Patent Publication Number: US-2023161126-A1

Title: Cable traction terminal structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from U.S. Provisional Patent Application No. 63/021100, filed May 7, 2020, and International Patent Application No. PCT/JP2021/015297, filed in Japan on Apr. 13, 2021, the contents of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Technical Field 
     The present invention relates to a cable traction terminal structure. 
     Description of Related Art 
     In recent years, with the development of optical communication technology using optical fibers, the number of optical fibers laid has increased dramatically. Therefore, when optical cables in which optical fibers are bundled are connected between data centers, in many cases, a cable traction terminal is used in order to route thousands of optical fibers at the same time. Various developments have been made on this cable traction terminal structure. For example, the cable traction terminal structure described in Patent Document 1 includes a flexible tube formed by helically connecting molded members having a substantially groove-shaped cross section to each other, a metal net body that covers the outer circumferential surface of the flexible tube, and a heat-shrinkable tube that covers the outer circumferential surface of the metal net body. This heat-shrinkable tube prevents water from entering the inner tube. 
     PATENT DOCUMENT 
     Patent Document 1: JP H 9-230186 
     Since the heat-shrinkable tube of Patent Document 1 has low extensibility (compressibility), wrinkles are formed on the inner diameter side of the heat-shrinkable tube when, for example, the cable traction terminal is bent. Then, when the cable traction end is routed, there is a possibility that water may enter the inner tube due to cracks on the outer circumferential surface of the heat-shrinkable tube, such as local friction and tearing against the wrinkles. 
     SUMMARY 
     A cable traction terminal structure according to one or more embodiments can prevent water from entering the inner tube. 
     According to one or more embodiments, there is provided an traction terminal structure comprising: an inner tube configured to house an optical cable inside and be formed by helically winding and connecting a strand; and a flexible outer tube provided on an outer circumferential surface of the inner tube, and a part of the outer tube enters an inside of a groove formed on the outer circumferential surface of the inner tube. 
     According to one or more embodiments, because a part of the outer tube enters the groove, the outer tube in the groove follows the bending of the inner tube even when a force for bending the inner tube is applied. As a result, it is possible to mitigate the occurrence of unevenness on the outer circumferential surface of the outer tube. Therefore, since cracks are less likely to occur on the outer circumferential surface of the inner tube, it is possible to prevent water from entering the inner tube. 
     A connecting member may be provided on the outer circumferential surface of a rear end of the inner tube. 
     A protrusion may be formed on an inner wall of the connecting member, and the protrusion may be fitted into the groove of the inner tube. 
     The connecting member may be overlapped with a rear end of the inner tube and may be overlapped with a rear end of the outer tube. 
     The connecting member may be adhered at least at an overlapping part overlapped with the rear end of the outer tube. 
     At the overlapping part, the connecting member may be formed with a recess portion at a position facing the outer tube, and an adhesive may be provided in the recess portion. 
     A gap may be provided between the outer tube and the connecting member in the longitudinal direction of the inner tube, and a water blocking member may be provided in the gap. 
     The water blocking member may be a resin material. 
     According to one or more embodiments, it is possible to prevent water from entering the inner tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view of a main part of an optical cable traction terminal structure according to one or more embodiments. 
         FIG.  2    is a cross-sectional view taken along the line II-II of  FIG.  1   . 
         FIG.  3    is a cross-sectional view of a main part of a rear end of the optical cable traction terminal structure according to one or more embodiments. 
         FIG.  4    is an exploded view of the rear end of the optical cable traction terminal structure according to one or more embodiments. 
         FIG.  5    is a cross-sectional view of a main part of an overlapping part between a connecting member and an inner tube. 
         FIG.  6    is a cross-sectional view of a main part of a modification example of the optical cable traction terminal structure according to one or more embodiments. 
         FIG.  7    is a cross-sectional view of a main part of an optical cable traction terminal structure according to one or more embodiments. 
         FIG.  8    is a view showing an inner tube which is not coated with an outer tube. 
         FIG.  9    is a view showing an inner tube coated with the outer tube. 
         FIG.  10    is a view showing a part of a tip end side of an optical cable traction terminal structure of one or more embodiments. 
         FIG.  11    is a view of an optical cable housed inside the optical cable traction terminal structure. 
     
    
    
     DETAILED DESCRIPTION 
     First Example 
     An optical cable traction terminal structure according to one or more embodiments will be described with reference to  FIGS.  1  to  6   . 
     As shown in  FIG.  1   , an optical cable traction terminal structure  1 A includes an inner tube  10 , an outer tube  20 , a cone-shaped head  30 , and a connecting member  40 . 
     Direction Definition 
     Here, in one or more embodiments, the longitudinal direction of the optical cable traction terminal structure  1 A is simply referred to as the longitudinal direction. The tip end side provided with the head  30  in the optical cable traction terminal structure  1 A may be referred to as a front end, and the base end side provided with the connecting member  40  in the optical cable traction terminal structure  1 A may be referred to as a rear end. Further, the direction intersecting a central axis O (refer to  FIG.  3   ) of the optical cable traction terminal structure  1 A is referred to as a radial direction. Further, a cross section orthogonal to the central axis O is referred to as a cross section. 
     As shown in  FIGS.  1  and  2   , the optical cable traction terminal structure  1 A of one or more embodiments further includes an optical cable  2 , a pair of tension members  3 , and a holder  4 . 
     The head  30  is provided on the tip end side of the optical cable traction terminal structure  1 A, and the connecting member  40  is provided on the base end side of the optical cable traction terminal structure  1 A. 
     The head  30  is a metal member and, as shown in  FIG.  1   , has a pulling eye  31  at the tip end. The head  30  is joined to the inner tube  10  by welding, for example. Further, the head  30  has an inclined portion  30   a.  The inclined portion  30   a  is configured such that the outer diameter gradually decreases from the base end toward the tip end. The pulling eye  31  is arranged at the tip end of the inclined portion  30   a.  By tying a rope or the like to the pulling eye  31 , the optical cable traction terminal structure  1 A is inserted into the inside of the duct pipe in the ground, and is likely to be hauled. 
     As shown in  FIG.  1   , the optical cable  2  is housed inside the inner tube  10 . In one or more embodiments, for example, 3456 optical fibers  5  are bundled, and a connector  6  is terminated in each optical fiber  5 . 
     As shown in  FIG.  2   , a pair of tension members  3  are provided so as to sandwich the optical cable  2  in the radial direction in a cross-sectional view (four in total). The tension member  3  functions as a member that receives a force such as tensile stress generated when the optical cable traction terminal structure  1 A is hauled. In one or more embodiments, the number of tension members is four, but the number is not limited thereto. 
     The holder  4  is made of a tubular metal having a through-hole  4   a  through which the optical cable  2  is inserted. The holder  4  is fixed to the inner tube  10  by bolts  7  via the connecting member  40 . 
     Further, the holder  4  has a tension member fixing portion (not shown) for fixing the tension member  3  on the inner circumferential surface of the through-hole  4   a.  By fixing the tension member  3  to the holder  4  in this manner, the force applied to the entire optical cable traction terminal structure  1 A can be reliably received, and the robustness can be improved. 
     As shown in  FIG.  3   , the inner tube  10  is configured as a tubular member (spiral tube) formed by helically winding a tape-shaped strand (for example, a stainless steel (SUS) plate)  10 A and connecting the strands in the longitudinal direction. For example, the strands  10 A are fitted by approximately ⅓ in the width direction and connected helically. With this configuration, the inner tube  10  has flexibility as a whole. Note that the optical cable  2  is not shown in  FIG.  3    in order to make the drawing easier to see. 
       FIG.  4    is an exploded view of the rear end of the optical cable traction terminal structure according to one or more embodiments. As shown in  FIG.  4   , on the outer circumferential surface of the strand  10 A, a groove  11  is formed in the central portion in the width direction along the longitudinal direction of the strand  10 A. The space between the grooves  11  adjacent to each other in the longitudinal direction is formed by a groove pitch P 1 . 
     In one or more embodiments, since the strands  10 A are fitted and connected helically, it is possible to maintain the inner diameter of the inner tube  10  even when tension is applied in the longitudinal direction. 
     As shown in  FIG.  3   , the outer tube  20  is provided on the outer circumferential surface of the inner tube  10  and has flexibility. A part of the outer tube  20  enters the inside of the groove  11  formed on the outer circumferential surface of the inner tube  10 . That is, the groove  11  is filled with a part of the outer tube  20 . Further, the outer tube  20  is not provided on the outer circumferential surface of a rear end  12  of the inner tube  10 . The material of the outer tube  20  is, for example, an elastic body such as polyvinyl chloride, a polyolefin resin, a fluoropolymer, and a thermoplastic elastomer. As a result, even when the inner tube  10  is bent, the restorability to the linear state is improved. 
     The method of allowing a part of the outer tube  20  to enter the groove  11  of the inner tube  10  is not particularly limited, but for example, by immersing the inner tube  10  in a liquid polyolefin resin, the polyolefin resin is inserted into the groove  11  of the inner tube  10 . Then, the liquid polyolefin resin is brought into close contact with the inner surface of the groove  11  and cured to have elastic force. 
     In the optical cable traction terminal structure  1 A of one or more embodiments, as shown in  FIG.  3   , the connecting member  40  is provided on the outer circumferential surface of the rear end  12  of the inner tube  10 . 
     As shown in  FIG.  4   , the connecting member  40  has a cylindrical shape. Inside the connecting member  40 , in order from the rear end  40 A side, an inner circumferential surface  41 , a first recess portion  42  recessed with respect to the inner circumferential surface  41 , and a second recess portion  43  recessed with respect to the first recess portion  42  are formed. The inner diameter of the first recess portion  42  and the inner diameter of the second recess portion  43  are larger in this order. 
     As shown in  FIGS.  4  and  5   , protrusions  45  are helically formed on the inner wall of the first recess portion  42  of the connecting member  40 . A protrusion pitch P 2  of the protrusion  45  is the same as the groove pitch P 1  of the groove  11 . The outer tube  20  is not provided on the outer circumferential surface of the rear end  12  of the inner tube  10 , and the protrusion  45  of the connecting member  40  and the groove  11  of the inner tube  10  are fitted to each other. That is, the connecting member  40  covers the outer circumferential surface of the rear end  12  of the inner tube  10 . As a result, as shown in  FIG.  3   , the rear end  12  of the inner tube  10  is housed in the first recess portion  42 . Therefore, the rear end  12  of the inner tube  10  is overlapped with the connecting member  40  in the radial direction. A first overlapping part  46  of the connecting member  40  and the inner tube  10  is adhered with an adhesive (not shown). 
     As shown in  FIG.  3   , the rear end  21  of the outer tube  20  is housed in the second recess portion  43 . That is, a front end  40 B of the connecting member  40  covers the outer circumferential surface of the rear end  21  of the outer tube  20 . The rear end  21  of the outer tube  20  is in contact with the second recess portion  43  without a gap, and is overlapped with the connecting member  40  in the radial direction. A second overlapping part  47  between the connecting member  40  and the outer tube  20  is adhered with an adhesive (not shown). 
     As described above, the optical cable traction terminal structure  1 A comprises: the inner tube  10  that can house the optical cable  2  inside and is formed by helically connecting the strand  10 A; and the flexible outer tube  20  provided on the outer circumferential surface of the inner tube  10 , and a part of the outer tube  20  enters the inside of the groove  11  formed on the outer circumferential surface of the inner tube  10 . With such a configuration, a part of the outer tube  20  penetrates (closely adheres) to the inner surface of the groove  11  of the inner tube  10 , such that the extensibility and the compressibility are improved. That is, even when the traction terminal structure  1  is bent, the positional relationship between the outer tube and the inner tube does not shift. Therefore, even when a bending force is applied to the inner tube  10 , the local bending stress applied to the outer tube  20  in the groove  11  disappears, and the outer tube  20  follows the bending of the inner tube  10 . As a result, the tensile stress on the outer circumferential surface of the outer tube  20  is mitigated. Then, for example, wrinkles do not occur on the outer surface of the outer tube  20  inside the bent cable, and it is possible to mitigate the unevenness generated on the outer surface. Then, a part of the outer skin is no longer locally subjected to the friction received when the optical cable traction terminal structure  1 A is inserted into and towed through the duct. Therefore, since cracks are less likely to occur on the outer circumferential surface of the inner tube  10 , it is possible to prevent water from entering the inner tube  10 . 
     Further, in the optical cable traction terminal structure  1 A of one or more embodiments, the connecting member  40  is provided on the outer circumferential surface of the rear end  12  of the inner tube  10 . With this configuration, it is possible to prevent the connector  6  from coming into contact with the connecting member  40  as compared with the configuration in which the connecting member is provided inside the inner tube, such that damage to the connector  6  can be suppressed. 
     Further, since the connecting member  40  is overlapped with the rear end  12  of the inner tube  10  and also overlapped with the rear end  21  of the outer tube  20 , the connecting member  40  is in surface contact with the rear end  12  of the inner tube  10  and the rear end  21  of the outer tube  20 . Accordingly, it is possible to maintain the strength of the adhesive. Furthermore, the connecting member  40  can more reliably prevent water from entering the inner tube  10  by the first overlapping part  46  and the second overlapping part  47 . 
     Although the outer tube  20  is adhered to the second recess portion  43  without a gap, there is a gap between the outer tube  20  and the second recess portion  43  of the connecting member  40 , and the gap may be filled with an adhesive. 
     Modification Example 
     As shown in  FIG.  6   , in an optical cable traction terminal structure  1 B of the modification example, an adhesive is provided on the second overlapping part  47 . That is, in one or more embodiments, the adhesive is provided on both the first overlapping part  46  of the connecting member  40  and the inner tube  10  and the second overlapping part  47  of the connecting member  40  and the outer tube  20 , but in the modification example, the adhesive is provided only on the second overlapping part  47 . 
     The connecting member  40  is formed with a recess portion  48  at a position facing the outer tube  20 . That is, the recess portion  48  is formed on a surface  40   a  that comes into contact with the outer tube  20 . The recess portion  48  is filled with an adhesive  49 . The front end  40 B of the connecting member  40  and the rear end  21  of the outer tube  20  are fixed by the adhesive  49 . 
     In the optical cable traction terminal structure  1 B, the adhesive  49  can fix the front end  40 B of the connecting member  40  and the rear end  21  of the outer tube  20  and prevent water from entering from the second overlapping part  47 . 
     Instead of the adhesive  49 , the front end  40 B of the connecting member  40  and the rear end  21  of the outer tube  20  may be fixed to the second overlapping part  47  by, for example, a retaining screw. 
     Second Example 
     Next, the second example will be described, but the basic configuration is the same as that of the first example. Therefore, the same configurations will be given the same reference numerals, a description thereof will be omitted, and only the different points will be described. 
     As shown in  FIG.  7   , an optical cable traction terminal structure  1 C of the second example is different from the first example in the arrangement of the outer tube  20  and the connecting member  40 . Further, in the optical cable traction terminal structure  1 C of  FIG.  7   , the optical cable traction terminal structure  1 A is simplified in order to make the drawings easier to be seen. 
     The second example is different from the first example in that the outer tube  20  and the connecting member  40  are arranged with spaces. That is, the rear end  21  of the outer tube  20  and the front end  40 B of the connecting member  40  are spaced apart in the longitudinal direction. 
     The reason for leaving a space between the rear end  21  of the outer tube  20  and the front end  40 B of the connecting member  40  is, for example, when fixing the connecting member  40  and the inner tube  10 , there is a case where the front end surface  40   b  of the connecting member  40  and the outer circumferential surface of the inner tube  10  are brazed. That is, in order to prevent the outer tube  20  from being melted by heat, it is necessary to leave a space between the rear end  21  of the outer tube  20  and the front end  40 B of the connecting member  40 . 
     A waterproof and flexible tape  50  is wound to cover the outer circumference of the rear end  21  of the outer tube  20  and the outer circumference of the front end  40 B of the connecting member  40 . 
     A gap  51  is formed by a rear end surface  21   a  of the outer tube  20 , a front end surface  40   b  of the connecting member  40 , the outer circumferential surface of the inner tube  10 , and the inner circumferential surface of the tape  50 . For example, a urethane gel (water blocking member: resin material)  52  is provided in the gap  51 . The size of the urethane gel  52  is larger than the size of the gap  51 , and the urethane gel  52  is arranged in the gap  51  in a compressed state. 
     In the optical cable traction terminal structure  1 C of one or more embodiments, the outer tube  20  and the connecting member  40  are arranged with spaces in the longitudinal direction of the inner tube  10 , and the urethane gel  52  is provided in the gap  51 . With such a configuration, it is possible to prevent water from entering the inner tube  10  by the urethane gel  52  while preventing the outer tube  20  from melting. 
     Further, by using a resin material (for example, urethane gel) as the water blocking member, even when the optical cable traction terminal structure  1 C is extended in the longitudinal direction by a traction force, the resin material follows the extension, such that water can be prevented from entering the inner tube  10 . 
     Third Example 
     Next, the third example will be described, but the basic configuration is the same as that of the first example. Therefore, the same configurations will be given the same reference numerals, a description thereof will be omitted, and only the different points will be described. 
     In the first example, the relationship between the elastic modulus of the inner tube  10  and the elastic modulus of the outer tube is not particularly limited, but in the optical cable traction terminal structure of the third example, the elastic modulus (Young&#39;s modulus) of the outer tube  20  is made of a material having a higher elastic modulus (Young&#39;s modulus) than that of the inner tube  10 . 
     With this configuration, the optical cable traction terminal structure may bend as a whole optical cable traction terminal structure due to the applied force, but when the force applied to the optical cable traction terminal structure is released, the shape thereof is restored to a linear shape. Further, since the material of the outer tube  20  is a polyolefin resin as in the first example, the material has elasticity in the longitudinal direction as well. With such a configuration, when the operator routes the optical cable traction terminal structure, a force is applied to the optical cable traction terminal structure to flex the inner tube  10  to the maximum curvature, and then when the force is released, the elastic force of the outer tube  20  acts in the direction of returning the curvature. Therefore, it is possible to return the bending of the outer tube  20 . As a result, workability is significantly improved. 
     Next, the elastic restoring force of the optical cable traction terminal structure will be specifically shown.  FIG.  8    is a view showing the inner tube  10  which is not coated with the outer tube  20 , and  FIG.  9    is a view showing the inner tube  10  coated with the outer tube  20 . 
     As shown in  FIG.  8   , it can be seen that the inner tube  10  which is not coated with the outer tube  20  maintains the curvature state because the restoring force for returning from the once bent state to the linear state does not occur. 
     On the other hand, as shown in  FIG.  9   , in the inner tube  10  coated with the outer tube  20 , it can be seen that the force of the once bent outer tube  20  to return to the linear state acts on the inner tube  10 .  FIG.  9    shows a state where the outer tube  20  is bent due to its own weight, but when the inner tube  10  coated with the outer tube  20  is routed in an actual duct pipe, the force to return to the substantially linear state acts. As a result, it is possible to obtain an optical cable traction terminal structure that is easy to bend when it is desired to be bent and can be easily returned to a linear state where the traction is easy when performing traction after bending. 
       FIG.  10    is a view showing a part of a tip end side of the optical cable traction terminal structure of one or more embodiments. As shown in  FIG.  10   , the outer tube  20  has a first part  25  to which an adhesive  20   a  is provided, and a second part  26  to which the adhesive  20   a  in not provided. The first part  25  is provided at the front end  22  of the outer tube  20 . By this first part  25 , the inner tube  10  and the outer tube  20  are in close contact with each other at least one circumference (the entire circumference in the circumferential direction) of the outer tube  20  in the longitudinal direction. 
     Further, at the rear end  21  of the outer tube  20 , similarly to the front end  22 , the outer tube  20  has a first part (not shown) to which an adhesive is provided, and a second part (not shown) to which an adhesive is not provided. Also at the rear end  21 , the inner tube  10  and the outer tube  20  are in close contact with each other by the first part. Accordingly, it is possible to prevent water from entering the inner tube  10  of the optical cable traction terminal structure. 
       FIG.  11    is a view of an optical cable housed inside the optical cable traction terminal structure. As shown in  FIG.  1   , there are provided a plurality of optical cables  2 . The plurality of optical cables  2  are covered with a transparent PVC (polyvinyl chloride) sheet  60 . The PVC sheet  60  is contracted to match the shape of a plurality of optical cables, and has, for example, a cut (perforation)  61  in the longitudinal direction thereof. The number of cuts  61  is two in parallel along the longitudinal direction. That is, after the optical cable traction terminal has been inserted into the duct pipe, the sheet  60  can be easily peeled off by the cut  61  when actually connecting to another optical fiber. In one or more embodiments, the number of cuts  61  is two in parallel along the longitudinal direction, but may be one or three or more. 
     The technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention, and the above-described embodiments and modification examples may be appropriately combined. 
     For example, the material of the inner tube  10  is stainless steel, but the material is not limited thereto. The material of the inner tube  10  may be made of plastic instead of metal. 
     Further, although the holder  4  is fixed to the inner tube  10  by the bolt  7  via the connecting member  40 , the holder  4  may be directly fixed to the inner tube  10 . 
     Further, in one or more embodiments, the inner tube  10  is configured such that the stainless steel plates are fitted by approximately ⅓ in the width direction and connected helically, but the inner tube  10  may not be fitted. In this case, it is possible to change the inner diameter of the inner tube  10 . 
     REFERENCE SIGNS LIST 
       1 A,  1 B, C: Optical cable traction terminal structure 
       2 : Optical cable 
       10 : Inner tube 
       11 : Groove 
       12 : Rear end of inner tube 
       20 : Outer tube 
       40 : Connecting member 
       45 : Protrusion 
       52 : Water blocking member