive time of each of the grating drive unit214, an axial drive unit63(described later), and a circumferential drive unit64(described later) of the support mechanism6. The control unit4is also implemented by a combination of computer hardware and software. The functions of the control unit4may be implemented in the processing unit3to integrate both.

(Output Unit)

The output unit5is used for outputting a result of processing with the processing unit3to a user or other equipment. The output unit5is, for example, a display or a printer, but may be an interface for connecting other equipment that receives the result of processing. Also, the output unit5may be one that transmits the result of processing to other equipment via a network.

(Support Mechanism)

The support mechanism6supports the object1so that the direction of X-rays radiated from the radiation source22of the phase-contrast X-ray optical system2is in the tangential direction of the curved carbon fibers12. Specifically, the support mechanism6of the present embodiment has: a base61fixed to the floor side; a support62mounted on the base61; an axial drive unit63for driving the support62; and a circumferential drive unit64for rotating the object1.

The support62has: a slide unit621that is movable in the axial direction of the object1(or the length direction of the base61) with respect to the base61; and two support arms622projecting upward from the slide unit621. The slide unit621can be moved by a predetermined distance in the axial direction of the object1by the axial drive unit63. The support arms622supports the central shaft13(seeFIG.3) protruding outward from the axial ends of the object1to hold the object1at an appropriate height. Thus, the support62of the present embodiment supports the object1so that the axis of the object1is oriented in horizontal direction.

Further, the support62arranges the object1between the G1 grating212and the G2 grating213. The support62of the present embodiment also supports the object1(SeeFIGS.5and6) so that the direction of X-rays radiated from the radiation source22of the phase-contrast X-ray optical system2is along the tangential direction of the curved carbon fibers12. Here,FIG.6schematically shows only the positional relationship between a part of the hoop-winding121in the carbon fiber12, the G2 grating213, and the X-rays. Further, the support62supports the object1so that the X-ray irradiation range (field of view) is off the axis of the object1(seeFIG.5).

The axial drive unit63can move the slide unit621by a predetermined distance at a predetermined time in response to a command from the control unit4.

The circumferential drive unit64is connected to the central shaft13of the object1, and can rotate the object1by a predetermined angle at a predetermined time in response to a command from the control unit4.

(Structure Information Acquisition Method in the Present Embodiment)

An example of a method of acquiring structure information of the object1using the above-described apparatus will be described below with further reference toFIG.7.

(Step SA-1inFIG.7)

First, the object1is supported by the support mechanism6, as shown inFIG.3. In this state, the object1is substantially horizontal. At this time, the object1is supported so that the direction of X-rays radiated from the radiation source22of the phase-contrast X-ray optical system2is along the tangential direction of the curved carbon fibers12(seeFIGS.5and6). Thereby, the object1can be irradiated with X-rays from the radiation source22of the phase-contrast X-ray optical system2in the tangential direction of the curved carbon fibers12. Here, a deviation of about ±5° is normally allowed as the X-ray irradiation angle. In other words, the irradiation angle of X-rays may be accurate enough for practical use, and does not need to be mathematically exact. In addition, in the present embodiment, as shown inFIG.5, the axis of the object1is off the field of view and the outer peripheral surface of the object1is arranged within the field of view. This facilitates the work of setting the X-ray irradiation direction to the tangential direction of the carbon fibers12.

(Step SA-2inFIG.7)

The X-rays radiated from the radiation source22toward the object1pass through the grating unit21and the object1and reach the detection unit23. More specifically, in the present embodiment, X-rays penetrate through the G0 grating211, the G1 grating212, the object1, and the G2 grating213in this order, and reach the detection unit23. The detection unit23acquires an intensity distribution image (that is, a detection signal or an image signal) of the X-rays that have reached the detection unit23. The acquired intensity distribution image is sent to the processing unit3. Here, in the present embodiment, a usual fringe scanning method is performed. In other words, the control unit4drives the grating drive unit214of the grating unit21to move the grating (G1 grating in this example) by appropriate steps. An intensity distribution image is acquired at each step.

(Step SA-3inFIG.7)

The scattering image generation unit31of the processing unit3acquires a scattering image using the obtained intensity distribution image. The scattering image acquisition method itself may be the same as a conventionally known method, so detailed description thereof will be omitted.

(Steps SA-4and SA-5inFIG.7)

Next, the extraction unit32of the processing unit3acquires structure information of the anisotropic materials based on the scattering image. More specifically, the extraction unit32extracts regions where intensive scattering occur, and identifies the regions as a sectional image of fibers in a specific angular range. The principle of this extraction will now be described with further reference toFIG.8.

FIG.8shows the relationship between the fiber angle θ° and the scattering intensity F(θ). As can be seen from this figure, the scattering intensity reaches a maximum at the fiber angle θ=0°, and decreases as θ increases (or decreases).

This point will be schematically described with further reference toFIG.9. If the curved fibers have layer structures as shown inFIG.9(A), the intensity distribution image resolved by X-rays radiated in a direction of an arrow in the figure (that is, the tangential direction of the fiber) has a gradation with unclearly defined regions and low contrast, as shown inFIG.9(B). This makes it difficult to measure the layer structures.

On the other hand, as shown inFIG.9(D), the scattering image has a fringe pattern with clear contrast according to the fiber angle θ. Thus, in the present embodiment, the scattering image can be used to determine fiber regions in a specific angular range. Note that the density inFIG.9(C)is lighter than that inFIG.9(A), but this is because a scattering image is used, and the physical structure of the object is the same as inFIG.9(A). In addition,FIG.9is for schematic description only. When an object including curved fibers is irradiated with X-rays, the direction of the fibers locally matches the direction of the X-rays (within approximately ±5°), generating intensive scattering. The extraction unit32can extract only this intensive scattering using, for example, an appropriate threshold value, to generate a sectional image having a slice thickness made up of a certain angular range component. From the sectional image, it is possible to determine the fiber regions that are substantially aligned with the X-ray irradiation direction.

(Step SA-6inFIG.7)

The extraction unit32can generate and output positional information (ends, area, length) of fiber regions that are substantially aligned with the X-ray irradiation direction and information on an angular distribution within the regions. In other words, the processing unit3can calculate various kinds of information, such as positional information and distribution information, about fiber regions within a specific angular range, and send the calculated information to the output unit5. The output unit5can output these pieces of information to the user or other equipment. A specific example of the information to be extracted will be described as Example 1 below.

After acquisition of information on a predetermined part, the control unit4drives the circumferential drive unit64to rotate the object1, and this makes it possible to acquire structure information of another part of the object1(a part shifted in the circumferential direction). Further, the control unit4drives the axial drive unit63to move the object1in the axial direction, and this makes it possible to acquire structure information of yet another part of the object1(a part shifted in the axial direction). Either of the circumferential drive unit64and the axial drive unit63may be driven first, or they may be driven at the same time. In addition, before or during processing in the processing unit3(that is, generation of the scattering image or extraction of information), the object1may be appropriately driven to sequentially acquire intensity distribution images at required positions.

According to the method of the present embodiment, the position of an anisotropic material such as carbon fiber can be acquired non-destructively and accurately based on the contrast of the scattering image, without using CT. In the present embodiment, since there is no need to use CT, it is possible to target a large object such as a hydrogen tank.

Example 1

There is shown an example of the scattering image acquired with the method of the present embodiment inFIG.10(A). Using a scattering image makes an image with a well-defined regions and clear contrast, and this makes it possible to identify the layer structures.FIG.10(B)shows an example in which the fiber orientation structures corresponding to the hoop-layer and the highly helical layer are identified based on the image. White lines here indicate the borders of the regions. Examples of information corresponding to individual specific regions are shown inFIGS.10(C) and10(D). These figures show histograms and statistics of scattering intensity within the regions. Here, for example, the histogram inFIG.10(C)is asymmetric with respect to the peak, and has many pixels with low luminance values. This suggests that there are many fibers oriented away from the X-ray incident direction. Conversely, the histogram inFIG.10(D)indicates that there are many pixels with high luminance values and many fibers are oriented close to the X-ray incident direction. Further, it is also possible to quantitatively evaluate the orientation unevenness of the fibers from statistical quantities such as the dispersion and the kurtosis of the scattering intensity within the region.

In addition,FIG.11illustrates two types of extracted regions and their areas (the number of pixels). This is also an example of information corresponding to the region.

Thus, in the present embodiment, quantitative information regarding the position and orientation of fibers can be acquired.

Example 2

Here, the positional relationship between the grating unit21and the object1will be described in detail as Example 2. In the embodiment described above, it is preferable to set the position of the object1(particularly, the region where the orientation of the fiber to be imaged matches the X-ray incident direction) within the range from the midpoint of the G1 grating212and the G2 grating213to the G2 grating213, with what is called an inverse geometry (meaning the grating period (G0 period) of the G0 grating211the grating period (G2 period) of the G2 grating213, with reference to T. Donath, et al, “Inverse geometry for grating-based x-ray phase-contrast imaging”, J. Appl. Phys., 106 (2009) 054703). The reason is as follows.

The optical system of the present embodiment is designed with the expectation of two effects. One is to decrease the effect of defocusing, and the other is to decrease the sensitivity to scattering. To maximize the former effect, it is desirable to place the object1at a position as close to the detection unit23as possible. The latter effect depends on the structure of the object1, so it does not necessarily have to be maximized, but at least it is important to keep the object1away from the G1 grating212and closer to the G2 grating213. This is because the scattering from the fiber that corresponds with the X-ray incident direction is extremely intensive, so that the measurement with the fiber being placed at a position close to the G1 grating212lowers the coherence of X-rays too much, requiring an extremely long period of measurement.

Here, in a general Talbot-Lau interferometer (G0 period>G2 period), the distance between the detection unit23and the G1 grating212is small, and it is difficult to bring the object1closer to the G2 grating213. Instead, it is preferable in the present embodiment to employ an inverse geometry so as to be G0 period<G2 period. This makes it easier to employ a configuration in which the object1is inserted between: the midpoint of the G1 grating212and the G2 grating213; and the G2 grating213, and the above two effects are likely to be exhibited.

Note that the description of the embodiment and examples is merely an example, and does not show the configuration essential to the present invention. The configuration of each unit is not limited to the above as long as the gist of the present invention can be achieved.

For example, the anisotropic material may be curved to form an ellipse.

Also, the number of layers in the carbon fibers12is not limited to two or three, and may be one, or four or more.

Further, although the above embodiment is described based on the fringe scanning method, a Fourier transform method can also be used to acquire an X-ray phase image. It is also possible to perform a substantial fringe scanning method by moving the object1instead of moving any of the gratings stepwise.

Further, the object1is not limited to a hydrogen tank. It is possible to use another structure with curved anisotropic materials, as an object. Here, the object1is not limited to a large-sized sample such as a tank, and may be a small-sized sample.

Further, the work of extracting structure information from the scattering image can be performed by an operator instead of the processing unit3.

Also, the G0 grating can be omitted by using a structured target substantially equivalent to the G0 grating as the radiation source22.

Further, as the grating unit21, a grating unit called edge illumination can be used to generate a scattering image without using the configuration of the Talbot-Lau interferometer (reference: A. Olivo, “Edge-illumination x-ray phase-contrast imaging”, J. Phys.: Condens. Matter 33 (2021) 363002).

In addition, if it is desired to increase the sensitivity to scattering for a structural reason of the object1, it is desirable to employ a general Talbot-Lau interferometer instead of an inverse geometry, and insert the object1between the midpoint of the G1 grating212and G2 grating213and the G1 grating212.

Furthermore, it is also possible to acquire a plurality of scattering images by varying the periodic direction in the grating unit and to compare them to extract the scattering component based on the anisotropy in a specific direction.

REFERENCE SIGNS LIST

1object11liner portion12carbon fiber (anisotropic material)121hoop-winding (hoop-layer)122high-angle helical winding (high-angle helical layer)123low-angle helical winding (low-angle helical layer)13central shaft2X-ray optical system3processing unit31scattering image generation unit32extraction unit21grating unit211G0 grating212G1 grating213G2 grating214grating drive unit22radiation source23detection unit4control unit5output unit6support mechanism61base62support621slide unit622support arm63axial drive unit64circumferential drive unit