Patent Publication Number: US-2018031020-A1

Title: Joining device and assembled structure having the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese Patent Application No. 2016-147650, filed Jul. 27, 2016, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a joining device and an assembled structure having the same, and particularly relates to a joining device used in assembling boards of ready-to-assemble furniture with each other and an assembled structure that is assembled using such a joining device. 
     Background 
     In the related art, ready-to-assemble furniture is known that is assembled into various forms by joining a plurality of boards in any combination. For example, when assembling ready-to-assemble furniture, such as shelf, a frame is formed with a top board, a base board, and right and left side boards, and a back board is attached to this frame, and further, a plurality of shelf boards are attached inside the frame. Here, a joining device that joins the top board, the base board, the side boards, the back board and the shelf boards with each other may be a screw. 
     However, a large force is required for joining the boards with each other by screwing a screw with a screw-driver while placing the boards on top of each other, and thus it is not an easy task to perform for women and elderly people. Also, when a screwing direction of a screw into the board is deviated, the screw may protrude from the board, and break the board. 
     Accordingly, in order to couple a plurality of boards, a coupling structure is known that couples a plurality of boards with each other without using tools such as a screw-driver, by pushing a joint member incorporated in one board, i.e., a male member, into an engaging member incorporated in another board, i.e., a female member, (e.g., see Japanese Patent No. 5719485). 
     A coupling structure described in Japanese Patent No. 5719485 is provided with a male member which is a rod-like member of a certain length and a hollow female member. An outer surface of the male member is provided with a joint member engagement portion wherein locking portions having concentric crests and troughs are continuously formed. The locking portion has a first inclined surface formed at a predetermined angle with respect to a longitudinal direction of the male member, and a second inclined surface formed approximately perpendicular to the longitudinal direction of the male member. On an inner surface of the female member, a plurality of hooks are formed. 
     When the male member is inserted into the female member, the locking portion is locked to the hooks of the female member, and the male member and the female member come to a mated state. 
     According to Japanese Patent No. 5719485, once the male member and the female member are mated, the mated state between the locking portion of the male member and the hooks of the female member is not released unless they are destroyed. Therefore, in a case where boards have been attached to each other in an incorrect combination or in a case where one wants to disassemble and move the furniture to another place, it is necessary to destroy the locking portion of the male member and the hooks of the female member to release the joined state between the boards. 
     The present disclosure is related to providing a joining device that enables joining and releasing of a male member and a female member, as well as an assembled structure having the same. 
     SUMMARY 
     According to an aspect of the present disclosure, a joining device comprises a male member including a shaft portion and a female member including a mating portion whereto the shaft portion is inserted and fitted, the female member having a bottomed tubular shape, the male member and the female member being capable of being detachably joined with each other, the shaft portion including a plurality of protruded portions on an outer surface thereof along an axial line direction and a slit at a tip portion in a direction of insertion into the mating portion, each protruded portion of the plurality of protruded portions having an arc shape in a cross section taken along the axial line direction and being protruded over an entire perimeter about an axial line of the shaft portion, the slit lying along the axial line, the mating portion having a plurality of recessed portions on an inner surface thereof along an axial line direction and a bottom portion configured to close the mating portion, each recessed portion of the plurality of recessed portions having an arc shape in a cross section taken along the axial line direction and being recessed over an entire perimeter about an axial line of the mating portion, the bottom portion having a rod-like projected portion projecting in a direction opposite to the direction of insertion and capable of being inserted into the slit, the slit having a length that divides the protruded portion provided on a side of the tip portion of the shaft portion along the axial line direction, the projected portion having a length that reaches the recessed portion provided at a position closest to the bottom portion among the plurality of recessed portions, wherein the shaft portion and the mating portion are capable of being joined by being engaged at the plurality of protruded portions and the plurality of recessed portions, an interference fit being created between the slit and the projected portion. 
     Preferably, the plurality of protruded portions are spaced apart from each other in the axial line direction of the shaft portion by a predetermined interval, and the plurality of recessed portions are spaced apart from each other in the axial line direction of the mating portion by a predetermined interval. 
     Also, preferably, the projected portion has a columnar portion formed integrally with the bottom portion and creating an interference fit with the slit, and a tapered portion formed integrally on a tip side of the columnar portion. 
     According to another aspect of the present disclosure, an assembled structure comprises a first assembly component, a second assembly component, and a male member including a shaft portion and a female member including an mating portion whereto the shaft portion is inserted and fitted, the male member and the female member being capable of being detachably joined with each other, the first and second assembly components being capable of being assembled by being joined with each other, the shaft portion including a plurality of protruded portions on an outer surface thereof along an axial line direction and a slit at a tip portion in a direction of insertion into the mating portion, each protruded portion of the plurality of protruded portions having an arc shape in a cross section taken along the axial line direction and being protruded over an entire perimeter about an axial line of the shaft portion, the slit lying along the axial line, the mating portion having a plurality of recessed portions on an inner surface thereof along an axial line direction and a bottom portion configured to close the mating portion, each recessed portion of the plurality of recessed portions having an arc shape in a cross section taken along a direction of the axial line and recessed over an entire perimeter about an axial line of the mating portion, the bottom portion having a rod-like projected portion projecting in a direction opposite to the direction of insertion and capable of being inserted into the slit, the slit having a length that divides the protruded portion provided on a side of the tip portion side of the shaft portion along the axial line direction, the projected portion having a length that reaches the recessed portion provided at a position closest to the bottom portion among the plurality of recessed portions, the female member being attached to one of the first assembly component and the second assembly component, the male member being attached to one of the second assembly component and the first assembly component, the first and second assembly components being joined with each other by engagement of the shaft portion of the male member and the mating portion of the female member at the plurality of protruded portions and the plurality of recessed portions, an interference fit being created between the slit and the projected portion. 
     According to the present disclosure, a male member and a female member can be joined and released. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a joining device according to a first embodiment. 
         FIG. 2  is a side elevation of a male member of the joining device according to the first embodiment. 
         FIG. 3A  is a perspective view showing a female member of the joining device according to the first embodiment. 
         FIG. 3B  is a cross-sectional view showing a female member of the joining device according to the first embodiment taken along an axial line of the female member. 
         FIG. 4  is a diagram showing a state where a tip portion of the male member is inserted into the female member. 
         FIG. 5  is a diagram showing a state where the male member is partially engaged with the female member. 
         FIG. 6  is a diagram showing a state where the male member and the female member are completely joined. 
         FIG. 7  is a side elevation of a male member of a joining device according to a second embodiment. 
         FIG. 8A  is a schematic perspective view of an assembled structure including joining devices according to the first and second embodiments. 
         FIG. 8B  is a cross-sectional view of an assembled structure including joining devices according to the first and second embodiments taken along line I-I in  FIG. 8A . 
         FIG. 9A  is an explanatory diagram of a joining operation using the joining device according to the first embodiment showing a state before joining. 
         FIG. 9B  is an explanatory diagram of a joining operation using the joining device according to the first embodiment showing a state after joining. 
         FIG. 10A  is an explanatory diagram of a joining operation using the joining device according to the second embodiment showing a state before joining. 
         FIG. 10B  is an explanatory diagram of a joining operation using the joining device according to the second embodiment showing a state after joining. 
     
    
    
     DETAILED DESCRIPTION 
     Further features of the present disclosure will become apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Note that embodiments described below are given by way of example, and may be of various configurations within the scope of the present disclosure. 
     First Embodiment 
       FIG. 1  is a diagram illustrating a joining device according to a first embodiment.  FIG. 2  is a side elevation of a male member of the joining device according to the first embodiment.  FIG. 3A  is a perspective view showing a female member of the joining device according to the first embodiment.  FIG. 3B  is a cross-sectional view showing a female member of the joining device according to the first embodiment taken along an axial line of the female member. 
     [Joining Device] 
     As shown in  FIG. 1 , a joining device  100  includes a male member  1  and a female member  5 . The joining device  100  is, for example, used in combining and joining a plurality of boards of ready-to-assemble furniture. The male member  1  and the female member  5  may be made of, for example, a synthetic resin such as nylon, a metallic material or wood, but the material is not particularly limited. 
     (Male Member) 
     The male member  1  is configured to be joined to the female member  5  by being inserted therein and fitted therewith (see  FIG. 6 ). As shown in  FIG. 2 , the male member  1  includes a head portion  10  and a shaft portion  11  that is formed integrally with the head portion  10 . 
     The head portion  10  is a portion having a circular shape in a plan view, and has a diameter greater than that of the shaft portion  11 . The head portion  10  has a spherical surface portion  10   a  that is formed spherically bulging outwardly at a side opposite to the shaft portion  11 . The spherical surface portion  10   a  serves as a contact surface that is pushed down when the male member  1  is inserted towards the female member  5  by a finger of the operator. 
     The shaft portion  11  is a columnar portion that is to be engaged with the female member  5  by being inserted and fitted thereto. A tip portion  14  of the shaft portion  11  is formed in a curved shape (a dome shape). 
     The shaft portion  11  has a plurality of protruded portions  12   a  to  12   d  bulging in an arc shape bulging outwardly in a radial direction on an outer peripheral surface at a portion that is spaced apart by a predetermined interval from the head portion  10 . The protruded portions  12   a  to  12   d  are formed integrally with the shaft portion  11 . 
     The protruded portions  12   a  to  12   d  are formed over an entire perimeter about an axial line X 1  of the shaft portion  11 , and arranged at positions that are spaced apart from each other at a predetermined interval in a direction of the axial line X 1 . A portion other than the protruded portions  12   a  to  12   d  and the tip portion  14  of the shaft portion  11  has a predetermined outer diameter OD 1 , and a maximum outer diameter OD 2  of the protruded portions  12   a  to  12   d  is greater than the outer diameter OD 1  of the shaft portion  11  (OD 1 &lt;OD 2 ). 
     The tip portion  14  of the shaft portion  11  is provided with a groove (hereinafter, also referred to as a “slit”)  13  that is formed from a tip of the tip portion  14  towards the head portion  10  along the axial line X 1 . The tip portion  14  of the shaft portion  11  is divided in two by the slit  13 , thus providing two parted portions  14   a  and  14   b . It is to be noted that, among the four protruded portions  12   a  to  12   d , although two protruded portions  12   a ,  12   b  that are closer to the tip portion  14  are divided in a direction of a perimeter by the presence of the slit  13 , the divided protruded portions  12   a  and  12   b  are also considered as being “provided along an entire perimeter around the axial line X 1 ”. 
     (Female Member) 
     As shown in  FIGS. 3A and 3B , the female member  5  has a bottomed cylindrical shape, and the shaft portion  11  of the male member  1  is inserted therein. The female member  5  has, on an outer peripheral surface thereof, a plurality of inclined surfaces  51   a  that are formed obliquely at a predetermined angle with respect to the axial line X 2  such that the inclined surfaces  51   a  come closer to the axial line X 2  towards a bottom portion  52 , and a plurality of vertical surfaces  51   b  formed perpendicularly to the axial line X 2 . That is to say, a plurality of stepped portions are formed on an outer peripheral surface of the female member  5  along the axial line X 2  by the plurality of inclined surfaces  51   a  and the plurality of vertical surfaces  51   b.    
     The female member  5  has, on an inner peripheral surface thereof, an insertion hole  53  whereto the shaft portion  11  of the male member  1  is inserted. The insertion hole  53  has an inner diameter ID 1  that is slightly greater than the outer diameter OD 1  of the shaft portion  11  (OD 1 &lt;ID 1 ). 
     At the insertion hole  53 , an inclined surface  54   a  that is inclined to gradually become farther from the axial line X 2  in an upward direction is formed at an upper opening end opposite the bottom portion  52 . The inclined surface  54   a  serves as a guiding section  54  that guides the shaft portion  11  of the male member  1  towards the bottom portion  52  when inserting the male member  1  to the insertion hole  53  of the female member  5 . The guiding section  54  is formed to have a shape of a substantially circular truncated cone centered on the axial line X 2 . 
     Further, an inner surface of the female member  5  defining the insertion hole  53  (hereinafter, also referred to as an “inner peripheral surface”) is provided with a plurality of recessed portions  55   a  to  55   c  that are recessed in a radial direction and formed in an arc shape in a cross-section taken along the axial line X 2 . The recessed portions  55   a  to  55   c  are provided on an entire perimeter around the axial line X 2 . The recessed portions  55   a  to  55   c  are disposed at positions that are spaced apart from each other at a predetermined interval along the axial line X 2  direction. The interval between the recessed portions  55   a  to  55   c  is the same as the interval between the protruded portions  12   a  to  12   d  of the shaft portion  11 . 
     A maximum inner diameter ID 2  of the recessed portions  55   a  to  55   c  is greater than the inner diameter ID 1  of the insertion hole  53  (ID 2 &gt;ID 1 ). It is preferable that the maximum inner diameter ID 2  of the recessed portions  55   a  to  55   c  be about the same size as or less than the maximum outer diameter OD 2  of the protruded portions  12   a  to  12   d  of the shaft portion  11  (ID 2 ≦OD 2 ). However, it is not limited thereto, and the maximum inner diameter ID 2  of the recessed portions  55   a  to  55   c  may be about the same size as or greater than the maximum outer diameter OD 2  of the protruded portions  12   a  to  12   d  of the shaft portion  11  (ID 2 ≧OD 2 ). When the male member  1  and the female member  5  are in a joined state, the recessed portions  55   a  to  55   c  correspond with the protruded portions  12   a  to  12   c  of the shaft portion  11 . The recessed portions  55   a  to  55   c  and the protruded portions  12   a  to  12   c  are portions that come into surface contact with each other. The recessed portions  55   a  to  55   c  of the female member  5  serve as an engaging section  55  that engages with the protruded portions  12   a  to  12   c  of the shaft portion  11  of the male member  1 . 
     Near the bottom portion  52  of the female member  5 , an inner peripheral surface  56   a  having an inner diameter that is the same as the maximum inner diameter ID 2  of the recessed portions  55   a  to  55   c  is provided continuously with the recessed portion  55   a . The inner peripheral surface  56   a  serves as an accommodating section  56  in which the tip portion  14  of the shaft portion  11  of the male member  1  is inserted and accommodated. 
     The shaft portion  11  of the male member  1  is inserted from the guiding section  54  of the female member  5 , and inserted and fitted to the engaging section  55  and the accommodating section  56 . That is, the guiding section  54 , the engaging section  55  and the accommodating section  56  of the female member  5  serve as a mating portion whereto the shaft portion  11  of the female member  5  is inserted and fitted. 
     At the bottom portion  52  of the female member  5 , a columnar projecting pin  57  projecting towards the guiding section  54  side is formed integrally with the bottom portion  52  at a center of the bottom portion  52 . The projecting pin  57  serving as a protrusion has a columnar part  57   a  having a fixed diameter and a tapered portion  57   b  having a diameter which gradually decreases from a tip side of the columnar part  57   a.    
     The projecting pin  57  has a certain length that reaches the recessed portion  55   a , but is formed shorter than a depth of the slit  13  in the tip portion  14  of the shaft portion  11  of the male member  1 . However, it is not limited thereto, and the length of the projecting pin  57  may be modified depending on the depth of the slit  13 . The columnar part  57   a  of the projecting pin  57  has a diameter D that is the same as or slightly greater than the width W of slit  13  (W≦D). 
     [Joining of Male Member and Female Member] 
     Now, an operation of joining the male member  1  and the female member  5  will be described with reference to  FIG. 1  and  FIGS. 4 to 6 .  FIG. 1  shows a state before insertion of the male member  1  into the female member  5 .  FIG. 4  is a diagram showing a state where the tip portion  14  of the male member  1  is inserted into the female member  5 .  FIG. 5  is a diagram showing a state where the male member  1  is partially engaged with the female member  5 .  FIG. 6  is a diagram showing a state where the male member  1  and the female member  5  are completely joined (joined state). 
     Regarding the joining device  100 , when joining the male member  1  to the female member  5  as shown in  FIG. 1 , the shaft portion  11  of the male member  1  is inserted into the female member  5  along an insertion direction A, i.e., the axial lines X 1  and X 2 . 
     When the male member  1  is inserted into the female member  5  along the insertion direction A, as shown in  FIG. 4 , at first, the protruded portion  12   a  provided at the most distal part of the shaft portion  11  comes into contact with the inclined surface  54   a  of the guiding section  54 . Even if the male member  1  is inserted into the female member  5  in a state where the axial line X 1  of the male member  1  does not match the axial line X 2  of the female member  5 , the shaft portion  11  is inserted with the protruded portion  12   a  being in contact with the inclined surface  54   a  of the guiding section  54 . Thus, the male member  1  is inserted into the female member  5 , while a deviation with respect to the axial line X 2  of the female member  5  is being absorbed, and the male member  1  becomes centered with respect to the female member  5 . 
     While being centered, the male member  1  is deformed such that the two parted portions  14   a  and  14   b  approach each other so that the slit  13  closes at a tip of the male member  1 . Thus, regarding the shaft portion  11 , the maximum outer diameter OD 2  at the protruded portions  12   a  and  12   b  becomes closer to the inner diameter ID 1  of the insertion hole  53 , and thus insertion of the male member  1  to the female member  5  becomes smooth and facilitated. 
     In the insertion direction A, when the male member  1  is further inserted, the protruded portion  12   a  at the most distal tip side of the shaft portion  11  engages the recessed portion  55   c  of the mating portion as shown in  FIG. 5 . Here, since the maximum outer diameter OD 2  of the protruded portions  12   a  to  12   d  is about the same size as the maximum inner diameter ID 2  of the recessed portions  55   a  to  55   c , the parted portion  14   a ,  14   b  of the shaft portion  11  which have been elastically deformed are restored to an original state. In this state, the slit  13  of the shaft portion  11  is opposing the projecting pin  57  of the female member  5 . 
     In the insertion direction A, when the male member  1  is further inserted, the projecting pin  57  is inserted into the slit  13  of the shaft portion  11  as shown in  FIG. 6 . As the projecting pin  57  is inserted into the slit  13 , the tapered portion  57   b  and subsequently the columnar part  57   a  of the projecting pin  57  are inserted into the slit  13 . When the male member  1  is further inserted, the protruded portion  12   a  closest the tip side of the shaft portion  11  engages the recessed portion  55   a , the protruded portion  12   b  engages the recessed portion  55   b , the protruded portion  12   c  engages the recessed portion  55   c , and the protruded portion  12   d  comes into contact with the inclined surface  54   a  of the guiding section  54 . 
     Since the width W of the slit  13  is smaller than the diameter D of the columnar part  57   a  of the projecting pin  57  (W&lt;D), an interference fit is created between the slit  13  and the columnar part  57   a . Further, since the parted portions  14   a  and  14   b  of the shaft portion  11  are pushed out towards the inner peripheral surface of the female member  5 , an engaged condition between the protruded portions  12   a  and  12   b  of the tip side of the shaft portion  11  and the recessed portions  55   a  and  55   b  becomes stronger. 
     Further, since the protruded portions  12   a  to  12   d  of the shaft portion  11  and the recessed portions  55   a  to  55   c  of the male member  1  the female member  5  are both formed with an arc shape, an insertion operation of the male member  1  to the female member  5  is facilitated. Further, with the joining device  100 , since the male member  1  can be joined with the female member  5  or withdrawn from the female member  5  while an engaged condition between the recessed portions  55   a  to  55   c  of the shaft portion  11  of the male member  1  and the protruded portions  12   a  to  12   d  of the female member  5  is fitted or released step-by-step, neither the male member  1  nor the female member  5  is damaged while being joined or being withdrawn. 
     Further, since two or more of the protruded portions  12   a  to  12   d  of the shaft portion  11  and two or more of the recessed portions  55   a  to  55   c  of the female member  5  are provided along the axial lines X 1  and X 2 , the joined state between the male member  1  and the female member  5  can be made stronger, and the joined state can be prevented from being released easily. 
     Rather than a case in which the female member  5  and the male member  1  are engaged at a single location between the protruded portion  12   a  and the recessed portion  55   c , the joining force increases exponentially when engaged at two parts between the protruded portions  12   a  and  12   b  and the recessed portions  55   c  and  55   b , respectively, or when engaged at three parts between the protruded portions  12   a  to  12   c  and the recessed portions  55   c  to  55   a , respectively. 
     Second Embodiment 
     Now, a joining device  200  according to a second embodiment will be described with reference to  FIG. 7 . Hereinafter, only those parts that are different from the configuration of the first embodiment will be described, and parts that are the same as those of the first embodiment will be given the same reference numerals, and will not be described in detail.  FIG. 7  is a side view of the male member  3  according to the second embodiment. It is to be noted that a joining device  200  includes a male member  3  shown in  FIG. 7 , in place of the male member  1  of the first embodiment, and the female member  5  of the first embodiment. The female member  5  will not be described here, since it has a configuration which is the same as the first embodiment. 
     The male member  3  of the joining device  200  has the shaft portion  11  lying along art axial line X 3  and a columnar portion  31  having a diameter greater than that of the shaft portion  11 . The columnar portion  31  has a flange  32  having a diameter greater than that of the columnar portion  31 , and the flange  32  is provided between the columnar portion  31  and the shaft portion  11 . The columnar portion  31  is fitted in one member (shelf board  340  shown in  FIG. 10 ) of two boards to be assembled with each other using the joining device  200 . 
     An outer peripheral surface of the columnar portion  31  has inclined surfaces  31   a  that are provided obliquely at a predetermined angle with respect to the axial line X 3  such that the inclined surfaces  31   a  come closer to the axial line X 3  towards a direction opposite the shaft portion  11 , and vertical surfaces  31   b  formed perpendicularly to the axial line X 3 . That is to say, a plurality of stepped portions are formed on an outer peripheral surface of the columnar portion  31  along the axial line X 3  by the plurality of inclined surfaces  31   a  and the plurality of vertical surfaces  31   b.    
     It is to be noted that, similarly to the male member  1  of the first embodiment, the male member  3  has a plurality of the protruded portions  12   a  to  12   d  formed integrally with the shaft portion  11 . Since the protruded portions  12   a  to  12   d  have the same configuration as the male member  1 , the description is omitted here. 
     &lt;Example of Application of Joining Device  100  and Joining Device  200 &gt; 
     With reference to  FIG. 8A  to  FIG. 10 , a specific example in which the joining devices  100  and  200  according to the first and second embodiments are applied to an assembled structure  300  will be described.  FIGS. 8A and 8B  are schematic diagrams of the assembled structure  300  including joining devices  100  and  200  according to the first and second embodiments.  FIG. 8A  is a schematic perspective view of the assembled structure  300  viewed at an angle from the rear.  FIG. 8B  is a cross-sectional view of the assembled structure  300  taken along line I-I in  FIG. 8A .  FIGS. 9A and 9B  are explanatory diagrams of a joining operation using the joining device  100  according to the first embodiment.  FIG. 9A  is a cross-sectional view showing a state before joining two assembly components  310  and  320 .  FIG. 9B  is a cross-sectional view showing a state after joining one assembly component  310  with another assembly component  320 .  FIGS. 10A and 10B  are explanatory diagrams of a joining operation using the joining device  200  according to the second embodiment.  FIG. 10A  is a cross-sectional view showing a state before joining two assembly components  330  and  340 .  FIG. 10B  is a cross-sectional view showing a state after joining one assembly component  330  with another assembly component  340 . 
     For example, in a case where the assembled structure  300  is a shelf, which is presented as an exemplary ready-to-assemble furniture, a plurality of boards (assembly components)  310 ,  320 ,  330 , and  340  are assembled and joined with each other as shown in  FIGS. 8A and 8B . 
     Specifically, the assembled structure  300  is provided with a top board  310 , a base board (not shown), a back board  320 , side boards  330 ,  330  and a shelf board  340 . The back board  320  is joined to end faces of longer sides of the top board  310  and the base board. The side boards  330 ,  330  are joined to side end faces at both side of shorter sides of the top board  310  and the base board. The shelf board  340  is joined between the side boards  330  and  330 . It is to be noted that a joining process described below does not necessarily correspond with an actual assembly procedure of the assembled structure  300 . 
     At first, referring to  FIGS. 9A and 9B , a joining process of the top board  310  and the back board  320  will be described. Here, the female member  5  is embedded and fixed in advance in the top board  310 , and the inclined surface  54   a  of the guiding section  54  is exposed at the surface. 
     An insertion hole  321  through which the shaft portion  11  of the male member  1  is inserted is formed at a position matching the female member  5  of the top board  310  when the back board  320  and the top board  310  are assembled. The diameter of the insertion hole  321  is slightly greater than the maximum outer diameter OD 2  of the protruded portions  12   a  to  12   d  of the shaft portion  11 , but smaller than the diameter of the head portion  10 . 
     With the insertion hole  321  of the back board  320  being made to correspond to the female member  5  fitted in the top board  310 , the male member  1  is inserted into a mating portion (guiding section  54 , engaging section  55 , accommodating section  56 ) of the female member  5  until the head portion  10  of the male member  1  abuts the back board  320 . Thus, the top board  310  and the back board  320  can be joined easily, quickly and firmly without using a tool. 
     Also, during the insertion, since the protruded portions  12   a  to  12   d  of the shaft portion  11  of the male member  1  engage the recessed portions  55   a  to  55   c  of the mating portion of the female member  5  in a step-by-step manner, assembling staff can feel the step-by-step engagement of the protruded portions  12   a  to  12   d  and the recessed portions  55   a  to  55   c . Thereby, the assembling staff can intuitively recognize that engagement between the male member  1  and the female member  5  is completed. 
     Note that, as shown in  FIG. 8A , the joining device  100  is also used in joining the back board  320  and the side board  330 . A position whereto the joining device  100  is attached when joining the back board  320  and the side board  330  is not particularly limited. However, considering the durability and vibration proof property of the assembled structure  300 , it is preferable that a triangle formed by connecting a corner C and two joining devices  100  disposed in the vicinity of the corner C and across the corner C with imaginary dash-dot lines is a right angled triangle. 
     Referring now to  FIGS. 10A and 10B , a joining process of the side board  330  and the shelf board  340  will be described. The female member  5  is embedded and fixed in advance in the side board  330 , and the columnar portion  31  of the male member  3  is embedded and fixed in advance in shelf board  340 . 
     Of the male member  3  embedded in the shelf board  340 , the shaft portion  11  exposed from shelf board  330  is inserted into the mating portion of the female member  5  until the side board  330  and the shelf board  340  abut each other. With such a simple operation, the side board  330  and the shelf board  340  can be joined firmly and quickly. Note that, as shown in  FIG. 8B , the joining device  200  is also used for joining the top board  310  and the side board  330 . Also, the male member  3  may be embedded in the side board  330 , and the female member  5  may be embedded in the top board  310  or the shelf board  340 . 
     Note that, regarding the male member  1 , the joining state between the back board  320  and the side board  330  can be easily released by an operator by, for example, simply gripping and pulling out the head portion  10  from the female member  5 . Here, since it is only the fitted state between the protruded portions  12   a  to  12   d  of the shaft portion  11  of the male member  1  and the recessed portions  55   a  to  55   c  of the female member  5  that is released, the male member  1  and the female member  5  are not damaged. 
     The female member  5  is fixed to the side board  330 . Accordingly, the fitted state between the protruded portion  12   a  to  12   d  of the shaft portion  11  of the male member  3  and the recessed portion  55   a  to  55   c  of the female member  5  is released by an operator simply pulling the side board  330  apart from the shelf board  340 . Thus, the joined state between the side board  330  and the shelf board  340  can be easily released. Also, in this case, the male member  3  and the female member  5  are not damaged. 
     When pulling out the male member  1 ,  3 , the female member  5  has its vertical surface  51   b  caught by the side board  330 , and thus the side board  330  can be prevented from being broken by being pulled out along when the male member  1 ,  3  are pulled out. 
     Other Embodiments 
     As for the joining devices  100  and  200  according to first and second embodiments, the male member  1 ,  3  is provided with the slit  13 , and the female member  5  is provided with the projecting pin  57 , but it is not limited thereto. For example, as long as a desired joined state is accomplished by a mutual strong engaging force between the male member  1 ,  3  and the female member  5  of the joining device  100 ,  200 , the joining device may be provided with a male member without a slit  13  and a female member without a projecting pin  57 . 
     The present disclosure is not limited to the first and second embodiments. For example, the joining device  100  according to the first embodiment may be used for joining the side board  330  and the shelf board  340 , and the joining device  200  according to the second embodiment may be used for joining the top board  310  and the back board  320 . Note that, for example, the manner of assembling the boards, specifically, the top board  310  and the side boards  330 ,  330  is not limited to what is described above, and the top board  310  may be assembled by being placed on top of the side boards  330 ,  330 . 
     In the first and second embodiment, the male member  1 ,  3  has four protruded portions  12   a  to  12   d , and the female member  5  has three recessed portions  55   a  to  55   c , but it is not limited thereto. The number of the protruded portions and the recessed portions may be modified as required, respectively, and, for example, the same number of protruded portions and the recessed portions may be provided, or the number of recessed portion may be greater than the number of protruded portions. 
     Further, the cross-sectional shape of the protruded portions  12   a  to  12   d  along the axial line X 1  of the shaft portion  11  is not limited to an arc shape, and may be other shapes such as a rectangular or triangle shape, and the design of the shape of the recessed portions  55   a  to  55   c  may be appropriately modified accordingly. Also, the protruded portion  12   a  may not be formed over an entire perimeter, but may be provided as a plurality of hemispherical protrusions independently provided in the direction of the perimeter. 
     The shaft portion  11  of the male member  1 ,  3  is not limited to a columnar shape, and may be form of prism, and not particularly limited. Also, the projecting pin  57  is not limited to a columnar shape, and may be a conical shape, a rectangular prism or rectangular conical shape, and not particularly limited. 
     The assembled structure  300  is not limited to a shelf as long as it includes at least two assembly components that are joined, and may be other various assembly structures such as drawers, a dressing table, a cupboard, a book shelf, a desk, a chair, a table, a bed, a chest, a television support, an audio rack, a loud speaker support, a personal computer rack, etc.