Abstract:
A method and apparatus are disclosed for retrieving a cable that has become stuck or wedged during the process of installation of the cable in an underground conduit. A projectile is sent down the opposite end of the conduit by pressurized air to engage a receiver attached to the leading edge of the stuck cable. After engagement of the projectile and the receiver the two are latched together. A retrieval line attached to the projectile can then be pulled from the open end of the conduit to free the wedged cable and extract the cable from the open end of the conduit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of Provisional Patent Application No. 60/369,427 Filed Apr. 1, 2002, for  Underground Cable Retrieval Tool.   
     
    
     
       BACKGROUND  
         [0002]    1. Field of Invention  
           [0003]    This invention relates to retrieval of a fiber optic cable that has become wedged during installation in a conduit.  
           [0004]    2. Prior Art  
           [0005]    Fiber optic cables have become a preferred transmission system for telecommunication and data communication. These cables are generally installed underground inside a conduit. The conduit is often laid in trenches and can extend a mile or more. The conduit generally has a smooth inside diameter throughout its length. Several methods exist for installing the fiber optic cable into the conduit.  
           [0006]    U.S. Pat. No. 4,836,503 (1989) to Giroux and U.S. Pat. No. 5,029,816 (1991) to Langston all relate to the installation of fiber optic cable in conduit. The methods described in these patents has to do with pulling the cable through the conduit. Intermediate devices are described in these patents so as to divide the required pull force into incremental quantities along the length of the conduit so as to not exceed the strength of the fiber optic cable. This requires excavation to access the conduit in the trench, splicing of the conduit, and the associated labor involved, at each intermediate station.  
           [0007]    Another method of installing the fiber optic cable in the conduit is using air pressure and air flow (sometimes referred to as air blown fiber (ABF)). A seal(s) is installed at the leading edge shuttle of the fiber optic cable. The shuttle provides a seal between the fiber optic cable and the inside diameter of the conduit. The shuttle is sometimes referred to as “bird” or a “parachute”. If the conduit is pressurized upstream of the shuttle, force is applied to the cable by the air pressure which causes the cable to move relative to the conduit, and hence, the cable is installed in the conduit.  
           [0008]    Yet another installation method is provided by an apparatus for grasping the fiber optic cable and pushing it into the conduit. This is sometimes referred to as “jetting”. This process is used in conjunction with the ABF process.  
           [0009]    Thus the cable is pushed into and pulled through the conduit. This combination of cable installation techniques is in favored use.  
           [0010]    One major concern, when using this push and pull method, is the remedy employed in the event that the shuttle and the trailing cable get wedged or stuck in the conduit. This can occur when there is too small a bend radius in the conduit, slightly deformed conduit, or just because the length of run is too long for the air blowing/ABF system. Radio transmitters have been designed to attach to the shuttle so that if the cable should get wedged or stuck in the conduit, the location of the shuttle can be determined by an appropriate signal locator. This remedy may be hampered by the location of adjacent utilities, such as gas, water, TV cable and electric wiring. The appropriate utility approvals must be obtained before any digging at the site can begin. Then, a trench must be opened, generally using a back hoe, to a depth of three to six feet. The conduit is then separated and the obstruction cleared. Sometimes the excavation site is then used to install an assist jetting machine and ABF to proceed with the installation of the fiber optic cable. The conduit is then repaired, and the trench back filled. Significant costs are associated with this remedy.  
         SUMMARY OF THE INVENTION  
         [0011]    Accordingly, it is the object of the present invention to provide a simple, cost effective way to retrieve a fiber optic cable that has become wedged or stuck in a conduit during the installation process. The advantages are:  
           [0012]    (a) no excavation of a trench is required to retrieve the stuck cable.  
           [0013]    (b) the exact location of the cable shuttle that is wedged or stuck is not required.  
           [0014]    (c) approval of the utilities is not required to open a trench.  
           [0015]    (d) the manpower to perform the retrieval is minimal.  
           [0016]    (e) heavy equipment for earth removal is not required.  
           [0017]    Still further objects and advantages will become apparent from a consideration of the ensuing description.  
           [0018]    In accordance with the present invention the retrieval method and mechanism comprises a projectile with an attached retrieval line, and a receiver attached to the shuttle of a fiber optic cable. If a shuttle becomes wedged in the conduit, the projectile is propelled by air pressure down the opposite end of the conduit and strikes the receiver. The projectile and receiver become latched together. Applying tension to the retrieval line serves to dislodge the shuttle and fiber optic cable from its wedged or stuck position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 shows a typical underground conduit and a cable partially installed.  
         [0020]    [0020]FIG. 2 shows a retrieval of a wedged cable in process.  
         [0021]    [0021]FIG. 3 shows orthogonal views of a projectile.  
         [0022]    [0022]FIG. 4 shows two views of a receiver.  
         [0023]    [0023]FIG. 5 shows a detailed cross-section of a receiver and an approaching projectile.  
         [0024]    [0024]FIG. 6 shows a detailed cross-section of a receiver and a captured projectile.  
         [0025]    [0025]FIG. 7 shows a means for unlatching the projectile form the receiver.  
         [0026]    [0026]FIG. 8 shows views of a receiver and an approaching projectile in a conduit.  
         [0027]    [0027]FIG. 9 shows a receiver and a connected projectile. 
     
    
     REFERENCE NUMBERS IN DRAWINGS  
       [0028]    [0028] 10  underground cable installation  
         [0029]    [0029] 12  cable  
         [0030]    [0030] 14  entrance manhole  
         [0031]    [0031] 16  conduit  
         [0032]    [0032] 18  jetting and air blowing mech.  
         [0033]    [0033] 20  cable reel  
         [0034]    [0034] 22  leading edge shuttle  
         [0035]    [0035] 24  exit manhole  
         [0036]    [0036] 26  air blowing apparatus  
         [0037]    [0037] 28  projectile  
         [0038]    [0038] 30  retrieval line  
         [0039]    [0039] 32  temporary inlet tube  
         [0040]    [0040] 50  body  
         [0041]    [0041] 52  large cylinder  
         [0042]    [0042] 54  small cylinder  
         [0043]    [0043] 56  threaded hole  
         [0044]    [0044] 58  dome  
         [0045]    [0045] 60  lug  
         [0046]    [0046] 62  pin  
         [0047]    [0047] 64  spring  
         [0048]    [0048] 80  receiver  
         [0049]    [0049] 82  main body  
         [0050]    [0050] 84  threaded hole  
         [0051]    [0051] 86  aperture  
         [0052]    [0052] 88  threaded portion  
         [0053]    [0053] 90  end cap  
         [0054]    [0054] 92  aperture  
         [0055]    [0055] 94  flange  
         [0056]    [0056] 96  chamfer  
         [0057]    [0057] 100  retrieval shuttle  
         [0058]    [0058] 102  seal  
         [0059]    [0059] 104  large seal support  
         [0060]    [0060] 106  small seal support  
         [0061]    [0061] 108  spacer  
         [0062]    [0062] 110  nut  
         [0063]    [0063] 112  eye bolt  
         [0064]    [0064] 114  attachment  
         [0065]    [0065] 116  eye bolt  
         [0066]    [0066] 120  tube  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0067]    [0067]FIG. 1 shows an underground cable installation  10  where a cable  12  is partially installed through a manhole  14  or other similar underground entrance. Cable  12  is fed through conduit  16  propelled by a combination jetting and air blowing mechanism  18 . Cable  12  is typically stored on and fed from cable reel  20 . Cable  12  can be a sheathed collection of fiber optic strands, or electric wires, or the like. At the leading edge of cable  12  is leading edge shuttle  22 . Conduit  16  spans from entrance manhole  14  to exit manhole  24 .  
         [0068]    In FIG. 2, shuttle  22  has become stuck or wedged in an intermediate position between entrance manhole  14  and exit manhole  24 . Air blowing apparatus  26  is temporarily provided at exit manhole  24  to propel projectile  28  through conduit  16 , in route to receiver  22 . Retrieval line  30  is attached to projectile  28  and may pass through a temporary inlet tube  32  that is provided to properly direct air flow into the end of conduit  16 . This air flow propels projectile  28  and retrieval line  30  toward receiver  22 . A reel  34  may be provided to store the unused portion of retrieval line  30 . Retrieval line  30  can be any type wire cable or rope suitable for pulling the wedged shuttle  22  and cable  12  through their obstruction and out the exit manhole  24 .  
         [0069]    In FIG. 3 projectile  28  is shown in three views. Body  50  consists a large cylinder  52  and a small cylinder  54 . Centrally located in the end of large cylinder  52  is threaded hole  56 . On the opposite end of body  50 , spherical dome  58  projects from small cylinder  54 . Two lugs  60  are installed in slots provided in small cylinder  54  and rotatably held by pins  62 . Lugs  60  protrude beyond the diameter of small cylinder  54  and are urged into this position by spring  64 . Lugs  60  are so designed to cooperate with the slots in small cylinder  54  so that, when urged against the force of spring  64 , lugs  60  can be recessed with the confines of small cylinder  54 .  
         [0070]    In FIG. 4, the two pieces of the receiver  80  are shown. Main body  82  contains a threaded hole  84  on one end. The other end has an aperture  86  of sufficient diameter to house small cylinder  54  (FIG. 3) with lugs  58  expanded. This end is also provided with an externally threaded portion  88  to accept a cooperating threaded portion of end cap  90 . End cap  90  has an aperture  92  sufficient to allow passage of small cylinder  54  with lugs  60  retracted (FIG. 3). Aperture  92  forms the inside diameter of flange  94 . A chamfer  96  is provided opposite the flange  94 .  
         [0071]    [0071]FIG. 5 shows projectile  28  approaching receiver  80 . Dome  58  and chamfer  96  cooperate to promote entry of projectile  28  into receiver  80 . As lugs  60  pass through aperture  92  spring  64  is compressed and lugs  60  retract into small cylinder  54 . Projectile  28  is fully engaged in receiver  80  in FIG. 6. Expanded lugs  60  now engage flange  94  and projectile  28  and receiver  80  are latched together.  
         [0072]    [0072]FIG. 7 shows end cap  90  unthreaded and removed from main body  82 , but with lugs  60  still latched to end cap  90 . Tube  120  can be inserted in the end of end cap  90  which will depress lugs  60  into small cylinder  54  of projectile  28 . This unlatches and allows removal of projectile  28  from end cap  90 .  
         [0073]    In FIG. 8, retrieval shuttle  100  is approaching leading edge shuttle  22  that has become wedged in conduit  16 . Shuttle  22  consists of flexible seals  102 , large seal supports  104 , small seal supports  106 , spacer  108 , nut  110 , and eye bolt  112 . Eye bolt  112  is threaded into receiver  80  and nut  110  secures the components of shuttle  22  in a proper relationship to receiver  80 .  
         [0074]    Flexible seals  102  and seal supports  104  and  106  are designed to provide an adequate sealed resistance to air pressure when applied from one direction in conduit  16 , but flex and allow air passage between the seals  102  and conduit  16  when air pressure is applied from the opposite direction. Seals  102  are spaced sufficiently apart to assure that receiver  80  is appropriately centered in conduit  80 .  
         [0075]    Attachment member  114  attaches cable  12  (not shown) to eyebolt  112 .  
         [0076]    Retrieval shuttle  100  is a mirror image of leading edge shuttle  22  and is attached to projectile  28 . Retrieval line  30  is attached to eyebolt  116 .  
         [0077]    [0077]FIG. 9 shows projectile  28  engaged and latched to receiver  80 .  
         [0078]    Operation:  
         [0079]    If, during installation of cable  12 , installation shuttle  22  and receiver  80  become wedged or stuck in conduit  16 , a temporary retrieval system is set up at the nearest downstream access, such as manhole  24 . Projectile  28  attached to shuttle  100  attached to retrieval line  30  is blown by air pressure through the opposite end of conduit  16  until projectile  28  impacts and becomes latched to receiver  80 . Then, by pulling on retrieval line  30 , force is exerted on the wedged shuttle  22  through retrieval line  30 , shuttle  100  and the latched combination of projectile  28  and receiver  80 . Once the wedge is cleared, shuttle  22  can be drawn to the exit manhole  24 , and, if desired, the cable can again be jetted and air blown at entrance manhole  14  or exit manhole  24  toward the next destination.  
         [0080]    Once the cable  12  has been retrieved, the projectile  28  and receiver  80  can be unlatched by unthreading end cap  90  from main body  82 . This will expose lugs  60  of projectile  28  which can then be retracted inserting tube  120  (FIG. 7), allowing the projectile  28  to be withdrawn from end cap  90 . End cap  90  can then be re-installed on main body  82  which makes the cable  12  ready for installation in the next span of conduit.  
         [0081]    It is worthy of note that the positions of projectile  28  and receiver  80  can be exchanged and the system will still function properly.  
         [0082]    Conclusion:  
         [0083]    The retrieval mechanism and method herein described is an effective alternative to existing methods of retrieval of a cable wedged or stuck in a conduit. It is extremely cost effective and simple to use and minimal manpower is required. It avoids having to know the exact location of the wedged cable shuttle. It avoids having to excavate the area where the wedged cable shuttle has been located. It avoids having to consult public utilities to identify any endangered systems near the excavation site and the associated length of time required to make that identity. It avoids having an idle crew while all of these processes take place. It avoids any necessity for the use of heavy earth removal equipment. It avoids having to part the conduit to relieve the interference and the subsequent repair of the parted conduit.  
         [0084]    It will be appreciated that while particular embodiments of the invention have been shown and described, modifications may be made. For example, other methods of latching the projectile to the receiver can be made. It is intended in the claims to cover all modification which come within the true spirit and scope of the invention.