Abstract:
The present invention is an apparatus and method for removing a portion of a cable sheath. First and second opposing blades are adjustable to a cutting depth using adjustment screws and continuity testers that signal contact between each blade and a metallic sub-sheath. The blades are inclined at an angle to a transverse plane of the cable, and are contoured to conform to the sheath radius. A guide including neoprene rollers keeps the cutting assembly aligned on the cable. The cutting assembly is drawn along the cable, removing the sheath.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to the repair of optical fiber cables having a polyethylene or other protective sheath. More particularly, the present invention is an apparatus and method for removing a portion of the poly sheath at a point on the cable remote from the ends. 
   BACKGROUND OF THE INVENTION 
   In the installation and maintenance of transmission cable such as fiber optic cable, the removal of poly sheathing frequently presents difficulties in safeguarding the delicate transmission fibers contained within the sheath. The problem is especially precarious during optical fiber cable work when there is working service on the fiber cable. In such situations, the cable sheath frequently must be removed at a location distant from the ends of the cable (“mid-sheath”), making the task even more difficult. The industry standard approach to that problem is presently for the OSP technician to use hand-held cutting knives to remove the polyethylene and steel membranes from around the fiber cable. In performing that task, the OSP technician could slip and cut the cable, in which case service would be lost during the process. A tool is needed that would allow the polyethylene and steel sheaths to be removed without the danger of damaging the fiber cable. 
   Small hand tools further present danger to the OSP technician, who is exposed to the sharp blades of the hand knives as they are forced through the sheath and along the cable. A device is needed that would safely remove the poly sheath. 
   Several specialized tools have been proposed for removing cable sheathing. U.S. Pat. No. 5,533,264 to Wheary, issued Jul. 9, 1996 and incorporated herein by reference in its entirety, describes an apparatus for removing metallic or non-metallic cable sheathing using a single sharpened wheel cutting element attached to a chain that is rolled around the cable to make a circular cut. The apparatus may include a continuity measurement circuit for measuring continuity between the cutting element and a shield layer of the cable. 
   U.S. Pat. No. 6,581,291 to Tarpill et al., issued Jun. 24, 2003 and incorporated herein by reference in its entirety, describes a cable stripping tool that longitudinally slits the cable sheath using a blade that is adjustable using an adjustment screw. The sheath must be removed after slitting using conventional methods. 
   U.S. Pat. No. 6,044,744 to Eslambolchi et al., issued Apr. 4, 2000 and incorporated herein by reference in its entirety, describes a fiber optic cable sheath removal tool that uses an electrically driven cutting wheel to make circumferential and longitudinal cuts in the cable sheath. Depth of cut is adjusted using an adjusting mechanism that displaces cable guides toward or away from the cutting wheel. The tool is used to make cuts in both directions before the sheath is removed. 
   Each of the above-described tools cuts the cable sheath but does not remove the sheath during the cutting step. The sheath must be subsequently removed using an additional step with the tool or with hand tools. 
   There is therefore presently a need for a method and apparatus for removing a section of fiber optic cable sheath at a mid-sheath location on a cable in a quick and efficient manner, without damaging the fibers within the cable and without endangering the OSP technician. To the inventors&#39; knowledge, there is currently no such apparatus or method employed to satisfactorily accomplish that task. 
   SUMMARY OF THE INVENTION 
   The present invention addresses the needs described above by providing a an apparatus and a method for removing a sheath on an optical fiber cable. In one embodiment, an apparatus includes a body having a central hole, the body being split for positioning around the cable. First and second opposed cutting blades have cutting edges protruding from the body into the central hole. The cutting edges face the cable, and the blades are positioned at a cutting angle to a transverse plane of the cable. The apparatus also includes first and second adjusting screws that are rotatably mounted in the body for urging the first and second cutting blades toward said cable. First and second continuity test circuits are provided for testing electrical continuity between a metallic sub-sheath of the cable and corresponding ones of the first and second cutting blades. Finally, a cable stabilizer bushing is included for contacting and aligning the body. The bushing has a central hole for accepting the cable, and has a plurality of elastomeric rollers extending into the hole for rolling on the cable. The bushing is split for positioning around the cable. 
   The cutting edges of the cutting blades may be elliptical. The apparatus may further include a locking clasp for locking the body on the cable. The cable stabilizer bushing may further include first and second locking clasps for locking the bushing on the cable. 
   The apparatus may also comprise a jumper wire for connecting the continuity circuits to the metallic sub-sheath of the cable. The continuity circuits each may include a battery, an indicator light and a continuity lug for connecting a jumper wire. The indicator light may be a green LED. 
   The apparatus may include first and second blade retainers slideably mounted in the housing and contacting corresponding adjusting screws. Those blade retainers have blade stops for backing up the cutting blades. The first and second blade supports may further comprise magnets proximate the blades for retaining the blades during removal and insertion of the blades to the body. 
   In another embodiment of the invention, a method is provided for removing a sheath at a mid-sheath point on an optical fiber cable. The method includes the step of clamping a cutter body around the cable. A first adjustment screw is turned to advance a first cutting blade into the sheath until a first continuity circuit indicates that there is electrical continuity between the first cutting blade and a metallic sub-sheath of the cable. A second adjustment screw is then turned to advance a second cutting blade opposing the first cutting blade into the sheath until a second continuity circuit indicates that there is electrical continuity between the second cutting blade and the metallic sub-sheath. The cutter body is then advanced in a longitudinal direction along the cable, whereby the first and second cutting blades remove portions of the sheath. 
   The method may also include the steps of clamping a cable stabilization bushing around the cable, and maintaining alignment of the cutter body by contacting the body with the cable stabilization bushing. 
   In another aspect of the invention, the method may also include the steps of assembling the first and second cutting blades on magnetized blade supports, and inserting the blade supports into the housing. 
   Another embodiment of the invention is an apparatus for removing a sheath on a cable. The apparatus includes a body having a central hole, and a plurality of opposed cutting blades having cutting edges protruding from the body into the central hole. The cutting edges face the cable, with the blades being positioned at cutting angles to a transverse plane of the cable. The apparatus also includes a plurality of adjusting screws rotatably mounted in the body for urging corresponding ones of the cutting blades toward said cable. At least one continuity test circuit is included for testing electrical continuity between a metallic sub-sheath of the cable and the cutting blades. 
   The apparatus may include a cable stabilizer bushing for contacting and aligning the body. The bushing has a central hole for accepting the cable. The bushing may have a plurality of elastomeric rollers extending into the hole for rolling on the cable. The bushing may further be split for positioning around the cable. 
   A jumper wire may be included for connecting the at least one continuity circuit to the metallic sub-sheath of the cable. The continuity circuits may include a battery, an indicator light and a continuity lug for connecting a jumper wire. 
   The apparatus may include a locking clasp for locking the body on the cable. The cutting edges of the cutting blades may be elliptical. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation view of an apparatus for removing a cable sheath according to one embodiment of the invention. 
       FIG. 2  is a side view of an adjusting screw and blade restrainer according to one embodiment of the invention. 
       FIG. 3  is a another side view of an adjusting screw and blade restrainer according to one embodiment of the invention. 
       FIG. 4  is a plan view of a cutting blade according to one embodiment of the invention. 
       FIG. 5  is a front elevation view of an apparatus for removing a cable sheath according to one embodiment of the invention. 
       FIG. 6  is a rear elevation view of an apparatus for removing cable sheath according to one embodiment of the invention. 
   

   DESCRIPTION OF THE INVENTION 
   An apparatus  100  according to the present invention is shown in  FIG. 1 . The apparatus is for removing polyethylene sheath from a cable  50  in a region between the ends of the cable. The apparatus is generally in the form of a draw knife that can be locked around the fiber cable. The poly sheath is then peeled as the unit is pulled along the cable  50 . 
   A dual handle assembly includes a cutter body  104  and two handles  105 ,  106  for grasping during the cutting stage of the sheath removal process. The cutter body  104  has a central bore  108  for receiving the cable  50  as described below. Disposed within the cutter body  104  are two blade adjustment/retention assemblies  155 ,  165  for holding the cutting blades  150 ,  160  in position for cutting and removing the sheath covering cable  50 . The blades  150 ,  160  protrude into the central bore  108 . While the apparatus of the invention will be described herein as comprising two blades and two adjustment/retention assemblies, the assembly may comprise three or more blades and still remain with the scope of the invention. 
   The blade adjustment/retention assemblies  155 ,  165  are mounted in threaded bores in the cutter body  104 . The blades  150 ,  160  are retained and adjusted using the adjustment/retention assemblies as described below. Those assemblies  155 ,  165  and the blades  150 ,  160  are positioned to form a cutting angle  185  between an axis  186  of the assemblies and a plane  180  that is transverse to a longitudinal axis  51  of the cable  50 . In a preferred embodiment, the cutting angle is about 45 degrees. 
   The apparatus  100  also includes a cable stabilizer bushing  110  having a central bore  112  for surrounding the cable  50 . Elastomeric guides  114 ,  115  such as rollers constructed of a neoprene composition are mounted in the bushing  110  for guiding the bushing on the cable. The guides  114 ,  115  are compressed between the cable  50  and the bushing  110  as the cable is inserted into the bushing, guiding and orienting the bushing on the cable without damaging the cable. In one embodiment, the guides are neoprene O-rings. In another embodiment, the guides are neoprene cylindrical members that roll on the cable. In use, the guides may be lubricated with a light oil or gel to facilitate travel of the bushing on the cable. 
   The bushing  110  is further provided with a cutter body guide surface  118  on an axial end of the bushing. The cutter body guide surface  188  abuts a corresponding guide surface  119  on the cutter body  104  to position and align the cutter body as it is drawn along the cable  50 . The guide surfaces  118 ,  119  may be flat surfaces or may be mating conical or toroidal surfaces. 
   Most commercially available fiber optic cable  50  includes a metallic strength member underlying the poly sheath. In a preferred embodiment of the invention, the sheath removal apparatus  100  is provided with at least one electrical continuity circuit for determining whether the blades  150 ,  160  have cut through the sheath and are in contact with the metallic strength member. 
   In the embodiment shown in  FIG. 1 , two continuity circuits are shown, one for each blade. Each circuit includes a battery  156 ,  166  for providing power to the circuit. The battery may be a standard 9 volt battery. One terminal of the battery is connected to a terminal of an indicator light  157 ,  167  such as a green LED for showing a technician that a continuous circuit has been completed. The other terminal of the indicator light is wired to a connecting lug  158 ,  168 . The other terminal of the batteries  156 ,  166  is electrically connected to the blades  150 ,  160 , preferably through the adjustment/retention assemblies  155 ,  165 . 
   To use the continuity circuits, a small window  55  is cut in the sheath of the cable  50  to expose the underlying metallic strength member (the “sub-sheath”) at an edge of the proposed sheath removal zone. A wire  160  is connected from the metallic sheath in the window  55  to the lugs  158 ,  168  of the continuity circuits. The indicator light is illuminated when the blades  150 ,  160  are extended sufficiently through the sheath to be set against the underlying metallic strength member. The continuity circuits may be used separately, first connecting the first blade  150  to the metallic strength member and extending that blade through the sheath, then connecting the second blade  160  and extending that blade through the sheath. Alternatively, both blades may be connected simultaneously and advanced together. 
   An adjustment/retention assembly  155  according to one embodiment of the invention is shown in  FIGS. 2 and 3 . The assembly includes a depth adjustment screw  215  having a knurled knob  210  for grasping and turning by the operator. The adjustment screw  215  has a threaded portion  220  for engagement with the mating female threads in the body. Rotation of the knob  210  causes the assembly  155  to advance in the body. 
   The adjustment/retention assembly  155  also includes a blade retainer  230  and shaft  228 . Those components preferably comprise a single element. The shaft  228  and adjustment screw  215  interface at a swivel point  225 , whereby the screw is permitted to turn while the shaft does not rotate. The adjustment screw  215  urges the blade retainer  230  and shaft  228  forward as the adjustment screw is advanced. The swivel point  225  may also have attachment means (not shown) for pulling the adjustment/retention assembly  155  out of the body  104  for blade replacement. 
   The blade retainer  230  includes a magnetic plate  235  embedded in the retainer. The magnetic plate holds a blade in place as the blade retainer is inserted into the body  104  ( FIG. 1 ). Blade retainer posts  240  are also provided on the blade retainer for precisely establishing a location of the blade and for providing fixed elements to back up the blade as it is advanced into the sheath. 
   A cutting blade  150  according to the invention is shown in  FIG. 4 . The blade includes slots  215 ,  216  for accepting the posts  240 . The posts and slots align the blade on the retainer  230 . The blade also includes a U-shaped razor cutting edge  250  for cutting the sheath. The cutting edge is shaped to conform to the shape of the sheath. In a preferred embodiment in which the cutting angle  185  is about 45 degrees, the cutting edge  250  has a shape tracing a 45 degree ellipse. 
   A blade may be replaced using the adjustment/retention assembly  155  by first backing out the adjustment screw and removing the blade retainer  230  from the body  104 . The blade will be drawn out of the body together with the blade retainer by the magnet  235 . The old blade is replaced with a new blade, which is retained by the magnet as it is inserted with the retainer into the body. The blade restrainer posts  240  assure that the new blade is aligned in the body. 
   The apparatus  100  of  FIG. 1  is shown in front view in  FIG. 5  to illustrate the two-piece construction of the body  104 . Similar elements are shown using similar element numbers. 
   In a preferred embodiment, the body  104  comprises a first body half  516  and a second body half  517  that fit around the fiber cable and may be locked around it. The assembly is hinged at hinge  518  to allow the two halves  516 ,  517  to be opened and the fiber cable to be placed inside the central hole  108  ( FIG. 1 ) of the apparatus. A locking clasp  519  is provided on a side of the body  104  opposite the hinge  518  for maintaining the body halves in a closed position around the cable. 
   Similarly, the cable stabilizer bushing  110  is split into first and second halves for assembly over the cable and removal from the cable. The bushing may have two locking clasps  541 ,  542  as shown. Alternatively, the bushing may be hinged in a manner similar to that shown for the body  104 . 
   Exit ports  545 ,  546  are provided in the body  104  proximate the cutting blades  150 ,  160  to provide an exit path for sheath shavings as they are cut from the cable. The exit ports are shaped to provide an unobstructed path with smooth transitions for the shavings. 
   The blade adjustment/retention assemblies  155 ,  165  are shown protruding from the body  104  in a rear view of the apparatus shown in  FIG. 6 . The adjustment knobs  210 ,  211  are accessible at the rear of the cutter body  104  for adjustment by the technician. The adjustment/retention assemblies  155 ,  165  enter the body  104  through slots  610 ,  621  to allow assembly of the blades and blade retainers from the rear of the body. 
   The apparatus of the invention is used in a preferred application to remove the polyethylene sheath from around the fiber cable  50  during restoration and planned cable intrusions. In those applications, the sheath must frequently be removed at points distant from the ends of the cable; i.e., “mid-sheath.” To use the apparatus  100 , a proposed sheath removal zone is first selected. A small window  55  ( FIG. 1 ) of the polyethylene is removed from the underlying metallic strength member at the edge of the proposed removal zone, and a continuity wire  160  is attached. 
   The cutter body  104  is then opened and the two halves  516 ,  517  are assembled over the cable near the window  55  and clamped using the locking clasp  519 . Similarly, the two halves of the cable stabilizer bushing  110  are assembled over the cable and clamped together using clasps  541 ,  542 , compressing the elastomeric guides  114 ,  115 . The cutting body  104  is then moved along the cable to contact the stabilizer  110  so that the stabilizing surfaces  118 ,  119  are aligned. 
   The continuity wire  160  is then connected to the first continuity circuit lug  158 . The depth adjustment knob  210  is turned, advancing the first blade  150  into the poly sheath. When the blade  150  has passed through the sheath and has contacted the underlying metallic strength member, the continuity circuit is closed and indicator light  157  is illuminated by the battery  156 . The technician then stops advancing the blade  150 , and may back it out slightly. 
   The continuity wire is then connected to the second lug  168  and the process is repeated for the second blade  160 , again advancing it through the poly sheath into contact with the underlying metallic strength member. 
   After the blades are set against the fiber cable and are penetrating the sheath, the device is pulled in the direction that the blade cutting edges  250  face along the cable. The polyethylene sheath is stripped away from the fiber cable, and the shavings exit through the debris exit ports  545 ,  546 . Once the poly has been removed, the metallic part of the fiber cable may be cut away using hand tools. That allows access to the fibers housed in the fiber cable for restoration, splicing, etc. 
   The foregoing Detailed Description is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the Detailed Description, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. For example, while the method of the invention is described herein with respect to fiber optic cable, the method and apparatus of the invention may be used with any cable containing delicate conveyances and having a plastic or other soft sheath. Further, while the cutter body described herein has two opposing blades, any number of opposing blades, together with associated adjustment/retention assemblies, may be installed in the body. It is to be understood that the embodiments shown and described herein are only illustrative of the principles of the present invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention.