GB2377089A

GB2377089A - Duct having internal grooves to hold cables.

Info

Publication number: GB2377089A
Application number: GB0210826A
Authority: GB
Inventors: Andrew Jonathon Hilton; Michael John Poole
Original assignee: CCS Technology Inc
Current assignee: Corning Research and Development Corp
Priority date: 2001-05-17
Filing date: 2002-05-13
Publication date: 2002-12-31
Also published as: GB0112010D0; GB0210826D0

Abstract

A duct 1 has an interior surface lined with a foam material 2 in which slits 3 are cut to enable a cable 4 to be pushed in. The foam 2 holds the cable 4 in place due to the resilient nature of the material 2. Cable 4 may be fed from a machine (8, fig 2) which automatically cuts the slit 3, using for example, a knife (34, fig 20), a router (fig 22) or a milling cutter (fig 23) and feeds the cable 4 into the slit 3 as it moves along the interior of the duct 1. A single channel (10, fig 2) or a number of channels (18, fig 6) may be provided as guides for wheels 9 mounted on the machine 8 to ensure a correct orientation of the machine 8 in the duct 1. The slits 3 may be a number of different shapes. Alternatively a structure 24 comprising tufts of stiff bristles may be provided, into which the cable 4 is pushed and held secure. Another alternative provides a number of stalks (31, fig 19) with enlarged heads past which a cable 4 is pushed and held into place.

Description

Cable Installations and Methods of Making them This invention relates to cable installations, especially but not exclusively to optical cable installations for telecommunications, and to methods of making them (including methods of adding cables to existing installations). The word"cable"is used herein in a broad sense to include any assembly comprising at least one optical fibre and/or at least one elongate electric conductor, in each case with sufficient protective covering to make it suitable for installation.

It is more especially concerned with installations in which one, or usually more than one, cable is located in a duct having a diameter large compared with the diameter of the cable (or any of them). An important application of the invention is in installations where the length of the duct is so great that it is impossible or impracticable to install a cable in it by pulling, pushing, blowing or otherwise moving it in the direction of its length from a stationary supply at one end of the duct and it is necessary to cause a supply of cable to travel through the duct unwinding as it goes.

It is relatively easy to install one cable in this way so that it lies loose in the duct (either continuously or discontinuously resting on the bottom of the duct, depending - among other things-whether excess length of cable over length of duct is present). However, it may well be necessary to install multiple cables: either initially, because a single cable of the required capacity would be too large in cross-section or too stiff for a supply sufficient to reach from one end of the duct to the other to be contained in a package (or group of packages) small enough to pass through the duct, or subsequently to increase the capacity of the system or otherwise upgrade it, or occasionally to replace a cable that has become defective but cannot be economically removed. The already installed cable is, in such circumstances, liable to become entangled with or otherwise obstruct the movement of the supply of new cable or of the

apparatus used to support and advance it.

In the context of conventional installation by pulling with a pilot line it has been proposed (for example US 0244752 and US 5360291) to subdivide the duct into separate compartments, one for the cables and another for the installation equipment, communicating through a narrow slot; but this is difficult and expensive (to a large extent because of the complication it causes where the duct has to be jointed). Other costs and complications arise with the use of brackets or the like (US 4780025, for example) intended to hold individual cables in set positions.

JP 03-183309 proposes an installation (and method of making it) in which the cable, laid from a package travelling through the duct and unwinding as it goes, is located in a recess formed in the wall of the duct by cutting and secured in it by filling the recess, for example with quick-setting cement. This requires the duct wall to be considerably thicker than otherwise necessary and is realistic for only a few possible duct materials, may be limited by the cutting tool blunting before the end of the duct is reached, may require a long installation time because the length of cable embedded in unset filling material must be limited, and is liable to failure if the speed of laying varies beyond the tolerance limit imposed by the setting time of the filling material (in the extreme, if advance is interrupted).

To overcome these difficulties, the present invention provides a cable installation characterised in that at least part of the internal surface of the duct is formed by an insert of a soft resilient material and at least one cable is contained in a recess at least partly bounded by that insert and is held there by the resilience of the material.

It also provides a method of installing at least one cable in a duct characterised by providing at least one insert forming part of the internal surface of the duct, forming a recess that is at least partly bounded by the insert and is at least in part less wide than the diameter of

the cable, and pushing the cable into the recess to be held there by the resilience of the insert material.

For installation of very small cables, the insert might be of a soft solid elastomeric material, but we prefer to use inserts of a cellular polymeric material, for example a resilient polyurethane foam. The latter has the particular advantage that it can easily be formed in situ by coating with liquid precursors which foam and cure spontaneously on mixing. Recesses could be formed in an insert of this kind prior to or at the time of installation of the insert, for example by foaming polyurethane in contact with a non-stick ribbed former, but for ease of location we prefer to form each recess simultaneously with the insertion of a cable into it and only a short distance ahead of the insertion point.

As an alternative to solid or cellular material, the insert or inserts may be of a structured flexible sheet material having resilient elements that can be deformed to create a recess just by pushing a cable into them or between them and another member, and if required are barbed or otherwise shaped to secure it. Examples include a brush or pile carpet structure either co-operating with a relatively stiff member or zigzag-folded to pre-define potential recesses with tufts projecting into them, fabrics with stiff hooked pile (loosely resembling one part of the fastening devices sold under the trademark Velcro) and sheets of elastomeric material moulded with multiple headed projections.

The recess (or each recess independently of the other (s) ) may be flat and either radial or oblique to the wall of the duct; it could even extend in a circumferential direction, though this might require the provision of an additional support member; or it could be curved. Preferred recess cross-sections include a simple slit formed by a flat knife, a parallel-sided slot with a flat or rounded base, a dovetail tapered slot with a flat or rounded base, or a keyhole section with a round, generally rectangular or oval

void and lips which may be touching or spaced apart.

In the simplest forms of the invention, a single insert covers the whole internal surface of the duct; but if the apparatus for laying the cable has wheels or other localised supports for engaging the walls of the duct, this may be undesirable as it might present a risk of impeding movement of the apparatus. In such cases, we prefer to use inserts that are longitudinally continuous (or nearly so) but confined to one or more parts of the duct wall which the supports are not to engage. For example, if the cable laying apparatus has wheels in three positions circumferentially spaced at 120 from each other, we prefer to use one, two or three separate inserts of suitable width each centred in midway (60 ) positions with respect to two of the three support positions; or if it has supports only on its underside, one or more inserts may be located at the top and/or sides of the duct.

If necessary or desired, the duct may be non-circular or provided with at least one longitudinally continuous guide formation to ensure that the cable-laying apparatus is correctly aligned, in particular so that a cable will be inserted in a predetermined position in the insert and clear of the position of any cable already present.

Where the nature of the insert material requires a recess to be cut (and permits), we prefer to cut with a knife without removing any material, unless the cable is too large to be securely held in a recess of this kind. If necessary, an undercut recess can be formed using a succession of knives, a shaped cutter (a"pastry cutter") or a rotating milling or routing tool. In some cases, this may result in the presence of an unwanted strip of insert material in the duct, but this should be flimsy enough not to offer any substantial obstruction. Knives and some other cutters may be oscillated to reduce the tendency to deform the insert material.

The invention will be further described, by way of example, with reference to the accompanying drawings in which: Each of Figures 1-6 is a diagrammatic transverse crosssection through a different unfinished cable installation in accordance with the invention, figures 1,2 and 6 showing cable-laying apparatus in position; Each of Figures 7-15 is a cross-section through a different form of recess in an insert of cellular resilient material that can be used in an installation in accordance with the invention, Figure 7 showing the recess before and after cable insertion at (a) and (b) respectively; Each of Figures 6-19 shows an alternative recessed structure; Figure 20 is a diagrammatic longitudinal section showing apparatus for forming a recess of the kind shown in Figure 7 using a simple knife as cutting tool; and Each of Figures 21-23 shows a cutting tool that might be used to form a recess of a different cross-section.

The simple form of installation shown in Figure 1 comprises an enclosing duct 1 which may be of metal or plastics and in the example shown is of plain circular crosssection. It is contemplated that the duct may have a diameter in the range 50 to about 800 mm (more especially 100 to 300 mm) and a length up to as much as about 100 km; the installation may thus be for a sea crossing or a limitedaccess city-to-city link.

The duct includes an insert 2 of resilient polyether polyurethane foam of nominally uniform thickness, which can either be formed (a) by lining sections of the duct before they are welded or otherwise joined together, either using preformed foam strips or by foaming in situ, as short interruptions or irregularities in the region of the duct welds are not critical to the functioning of the invention or (b) in a continuous process in which apparatus (a"pig")

travelling through the duct sprays liquid polymer base and hardener compositions from separate nozzles so that they meet, mix and react on the internal surface of the duct.

In this resilient foam insert are a number of recesses 3 (to be further discussed below) each of which accommodates a cable 4. The figure shows a new cable 5 taken from an annular package 6 being installed into a recess being formed for the purpose in a position well clear of the existing cables 4.

For purpose of illustration, the installation apparatus is shown as a simple sliding body that may be advanced through the duct by flowing a fluid though it. It is to be noted that a sensor is likely to be needed to detect and correct any tendency for the cable guide 7 to rotate around the axis of the duct, or there may be a risk of cutting the recess into one of the previously installed cables 4.

Figure 2 shows one way in which a duct of non-circular section can be used to avoid potential problems of this kind and to facilitate the use of cable-laying apparatus 8 supported on wheels 9. The lower part 10 of the duct is dedicated to supporting and guiding the apparatus and the polyurethane insert is confined to an upper part 11 of the duct (top and sides).

Figures 3,4 and 5 illustrate minor variations on this design where respectively there are two separate inserts 12, 13 on the sides only of the duct, three 14-16 on the top and sides, and one 17 confined to the top.

The forms of the invention illustrated by Figures 2-5 presuppose that the duct is the right way up and that gravity will keep the cable-laying apparatus on the bottom of it.

This is reasonable for an installation on land and where the duct is air-filled, but where the duct is to be laid into the sea (or any body of water) it will seldom be possible to prevent twisting and if the duct is filled with water or any other buoyant liquid, the apparatus may tend to float away from the bottom. Figure 6 shows a duct design suitable for use in those circumstances: it is basically circular but is

formed with two sets of internal recesses: narrow recesses 18 serve as guide rails for wheels 9 set at 120 around the circumference of the cable-laying apparatus, while one or more of three wider recesses 19 accommodates a respective polyurethane insert 20, 21, 22.

If the cable 5 to be installed (or each of them) is reasonably small (in relation, mainly, to the thickness of the resilient insert), a recess of nominally zero width, such as may be formed by drawing a sharp knife longitudinally of the insert and as shown at (a) in Figure 7, is satisfactory and may be optimal; it will open in the vicinity of the (or each) inserted cable as shown at (b) while its lips 23 remain in contact.

Figures 8-13 show some of the many alternative crosssectional shapes that might be used for the recesses. The circular keyhole shapes of Figures 8 and 9 (the latter featuring spaced lips 23) are primarily suitable for accommodating a single cable with a diameter broadly similar to that of its circular part: slightly smaller, if it is desired that the cable should have freedom to move longitudinally, for example because significant temperature cycling is expected; slightly larger, if a firm grip is desired.

The rectangular recess shown in solid lines in Figure 10 is suitable to receive either two relatively large cables that will be gripped between its sides or several small cables that will be retained only because they cannot pass freely between the lips; the alternative wide-mouthed section shown in dashes is only suitable for one, two or perhaps three of the larger cables. The oval section of Figure 11 is intended mainly for holding several relatively small cables, while the round-bottomed recess of Figure 12 and the dovetail recess of Figure 13 are alternative dual-purpose shapes.

Figures 14 and 15 respectively illustrate the possibility that the recess 3 may be obliquely inclined to

the surface of the insert 2 and that it may be curved. In some cases, this may allow use of a thinner insert than otherwise required.

Figures 16-19 illustrate various alternatives to the use of cellular polymeric material. In Figure 16, a tufted sheet 24, resembling a brush or a pile carpet, is partly enclosed by a relatively stiff co-operating member 25 (which may be of plastics material or metal) so as to define two pre-determined recesses 3 between the free ends of the tufts and member 25 into which cables may be pushed after passing through access opening 26.

Figure 17 shows how a carpet-like material 27 may be zigzag folded to form recesses 28 into which cables 4 can be pushed to be held by the resilience of tufts 29. It may be desirable for this kind of recess structure to be discontinuous so that a cable is not compelled to follow the same recess for the whole length of the duct.

Figure 18 illustrates the possibility that cables 4 (primarily very small ones) may be held simply by pushing into the natural recesses 3 of a fabric with barbed pile members 30. The structure suggested could be made, among other techniques, by weaving a loop pile fabric (terry weave, for example) in which the loops are formed of a stiff synthetic monofilament yarn, heat-treating to relax the monofilament in its looped configuration, and then cutting at least some of the loops at one side.

Figure 19 shows a somewhat similar arrangement using an insert of solid rubbery material moulded with many upstanding headed stalks 31, allowing cable 4 to be held in recessed between them.

Figure 20 may be considered a vertical longitudinal section through the installation and apparatus of Figure 2 or an inclined longitudinal section through that of Figure 6.

The cable-laying apparatus 8 will typically be a part of a "pig train" formed by a number of articulated units, at least one of which will provide means for advancing the train

through the duct while more than one may hold a supply of cable such as the one seen at 32. The advancing means could be a unit that simply occludes the duct to the extent that the train can be driven through the duct by flowing a suitable fluid (air or water, for instance) through the duct or it could be a powered driving unit, either using stored energy (batteries operating electric motors, for instance) or drawing power from fluid flowing in the duct more rapidly than the train is to travel. The apparatus includes an arm 32 rotatable about the axis 33 which preferably coincides with that of a circular part of the duct and which can preferably be locked in any one of a number of well-spaced pre-set positions. This arm 32 supports a knife 34 that cuts the insert 2 to form recess 3 as the apparatus advances in the direction indicated by arrow 35. Knife 34 is preferably adjustably mounted and may be oscillated in any appropriate direction to facilitate clean cutting and minimise distortion adjacent the recess. The arm 32 also supports a pulley or other guide 36, preferably adjustably positioned, for locating cable 5 into the recess 3 formed by the knife.

Figures 21-23 show by way of example a few of the many types of cutting tool that may be used to form recesses in making installations in accordance with the invention, depending on the particular properties of the material to be cut. The tool of figure 21 is a"pastry cutter"with a sharpened cutting edge 37 that will (in suitable material) form a recess of the general shape illustrated by Figure 13, discarding a strip 38 of waste insert material (which may or may not fragment, depending on materials and dimensions).

Figure 22 shows a rotary tool of the router type for forming a recess of similar shape and Figure 23 a rotary tool of the milling cutter or rasp type for making the type of recess illustrated by Figure 10: in both of these cases, the waste material will be particulate.

Any discussion of the background to the invention herein is included to explain the context of the invention. Where any document or information is referred to as"known", it is admitted only that it was known to at least one member of the public somewhere prior to the date of this application.

Unless the content of the reference otherwise clearly indicates, no admission is made that such knowledge was available to the public or to experts in the art to which the invention relates in any particular country (whether a member-state of the PCT or not), nor that it was known or disclosed before the invention was made or prior to any claimed date. Further, no admission is made that any document or information forms part of the common general knowledge of the art either on a world-wide basis or in any country and it is not believed that any of it does so.

Claims

Claims: 1 A cable installation in which at least one cable is located in a recess formed in the wall of the duct and secured in it characterised in that at least part of the internal surface of the duct is formed by an insert of a soft resilient material and at least one cable is contained in a recess at least partly bounded by that insert and is held there by the resilience of the material.
2 A cable installation as claimed in claim 1 in which at least one insert is of a cellular polymeric material.
3 A cable installation as claimed in claim 1 in which at least one insert is of a resilient polyurethane foam.
4 A cable installation as claimed in claim 1 in which at least one insert is of a structured flexible sheet material having resilient elements that can be deformed to create a recess just by pushing a cable into them or between them and another member, and if required barbed or otherwise shaped to secure it.
5 A cable installation as claimed in any one of claims 1-4 in which the cross-section of at least one recess is selected from a simple slit formed by a flat knife, a parallel-sided slot with a flat or rounded base, a dovetail tapered slot with a flat or rounded base, or a keyhole section with a round, generally rectangular or oval void and lips which may be touching or spaced apart.
6 A cable installation as claimed in any one of claims 1-5 in which the or each insert is longitudinally continuous or nearly so but confined to one or more parts of the duct wall leaving other parts for cable-laying apparatus to engage.
7 A cable installation as claimed in claim 6 in which the duct is non-circular or provided with at least one longitudinally continuous guide formation to ensure that cable-laying apparatus may be correctly aligned.
8 A method of installing at least one cable in a duct comprising forming at least one recess in the wall of the duct, and inserting the cable into the recess characterised

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by providing at least one insert forming part of the internal surface of the duct, forming the recess so that it is at least partly bounded by the insert and is at least in part less wide than the diameter of the cable, and pushing the cable into the recess to be held there by the resilience of the insert material.
9 A method in accordance with claim 8 comprising using an insert of a cellular polymeric material.
10 A method in accordance with claim 8 comprising using an insert of a cellular polyurethane foam.
11 A method as claimed in claim 10 comprising forming the insert in situ by coating with liquid precursors which foam and cure spontaneously on mixing.
12 A method as claimed in any one of claims 8-11 in which each recess is formed simultaneously with the insertion of a cable into it and only a short distance ahead of the insertion point.
13 A method as claimed in any one of claims 8-12 comprising forming a recess by cutting with a knife.
14 A method as claimed in any one of claims 8-12 comprising forming a recess by cutting with a knife without removing any material.
15 A method as claimed in any one of claims 8-12 comprising forming a recess by cutting with a succession of knives, a shaped cutter or a rotating milling or routing tool.
16 A method as claimed in claim 13 or claim 14 in which the knife is oscillated.
17 A cable installation substantially as described with reference to any one of claims 1-6 and/or any one of claims 7-19.
18 A method of making a cable installation or of adding a cable to it, substantially as described with reference to Figures 2 and 20, Figures 6 and 20, or any one of Figures 21-23.