HK1063694A - Cable assembly and method - Google Patents

Description

Cable assembly and method

Technical Field

The present invention relates to a cable and a method of inserting a cable into a conduit. More particularly, the present invention relates to fiber optic cables and the like, and equipment for facilitating the insertion of the cables into semi-rigid conduits such as PVC tubing. A method of inserting the cable assembly into a conduit is also disclosed.

Background

Heretofore, telecommunication cables, coaxial cables, fiber optic cables and the like have been inserted into pipes or ducts in a variety of different ways. The "pull" method generally involves attaching a pull cord or tape, which has been placed in a conduit, to one end of the cable and then pulling the cord or tape from the other end of the conduit until the cable exits the conduit. This approach has several disadvantages.

First, the force applied to the cable in order to pull the cable out of the conduit must be kept relatively small. Fiber optic cables typically cannot withstand forces in excess of 600 pounds, otherwise the optical properties of the glass fibers can be adversely affected. Second, the forces applied to the cable cause the cable manufacturer to use several layers of strength members in the cable. These reinforcing elements are usually made of steel fibres or of aramid (Kevlar)^) Or other tightly woven sheaths of aromatic nylon fibers with little or no elongation. The strength components are formed and secured as the inner layer of the cable, typically beneath an extruded outer sheath of high density polyethylene. Because glass fibers are inelastic and susceptible to damage from microbending or other mechanical strains, the strength components must withstand a large portion of the forces exerted by traction and other handling to protect the optical fibers. These additional layers of strength components add significant cost to the fiber optic cable.

Another commonly used method of inserting a cable into a conduit is the "push" or "blow" method, in which the cable is subjected to high pressure air which blows the cable into the conduit for assembly. Of course, the cable assembly may also utilize a vacuum or low pressure applied at the distal end of the conduit to draw the cable into the conduit. This method is also limited and requires considerable energy and air pressure to assemble the cable through a long conduit.

Moreover, one disadvantage of both of the above approaches is the friction between the outer sheath of the cable and the inner wall of the catheter. The outer sheath of the fiber optic or coaxial cable is typically an extruded polymer, such as polyethylene or polyvinyl chloride, having a melting or softening point typically in the range of 100 to 150 ℃. The friction between the outer sheath of the cable and the inner wall of the conduit significantly limits the speed of the cable through the conduit. If the cable is pulled through the conduit at too great a rate, some of the contact surfaces of the cable sheath will melt or burn through. To address this problem, a large amount of lubricant is used at the junction of the cable and the conduit. Even at moderate speeds, supplying a large amount of lubricant necessary to pull the cable out of the extended length is an expensive and time consuming process. Moreover, these lubricants may negatively impact the cable environment.

It would therefore also be advantageous to provide a cable assembly method that reduces the friction between the cable and the inner wall of the conduit, which significantly reduces or eliminates the need for the use of lubricants, and which increases the speed at which the cable is inserted into the conduit while subjecting the optical fibers to a minimum amount of stress to allow for safe assembly. Furthermore, it is necessary to provide a cable assembly method that allows considerable force to be applied to the cable equipment to insert it into the conduit. Moreover, there is a need to provide a cable arrangement that can be inserted into a conduit faster and less expensive than current cables.

Summary of The Invention

It is therefore a principal object of the present invention to provide a cable assembly having an outer jacket disposed about the cable so as to be slidable therebetween.

Another main object of the present invention is to provide a cable installation that can withstand much higher traction forces than all current cables without jeopardizing the critical parts of the cable, such as the copper, the optical fibres, etc.

It is a further object of the present invention to provide a cable arrangement and method that allows a cable to be inserted into a conduit at a much higher speed and over a longer haul-off distance than in the prior art without having to increase the strength of the cable itself.

It is a further important object of the present invention to provide an apparatus and method that allows for the efficient insertion of several cables into a conduit at high speeds using one outer jacket assembly.

It is yet another important object of the present invention to provide an inexpensive and efficient method and apparatus for inserting a cable into a conduit that can replace current methods and apparatus.

It is also an important object of the present invention to provide a cable assembly having an outer jacket which is abrasion resistant and has a sufficiently high melting point to prevent burn-through due to friction between the jacket and the inner wall of the conduit.

Brief description of the drawings

These features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. Wherein:

FIG. 1 is a perspective view of a cable assembly showing the cable assembly slidably disposed within an outer jacket assembly;

FIG. 2 is a side view of the jacket assembly being pulled from the spool by a pull cable or pull tape, also showing the cable assembly being pulled;

FIG. 3 is a perspective view of the cable assembly showing a plurality of cables carried by an outer jacket assembly; and

FIG. 4 is a perspective view of a cable assembly for use with the innerduct structure.

Detailed Description

As shown in fig. 1, a cable assembly 2 includes a cable assembly 4 and an outer jacket assembly 6 slidably disposed on the exterior of the cable assembly. In a preferred embodiment, the outer jacket member is a low friction synthetic fiber such as a fabric made of polyester, nylon, Teflon, polyaramid, PEEK (polyetheretherketone) or polyvinylidene fluoride. The outer jacket assembly extends as a sleeve at least the same length as the cable assembly. Outer jacket member 6 may be woven along cable member 4 during manufacture or cable member 4 may be inserted into outer jacket 6 after manufacture.

In use, as shown in FIG. 2, the outer jacket 6 with the cable assembly 4 is attached to one end of a pull cable or strap 8, with the pull cable or strap 8 extending through the entire conduit (not shown). A pulling force is applied to the distal end of pull cable 8 to cause outer jacket assembly 6 and cable assembly 4 to pass through the catheter. The outer jacket assembly 6 is subjected to most of the traction forces and the only force applied directly to the cable assembly 4 is the frictional force between the jacket and the cable. Because the jacket must withstand such traction forces, it must have sufficient tensile strength in the longitudinal direction to allow successful installation without mechanical failure. The jacket preferably has a break strength in the longitudinal direction of greater than 600 pounds. High tenacity fibers and yarns are the preferred materials for making the outer jacket. An alternative is to blow the cable arrangement into the conduit as previously described.

The outer jacket also serves another purpose of reducing friction during cable insertion. The outer sheath 10 of a typical fiber optic cable is typically an extruded polyolefin layer, particularly a medium or High Density Polyethylene (HDPE). The solid outer sheath 10 serves to protect the optical fibers 12 from environmental degradation and the strength components from abrasion, since conventional strength components have very low abrasion resistance and cannot be used outside of the cable equipment. The outer sheath of the coaxial cable is typically polyvinyl chloride (PVC), which is used because of its flame retardancy. Typically the catheter material is highly filled with rigid PVC.

Example 1

The friction coefficient between HDPE and PVC was experimentally determined with and without a silicone lubricant. The test results are shown in table 1. The test was conducted according to ASTM D4518, test method B-horizontal traction test for dynamic sliding friction measurement.

TABLE 1

Material	COF (silicone) with lubricant	Lubricants-free COF
			HDPE cable sheath and PVC conduit	0.09-0.2	＞0.2

COF (coefficient of friction)

For comparison, friction tests between different fabrics and HDPE combinations were also performed to determine the coefficient of friction. The fabrics used in these tests were made from 520 denier monofilament polyester in the warp direction and nylon in the fill direction. In both tests, the cable used was an AT&T Fitel^A cable. This test was also performed according to test method B of ASTM D4518-horizontal traction test for friction measurement. The results are shown in Table 2.

TABLE 2

COF (coefficient of friction)

Material	COF with lubricant	Lubricants-free COF
			Fabric and fabric	0.10	0.12
Fabric and HDPE	0.07	0.17
			Fabric and PVC conduit	0.07	0.09

From the above table it can be seen that the unlubricated fabric and HDPE show the same range of friction coefficients as the lubricated HDPE and PVC. This fact illustrates that significant cost savings can be achieved in the process because the method and apparatus of the present invention eliminates the need for lubricants, as well as the need for containers, pumps and other hardware for transporting such lubricants to apply the lubricant.

The melting point of the jacket should be greater than 150 c, consistent with the melting point of the preferred material used to make the jacket. For example, polyester fibers and nylon 66 fibers have melting points in the range of 250-265 ℃. This range is significantly higher than the melting point of HDPE (typically between 120 and 130 ℃), which is the preferred sheath for most fiber optic cables. In this way, the low coefficient of friction of the jacket, combined with the high melting point, allows the cable equipment to be run through the conduit at high speeds without permanent damage caused by melting or burning through of the sheath.

As shown in FIG. 3, outer jacket assembly 6 slidably carries a plurality of cable assemblies 4. In a preferred embodiment, the jacket 6 is braided around the cable 4 during manufacture, but it is also contemplated that the cable 4 may be inserted into the jacket assembly 6 in a separate step after manufacture. Alternatively, the outer jacket assembly may be fire resistant, particularly when the cable assembly is used inside a building or other structure. The fire resistant material may be selected so that the jacket is fire resistant, or a fire resistant coating may be used. Alternatively, the outer jacket may be made of a reinforced composite material, such as a fiberglass reinforced resin or polyester composite, a resin impregnated fabric composite, or an organic/inorganic hybrid composite.

Figure 4 shows a cable installation 2 comprising an outer jacket assembly 6 and a cable assembly 4, in use, disposed within a rigid or semi-rigid conduit within an inner tubular structure 14. The illustrated innerduct structure is described and claimed in U.S. patent 09/400778, which is incorporated herein by reference in its entirety. This arrangement allows the outer jacket assembly 6 to be provided with one or more channels for the cables 4 through the inner tube 14 without subjecting the cables 4 directly to high friction. The fabric-to-fabric coefficients of friction in table 2 illustrate that in the fabric innerduct structure, cable equipment does not require a lubricant for quick and efficient insertion. It should be understood, however, that a lubricant may be used with the jacketed cable assembly if necessary.

Thus, it has been shown that a braided outer jacket can be slidably disposed about a cable or cables to allow the cable to be inserted into a rigid or semi-rigid conduit at higher speeds, with less friction and less trauma to the cable. Moreover, because the outer jacket bears a substantial portion of the force necessary to pull the cable assembly through the conduit, cables, particularly fiber optic cables, are manufactured without the use of strength components therein. The jacket has wear resistance and cutting resistance.

Although the preferred embodiments have been disclosed and described in considerable detail, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein. For example, although the cable assembly described herein is more specifically directed to fiber optic cables, it should be understood that any other cable may be used with the cable assembly. Optional features or components serving the same, equivalent or similar purpose may replace all the features disclosed in the present specification unless otherwise specifically noted. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

Claims (24)

1. A cable assembly comprising:

at least one cable assembly; and

a jacket assembly disposed outside the cable assembly so as to be slidable therebetween.

2. The cable assembly set forth in claim 1, wherein said outer jacket member is a braid.

3. The cable assembly set forth in claim 2, wherein said outer jacket member is made of a material selected from the group consisting of polyester, nylon, teflon, PEEK and polyvinylidene fluoride, or combinations thereof.

4. The cable assembly set forth in claim 1, wherein said jacket member is made of monofilament fibers.

5. The cable assembly set forth in claim 1, wherein said jacket member exhibits a dynamic sliding coefficient of friction for solid PVC conduit material in the range of 0.07 to 0.09 as measured according to ASTM D4518 test method B.

6. The cable apparatus of claim 1 wherein the jacket member exhibits a break strength in the longitudinal direction of greater than 600 pounds.

7. The cable assembly set forth in claim 1, wherein said outer jacket member is made of a fire resistant material such as polytetrafluoroethylene, polyvinylidene fluoride or PEEK.

8. The cable assembly set forth in claim 1, wherein said outer jacket member is made of a material having a melting point greater than 150 ℃.

9. The cable assembly set forth in claim 1, wherein said outer jacket member is at least as long as said cable member.

10. The cable assembly set forth in claim 1, wherein a plurality of cable components are disposed in a single outer jacket component.

11. The cable assembly set forth in claim 1, wherein said outer jacket member is a fiber or fabric reinforced composite material.

12. A method of inserting a cable into a conduit, the method comprising the steps of:

providing at least one cable assembly;

providing an outer jacket member positioned about the periphery of the cable member such that the cable member is slidably disposed within the outer jacket member; and

applying a force to the outer jacket member to insert it into a conduit, wherein the outer jacket member carries the cable assembly through the conduit.

13. The method for inserting a cable into a conduit as set forth in claim 12, wherein the step of applying a force to said outer jacket member includes pulling said outer jacket member through said conduit.

14. The method for inserting a cable into a conduit as set forth in claim 12, wherein the step of applying a force to said outer jacket member includes blowing said outer jacket member through said conduit.

15. The method for inserting a cable into a conduit as set forth in claim 12, wherein said outer jacket member is made of a material selected from the group consisting of polyester, nylon, teflon, PEEK and polyvinylidene fluoride, or combinations thereof.

16. The method for inserting a cable into a conduit as set forth in claim 12, wherein said outer jacket member is made of monofilament fibers.

17. The method for inserting a cable into a conduit as set forth in claim 12, wherein said outer jacket member is a braid.

18. The method for inserting a cable into a conduit as set forth in claim 12, wherein said outer jacket member is at least the same length as said cable member.

19. A method of inserting a cable into a conduit as set forth in claim 12, wherein said jacket member exhibits a coefficient of friction against a solid PVC conduit material in the range of 0.07 to 0.09 as measured according to ASTM D4518 test method B.

20. The method for inserting a cable into a conduit as set forth in claim 12, wherein said outer jacket member has a break strength in the longitudinal direction of greater than 600 pounds.

21. A method of inserting a cable into a conduit as claimed in claim 12, wherein the outer jacket member is made of a fire resistant material such as a fluoropolymer, aramid, PEEK or polyimide.

22. The method for inserting a cable into a conduit as set forth in claim 12, wherein said outer jacket member is made of a material having a melting point in excess of 150 ℃.

23. The method for inserting a cable into a conduit as set forth in claim 12, further including the steps of:

providing an inner tubular structure within said catheter; and

inserting the outer jacket assembly and cable assembly into and through the inner tubular structure in the conduit.

24. The method for inserting a cable into a conduit as set forth in claim 12, wherein said outer jacket member is a fiber or fabric reinforced composite material.