Patent Publication Number: US-11382581-B2

Title: Radiation detection device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation of copending application Ser. No. 16/568,864, filed on Sep. 12, 2019, which claims priority under 35 U.S.C. § 119(a) to Application No. 2018-184311, filed in Japan on Sep. 28, 2018, all of which are hereby expressly incorporated by reference into the present application. 
    
    
     BACKGROUND 
     Technical Field 
     The present invention relates to a radiation detection device. 
     Related Art 
     JP2012-063341A discloses a structure of a portable radiation image detection device. In the portable radiation image detection device, a flat panel detector (FPD) formed by laminating a charge generation layer, which absorbs X-rays and converts the X-rays into electric charges, on a thin film transistor (TFT) active matrix substrate is stored inside a housing with an approximately rectangular planar shape. In addition, a circuit board is disposed on the rear surface side of the FPD. 
     SUMMARY 
     The portable radiation image detection device disclosed in JP2012-063341A may be attached to the imaging table in the imaging room, or may be taken out of the imaging room and inserted between the bed in the patient&#39;s room and the patient. Thus, the portable radiation image detection device is used in various forms. For this reason, compared with a non-portable radiation image detection device, there is a possibility that a local impact may be applied due to an unexpected drop or the like. Since a radiation detection panel is stored inside the portable radiation image detection device, it is preferable to appropriately protect the radiation detection panel. 
     Therefore, it is an object of the invention to provide a radiation detection device capable of protecting a radiation detection panel stored thereinside. 
     In order to achieve the aforementioned object, a radiation detection device according to the invention comprises: a front surface member; a rear surface member that is assembled with the front surface member and that comprises an outer rib formed along an outer edge and an inner rib formed along the outer rib inside the outer rib; and a radiation detection panel that is disposed between the front surface member and the rear surface member and detects radiation incident from the front surface member side. 
     In the radiation detection device according to the invention, the outer rib and the inner rib are formed in a frame shape. 
     In the radiation detection device according to the invention, the outer rib has a portion formed thicker than the inner rib. 
     In the radiation detection device according to the invention, the outer rib and the inner rib are connected to each other by a connection rib. 
     In the radiation detection device according to the invention, at least a part of the connection rib is a corner portion connection rib extending from a corner portion of the outer rib to the inner rib, and the inner rib is disposed perpendicular to the corner portion connection rib. 
     In the radiation detection device according to the invention, the outer rib, the inner rib, and the connection rib form a truss structure. 
     The radiation detection device according to the invention further comprises a support plate that supports the radiation detection panel, and the support plate is bonded to the rear surface member. 
     In the radiation detection device according to the invention, the support plate is bonded to a corner portion of the rear surface member. 
     In the radiation detection device according to the invention, a reinforcing rib is formed on the support plate, and the reinforcing rib and the rear surface member are bonded to each other. 
     In the radiation detection device according to the invention, an opening portion through which an externally inserted member is inserted is formed on side surfaces of the outer rib and the inner rib, and an opening connection rib is formed at both ends of the opening portion. 
     In the radiation detection device according to the invention, the opening portion is formed in a central portion of the rear surface member. 
     In the radiation detection device according to the invention, the opening portion is formed on two sides adjacent to each other in the rear surface member. 
     In the radiation detection device according to the invention, a protection rib surrounding the externally inserted member inserted through the opening portion is formed on the support plate. 
     In the radiation detection device according to the invention, the radiation detection panel is disposed between the front surface member and the rear surface member. In the rear surface member, the outer rib is formed along the outer edge, and the inner rib is formed inside the outer rib. Therefore, the stiffness of the rear surface member is higher than that in a structure that does not have either the inner rib or the outer rib or a structure that does not have any of the inner rib and the outer rib. For this reason, for example, even in a case where an impact at the time of drop is applied to the radiation detection device, the rear surface member is hardly deformed. Accordingly, the radiation detection panel is protected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary Embodiments of the present invention will be described in detail with reference to the following figures, wherein: 
         FIG. 1  is a perspective view showing a radiation detection device according to the present embodiment. 
         FIG. 2  is an exploded side sectional view showing a state in which the radiation detection device according to the present embodiment is disassembled. 
         FIG. 3  is a side sectional view showing the radiation detection device according to the present embodiment. 
         FIG. 4  is a front view showing a rear surface member in the radiation detection device according to the present embodiment. 
         FIG. 5  is a front view showing a support plate in the radiation detection device according to the present embodiment. 
         FIG. 6  is a front view showing a radiation detection panel in the radiation detection device according to the present embodiment. 
         FIG. 7  is a front view showing a control substrate in the radiation detection device according to the present embodiment. 
         FIG. 8  is a front view showing a modification example in which a truss structure is formed by reinforcing ribs of the rear surface member in the radiation detection device according to the present embodiment. 
         FIG. 9  is a front view showing a modification example in which an inner rib and an outer rib of the rear surface member in the radiation detection device according to the present embodiment are formed so as to have the same thickness. 
         FIG. 10  is a perspective view showing a modification example in which an opening portion for battery insertion is provided only on the short side in the radiation detection device according to the present embodiment. 
         FIG. 11  is a perspective view showing a modification example in which two opening portions for battery insertion are provided on the same side surface in the radiation detection device according to the present embodiment. 
         FIG. 12  is a perspective view showing a modification example in which an opening portion for battery insertion is provided on the back surface of the rear surface member in the radiation detection device according to the present embodiment. 
         FIG. 13  is a cross-sectional view showing a modification example in which a support post formed on the support plate in the radiation detection device according to the present embodiment is formed such that the thickness of the support post gradually increases from a distal end portion thereof toward the support plate. 
         FIG. 14  is a cross-sectional view showing a modification example in which a support post formed on the support plate in the radiation detection device according to the present embodiment is formed such that the thickness of the support post gradually increases from a central portion in the axial direction toward the support plate. 
         FIG. 15  is a cross-sectional view showing a modification example in which an end portion of a reinforcing rib formed on the support plate in the radiation detection device according to the present embodiment is formed such that the thickness of the end portion gradually increases toward the support plate. 
         FIG. 16  is a cross-sectional view showing a modification example in which a reinforcing rib is formed inside the support post formed on the support plate in the radiation detection device according to the present embodiment. 
         FIG. 17  is a cross-sectional view showing a modification example in which the support post and the support plate in the radiation detection device according to the present embodiment are formed as separate bodies. 
         FIG. 18  is a cross-sectional view showing a modification example in which the support post and the support plate in the radiation detection device according to the present embodiment are formed as separate bodies and the axial direction of the support post is a direction along the in-plane direction of the support plate. 
         FIG. 19  is a cross-sectional view showing a modification example in which the support post is formed integrally with a bottom plate of the rear surface member in the radiation detection device according to the present embodiment. 
         FIG. 20  is an enlarged plan view showing a modification example in which the support posts in the radiation detection device according to the present embodiment are formed as only support posts having the same shape. 
         FIG. 21  is an enlarged plan view showing a modification example in which the support posts in the radiation detection device according to the present embodiment are formed in an octagonal shape. 
     
    
    
     DETAILED DESCRIPTION 
     Radiation Detection Device 
       FIG. 1  is a schematic perspective view of a radiation detection device  10  according to an embodiment of the invention. The radiation detection device  10  is an electronic cassette having an approximately rectangular shape in a plan view, and is driven by a battery  100  mounted on a housing  12  configured to include a front surface member  20  and a rear surface member  30 . 
     The planar size of the housing  12  is, for example, a size according to the international standard ISO4090: 2001 similar to a half size (383.5 mm×459.5 mm) film cassette or imaging plate (IP) cassette. Therefore, the radiation detection device  10  can also be used in a state in which the radiation detection device  10  is attached to an imaging table for a film cassette or an IP cassette. 
     The battery  100  is mounted on the radiation detection device  10  by being inserted into opening portions  30 A and  30 B formed at the central portions of two adjacent sides of the rear surface member  30  having an approximately rectangular shape in a plan view. The radiation detection device  10  is driven in a state in which the battery  100  is mounted in at least one of the opening portions  30 A and  30 B. 
     The opening portion  30 A is an opening portion formed at the central portion of a side surface (short side) along the Y direction shown in  FIG. 1  in the radiation detection device  10 , and the opening portion  30 B is an opening portion formed at the central portion of a side surface (long side), which is adjacent to the side surface on which the opening portion  30 A is formed and extends along the X direction perpendicular to the Y direction. 
     The front surface member  20  attached to the rear surface member  30  is configured to include an approximately rectangular transmission plate  22 . The transmission plate  22  is formed of, for example, a carbon material having a high X-ray transmittance. Radiation (X-rays P in the present embodiment) is incident from a direction approximately perpendicular to the in-plane direction of the transmission plate. 
     The front surface member  20  and the rear surface member  30  are formed by die casting using a magnesium alloy (Mg alloy) in the present embodiment. However, the material and manufacturing method of the front surface member  20  and the rear surface member  30  are not limited thereto, and the front surface member  20  and the rear surface member  30  can be molded using various metals, resins, and the like. 
       FIG. 2  is an exploded cross-sectional view of the housing  12  (refer to  FIGS. 1 and 3 ). As shown in  FIG. 2 , a radiation detection panel  40 , a support plate  50  to which the radiation detection panel  40  is attached, and a control substrate  60  for controlling the radiation detection panel  40  are provided inside the housing  12  so as to be interposed between the front surface member  20  and the rear surface member  30 . 
     The radiation detection device  10  shown in  FIG. 3  is formed by assembling the front surface member  20 , the rear surface member  30 , the radiation detection panel  40 , the support plate  50 , the control substrate  60 , the battery  100 , and the like (refer to  FIG. 1 ). 
     In  FIGS. 2 and 3 , the configuration of the support plate  50  is shown in a simplified manner. That is, the support plate  50  shown in  FIGS. 2 and 3  schematically shows the configuration of the support plate  50  in which a support post  54 , a reinforcing rib  56 B, and a protection rib  56 D to be described later are omitted. 
     Back Member-Double Frame 
     The rear surface member  30  is formed to comprise a double frame  32  (an outer rib  32 A and an inner rib  32 B) and a bottom plate  34 . As shown in  FIG. 4 , the double frame  32  is formed in a rectangular frame shape along the X and Y directions described above, and as shown in  FIG. 2 , the bottom plate  34  is fitted onto the bottom surface. The bottom plate  34  is fixed to the double frame  32  using a screw or the like. 
     In the double frame  32 , the inner rib  32 B for reinforcing a rectangular opening end into which the bottom plate  34  is fitted is erected toward the front surface member  20 . The double frame  32  is gradually raised from the bottom surface onto which the bottom plate  34  is fitted to the outer edge portion in a direction of the front surface member  20 , and the raised portion is the outer rib  32 A. 
     The rising height H 1  of the outer rib  32 A is set to be larger than the rising height H 2  of the inner rib  32 B, and the thickness W 1  of the outer rib  32 A is set to be larger than the thickness W 2  of the inner rib  32 B. As an example, the thickness W 1  is about 4 mm to 5 mm, and the thickness W 2  is about 0.8 mm. In the present embodiment, the outer rib  32 A is formed to be thicker than the inner rib  32 B over the entire circumference. However, the embodiment of the invention is not limited thereto, and the outer rib  32 A may be formed partially thinner than the inner rib  32 B. In other words, the inner rib  32 B may be formed partially thicker than the outer rib  32 A. 
     A packing (not shown) formed of resin is disposed between the front surface member  20  and the surface of the outer rib  32 A, which faces the front surface member  20 , in the rear surface member  30  and is compressed between the front surface member  20  and the rear surface member  30 , so that the internal space formed between the front surface member  20  and the rear surface member  30  is a watertight space. 
       FIG. 4  shows a plan view of the rear surface member  30  (a state in which the rear surface member  30  is viewed from the incidence direction of an X-ray P shown in  FIG. 1 ). As shown in  FIG. 4 , the outer rib  32 A is formed along the outer edge of the rear surface member  30  in a frame shape in which each side extends along the X and Y directions. On the inner side of the outer rib  32 A, the inner rib  32 B is formed in a frame shape along the outer rib  32 A. 
     It is assumed that “along” in the invention includes not only a state in which the outer rib  32 A and the inner rib  32 B are disposed in parallel so as to be spaced apart from each other but also a state in which the outer rib  32 A and the inner rib  32 B are disposed in parallel so as to be in contact with each other. In addition, the outer rib  32 A and the inner rib  32 B do not need to be strictly parallel, and a case where there is twisting due to manufacturing variations or a state in which at least one of the outer rib  32 A or the inner rib  32 B is disposed in a zigzag or wave shape is also included. 
     The “frame shape” in the invention indicates a state in which the outer rib  32 A is disposed in a portion, which covers the length of half or more of the circumferential length, in the outer edge portion of the rear surface member  30 . The outer rib  32 A does not need to be continuous, and may have an intermittent portion. In addition, as will be described later, an opening portion by a through hole may be formed in the outer rib  32 A. The same applies to the inner rib  32 B. 
     Through holes  32 AA and  32 AB are formed in the outer rib  32 A, so that the battery  100  (refer to  FIG. 1 ) can be inserted thereinto. The inner rib  32 B is not formed on the inner side in the insertion direction of the battery  100  in the through holes  32 AA and  32 AB. In other words, in the inner rib  32 B, intermittent portions  32 BA and  32 BB are formed on the inner sides of the through holes  32 AA and  32 AB in the outer rib  32 A. 
     The opening portion  30 A is formed by the through hole  32 AA and intermittent portion  32 BA, and the opening portion  30 B is formed by the through hole  32 AB and intermittent portion  32 BB. The through holes  32 AA and  32 AB and the intermittent portions  32 BA and  32 BB are examples of the “opening portion” in the invention. 
     Back Member-Connection Rib 
     As shown in  FIG. 4 , a plurality of connection ribs  36  are bonded to the outer rib  32 A and the inner rib  32 B, and the outer rib  32 A and the inner rib  32 B are connected to each other by the connection ribs  36 . The connection rib  36  extends in a direction approximately perpendicular to the outer rib  32 A and the inner rib  32 B. In the following description, the connection rib  36  extending from the corner portion of the outer rib  32 A toward the inner rib  32 B is referred to as a corner portion connection rib  36 A. In addition, the connection ribs  36  formed at both ends of the opening portions  30 A and  30 B are referred to as opening connection ribs  36 B. 
     The “corner portion” of the outer rib  32 A refers to a portion that is closer to the outer rib  32 A along the X direction than a center line CL 1  along the X direction of the rear surface member  30  and closer to the outer rib  32 A along the Y direction than a center line CL 2  along the Y direction of the rear surface member  30 . In addition, the “central portion” of the outer rib  32 A refers to a portion other than the “corner portion” described above, which is a portion including the center lines CL 1  and CL 2 . 
     A plurality of corner portion connection ribs  36 A are formed for each corner portion, and extend from the corner portion of the outer rib  32 A toward the inner rib  32 B in a direction crossing the X and Y directions. In the inner rib  32 B, an oblique portion  32 C extending in a direction approximately perpendicular to the corner portion connection rib  36 A is formed in a portion facing the corner portion of the outer rib  32 A. In other words, the inner rib  32 B is formed in a frame shape in which a part of the rectangular corner portion is chamfered, and the oblique portion  32 C connected such that the corner portion connection rib  36 A is perpendicular thereto is formed in the chamfered portion. 
     The oblique portion  32 C is formed in an end portion of a side, which is a side along the short side of the radiation detection device  10  (that is, a side along the Y direction) and on which the opening portion  30 A is formed, among the sides of the inner rib  32 B. 
     On the other hand, a side, which is a side along the short side of the radiation detection device  10  (that is, a side along the Y direction) and on which the opening portion  30 A is not formed, among the sides of the inner rib  32 B is disposed such that the separation distance from the outer rib  32 A is larger than those of the other sides. 
     The opening connection rib  36 B connects the outer rib  32 A and the inner rib  32 B at both end portions of the intermittent portions  32 BA and  32 BB in the inner rib  32 B. A mounting rib  38  that forms a mounting hole for fixing the support plate  50  (refer to  FIG. 2 ) is connected to the opening connection rib  36 B. 
     A plurality of mounting ribs  38  are provided, and are also connected to the connection rib  36  disposed in the vicinity of the corner portion connection rib  36 A in addition to the opening connection rib  36 B. The mounting rib  38  is also connected to the side of the inner rib  32 B where the separation distance from the outer rib  32 A is larger than those of the other sides. In addition, “vicinity of the corner portion connection rib  36 A” refers to a portion included in the “corner portion” described above. 
     Support Plate 
       FIG. 5  shows a plan view of the support plate  50  (a state in which the support plate  50  is viewed from a direction opposite to the incidence direction of the X-ray P shown in  FIG. 1 ). That is, a surface opposite to the surface to which the radiation detection panel  40  shown in  FIG. 2  is attached is shown. 
     The support plate  50  is formed using a magnesium lithium alloy (MgLi alloy) in which the mixing ratio (mass percentage) of lithium (Li) to magnesium (Mg) is 9%. 
     The mixing ratio of lithium (Li) is not limited to 9%, and may be 1.5% or more and 14% or less. In a case where the mixing ratio is less than 1.5%, it is difficult to obtain the weight reduction effect. That is, between a MgLi alloy and a Mg alloy having the same stiffness, the weight of the Mg alloy can be reduced. In a case where the mixing ratio is larger than 14%, it is necessary to consider corrosion resistance. 
     A support post  52  is formed integrally with the support plate  50 , and as shown in  FIG. 2 , is formed in a tubular shape having an axial direction along the out-of-plane direction (a direction perpendicular to the in-plane direction, that is, a normal direction) of the support plate  50 . The wall surface of the support post  52  is formed perpendicular to the support plate  50 . 
     As shown in  FIG. 3 , in a state in which the housing  12 , the radiation detection panel  40 , and the support plate  50  are assembled, the transmission plate  22  is disposed in contact with the radiation detection panel  40 . In addition, the support post  52  and the support post  54  to be described later are disposed in contact with the bottom plate  34  in the rear surface member  30 . “Disposed in contact” includes a state in which there is a gap that allows the support posts  52  and  54  to be in contact with the bottom plate  34  in a case where the transmission plate  22  is pressed from the outside at the time of use of the radiation detection device  10 . Although described in detail later, a case where the support post and the bottom plate are integrally formed is included. 
     As shown in  FIG. 5 , the support posts  52  are formed in an approximately regular hexagonal shape, and are disposed at predetermined intervals in a plan view. More specifically, the center of the support post  52  is disposed on the grid point of the equilateral triangle grid filling the plane. Each apex in the hexagonal support post  52  is chamfered in a curvilinear shape and disposed on the side of a triangle forming the equilateral triangle grid. 
     Between the support posts  52 , the hexagonal support post  54  in which adjacent sides have different lengths is disposed. More specifically, the center of the support post  54  is disposed on the center of gravity of the triangle forming the above-described equilateral triangle grid. In the support post  54 , a short side  54 A and a long side  54 B are formed so as to be alternately adjacent to each other, the short side  54 A faces a side  52 A of the support post  52 , and the long side  54 B faces the long side  54 B of the adjacent support post  54 . 
     In addition, between the support posts  52  adjacent to each other, the reinforcing rib  56 A is formed along the equilateral triangle grid described above. In addition, the reinforcing rib  56 B is formed between the support post  52  and the support post  54  adjacent to each other and between the support posts  54  adjacent to each other. 
     Furthermore, a frame-shaped outer peripheral portion reinforcing rib  56 C is formed along the outer periphery of the support plate  50  so as to surround the support posts  52  and  54  and the reinforcing ribs  56 A and  56 B. A protruding portion  58  is formed in the outer peripheral portion reinforcing rib  56 C that is an example of a reinforcing rib in the invention. The protruding portion  58  is formed at a position corresponding to the mounting hole formed by the mounting rib  38  of the rear surface member  30  described above. By inserting the protruding portion  58  into the mounting hole and bonding these to each other, the rear surface member  30  and the support plate  50  are bonded to each other. The mounting rib  38  is connected to the connection rib  36  disposed in the vicinity of the opening connection rib  36 B and the corner portion connection rib  36 A in the rear surface member  30 . Therefore, the outer peripheral portion reinforcing rib  56 C of the support plate  50  is bonded to the rear surface member  30  at the corner portions of the rear surface member  30  and both end portions of the opening portions  30 A and  30 B. 
     Furthermore, the protection rib  56 D is formed at positions corresponding to the opening portions  30 A and  30 B in the rear surface member  30 . The protection rib  56 D divides the outer peripheral portion reinforcing rib  56 C, and is disposed so as to surround the battery  100  (refer to  FIG. 1 ) inserted into the opening portions  30 A and  30 B. 
     Radiation Detection Panel 
     The radiation detection panel  40  is a quadrilateral flat plate having four sides at the outer edge in a plan view. As shown in  FIG. 6 , the radiation detection panel  40  includes a TFT active matrix substrate (TFT substrate)  47  in which a thin film transistor  48 A and a capacitor  48 B are formed on an insulating substrate. On the TFT substrate  47 , a scintillator (not shown) for converting incident X-rays into light is disposed. On the TFT substrate  47 , a sensor unit  48 C that generates electric charges by incidence of light converted by the scintillator is formed. 
     On the TFT substrate  47 , a plurality of pixels  48  each including the sensor unit  48 C, the capacitor  48 B, and the thin film transistor  48 A are provided in a two-dimensional manner in a predetermined direction (horizontal direction in  FIG. 6 =row direction) and a direction (vertical direction in  FIG. 6 =column direction) crossing the predetermined direction. 
     A plurality of gate lines  42 B for turning on and off each thin film transistor  48 A and a plurality of data lines  42 A for reading out electric charges through the thin film transistor  48 A in the ON state are provided in the radiation detection panel  40 . The gate lines  42 B and the data lines  42 A extend in a direction crossing each other. 
     A plurality of connectors  44 A for line connection are provided side by side on one end side of the data line  42 A, and a plurality of connectors  44 B are provided side by side on one end side of the gate line  42 B. 
     One end of a flexible cable  46 A is connected to the connector  44 A, and one end of the flexible cable  46 B is connected to the connector  44 B. 
     Control Substrate 
     As shown in  FIG. 7 , a signal processing unit  62 A, a gate line driver  62 B, an image memory  62 C, a controller  62 D, a wireless communication unit (not shown), and the like are provided on the control substrate  60 . 
     Each gate line  42 B of the TFT substrate  47  is connected to the gate line driver  62 B through the flexible cable  46 B, and each data line  42 A of the TFT substrate  47  is connected to the signal processing unit  62 A through the flexible cable  46 A. 
     The gate line driver  62 B and the signal processing unit  62 A are disposed along two adjacent sides of the support plate  50 , and are directly bonded to the support plate  50 . That is, the gate line driver  62 B and the signal processing unit  62 A are disposed so as to be in direct contact with the support plate  50  without using a mount member, such as a resin. 
     The gate line driver  62 B and the signal processing unit  62 A are attached to a side of the support plate  50  different from the side on which the protection rib  56 D for protecting the battery  100  is provided. The image memory  62 C and the controller  62 D are attached at positions that do not interfere with the support posts  52  and  54 . 
     The arrangement of the gate line driver  62 B, the signal processing unit  62 A, the image memory  62 C, and the controller  62 D shown in  FIG. 7  is an example, and can be appropriately changed according to the shapes or the arrangement of the support posts. In other words, the arrangement of the support posts can be appropriately adjusted according to the sizes or the shapes of the gate line driver  62 B, the signal processing unit  62 A, and the image memory  62 C. 
     The thin film transistors  48 A of the TFT substrate  47  are sequentially turned on row by row by a signal supplied from the gate line driver  62 B through the gate line  42 B. The electric charges read out by the thin film transistor  48 A that is turned on are transmitted as an electric signal through the data line  42 A and input to the signal processing unit  62 A. As a result, the electric charges are sequentially read out row by row, and a two-dimensional radiation image can be acquired. 
     Although not shown, the signal processing unit  62 A includes a sample and hold circuit and an amplification circuit for amplifying the input electric signal for each data line  42 A, and the electric signal transmitted through each data line  42 A is amplified by the amplification circuit and then held in the sample and hold circuit. In addition, a multiplexer and an analog/digital (A/D) converter are connected in order to the output side of the sample and hold circuit. The electric signals held in the respective sample and hold circuits are sequentially (serially) input to the multiplexer and converted into digital image data by the A/D converter. 
     The image memory  62 C is connected to the signal processing unit  62 A, and the image data output from the A/D converter of the signal processing unit  62 A is sequentially stored in the image memory  62 C. The image memory  62 C has a storage capacity capable of storing image data of a predetermined number of sheets, and image data obtained by imaging is sequentially stored in the image memory  62 C each time a radiation image is captured. 
     The image memory  62 C is connected to the controller  62 D. The controller  62 D is a microcomputer, and comprises a central processing unit (CPU), a memory including a read only memory (ROM) and a random access memory (RAM), and a non-volatile storage unit including a flash memory and the like. The controller  62 D controls the overall operation of the radiation detection device  10 . 
     A wireless communication unit (not shown) is connected to the controller  62 D. The wireless communication unit complies with a wireless local area network (LAN) standard represented by Institute of Electrical and Electronics Engineers (IEEE) 802.11a/b/g or the like, and controls transmission of various kinds of information to and from an external apparatus by wireless communication. The controller  62 D can wirelessly communicate with an external apparatus, such as a console that controls the entire radiation imaging, through the wireless communication unit, so that it is possible to transmit and receive various kinds of information to and from the console. 
     The various circuits or elements (the gate line driver  62 B, the signal processing unit  62 A, the image memory  62 C, the wireless communication unit, or the microcomputer functioning as the controller  62 D) operate with the power supplied from the battery  100 . In  FIG. 7 , wirings for connecting the battery  100  to various circuits or elements are not shown. 
     In the radiation detection device  10  according to the embodiment of the invention, as shown in  FIGS. 2 and 3 , the radiation detection panel  40  is disposed between the front surface member  20  and the rear surface member  30 . The outer rib  32 A is formed along the outer edge of the rear surface member  30 , and the inner rib  32 B is formed on the inner side of the outer rib  32 A. Therefore, the stiffness of the rear surface member  30  is higher than that in a structure that does not have either the inner rib  32 B or the outer rib  32 A or a structure that does not have any of the inner rib  32 B and the outer rib  32 A. For this reason, for example, even in a case where an impact at the time of drop is applied to the radiation detection device  10 , the rear surface member  30  is hardly deformed. Accordingly, the radiation detection panel  40  is protected. 
     In the radiation detection device  10 , as shown in  FIG. 4 , the outer rib  32 A and the inner rib  32 B are formed in a frame shape. For this reason, the rear surface member  30  is less likely to be distorted as compared with a case where at least one of the outer rib or the inner rib is formed, for example, only in a corner portion of the rear surface member  30  or only on a side along the X direction or the Y direction. Therefore, the effect of protecting the radiation detection panel  40  is high. 
     In the radiation detection device  10 , the outer rib  32 A is formed thicker than the inner rib  32 B. Therefore, for example, compared with a case where the thickness of the inner rib is larger than that of the outer rib or a case where the inner rib and the outer rib have the same thickness, the outer rib to which the impact from the outside is directly applied is less likely to be deformed. As a result, deformation of the rear surface member  30  due to impact can be efficiently suppressed. 
     In the radiation detection device  10 , the outer rib  32 A and the inner rib  32 B are connected to each other by the connection rib  36 . Therefore, the impact received by the outer rib  32 A can be transmitted to the inner rib  32 B through the connection rib  36 . As a result, compared with a configuration without the connection rib  36 , the effect of improving the stiffness of the rear surface member  30  by the inner rib  32 B can be enhanced. 
     A part of the connection rib  36  is the corner portion connection rib  36 A extending from the corner portion of the outer rib  32 A toward the inner rib  32 B, and the oblique portion  32 C in the inner rib  32 B is formed so as to be perpendicular to the corner portion connection rib  36 A. 
     Therefore, an impact C applied to the corner portion of the outer rib  32 A is transmitted to the oblique portion  32 C through the corner portion connection rib  36 A. In this case, the corner portion connection rib  36 A can function as a compression member between the outer rib  32 A and the oblique portion  32 C to resist an impact. 
     In a case where the impact C is applied to the corner portion of the outer rib  32 A, a tensile force T acts on a corner portion adjacent to the corner portion to which the impact is applied. In this case, the corner portion connection rib  36 A can function as a tension member between the outer rib  32 A and the oblique portion  32 C to suppress the deformation of the rear surface member  30 . 
     As shown in  FIGS. 2 and 3 , the radiation detection device  10  comprises the support plate  50  for supporting the radiation detection panel  40 , and the protruding portion  58  in the support plate  50  is inserted into the mounting hole formed by the mounting rib  38  in the rear surface member  30  and bonded thereto. Therefore, the rear surface member  30  is stiffened by the support plate  50  that is a plate material, and shear deformation along the in-plane direction of the support plate  50  is suppressed. In addition, bending deformation along the out-of-plane direction of the support plate  50  is suppressed. 
     The support plate  50  is bonded to the rear surface member  30  at the corner portion of the rear surface member  30 . Therefore, for example, compared with a case where the support plate  50  is bonded to the rear surface member  30  at a portion other than the corner portion, the area of a portion surrounded by the bonded portion is increased. As a result, the effect of improving the stiffness of the rear surface member  30  is enhanced. 
     As a method of bonding the support plate  50  and the rear surface member  30  to each other, in addition to the method of inserting the protruding portion  58  into the mounting hole formed by the mounting rib  38 , various methods such as screwing, welding, and bonding can be adopted. Materials of the support plate  50  and the rear surface member  30  can be freely selected, and any bonding method suitable for the materials can be selected. 
     Furthermore, as shown in  FIG. 5 , a reinforcing rib  56  is formed on the support plate  50 . The protruding portion  58  is formed in the outer peripheral portion reinforcing rib  56 C formed in a frame shape among the reinforcing ribs  56 . The support plate  50  is fixed to the rear surface member  30  by the protruding portion  58 . Therefore, the rear surface member  30  has a triple frame structure of the outer rib  32 A, the inner rib  32 B, and the outer peripheral portion reinforcing rib  56 C in a state in which the rear surface member  30  is bonded to the support plate  50 . As a result, the effect of suppressing the deformation of the rear surface member  30  is further enhanced. 
     In a portion surrounded by the outer peripheral portion reinforcing rib  56 C in the support plate  50 , the reinforcing ribs  56 A and  56 B and the support posts  52  and  54  are connected to each other. Therefore, compared with the configuration without the reinforcing ribs  56 A and  56 B and the support posts  52  and  54 , the outer peripheral portion reinforcing rib  56 C is less likely to be deformed. As a result, the effect of suppressing the deformation of the rear surface member  30  is further enhanced. 
     Since the support plate  50  and the rear surface member  30  are bonded to each other as described above, the rear surface member  30  is reinforced, and the support plate  50  is similarly reinforced. That is, in the support plate  50 , the protruding portion  58  in the outer peripheral portion reinforcing rib  56 C formed in the outer peripheral portion of the support plate  50  is fixed to the rear surface member  30 . Therefore, the stiffness of the support plate  50  is higher than that in a configuration in which the support plate  50  is not fixed to the rear surface member  30 . 
     The rear surface member  30  comprises the mounting rib  38  to which the protruding portion  58  of the support plate  50  is attached, the connection rib  36  to which the mounting rib  38  is connected, and the outer rib  32 A and the inner rib  32 B connected to each other by the connection rib  36 . Therefore, the rear surface member  30  is stiffened by the frame-shaped outer rib  32 A and inner rib  32 B. 
     In the radiation detection device  10 , as shown in  FIG. 4 , the intermittent portions  32 BA and  32 BB and the through holes  32 AA and  32 AB as opening portions, through which the battery  100  as an externally inserted member is inserted, are formed in the outer rib  32 A and the inner rib  32 B. The opening connection rib  36 B is formed at both ends of the opening portions  30 A and  30 B in the rear surface member  30  formed as described above. Therefore, since the opening portions  30 A and  30 B are reinforced, the opening portions  30 A and  30 B are hardly deformed. 
     The mounting rib  38  is connected to the opening connection rib  36 B, and the support plate  50  is bonded to the mounting hole formed by this mounting rib  38 . Therefore, the opening portions  30 A and  30 B are reinforced. In addition, since the protection rib  56 D is formed on the support plate  50 , the battery  100  inserted through the opening portions  30 A and  30 B is protected. 
     The opening portions  30 A and  30 B are formed at the central portion of the rear surface member  30 , that is, on the center lines CL 1  and CL 2 . Therefore, compared with a case where the opening portion is formed in the vicinity of the corner portion of the rear surface member  30 , the influence in a case where an impact is applied to the corner portion is hardly received. For this reason, the opening portions are hardly deformed. 
     The opening portions  30 A and  30 B are formed on two sides adjacent to each other in the rear surface member  30 . Therefore, as shown in  FIG. 7 , interference between the battery  100  and the signal processing unit  62 A and the gate line driver  62 B on the control substrate  60 , which are provided along the two adjacent sides of the support plate  50 , is suppressed. In addition, interference between the battery  100  and the flexible cables  46 A and  46 B connected to the signal processing unit  62 A and the gate line driver  62 B is suppressed. 
     In the radiation detection device  10 , as shown in  FIGS. 2 and 3 , the bottom plate  34  of the rear surface member  30  is fixed to the double frame  32  using a screw or the like. Therefore, by removing the screw, the signal processing unit  62 A, the gate line driver  62 B, the image memory  62 C, the controller  62 D, and the like on the control substrate  60  can be replaced or maintenance therefor can be performed. In addition, the double frame  32  and the bottom plate  34  can be integrally formed. In this case, the stiffness of the double frame  32  can be further improved. 
     In the radiation detection device  10 , the double frame  32  in the rear surface member  30  is gradually raised from the bottom surface onto which the bottom plate  34  is fitted to the outer edge portion in the direction of the front surface member  20 , and the raised portion is the outer rib  32 A. Therefore, for example, in the case of inserting the radiation detection device  10  between the bed and the patient, a situation in which the outer rib  32 A is caught on a sheet or clothes is suppressed. As a result, the workability is improved. 
     A packing (not shown) is disposed between the front surface member  20  and the surface of the outer rib  32 A, which faces the front surface member  20 , in the rear surface member  30 , so that the internal space formed between the front surface member  20  and the rear surface member  30  is a watertight space. Therefore, it is possible to protect the support plate  50  formed of a MgLi alloy having lower corrosion resistance than a Mg alloy. 
     In the radiation detection device  10 , a side, which is a side along the short side of the radiation detection device  10  (that is, a side along the Y direction) and on which the opening portion  30 A is not formed, among the sides of the inner rib  32 B is disposed such that the separation distance from the outer rib  32 A is larger than those of the other sides. Therefore, compared with a case where the separation distance is the same as those of the other sides, the effect of suppressing deformation with respect to the impact along the X direction is enhanced. 
     In the radiation detection device  10 , the opening portions  30 A and  30 B through which the battery  100  is inserted are formed on the side surface of the rear surface member  30 . Therefore, for example, in a case where the radiation detection device  10  is used in a state in which the radiation detection device  10  is attached to the imaging table, the battery  100  and the imaging table are not easily caught with each other, so that the imaging table is easily ejected. 
     On the other hand, for example, in a case where an opening portion for installing the battery  100  is formed on the back surface of the rear surface member  30 , the battery cover or the like may protrude from the back surface to be caught with the imaging table. In a case where the opening portion for the battery is provided on the back surface which often contacts various places, such as a work table and a bed, dust or the like is likely to clog a gap between the battery and the rear surface member  30 . 
     In the radiation detection device  10 , as shown in  FIGS. 2 and 5 , a plurality of tubular support posts  52  and  54  are formed in contact with the surface of the support plate  50  not facing the radiation detection panel  40 , and the support posts  52  and  54  are disposed in contact with the bottom plate  34  of the housing  12 . In addition, “in contact with” includes a state of being formed integrally with the support plate  50  as in the case of the support posts  52  and  54 . 
     Here, the support plate  50  is formed of a MgLi alloy. The MgLi alloy has a smaller specific gravity than, for example, a Mg alloy or an aluminum alloy (Al alloy). For this reason, by using the MgLi alloy as the support plate  50 , the weight can be reduced as compared with the Mg alloy or the like. 
     The MgLi alloy has a smaller Young&#39;s modulus and a lower stiffness than the Mg alloy, the Al alloy, and the like. In the present embodiment, in a case where the radiation detection device  10  is pressed from the outside at the time of use of the radiation detection device  10  and a load in the out-of-plane direction acts on the radiation detection panel  40 , the load received by the support plate  50  is transmitted to the housing  12  by the support posts  52  and  54 . Therefore, the support plate  50  is hardly deformed. In addition, by forming the support posts  52  and  54  in a tubular shape, both suppression of deformation of the support plate  50  and reduction in the weight of the support plate  50  can be realized. 
     In the radiation detection device  10 , the support posts  52  and  54  are formed in a hexagonal shape, and the support posts  52  and  54  adjacent to each other are disposed such that the side  52 A and the short side  54 A face each other. In addition, the support posts  54  adjacent to each other are disposed such that the long sides  54 B face each other. 
     Therefore, the supporting force of the support posts  52  and  54  can be increased. That is, in a case where the radiation detection device  10  is pressed from the outside at the time of use of the radiation detection device  10  and a load in the out-of-plane direction acts on a portion of the radiation detection panel  40  between the support posts  52  and  54 , the load is transmitted to the support posts  52  and  54 . 
     In this case, since the load is supported by the side  52 A and the short side  54 A, the internal stress generated in the support posts  52  and  54  is dispersed, for example, in the case of supporting the support posts  52  and  54  at the apex of the hexagonal shape. Therefore, the supporting force of the support posts  52  and  54  is increased. 
     In the radiation detection device  10 , the support posts  52  and  54  are formed along a direction perpendicular to the in-plane direction, and the axial direction of each of support posts  52  and  54  is the out-of-plane direction of the support plate  50 . Therefore, the supporting force against the external force from the direction perpendicular to the support plate  50  and the transmission plate  22  is high. 
     In the radiation detection device  10 , the support posts  52  and  54  are molded integrally with the support plate  50 . Therefore, the load received by the support plate  50  is easily transmitted to the support posts  52  and  54 . In addition, for example, compared with a case where the support posts  52  and  54  and the support plate  50  are bonded to each other, the followability to the out-of-plane deformation of the support plate  50  is high, and the durability is high. 
     In the radiation detection device  10 , the reinforcing ribs  56 A and  56 B in contact with the support plate  50  are bridged between the support posts  52 , between the support posts  54 , and between the support posts  52  and  54 . Therefore, in a case where the load in the out-of-plane direction acts between the support posts  52 , between the support posts  54 , and between the support posts  52  and  54 , the load is transmitted to the reinforcing ribs  56 A and  56 B and further transmitted to the support posts  52  and  54 . 
     As described above, since the load is once transmitted to the reinforcing ribs  56 A and  56 B before the load is transmitted to the support posts  52  and  54 , the reinforcing ribs  56 A and  56 B function as beam members to suppress the out-of-plane deformation of the support plate  50 . 
     In the present embodiment, the gate line driver  62 B and the signal processing unit  62 A are disposed so as to be in direct contact with the support plate  50  without using a mount member, such as a resin. Therefore, since the heat emitted from the gate line driver  62 B and the signal processing unit  62 A is dissipated to the support plate  50 , the durability of the gate line driver  62 B and the signal processing unit  62 A is improved. In addition, local heating of the inside of the radiation detection device  10  is suppressed. 
     Other Embodiments 
     In the above embodiment, as shown in  FIG. 4 , the connection rib  36  extends in a direction approximately perpendicular to the outer rib  32 A and the inner rib  32 B. However, the embodiment of the invention is not limited thereto. For example, as in the case of a connection rib  36 C shown in  FIG. 8 , a connection rib may be provided so as to extend in a direction crossing the outer rib  32 A and the inner rib  32 B so that a triangle is formed by the connection rib  36 C and the outer rib  32 A or the inner rib  32 B. In this case, since the outer rib  32 A, the inner rib  32 B, and the connection rib  36 C form a truss structure, it is possible to increase the stiffness of the double frame  32 . 
     In the above embodiment, the connection rib  36  is “bonded” to the outer rib  32 A and the inner rib  32 B. However, the embodiment of the invention is not limited thereto. For example, a gap may be provided between the connection rib  36  and the inner rib  32 B. The size of the gap is preferably such that the gap is closed in a case where an external force is applied to the outer rib  32 A to bring the connection rib  36  and the inner rib  32 B into contact with each other. In this case, the external force can be transmitted to the inner rib  32 B. 
     In a case where it is necessary to increase the gap between the connection rib  36  and the inner rib  32 B, for example, the connection rib  36  is formed thick, so that the external force applied to the outer rib  32 A is transmitted from the connection rib  36  to the rear surface side (back side of the sheet in  FIG. 4 ) of the connection rib  36  in the double frame  32 . By forming the gap in this manner, various wirings in the radiation detection panel  40  or the control substrate  60  can be disposed inside the double frame, that is, between the outer rib  32 A and the inner rib  32 B. This can improve the degree of freedom in wiring arrangement. 
     In addition, in order to improve the degree of freedom in wiring arrangement, at least one of the inner rib  32 B and the connection rib  36  may be partially lowered or cut away to form a defect portion, and the wiring may be made to pass through the defect portion. Instead of or in addition to the defect portion, a through hole may be formed in the inner rib  32 B and the connection rib  36 , and the wiring may be made to pass through the through hole. 
     In the above embodiment, as shown in  FIG. 4 , the thickness H 2  of the inner rib  32 B is set to be smaller than the thickness H 1  of the outer rib  32 A. However, the embodiment of the invention is not limited thereto. For example, as in the case of an inner rib  32 D shown in  FIG. 9 , the inner rib may have the same thickness as the outer rib  32 A. In this case, the stiffness of the double frame  32  can be improved. Alternatively, the width H 3  of the double frame  32  can be reduced while maintaining the stiffness of the double frame  32 . By reducing the width H 3  of the double frame  32 , for example, the sizes of the support plate  50  and the radiation detection panel  40  can be increased to increase the detectable radiation dose. 
     In the above embodiment, as shown in  FIG. 4 , the inner rib  32 B on the short side where the opening portion  30 A is not formed is disposed such that the separation distance from the outer rib  32 A is larger than that in the case of the inner rib  32 B on the other sides. However, the embodiment of the invention is not limited thereto. For example, as shown in  FIG. 9 , the separation distance between the inner rib  32 D and the outer rib  32 A on the short side where the opening portion  30 A is not formed may be the same as the separation distance between the inner rib  32 D and the outer rib  32 A on the other sides. In this case, it is preferable to provide the oblique portion  32 C at both ends of the inner rib  32 D on the short side where the opening portion  30 A is not formed. 
     In the embodiment shown in  FIG. 9 , the thick inner rib  32 D may be replaced with the thin inner rib  32 B. Alternatively, the separation distance between the thick inner rib  32 D and the outer rib  32 A on the short side where the opening portion  30 A is not formed may be larger than the separation distance between the inner rib  32 D and the outer rib  32 A on the other sides. 
     In the above embodiment, as shown in  FIG. 1 , the opening portions  30 A and  30 B through which the battery  100  is inserted are formed on the adjacent side surfaces of the rear surface member  30 . However, the embodiment of the invention is not limited thereto. For example, as shown in  FIG. 10 , the opening portion  30 A may be formed on only one short side of the rear surface member  30 . Alternatively, the opening portions  30 A and  30 C may be formed on two short sides facing each other. 
     Alternatively, as shown in  FIG. 11 , two opening portions  30 D and  30 E may be formed on only one long side of the rear surface member  30 . Alternatively, although not shown, one opening portion may be provided on only one long side of the rear surface member  30 . 
     In addition, as in the case of an opening portion  30 F shown in  FIG. 12 , an opening portion may be provided not on the side surface of the rear surface member  30  but on the rear surface thereof. In the embodiment having two opening portions, one battery may be an externally inserted battery, and the other battery may be a built-in battery. The built-in battery comprises a terminal, and is charged by connecting a charging cable from the outside. As components inserted through the opening portion, not only the battery but also a memory card, a communication device, and the like can be appropriately adopted. 
     In the above embodiment, the outer rib  32 A and the inner rib  32 B are formed in a frame shape. However, the embodiment of the invention is not limited thereto. For example, by forming at least one of the outer rib  32 A or the inner rib  32 B only in the corner portion of the rear surface member  30 , it is possible to efficiently protect the corner portion that is susceptible to collision and deformation. 
     Alternatively, the outer rib  32 A and the inner rib  32 B may be partially formed in a part of the side surface along the X and Y directions without being limited to the corner portion of the rear surface member  30 . Since the stiffness of the part is also increased by partially forming the outer rib  32 A and the inner rib  32 B, the effect of protecting the radiation detection panel  40  can be obtained. 
     In the above embodiment, as shown in  FIG. 2 , the wall surface of the support post  52  is formed perpendicular to the support plate  50 . However, the embodiment of the invention is not limited thereto. For example, as in the case of a support post  52 B shown in  FIG. 13 , a support post may be formed such that the thickness of the support post gradually increases from the distal end of the support post  52 B toward the support plate  50 . In this manner, since the strength is improved compared with the support post  52  and the draft after molding is obtained, it is possible to enhance the manufacturing efficiency. The draft angle is preferably about 6° with respect to the normal direction of the support plate  50 . 
     Alternatively, as in the case of a support post  52 C shown in  FIG. 14 , a support post may be formed such that the thickness of the support post gradually increases toward the support plate  50  from an intermediate portion in a height direction along the axial direction. In this manner, it is possible to reinforce the root portion of the support post  52 C on which stress is easily concentrated while suppressing an increase in the weight of the entire support plate  50 . 
     In the above embodiment, as shown in  FIG. 2 , the thickness of the reinforcing rib  56 A along the axial direction of the support post  52  is fixed. However, the embodiment of the invention is not limited thereto. For example, as in the case of a reinforcing rib  56 E shown in  FIG. 15 , the thickness of a reinforcing rib along the axial direction of the support post  52  may be gradually increased at a place of connection with the support post  52 . In this case, in a case where a load is input from the support plate  50  to the reinforcing rib  56 E, the resistance against bending moment and shear force acting on the boundary between the reinforcing rib  56 E and the support post  52  is increased. Therefore, the load can be efficiently transmitted to the support post  52 . 
     The configuration in which the thickness is gradually increased along the axial direction of the support post  52  at the place of connection with the support post  52  as described above can also be applied to the reinforcing rib  56 B. 
     In the above embodiment, as shown in  FIG. 2 , the inside of the tubular support post  52  is hollow. However, the embodiment of the invention is not limited thereto. For example, as shown in  FIG. 16 , an inner reinforcing rib  56 F may be bridged between the inner walls of the support post  52 . In this case, the buckling of the support post  52  can be suppressed. 
     In addition, as shown by the broken line in  FIG. 5 , the inner reinforcing rib  56 F is preferably disposed on the extension of the reinforcing rib  56 A. In this case, deformation of the support post  52  due to the load transmitted from the reinforcing rib  56 A is suppressed. 
     In the above embodiment, the support post  52  is formed integrally with the support plate  50 , and is formed in a tubular shape in which the axial direction is the out-of-plane direction (direction perpendicular to the in-plane direction) of the support plate  50 . However, the embodiment of the invention is not limited thereto. 
     As an example, as in the case of a support post  52 D shown in  FIG. 17 , a support post and the support plate  50  may be provided as separate bodies. In this case, the reinforcing ribs  56 A and  56 B may be formed integrally with the support post  52 D or may be formed as separate bodies. In a case where the reinforcing ribs  56 A and  56 B and the support post  52 D are separate bodies, the reinforcing ribs  56 A and  56 B and the support post  52 D are fixed by bonding. It is preferable that the support post  52 D and the reinforcing ribs  56 A and  56 B are bonded to the support plate  50 . 
     As another example, as in the case of a support post  52 E shown in  FIG. 18 , a support post may be formed such that the axial direction of the support post follows the in-plane direction of the support plate  50 . 
     As still another example, as in the case of a support post  52 F shown in  FIG. 19 , a support post may be formed integrally with the bottom plate  34  of the rear surface member  30 . 
     Also by the support posts  52 D,  52 E, and  52 F, in a case where a load in the out-of-plane direction acts on the transmission plate  22  and the radiation detection panel  40 , it is possible to stand the load. The configurations of the support posts  52 D,  52 E, and  52 F can also be applied to the support post  54  shown in  FIG. 5 . 
     In the case of providing the support post and the support plate  50  as separate bodies, the support post can be formed of various materials. As the support post, metal-based materials, such as an Al alloy and a Mg alloy, can be used as an example. 
     As another example, it is possible to use resin materials, such as acrylonitrile butadiene styrene (ABS) resin, polycarbonate (PC) resin, modified-polyphenyleneether (PPE) resin, polyethylene (PE) resin, high density polyethylene (HDPE) resin, polypropylene (PP) resin, polyoxymethylene (POM) resin, liquid crystal polymer (LCP) resin, and polyetheretherketone (PEEK) resin. 
     As still another example, it is possible to use composite resin materials (reinforced plastics) reinforced by adding glass fiber, cellulose nanofiber, talc (calcium-based reinforcing material), magnesium fiber, and the like to the resin materials. As still another example, a carbon material, fiber-reinforced plastics (FRP), and the like can be used. 
     In the above embodiment, the two support posts  52  and  54  having different shapes are disposed on the support plate  50 . However, the embodiment of the invention is not limited thereto. For example, as shown in  FIG. 20 , only the support post  52  having an approximately regular hexagonal shape may be used. In such a case, it is preferable that the sides  52 A of the support posts  52  adjacent to each other are disposed so as to face each other. 
     In the above embodiment, the support posts  52  and  54  are formed in a hexagonal shape. However, the embodiment of the invention is not limited thereto. For example, as in a support post  52 G shown in  FIG. 21 , a support post may have an octagonal shape. Also in such a case, it is preferable that sides  52 GA of the support posts  52 G adjacent to each other are disposed so as to face each other.