Patent Publication Number: US-2023149247-A1

Title: Part fastening structure and mounting tool

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-185074 filed on Nov. 12, 2021, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a part fastening structure and a mounting tool. 
     2. Description of Related Art 
     Japanese Unexamined Patent Application Publication No. 2017-35220 (JP 2017-35220 A) discloses a walking training device including a walking assisting device attached to a trainee&#39;s leg. The walking assist device includes a thigh frame and a lower leg frame. The thigh frame is attached to the trainee&#39;s thigh and the lower leg frame is attached to the trainee&#39;s lower leg. 
     SUMMARY 
     In such a walking training device, various trainees wear walking assist devices (also referred to as leg braces or mounting tools) for training. Thus, it is necessary for an assistant to adjust the walking assist device according to the trainee. For example, the assistant adjusts a frame length according to a length of a trainee&#39;s leg. In such a case, a part fastening structure for fastening two parts (for example, an upper frame and a lower frame) is used. That is, a frame is formed by fastening the two parts with the part fastening structure. 
     The frame length can be adjusted by the assistant loosening bolts and nuts and removing the two parts. That is, the assistant adjusts the frame length according to the leg length by changing the fastening position of the parts. Thus, it is desirable to easily and reliably attach and remove the parts. For example, it is desirable to attach and detach without a special tool. Further, a structure that does not loosen during use is desired. 
     The present disclosure has been made to solve such a problem, and provides a part fastening structure capable of simply and reliably fastening parts. 
     The part fastening structure in the present embodiment is a part fastening structure that fastens a part using a bolt and a nut. The bolt includes: a shaft portion extending along a central axis; a head portion protruding to an outer side from the shaft portion; a recess portion that is provided on a peripheral surface of the shaft portion and that is recessed to the central axis side; and a thread groove that is provided on the peripheral surface of the shaft portion, on the head portion side of the recess portion, in which the nut includes: a first nut member that is screwed with the thread groove; a second nut member that is disposed on an outer peripheral side of the first nut member; and a first urging member that is disposed between the first nut member and the second nut member and that urges the second nut member toward the head portion, in which the first nut member is provided with a lever that rotates around a rotation shaft extending in a direction parallel to an axial direction of the bolt, in which a protruding portion is provided on one end side of the lever, in which a second urging member that urges the lever is provided such that the protruding portion is inserted into the recess portion, in which the second nut member includes: a cylindrical portion having a hollow portion in which the first nut member is disposed; an accommodation port that accommodates the lever such that another end side of the lever is passed to an outer peripheral side of the cylindrical portion; and a knob that protrudes toward the outer peripheral side of the cylindrical portion. 
     In the part fastening structure described above, a plurality of the recess portions may be provided on the peripheral surface such that the recess portions are spaced away from each other in a circumferential direction. 
     In the part fastening structure described above, a first pin hole may be provided on an outer peripheral surface of the first nut member, a second pin hole that reaches an inner peripheral surface of the cylindrical portion from the outer side may be provided in the cylindrical portion of the second nut member, and the first nut member may be held by the second nut member by a pin inserted into the first pin hole through the second pin hole. 
     In the part fastening structure described above, the first pin hole may be an elongated hole in which a longitudinal direction coincides with the axial direction. 
     A mounting tool according to the present embodiment is a mounting tool that is worn by a user, the mounting tool including: a first part including a plurality of first through holes; a second part including a second through hole; and the part fastening structure described above, in which the bolt is inserted through the first through hole and the second through hole. 
     According to the present disclosure, it is possible to provide a part fastening structure and a mounting tool capable of simply and reliably fastening parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG.  1    is a front view showing two parts fastened by a part fastening structure; 
         FIG.  2    is a side view showing the two parts fastened by the part fastening structure; 
         FIG.  3    is a bottom view of the part fastening structure; 
         FIG.  4    is a perspective view showing a configuration of the part fastening structure; 
         FIG.  5    is an exploded perspective view showing the configuration of the part fastening structure; 
         FIG.  6    is a cross-sectional view of the part fastening structure cut along a plane orthogonal to a central axis; 
         FIG.  7    is a cross-sectional view of the part fastening structure cut along the plane orthogonal to the central axis; 
         FIG.  8    is a cross-sectional view for describing an operation of the part fastening structure at the time of fastening; 
         FIG.  9    is a cross-sectional view for describing the operation of the part fastening structure at the time of fastening; 
         FIG.  10    is a cross-sectional view for describing the operation of the part fastening structure at the time of fastening; and 
         FIG.  11    is a schematic perspective view showing a mounting tool having the part fastening structure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, the present disclosure will be described through embodiments of the disclosure. However, the disclosure according to the claims is not limited to the following embodiments. Moreover, all of the configurations described in the embodiments are not necessarily indispensable as means for solving the issue. 
     A part fastening structure  1  for fastening a first part  10  and a second part  20  will be described with reference to  FIGS.  1  to  3   . The first part  10  and the second part  20  configure, for example, a frame to be attached to a leg of a trainee who performs walking training. Here, the first part  10  and the second part  20  are fastened by the part fastening structure  1  to form a frame disposed along a lower leg of the trainee. An assistant (also called a user) who assists the trainee adjusts the length of the frame according to the trainee. 
       FIG.  1    is a front view showing parts fastened by the part fastening structure  1  and  FIG.  2    is a side view showing the parts fastened by the part fastening structure  1 .  FIG.  3    is a bottom view of the part fastening structure  1 . 
     One of the first part  10  and the second part  20  is disposed on an upper side, and the other is disposed on a lower side. Here, the first part  10  is disposed on a knee side and the second part  20  is disposed on an ankle side. The part fastening structure  1  is disposed laterally to a shin. Of course, the first part  10  and the second part  20  are not limited to the lower leg frame and the leg brace. Further, the vertical arrangement of the first part  10  and the second part  20  is not particularly limited. 
     As shown in  FIG.  3   , the part fastening structure  1  includes a bolt  30  and a nut  60 . In the part fastening structure  1 , the first part  10  and the second part  20  are fastened using the bolt  30  and the nut  60 . The bolt  30  is passed through through holes provided in the first part  10  and the second part  20 . In  FIG.  3    and the like, a straight line along an axis center of the bolt  30  is shown as a central axis AX. The bolt  30  and the nut  60  are attached by rotating the bolt  30  or the nut  60  around the central axis AX. By attaching the nut  60  to the bolt  30 , the first part  10  and the second part  20  are fastened. 
     The first part  10  and the second part  20  are members whose longitudinal direction is along the lower leg. In  FIG.  1   , the first part  10  and the second part  20  are both channel steels. For example, the first part  10  and the second part  20  are each made of a metal material such as aluminum. A direction along the central axis AX is a thickness direction of the first part  10  and the second part  20 . 
     As shown in  FIGS.  1  and  2   , the first part  10  is provided with a plurality of through holes  11 . The through hole  11  extends through in the thickness direction of the first part  10 . The through holes  11  are disposed in one row along the longitudinal direction of the first part  10 . Here, the through holes  11  are formed at equal intervals along the longitudinal direction of the first part  10 . Each of the through holes  11  has an elongated hole shape to suppress rotation on the bolt side. The through holes  11  have the same size and the same shape. 
     The second part  20  includes one through hole  21 . The through hole  21  extends through the second part  20  in a thickness direction of the second part  20 . The first part  10  and the second part  20  are disposed so as to partially overlap each other. The first part  10  and the second part  20  are disposed so that the through hole  21  of the second part  20  overlaps with one through hole  11  of the first part  10 . The bolt  30  is inserted into the through hole  21  of the second part  20  and the through hole  11  of the first part  10 . Then, the nut  60  is attached to the bolt  30  inserted into the through hole  11  and the through hole  21 . As a result, the first part  10  and the second part  20  are fixed. Here, the bolt  30  is in contact with the first part  10  and the nut  60  is in contact with the second part  20 . 
     Further, by changing the through hole  11  into which the bolt  30  is inserted, a length of an overlapping portion of the first part  10  and the second part  20  is changed. Thus, the total length of the frame can be adjusted. For example, by inserting the bolt  30  into the through hole  11  on the lower side of  FIGS.  1  and  2    among the through holes  11 , the overlapping portion of the first part  10  and the second part  20  is shortened. Thus, the frame length can be increased. By inserting the bolt  30  into the through hole  11  on the upper side of  FIGS.  1  and  2    among the through holes  11 , the overlapping portion of the first part  10  and the second part  20  becomes longer. Thus, the frame length can be shortened. In this way, the frame length can be made variable by changing the fastening position by the part fastening structure  1 . 
     Next, the part fastening structure  1  will be described with reference to  FIGS.  4  to  10   .  FIG.  4    is a perspective view showing the part fastening structure  1  in a state before the bolt  30  and the nut  60  are attached.  FIG.  5    is an exploded perspective view of the part fastening structure  1 .  FIGS.  6  and  7    are diagrams for explaining an operation of an internal structure of the nut  60 . Specifically,  FIG.  6    shows a state during fastening, and  FIG.  7    shows a state after fastening.  FIGS.  8  to  10    are cross-sectional views for describing the operation of the part fastening structure.  FIG.  8    shows the operation of the part fastening structure at the time when the fastening is started, and  FIG.  10    shows the operation of the part fastening structure at the time when the fastening is completed.  FIG.  9    shows the process of fastening between  FIGS.  8  and  10   . 
     First, the configuration of the bolt  30  will be described with reference to  FIGS.  4 ,  5   , and the like. The bolt  30  includes a shaft portion  31  and a head portion  32 . The bolt  30  is made of a metal material such as iron. 
     The shaft portion  31  is a substantially columnar portion, and is a portion inserted into the through hole  11  shown in  FIG.  1    or the like. In  FIGS.  4  and  5   , the center of the shaft portion  31  is defined as the central axis AX. A direction parallel to the central axis AX of the shaft portion  31  is defined as an axial direction. The axial direction is the direction in which the bolt  30  is inserted into the through hole  11 . Further, as shown in  FIGS.  4 ,  5   , and the like, a direction around the central axis AX is defined as a circumferential direction. Thus, like a cylindrical coordinate system, a position in the circumferential direction is represented by an angle of 0 to 360° with a reference position (origin position) as 0°. As shown in  FIG.  5   , the head portion  32  side in the axial direction is a base end side, and the opposite side is a tip end side. 
     The shaft portion  31  includes a tip end surface  34  and a peripheral surface  33 . The tip end surface  34  corresponds to a bottom surface of a cylinder, and the peripheral surface corresponds to a side surface of the cylinder. The tip end surface  34  is provided on the tip end side of the shaft portion  31 . The tip end surface  34  is the bottom surface located on the tip end side of the columnar shaft portion  31 . The tip end surface  34  is a plane orthogonal to the central axis AX. 
     The head portion  32  is provided on the base end side of the shaft portion  31 . The head portion  32  is a disc-shaped dish portion. An outer diameter of the head portion  32  is larger than an outer diameter of the shaft portion  31 . The outer diameter of the shaft portion  31  is smaller than the through holes  11  and  21  so as to be inserted into the through holes  11  and  21 . The outer diameter of the head portion  32  is larger than that of the through holes  11  and  21 . Therefore, the head portion  32  comes into contact with the first part  10 . A washer, a disc spring, or the like may be disposed between the head portion  32  and the first part  10 . 
     The peripheral surface  33  is a portion from the tip end surface  34  to the head portion  32 . That is, the peripheral surface  33  is a side surface (outer peripheral surface) of the shaft portion  31  having a substantially columnar shape. A thread groove  35  and a recess portion  36  are formed on the peripheral surface  33 . The recess portion  36  is provided on the tip end side of the thread groove  35 . In the axial direction, the recess portion  36  is disposed between the tip end surface  34  and the thread groove  35 . The thread groove  35  is formed in a spiral shape on the peripheral surface  33 . The thread groove  35  is provided on the head portion  32  side of the bolt  30  with respect to the recess portion  36 . 
     The recess portion  36  is a recess provided on the peripheral surface  33 . The recess portion  36  is recessed toward the central axis AX side. The recess portion  36  is larger than a pitch of the thread groove  35  and is formed deeper than the thread groove  35 . As will be described later, a tip end portion  68   a  of a lever  68  is inserted into the recess portion  36 . The peripheral surface  33  is provided with two recess portions  36 . The recess portions  36  are provided at two points on the peripheral surface  33 . In the circumferential direction, the two recess portions  36  are provided apart from each other. Specifically, assuming that the position of one recess portion  36  in the circumferential direction is 0°, the position of the other recess portion  36  in the circumferential direction is 180°. That is, the two recess portions  36  are disposed symmetrically with respect to the central axis AX. In the axial direction, the positions of the two recess portions  36  may be the same or different. 
     Next, the configuration of the nut  60  will be described with reference to  FIGS.  4  to  7   . The nut  60  includes a first nut member  61 , a second nut member  62 , and a disc spring  64 . Further, the nut  60  includes a spring  63  and the lever  68 . The spring  63  and the lever  68  are attached to the second nut member  62 . The first nut member  61  and the lever  68  are made of a metal material such as iron. The second nut member  62  is made of a metal material such as aluminum. 
     The first nut member  61  is a cylindrical member or a ring-shaped member. That is, the first nut member  61  is a member having a hollow portion  61   a  provided along the central axis AX. The hollow portion  61   a  is a columnar space along the axial direction. The shaft portion  31  is inserted into the hollow portion  61   a . The first nut member  61  is screwed into the thread groove  35 . 
     The surface of the first nut member  61  on the hollow portion  61   a  side is defined as an inner peripheral surface  61   b . The outer peripheral surface of the first nut member  61  is referred to as an outer peripheral surface  61   c . The shaft portion  31  of the bolt  30  is inserted into the hollow portion  61   a . A thread groove  61   s  is formed on the inner peripheral surface  61   b . The thread groove  61   s  is screwed with the thread groove  35  of the bolt  30 . The thread groove  61   s  is provided on the entire inner peripheral surface  61   b.    
     With the thread groove  35  of the bolt  30  and the thread groove  61   s  of the nut  60  meshing with each other, the user rotates the bolt  30  or the nut  60  in the circumferential direction. By doing so, the relative position of the bolt  30  with respect to the nut  60  changes in the axial direction. For example, the user can tighten or loosen the bolt  30  and the nut  60  by rotating the nut  60  in the circumferential direction. 
     As shown in  FIG.  5    and the like, a pin hole  61   h  into which a pin  71  is inserted is formed on the outer peripheral surface  61   c  of the first nut member  61 . Here, the pin hole  61   h  does not have to reach the inner peripheral surface  61   b . That is, the pin hole  61   h  may be a recess provided in the outer peripheral surface  61   c . The pin hole  61   h  may be a through hole that reaches the inner peripheral surface  61   b  from the outer peripheral surface  61   c.    
     As shown in  FIG.  6    and the like, the pin holes  61   h  are provided at two locations on the outer peripheral surface  61   c . In the circumferential direction, the two pin holes  61   h  are disposed apart from each other. The two pin holes  61   h  are disposed symmetrically with respect to the central axis AX. Each pin hole  61   h  has an elongated hole shape with the axial direction as the longitudinal direction. As will be described later, the size of the pin hole  61   h  in the longitudinal direction defines the amount of movement of the first nut member  61  with respect to the second nut member  62 . 
     Further, the first nut member  61  is provided with an accommodation portion  61   f  for accommodating the lever  68  and the spring  63 . The accommodation portion  61   f  is a recess provided on the outer peripheral surface  61   c . The lever  68  and the spring  63  are accommodated in the accommodation portion  61   f  Further, the accommodation portion  61   f  reaches from the outer peripheral surface  61   c  to the inner peripheral surface  61   b . That is, the tip end portion  68   a  of the lever  68  is a protruding portion protruding from the inner peripheral surface  61   b  toward the hollow portion  61   a . An operation portion  68   b  of the lever  68  is disposed outside an outer peripheral surface  65   c  of the second nut member  62 . 
     The lever  68  is rotatably attached to the first nut member  61  via a rotation shaft  69 . For example, the lever  68  is provided with a through hole for the rotation shaft  69  to pass through. The rotation shaft  69  extends through the lever  68 . The rotation shaft  69  is attached to the first nut member  61 . As a result, the lever  68  rotates around the rotation shaft  69 . The rotation shaft  69  is disposed along the direction parallel to the central axis AX. In a plan view orthogonal to the central axis AX, the rotation shaft  69  is at a position deviated from the central axis AX. The side opposite to the tip end portion  68   a  of the lever  68  is set as the operation portion  68   b . The operation portion  68   b  is a portion protruding from the first nut member  61  in a plan view orthogonal to the central axis AX. That is, in the state shown in  FIG.  7   , the portion outside the outer peripheral surface  61   c  is the operation portion  68   b.    
     The rotation shaft  69  is disposed in the accommodation portion  61   f . The lever  68  is disposed along the plane orthogonal to the central axis AX. The rotation shaft  69  is disposed between the operation portion  68   b  and the tip end portion  68   a  in the longitudinal direction of the lever  68 . That is, the tip end portion  68   a  is provided on one end side of the lever  68 , and the operation portion  68   b  is provided on the other end side of the lever  68 . 
     For example, in  FIG.  7   , the tip end portion  68   a  is disposed on a left side of the rotation shaft  69 , and the operation portion  68   b  is disposed on a right side of the rotation shaft  69 . When the user operates the operation portion  68   b , the lever  68  rotates. As the lever  68  rotates around the rotation shaft  69 , the position of the tip end portion  68   a  changes. The rotation operation of the lever  68  will be described later. 
     As shown in  FIGS.  5  and  6   , the spring  63  is attached to the lever  68 . The spring  63  urges the lever  68  so that the lever  68  rotates. For example, the accommodation portion  61   f  has a cylindrical recess portion and accommodates the spring  63  as shown in  FIG.  7   . One end of the spring  63  abuts on the lever  68  and the other end abuts on the first nut member  61 . The spring  63  urges the operation portion  68   b  side of the lever  68  so that the lever  68  rotates about the rotation shaft. An expansion/contraction direction of the spring  63  is, for example, parallel to the plane orthogonal to the central axis AX. The spring  63  is contracted more than its natural length in the state shown in  FIG.  7   . In  FIG.  7   , the spring  63  urges the lever  68  in the direction in which the lever  68  rotates clockwise. 
     The spring  63  is, for example, a coil spring. In the present embodiment, the spring  63  has a diameter of 2 mm, a natural length of 15 mm, and a spring constant of 0.5 N/mm. A mounting length in the state shown in  FIG.  7    is 12.5 mm, and a mounting load is 1.25 N. In the state shown in  FIG.  6   , it is in the most contracted state, and its spring length is 10 mm. A maximum load in the state shown in  FIG.  6    is 2.5N. The spring  63  is a second urging member that generates an urging force for rotating the lever  68 . Of course, the urging member is not limited to the spring  63 , and an elastic body such as resin may be used. 
     Next, the second nut member  62  will be described. The second nut member  62  is a case for accommodating the first nut member  61 . As shown in  FIG.  5   , the second nut member  62  includes a hollow portion  62   a  into which the shaft portion  31  is inserted. 
     The second nut member  62  includes a cylindrical portion  65  and a bottom portion  66 . The cylindrical portion  65  is a cylindrical or ring-shaped portion. An inner surface of the cylindrical portion  65  is an inner peripheral surface  65   b , and an outer surface is the outer peripheral surface  65   c . The inner peripheral surface  65   b  is a surface facing the outer peripheral surface  61   c  of the first nut member  61 . In a plan view orthogonal to the central axis AX, the diameter of the inner peripheral surface  65   b  is larger than the diameter of the outer peripheral surface  61   c . Thus, the first nut member  61  is housed inside the cylindrical portion  65 . 
     The bottom portion  66  is disposed on the base end side of the cylindrical portion  65 , that is, the end portion on the head portion  32  side. The bottom portion  66  has a disc shape parallel to the plane orthogonal to the central axis AX. The bottom portion  66  has a disc shape in which the hollow portion  62   a  is vacant. In the axial direction, the bottom portion  66  is disposed between the head portion  32  and the first nut member  61 . The hollow portion  62   a , the hollow portion  61   a , the cylindrical portion  65 , and the shaft portion  31  are concentric in a plan view orthogonal to the central axis AX. That is, the centers of the hollow portion  62   a , the hollow portion  61   a , and the cylindrical portion  65  coincide with the central axis AX. 
     The side opposite to the bottom portion  66  of the cylindrical portion  65 , that is, the tip end side is open. Then, the first nut member  61  is housed in the second nut member  62  from the tip end side of the cylindrical portion  65 . The first nut member  61  is disposed in a cylindrical space  62   g  defined by the cylindrical portion  65  and the bottom portion  66 . 
     The disc spring  64  is disposed between the bottom portion  66  and the first nut member  61  in the axial direction. The disc spring  64  generates an urging force in the direction in which the first nut member  61  and the bottom portion  66  of the second nut member  62  are separated from each other. The disc spring  64  urges the second nut member  62  to the base end side, that is, to the head portion  32  side. The disc spring  64  urges the first nut member  61  toward the tip end side. In the axial direction, the disc spring  64  becomes the first urging member that generates an urging force between the first nut member  61  and the second nut member  62 . The amount of expansion and contraction of the disc spring  64  is defined by the axial size of the pin hole  61   h . That is, a spring length of the disc spring  64  has a stroke corresponding to the size of the pin hole  61   h  in the axial direction. 
     The cylindrical portion  65  is provided with two knobs  65   e . The knobs  65   e  are portions of the cylindrical portion  65  protruding outward from the outer peripheral surface  65   c . That is, the knobs  65   e  are portions extending in a direction away from the central axis AX from the outer peripheral surface  65   c  of the cylindrical portion  65 . The two knobs  65   e  are disposed so as to face each other with the central axis AX interposed therebetween. The user can rotate the nut  60  in the circumferential direction by operating the two knobs  65   e . By providing the second nut member  62  with the knobs  65   e  protruding outward from the cylindrical portion  65 , the user can easily rotate the nut  60 . 
     Further, the cylindrical portion  65  is provided with an accommodation port  65   f  for accommodating the lever  68 . The accommodation port  65   f  is a space that reaches the inner peripheral surface  65   b  from the outer peripheral surface  65   c . Further, the accommodation port  65   f  is formed from the cylindrical portion  65  to the knob  65   e . That is, a space serving as an accommodation port  65   f  is formed in the knob  65   e  and the cylindrical portion  65 . 
     Each knob  65   e  is provided with a pin hole  65   h . The pin hole  65   h  extends through from the outer peripheral side of the knob  65   e  through the cylindrical portion  65  to the inner peripheral surface  65   b . As shown in  FIG.  6   , in a plan view orthogonal to the central axis AX, the pin hole  65   h  is a through hole extending through the second nut member  62 . In a plan view orthogonal to the central axis AX, the two pin holes  65   h  are disposed so as to face each other with the central axis AX therebetween. For example, the two pin holes  65   h  pass through the central axis AX and are disposed on a straight line orthogonal to the central axis AX. The pin hole  65   h  is formed so as to be connected to the pin hole  61   h  of the first nut member  61 . 
     Then, as shown in  FIGS.  6  and  7   , the pin  71  is inserted into the pin hole  65   h  and the pin hole  61   h  from the outside. The pin  71  reaches the pin hole  61   h  from the outside of the knob  65   e  via the pin hole  65   h . The pin  71  projects from the inner peripheral surface  65   b  toward the central axis AX. Thus, since the tip of the pin  71  is inserted into the pin hole  61   h , the second nut member  62  and the first nut member  61  cannot be removed. 
     In this way, the first nut member  61  is attached to the second nut member  62 . When the pin  71  is inserted into the pin hole  61   h , the second nut member  62  holds the first nut member  61 . It is possible to suppress the first nut member  61  from coming off from the second nut member  62 . Further, the pin hole  61   h  is an elongated hole in which the longitudinal direction is the axial direction. Thus, the first nut member  61  moves relative to the second nut member  62  along the axial direction. 
     An operation of the lever will be described with reference to  FIGS.  6  and  7   .  FIGS.  6  and  7    are diagrams schematically showing a cross-sectional structure in which the part fastening structure  1  is cut along a plane orthogonal to the axial direction.  FIGS.  6  and  7    show states in which rotation angles of the lever  68  around the rotation shaft  69  are different.  FIG.  6    shows a state during fastening, and  FIG.  7    shows a state after fastening. A rotation position shown in  FIG.  6    is a movable position, and a rotation position shown in  FIG.  7    is a fixed position. 
     In  FIGS.  6  and  7   , the spring  63  urges the lever  68  in the direction in which the lever  68  rotates clockwise. That is, the spring  63  generates an urging force in the direction in which the tip end portion  68   a  of the lever  68  approaches the central axis AX. In other words, the spring  63  generates an urging force in the direction in which the operation portion  68   b  of the lever  68  protrudes from the accommodation port  65   f.    
     In the movable position shown in  FIG.  6   , the tip end portion  68   a  of the lever  68  is not inserted into the recess portion  36 . Specifically, the axial positions of the tip end portion  68   a  and the recess portion  36  are deviated from each other. Since the tip end portion  68   a  is in contact with the peripheral surface  33 , the tip end portion  68   a  cannot move to the central axis AX side. In  FIG.  6   , the bolt  30  and the nut  60  are in a state where they can be rotated. This state is referred to as a movable state. In the movable state, the rotation between the bolt  30  and the nut  60  is not restricted. 
     When the recess portion  36  and the tip end portion  68   a  are misaligned, the tip end portion  68   a  is in contact with the peripheral surface  33 . The peripheral surface  33  regulates the rotation of the lever  68 . Thus, the rotation angle of the lever  68  is constant. When the user rotates the nut  60 , the tip end portion  68   a  moves relative to the peripheral surface  33 . When the nut  60  is rotated, the tip end portion  68   a  moves spirally on the peripheral surface  33 . Thus, the bolt  30  and the nut  60  can be relatively moved in the axial direction without the user having to operate the lever  68 . By rotating the bolt  30  and the nut  60 , the positions in the axial direction are displaced. Thus, the bolt  30  can be removed from the nut  60  by rotating the bolt  30  or the nut  60  in the circumferential direction. Alternatively, the bolt  30  can be attached to the nut  60  by rotating the bolt  30  or the nut  60  in the circumferential direction. 
     At the fixed position shown in  FIG.  7   , the tip end portion  68   a  of the lever  68  is inserted into the recess portion  36 . Thus, the bolt  30  cannot be rotated with respect to the nut  60 . This state is defined as a fixed state. In the fixed state, rotation between the bolt  30  and the nut  60  is restricted. 
     Specifically, the spring  63  urges the lever  68  in the direction in which the tip end portion  68   a  approaches the central axis AX. When the positions of the recess portion  36  and the tip end portion  68   a  match, the tip end portion  68   a  is inserted into the recess portion  36 . That is, the lever  68  rotates around the rotation shaft  69 , and the tip end portion  68   a  moves toward the central axis AX side with respect to the peripheral surface  33 . In  FIG.  7   , the rotation of the lever  68  is restricted by the lever  68  coming into contact with the cylindrical portion  65  at the accommodation port  65   f.    
     When the tip end portion  68   a  is fitted into the recess portion  36 , the rotational operation of the nut  60  and the bolt  30  is restricted. Thus, unless the user operates the lever  68 , the bolt  30  and the nut  60  cannot be rotated. That is, the bolt  30  and the nut  60  cannot be rotated unless the user rotates the lever  68  in the direction opposite to the urging force of the spring  63 . In the state where the tip end portion  68   a  is in the recess portion  36  in this way, the rotation of the bolt  30  and the nut  60  is restricted. That is, the nut  60  is fixed to the bolt  30  in a fixed state. 
     Further, in order to rotate the bolt  30  and the nut  60 , the user pushes the operation portion  68   b  so that the lever  68  is accommodated in the accommodation portion  61   f  and the accommodation port  65   f . Then, as shown in  FIG.  6   , when the lever  68  is accommodated, the tip end portion  68   a  is taken out from the recess portion  36 . As a result, the part fastening structure  1  is in a movable state in which the rotation restriction is released, and the bolt  30  and the nut  60  can rotate. 
     The operation at the time of fastening will be described in detail with reference to  FIGS.  8  to  10   .  FIGS.  8  to  10    are cross-sectional views showing the structure of the part fastening structure  1  for fastening the first part  10  and the second part  20 .  FIGS.  8  to  10    are cross-sectional views of the part fastening structure  1  cut along a plane including the central axis AX.  FIGS.  8  and  9    show a movable state in which the tip end portion  68   a  is not inserted into the recess portion  36 .  FIG.  10    shows a fixed state in which the tip end portion  68   a  is inserted into the recess portion  36 . 
       FIG.  8    is a cross-sectional view at a position where the thread groove  35  of the bolt  30  and the thread groove  61   s  of the nut  60  start meshing (hereinafter referred to as a meshing start position).  FIG.  10    is a cross-sectional view at a position where the fastening of the bolt  30  and the nut  60  is completed (hereinafter referred to as a fastening completed position).  FIG.  9    is a cross-sectional view showing a configuration at a position between the meshing start position and the fastening completion position. Specifically,  FIG.  9    shows the position where the second nut member  62  is in contact with the second part  20 . 
     When the shaft portion  31  of the bolt  30  is inserted into the hollow portions  61   a  and  62   a  along the axial direction from the state where the bolt  30  and the nut  60  are not attached (see  FIG.  4   ), the bolt  30  and the nut  60  are in the meshing start position shown in  FIG.  8   . The thread groove  35  and the thread groove  61   s  come into contact with each other. The tip end side of the thread groove  35  and the base end side of the thread groove  61   s  mesh with each other. In this state, the tip end portion  68   a  comes into contact with the peripheral surface  33 . In the state shown in  FIG.  8   , the second part  20  and the second nut member  62  are separated from each other in the axial direction. 
     When the shaft portion  31  of the bolt  30  is inserted into the hollow portions  61   a  and  62   a  along the axial direction, the user operates the lever  68  so as to cancel the urging force of the spring  63  until the tip end portion  68   a  is in contact with the peripheral surface  33 . That is, the user pushes the lever  68  toward the accommodation port  65   f  until the thread groove  35  and the thread groove  61   s  mesh with each other. By doing so, the tip end portion  68   a  is located outside the peripheral surface  33  in a plan view orthogonal to the central axis AX. When the tip end portion  68   a  comes into contact with the peripheral surface  33 , the tip end portion  68   a  receives the reaction force of the urging force of the spring  63  from the peripheral surface  33 . Thus, the user may release the lever  68  after the thread groove  35  and the thread groove  61   s  are meshed with each other. 
     When the nut  60  is rotated in a tightening direction from the position shown in  FIG.  8   , it becomes as shown in  FIG.  9   . In  FIG.  9   , the nut  60  is seated on the second part  20 . That is, the bottom portion  66  of the second nut member  62  and the second part  20  come into contact with each other. The relative displacement amount in the axial direction due to the rotation of the nut  60  between  FIGS.  8  and  9    is 1.3 mm. That is, in the state shown in  FIG.  9   , the nut  60  approaches the first part  10  by 1.3 mm from the state shown in  FIG.  8    in the axial direction. 
     In the state up to  FIG.  9   , since the peripheral surface  33  and the tip end portion  68   a  are in contact with each other, the tip end portion  68   a  is not in the recess portion  36 . The tip end portion  68   a  receives a reaction force of the urging force of the spring  63  from the peripheral surface  33 . Thus, the user can rotate the nut  60  without operating the lever  68 . 
     Further, in the axial direction, the disc spring  64  generates an urging force between the first nut member  61  and the second nut member  62 . That is, the disc spring  64  urges the first nut member  61  toward the tip end side and the second nut member  62  toward the base end side. From the state of  FIG.  8    to the state shown in  FIG.  9   , the expansion and contraction amount of the disc spring  64  is zero (natural length). 
     When the nut  60  is further rotated in the tightening direction from the position shown in  FIG.  9   , it becomes as shown in  FIG.  10   . The relative displacement amount in the axial direction due to the rotation of the nut  60  between  FIGS.  9  and  10    is 0.7 mm. 
     In  FIG.  10   , the tip end portion  68   a  is disposed in the recess portion  36 . In this state, as shown in  FIG.  7   , the lever  68  protrudes from the accommodation portion  61   f  and the accommodation port  65   f  As described above, the rotation of the bolt  30  and the nut  60  is restricted. In other words, the fastening of the bolt  30  and the nut  60  is maintained unless the user pushes in the lever  68 . It is possible to suppress the bolt  30  from coming off from the nut  60 . Thus, the first part  10  and the second part  20  can be securely fastened. 
     When removing the first part  10  and the second part  20 , the user operates the lever  68  from the states shown in  FIGS.  7  and  10   . That is, the user pushes the lever  68  toward the accommodation portion  61   f  As a result, the lever  68  rotates counterclockwise in  FIG.  6   , and the tip end portion  68   a  moves to the outside of the recess portion  36 . Thus, the restriction on the rotation of the bolt  30  and the nut  60  is lifted. With the lever  68  pushed in, the user rotates the nut  60  in the loosening direction. By doing so, the nut  60  is removed from the bolt  30 , so that the first part  10  and the second part  20  can be removed. 
     As described above, in the present embodiment, the nut  60  includes the first nut member  61 , the second nut member  62 , the spring  63 , and the lever  68 . When the user pushes the spring  63 , the lever  68  rotates, so that the bolt  30  and the nut  60  can be attached and detached. The user can easily and surely fasten the first part  10  and the second part  20 . 
     Further, the user can remove the bolt  30  and the nut  60  by just lever operation and rotating the nut  60 . Thus, simple attachment and detachment is possible. No special tools are required for installation and removal. That is, attachment and detachment can be performed with the user&#39;s own hand or finger. Further, durability and workability can be improved. 
     In other words, unless the user pushes in the lever  68 , the bolt  30  will not come off the nut  60 . As a result, the bolt  30  and the nut  60  can be securely fixed. Loosening of the bolt  30  can be suppressed, and the two parts can be securely fastened. That is, it is possible to suppress the bolt  30  from coming off from the nut  60  when the parts are fastened. 
     Further, when the nut  60  is further rotated from the position shown in  FIG.  9    in the direction of tightening further, the disc spring  64  contracts. In the axial direction, the size of the pin hole  61   h  in the longitudinal direction ensures the displacement amount (stroke) of the pin  71  in the pin hole  61   h . That is, within the size of the pin hole  61   h , the axial distance between the bottom portion  66  and the first nut member  61  changes. Further, the distance between the first nut member  61  and the second nut member  62  in the axial direction changes according to the amount of expansion and contraction of the disc spring  64 . 
     Further, as the disc spring  64  contracts, the urging force between the first nut member  61  and the second nut member  62  becomes stronger. Thus, after the nut  60  comes into contact with the second part  20 , the disc spring  64  contracts when the nut  60  is rotated in the tightening direction. The more the nut  60  is rotated in the tightening direction, the stronger the force required to rotate the nut  60 . 
     Thus, in the present embodiment, the two recess portions  36  are disposed apart from each other in the circumferential direction on the peripheral surface  33 . This makes it possible to suppress the force for rotating the nut  60  from increasing. In the present embodiment, the two recess portions  36  are disposed 180° apart in the circumferential direction. The rotation angle of the nut  60  from the height at which the tip end portion  68   a  fits in the recess portion  36  to the rotation angle of the nut  60  until the axial positions of the recess portion  36  and the tip end portion  68   a  match can be made less than 180°. On the other hand, when only one recess portion  36  is provided on the peripheral surface  33 , the rotation angle of the nut  60  until the axial positions of the recess portion  36  and the tip end portion  68   a  match is a maximum of 360°. Therefore, by forming the two or more recess portions  36  apart in the circumferential direction, it is possible to suppress the force for rotating the nut  60  from increasing. 
     A method of attaching the first nut member  61  to the second nut member  62  will be described with reference to  FIG.  5   . First, the user attaches the lever  68  to the accommodation portion  61   f  in a state where the spring  63  is accommodated in the accommodation portion  61   f . Then, the user attaches the lever  68  to the first nut member  61  by using the rotation shaft  69 . As a result, the first nut member  61  as shown in  FIG.  5    can be prepared. 
     Next, the user attaches the first nut member  61  having the lever  68  to the second nut member  62 . Specifically, with the first nut member  61  tilted with respect to the axial direction, the operation portion  68   b  is passed through the accommodation port  65   f  from the inner peripheral surface  65   b  side. The user passes the operation portion  68   b  of the lever  68  from the inner peripheral surface  65   b  side to the outer peripheral surface  65   c  side. The user matches the circumferential direction of the pin hole  61   h  and the pin hole  65   h . Then, the pin  71  is press-fitted into the pin hole  65   h  so as to be caught in the pin hole  61   h . As a result, since the first nut member  61  is attached to the second nut member  62 , the nut  60  shown in  FIG.  4    is formed. 
     Further, by making the pin hole  61   h  a through hole, the first nut member  61  can be removed from the second nut member  62 . Specifically, by pushing the pin  71  toward the central axis AX, the pin  71  protrudes from the inner peripheral surface  61   b . Thus, the pin  71  can be removed from the hollow portion  61   a . By removing the two pins  71 , the first nut member  61  can be taken out from the second nut member  62 . 
       FIG.  11    is a diagram showing an example of a mounting tool using the part fastening structure  1 .  FIG.  11    is a perspective view schematically showing a mounting tool  120  worn by the user. The mounting tool  120  mainly includes a control unit  121 , a plurality of frames that support each part of the affected leg, and a load sensor  222  for detecting a load applied to the sole of the foot. The mounting tool  120  functions as a walking assist device having a drive unit and a control unit. 
     The control unit  121  includes an auxiliary control unit  220  that controls the mounting tool  120 , and also includes a motor (not shown) that generates a driving force for assisting the extension movement and the flexion movement of the knee joint. The frame supporting each part of the affected leg includes a thigh frame  122  and a lower leg frame  123  rotatably connected to the thigh frame  122 . Further, this frame includes a foot flat frame  124  rotatably connected to the lower leg frame  123 , a front side connecting frame  127 , and a rear side connecting frame  128 . 
     The thigh frame  122  and the lower leg frame  123  rotate relative to each other around a hinge axis H a  shown in the figure. The motor of the control unit  121  rotates in accordance with an instruction of the auxiliary control unit  220  to assist the thigh frame  122  and the lower leg frame  123  to open or close relatively around the hinge axis H a . An angle sensor  223  housed in the control unit  121  is, for example, a rotary encoder, and detects an angle formed by the thigh frame  122  and the lower leg frame  123  around the hinge axis H a . The lower leg frame  123  and the foot flat frame  124  rotate relative to each other around the hinge axis H b  shown in the figure. The relative rotating angle range is pre-adjusted by the adjusting mechanism  126 . 
     The thigh frame  122  includes a thigh belt  129 . The thigh belt  129  is a belt integrally provided on the thigh frame, and is wrapped around the thigh portion of the affected leg to fix the thigh frame  122  to the thigh portion. This suppresses the entire mounting tool  120  from shifting with respect to the trainee&#39;s legs. 
     The load sensor  222  is a load sensor embedded in the foot flat frame  124 . The load sensor  222  can also be configured to detect the magnitude and distribution of the vertical load received by the trainee&#39;s sole, for example, to detect a center of pressure (COP). The load sensor  222  is, for example, a resistance change detection type load detection sheet in which electrodes are disposed in a matrix. 
     The lower leg frame  123  includes the first part  10  and the second part  20  shown in  FIG.  1   . Then, the first part  10  and the second part  20  are connected via the part fastening structure  1 . That is, the user attaches the first part  10  and the second part  20  by the part fastening structure  1 . Thus, the length of the lower leg frame  123  can be adjusted in accordance with the leg length of the user who wears the mounting tool  120 . The user can easily and surely fasten the first part  10  and the second part  20  of the lower leg frame  123 . Therefore, the user can easily adjust the frame length. The number of parts to be fastened by the part fastening structure  1  may be 3 or more. 
     Although the disclosure made by the present inventor has been specifically described above based on the embodiment, the present disclosure is not limited to the above embodiment and can be variously modified within a range that does not depart from the gist thereof.