Image acquisition system and image acquisition method

An image acquisition system includes a radiation source configured to output radiation toward an object, a rotating stage configured to rotate the object around a rotation axis, a radiation camera having an input surface to which the radiation transmitted through the object is input and an image sensor capable of TDI control, and an image processing apparatus configured to generate a radiographic image of the object at an imaging plane P based on the image data. The angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera is set in accordance with the FOD which is the distance between the radiation source and an imaging plane in the object. The radiation camera is configured to perform TDI control in the image sensor in synchronization with the rotational speed of the object rotated by the rotating stage.

TECHNICAL FIELD

The present disclosure relates to an image acquisition system and an image acquisition method.

BACKGROUND ART

Conventionally, there is known an apparatus that irradiates a conveyed object with X-rays, detects the X-rays transmitted through the object, and performs TDI (time delay integration) control, thereby acquiring an X-ray image of the object (see Patent Documents 1 and 2). The apparatus disclosed in Patent Document 1 is configured to convey an object by means of a belt conveyor. An X-ray sensor is configured such that a plurality of element rows each having a plurality of detection elements arranged in a direction orthogonal to the conveying direction are arranged in the conveying direction. The apparatus disclosed in Patent Document 2 is configured to rotate a container containing a sample (object) while moving the container in the X direction. A TDI camera performs image capturing in synchronization with the conveying speed of a sample. The angular speed of the container is set to be equal to the ratio between the moving speed in the TDI direction and the distance from the focus of an X-ray source to the rotation center.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the present disclosure, an apparatus that irradiates an object rotated about the rotation axis with radiation and acquires a radiographic image by using a camera capable of TDI control is considered. In this apparatus, the rotation axis intersects with the light receiving surface of the sensor of the camera (or its extended plane). The speed of the inner peripheral portion of an object is different from that of the outer peripheral portion of the object. When TDI control is performed based on the speed of the inner peripheral portion, the acquired radiographic image may be blurred at an outer peripheral portion. That is, when TDI control is performed based on the speed of a given portion of the object in the radial direction, the acquired radiographic image may be blurred at other portions. As described above, speed (peripheral speed) differences due to differences in radius make it difficult to acquire sharp radiographic images by TDI control.

The present disclosure describes an image acquisition system and an image acquisition method which can acquire sharp radiographic images of any portions of an object in the radial direction.

Solution to Problem

An image acquisition system according to one aspect of the present disclosure includes a radiation source configured to output radiation toward an object, a rotating stage configured to rotate the object around the rotation axis, a radiation camera having an input surface to which the radiation transmitted through the object is input and an image sensor capable of TDI (time delay integration) control and configured to capture an image of the input radiation and output image data, and an image processing apparatus configured to generate a radiographic image of the object at an imaging plane based on the image data. The angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera is an acute angle and is set in accordance with the FOD which is the distance between the radiation source and an imaging plane in the object. The radiation camera is configured to perform TDI control in the image sensor in synchronization with the rotational speed of the object rotated by the rotating stage.

An image acquisition method according to another aspect of the present disclosure includes a step (rotation step) of rotating an object around a rotation axis at a predetermined speed by using a rotating stage, a step (radiation output step) of outputting radiation from a radiation source toward the rotating object, a step (radiation image capturing step) of capturing an image of the input radiation and outputting image data by using a radiation camera having an input surface to which the radiation transmitted through the object is input and an image sensor capable of TDI (time delay integration) control, and a step (image generation step) of generating a radiographic image of the object at an imaging plane based on the image data. The angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera is an acute angle and is set in accordance with the FOD which is the distance between the radiation source and an imaging plane in the object. In the step of outputting image data, TDI control in the image sensor is performed in synchronization with the rotational speed of the object rotated by the rotating stage.

According to the image acquisition system and the image acquisition method described above, TDI control in the image sensor is performed in synchronization with the rotational speed of an object rotated by the rotating stage. The speed of an inner peripheral portion (a portion nearest to the rotation axis) of an imaging plane of the object is lower than that of an outer peripheral portion (a portion farthest from the rotation axis). An acute angle is formed between the rotation axis of the rotating stage and the input surface of the radiation camera. The distance between the radiation source and the input surface to which the radiation transmitted through the inner peripheral portion is input is longer than the distance between the radiation source and the input surface to which the radiation transmitted through the outer peripheral portion is input. This indicates that the enlargement factor at the inner peripheral portion is larger than that at the outer peripheral portion. A conveying speed suitable for a predetermined line speed in TDI control is inversely proportional to the enlargement factor. According to the magnitude relationship between the enlargement factors described above, the influence of the speed difference between the inner peripheral portion and the outer peripheral portion is reduced. In addition, the angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera is set in accordance with the FOD which is the distance between the radiation source and an imaging plane in an object to make the ratio between the enlargement factors become the reciprocal of the speed ratio, thereby achieving focus on the inner peripheral portion and the outer peripheral portion. This makes it possible to achieve focus on any portion between the inner peripheral portion and the outer peripheral portion. It is therefore possible to acquire sharp radiographic images of any portions of the object in the radial direction.

According to some aspects, the image acquisition system further includes a stage movement control unit configured to bring the object closer to or move it further from the radiation source by controlling movement of the rotating stage in the rotation axis direction. The stage movement control unit can adjust the distance between the radiation source and the object. In other words, an imaging plane based on the above FOD can be set at an arbitrary position in the object in the rotation axis direction (i.e., the thickness direction). In this case, if the radiation source is immovable, the FOD can be considered constant. It is possible to acquire a radiographic image at an arbitrary position in the object in the thickness direction.

According to some aspects, the image acquisition system further includes an angle adjusting unit configured to hold the rotating stage or the radiation camera and adjust an angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera. In this case, the angle adjusting unit can adjust the angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera to a proper angle in accordance with the FOD.

According to some aspects of the image acquisition system, the angle adjusting unit is configured to adjust an angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera in accordance with an FOD which is a distance between the radiation source and an imaging plane in the object. In this case, focus can be achieved with respect to an arbitrary FOD.

According to some aspects of the image acquisition system, the angle adjusting unit holds the radiation camera so as to tilt the input surface of the radiation camera with respect to the rotation axis. In this case, the angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera can be adjusted to a proper angle in accordance with the FOD by adjusting the posture of the radiation camera.

According to some aspects of the image acquisition system, the angle adjusting unit holds the rotating stage so as to tilt the rotation axis with respect to the input surface of the radiation camera. In this case, the angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera can be adjusted to a proper angle in accordance with the FOD by adjusting the posture of the rotating stage.

According to some aspects of the image acquisition system, the radiation camera includes a scintillator having an input surface, and the image sensor captures an image of scintillation light generated by the scintillator in accordance with input of the radiation. In this case, a sharp radiographic image of the object can be acquired.

According to some aspects of the image acquisition system, the image sensor is a direct conversion type radiation image sensor having the input surface. In this case, a sharp radiographic image of the object can be acquired.

According to some aspects, the image acquisition method further includes a step (movement step) of bringing the object closer to or moving it further from the radiation source by controlling movement of the rotating stage in the rotation axis direction. This step enables adjustment of the distance between the radiation source and the object. In other words, an imaging plane based on the above FOD can be set at an arbitrary position in the rotation axis direction (i.e., the thickness direction) of the object. In this case, if the radiation source is immovable, the FOD can be considered constant. It is possible to acquire a radiographic image at an arbitrary position in the thickness direction of the object.

According to some aspects, the image acquisition method further includes a step (adjusting step) of adjusting an angle between the rotation axis of the rotating stage and the input surface of the radiation camera by causing the rotating stage or the radiation camera to pivot. In this case, the step of adjusting the angle enables adjustment of the angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera to a proper angle in accordance with the FOD.

According to some aspects of the image acquisition method, in the adjusting step, an angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera is adjusted in accordance with an FOD which is a distance between the radiation source and an imaging plane in the object. In this case, focus can be achieved with respect to an arbitrary FOD.

According to some aspects of the image acquisition method, in the adjusting step, the radiation camera is caused to pivot to tilt the input surface of the radiation camera with respect to the rotation axis. In this case, the angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera can be adjusted to a proper angle in accordance with the FOD by adjusting the posture of the radiation camera.

According to some aspects of the image acquisition method, in the adjusting step, the rotating stage is caused to pivot to tilt the rotation axis with respect to the input surface of the radiation camera. In this case, the angle formed between the rotation axis of the rotating stage and the input surface of the radiation camera can be adjusted to a proper angle in accordance with the FOD by adjusting the posture of the rotating stage.

According to some aspects of the image acquisition method, the radiation camera includes a scintillator having the input surface, and in the radiation image capturing step, an image of scintillation light generated by the scintillator in accordance with input of the radiation is captured. In this case, a sharp radiographic image of the object can be acquired.

According to some aspects of the image acquisition method, the image sensor is a direct conversion type radiation image sensor having the input surface. In this case, a sharp radiographic image of the object can be acquired.

Advantageous Effects of Invention

According to some aspects of the present disclosure, it is possible to acquire sharp radiographic images of any portions of an object in the radial direction.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described below with reference to the accompanying drawings. Note that the same reference signs denote the same elements in the description of the drawings, and any overlapping description will be omitted. Also, the respective drawings are prepared for the purpose of description, and are drawn so that the portions to be described are especially emphasized. Therefore, the dimensional ratios of respective members in the drawings are not always coincident with actual ratios.

As shown inFIGS. 1 and 2, an image acquisition system1is an apparatus for acquiring a radiographic image of an object20. The image acquisition system1acquires a radiographic image of a given portion of the object20along, for example, the radial direction. The object20includes a cylindrical wheel portion22centered on, for example, a rotation axis L and a roll portion21wound around the wheel portion22. An annular boundary surface23is formed between the wheel portion22and the roll portion21. The image acquisition system1may be configured such that the wheel portion22is not included in a radiographic image. That is, the image acquisition system1may be configured to acquire a radiographic image of only the roll portion21. The roll portion21is, for example, a chip capacitor wound in a roll shape. The roll portion21may be, for example, a separator wound in a roll shape. The object20may be, for example, one disk without the wheel portion22. In this case, the object20has the rotation axis L. The shape and size of the object20are not specifically limited. The object20may be a circular object (cylindrical or disk-shaped object). Alternatively, the object20may be a non-circular object, which may be, for example, a box-shaped object having corners. The object20may be either an object having finiteness or a deformable object made of a soft material. When the image acquisition system1is used to inspect the object20, the roll portion21is a portion to be inspected, i.e., an inspection portion.

The image acquisition system1acquires a radiographic image at an imaging plane located at a predetermined position in the thickness direction, i.e., the rotation axis L direction. In other words, the image acquisition system1acquires a radiographic image of a portion of the roll portion21at which an imaging plane is focused. The image acquisition system1can detect, for example, a foreign substance or defect that may exist in the roll portion21of the object20by acquiring a radiographic image. The image acquisition system1can detect, for example, an object made of polyamide fiber, polyolefin fiber, split type composite fiber, single fiber, or core-in-sheath type composite fiber and a foreign substance made of a metal that may exist in the object.

The image acquisition system1includes a radiation generator3that generates radiation such as white X-rays. The radiation generator3includes a radiation source2that outputs radiation toward the object20. The radiation source2emits (outputs) cone beam X-rays from an X-ray emission portion. The radiation source2may be, for example, a microfocus X-ray source or millifocus X-ray source. The X-rays emitted from the radiation source2form a radiation flux2a. A region where the radiation flux2aexists is the emission region of the radiation source2. The shape or structure of the X-ray emission portion may be devised such that the wheel portion22of the object20is not included in a radiographic image. The radiation source2is configured so as to be able to adjust a tube voltage and a tube current.

The image acquisition system1includes a rotating stage6configured to hold the object20and rotate the object20around the rotation axis L and a radiation camera4that receives and captures an image of radiation output from the radiation source2and transmitted through the object20. The rotating stage6may include, for example, a motor driven by power feeding, a gear portion coupled to the motor, and a stage body rotated through the gear portion. The rotating stage6rotates, for example, the stage body at a constant speed. In other words, the rotating stage6(or its stage body) has the rotation axis L. The rotational speed of the rotating stage6can be adjusted as appropriate to the display device.

The radiation camera4includes, for example, an input surface11ato which radiation transmitted through the object20is input, a scintillator11that generates scintillation light in accordance with the input of radiation, an FOP (fiber optic plate)12that transmits scintillation light generated by the scintillator11, a light receiving surface13ato which scintillation light transmitted through the FOP12is input, and an image sensor13that captures an image of scintillation light and outputs the image data. The radiation camera4is, for example, an indirect conversion type camera having the FOP12with the scintillator11coupled to the image sensor13. The radiation camera4indirectly captures an image of radiation input to the input surface11aof the scintillator11and outputs the image data.

The scintillator11is a wavelength conversion member having a plate shape (for example, a flat plate shape). The scintillator11converts radiation transmitted through the object20and input to the input surface11ainto scintillation light. Radiation having relatively low energy is converted on the input surface11aside and exits (is output) from the input surface11a. Radiation having relatively high energy is converted on the back surface of the scintillator11and exits (is output) from the back surface.

The FOP12is an optical device having a plate shape (for example, a flat plate shape). The FOP12is formed from, for example, glass fiber, and transfers scintillation light, etc., at high efficiency. The FOP12blocks radiation such as white X-rays.

The image sensor13is an area image sensor that can be TDI (time delay integration)-driven. The image sensor13is, for example, a CCD area image sensor. The image sensor13is configured such that a plurality of element rows each having a plurality of CCDs arranged in series in the pixel direction are arranged in the integration direction in accordance with the moving direction of the object20. The integration direction is a direction orthogonal to the pixel direction and corresponds to a direction perpendicular to the drawing surface inFIGS. 1 to 3. A timing control unit16(to be described later) controls the image sensor13so as to perform charge transfer in accordance with the speed (peripheral speed) of the object20. That is, the image sensor13performs charge transfer on the light receiving surface13ain synchronization with the rotational speed of the object20rotated by the rotating stage6. This makes it possible to obtain a radiographic image with a high S/N ratio.

Note that the image sensor13may be a CMOS area image sensor that can be TDI (time delay integration)-driven. Alternatively, the image sensor13may be a CCD-CMOS image sensor that can be TDI (time delay integration)-driven. For example, a CCD-CMOS image sensor is the image sensor disclosed in Japanese Unexamined Patent Publication No. 2013-098420 or 2013-098853. Note that “being able to be TDI-driven” is equivalent to “being able to be TDI-controlled.”

The image acquisition system1includes an image processing apparatus10that generates a radiographic image of the object20at an imaging plane P based on image data output from the radiation camera4, a display device15that displays the radiographic image generated by the image processing apparatus10, and the timing control unit16that controls the image capturing timing of the radiation camera4. In the image acquisition system1, the radiation generator3is fixed to the radiation camera4, and the object20rotates. The imaging plane P is, for example, a portion set at a predetermined position in or on the object20and is a region that is fixed and is immovable once set.

The image processing apparatus10is composed of, for example, a computer including a CPU (central processing unit), ROM (read only memory), RAM (random access memory), and input/output interface. The image processing apparatus10may include an image processing processor that generates a radiographic image of the object20based on the radiographic image data output from the radiation camera4. The image processing processor, for example, inputs radiographic image data and executes predetermined processing such as image processing for the input radiographic image data. The image processing processor outputs the generated radiographic image.

As the display device15, a known display can be used. Note that an input device (not shown) may be connected to the image processing apparatus10. The input device can be, for example, a keyboard or mouse. The user can input various types of parameters such as the thickness of the object20, the position of the boundary surface23at the object20, and the position of the imaging plane P by using the input device.

The timing control unit16is composed of, for example, a computer including a CPU, ROM, RAM, and input/output interface. The timing control unit16may include a control processor that controls the image capturing timing of the radiation camera4. The control processor controls the radiation camera4and the rotating stage6based on, for example, the thickness of the object20, which is stored upon input, etc., by the user, and the position of the boundary surface23at the object20or the position of the imaging plane P. Note that the image processing apparatus10and the timing control unit16may be configured as programs executed by a single computer or configured as separate units.

The image acquisition system1further includes a stage lifting and lowering machine7for lifting and lowering the rotating stage6in the rotation axis L direction and a stage lifting and lowering control unit (stage movement control unit)17configured to control lifting and lowering (movement) of the rotating stage6of the stage lifting and lowering machine7. As the stage lifting and lowering machine7, a known lifting and lowering machine can be used. The stage lifting and lowering machine7may include, for example, a ball screw disposed on the rotation axis L and penetrating the rotating stage6and the object20and a motor (drive source). The stage lifting and lowering machine7is not limited to a screw-operated lifting and lowering machine and may be, for example, a telescoping lifting and lowering machine using a hydraulic source as a drive source.

The stage lifting and lowering control unit17is composed of, for example, a computer including a CPU, ROM, RAM, and input/output interface. The stage lifting and lowering control unit17may include a control processor that controls the movement of the rotating stage6in the rotation axis L direction. The control processor controls the stage lifting and lowering machine7based on, for example, the thickness of the object20, which is stored upon input, etc., by the user, or the position of the imaging plane P. The stage lifting and lowering control unit17brings the object20closer to or moves it further from the radiation source2by controlling the stage lifting and lowering machine7. That is, the stage lifting and lowering control unit17is configured to bring the object20closer to or move it further from the radiation source2.

Each component of the image acquisition system1described above may be accommodated and fixed in a housing (not shown). Each component described above may be mounted on, for example, a base instead of being accommodated in the housing. All or at least one of the radiation source2, the radiation camera4, and the rotating stage6may be movable to allow the adjustment of the relative positional relationship between them. The image processing apparatus10may be accommodated in the housing or installed outside the housing. All or at least one of the image processing apparatus10, the display device15, the timing control unit16, and the stage lifting and lowering control unit17may be installed in a place separated from the place where the radiation source2, the radiation camera4, and the rotating stage6are provided. The image processing apparatus10, the timing control unit16, and the stage lifting and lowering control unit17may perform control by remote control operations using wireless communication.

The placement and positional relationship of the radiation source2, the rotating stage6, and the radiation camera4will be described next. As shown inFIGS. 1 and 2, the rotating stage6is installed between, for example, the radiation source2and the radiation camera4. More specifically, the rotating stage6is provided at a position where the rotation axis L of the rotating stage6passes through a side of the radiation source2. This positions the boundary surface23of the object20immediately below the radiation source2. In other words, the radiation generator3and the rotating stage6are arranged such that an extended plane of the boundary surface23(a cylindrical surface centered on the rotation axis L in this embodiment) passes through the radiation source2. The emission region of the radiation source2includes or passes through the roll portion21. The radiation camera4is disposed to cause radiation transmitted through the roll portion21of the object20to be input to the input surface11aof the radiation camera4(seeFIG. 2). In other words, the input surface11aof the radiation camera4is provided so as to include a virtual plane including the radiation source2and the rotation axis L.

In this embodiment, the radiation camera4is installed to be tilted such that the input surface11aforms an acute angle with respect to the rotation axis L of the rotating stage6. This reduces the influence of the speed difference between inner and outer peripheral portions of the roll portion21in an obtained radiographic image (to be described in detail later). In this specification, the terms “inner periphery,” “outer periphery,” “radius,” and “radial direction” are used with reference to the rotation axis L. Note that in this specification, the term “radial direction” or “radius” does not necessarily mean that the object20is circular. These terms should be understood as a concept of “a predetermined direction orthogonal to the rotation axis L or a line extending in the direction.”

In this embodiment, the radiation camera4is tilted. In addition, the angle (the acute angle described above) formed between the rotation axis L and the input surface11aof the radiation camera4is set in accordance with the FOD (focus-object distance) as the distance between the radiation source2and the imaging plane P in the object20. This setting will be described in detail below with reference toFIGS. 3 and 4.

The calculation of an FDDoutat an outer peripheral portion and a tilt angle θ of the radiation camera4which are suitable for an FDDinon the inner peripheral side with reference to the FDDinwill be described with reference toFIG. 3. In this case, the FDD (focus-detector distance) is the distance between the radiation source2and the input surface11aof the radiation camera4, and the suffixes “in” and “out” respectively indicate an “inner peripheral portion” and “outer peripheral portion.” First, when the radiation camera4as a TDI camera is driven at an arbitrary line speed, a conveying speed corresponding to the line speed is inversely proportional to an X-ray geometric magnification (i.e., an enlargement factor). An enlargement factor Minat an inner peripheral portion and an enlargement factor Moutat an outer peripheral portion are respectively represented by equations (1) and (2) given below.

In this case, if the relationship represented by equation (3) given below holds, both the inner peripheral portion and the outer peripheral portion come into focus.

Equation (5) is derived from equations (1), (2), and (3) and relational expression (4) (seeFIG. 4) between an angular speed co and a speed v in the tangential direction.

Adjusting the FDD by tilting the radiation camera4so as to satisfy equation (5) will achieve focus on both the inner peripheral portion and the outer peripheral portion. Note that equation (4) is derived from equations (6) and (7) (see alsoFIG. 4) given below. The FOD can be adjusted by changing the ratio between the line speed of the radiation camera4and the rotational speed of the rotating stage6.

Subsequently, when a winding thickness w of the roll is determined according to equation (8), the FDDoutat the outer peripheral portion and the tilt angle θ of the radiation camera4suitable for the FDDinat the inner peripheral portion are calculated with reference to the FDDinaccording to equations (9) to (11). Note that the tilt angle θ can be the angle formed between a plane perpendicular to the rotation axis L and the input surface11aof the radiation camera4.

As described above, in this embodiment, an angle β formed between the rotation axis L and the input surface11aof the radiation camera4is set in accordance with the FOD (focus-object distance) which is the distance between the radiation source2and the imaging plane P in the object20. It is obvious that the relationship of angle β=π/2− angle θ holds. Basically, when the enlargement factor multiplies n-fold, the moving speed of an image on the image sensor13also multiplies n-fold, and hence the TDI control speed (charge transfer speed) multiplies n-fold. In consideration of a practical enlargement factor, the angle θ needs to be set to 20° to 30°.

The operation of the image acquisition system1, i.e., a method for acquiring a radiographic image, will be described next with reference toFIGS. 5 and 6. First, the object20such as a chip capacitor wound in a roll shape is attached to the rotating stage6and is held by the rotating stage6. Next, as shown inFIG. 6, the FOD is determined (Step S01). The FOD can be determined based on a desired enlargement factor.

Next, the stage lifting and lowering control unit17drives the stage lifting and lowering machine7in accordance with the FOD and moves the rotating stage6in the rotation axis L direction (Step S02(movement step)). Next, the object20is rotated about the rotation axis L at a predetermined speed by using the rotating stage6(Step S03(rotation step)). Next, the radiation source2outputs/emits radiation toward the rotating object20(Step S04(radiation output step)). The radiation transmitted through the roll portion21of the object20is input to the input surface11a.

Next, the radiation camera4performs TDI control in the image sensor13in synchronization with the rotational speed of the object20rotated by the rotating stage6(Step S05). That is, the image sensor13is driven at a speed synchronous with the rotational speed of the roll. The radiation camera4then captures an image of an imaging plane (Step S06) and outputs the image data (Step S07) (Steps S05to S07(radiographic image capturing step)). The image processing apparatus10receives the image data output from the radiation camera4and generates a radiographic image at the imaging plane P of the object20(Step S08(image generation step)).

A radiographic image of the imaging plane P is acquired through the above series of processings. With the image acquisition system1and the image acquisition method according to this embodiment, TDI control is performed on the image sensor13in synchronization with the rotational speed of the object20rotated by the rotating stage6. The speed of the inner peripheral portion (the portion nearest to the rotation axis) of the imaging plane P of the object20is lower than that of the outer peripheral portion (the portion farthest from the rotation axis). The angle β as an acute angle is formed between the rotation axis L of the rotating stage6and the input surface11aof the radiation camera4. The distance FDDinbetween the radiation source2and a portion of the input surface11ato which radiation transmitted through the inner peripheral portion is input is longer than the distance FDDoutbetween the radiation source2and a portion of the input surface11ato which radiation transmitted through the outer peripheral portion is input (seeFIG. 3). This indicates that the enlargement factor at the inner peripheral portion is larger than that at the outer peripheral portion (see equations (1) and (2)). A conveying speed suitable for a predetermined line speed in TDI control is inversely proportional to an enlargement factor. According to the above magnitude relationship between enlargement factors, the influence of the speed difference between the inner peripheral portion and the outer peripheral portion is reduced. In addition, the angle formed between the rotation axis L of the rotating stage6and the input surface11aof the radiation camera4is set in accordance with the FOD as the distance between the radiation source2and the imaging plane P in the object20to make the ratio between the enlargement factor at the inner peripheral portion and the enlargement factor at the outer peripheral portion become the reciprocal of the speed ratio, thereby achieving focus on the inner peripheral portion and the outer peripheral portion. This makes it possible to achieve focus on any portion between the inner peripheral portion and the outer peripheral portion. It is therefore possible to acquire a sharp radiographic image of any portion of the object20in the radial direction.

In this case, the image acquisition method may further include a step of bringing the object20closer to or moving it further from the radiation source2by controlling the movement of the rotating stage6in the rotation axis L direction. For example, after Steps S01to S08described above are completed, the object20may be moved in the rotation axis L direction (Step S02). As shown inFIG. 5(a), in the first image generation process, the imaging plane P is set near the lower surface of the roll portion21. Accordingly, as shown inFIG. 5(b), the rotating stage6is lowered by a distance corresponding to ¼ (1/n: n is a natural number) of the thickness in the rotation axis L direction. This makes it possible to move the imaging plane P upward from the lower surface of the roll portion21by a distance corresponding to about ¼ of the thickness and obtain a sharp radiographic image of the imaging plane P. Likewise, as shown inFIG. 5(c)andFIG. 5(d), the position of the imaging plane P can be raised stepwise by lowering the rotating stage6.

This step allows the adjustment of the distance between the radiation source2and the object20. In other words, the imaging plane P based on the FOD described above can be set at an arbitrary position on the object20in the rotation axis L direction (that is, in the thickness direction). In this case, if the radiation source2is immovable, the FOD can be considered constant. It is possible to acquire a radiographic image at an arbitrary position in the object20in the thickness direction.

The radiation camera4including the scintillator11having the input surface11aand the image sensor13that captures an image of scintillation light generated by the scintillator11in accordance with the input of radiation can acquire a sharp radiographic image of the object20.

In the image acquisition method using the image acquisition system1, for example, the image processing apparatus10, the timing control unit16, the stage lifting and lowering control unit17, and the display device15may be set in advance to automatically perform Steps S02to S08at the stage where the input of first parameters (the FOD, etc.) has been completed. In addition, after one radiographic image is acquired at a given imaging plane P, the stage lifting and lowering control unit17may perform 1/n movement to acquire a radiographic image at the next imaging plane P. Acquiring radiographic images at different positions in the thickness direction in this manner can feed back, for example, information concerning a found foreign substance (for example, positional information in the radial direction or thickness direction) to a manufacturing process.

A modification of the first embodiment will be described with reference toFIG. 7. As shown inFIG. 7, the stage lifting and lowering machine7and the stage lifting and lowering control unit17may be omitted, and an image acquisition system1A including a mechanism for lifting and lowering (moving in the rotation axis L direction) the radiation generator3(the radiation source2) instead of the omitted components may be provided.FIG. 7omits the illustration of the lifting and lowering mechanism for the radiation generator3.FIG. 7also omits the illustration of the image processing apparatus10, the display device15, and the timing control unit16(the same applies toFIGS. 10 and 11described below).

Using the image acquisition system1A described above makes it also possible to calculate the tilt angle θ of the radiation camera4in accordance with the FOD by equation (12) given below.

An image acquisition system1B according to the second embodiment will be described next with reference toFIGS. 8 and 9. The image acquisition system1B differs from the image acquisition system1according to the first embodiment in that the stage lifting and lowering machine7and the stage lifting and lowering control unit17are omitted, and the apparatus includes, instead of the omitted components, a pivoting mechanism18and an angle adjusting unit19which are configured to adjust the angle formed between a rotation axis L of a rotating stage6and an input surface11aof a radiation camera4by causing the radiation camera4to pivot. The pivoting mechanism18includes a pivot shaft18acoupled to the radiation camera4, and has a motor, gears, etc., (not shown) to cause the radiation camera4to pivot. The pivoting mechanism18holds the radiation camera4so as to tilt the input surface11aof the radiation camera4with respect to the rotation axis L. The pivot shaft18aof the pivoting mechanism18may be vertical to a virtual plane including a rotation axis L and a radiation source2.

As shown inFIG. 9, an image acquisition method using the image acquisition system1B differs from the image acquisition method using the image acquisition system1in that the FDD is determined (Step S10) and an object20is installed in accordance with the FDD (Step S11) before the determination of the FOD (Step S01), and a tilt angle θ is calculated, after the determination of the FOD (Step S01), based on the FDD, the FOD, and a winding thickness w (see Step S12and equations (11) and (12)) to cause the angle adjusting unit19to control the pivoting mechanism18to set the tilt angle θ, thus adjusting the angle of the radiation camera4(Step S13(adjustment step)). The movement of the stage by the image acquisition system1(see Step S02inFIG. 6) is not performed in this embodiment.

Using the image acquisition system1B makes it also possible to achieve functions and effects similar to those obtained by using the image acquisition systems1and1A. In addition, providing the step of adjusting the angle can properly adjust the angle formed between the rotation axis L of the rotating stage6and the input surface11aof the radiation camera4in accordance with the FOD.

In the step of adjusting the angle, the angle formed between the rotation axis L of the rotating stage6and the input surface11aof the radiation camera4is adjusted in accordance with the FOD as the distance between the radiation source2and the imaging plane P in the object20, and hence focus can be achieved in accordance with an arbitrary FOD.

In the step of adjusting the angle, because the radiation camera4is made to pivot to tilt the input surface11aof the radiation camera4with respect to the rotation axis L, the angle formed between the rotation axis L of the rotating stage6and the input surface11aof the radiation camera4can be adjusted to a proper angle in accordance with the FOD by adjusting the posture of the radiation camera4.

An image acquisition system1C according to the third embodiment will be described with reference toFIGS. 10 and 11. The image acquisition system1C differs from the image acquisition system1according to the first embodiment in that the stage lifting and lowering machine7and the stage lifting and lowering control unit17are omitted, a rotating stage6and an object20are tilted so as not to make an extended plane of a boundary surface23pass through a radiation source2, and a radiation camera4is disposed to make an edge (optical axis) of a radiation flux2acorresponding to the inner peripheral portion of an imaging plane P become orthogonal to an input surface11aof the radiation camera4.

The image acquisition system1C can also achieve effects similar to those represented by equations (1) to (5), and calculates a tilt angle θ of the object20according to equation (13) given below. In the image acquisition system1C, it is obvious that the relationship of angle β=π/2− angle θ holds with respect to the angle β formed between the rotation axis L and the input surface11a.

Note that mechanisms similar to the pivoting mechanism18and the angle adjusting unit19of the image acquisition system1B described above may be applied to the rotating stage6of the image acquisition system1C. In this case, the angle formed between the rotation axis L of the rotating stage6and the input surface11aof the radiation camera4can be adjusted to a proper angle in accordance with the FOD by adjusting the posture of the rotating stage6.

Although the embodiments of the present disclosure have been described above, the present invention is not limited to the above embodiments. For example, the above embodiments each have exemplified the case in which the radiation camera4is an indirect conversion type camera including the FOP12having the scintillator11and coupled to the image sensor13. However, the radiation camera is not limited to this aspect. For example, the present invention may adopt an indirect conversion type radiation camera including the scintillator11coupled to the image sensor13with the FOP12being omitted. In this case as well, the input surface11aof the scintillator11is the input surface of the radiation camera and serves as the angle reference described above. Alternatively, the present invention may adopt a direct conversion type radiation camera constituted by only the image sensor13. In this case, the light receiving surface13aof the image sensor13is the input surface of the radiation camera and serves as the angle reference described above. The direct conversion type radiation camera also allows TDI control by the image sensor13. Alternatively, the present invention may adopt a direct conversion type radiation camera having the FOP coupled to the image sensor13. In this case, the surface of the FOP is the input surface of the radiation camera and serves as the angle reference described above. Even using these direct conversion type radiation image sensors makes it possible to acquire a sharp radiographic image of an object.

The angle formed between the rotation axis L of the rotating stage6and the input surface11aof the radiation camera4may be set in accordance with the FOD and need not be equal to equations (11), (12), and (13). Even if the angle is slightly different from equations (11), (12), and (13), it is possible to acquire sharp radiographic images of any portions in the radial direction. In addition, the present invention is not limited to the image acquisition system in an aspect in which the rotating stage6or the radiation camera4can pivot, and an image acquisition system in which the rotating stage6or the radiation camera4is fixed at the angle “set in accordance with the FOD” with subsequent angle adjustment being inhibited may be provided as one aspect of the present invention.

The present invention may adopt an arrangement capable of adjusting both the angles of the rotating stage6and the radiation camera4. Note that when the rotating stage6is to be tilted, the radiation camera4needs to be tilted more.

An image acquisition system may be provided, which is obtained by combining two or more of the plurality of embodiments described above. For example, an image acquisition system may be provided, which is obtained by combining two or more of the operations of tilting the radiation camera and lifting and lowering the rotating stage6in the image acquisition system1, lifting and lowering the radiation generator3in the image acquisition system1A, making the radiation camera4pivot (angle adjustment) in the image acquisition system1B, and tilting the rotating stage6and the object20in the image acquisition system1C.

A simulation was performed to examine the effects of the image acquisition system1according to the first embodiment. It was assumed that the radius of an inner peripheral portion was represented by rin=120 mm, and the radius of the outer peripheral portion was represented by rout=150 mm. As shown inFIG. 12, with reference to a foreign substance No.1(denoted by reference symbol F1) located in the inner peripheral portion, the speed ratio of a foreign substance No.2(denoted by reference symbol F2) located in the middle in the winding thickness direction is 1.125, and the speed ratio of a foreign substance No.3(denoted by reference symbol F3) located in the outer peripheral portion is 1.25.

In the first comparative example, a simulation was performed under the condition that the radiation camera4was not tilted, i.e., the input surface11aof the radiation camera4was orthogonal to the rotation axis L in the image acquisition system1. In the second comparative example, a simulation was performed under the condition that the radiation camera4was tilted to make the input surface11aof the radiation camera4have an acute angle with respect to the rotation axis L, which was about half of a proper angle corresponding to the FOD. In the first and second comparative examples, a TDI transfer speed was set in accordance with the conveying speed of the foreign substance No.1in the inner peripheral portion. In an embodiment, a simulation was performed under the condition that the input surface11aof the radiation camera4formed an acute angle with respect to the rotation axis L, which was a proper angle corresponding to the FOD. Note that the tilt angle was about 34° in the embodiment, and the tilt angle was about 17° in the second comparative example. The simulation conditions were FDD: 300 mm, and FOD: 100 mm.FIGS. 13, 14, and 15respectively show simulation results in the first comparative example, the second comparative example, and the embodiment. Note that in each drawing, a conveying direction D is also written.

As shown inFIG. 13, when the radiation camera4was not tilted, a radiographic image of the foreign substance No.1was sharp, but images of the foreign substances No.2and No.3were blurred in the conveying direction D because of the speed difference with respect to the foreign substances No.2and No.3, thus resulting in a deterioration in contrast. In addition, as shown inFIG. 14, even when the radiation camera4was tilted but the tilt angle is not proper, images of the foreign substances No.2and No.3were blurred in the conveying direction D because of the speed difference with respect to the foreign substances No.2and No.3, thus resulting in a deterioration in contrast.

As shown inFIG. 15, when the radiation camera4was tilted to set a proper angle corresponding to the FOD, the speed difference (speed ratio) was absorbed, and object images were able to be captured at all positions in the radial direction without blurring.

INDUSTRIAL APPLICABILITY

According to several aspects of the present disclosure, sharp radiographic images of any portions of an object in the radial direction can be acquired.

REFERENCE SIGNS LIST