Patent Publication Number: US-2022233161-A1

Title: Radiography apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application No. PCT/JP2020/039422, filed Oct. 20, 2020, the disclosure of which is incorporated herein by reference in its entirety. Further, this application claims priority from Japanese Patent Application No. 2019-199330, filed on Oct. 31, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a radiography apparatus. 
     2. Description of the Related Art 
     A radiography apparatus is known which includes an arm having two end portions of a first end portion and a second end portion, one of which an irradiation unit that emits radiation is provided in and the other of which an image receiving unit that receives the radiation emitted from the irradiation unit and transmitted through a subject is attachable to (see JP1996-229027A (JP-H08-229027A)). The arm has an arc shape in a side view and is called, for example, a C-arm. 
     This arm can be orbitally rotated around the subject in a posture in which the irradiation unit and the image receiving unit face each other. The arm is supported by a support portion that has a track portion fitted to an arc-shaped outer peripheral portion of the arm. In a case in which the outer peripheral portion of the arm is moved along the track portion, the arm is orbitally rotated about the center of the arc shape as the center of rotation. 
     In addition, the arm is provided with a cable that is used for electrical connection to each of the irradiation unit and the image receiving unit. The cable is provided in the outer peripheral portion of the arm and is drawn into the support portion. For example, in a case in which the cable is provided from the first end portion of the arm to the support portion, the length of the cable is determined according to the rotation range of the orbital rotation of the arm. The maximum length of the cable from the support portion to the first end portion of the arm is the length to a position where the first end portion is farthest from the support portion. Therefore, in a case in which the arm is orbitally rotated in a first direction in which the first end portion approaches the support portion, the cable is loosened by the amount of movement the first end portion to the support portion. In a case in which the cable is loosened, a loosened portion interferes with work. Therefore, it is necessary to take measures to suppress the loosening of the cable. 
     In order to solve this problem, for example, the radiography apparatus (X-ray apparatus) disclosed in JP1996-229027A (JP-H08-229027A) comprises a winding drum that winds the cable (electric wire), a pulley that can be coaxially rotated integrally with the winding drum, and a wire that is wound around the pulley and applies tension to the cable. 
     According to the radiography apparatus disclosed in JP1996-229027A (JP-H08-229027A), in a case in which the arm is orbitally rotated, the wire is unwound from the pulley to rotate the pulley. The cable is wound around the winding drum by rotating the pulley to rotate the winding drum. Tension is applied to the cable by unwinding the wire to rotate the pulley and the winding drum in this way, and the loosening of the cable is suppressed by the application of the tension. 
     SUMMARY 
     However, in a case in which there is a difference between the diameter of the cable (electric wire) and the diameter of the wire, the winding perimeters of the winding drum and the pulley change depending on the amount of winding. The winding perimeter indicates the amount of winding of the cable or the wire in the unit amount of rotation of each of the winding drum and the pulley and is, for example, the length of the cable that can be wound in a case in which the winding drum makes one rotation. In a case in which the diameter of the cable is large and the cable is wound in double or triple layers, the diameter of the winding drum becomes large. Therefore, the winding perimeter also becomes large. In addition, in a case in which there is a difference between the diameter of the cable and the diameter of the wire and the amount of winding increases due to lap winding, a difference between the amount of change in the winding perimeter of the cable on the winding drum and the amount of change in the winding perimeter of the wire on the pulley increases. 
     In a case in which there is a difference between the winding perimeter of the cable on the winding drum and the winding perimeter of the wire on the pulley, the following problems occur. For example, as a first case, the following is considered: in a case in which the winding perimeter of the cable on the winding drum is larger than the winding perimeter of the wire on the pulley, the arm is rotated in a direction in which the cable is wound around the drum, that is, in a direction in which the first end portion connected to the cable approaches the support portion. 
     In the first case, the amount of unwinding of the wire from the pulley having one end fixed to the second end portion is determined according to the amount of orbital rotation of the arm, and the pulley and the winding drum are rotated in the same direction by the same amount according to the amount of unwinding. Then, since the winding perimeter of the winding drum is larger than that of the pulley, the cable is wound on the winding drum by an amount equal to or more than the amount of unwinding, and tension more than necessary which exceeds the tension required for winding is applied to the cable. In a case in which tension more than necessary is applied to the cable, there is a concern that the cable will be broken, which is not preferable. 
     Further, as a second case, the following is considered: the arm is orbitally rotated in a direction in which the cable is unwound from the winding drum, contrary to the first case. In the second case, the amounts of rotation of the winding drum and the pulley are determined according to the amount of unwinding of the cable from the winding drum. Since the winding perimeter of the pulley is smaller than the winding perimeter of the winding drum, the amount of winding of the wire is insufficient with respect to the amount of unwinding of the cable. Therefore, in the second case, the wire is loosened. 
     As described above, the following problem occurs: tension more than necessary is applied to the cable or a tension member that applies tension to the cable is loosened due to the difference between the winding perimeter of the cable and the winding perimeter of the tension member. 
     Here, the X-ray apparatus disclosed in JP1996-229027A (JP-H08-229027A) is configured such that a conical pulley whose diameter changes along the direction of the rotation shaft is used as the pulley and a wire guide groove through which the wire is guided is spirally formed in a conical surface of the pulley to prevent the occurrence of the difference between the winding perimeter of the cable (electric wire) wound over and over and the winding perimeter of the wire (see paragraph 0022 and FIG. 12 in JP1996-229027A (JP-H08-229027A)). However, in a case in which the conical pulley having the spiral wire guide groove formed therein is manufactured, processing is complicated and costly. Therefore, it has been required to more easily solve the problems caused by the difference between the winding perimeter of the cable and the winding perimeter of the tension member. 
     The technology according to the present disclosure provides a radiography apparatus that can more easily solve problems caused by a difference between a winding perimeter of a cable and a winding perimeter of a tension member. 
     According to a first aspect of the present disclosure, there is provided a radiography apparatus comprising: an arm that has a first end portion and a second end portion, one of which an irradiation unit that emits radiation is provided in and the other of which an image receiving unit that receives the radiation emitted from the irradiation unit and transmitted through a subject is attachable to, has an arc shape in a side view, and is orbitally rotatable around the subject in a posture in which the irradiation unit and the image receiving unit face each other; a support portion that has a track portion fitted to an outer peripheral portion of the arc shape of the arm and supports the arm to be orbitally rotatable; a cable that has one end electrically connected to at least one of the irradiation unit or the image receiving unit and is provided along an outer periphery of the arm from the first end portion of the arm to the support portion; a tension member that is used to apply tension to the cable in a case in which the arm is orbitally rotated in a first direction in which the first end portion approaches the support portion, has one end fixed to the second end portion of the arm, and is provided along the outer periphery of the arm from the second end portion to the support portion; a first reel that is rotated in a direction in which the cable is wound in a case in which the arm is orbitally rotated in the first direction and is rotated in a direction in which the cable is unwound in a case in which the arm is orbitally rotated in a second direction in which the second end portion approaches the support portion; a second reel that is rotated in a direction in which the tension member is unwound in a case in which the arm is orbitally rotated in the first direction, is rotated in a direction in which the tension member is wound in a case in which the arm is orbitally rotated in the second direction, and is provided to be independently rotatable with respect to the first reel; and a rotational force transmission member that, in a case in which one of the first reel and the second reel is rotated, transmits a rotational force in the same direction to the other, biases the first reel in a winding direction of the cable, biases the second reel in a winding direction of the tension member, and allows occurrence of a difference between an amount of rotation of the first reel and an amount of rotation of the second reel within a preset range in the transmission of the rotational force. 
     According to the above configuration, the cable that is provided along the outer periphery of the arm from the first end portion of the arm is wound around the first reel. Further, the tension member that is provided along the outer periphery of the arm from the second end portion of the arm is wound around the second reel. Therefore, in a case in which the arm is orbitally rotated, one of the cable and the tension member is wound and the other is unwound. 
     Here, the first reel and the second reel can be rotated independently of each other. In a case in which one of the first reel and the second reel is rotated, the rotational force in the same direction is transmitted to the other by the rotational force transmission member. The rotational force transmission member biases the first reel in the winding direction of the cable and biases the second reel in the winding direction of the tension member (the side opposite to the winding direction of the cable on the first reel). Further, the rotational force transmission member allows the occurrence of the difference between the amount of rotation of the first reel and the amount of rotation of the second reel within the preset range in a case in which the rotational force is transmitted. 
     Therefore, in a case in which the arm is orbitally rotated in the first direction, the second end portion is separated from the support portion. Therefore, the tension member rotates the second reel in the unwinding direction. The rotational force is transmitted from the second reel to the first reel by the rotational force transmission member, and the first reel is rotated in the same direction as the second reel. Since the unwinding direction of the second reel is the same as the winding direction of the first reel, the first reel winds the cable. Therefore, the loosening of the cable between the first end portion and the support portion is suppressed. 
     In addition, the rotational force transmission member biases the first reel in the winding direction of the cable and biases the second reel in the winding direction of the tension member. Further, the rotational force transmission member allows the occurrence of the difference between the amount of rotation of the first reel and the amount of rotation of the second reel within the preset range in a case in which the rotational force is transmitted. 
     Therefore, even in a case in which the winding perimeter of the cable on the first reel and the winding perimeter of the tension member on the second reel change due to the difference between the diameter of the cable and the diameter of the tension member, it is possible to perform the unwinding of the tension member and the winding of the cable while adjusting the amount of rotation of the first reel and the amount of rotation of the second reel by the difference between the winding perimeters. Therefore, it is possible to prevent tension more than necessary from being applied to the tension member and the cable or the occurrence of loosening due to the difference between the winding perimeters. 
     In the related art, in order to solve these problems, complicated processing, such as manufacturing a conical pulley having a spiral wire (tension member) guide groove formed therein, is performed to prevent the occurrence of the difference between the winding perimeters. On the other hand, according to the technology of the present disclosure, it is not necessary to perform the complicated processing. Therefore, it is possible to more easily solve the problems caused by the difference between the winding perimeter of the cable and the winding perimeter of the tension member. 
     According to a second aspect of the present disclosure, in the radiography apparatus according to the first aspect, the first reel and the second reel may be disposed coaxially. 
     According to the above configuration, since the first reel and the second reel are disposed coaxially, the configuration is simpler than a configuration in which the first reel and the second reel are disposed on different axes, and it is possible to save space. 
     According to a third aspect of the present disclosure, in the radiography apparatus according to the first aspect or the second aspect, the first reel and the second reel may be provided in the support portion. 
     According to the above configuration, since the support portion is a connection portion between the arm and the main body portion, it functions as a cable relay portion between the arm and the main body portion. The provision of the first reel in the support portion makes it easy to provide the cable. In addition, since the support portion is a portion serving as a base point of the arm that is orbitally rotated, it is an optimal position for drawing the cable and the tension member provided in the outer peripheral portion of the arm from the viewpoint of suppressing the complexity of the configuration. The provision of the first reel and the second reel at this position makes it possible to suppress the complexity of the configuration. 
     According to a fourth aspect of the present disclosure, in the radiography apparatus according to any one of the first to third aspects, in a case in which a thickness of the cable is larger than a thickness of the tension member, a first radius of a winding portion of the first reel in a state in which the cable is not wound may be smaller than a second radius of a winding portion of the second reel in a state in which the tension member is not wound. 
     According to the above configuration, in a case in which the thickness of the cable is larger than the thickness of the tension member, the first radius of the winding portion of the first reel is smaller than the second radius of the winding portion of the second reel. Therefore, it is possible to suppress an increase in the difference between the winding perimeter of the cable and the winding perimeter of the tension member in a case in which the cable and the tension member are wound by the first reel and the second reel, respectively. In addition, the winding portion means a portion on which the cable or the tension member is wound in the first reel and the second reel. 
     According to a fifth aspect of the present disclosure, in the radiography apparatus according to the fourth aspect, the first radius may be smaller than the second radius, and a difference between the first radius and the second radius may be equal to a difference between the thickness of the cable and the thickness of the tension member. 
     According to the above configuration, the difference between the first radius of the first reel and the second radius of the second reel is equal to a difference between the height of the cable and the height of the tension member. Therefore, in a state in which the cable and the tension member are wound once around the first reel and the second reel, respectively, the winding perimeter of the cable and the winding perimeter of the tension member are equal to each other. 
     This configuration in which the winding perimeter of the first reel in a state in which the cable is wound once and the winding perimeter of the second reel in a state in which the tension member is wound once are equal to each other makes it possible to reduce the maximum value of the difference between the winding perimeter of the cable and the winding perimeter of the tension member in a case in which the cable is wound a plurality of times. 
     According to a sixth aspect of the present disclosure, in the radiography apparatus according to any one of the first to fifth aspects, the cable may include a first cable for applying a voltage to a radiation tube of the irradiation unit. 
     According to the above configuration, since a relatively high voltage is applied to the radiation tube, the thickness of the insulating coating of the cable for applying the voltage is large. Therefore, the diameter of the cable for applying the voltage tends to be large. On the other hand, since the tension member only needs to apply tension, it is possible to reduce the diameter of the tension member. As described above, in a case in which the cable is a cable for applying a voltage to the radiation tube, a change in the difference between the winding perimeters corresponding to the amount of winding of the first reel and the difference between the winding perimeters of the first reel and the second reel also tend to be large. Therefore, it is highly necessary to adopt the technology of the present disclosure. 
     According to a seventh aspect of the present disclosure, in the radiography apparatus according to the sixth aspect, the cable may include the first cable and a second cable that is connected to the image receiving unit. The first cable and the second cable may be provided as a bundled cable group in an outer peripheral portion of the arm between the first reel and the first end portion, and the cable group may be fixed in the first end portion. The first cable and the second cable may branch off on a side opposite to the first reel with respect to a position where the cable group is fixed, one of the first cable and the second cable may be connected to one of the irradiation unit and the image receiving unit which is provided in the first end portion, and the other cable may be provided inside the arm to extend to the second end portion and may be connected to the other of the irradiation unit and the image receiving unit which is provided in the second end portion. 
     According to the above configuration, the first cable and the second cable are provided as a bundled cable group in the outer peripheral portion of the arm between the first reel and the first end portion. Since the cables provided in the outer peripheral portion of the arm are concentrated on the first end portion side of the arm, the complexity of electrical wiring is suppressed, as compared to a case in which the cables are provided in each of the first end portion and the second end portion in the outer peripheral portion of the arm. 
     According to an eighth aspect of the present disclosure, in the radiography apparatus according to any one of the first to seventh aspects, the irradiation unit may be provided in the first end portion. 
     According to the above configuration, in a case in which the radiography apparatus is used for moving image capture (also referred to as fluoroscopy), the irradiation unit is often disposed below the subject, and the image receiving unit is often disposed above the subject. In many cases, a moving image is captured during surgery. In this case, it is not preferable that a portion of the arm in which the cable is provided is disposed above the subject. For example, the reason is that, in a case in which the cable is loosened above the subject, the loosening may interfere with the surgery. 
     Therefore, the irradiation unit, which is often disposed below the subject in the capture of a moving image, is provided in the first end portion of the arm. As a result, in a case in which a moving image is captured, the portion of the arm in which the cable is provided can be disposed below the subject. 
     According to a ninth aspect of the present disclosure, in the radiography apparatus according to any one of the first to eighth aspects, the other end of the tension member may be fixed to the second reel. 
     According to the above configuration, since the other end of the tension member is fixed to the second reel, the length of the tension member can be smaller than that in, for example, a configuration in which both ends of the tension member are fixed to one end and the other end of the arm through the second reel. Therefore, it is possible to prevent the configuration of the second reel from being complicated. 
     According to a tenth aspect of the present disclosure, in the radiography apparatus according to any one of the first to ninth aspects, the tension member may be a belt or a wire. 
     According to the above configuration, since the belt or the wire is used as the tension member, it is possible to reduce the diameter of the tension member, and tension can be applied to the cable by the tension member. 
     According to an eleventh aspect of the present disclosure, in the radiography apparatus according to any one of the first to tenth aspects, the rotational force transmission member may be a spring that connects the first reel and the second reel and is expanded and contracted in a case in which the first reel and the second reel are rotated in opposite directions. 
     According to the above configuration, since the spring is used as the rotational force transmission member, it is possible to bias the first reel and the second reel in the winding directions of the cable and the tension member, respectively, while transmitting the rotational force with a simple configuration. 
     According to a twelfth aspect of the present disclosure, in the radiography apparatus according to the eleventh aspect, the spring may have one end that is attached to a first pin provided on a side surface of the first reel and the other end that is attached to a second pin provided on a side surface of the second reel. 
     According to the above configuration, since the first pin and the second pin attached to both ends of the spring are provided on the side surface of the first reel and the side surface of the second reel, respectively, it is possible to attach the spring to the first reel and the second reel with a simple configuration. 
     According to the technology of the present disclosure, it is possible to more easily solve the problems caused by the difference between the winding perimeter of the cable and the winding perimeter of the tension member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments according to the technique of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is an overall perspective view illustrating a radiography apparatus according to an example of an embodiment, 
         FIG. 2A  is a side view illustrating the radiography apparatus according to an example of the embodiment, 
         FIG. 2B  is a side view illustrating a state in which an arm of the radiography apparatus illustrated in  FIG. 2A  is rotated in a direction of an arrow M 1 , 
         FIG. 2C  is a side view illustrating a state in which the arm of the radiography apparatus illustrated in  FIG. 2A  is rotated in a direction of an arrow M 2 , 
         FIG. 3A  is a front view illustrating the radiography apparatus according to an example of the embodiment, 
         FIG. 3B  is a front view illustrating a state in which the arm of the radiography apparatus illustrated in  FIG. 3A  is rotated in a direction of an arrow N 1 , 
         FIG. 3C  is a front view illustrating a state in which the arm of the radiography apparatus illustrated in  FIG. 3A  is rotated 180° in a direction of an arrow N 2 , 
         FIG. 4  is an overall side view illustrating a cable and a tension member of the radiography apparatus according to an example of the embodiment, 
         FIG. 5  is a cross-sectional view taken along the line A-A of  FIG. 4 , 
         FIG. 6  is a partial perspective view illustrating a first end portion of the radiography apparatus according to an example of the embodiment, 
         FIG. 7  is a partial perspective view illustrating a state in which the cable and the tension member of the radiography apparatus according to an example of the embodiment are wound around a first reel and a second reel, respectively, 
         FIG. 8A  is an exploded perspective view illustrating the first reel, the second reel, and a rotational force transmission member of the radiography apparatus according to an example of the embodiment, 
         FIG. 8B  is a perspective view illustrating a state in which the first reel, the second reel, and the rotational force transmission member illustrated in  FIG. 8A  are assembled, 
         FIG. 9A  is a diagram illustrating a perimeter difference between a winding perimeter of the first reel and a winding perimeter of the second reel and illustrates a first radius of the first reel and a diameter of the cable, 
         FIG. 9B  is a diagram illustrating the perimeter difference between the winding perimeter of the first reel and the winding perimeter of the second reel and illustrates a second radius of the second reel and a thickness of the belt, 
         FIG. 10  is a cross-sectional view illustrating the first reel and the second reel of the radiography apparatus according to an example of the embodiment, 
         FIG. 11  is a side view schematically illustrating the first reel and the second reel in a case in which the arm of the radiography apparatus according to an example of the embodiment is orbitally rotated in a first direction, 
         FIG. 12  is a side view schematically illustrating the first reel and the second reel in a case in which the arm of the radiography apparatus according to an example of the embodiment is orbitally rotated in a second direction, 
         FIG. 13  is a side view schematically illustrating a first reel and a second reel in a case in which an arm of a radiography apparatus according to a comparative example is orbitally rotated in the first direction, and 
         FIG. 14  is a side view schematically illustrating the first reel and the second reel in a case in which the arm of the radiography apparatus according to the comparative example is orbitally rotated in the second direction. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a radiography apparatus according to an example of an embodiment of the present disclosure will be described with reference to the drawings. In addition, in the drawings, an arrow X indicates a front-rear direction of the radiography apparatus, an arrow Y indicates a width direction of the radiography apparatus, and an arrow Z indicates a vertical direction. 
     (Overall Configuration of Radiography Apparatus) 
     A radiography apparatus  10  according to this embodiment illustrated in  FIG. 1  is an apparatus that captures a radiographic image of a subject H. The radiography apparatus  10  can capture, for example, moving images and still images of the subject H. The capture of the moving image is performed, for example, in a case in which a treatment target part of the subject H is displayed as a moving image during surgery (also referred to as fluoroscopy or the like). In the capture of the moving image, for example, the moving image of the subject H is displayed on a monitor (not illustrated) that is provided separately from the radiography apparatus  10 . Of course, data of the captured moving image may be stored in a memory of the radiography apparatus  10 . In addition, in the case of the capture of the still image, the captured still image may be displayed on the monitor or may be stored in the memory of the radiography apparatus  10 . 
     As illustrated in  FIG. 1 , the radiography apparatus  10  includes an arm  12  (referred to as a C-arm or the like) which has a C-shape (an arc shape) in a side view, a support portion  14  that supports the arm  12  such that the arm  12  can be orbitally rotated, and a main body portion  16  that supports the arm  12  to be axially rotatable. In addition, hereinafter, it is assumed that the side of the radiography apparatus  10  on which the arm  12  is provided is the front side of the radiography apparatus  10  and the side on which the main body portion  16  is provided is the rear side of the radiography apparatus  10 . 
     (Configuration of Arm) 
     The arm  12  has two end portions of a first end portion  12 A and a second end portion  12 B. An irradiation unit  18  is provided in the first end portion  12 A of the arm  12 , and an image receiving unit  20  is provided in the second end portion  12 B. The arm  12  can hold the irradiation unit  18  and the image receiving unit  20  in a posture in which they face each other. A space, into which the subject H and a bed S on which the subject H lies supine can be inserted, is ensured between the irradiation unit  18  and the image receiving unit  20 . Further, in the following description, in some cases, in a side view of the arm  12  (as viewed from the Y direction in  FIG. 1 ), a direction in which the irradiation unit  18  and the image receiving unit  20  are provided is referred to as the front side of the arm  12 , and a side close to the support portion  14  is referred to as the rear side of the arm  12 . The irradiation unit  18  is an example of an irradiator according to the present disclosure. The image receiving unit  20  is an example of an image receiver according to the present disclosure. 
     As illustrated in  FIG. 2A , the arm  12  is orbitally rotatable about an axis line M (an axis line parallel to the Y axis) with respect to a track portion  22 B that is provided in the support portion  14 . Further, the arm  12  is axially rotatable about an axis line N (an axis line parallel to the X axis) with respect to a bearing portion  23  that is provided in the main body portion  16 . 
     Specifically, the track portion  22 B has an arc shape that has the same radius as the arc of the arm  12 . Moreover, a fitting portion  22 A that is fitted to the track portion  22 B is provided in an outer peripheral portion of the arm  12 . The fitting portion  22 A has an arc shape following the shape of the arm  12 . As illustrated in  FIG. 5 , the track portion  22 B has, for example, a groove shape, and the fitting portion  22 A having a protruding shape is fitted to the track portion  22 B. In addition, a roller (not illustrated) that assists the sliding of the fitting portion  22 A with respect to the track portion  22 B is interposed between the track portion  22 B and the fitting portion  22 A. 
     As illustrated in  FIG. 2A , the fitting portion  22 A formed in the arm  12  slides along the track portion  22 B formed on the support portion  14 . Therefore, the arm  12  can be orbitally rotated about the axis line M at the center of the arc of the arm  12  as a rotation center with respect to the support portion  14  and the main body portion  16 . 
     That is, as illustrated in  FIGS. 2B and 2C , it is possible to orbitally rotate the arm  12  about the axis line M in the direction of an arrow M 1  (counterclockwise in  FIG. 2B ) and the direction of an arrow M 2  (clockwise in  FIG. 2C ). Therefore, the irradiation unit  18  and the image receiving unit  20  provided at both ends of the arm  12  can be rotated about the body axis (an axis parallel to the Y axis) of the subject H (see  FIG. 1 ) in a posture in which they face each other. 
     Further, as illustrated in  FIG. 2A , one end of a support shaft  24  that extends in a front-rear direction (X direction) of the radiography apparatus  10  is fixed to the arm  12 . The other end of the support shaft  24  is supported by the main body portion  16  through the bearing portion  23 . The support shaft  24  is rotated about the axis line N with respect to the bearing portion  23  such that the arm  12  and the support portion  14  are rotatable about the axis line N of the support shaft  24  as a rotation center with respect to the main body portion  16  as illustrated in  FIGS. 3A to 3C . 
     That is, as illustrated in  FIGS. 3B and 3C , it is possible to rotate the arm  12  about the axis line N in the direction of an arrow N 1  (counterclockwise in  FIG. 3B ) and the direction of an arrow N 2  (clockwise in  FIG. 3C ). Therefore, it is possible to reverse the positions of the irradiation unit  18  and the image receiving unit  20  provided at both ends of the arm  12  with respect to the subject H (see  FIG. 1 ) in the vertical direction (Z-axis direction). 
     Here, in the posture of the arm  12  in which the irradiation unit  18  is disposed above the image receiving unit  20  as illustrated in  FIG. 3A , a radiation tube  32  (see  FIG. 1 ) included in the irradiation unit  18  is located above the subject H. Therefore, this posture is called, for example, an overtube posture. In addition, in the posture of the arm  12  in which the irradiation unit  18  is disposed below the image receiving unit  20  illustrated in  FIG. 3C , the radiation tube  32  is located below the subject H. Therefore, this posture is called, for example, an undertube posture. 
     In the overtube posture, it is possible to increase a distance between the irradiation unit  18  and the subject H (see  FIG. 1 ), as compared to the undertube posture. This makes it possible to image a relatively wide region in the overtube posture. Therefore, the overtube posture is mainly used to capture the still image of the subject H. On the other hand, in the undertube posture, the radiation emitted from the irradiation unit  18  is partially shielded by, for example, the bed S. Therefore, in the undertube posture, it is possible to reduce the amount of radiation exposure to, for example, a radiology technician or an operator (not illustrated) around the subject H (see  FIG. 1 ). Therefore, the undertube posture is used for the capture of the moving image of the subject H in which radiation is continuously emitted. 
     (Configuration of Main Body Portion) 
     As illustrated in  FIG. 1 , a plurality of casters  26  are attached to a lower part of the main body portion  16  of the radiography apparatus  10 , and the operator can push the radiography apparatus  10  by hand to move the radiography apparatus  10  into, for example, an operating room or a hospital ward. That is, the radiography apparatus  10  according to this embodiment is a mobile type. 
     Further, the main body portion  16  includes a control unit  28  that controls each unit of the radiography apparatus  10 , such as the irradiation unit  18 , and an operation panel  30  that is, for example, a touch panel type. In addition, the main body portion  16  comprises various switches (not illustrated) including, for example, a power switch of the radiography apparatus  10 , a power circuit that supplies power to each unit of the radiography apparatus  10 , a battery, and the like. 
     The operation panel  30  functions as an operation unit that inputs an operation instruction to each unit of the radiography apparatus  10  to operate each unit and a display unit that displays various kinds of information, such as a warning message and a radiographic image output from the image receiving unit  20 . 
     (Configuration of Control Unit) 
     The control unit  28  transmits a control signal to the radiation tube  32  of the irradiation unit  18 , which will be described below, to control, for example, the tube voltage, tube current, and irradiation time of radiation of the radiation tube  32 . The control unit  28  controls the tube voltage to control the energy of the radiation. In addition, the control unit  28  controls the tube current and the irradiation time to control a radiation dose. In practice, since a high voltage is applied to the radiation tube  32 , the control unit  28  controls the radiation tube  32  through a high-voltage generation device (not illustrated). In imaging, imaging conditions including, for example, the tube voltage, the tube current, and the irradiation time are set through the operation panel  30 . The control unit  28  operates the irradiation unit  18  on the basis of the set imaging conditions. 
     The control unit  28  directs the irradiation unit  18  to perform moving image capture irradiation in which the irradiation unit  18  continuously emits radiation such that a moving image of the subject H can be captured. In a case in which a moving image is captured, the control unit  28  operates a detector of the image receiving unit  20  which will be described below in synchronization with the moving image capture irradiation by the irradiation unit  18 . In a case in which a moving image is captured, basically, the irradiation time is not set as the imaging condition, and instructions to start and end the capture of the moving image are input through the operation panel  30 . In a case in which the instruction to start the capture of a moving image is input, the control unit  28  directs the irradiation unit  18  to start the emission of radiation under preset imaging conditions. 
     In the capture of a moving image, the detector repeats an image detection operation at a preset frame rate while the moving image capture irradiation is performed. An image output by the detector is transmitted to the control unit  28 . The control unit  28  sequentially outputs the received images to a monitor (not illustrated). Therefore, the moving image of the subject H is displayed on the monitor. 
     In addition, the control unit  28  directs the irradiation unit  18  to perform still image capture irradiation in which the irradiation unit  18  emits radiation for a shorter time than in the moving image capture irradiation such that a still image of the subject H can be captured. 
     In the capture of a still image, the control unit  28  operates the detector of the image receiving unit  20  in synchronization with the irradiation timing in the still image capture irradiation by the irradiation unit  18 . For example, an instruction to capture a still image is input through an irradiation switch (not illustrated) that is connected to the control unit  28 . In the capture of a still image, the irradiation time is, for example, in the order of several tens of milliseconds to several hundreds of milliseconds. In a case in which the instruction to capture a still image is input, the control unit  28  operates the irradiation unit  18  on the basis of preset imaging conditions. In the capture of a still image, in a case in which the set irradiation time elapses, the irradiation operation of the irradiation unit  18  ends since the irradiation time is set in the imaging conditions. 
     In a case in which the irradiation ends, the detector starts to output the detected image. The image output by the detector is transmitted to the control unit  28 . The control unit  28  stores data of the still image in a memory (not illustrated). Then, the stored still image is displayed on the monitor (not illustrated). Therefore, the still image of the subject H is displayed on the monitor. Further, the still image may be displayed on the operation panel  30  in order to check the captured still image immediately after imaging. 
     (Configuration of Irradiation Unit) 
     The irradiation unit  18  comprises a radiation source  31  and an irradiation field limiter  34 . The radiation source  31  comprises the radiation tube  32  that generates radiation. The radiation is, for example, X-rays. The radiation tube  32  generates radiation by colliding electrons generated from a cathode with a target (anode). The position where the electrons collide with the target is a focus where radiation is emitted. 
     In addition, the irradiation field limiter  34  is provided below the radiation source  31 . The irradiation field limiter  34  (also referred to as a collimator or the like) has a rectangular irradiation opening  34 A. The radiation generated by the radiation tube  32  is emitted to the subject H through the irradiation opening  34 A. The irradiation field limiter  34  can adjust the opening area of the irradiation opening  34 A. The irradiation field limiter  34  has, for example, four shielding plates (not illustrated) that shield radiation. In each of the four shielding plates, each side corresponds to each side of the irradiation opening  34 A and defines the irradiation opening  34 A. The position of the shielding plates is changed to adjust the opening area of the irradiation opening  34 A, and the irradiation field of the radiation emitted from the irradiation unit  18  is changed. 
     Further, the irradiation unit  18  can be rotated about an axis line of a rotation shaft  36  that extends in the width direction (the Y direction in  FIG. 1 ) of the radiography apparatus  10  as a rotation center with respect to the arm  12 . Specifically, a pair of attachment plates  38  (only one attachment plate is illustrated in  FIG. 1 ) are fixed to the first end portion  12 A of the arm  12 . 
     The pair of attachment plates  38  are disposed such that both sides of the irradiation unit  18  in the width direction are interposed therebetween and are connected to both side surfaces of the irradiation unit  18  in the width direction. The rotation shafts  36  are provided on each of the side surfaces of the irradiation unit  18  facing the attachment plates  38  so as to protrude. The rotation shafts  36  are supported by the pair of attachment plates  38  through bearings (not illustrated). Therefore, the irradiation unit  18  can be rotated about the axis line of the rotation shaft  36  as the rotation center with respect to the attachment plates  38 , and the orientation of the irradiation opening  34 A of the irradiation unit  18  can be changed in the front-rear direction of the arm  12 . The orientation of the irradiation opening  34 A can be changed to change the irradiation direction of radiation. 
     (Configuration of Image Receiving Unit) 
     As illustrated in  FIG. 1 , the image receiving unit  20  is provided in the second end portion  12 B of the arm  12  which is a position facing the irradiation unit  18 . In addition, in this embodiment, the image receiving unit  20  is fixed to the second end portion  12 B of the arm  12  so as not to be detachable. However, the image receiving unit  20  may be attached to the second end portion  12 B of the arm  12  so as to be detachable. 
     The image receiving unit  20  comprises the detector provided in a housing. The image receiving unit  20  has an image receiving surface  20 A that receives the radiation which has been emitted from the irradiation unit  18  and then transmitted through the subject H. The radiation carrying the information of the subject H is incident on the image receiving surface  20 A. 
     The detector is, for example, a flat panel detector (FPD) of a digital radiography (DR) type. The FPD has a detection surface in which a plurality of pixels are two-dimensionally arranged and a thin film transistor (TFT) panel (not illustrated) for driving the pixels. The radiation is incident on the detection surface of the detector through the image receiving surface  20 A. The detector converts the incident radiation into an electric signal and outputs a radiographic image indicating the subject H on the basis of the converted electric signal. For example, the detector is an indirect conversion type that converts radiation into visible light using a scintillator and converts the converted visible light into an electric signal. In addition, the detector may be a direct conversion type that directly converts radiation into an electric signal. Further, the image receiving unit  20  may have any configuration other than the configuration using the FPD. For example, the image receiving unit  20  may have a configuration in which an image intensifier (I.I) and a camera are combined. 
     (Configuration of Cable) 
     As illustrated in  FIG. 4 , the irradiation unit  18  and the image receiving unit  20  are connected to, for example, the control unit  28  (see  FIG. 1 ) and a power circuit (not illustrated) of the main body portion  16  by a cable  40  including a signal line for transmitting a control signal and a power line for supplying power. 
     As illustrated in  FIGS. 5 and 6 , the cable  40  comprises a plurality of (for example, three in this embodiment) first cables  42  and a plurality of (for example, three in this embodiment) second cables  44 . The first cable  42  is for applying a voltage to the radiation tube  32  (see  FIG. 1 ) of the irradiation unit  18  and has one end electrically connected to the irradiation unit  18  provided in the first end portion  12 A of the arm  12  as illustrated in  FIG. 4 . 
     On the other hand, the second cable  44  supplies driving power to the image receiving unit  20  and relays various signals transmitted and received between the control unit  28  (see  FIG. 1 ) and the detector in the image receiving unit  20 . The various signals include, for example, a control signal transmitted from the control unit  28  to the detector and an image signal transmitted from the detector to the control unit  28 . One end of the second cable  44  is electrically connected to the image receiving unit  20  provided in the second end portion  12 B of the arm  12 . Further, the second cable  44  is provided inside the arm  12  and extends to the first end portion  12 A of the arm  12  along the arm  12 . 
     As illustrated in  FIG. 5 , the arm  12  is a cylindrical body having a cavity therein and comprises a first hollow portion  46  that is provided on the inner peripheral side (front side) and a second hollow portion  48  that is provided on the outer peripheral side (rear side). The second cable  44  is provided in the first hollow portion  46  inside the arm  12 . 
     Further, as illustrated in  FIGS. 4 and 6 , the first end portion  12 A of the arm  12  is provided with a holding member  50  that holds one end of the cable  40  extending from the support portion  14 . In the holding member  50 , the cable  40  branches into the first cables  42  and the second cables  44 . The first cable  42  extends to the irradiation unit  18  from the holding member  50  as a base point and is connected to the irradiation unit  18 . On the other hand, the second cable  44  extends to the image receiving unit  20  and is connected to the image receiving unit  20 . 
     In other words, the first cable  42  having one end connected to the irradiation unit  18  and the second cable  44  having one end connected to the image receiving unit  20  are fixed in the first end portion  12 A of the arm  12  and are bundled into one cable group by the holding member  50 . Then, one bundled cable group is provided as the cable  40  in the outer peripheral portion of the arm  12  and extends from the first end portion  12 A to the support portion  14  along the outer periphery of the arm  12 . 
     (Configuration of Belt) 
     Further, as illustrated in  FIG. 4 , one end of a belt  52  as a tension member is fixed to the second end portion  12 B of the arm  12 . The belt  52  is a member that is used to apply tension to the cable  40  and is provided from the second end portion  12 B of the arm  12  to the support portion  14  along the outer periphery of the arm  12 . 
     Specifically, as illustrated in  FIG. 5 , a groove  48 A that extends along the arc of the arm  12  is formed in a front inner surface of the second hollow portion  48  of the arm  12 , and the belt  52  extends along the arc of the arm  12  while being accommodated in the groove  48 A. The belt  52  has a flat shape and is provided in a posture in which a longitudinal direction in a cross-sectional shape illustrated in  FIG. 5  is aligned with the Y direction and a lateral direction (thickness direction) is aligned with the X direction. A thickness D 2  of the belt  52  is smaller than a diameter (thickness) D 1  of the cable  40 . 
     (Configuration of Reel Unit) 
     As illustrated in  FIG. 4 , a reel unit  54  is provided in the support portion  14  of the radiography apparatus  10 . The reel unit  54  winds and unwinds the cable  40  and the belt  52  as the arm  12  is orbitally rotated. As illustrated in  FIG. 7 , the reel unit  54  comprises a first reel  56  and a second reel  58  that is provided so as to be rotatable independently of the first reel  56 . 
     As illustrated in  FIG. 8A , the first reel  56  comprises a cylindrical winding portion  56 A and a pair of flanges  56 B that are provided on both end faces of the winding portion  56 A. On the other hand, the second reel  58  comprises a cylindrical winding portion  58 A and one flange  58 B that is provided on one end surface of the winding portion  58 A. 
     A shaft hole  60  is formed in the first reel  56 , and a shaft hole  62  is formed in the second reel  58 . As illustrated in  FIG. 10 , one rotation shaft  64  is inserted into each of the shaft hole  60  and the shaft hole  62  through a bearing portion (not illustrated). The rotation shaft  64  (see  FIG. 7 ) has a cylindrical shape, and both end portions of the rotation shaft  64  in the axial direction are fixed to a frame (not illustrated) of the support portion  14 . Therefore, the first reel  56  and the second reel  58  can be coaxially rotated independently about the axis line of the rotation shaft  64  as the center of rotation. 
     The cable  40  having one end fixed to the first end portion  12 A (see  FIG. 4 ) of the arm  12  extends to the support portion  14  and is wound around the winding portion  56 A of the first reel  56  in the support portion  14 . Further, as illustrated in  FIG. 10 , the other end of the cable  40  is drawn into the first reel  56 , passes through the rotation shaft  64 , extends to the main body portion  16  illustrated in  FIGS. 1 and 4 , and is connected to, for example, the control unit  28  (see  FIG. 1 ) and the power circuit (not illustrated) of the main body portion  16 . 
     On the other hand, the belt  52  having one end fixed to the second end portion  12 B (see  FIG. 4 ) of the arm  12  extends to the support portion  14  and is wound around the winding portion  58 A of the second reel  58  in the support portion  14 . Further, the other end of the belt  52  is fixed to an outer peripheral surface of the winding portion  58 A of the second reel  58  by a fixing member  66  (see  FIG. 10 ). 
     As illustrated in  FIG. 8A , the first reel  56  and the second reel  58  are disposed side by side in the axial direction of the rotation shaft  64 , and portions thereof which face each other in the axial direction come into contact with each other. Specifically, one flange  56 B of the first reel  56  and the winding portion  58 A of the second reel  58  come into contact with each other. 
     In addition, as illustrated in  FIGS. 9A and 9B , in this embodiment, a first radius E 1  of the winding portion  56 A of the first reel  56  in a state in which the cable  40  is not wound is smaller than a second radius E 2  of the winding portion  58 A of the second reel  58  in a state in which the belt  52  is not wound. Further, a difference (E 2 −E 1 ) between the first radius E 1  and the second radius E 2  is equal to a difference (D 1 −D 2 ) between the diameter (thickness) D 1  of the cable  40  and the thickness D 2  of the belt  52 . 
     That is, as illustrated in  FIG. 10 , the sum (E 1 +D 1 ) of the first radius E 1  of the winding portion  56 A of the first reel  56  and the diameter D 1  of the cable  40  is equal to the sum (E 2 +D 2 ) of the second radius E 2  of the winding portion  58 A of the second reel  58  and the thickness D 2  of the belt  52 . Therefore, in a state in which the cable  40  and the belt  52  are wound once around the first reel  56  and the second reel  58 , respectively, a winding perimeter of the cable  40  and a winding perimeter of the belt  52  are equal to each other. 
     Here, a winding perimeter RL indicates the amount of winding of the cable  40  and the belt  52  in the unit rotation amount of each of the first reel  56  and the second reel  58 . The winding perimeter RL becomes larger as the amount of winding of the cable  40  and the belt  52  becomes larger. 
     For example, a winding perimeter RL 1 ( 1 ) of the cable  40  in the first turn of the first reel  56  is a circumference corresponding to the length of the first radius E 1 . Specifically, RL 1 ( 1 )=2×E 1 ×π is established. Then, a winding perimeter RL 1 ( 2 ) of the cable  40  in the second turn is a circumference corresponding to the length obtained by adding the diameter D 1  of the cable  40  to the first radius E 1 . Specifically, RL 1 ( 2 )=2×(E 1 +D 1 )×π is established. Then, a winding perimeter RL 1 ( 3 ) of the cable  40  in the third turn is a circumference corresponding to the length obtained by adding twice the diameter D 1  to the first radius E 1 . Specifically, RL 1 ( 3 )=2×(E 1 +2×D 1 )×π is established. 
     Similarly, a winding perimeter RL 2 ( 1 ) of the belt  52  in the first turn of the second reel  58  is a circumference corresponding to the length of the second radius E 2 . Specifically, RL 2 ( 1 )=2×E 2 ×π is established. Then, a winding perimeter RL 2 ( 2 ) of the belt  52  in the second turn is a circumference corresponding to the length obtained by adding the thickness D 2  of the belt  52  to the second radius E 2 . Specifically, RL 2 ( 2 )=2×(E 2 +D 2 )×π is established. Then, a winding perimeter RL 2 ( 3 ) of the belt  520  in the third turn is a circumference corresponding to the length obtained by adding twice the thickness D 2  to the second radius E 2 . Specifically, RL 2 ( 3 )=2×(E 2 +2×D 2 )×π is established. 
     As described above, the winding perimeter RL 1  of the cable  40  on the first reel  56  and the winding perimeter RL 2  of the belt  52  on the second reel  58  become larger as the amounts of winding of the cable  40  and the belt  52  become larger. Then, in a case in which there is a difference ΔD (ΔD=D 1 −D 2 ) between the diameter D 1  of the cable  40  and the thickness D 2  of the belt  52 , the rate of change in the winding perimeter RL 1  and the winding perimeter RL 2  also differs depending on the difference ΔD. Therefore, a perimeter difference ΔRL (ΔRL=RL 1 −RL 2 ) between the winding perimeter RL 1  and the winding perimeter RL 2  occurs depending on the amounts of winding of the cable  40  and the belt  52 . 
     In addition, in this example, the first radius E 1  of the first reel  56  and the second radius E 2  of the second reel  58  are different from each other. However, the difference between the first radius E 1  and the second radius E 2  is not the essential cause of the perimeter difference ΔRL which is a problem in the technology according to the present disclosure. The essential cause of the perimeter difference ΔRL which is a problem in the technology according to the present disclosure is that the diameter D 1  of the cable  40  and the thickness D 2  of the belt  52  are different from each other. Therefore, the first radius E 1  and the second radius E 2  may be equal to each other. Even in this case, the perimeter difference ΔRL occurs. 
     (Configuration of Rotational Force Transmission Member) 
     Further, as illustrated in  FIG. 8A , a spring  68  as a rotational force transmission member is provided between the first reel  56  and the second reel  58 . The spring  68  is, for example, an extension spring. In one flange  56 B of the first reel  56 , a first pin  70 A is provided on an outer surface which faces the second reel  58  so as to protrude. On the other hand, in the winding portion  58 A of the second reel  58 , a second pin  70 B is provided on an inner surface of the flange  58 B which faces the first reel  56  so as to protrude. 
     As illustrated in  FIG. 8B , one end of the spring  68  is fixed to the first pin  70 A and the other end thereof is fixed to the second pin  70 B such that the first reel  56  and the second reel  58  are connected by the spring  68 . Further, the spring  68  is expanded and contracted in a case in which the first reel  56  and the second reel  58  are rotated in opposite directions. 
     In a case in which one of the first reel  56  and the second reel  58  is rotated by the spring  68 , the rotational force in the same direction is transmitted to the other. Specifically, in a case in which the arm  12  is orbitally rotated in a first direction (the direction of the arrow M 1  in  FIG. 4 ) in which the first end portion  12 A approaches the support portion  14 , the second end portion  12 B of the arm  12  is moved in a direction away from the support portion  14 . In a case in which the second end portion  12 B is moved in the direction away from the support portion  14 , the belt  52  having one end fixed to the second end portion  12 B is unwound from the second reel  58 . Therefore, the second reel  58  around which the belt  52  is wound is rotated in the direction in which the belt  52  is unwound (in the direction of an arrow F 1  illustrated in  FIGS. 7 and 8B ). 
     In this case, the rotational force of the second reel  58  is transmitted to the first reel  56  by the spring  68  (see  FIG. 10 ), and the first reel  56  is rotated in the same direction (the direction of the arrow F 1  illustrated in  FIGS. 7 and 8B ) as the second reel  58 . The rotation in the direction of the arrow F 1  is rotation in the direction in which the first reel  56  winds up the cable  40 . Therefore, the cable  40  is wound around the first reel  56  by the rotation of the first reel  56  in the direction of the arrow F 1 . In a case in which the arm  12  is orbitally rotated in the first direction (the direction of the arrow M 1  in  FIG. 4 ) in which the first end portion  12 A approaches the support portion  14 , the cable  40  is loosened. Therefore, the loosening of the cable  40  is suppressed by the rotation of the first reel  56  in the direction of the arrow F 1 . 
     On the other hand, when the arm  12  is orbitally rotated in the second direction (the direction of the arrow M 2  in  FIG. 4 ) in which the second end portion  12 B approaches the support portion  14 , the first end portion  12 A of the arm  12  is moved in the direction away from the support portion  14 . In a case in which the second end portion  12 B is moved in the direction approaching the support portion  14 , the cable  40  having one end fixed to the first end portion  12 A is unwound. Then, the first reel  56  around which the cable  40  is wound is rotated in the direction in which the cable  40  is unwound (the direction of the arrow F 2  in  FIGS. 7 and 8B ). 
     In this case, the rotational force of the first reel  56  is transmitted to the second reel  58  by the spring  68  (see  FIG. 10 ), and the second reel  58  is rotated in the same direction as the first reel  56  (the direction of the arrow F 2  in  FIGS. 7 and 8B ). The rotation in the direction of the arrow F 2  is rotation in the direction in which the second reel  58  winds up the belt  52 . Therefore, the belt  52  is wound around the second reel  58  by the rotation of the second reel  58  in the direction of the arrow F 2 . In a case in which the arm  12  is orbitally rotated in the second direction (the direction of the arrow M 2  in  FIG. 4 ) in which the second end portion  12 B approaches the support portion  14 , the belt  52  is loosened. Therefore, the loosening of the belt  52  is suppressed by the rotation of the second reel  58  in the direction of the arrow F 2 . 
     Further, in this embodiment, the spring  68  is fixed to the first reel  56  and the second reel  58  in a state in which it is expanded to a length preset with respect to the natural length. That is, in the state in which the spring  68  is fixed to the first reel  56  and the second reel  58 , biasing force is generated in the spring  68  in a direction in which the spring  68  is contracted (the direction of an arrow G in  FIG. 8B ) as illustrated in  FIG. 8B . 
     The biasing force of the spring  68  biases the first reel  56  in the winding direction of the cable  40  (the direction of the arrow F 1  in  FIG. 8B ) and biases the second reel  58  in the winding direction of the belt  52  (the direction of the arrow F 2  in  FIG. 8B ). 
     Further, in a case in which the spring  68  transmits the rotational force of one of the first reel  56  and the second reel  58  to the other, it is allowed that the difference between the amount of rotation of one of the first reel  56  and the second reel  58  and the amount of rotation of the other occurs in a preset range, that is, a range in which the spring  68  can be expanded. Therefore, one of the first reel  56  and the second reel  58  can be rotated with respect to the other according to the biasing force of the spring  68  or against the biasing force of the spring  68 . 
     (Operation and Effect) 
     Next, the operation and effect of the radiography apparatus  10  according to this embodiment will be described with reference to  FIGS. 11 to 14 .  FIGS. 11 and 12  illustrate the arm  12  and the support portion  14  of the radiography apparatus  10  according to this embodiment. On the other hand,  FIGS. 13 and 14  illustrate an arm  120  and a support portion  140  of a radiography apparatus  100  according to a comparative example. The difference between the radiography apparatus  10  according to this embodiment and the radiography apparatus  100  according to the comparative example is that the comparative example does not have the spring  68  as the rotational force transmission member and the first reel  56  and the second reel  58  are integrated and always rotated in the same direction. 
     In addition, as illustrated in  FIG. 7 , the first reel  56  and the second reel  58  constituting the reel unit  54  are disposed at the position where they overlap each other in a side view (a direction seen from the Y direction) of the radiography apparatus  10 . However, in  FIGS. 11 to 14 , for the sake of simplicity, the first reel  56  and the second reel  58  are illustrated side by side at positions that deviate from each other in the vertical direction (Z direction). 
     As illustrated in  FIG. 11 , in a case in which the arm  12  is orbitally rotated in the first direction (the direction of the arrow M 1 ) in which the first end portion  12 A of the arm  12  approaches the support portion  14 , the cable  40  having one end fixed to the first end portion  12 A also approaches the support portion  14  as the first end portion  12 A is moved. In this case, it is necessary to wind the cable  40  with the first reel  56  provided in the support portion  14  to apply tension to the cable  40 , in order to suppress the loosening of the cable  40 . 
     The belt  52  is a member for applying tension to the cable  40 , and one end thereof is fixed to the second end portion  12 B of the arm  12 . Therefore, in a case in which the arm  12  is orbitally rotated in the first direction (the direction of the arrow M 1 ), the belt  52  is unwound from the second reel  58 . The first reel  56  and the second reel  58  are held to be independently rotatable. However, in a case in which one of the first reel  56  and the second reel  58  is rotated, the rotational force in the same direction is transmitted to the other by the spring  68 . 
     That is, in a case in which the arm  12  is orbitally rotated in the first direction (the direction of the arrow M 1 ), the first end portion  12 A of the arm  12  approaches the support portion  14 , but the second end portion  12 B of the arm  12  is conversely separated from the support portion  14 . Therefore, the belt  52  having one end fixed to the second end portion  12 B is unwound from the second reel  58 , and the second reel  58  is rotated in the direction in which the belt  52  is unwound. 
     Further, the rotational force of the second reel  58  is transmitted to the first reel  56  by the spring  68  such that the first reel  56  is rotated in the same direction as the second reel  58 . This rotation direction is the direction in which the belt  52  is unwound from the second reel  58  and the direction in which the cable  40  is wound around the first reel  56 . Therefore, the cable  40  is wound around the first reel  56  even in a case in which the arm  12  is orbitally rotated in the first direction (the direction of the arrow M 1 ). As a result, tension is applied to the cable  40 , and the loosening of the cable  40  is suppressed. 
     Further, the spring  68  biases the first reel  56  in the winding direction of the cable  40  and biases the second reel  58  in the winding direction of the belt  52 . In addition, the spring  68  allows the occurrence of the difference between the amount of rotation of the first reel  56  and the amount of rotation of the second reel  58  in a preset range in a case in which the rotational force is transmitted. Therefore, the following effects can be obtained. 
     That is, in a case in which there is a difference between the diameter D 1  of the cable  40  and the thickness D 2  of the belt  52 , the perimeter difference ΔRL (ΔRL=RL 1 −RL 2 ) between the winding perimeter RL 1  of the cable  40  on the first reel  56  and the winding perimeter RL 2  of the belt  52  on the second reel  58  occurs due to the thickness difference ΔD (ΔD=D 1 −D 2 ) as illustrated in  FIG. 9 . 
     In a case in which the amount of winding of the cable  40  on the first reel  56  changes, the diameter of the first reel  56  changes. Therefore, the winding perimeter RL 1  also changes. As described above, assuming that the winding perimeter of the cable  40  in the first turn on the first reel  56  is set as RL 1 ( 1 ), the winding perimeter RL 1 ( 2 ) of the cable  40  in the second turn is larger than the winding perimeter RL 1 ( 1 ). This is because the diameter of the first reel  56  including the second turn of the cable  40  is increased by a value corresponding to the diameter of the first turn of the cable  40 . This holds for the second reel  58 . 
     In a case in which the diameter D 1  of the cable  40  and the thickness D 2  of the belt  52  are equal to each other, the difference ΔD is zero. Therefore, even in a case in which the winding perimeters RL 1  and RL 2  of the first and second turns change in the first reel  56  and the second reel  58 , respectively, the amounts of change in the winding perimeters RL 1  and RL 2  are the same. Therefore, in the first reel  56  and the second reel  58  that are rotated at the same timing, there is no perimeter difference ARL between the winding perimeter RL 1  of the cable  40  on the first reel  56  and the winding perimeter RL 2  of the belt  52  on the second reel  58 . 
     However, in this embodiment, the diameter D 1  of the cable  40  is larger than the thickness D 2  of the belt. Since the belt  52  is for applying tension, the thickness D 2  is small, and a change in the winding perimeter RL 2  corresponding to the amount of rotation of the second reel  58  is negligible. On the other hand, since the cable  40  electrically connected to the irradiation unit  18  is a cable for applying a high voltage, the diameter D 1  of the cable  40  is larger than that of a simple signal cable for control. Therefore, the change in the winding perimeter RL 1  corresponding to the amount of rotation of the first reel  56  is not negligible, and the thickness difference ΔD from the belt  52  is also large. 
     Therefore, the change in the winding perimeter RL 1  of the cable  40  on the first reel  56  and the winding perimeter RL 2  of the belt  52  on the second reel  58  is so large that it is not negligible according to the change in the amount of winding of the first reel  56 . In a case in which the perimeter difference ARL between the winding perimeters RL 1  and RL 2  of the first reel  56  and the second reel  58  occurs as described above, the following problems occur. 
     For example, in a case in which the winding perimeter RL 1  of the cable  40  on the first reel  56  is larger than the winding perimeter RL 2  of the belt  52  on the second reel  58 , the following two cases of a first case and a second case are considered. 
     In the first case, as illustrated as a comparative example in  FIG. 13 , the arm  12  is orbitally rotated in the first direction (the direction of the arrow M 1 ) such that the belt  52  is unwound from the second reel  58  and the cable  40  is wound around the first reel  56 . In the first case, in a case in which the amount of rotation of the second reel  58  and the amount of rotation of the first reel  56  are completely equal to each other, the amount of winding of the cable  40  around the first reel  56  is larger than the amount of unwinding of the belt  52  from the second reel  58 , and a tension more than necessary is applied to the cable  40 . 
     That is, in a case in which the arm  12  is orbitally rotated in the first direction, the amount of unwinding P of the belt  52  from the second reel  58  is determined according to the amount of movement (represented by P) of the arm  12 . The amount of rotation of the second reel  58  is determined according to the amount of unwinding P. The amount of rotation and the rotation direction of the first reel  56  are the same as those of the second reel  58 . 
     Since the diameter D 1  of the cable  40  is larger than the thickness D 2  of the belt  52 , the winding perimeter RL 1  of the first reel  56  is larger than the winding perimeter RL 2  of the second reel  58 . Therefore, the amount of winding P+a of the cable  40  on the first reel  56  is larger than the amount of winding P of the belt  52  on the second reel  58 . As a result, a tension equal to or more than the tension required to suppress loosening is applied to the cable  40 . In a case in which the tension is too high, there is a concern that the cable  40  will be broken. 
     Further, in the second case, as illustrated as a comparative example in  FIG. 14 , the arm  12  is orbitally rotated in the second direction (the direction of the arrow M 2 ) such that the cable  40  is unwound from the first reel  56  and the belt  52  is wound around the second reel  58 . In the second case, in a case in which the amount of rotation of the second reel  58  and the amount of rotation of the first reel  56  are completely equal to each other, the amount of winding of the belt  52  on the second reel  58  is smaller than the amount of unwinding of the cable  40  from the first reel  56 . Therefore, the belt  52  is loosened. Reference numeral  52 A indicates a portion in which the belt  52  is loosened. 
     That is, in a case in which the arm  12  is orbitally rotated in the second direction, the amount of unwinding P of the cable  40  from the first reel  56  is determined according to the amount of movement (represented by P) of the arm  12 . The amount of rotation of the first reel  56  is determined according to the amount of unwinding P. The amount of rotation and the rotation direction of the second reel  58  are also the same as those of the first reel  56 . 
     Since the diameter D 1  of the cable  40  is larger than the thickness D 2  of the belt  52 , the winding perimeter RL 2  of the second reel  58  is smaller than the winding perimeter RL 1  of the first reel  56 . Therefore, the amount of winding P−α of the belt  52  on the second reel  58  is less than the amount of unwinding P of the cable  40  from the first reel  56 . As a result, the belt  52  is loosened. 
     On the other hand, as illustrated in  FIGS. 11 and 12 , in the radiography apparatus  10  according to this embodiment, the first reel  56  and the second reel  58  are connected by the spring  68  as the rotational force transmission member. In a case in which one of the first reel  56  and the second reel  58  is rotated, the spring  68  not only transmits the rotational force in the same direction to the other, but also biases the first reel  56  in the winding direction of the cable  40  and the second reel  58  in the winding direction of the belt  52 . Further, the spring  68  allows the occurrence of the difference between the amount of rotation of the first reel  56  and the amount of rotation of the second reel  58  within a preset range in a case in which the rotational force is transmitted. 
     In the first case illustrated in  FIG. 13 , the amount of winding P+α of the cable  40  is more than the amount of moving P of the arm  12 . Therefore, tension more than necessary which exceeds the tension required for winding and is equal to or more than the biasing force of the spring  68  against the first reel  56  in the winding direction is applied to the cable  40 . 
     In the first case, according to the radiography apparatus  10  of this embodiment, as illustrated in  FIG. 11 , the spring  68  is expanded by the tension applied to the cable  40 , and the amount of rotation of the first reel  56  is less than the amount of rotation of the second reel  58 . That is, the first reel  56  is rotated with respect to the second reel  58  in the unwinding direction of the cable  40  against the biasing force of the spring  68 . 
     Since the amount of rotation of the first reel  56  in the winding direction is reduced, the amount of winding P of the cable  40  is equal to the amount of movement P of the arm  12 , and the tension acting on the cable  40  from the first reel  56  is reduced. As a result, the application of the tension more than necessary to the cable  40  caused by the difference ΔRL between the winding perimeter RL 1  of the first reel  56  and the winding perimeter RL 2  of the second reel  58  is suppressed, and the concern that the cable  40  will be broken is suppressed. 
     Further, in the second case illustrated in  FIG. 14 , the amount of winding P−α of the belt  52  is less than the amount of movement P of the arm  12  due to the difference between the winding perimeter RL 1  of the first reel  56  and the winding perimeter RL 2  of the second reel  58 , and the belt  52  is loosened. 
     In the second case, according to the radiography apparatus  10  of this embodiment, as illustrated in  FIG. 12 , the amount of rotation of the second reel  58  is more than the amount of rotation of the first reel  56  by the contraction of the spring  68 . That is, the second reel  58  is rotated in the winding direction of the belt  52  by the biasing force of the spring  68  that biases the second reel  58  in the winding direction of the belt  52 . Since the amount of rotation of the second reel  58  in the winding direction is increased, the amount of winding P of the belt  52  is equal to the amount of movement P of the arm  12 , and the loosening of the belt  52  is suppressed. In  FIG. 12 , the loosening  52 A of the belt  52  illustrated in  FIG. 14  does not occur. 
     That is, according to the radiography apparatus  10  of this embodiment, the spring  68  biases the first reel  56  in the winding direction of the cable  40  and biases the second reel  58  in the winding direction of the belt  52 . Therefore, the loosening of the cable  40  and the belt  52  wound around the first reel  56  and the second reel  58 , respectively, is suppressed. 
     In addition, the spring  68  allows the difference between the amounts of rotation of the first reel  56  and the second reel  58 . Therefore, the application of tension more than necessary to the cable  40  and the belt  52  caused by the difference between the winding perimeters of the first reel  56  and the second reel  58  is suppressed. 
     Further, the configuration in which the first reel  56  and the second reel  58  can be rotated independently is necessary as a premise for achieving the function of the spring  68 . That is, for the winding direction of the cable  40  on the first reel  56  and the winding direction of the belt  52  on the second reel  58 , since the rotation directions are opposite to each other, the first reel  56  and the second reel  58  need to be rotated independently. Further, the first reel  56  and the second reel  58  need to be rotated independently in order to allow the difference between the amounts of rotation of the first reel  56  and the second reel  58 . The above-mentioned function can be achieved by connecting the first reel  56  and the second reel  58 , which can be rotated independently, with the spring  68 . 
     Therefore, unlike the related art, it is not necessary to perform complicated processing such as manufacturing a conical pulley having a spiral guide groove formed therein. Therefore, it is possible to more easily solve the problems caused by the difference ΔRL between the winding perimeter RL 1  of the cable  40  and the winding perimeter RL 2  of the belt  52 , that is, the application of tension more than necessary to the cable  40  and the belt  52  and the occurrence of loosening. 
     Further, according to this embodiment, the first reel  56  and the second reel  58  constituting the reel unit  54  are disposed around the same rotation shaft  64 , that is, coaxially. Therefore, this configuration can be simpler than the configuration in which the first reel  56  and the second reel  58  are disposed on different shafts, and it is possible to save space. 
     Furthermore, according to this embodiment, each of the first reel  56  and the second reel  58  is provided in the support portion  14  of the radiography apparatus  10 . Since the support portion  14  is a connection portion between the arm  12  and the main body portion  16 , it functions as a relay portion of the cable  40  between the arm  12  and the main body portion  16 . The provision of the first reel  56  makes it easy to provide the cable  40 . 
     In addition, since the support portion  14  is a portion serving as the base point of the arm  12  that is orbitally rotated, the support portion  14  is most suitable as a position for drawing the cable  40  and the belt  52  disposed in the outer peripheral portion of the arm  12  from the viewpoint of suppressing the complexity of the configuration. The provision of the first reel  56  and the second reel  58  at this position makes it possible to suppress the complexity of the configuration. 
     Further, according to this embodiment, the diameter (thickness) D 1  of the cable  40  is larger than the thickness D 2  of the belt  52 , and the first radius E 1  of the winding portion  56 A of the first reel  56  in a state in which the cable  40  is not wound is smaller than the second radius E 2  of the winding portion  58 A of the second reel  58  in a state in which the belt  52  is not wound. 
     As described above, in this embodiment, the first radius E 1  of the winding portion  56 A of the first reel  56  for winding the cable  40  having the diameter D 1  is smaller than the second radius E 2  of the winding portion  58 A of the second reel  58  for winding the belt  52  having the thickness D 2  smaller than the diameter D 1 . The winding perimeter RL 1  of the first reel  56  for winding the cable  40  (diameter D 1 ) becomes larger than the winding perimeter RL 2  of the belt  52  (thickness D 2 ) of the second reel  58  as the amount of winding becomes larger. 
     The configuration in which the first radius E 1  is set to be smaller than the second radius E 2  in an initial state in which the cable  40  and the belt  52  are not wound makes it possible to suppress an excessive increase in the perimeter difference ΔRL between the winding perimeter RL 1  of the cable  40  and the winding perimeter RL 2  of the belt  52  in a case in which the cable  40  and the belt  52  are wound by the first reel  56  and the second reel  58 , respectively. 
     More details are as follows. A state in which the amount of winding of the cable  40  on the first reel  56  is minimized is a state in which the arm  12  is orbitally rotated in the second direction (the direction of the arrow M 2  in  FIG. 12 ) and the first end portion  12 A is moved to the maximum in the second direction. On the contrary, a state in which the amount of winding of the cable  40  on the first reel  56  is maximized is a state in which the arm  12  is orbitally rotated in the first direction and the second end portion  12 B is moved to the maximum in the first direction (the direction of the arrow M 1  in  FIG. 11 ). The fact that the first radius E 1  is small means that the winding perimeter RL 1 ( 1 ) of the cable  40  in the first turn by the first reel  56  is smaller than the winding perimeter RL 2 ( 1 ) of the belt  52  in the first turn by the second reel  58 . 
     Considering a case in which the arm  12  is orbitally rotated in the first direction (the direction of the arrow M 1  in  FIG. 11 ) from the state in which the first end portion  12 A is moved to the maximum in the second direction (the direction of the arrow M 2  in  FIG. 12 ), as the first radius E 1  of the first reel  56  becomes smaller than the second radius E 2  of the second reel  58 , the amount of winding of the cable  40  on the first reel  56  becomes smaller than the amount of unwinding of the belt  52  on the second reel  58 . Therefore, as the first radius E 1  is smaller than the second radius E 2 , the tension applied to the cable  40  by the winding of the first reel  56  is more suppressed. On the other hand, the loosening of the cable  40  increases. 
     As described above, in a case in which the first radius E 1  is smaller than the second radius E 2 , there is an advantage that tension more than necessary is prevented from being applied to the cable  40 , but there is a disadvantage that the loosening of the cable  40  increases. However, in general, it is not preferable that tension more than necessary is applied to the cable  40  since there is a concern that the cable  40  will be broken. Therefore, the configuration in which the first radius E 1  of the first reel  56  is smaller than the second radius E 2  of the second reel  58  makes it possible to obtain an advantage exceeding the disadvantage that the loosening of the cable  40  increases. 
     In particular, according to this embodiment, the difference between the first radius E 1  and the second radius E 2  is equal to the difference between the diameter (thickness) D 1  of the cable  40  and the thickness D 2  of the belt  52 . That is, in a state in which the cable  40  and the belt  52  are wound once around the first reel  56  and the second reel  58 , respectively, the winding perimeter RL 1  of the cable  40  and the winding perimeter RL 2  of the belt  52  are equal to each other. 
     As described above, the maximum value of the difference ARL between the winding perimeter RL 1  of the cable  40  and the winding perimeter RL 2  of the belt  52  in a case in which the cable  40  is wound a plurality of times can be reduced by making the winding perimeter RL 1 ( 1 ) of the first reel  56  in a state in which the cable  40  is wound once equal to the winding perimeter RL 2 ( 1 ) of the second reel  58  in a state in which the belt  52  is wound once. That is, an excessive increase in the perimeter difference ARL between the winding perimeter RL 1  of the cable  40  and the winding perimeter RL 2  of the belt  52  is suppressed. 
     Further, according to this embodiment, the cable  40  includes the first cable  42  for applying a voltage to the radiation tube  32  of the irradiation unit  18 . In general, a relatively high voltage is applied to the radiation tube  32 . For this reason, the cable for applying a voltage tends to have a thick insulating coating and a large diameter. On the other hand, the thickness of the belt  52  can be reduced as long as the belt  52  can apply tension. 
     As described above, in a case in which the cable  40  includes the first cable  42  for applying the voltage to the radiation tube  32 , the perimeter difference ΔRL between the winding perimeter RL 1  of the first reel  56  and the winding perimeter RL 2  of the second reel  58  tends to be large. Therefore, it is highly necessary to adopt the technology of this embodiment. 
     Further, the cable  40  includes the second cable  44  connected to the image receiving unit  20  in addition to the first cable  42 . The first cable  42  and the second cable  44  are provided as a bundled cable group in the outer peripheral portion of the arm  12  between the first reel  56  and the first end portion  12 A of the arm  12 . 
     Then, the cable group (cable  40 ) is fixed in the first end portion  12 A by the holding member  50 . Further, the first cable  42  and the second cable  44  branch off on the side opposite to the first reel  56  with respect to the position where the cable group is fixed, and the first cable  42  is connected to the irradiation unit  18  provided in the first end portion  12 A. On the other hand, the second cable  44  is provided inside the arm  12  so as to extend to the second end portion  12 B and is connected to the image receiving unit  20  provided in the second end portion  12 B. 
     As described above, the cable group (cable  40 ) is fixed, and the first cable  42  and the second cable  44  branch off on the side opposite to the first reel  56  with respect to the fixed position. Therefore, it is possible to prevent the tension applied to the cable group (cable  40 ) and the loosening of the cable group (cable  40 ) from affecting the first cable  42  and the second cable  44 . 
     In addition, the cable  40  is provided as a cable group, which is a bundle of the first cables  42  and the second cables  44 , in the outer peripheral portion of the arm  12  between the first reel  56  and the first end portion  12 A. Therefore, the cable  40  disposed in the outer peripheral portion of the arm  12  can be aggregated in the first end portion  12 A of the arm  12 . As a result, it is possible to suppress the complexity of electrical wiring as compared to a case in which the cable  40  is provided in each of the first end portion  12 A and the second end portion  12 B in the outer peripheral portion of the arm  12 . 
     Further, in this embodiment, the cable group (cable  40 ) is provided between the support portion  14  and the first end portion  12 A of the arm  12  in which the irradiation unit  18  is provided. In general, in a case in which the radiography apparatus  10  is used to capture a moving image, the irradiation unit  18  is disposed below the subject H, and the image receiving unit  20  is disposed above the subject H. In many cases, a moving image is captured during surgery. In this case, it is not preferable that a portion of the arm  12  in which the cable  40  is provided is disposed above the subject H. For example, the reason is that, in a case in which the cable  40  is loosened above the subject H, the loosening may interfere with the surgery. 
     Here, the cable group (cable  40 ) is provided between the support portion  14  and the first end portion  12 A which is often disposed below the subject H in the capture of a moving image. Therefore, in a case in which a moving image is captured, the portion of the arm  12  in which the cable  40  is provided can be disposed below the subject H. 
     Further, according to this embodiment, the other end of the belt  52  is fixed to the outer peripheral surface of the second reel  58  by the fixing member  66 . This configuration in which the other end of the belt  52  is fixed to the second reel  58  makes it possible to reduce the length of the belt  52  and to suppress the complexity of the configuration of the second reel  58 , as compared to, for example, a configuration in which both ends of the belt  52  are fixed to one end and the other end of the arm  12  through the second reel  58 , respectively. 
     In addition, according to this embodiment, the belt  52  is used as the tension member. The use of the belt  52  as the tension member makes it possible to reduce the thickness of the tension member and to apply tension to the cable  40  with the tension member. 
     Further, according to this embodiment, the spring  68  connects the first reel  56  and the second reel  58  and is expanded and contracted in a case in which the first reel  56  and the second reel  58  are rotated in opposite directions. The spring  68  constitutes the rotational force transmission member. The use of the spring  68  as the rotational force transmission member makes it possible to bias the first reel  56  and the second reel  58  in the winding directions of the cable  40  and the belt  52 , respectively, while transmitting the rotational force with a simple configuration. 
     In particular, according to this embodiment, the spring  68  has one end that is attached to the first pin  70 A provided on the side surface of the first reel  56  and the other end that is attached to the second pin  70 B provided on the side surface of the second reel  58 . This configuration in which the first pin  70 A and the second pin  70 B, to which both ends of the spring  68  are attached, are provided on the side surface of the first reel  56  and the side surface of the second reel  58 , respectively, makes it possible to attach the spring  68  to the first reel  56  and the second reel  58  with a simple configuration. 
     &lt;Other Embodiments&gt; 
     An example of the embodiment of the present disclosure has been described above. However, the present disclosure is not limited to the above-described embodiment, and various modifications and changes can be made without departing from the gist of the present disclosure. 
     For example, in the above-described embodiment, the belt  52  is used as the tension member. However, the tension member is not limited to the belt  52  as long as it can apply tension to the cable  40 . However, it is preferable that the tension member has a smaller thickness than the cable  40  and that a belt or a wire is used as the tension member. 
     Further, in the above-described embodiment, the spring  68  is used as the rotational force transmission member. However, the rotational force transmission member is not limited to the spring  68  as long as it can transmit the rotational force of one of the first reel  56  and the second reel  58  to the other, bias the first reel  56  and the second reel  58  in the winding directions of the cable  40  and the belt  52 , respectively, and allow the occurrence of the difference between the amount of rotation of the first reel  56  and the amount of rotation of the second reel  58 . In addition to the spring  68 , for example, a rubber member or a magnet can be used as the rotational force transmission member. 
     Further, in the above-described embodiment, the first reel  56  and the second reel  58  are disposed around the same rotation shaft  64 . However, they may be disposed around different rotation shafts. In this case, as illustrated in  FIGS. 11 and 12  for convenience of explanation, the different rotation shafts may be provided on the same axis line or may be provided on different axis lines. 
     Further, in the above-described embodiment, the first reel  56  and the second reel  58  are separately provided in the support portion  14  of the radiography apparatus  10 . However, the first reel  56  and the second reel  58  may not necessarily be provided in the support portion  14  and may be separately provided in, for example, the main body portion  16  of the radiography apparatus  10 . 
     Further, in the above-described embodiment, the first radius E 1  of the winding portion  56 A of the first reel  56  is smaller than the second radius E 2  of the winding portion  58 A of the second reel  58 . However, the first radius E 1  and the second radius E 2  may be equal to each other. Furthermore, in a case in which the thickness of the tension member is larger than the diameter D 1  of the cable  40 , the first radius E 1  of the winding portion  56 A of the first reel  56  may be larger than the second radius E 2  of the winding portion  58 A of the second reel  58 . 
     In addition, in the above-described embodiment, X-rays have been described as an example of the radiation. However, the radiation is not limited to the X-rays and may be, for example, γ-rays. 
     The disclosure of JP2019-199330 filed on Oct. 31, 2019 is incorporated herein by reference in its entirety. All of the documents, patent applications, and technical standards described in the specification are incorporated herein by references to the same extent as the incorporation of the individual documents, patent applications, and technical standards by references are described specifically and individually.