Patent Publication Number: US-2022229245-A1

Title: Optical connector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a national phase application of International Patent Application No. PCT/JP2020/027003 filed Jul. 10, 2020, which claims priority to Japanese Patent Application No. 2019-142037 filed Aug. 1, 2019 and Japanese Patent Application No. 2020-020953 filed Feb. 10, 2020. The full contents of these applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an optical connector. 
     BACKGROUND 
     Patent Document 1 below discloses a method of manufacturing an optical fiber assembly in which a plurality of optical fibers aligned at a predetermined pitch are integrated together by curing an adhesive. 
     PATENT DOCUMENT 
     [Patent Document 1] 
     
         
         Japanese Unexamined Patent Application, First Publication No. 2019-113730 
       
    
     For the optical fiber assembly, coating parts of a plurality of optical fibers aligned by hardened parts of an adhesive are stripped away, and the exposed bare parts are inserted into a ferrule of a mechanically transferable (MT) connector. However, since the hardened parts are arranged outside the ferrule, when the positional relationship between the ferrule and the hardened parts changes, flexure or deflection may occur on the optical fibers between the ferrule and the hardened parts. Thereby, there is a possibility that the bare parts are bent. 
     SUMMARY 
     The present invention provides an optical connector capable of suppressing the bending of bare parts. 
     An optical connector according to one or more embodiments of the present invention includes a plurality of optical fibers having bare parts in which coating parts of the plurality of optical fibers are stripped off; a ferrule in which a plurality of insertion holes are formed, and the bare parts are configured to be inserted into the insertion holes; and a pitch fixing member inserted into the ferrule, a plurality of fixing parts configured to fix a pitch of the coating parts of the plurality of optical fibers to a pitch of the plurality of insertion holes are formed in the pitch fixing member. 
     According to the configuration, since the pitch fixing member for fixing a pitch of the optical fibers is inserted into the ferrule, the positional relationship between the ferrule and the pitch fixing member is kept constant, thereby occurring flexure and deflection on the optical fibers can be suppressed between the ferrule and the pitch fixing member. As a result, the bending of the bare parts can be suppressed. Furthermore, since the pitch fixing member fixes the pitch of the coating parts of the optical fibers, a part which is bent according to fixing the pitch is the coating part. Therefore, bending in the bare parts can be suppressed. 
     In the optical connector, the plurality of insertion holes may be formed in a plurality of rows in the ferrule, and the plurality of fixing parts may be formed to correspond to the plurality of insertion holes. 
     In the optical connector, a boot in which a mounting part that mounts the pitch fixing member is formed, and which is attached to the ferrule together with the pitch fixing member may be further provided. 
     In the optical connector, a step may be formed in the pitch fixing member, and inlet parts of the plurality of fixing parts may be formed on the step. 
     In the optical connector, the plurality of fixing parts may be formed by a plurality of hole parts. 
     In the optical connector, the plurality of fixing parts may be formed by a plurality of groove parts and a top wall part that restricts the disengagement of the coating parts from the plurality of groove parts. 
     In the optical connector, the plurality of groove parts may be formed by V-shaped grooves. 
     In the optical connector, the top wall part may be formed by a plurality of V-shaped grooves. 
     In the optical connector, the coating part of the optical fiber may be supported by the fixing part at four points. 
     According to one or more embodiments of the present invention, the bending of the bare parts can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an optical connector according to a first embodiment. 
         FIG. 2  is an exploded perspective view of the optical connector according to the first embodiment. 
         FIG. 3  is a vertical sectional view of the optical connector according to the first embodiment. 
         FIG. 4  is a perspective view of a pitch fixing member according to the first embodiment. 
         FIG. 5  is a plan sectional view taken along a step of the pitch fixing member according to the first embodiment. 
         FIG. 6  is a front view of an outlet part side of the pitch fixing member according to the first embodiment. 
         FIG. 7  is a perspective view of a pitch fixing member according to a second embodiment. 
         FIG. 8  is a plan sectional view taken along a step of the pitch fixing member according to the second embodiment. 
         FIG. 9  is a front view of an outlet part side of the pitch fixing member according to the second embodiment. 
         FIG. 10  is a perspective view of a pitch fixing member according to a third embodiment. 
         FIG. 11  is a plan sectional view taken along a step of the pitch fixing member according to the third embodiment. 
         FIG. 12  is a front view of an outlet part side of the pitch fixing member according to the third embodiment. 
         FIG. 13  is a perspective view of an optical connector according to a fourth embodiment. 
         FIG. 14  is an exploded perspective view of the optical connector according to the fourth embodiment. 
         FIG. 15  is a vertical sectional view of the optical connector according to the fourth embodiment. 
         FIG. 16  is a perspective view of a pitch fixing member according to the fourth embodiment. 
         FIG. 17  is a front view of an outlet part side of the pitch fixing member according to the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a perspective view of an optical connector  1  according to a first embodiment.  FIG. 2  is an exploded perspective view of the optical connector  1  according to the first embodiment.  FIG. 3  is a vertical sectional view of the optical connector  1  according to the first embodiment. 
     As shown in  FIG. 1 , the optical connector  1  includes a plurality of optical fibers  2 , and a ferrule  10  into which the plurality of optical fibers  2  are inserted. 
     As shown in  FIG. 2 , the optical fibers  2  include coating parts  2   a  that cover core wires, and bare parts  2   b  in which the coating parts  2   a  are stripped off and the core wires are exposed. In the present embodiment, the coating parts  2   a  of the plurality of optical fibers  2  may be collectively coated with a resin material (outer cover) (not shown) to form a tape-shaped multi-core optical fiber cable. In the multi-core optical fiber cable, the optical fibers  2  can be separated one by one by tearing the outer cover described above. The separated optical fibers  2  are inserted into the ferrule  10 . 
     The ferrule  10  is an MT ferrule, and a plurality of insertion holes  11  are formed in a connection end surface  10   a  of the ferrule  10 . The bare parts  2   b  of the plurality of optical fibers  2  are inserted into the plurality of insertion holes  11 . The connection end surface  10   a  of the ferrule  10  is an inclined surface inclined with respect to a connection direction of the ferrule  10 . Further, the connection end surface  10   a  of the ferrule  10  may be a perpendicular surface at a right angle to the connection direction of the ferrule  10 . 
     In addition, a pair of guide holes  12  for alignment are formed on the connection end surface  10   a  of the ferrule  10 . On the other hand, a pair of guide pins to be inserted into the guide holes  12  are provided on the connection end surface of the ferrule on the other side (not shown). Further, the guide pins may be provided on the connection end surface  10   a  of the ferrule  10  instead of the guide holes  12 . In addition, the guide holes  12  and the guide pins may each be provided on the connection end surface  10   a  of the ferrule  10 . 
     As shown in  FIG. 3 , an opening part  14  is formed on a surface opposite to the connection end surface  10   a  of the ferrule  10 . A boot  30  is inserted into the opening part  14  together with a pitch fixing member  20  described later. The boot  30  is a flexible member formed of rubber, elastomer, or the like. The boot  30  includes a tubular body part  31  and a mounting part  32 . 
     The tubular body part  31  protrudes rearward from the opening part  14  and flexibly supports the optical fibers  2  outside the ferrule  10 . As shown in  FIG. 2 , a long hole  31   a  through which the plurality of optical fibers  2  (tape-shaped cable part) are inserted is formed in the tubular body part  31 . The long hole  31   a  extends to the mounting part  32 . As shown in  FIG. 3 , the mounting part  32  is inserted into the ferrule  10 , and also is fitted to an inner wall surface of the opening part  14  in a slightly compressed press-fit state. 
     The mounting part  32  includes a pair of holding parts  33  and a sealing part  34 . As shown in  FIG. 3 , the pair of holding parts  33  and the sealing part  34  are connected in a C shape in a cross-sectional view. A space part for mounting the pitch fixing member  20  is formed inside the C-shape. As shown in  FIG. 2 , the pair of holding parts  33  are formed in a plate shape having substantially the same dimensions as the width and the length of the pitch fixing member  20  to sandwich the pitch fixing member  20  by the upper side of the holding parts  33  and the lower side of the holding parts  33 . 
     The sealing part  34  is formed in a lid shape (plate shape) in contact over an entire circumference with the inner wall surface of the opening part  14  of the ferrule  10  behind the pair of holding parts  33 . A step  15  is formed in an inner space S of the ferrule  10  in front of the boot  30 . Tapered hole parts  11   a  that bring the bare parts  2   b  of the optical fibers  2  into the insertion holes  11  described above are formed in the step  15 . 
     The inner space S is filled with an adhesive (not shown). The adhesive is filled in the inner space S from a window part  13  formed in the ferrule  10 . The sealing part  34  prevents the adhesive filled in the inner space S from leaking from the opening part  14 . Further, since the pair of holding parts  33  and the pitch fixing member  20  are designed in conformity with the dimensions of the opening part  14 , a gap between the pair of holding parts  33  and the pitch fixing member  20 , and the opening part  14  becomes small. As a result, the leakage of the adhesive can be prevented even in this portion. 
     As shown in  FIG. 2 , the pitch fixing member  20  is formed in a substantially rectangular plate shape. A plurality of fixing parts  21  through which the plurality of optical fibers  2  are inserted are formed in the pitch fixing member  20 . The plurality of fixing parts  21  fix the pitch of the coating parts  2   a  of the plurality of inserted optical fibers  2  to the pitch of the plurality of insertion holes  11 . In other words, the pitch of the plurality of fixing parts  21  and the pitch of the plurality of insertion holes  11  are equal to each other. A step  22  is formed on an insertion side of the optical fibers  2  of the pitch fixing member  20 . 
       FIG. 4  is a perspective view of the pitch fixing member  20  according to the first embodiment.  FIG. 5  is a plan sectional view taken along the step  22  of the pitch fixing member  20  according to the first embodiment.  FIG. 6  is a front view of the pitch fixing member  20  according to the first embodiment on a side of outlet parts  21   b.    
     As shown in  FIGS. 4 and 6 , the plurality of fixing parts  21  of the present embodiment are formed by a plurality of hole parts. 
     An inner diameter of the fixing part  21  (hole part) is slightly larger than a coating diameter of the optical fiber  2 . In other words, the fixing part  21  has an inner diameter through which the coating part  2   a  of the optical fiber  2  can be inserted. As shown in  FIG. 6 , a partition wall  23  is formed between the adjacent fixing parts  21 . Furthermore, as shown in  FIG. 4 , inlet parts  21   a  of the plurality of fixing parts  21  are formed on the step  22  of the pitch fixing member  20 . The inlet part  21   a  has a semicircular groove shape in which the lower half of the fixing part  21  (hole part) is extended to the step  22 . 
     As shown in  FIG. 5 , the plurality of fixing parts  21  are formed at a constant pitch P 1  from the inlet parts  21   a  to the outlet parts  21   b . The pitch P 1  of the fixing parts  21  is equal to the pitch of the insertion holes  11  of the ferrule  10  described above, and is larger than the pitch P 2  of the optical fibers  2 . Here, the pitch P 2  of the optical fibers  2  is a pitch of the optical fibers  2  which is the tape-shaped multi-core optical fiber cable. In general, the pitch P 2  of the optical fibers  2  is equal to the coating diameter of the optical fiber  2 . 
     For example, the pitch P 2  (coating diameter) of the optical fibers  2  is 160 μm or 200 μm, and the pitch P 1  of the fixing parts  21  is 250 μm. Therefore, the optical fibers  2  can be converted to the pitch P 1  by simply inserting the optical fibers  2  into the fixing parts  21  without using a special jig or an adhesive. The pitch fixing member  20  may be made of a plastic material, thereby forming fixing parts  21  (hole parts) having high dimensional accuracy. 
     According to the optical connector  1  having the above configuration, the plurality of optical fibers  2 , the ferrule  10  provided with the plurality of insertion holes  11  into which the bare parts  2   b  stripped where the coating parts  2   a  of the plurality of optical fibers  2  are stripped off are inserted, and the pitch fixing member  20  inserted into the ferrule  10 , and provided with the plurality of fixing parts  21  that fix a pitch of the coating parts  2   a  of the plurality of optical fibers  2  to a pitch of the plurality of insertion holes  11  are provided. Therefore, bending in the bare parts  2   b  of the optical fibers  2  can be suppressed. 
     That is, as shown in  FIG. 3 , since the pitch fixing member  20  that fixes a pitch of the optical fibers  2  is inserted into the ferrule  10 , the positional relationship between the ferrule  10  and the pitch fixing member  20  is kept constant, and occurring flexure and deflection on the optical fibers  2  can be suppressed between the ferrule  10  and the pitch fixing member  20 . As a result, the bending of the bare parts  2   b  can be suppressed. Furthermore, since the pitch fixing member  20  fixes a pitch in the coating parts  2   a  of the optical fibers  2 , the coating parts  2   a  are bent as the pitch is fixed (changed from the pitch P 2  to the pitch P 1  shown in  FIG. 5 ), and bending in the bare parts  2   b  can be suppressed. 
     In addition, as shown in  FIG. 2 , since the present embodiment has the boot  30  in which the mounting part  32  that mounts the pitch fixing member  20  is formed and is attached to the ferrule  10  together with the pitch fixing member  20 , the pitch fixing member  20  can be easily assembled into the ferrule  10  with no additional processing on a side of the ferrule  10 . Moreover, since the pitch fixing member  20  is covered with the boot  30 , the adhesive filled in the inner space S of the ferrule  10  can be prevented from leaking from the opening part  14 . 
     In addition, in the present embodiment, as shown in  FIG. 4 , the optical fibers  2  are easily inserted into the fixing parts  21 , since the step  22  is formed in the pitch fixing member  20 , and the inlet parts  21   a  of the plurality of fixing parts  21  are formed on the step  22 . 
     Furthermore, in the present embodiment, as shown in  FIG. 6 , since the plurality of fixing parts  21  are formed by the plurality of hole parts, the partition wall  23  is formed between the adjacent fixing parts  21 . As a result, once the optical fibers  2  are inserted into the fixing parts  21 , the optical fibers  2  on the left and right will not be misplaced. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described. In the following description, the same or equivalent configuration as that in the above-described embodiment are designated by the same reference numerals, and a description thereof will be simplified or omitted. 
       FIG. 7  is a perspective view of the pitch fixing member  20  according to the second embodiment.  FIG. 8  is a plan sectional view taken along the step  22  of the pitch fixing member  20  according to the second embodiment.  FIG. 9  is a front view of the pitch fixing member  20  according to the second embodiment on a side of the outlet parts  21   b.    
     As shown in  FIGS. 7 and 9 , the plurality of fixing parts  21  of the second embodiment are formed by a plurality of groove parts  24  and a top wall part  25  that restricts the disengagement of the optical fibers  2  (coating parts  2   a ) from the plurality of groove parts  24 . 
     As shown in  FIG. 8 , the plurality of groove parts  24  are formed at a constant pitch P 1  from the inlet parts  21   a  to the outlet parts  21   b  of the fixing parts  21 . As shown in  FIG. 9 , the groove part  24  is a semicircular groove that surrounds the lower half of the optical fiber  2 . The top wall part  25  faces the groove parts  24  with a gap between the top wall part  25  and each of the plurality of groove parts  24 . The minimum gap between the top wall part  25  and the groove parts  24  may be set to be less than a diameter (coating diameter) of the optical fiber  2 . The minimum gap may also be set equal to or less than a radius of the optical fiber  2  which is a half of the optical fiber  2  to prevent the optical fiber  2  from being disengaged from the groove part  24 . 
     According to the second embodiment having the above configuration, the plurality of fixing parts  21  are formed by the plurality of groove parts  24  and the top wall part  25  that restricts the disengagement of the coating parts  2   a  from the plurality of groove parts  24 . With this configuration, as shown in  FIG. 9 , the adjacent fixing parts  21  can be spatially communicated with each other, and the partition wall  23  (see  FIG. 6 ) of the first embodiment described above can be eliminated. When the pitch P 1  of the fixing parts  21  is narrow, the thickness of the partition wall  23  is thin and the partition wall  23  tends to be brittle. Therefore, according to the second embodiment, a suitable structure can be provided even when the pitch P 1  of the fixing part  21  is narrow. 
     Third Embodiment 
     Next, a third embodiment of the present invention will be described. In the following description, the same or equivalent configuration as that in the above-described embodiment are designated by the same reference numerals, and a description thereof will be simplified or omitted. 
       FIG. 10  is a perspective view of the pitch fixing member  20  according to the third embodiment.  FIG. 11  is a plan sectional view taken along the step  22  of the pitch fixing member  20  according to the third embodiment.  FIG. 12  is a front view of the pitch fixing member  20  according to the third embodiment on a side of the outlet parts  21   b.    
     As shown in  FIGS. 10 and 12 , the plurality of fixing parts  21  of the third embodiment are different from the second embodiment in that V-shaped groove parts  26  are provided. 
     As shown in  FIG. 11 , the plurality of groove parts  26  are formed at a constant pitch P 1  from the inlet parts  21   a  to the outlet parts  21   b  of the fixing parts  21 . As shown in  FIG. 12 , the groove part  26  is a V-shaped groove to be in contact with the lower half of the optical fiber  2  at least two points. The top wall part  25  faces the groove parts  26  with a gap between the top wall part  25  and each of the plurality of groove parts  26 . The minimum gap between the top wall part  25  and the groove part  26  may be set to be less than a diameter (coating diameter) of the optical fiber  2 . The minimum gap may also be set equal to or less than a radius of the optical fiber  2  which is a half of the optical fiber  2  to prevent the optical fiber  2  from being disengaged from the groove part  26 . 
     According to the third embodiment having the above configuration, in addition to the same effects as those of the second embodiment, since the plurality of groove parts  26  are formed by V-shaped grooves, the number of contact points is increased to at least two with respect to one optical fiber  2 , and the optical fiber  2  can be stably supported in the fixing part  21 . Therefore, the pitch of the optical fibers  2  can be changed to the pitch of the insertion holes  11  of the ferrule  10  with high accuracy, and bending can be more reliably suppressed in the bare parts  2   b.    
     Fourth Embodiment 
     Next, a fourth embodiment of the present invention will be described. In the following description, the same or equivalent configuration as that in the above-described embodiment are designated by the same reference numerals, and a description thereof will be simplified or omitted. 
       FIG. 13  is a perspective view of an optical connector  1  according to the fourth embodiment.  FIG. 14  is an exploded perspective view of the optical connector  1  according to the fourth embodiment.  FIG. 15  is a vertical sectional view of the optical connector  1  according to the fourth embodiment. 
     As shown in  FIG. 13 , the ferrule  10  of the fourth embodiment is different from the above embodiment in that the plurality of insertion holes  11  into which the optical fibers  2  are inserted are formed in a plurality of rows. In other words, the insertion holes  11  arranged in a row in a predetermined direction are formed in a plurality (of rows) on the connection end surface  10   a  of the ferrule  10 . Further, in the ferrule  10  shown in  FIG. 13 , the insertion holes  11  are formed in two rows, but the insertion holes  11  may be formed in two or more rows (e.g., four rows, six rows, etc.). 
     As shown in  FIGS. 14 and 15 , the pitch fixing member  20  is inserted into the opening part  14  that is a side opposite to the connection end surface  10   a  of the ferrule  10 . A plurality of rows (two rows) of fixing parts  21  corresponding to the plurality of rows (two rows) of the insertion holes  11  of the ferrule  10  is formed in the pitch fixing member  20 . Further, a thickness of the pitch fixing member  20  is increased by forming a plurality of rows of the fixing parts  21 , and the boot  30  of the above embodiment is not provided. Further, if the opening part  14  is formed to be large, the pitch fixing member  20  may be mounted on the boot  30 , similarly to the above embodiments. 
     Stair-like steps  22  corresponding to a plurality of rows (two rows) of insertion holes  11  are provided on a side of the pitch fixing member  20  into which the optical fibers  2  are inserted, and as shown in  FIG. 15 , at least a part of the steps  22  protrude from the opening part  14  of the ferrule  10  to an outside of the ferrule  10 . Instead of the boot  30 , a plurality of steps  22  protruding from the ferrule  10  may be applied with an adhesive  40 . The adhesive  40  may be a silicone-based adhesive having flexibility capable of absorbing impact similarly to the boot  30 , and as a result the optical fibers  2  extending from the pitch fixing member  20  can be molded at the steps  22  to absorb a bending load applied to the optical fibers  2 . 
     As shown in  FIG. 15 , the pitch fixing member  20  is inserted into the ferrule  10 , and also is fitted to an inner wall surface of the opening part  14 . A plurality of steps (two steps)  15  corresponding to a plurality of rows of insertion holes  11  of the optical fibers  2  are formed in the inner space S of the ferrule  10  located forward in a direction in which the optical fibers  2  are inserted from the pitch fixing member  20 . Tapered hole parts  11   a  that bring the bare parts  2   b  of the optical fibers  2  into the insertion holes  11  as described above are formed in each of the plurality of steps  15 . With this configuration, the optical fibers  2  can be smoothly inserted from the pitch fixing member  20  toward the ferrule  10 . The inner space S is filled with an adhesive (not shown). The adhesive is filled in the inner space S from a window part  13  formed in the ferrule  10 . The pitch fixing member  20  prevents the adhesive filled in the inner space S from leaking from the opening part  14 . 
       FIG. 16  is a perspective view of the pitch fixing member  20  according to a fourth embodiment.  FIG. 17  is a front view of the pitch fixing member  20  according to the fourth embodiment on a side of the outlet parts  21   b.    
     As shown in  FIGS. 16 and 17 , in the plurality of fixing parts  21  of the fourth embodiment, not only the plurality of groove parts  26  but also the top wall part  25  are formed by a plurality of V-shaped grooves  25   a.    
     As shown in  FIG. 16 , inlet parts  21   a  of the plurality of fixing parts  21  are formed in each of the plurality of steps  22  of the pitch fixing member  20 . The inlet part  21   a  is a V-shaped groove in which the lower half (groove part  26 ) of the fixing part  21  is extended to the step  22 . Furthermore, as shown in  FIG. 17 , the V-shaped groove  25   a  of the top wall part  25  has a shape in which the groove part  26  is turned upside down. Moreover, the V-shaped grooves  25   a  of the top wall part  25  have the same number and the same pitch as those of the groove parts  26 . 
     According to the fourth embodiment having the above configuration, in addition to the same effects as those of the third embodiment, since not only the groove parts  26  but also the top wall part  25  is formed by the plurality of V-shaped grooves  25   a , the coating part  2   a  of the optical fiber  2  is supported by the fixing part  21  at four points. In other words, the number of contact points of the fixing part  21  is increased to at least two in the upper half (top wall part  25 ) with respect to one optical fiber  2  (coating part  2   a ), and the optical fiber  2  can be stably supported in the fixing part  21  at a total of four points. Therefore, the pitch of the optical fibers  2  can be changed to the pitch of the insertion holes  11  of the ferrule  10  with high accuracy, and bending can be more reliably suppressed in the bare parts  2   b.    
     While a limited number of embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Additions, omissions, substitutions, and other modifications can be made without departing from the scope of the invention. Accordingly, the invention is not to be considered as being limited by the foregoing description and is only limited by the scope of the appended claims. 
     For example, in the first to third embodiments, a configuration in which the pitch fixing member  20  is mounted to the boot  30  and inserted into the ferrule  10  has been illustrated, but, as in the fourth embodiment, the pitch fixing member  20  alone may be inserted and mounted inside the ferrule  10 . 
     In addition, for example, in the fourth embodiment, the configuration in which the coating part  2   a  of the optical fiber  2  is supported by the fixing part  21  at four points by forming the V-shaped groove  25   a  in the top wall part  25  has been described, but for example, if the shape of the fixing part  21  (hole part) of the first embodiment (see  FIG. 6 ) is a diamond shape, the coating part  2   a  of the optical fiber  2  can be supported by the fixing part  21  (diamond-shaped hole part) at four points, similarly to the fourth embodiment. 
     REFERENCE NUMERALS LIST 
     
         
         
           
               1 : Optical connector 
               2 : Optical fiber 
               2   a : Coating part 
               2   b : Bare part 
               10 : Ferrule 
               11 : Insertion hole 
               20 : Pitch fixing member 
               21 : Fixing part 
               21   a : Inlet part 
               22 : Step 
               24 : Groove part 
               25 : Top wall part 
               25   a : V-shaped groove 
               26 : Groove part 
               30 : Boot 
               32 : Mounting part