Abstract:
A composite cable for conducting electrical and optical signals is disclosed. The composite cable comprises a cable housing having a ribbon slot with an optical fiber ribbon arranged in the ribbon slot. The cable housing also has a tubular opening with a multiplicity of copper pairs arranged therein for conducting electric power through the oval slotted composite copper pair and optic ribbon cable, for providing strength to the cable, and for bending without elastic recovery to shape the cable. The composite cable may also include a removable compression cap for covering the ribbon slot.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to cables that provide both optical and electric signals in the same cable. 
     2. Discussion of Related Art 
     Composite cables having copper pairs for conducting electricity and optical fibers for conducting light are known in the art. 
     FIG. 1 shows one such prior art composite cable generally indicated as  10 , having an oversheath  12  wrapped around a fiber cable generally indicated as  20  and a copper cable generally indicated as  40 . The oversheath  12  has ripcords  14 . The fiber cable  20  has a jacket  22 , a ripcord  24 , flexline  26 , a buffer tube  28 , optical fiber  30  and filling compound  32 . The copper cable  40  has a jacket  42 , polyethylene  44 , tape  46 , and copper pairs generally indicated as  48 . 
     U.S. Pat. Nos. 5,050,960 and 5,082,380 show and describe an optical fiber cable construction having a non-electrically conductive rigid rod or core made of glass reinforced resin by a pultrusion or similar process, a binder, and an extruded sheath. The non-electrically conductive rigid rod or core has a fiber slot, a fiber arranged therein, and a cap for the fiber slot. The slot has convexly radiused edges, and the cap has concavely radiused edges for mating with the convexly radiused edges of the cap. 
     U.S. Pat. No. 4,110,001 shows and describes an optical fiber cable construction having a plastic core, a central steel strength member arranged therein, a core wrap surrounding the plastic core, metal tape around the core wrap, steel armor around the metal tape, and an outer jacket around the steel armor. The plastic core has a fiber channel for receiving optical fiber, and a copper pair channel for receiving copper pairs. 
     Some shortcomings of the prior art composite cable include: (1) the stranded fiber optic cable in FIG. 1 is large and requires additional material; (2) the cables do not optimize requirements of a fiber optic cable material versus the typical concerns of shrinkage at cold temperatures in a range of −40 to −50 degrees Celsius; (3) the steel central strength member or the pultruded glass reinforced plastic (GRP) strength member in the prior art cables is not capable of being shaped by bending without elastic recovery; and (4) when bent beyond elastic recovery, the steel central strength member buckles, and the pultruded strength member fractures or breaks, resulting in the steel being kinked or the GRP no longer being effective as a strength member. Failure to meet the restrictions on shrinkage results in attenuation of the signal carried by the optical fibers. 
     SUMMARY OF THE INVENTION 
     The present invention provides a composite cable for providing electrical and optical signals, having a cable housing, one or more optical fibers, and malleable conductive copper pairs. The cable housing has a fiber ribbon slot and a tubular opening therein. The one or more optical fibers are arranged in the fiber ribbon slot, for providing the optical signals through the composite cable. The malleable conductive copper pairs are arranged in the tubular opening and provide the electrical signals through the composite cable, provide central strength to the composite cable, and permit bending without elastic recovery to shape the composite cable. 
     The composite cable may have a removable compression cap for covering the ribbon slot. The compression cap and the cable housing together define a generally oval exterior surface when the compression cap is assembled on the cable housing. The cable housing and the compression cap are dimensioned so as to provide a pry slot for receiving a screwdriver for prying the compression cap free of the cable housing. The pry slot is defined by a cable housing-surface and a cap-surface, the cable housing-surface and the cap-surface being opposed to each other and separated by a distance sufficient to permit the blade of a screwdriver to fit therebetween when the compression cap is assembled on the cable housing. 
     One important advantage of the present invention is that it provides a very versatile cable that is easily accessed, less costly to manufacture, and more easily handled and installed because it is smaller and lighter than composite cables known in the prior art. The groups of copper pairs also are more elastic and do not buckle, kink, fracture or break when subjected to typical bending demands during installation or reentry and installation of the composite cable, and allow the cable to be wrapped in a small coil and stay coiled (i.e. not elastically spring back and straighten out). 
     Moreover, the present invention results in a reduction in material and more compact composite cable when compared with other composite cable designs. The use of copper pairs as a central strength member replacing glass reinforced or steel rods reduces the overall amount of plastics required, in turn reducing the resulting shrinkage forces of plastics at cold temperatures. The use of copper pairs provides the desired tensile strength for the composite cable. The copper pairs may be used for transmitting data, voice or power. 
     Moreover still, the oval shape of the composite cable generates rotation during crush load, resulting in the copper pairs that are tightly packed to absorb the crush load, while loosely packed optical fiber or fiber ribbon are not subject to crush load. The copper pairs have less elastic recovery than the glass reinforced or steel rods, thus allowing the composite cable to be routed or fitted to a contour shape best utilizing available space, which reduces the amount of composite cable used during installation and the cost for installing the same. 
     Other objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description read in conjunction with the attached drawings and claims appended hereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, not drawn to scale, in which: 
     FIG. 1 is a diagram of a cross sectional view of a prior art composite cable. 
     FIG. 2 is a diagram of a cross sectional view of a composite cable according to the present invention. 
     FIG. 3 is a diagram of a cross sectional view of the compression cap showing the removable cap separated from the cable housing. 
     FIG. 4 is a diagram of a partial cross sectional view of a portion of the cable housing and compression cap showing the pry slot for prying the compression cap free of the cable housing. 
     FIG. 5 is a diagram of a cross sectional view of another embodiment of a composite cable according to the present invention. 
     FIG. 6 is an Excel spreadsheet of a design for a composite cable using the present invention that meets a cable contraction requirement in a temperature range of 23 to −40 degrees Celsius. 
     FIG. 7 is a sketch of a cross sectional view of another embodiment of a composite cable according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The Composite Cable  100   
     FIG. 2 shows a composite cable  100  of the present invention that has a cable housing  102  having a ribbon slot  104  with optical ribbons  106  arranged therein, and having a tubular opening  108  with malleable conductive copper pairs generally indicated as  110  arranged in the tubular opening  108 . The optical ribbons  106  are stacked in the ribbon slot  104  and provide an optical signal through the composite cable  100 . The malleable conductive copper pairs  110  provide the electrical signals through the composite cable, provide central strength to the composite cable, and bend without elastic recovery to shape the composite cable  100 . 
     The composite cable  100  also has a removable compression cap  112  for removably covering the ribbon slot  104 . The optical ribbons  106  have optical fibers generally indicated as  114 . The ribbon slot  104  is generally rectangular, although the scope of the invention is not intended to be limited to any particular shape. The composite cable  100  has a pry slot  116  between the cable housing  102  and the removable cap  112  for receiving a blade (not shown) of a screwdriver (not shown). The composite cable  100  has a protective jacket  118  with ripcords  120 ,  122  and with longitudinal V-shaped grooves  124 ,  126 . The ripcords  120 ,  122  are for splitting the protective jacket  118 . The longitudinal V-shaped grooves  124 ,  126  may be positioned on the protective jacket  118  in order to correspond with the location of the ribbon slot  104 . The protective jacket  118  may be made from polyethylene or other suitable material, and has indicia  130  marked thereon for indicating which side contains copper or fiber. As shown, the cable housing  102  and the removable cap  112  form a smooth oval exterior  132  when coupled together. The oval shape facilitates cable rotation during a load so the copper pairs absorb as much of the load as possible so the optical fiber does not crush. It should be noted that other shapes besides oval may be used. 
     FIGS. 3 and 4 show the compression cap  112  removed from the cable housing  102 . As shown, the compression cap  112  has a first stepped cap surface generally indicated as  140  and a second stepped cap surface generally indicated as  150 . The first and second stepped cap surfaces  140 ,  150  each resemble two steps of a staircase. The first stepped cap surface  140  includes a first horizontal surface  142 , a first vertical surface  144 , a second horizontal surface  146 , and a second vertical surface  148 . The second stepped cap surface  150  includes a first horizontal surface  152 , a first vertical surface  154 , a second horizontal surface  156 , and a second vertical surface  158 . 
     The cable housing  102  has a first mating stepped surface  160  and a second mating stepped surface  170  for engaging the first and second stepped cap surfaces  140 ,  150  respectively, of the compression cap  112 . The cable housing  102  may be made of polypropylene, polyethylene or glass reinforced plastic. Similarly, the compression cap  112  may be made of one of these same three materials and is preferably made from the same material as the cable housing  102 . It is noted, however, that if the cable housing  102  is made of a material which is softer than the material of the compression cap  112 , the cable housing  36  may not need to have the mating stepped surfaces  160 ,  170 . Instead, the first and second stepped cap surfaces  140 ,  150  will be forceably imbedded in the material of the cable housing  102 . 
     The vertical surfaces  144 ,  148 ,  154 ,  158  of the first and second stepped cap surfaces  140 ,  150  permit the compression cap  112  to be easily positioned and frictionally engaged with respect to the mating stepped surfaces  160 ,  170  of the cable housing  102 . It should be apparent to those skilled in the art that the first and second stepped cap surfaces  140 ,  150  may be formed as a single step, instead of two steps. 
     FIG. 4 shows that the first horizontal surface  142  of the compression cap  112  is separated by a distance D from the cable housing  102 . The distance D is dimensioned sufficient to define the pry slot  116  for inserting a screwdriver blade (not shown) therein. When the screwdriver blade (not shown) is inserted into the pry slot  116 , the screwdriver (not shown) can be used to pry the compression cap  112  free of the cable housing  102  in order to expose the ribbon slot  104 . 
     The ribbon slot  104  may have a gel or water-swellable powder disposed therein to prevent water from damaging the optical fiber ribbons  106 . 
     The composite cable  100  of the present invention has several advantages over the prior art composite cables. First, the composite cable  100  of the present invention is easily designed and manufactured to meet the requirements of an optical fiber cable, and in particular meets the requirements on contraction in the temperature range from −40° to −50° Celsius, as described below. Furthermore, the composite cable  100  of the present invention does not have a steel strength member or buffer tubes associated with the optical fibers and copper pairs; therefore, the present invention is smaller, lighter and less costly than the prior art composite cables having such strength members and buffer tubes. Finally, the composite cable  100  of the present invention is easily shaped by bending without elastic recovery and suitable for many different applications. 
     The Composite Cable  200  in FIG.  5   
     FIG. 5 shows a composite cable  200 , which is an alternative embodiment of the present invention. The reference numerals used to describe the composite cable  200  are substantially similar to those used to describe the composite cable  100  with the addition of one hundred (i.e.  100 ). 
     The composite cable  200  has a cable housing  202  having a ribbon slot  204  with optical ribbons  206  arranged therein, and has a tubular opening  208  with copper pairs generally indicated as  210  arranged in the tubular opening  208 . The ends of the optical ribbons  206  rest against a bottom surface of the ribbon slot  204 . (Compare to the ribbons  106  in FIG. 2.) As shown, the composite cable  200  also has a removable compression cap  212  for removably covering the ribbon slot  204 . The optical ribbons  206  have optical fiber ribbons generally indicated as  214 . As shown, the ribbon slot  204  is rectangular, although the scope of the invention is not intended to be limited to any particular shape. The composite cable  200  has a pry slot  216  between the cable housing  202  and the removable cap  212  for receiving a blade of a screwdriver (not shown). The composite cable  200  has a protective jacket  218  with ripcords  220 ,  222  and with V-shaped grooves  224 ,  226 . The protective jacket  218  has indicia  230  marked thereon for indicating which side contains copper or fiber. As shown, the cable housing  202  and the removable cap  212  form a smooth oval exterior  232  when coupled together. 
     The Cold Temperature Test and Excel Spreadsheet 
     As discussed above, the present invention enables a composite cable to be designed that meets the industry standard for cold temperature testing requirements. In order to design such a composite cable, one can approximate an effective thermal coefficient of expansion and contraction by an Equation (1), as follows: 
     
       
         α eff =(Σ A   i   E   i α i )/(Σ A   i   E   i ),  (Equation (1))  
       
     
     where the parameter α eff  is the effective coefficient of expansion and contraction, the parameter A is an area of material in the cable, the parameter E is a modulus of the material, and the parameter α is a coefficient of thermal expansion and contraction. In Equation (1), the parameters A i E i  represent a weighting function used to determine the effective coefficient of expansion and contraction of the composite cable. The target is to design the composite cable having a structural contraction of about 0.30% to meet the industry standard. 
     FIG. 6 shows an Excel spreadsheet for a composite cable having optical fiber ribbon, six copper pairs with copper and insulation, a cable housing with an inner diameter (ID) and outer diameter (OD), a cap and a jacket. It has been found through computer modelling that the use of fewer than six copper pairs undesirably alters the need for the cable housing, in effect requiring too much material, which increases the size the size. 
     In this example, a copper pair has insulation wrapping with a diameter of 1.27 millimeters, and copper therein with a diameter of 0.635 millimeters. A fiber ribbon has a thickness of 0.30 millimeters and a width of 1.40 millimeters. The housing and cap have an approximate area of 1.5[π(OD 2 −ID 2 )]/4, where ID=(#pairs*2) ½  and OD=1 millimeter*2+ID (Nb: Assume area for copper equals slot for ribbon or ribbons have approximately 2 times area for contraction movement.) The approximate jacket area=((2+OD+2)*(OD+2))−(2*OD*OD) with a jacket wall of 0.75 millimeters. 
     The Composite Cable  300  in FIG.  7   
     FIG. 7 shows a composite cable  300 , which is an alternative embodiment of the present invention. The reference numerals used to describe the composite cable  300  are substantially similar to those used to describe the composite cable  100  with the addition of two hundred (i.e.  200 ). 
     The composite cable  300  has an I-beam shaped cable housing  302  having a ribbon slot  304  with optical ribbons  306  arranged therein, and has a copper pairs slot  305  with copper pairs generally indicated as  310  arranged therein. As shown, the composite cable  300  also has two removable compression caps  312 ,  313  for removably covering the ribbon slot  304  and the copper pairs  310 . The composite cable  300  has pry slots  316 ,  317  between the cable housing  302  and the removable caps  312 ,  313  for receiving a blade (not shown) of a screwdriver (not shown). The composite cable  300  has a protective jacket  318  and may have ripcords, V-shaped grooves, indicia marked thereon for indicating which side contains copper or fiber, similar to that shown in FIGS. 2 and 5. The cable housing  302  and the removable cap  312 ,  313  form a smooth oval exterior when coupled together. The I-beam construction provides excellent crush resistance. 
     Although the present invention has been described with respect to one or more particular embodiments of the apparatus, it will be understood that other embodiments of the present invention may be made without departing from the spirit and scope of the present invention. Hence, the present invention is deemed limited only by the appended claims and the reasonable interpretation thereof.