Abstract:
A connection mechanism is provided with a shaft member formed with an outer-screw portion which is formed with an outer screw, a plate member formed with a connection hole in which the shaft member is fitted, a nut member formed with an inner-screw to engage with the outer-screw of the shaft member, the nut member engaged with the shaft member being urged toward the plate member fitted on the shaft member to fixedly secure the plate member onto the shaft member, and a fixing mechanism that fixes the plate member and the nut member with each other to retain a status where the plate member and the nut member are urged oppositely in a rotational direction about a central axis of the shaft member.

Description:
BACKGROUND OF THE INVENTION 
     The following descriptions relate to a connection mechanism for connecting a plate member and a shaft member employed, for example, in an endoscope. 
     Generally, at an operation section of an endoscope, connection mechanisms such as a mechanism for operating a bending portion of an insertion section of the endoscope, a mechanism for changing a rising angle of a treatment tool and the like are provided. Such a mechanism employs a connection mechanism which connects the plate member with the shaft member such that the plate member does not rotate relative to the shaft member. 
     Typically, in such a connection mechanism, a portion of the shaft member is formed to have an outer-screwed portion. The outer-screwed portion is inserted through an opening formed on the plate member, and with use of a nut having an inner-screw, the plate member is secured to the shaft member. An example of such a configuration is disclosed in Japanese Patent Provisional Publication No. HEI 7-194519. 
       FIG. 10  shows an example of a conventional connection mechanism. As shown in  FIG. 10 , a shaft member  90  is formed with a polygonal column section  92  next to an outer-screw section  91 . A plate member  93  is formed with a polygonal hole  94  to be fitted on the polygonal column section  92 . The plate member  93  is fitted on the polygonal column section  92  and contacts a stepped portion  96  formed at the end of the polygonal column section  92 , and urged toward the stepped portion  96  by fastening a nut member  95  provided with an inter-screw which engages with the outer-screw section  91 . 
     Between the polygonal column section  92  and the polygonal hole  94 , some play may occur in the rotational direction due to manufacturing errors. Because of such play, fastening of the nut member  95  with respect to the plate member  93  may be loosened in a certain period of time. In such a case, play may occur between the plate member  93  and the shaft member  90 . 
       FIG. 11  shows another example of a conventional connection mechanism. In this example, the shaft member  90  is formed with a cylindrical member formed with an outer-screw, and both the plate member  93  and the nut member  95  engage with the outer-screw of the shaft member such that the plate member  93  and the nut member  95  are urged against each other. 
     Also in this structure, due to an external force applied to the plate member, the play may occur during usage of the connection mechanism. 
     SUMMARY OF THE INVENTION 
     The present invention is advantageous in that an improved connection mechanism, which is configured such that the plate member is secured to the shaft member using the nut member, capable of maintaining secured connected state for a long period. 
     According to an aspect of the invention, there is provided a connection mechanism, which is provided with a shaft member formed with an outer-screw portion which is formed with an outer screw, a plate member formed with a connection hole in which the shaft member is fitted, a nut member formed with an inner-screw to engage with the outer-screw of the shaft member, the nut member engaged with the shaft member being urged toward the plate member fitted on the shaft member to fixedly secure the plate member onto the shaft member, and a fixing mechanism that fixes the plate member and the nut member with each other to retain a status where the plate member and the nut member are urged oppositely in a rotational direction about a central axis of the shaft member. 
     With the above structure, the plate member can be secured to the shaft member using the nut member, capable of maintaining a secured connected state for a long period. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         FIG. 1  is an exploded perspective view of a connection mechanism according to a first embodiment. 
         FIG. 2  is a side view of an endoscope employing the connection mechanism shown in  FIG. 1 . 
         FIG. 3  is a cross-sectional side view of the connection mechanism according to the first embodiment. 
         FIG. 4  is a cross-sectional plan view of the connection mechanism taken along line IV-IV in  FIG. 3 . 
         FIG. 5  is a partial cross-sectional side view of the connection mechanism according to a modification of the first embodiment. 
         FIG. 6  is an exploded perspective view of a connection mechanism according to a second embodiment. 
         FIG. 7  is a cross-sectional side view of the connection mechanism according to the second embodiment. 
         FIG. 8  is a cross-sectional plan view of the connection mechanism taken along line VIII-VIII in  FIG. 7 . 
         FIG. 9  is a partial cross-sectional side view of the connection mechanism according to a modification of the second embodiment. 
         FIG. 10  is a cross-sectional side view of a first example of a conventional connection mechanism. 
         FIG. 11  is a cross-sectional side view of a second example of the conventional connection mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, referring to the accompanying drawings, connection mechanisms according to embodiments of the invention will be described. 
       FIG. 2  shows a side view of an endoscope  100  to which a connection mechanism according to the invention is applicable. The endoscope  100  has a flexible insertion section  1  and a distal end portion thereof is formed to be a bendable section  2 . The bendable section  2  is driven by operation of an operation unit  3  connected to the proximal end of the insertion section  1 . 
     Specifically, the operation unit  3  is provided with a bendable section operating knob  4  (hereinafter, simply referred to as a knob), which is rotatable with respect to the operation unit  3 . By rotating the knob  4 , one of a plurality of operating wires connected to the bendable section  2  is pulled, and the bendable section  2  is bent by an amount (i.e., angle) corresponding to the rotated amount of the knob  4 . In  FIG. 2 ,  6  denotes a bent state retaining knob to be used for retaining the bent state of the bendable section  2 . 
       FIG. 3  is a cross-sectional side view of the connection mechanism according to the first embodiment. In  FIG. 3 ,  60  denotes a braking mechanism for applying frictional force for preventing the rotational movement of the knob  4  in accordance with the operation of the bent state retaining knob  6 . The braking mechanism  60  is of a well-known type, an example of which is disclosed in Japanese Patent Provisional Publication No. 2007-313292. The braking mechanism  60  is secured to a shaft member  7  which is fixedly secured onto the frame of the operation unit  3 . A plate member  11  unrotatably engages with the shaft member  7  is fixedly secured thereto by a nut member  12 . The plate member  11  serves as a fixed member for braking operation. 
     It should be noted that the various braking mechanisms have been known, and since the present invention relates to a connection mechanism, which is a part of the braking mechanism and may be applied to other connecting mechanism, the operation of the braking mechanism  60  will not be described for brevity. 
     The shaft member  7  is provided with a polygonal column portion  7   x . According to the first embodiment, a regular hexagonal column is employed. However, any other polygonal column may be used. The shaft member  7  has a cylindrical shape at portions other than the polygonal column portion  7   x . At a boundary between the cylindrical portion and the polygonal portion  7   x , as shown in  FIG. 3 , a step  7   a  is formed. 
     As shown in  FIG. 1 , an outer-screw portion  7   s  is also formed to be a polygonal column shape. That is, the outer-screw is formed on the ridge portions of the polygonal column portion  7   x.    
     The plate member  11  has a connection hole  11   a  which is formed at the center of the plate member  11 . The connection hole  11   a  has a polygonal shape in which the polygonal column portion  7   x  of the shaft member  7  is tightly fitted. The nut member  12  has an inner-screw  12   s  which is formed at the center of the nut member  12 . The inner screw  12   s  engages with the outer-screw  7   s  of the shaft member  7 . 
     As clearly shown in  FIG. 1 , the nut member  12  has a disk-like member. On the plate member  11 , a circular recess  13  is formed such that the nut member  12  is loosely fitted in the recess  13 . 
     As the polygonal column portion  7   x  is inserted in the connection hole  11   a , the plate member  11  is unrotatably engaged with the shaft member  7 . Then, with use of the nut member  12  which screwed on the outer-screw portion  7   s , the plate member  11  is urged toward the step portion  7   a  of the shaft member  7 , thereby fixedly secured to the shaft member  7 . It should be noted, however, there may exist play between the polygonal column portion  7   x  and the connection hole  11  in the rotational direction due to manufacturing errors. 
     As shown in  FIG. 1  and  FIG. 4 , a screw hole  8  is formed on the plate member  11  such that a central axis  8   ax  of the screw hole  8  extends from an outer circumferential surface of the plate member  11  to the recess  13 . As shown in  FIG. 4 , the direction where the screw hole  8  extends (i.e., the direction of the central axis  8   ax  of the screw hole  8 ) is inclined with respect to a tangential line  7   t  at which the central axis  8   ax  of the screw hole  8  intersects the circumferential surface of the nut member  12  (i.e., the direction where the screw hole  8  extends is deflected from the radial direction). Further, a screw  9  having a conical tip end is screwed in the screw hole  8  from the outer periphery of the plate member  11  toward the nut member  12 . 
     By fastening the screw  9  tightly, the plate member  11  and the nut member  12  are urged to rotate in opposite directions as indicated by arrows in  FIG. 4 . With this structure, the fastening force of the nut member  12  for urging the plate member toward the step portion  7   a  of the shaft is amplified. As a result, the plate member  11  is fixedly secured to the shaft member  7  without any play at all in the rotational direction. It should be noted that the screw hole  8  is formed such that the nut member  12  is urged to rotate in a direction where the urging force applied by the nut member  7  to the plate member  11  increases, as indicated in  FIG. 4 . If the screw  9  applies force to the nut in the opposite direction, the nut member  12  is loosened. 
     With the above structure, as the nut member  12  is urged in the direction where the nut member  12  press-contacts the plate member  11 , and thus, the plate member  11  is urged toward the step portion  7   a , and thus the plate member  11  is fixedly secured to the shaft member  7 , and the fixedly secured condition is maintained by the screw  9 . 
     According to the above-described structure, the nut member  12  will not be loosened even after a certain period of time and the play will not occur between the polygonal column portion  7   x  and the connection hole  11   a . Therefore, the tightly connected condition between the plate member  11  and the nut member  12  can be maintained for a relatively long period, stably and without play. 
       FIG. 5  is a cross-sectional side view of a connection mechanism according to a modification of the first embodiment. According to the second embodiment, a groove  12   a  having a V-shaped cross section may be formed on the circumferential surface of the nut member  12  so that part of the pressing force of the screw  9  is converted to urge the nut member  12  toward the plate member  11 . 
       FIG. 6  is an exploded perspective view,  FIG. 7  is a cross-sectional side view of a connection mechanism according to a second embodiment, and  FIG. 8  is cross-sectional plan view of the connection mechanism taken along line VIII-VIII of  FIG. 7 . According to the second embodiment, as shown in  FIG. 6 , the entire area of the shaft member  7  is formed as a screw (although it is not necessarily be the entire area). In the connection hole  11   a , an inner-screw meshes with the outer-screw of the shaft member  7 . Thus, both the plate member  11  and the nut member  12  are screwed on the shaft member  7 . The other structure is the same as that of the first embodiment. 
     As a result of the structure according to the second embodiment, the plate member  11  and the nut member  12  can be tightly press-contacted with each other as a double-nut structure, and the tightly press-contacted condition between the plate member  11  and the nut member  12  is amplified by fastening the screw  9 . Therefore, the connection state between the plate member  11  and the nut member  12  can be maintained for a relatively long period, without causing the play therebetween. 
     As shown in  FIG. 9 , the second embodiment can be modified as in the modification of the first embodiment. That is, a V-shaped groove  12   a  may be formed on the outer circumferential surface of the nut member  12  so that part of the pressing force of the screw  9  is converted into the force for urging the nut member  12  toward the plate member  11 . 
     The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2007-164778, filed on Jun. 22, 2007, which is expressly incorporated herein by reference in its entirety.