EP2411854A1

EP2411854A1 - An optical fibre conduit, and a method of manufacturing same

Info

Publication number: EP2411854A1
Application number: EP10723306A
Authority: EP
Inventors: Kenneth Barber
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2009-03-27
Filing date: 2010-03-23
Publication date: 2012-02-01
Also published as: WO2010109339A1; AU2010227148A1

Abstract

The invention provides an elongate optical fibre channel (1.002) having a substantially flat base (1.004) into which optical fibres (1.010) or optical fibre cable (1.012) can be laid in an overlength manner, and a substantially flat cover (2.022) adapted to be applied to the channel after the optical fibre has been installed in the channel.

Description

An Optical Fibre Conduit, and a Method of Manufacturing Same

Field of the invention

[001] This invention relates to an optical fibre conduit, and a method of encapsulating an optical fibre or optical fibre tape.

[002] The invention is particularly suited for optical fibre tapes adapted for inclusion in cables. In particular, the optical fibre conduit can be used in power cables as a distributed temperature sensor.

Background of the invention

[003] It is known to incorporate a circular optical fibre tube or conduit into cables such as power cables. However, one problem is the possibility of damage to the optical fibres when the cable is being handles or bent. To reduce the likelihood of damage to the fibres, attempts have been made to install an overlength of fibre in the tube. However, with a circular tube, it is difficult to obtain a sufficient overlength.

[004] EP0825465 describes a cable with an optical fibre tube in the form of a flattened metal tube encapsulating an optical fibre tape applied to a cable core in a sinusoidal manner. The cable jacket is extruded over the cable core and tube. The fibres are also said to be oscillated within the tube. The tube is formed by first feeding the fibres 11.012 into a circular metal tube 11.110 (see Figure 11 ), then flattening the tube 12.1 11 (Figure 12), then applying a sinusoidal form to the tube before applying the sinusoidal flattened tube to the cable, and then extruding the jacket over the cable core and tube.

[005] In this method of manufacture, the overlength imposed on the optical fibre or optical fibre tape is to some extent limited by the diameter of the tube before flattening (see Figure 12).

Summary of the invention

[006] This invention proposes an optical fibre tube or duct, and method of manufacturing such an optical fibre tube or duct.

[007] The invention provides an optical fibre duct having a closable exterior case in which one or more optical fibres can be deployed with an overlength before the case is closed. [008] According to an embodiment of the invention, there is provided an optical fibre duct having an exterior case formed of two parts joined to form a conduit, the conduit enclosing one or more optical fibres or optical fibre tapes, the optical fibre or optical fibre tape being deployed within the conduit in an overlength configuration.

[009] According to an embodiment of the invention, there is provided an elongate channel having a substantially flat base into which optical fibres or optical fibre cable can be laid in an overlength manner, and a substantially flat cover adapted to be applied to the channel after the optical fibre has been installed in the channel.

[010] The optical fibre or optical fibre tape can be laid on a substrate before being enclosed by the conduit.

[011] A soft thixotropic filling compound, viscous liquid or jelly, such as petroleum jelly, can be incorporated with the optical fibre or optical fibre tape in the duct or on the substrate before being enclosed by the conduit.

[012] The viscous liquid or jelly can be applied to the substrate before, after or simultaneously with the optical fibres or optical fibre tapes.

[013] The optical fibre can be deployed in a meander path.

[014] The optical fibre can be deployed in a sinusoidal path.

[015] The optical fibre can be deployed on a carrier, such as a tape or ribbon.

[016] The conduit can include a U-shaped channel

[017] The conduit can include a cap attachable to the channel.

[018] The channel and cap can be provided with a mutual attachment means.

[019] The mutual attachment means can include a snap-fit arrangement.

[020] The mutual attachment means can include a toothless zip closure, such as used for plastic bags.

[021] The overlength configuration can be produced by gathering of the optical fibres or optical fibre tapes.

[022] The overlength configuration can be produced by a differential feed rate between the fibre and the channel. [023] The overlength configuration can be produced by a reciprocating movement having a transverse component relative to the longitudinal axis of the duct

[024] The duct can be glued to a cable

[025] The duct need not be wrapped around a cable, (linear rather than spiral or undulating).

[026] The duct can be applied on the same axis as the cable

[027] The conduit can be manufactured by an assembly process including the steps of; providing an elongate conduit base member; providing an elongate conduit cover member; deploying one or more optical fibres or optical fibre tapes in an overlength configuration on the base member; applying the cover member over the base member.

[028] The method can also include the step of incorporating a viscous liquid or jelly with the optical fibres or optical fibre tapes.

[029] The method can also include the step of deploying the optical fibres or optical fibre tapes to a substrate before applying the optical fibres or optical fibre tapes to the base member together with the substrate.

[030] The invention also provides cable duct manufacturing apparatus including: optical fibre supply means; channel supply means; cover supply means; optical fibre overlength delivery means; an optical fibre/channel combiner; and a cover/channel combiner adapted to apply the cover to the channel after the optical fibre has been deployed in the channel.

Brief description of the drawings

[031 ] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [032] Figure 1 is a schematic representation of an illustrative view of a fibre cable laid in a channel according to an embodiment of the invention.

[033] Figures 2 and 3 together form a schematic illustration of an exploded view of a channel and cover according to an embodiment of the invention.

[034] Figure 4 is an illustration of an end view of an optical fibre cable in a covered duct according to an embodiment of the invention.

[035] Figure 5 is a schematic illustration of a closure mechanism for joining a cap to a base.

[036] Figure 6 illustrates a of an optical fibre duct according to an embodiment of the invention.

[037] Figure 7 illustrates a section through a cable according to an embodiment of the invention.

[038] Figure 8 illustrates a section through a cable according to an embodiment of the invention.

[039] Figure 9 is a schematic illustration of a cable fabrication plant according to an embodiment of the invention.

[040] Figure 10 is a schematic illustration of the splaying of the arms of the latch cavity.

[041] Figures 1 1 & 12 illustrate the method of forming an optical fibre duct similar to that described in EP0825465.

[042] Figure 13 illustrates an optical fibre duct according to an embodiment of the invention applied to an electrical cable.

[043] The numbering convention used in the drawings is that the digits in front of the full stop indicate the drawing number, and the digits after the full stop are the element reference numbers. Where possible, the same element reference number is used in different drawings to indicate corresponding elements.

Detailed description of the embodiment or embodiments

[044] The invention will be described with reference to the embodiments illustrated in the drawings. In the description and claims, the reference to "optical fibre" includes "optical fibre tape" or "optical fibre cable" having two or more optical fibres in a ribbon cable configuration, unless the context requires otherwise. [045] Figure 1 illustrates a portion of the base channel 1.002 of an elongate fibre duct according to an embodiment of the invention.

[046] An optical fibre or optical fibre cable 1.010, 4.012 is deployed on the base.

[047] The duct can be of substantially similar length to the electrical cable in which it is intended to be inserted.

[048] The channel has a base 1.004, and side walls 1.006, 1.008. The inside transverse dimension of the base 1.004 is sufficient to permit a fibre or fibre cable to be laid therein with a meander or sinusoidal path of sufficient amplitude to permit the required overlength. For example, lengthwise pitch and the transverse peak-to-peak distance ("wavelength") of the cable laid in sinusoidal form ensures that the cable is of the required overlength.

[049] Figures 2 and 3 illustrate an exploded view of a duct having a cap

2.022, and a channel 3.004. The cap includes longitudinal rims or snap-fit elements such as 2.024 adapted to provide a liquid seal along the longitudinal walls 3.006, 3.008 of the duct.

[050] In the arrangement shown, the cap includes a pair of projections such as 2.024, 2.026 forming a recess 2.028 along each edge of the cap. The recess 2.028 is adapted to receive the walls 2.006, 2.008 of the channel 3.004 in an interference fit to provide a seal along the edges of the channel. The ends of the projections 2.024, 2.026 can be chamfered or flared to facilitate initial engagement between the projections and the walls 3.006, 3.008. Alternatively or additionally, the tops of the walls 3.006, 3.008 can be tapered for the same reason.

[051] However, alternative means can be provided for attaching the cap to the channel without departing from the inventive concept. As shown in Figure 5, a toothless zipper arrangement similar to that employed for some plastic bags can be utilized. In this arrangement, the tops of the wall 5.006 of the channel 5.004 are provided with a bulbous termination 5.007, and the ends of the cap projections are provided with tapered inward projections 5.025, 5.027. The arms 5.024, 5.026 are sufficiently resilient to permit the bulbous bead 5.007 to be inserted through the tapered aperture formed by the tapered projections 5.025, 5.027. However, withdrawal requires greater force as the inner sides of the projections 5.025, 5.027 are not tapered to facilitate withdrawal. Of course, where it is desired to facilitate separation of the cap and channel, the inner sides can be tapered. [052] In addition, the corners of the cap and channel can be chamfered to reduce sharp edges and corners.

[053] Figure 5 is a schematic illustration of a closure mechanism for joining a cap to a base according to an embodiment of the invention. The projecting arms

5.024, 5.026, of the cap define a closure cavity or latch recess extending along one side of the cap and adapted to receive the bead 5.007 at the end of the wall 5.006 of the base 5.004. The ends of the arms 5.024, 5.026 have inwardly projecting latches

5.025, 5.027 which are tapered to facilitate the insertion of the bead 5.007. The arms are flexible and can deflect to facilitate the insertion of the bead. In one refinement to facilitate the insertion of the bead in the latch recess, the cap is sufficiently resilient that, when the cap is bent with the arms on the outer side of the curve, the arms will splay apart due to the greater radius of curvature at the latch end of the arms, increasing the distance between the tips of the tapered latches 5.025, 5.027. The bead is dimensioned so that it can be inserted into the latch cavity, and is retained therein by the tapered latches 5.025, 5.027 which are shaped to facilitate insertion of the bead, and to resist removal of the bead once inserted.

[054] Figures 6, 7, & 8 show elements of alternative optical fibre cable arrangements according to embodiments of the invention.

[055] The optical fibre or optical fibre tape 6.010 s deployed in an overlength configuration on the base 6.004. A pair of strength elements 6.032, 6.034, extend along the longitudinal edges of the cable.

[056] As shown in Figure 7, the duct can be formed of a unitary construction

7.004 in the form of a flat strip which is sufficiently resilient to permit it to be folded over the strength members 7.032, 7.034 so the ends can be joined to form the housing, shown in dotted line, for the optical fibres. Folding notches such as 7.036 can be provided to facilitate bending and assist in accommodating the compression of the material of the housing at the bends.

[057] The optical fibre cable 7.012 can include a number of optical fibres,

7.013, 7.014, 7.015, 7.016. The dotted outlined optical fibres correspond to the solid line fibres at a further distance, such as half pitch, along the cable, as indicated at 7.016'. The optical fibre cable is applied to the ribbon 7.040 before being inserted in to the channel. The petroleum jelly can be applied to the ribbon 7.040 before the optical fibres are applied to the ribbon.

[058] The housing 7.004 can be of a unitary construction, with the base being folded over the optical fibres and strength elements. The strength elements 7.032, 7.034, such as pultruded glass reinforcement rods, can be affixed to the base prior to the deployment of the optical fibres. Thus the strength elements remain at the edges of the duct to provide structural integrity during handling of the duct.

[059] As shown at 8.018 in Figure 8, the ends of the housing can be overlapped and joined by welding, ultrasonic scrubbing, gluing or other suitable means.

[060] Figure 9 schematically illustrates elements of a cable drawing plant suitable for manufacturing a cable according to an embodiment of the invention.

[061 ] A number of feed reels provide the feed stock for the cable. The cover reel 9.062, the fibre reel 9.064, the tape reel 9.066, and the base reel 9.068. A jelly supply 9.070 is provided to apply jelly to the tape before the fibre is applied. The fibre is deployed on the tape at a first station 9.072. The circled dot and cross 9.078 indicate that the fibre is applied to the tape with a transverse reciprocating motion to supply the fibre overlength. Alternatively, the fibre can be applied at a higher delivery speed than the tape without the transverse reciprocation, relying on the speed differential to produce the overlength.

[062] The tape and fibre are then deployed in the base channel at second station 9.074.

[063] The cover is then applied to the base at station 9.076.

[064] Instead of providing the cap and channel from reels, they can be drawn from extrusion machines, cooled, and directly fed to the cable forming apparatus.

[065] Figure 10 schematically illustrates the splaying of the arms 10.024,

10.026 of a latch cavity of a cap. The cap is bent about an arc at 10.088, and this causes the arms 10.024, 10.026 to splay outwards due to the difference in the radius of curvature from the base 1.004 to the ends of the arms 10.024, 10.026. As shown at 10.082, the base itself can deflect in a curve due to the stress differentials derived from the arms. Accordingly the latch space 10.086 proximate the bend 10.088 is greater than the latch space 10.084 at the unbent section of the cap. This can be used to facilitate the insertion of the latch beads from the walls of the base into the latch cavity of the cap.

[066] In alternative embodiments, the bead can be part of the cap and the latch cavity can be part of the channel, or one side can be the opposite of the other, the channel having one bead on one side and one latch cavity on the other side, and the cap having a mating arrangement.

[067] The optical fibre duct of the present invention can be applied to an electrical cable without the need to impose an overlength configuration to the duct. Figure 13 illustrates schematically a bared end of an electrical cable with an optical fibre duct 13.020 according to an embodiment of the invention inserted between an inner insulation layer 13.122, and an outer jacket 13.124. The duct is laid parallel to the axis of the cable during manufacture of the cable without the need for the imposition on the duct of the sinusoidal configuration illustrated in EP0825465. In previous arrangements, the optical fibre units have been helically applied unless they are put in the centre of the cable.

[068] The duct can be applied to the insulation layer 13.122 with zero twist, as the undulation of the fibres within the duct provide adequate allowance to isolate the fibres from excess tensile load. However, the duct can also be applied with a degree of spiral twist if necessitated by manufacturing or application purposes. For example, it may be a requirement that the fibre be accessible on one side of the cable at a point over a given distance of cable, so a spiral wrap of the duct can ensure this.

[069] Alternatively, the duct can be attached to the exterior of the cable prior to packing the cable on a drum.

[070] In this specification, reference to a document, disclosure, or other publication or use is not an admission that the document, disclosure, publication or use forms part of the common general knowledge of the skilled worker in the field of this invention at the priority date of this specification, unless otherwise stated.

[071] In this specification, terms indicating orientation or direction, such as

"up", "down", "vertical", "horizontal", "left", "right" "upright", "transverse" etc. are not intended to be absolute terms unless the context requires or indicates otherwise. These terms will normally refer to orientations shown in the drawings.

[072] Where ever it is used, the word "comprising" is to be understood in its

"open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear. [073] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.

[074] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims

1. An optical fibre duct (1.002) having a closable exterior case (1.004), (2.022) characterized in that one or more optical fibres (1.010) are deployed with an overlength before the case is closed.

2. An optical fibre duct characterized in that the duct includes an exterior case formed of two parts (1.004), (2.022) joined to form a conduit, the conduit enclosing one or more optical fibres (1.010) or optical fibre tapes (4.012), the optical fibre or optical fibre tape being deployed within the conduit in an overlength configuration.

3. An optical fibre duct characterized in that the duct forms an elongate channel having a substantially flat base 1.004 into which optical fibres (1.010) or optical fibre cable (1.012) can be laid in an overlength manner, and a substantially flat cover (2.022) adapted to be applied to the channel after the optical fibre has been installed in the channel.

4. An optical fibre duct as claimed in any one of claims 1 to 3, characterized in that the optical fibre or optical fibre tape is laid on a substrate or carrier (7.040) before being enclosed by the conduit.

5. An optical fibre duct as claimed in any one of claims 1 to 4, characterized in that a viscous liquid or jelly (7.070) is incorporated with the optical fibre or optical fibre tape in the duct before being enclosed by the conduit, and wherein the viscous liquid or jelly is applied to the substrate or carrier before, after, or simultaneously with the optical fibres or optical fibre tapes.

6. An optical fibre duct as claimed in any one of the preceding claims, characterized in that the optical fibre is deployed in a meander path or a sinusoidal path.

7. An optical fibre duct as claimed in any one of the preceding claims, characterized in that the conduit includes a U-shaped channel.

8. An optical fibre duct as claimed in any one of the preceding claims, characterized in that the duct includes a cap (2.020) attachable to the channel.

9. An optical fibre duct as claimed in claim 9, characterized in that the channel and cap are provided with a mutual attachment means (5.025), (5.027), (5.007).

10. An optical fibre duct as claimed in claim 9, characterized in that the mutual attachment means includes a snap-fit arrangement or a toothless zip closure.

1 1. An electrical power cable characterized in that the cable includes an optical fibre duct as claimed in any one of claims 1 to 10.

12. A method of manufacturing an optical fibre duct characterized in that the method includes the steps of: providing an elongate conduit base member (9.068); providing an elongate conduit cover member (9.062); deploying one or more optical fibres or optical fibre tapes (9.064) in an overlength configuration on the base member; applying the cover member over the base member.

13. A method as claimed in claim 13, characterized in that the method includes the step of providing the overlength configuration by gathering of the optical fibres or optical fibre tapes, or by feeding the fibre at a higher speed than the channel or by imposing on the fibre a reciprocating movement having a transverse component relative to the longitudinal axis of the cable.

14. A method as claimed in any one of claims 12 or 13, characterized in that the method includes the step of incorporating a viscous liquid or jelly with the optical fibres or optical fibre tapes.

15. A method as claimed in any one of claims 12 to 14 characterized in that the method includes the step of deploying the optical fibres or optical fibre tapes to a substrate before applying the optical fibres or optical fibre tapes together with the substrate to the base member.

16. Cable manufacturing apparatus including: optical fibre supply means (9.064); characterized in that the apparatus includes channel supply means (9.068); cover supply means (9.062); optical fibre overlength delivery means (9.078); an optical fibre/channel combiner (9.072/9.074); and a cover/channel combiner (9.076) adapted to apply the cover to the channel after the optical fibre has been deployed in the channel.

17. An electrical cable as claimed in claim 11 , characterized in that the optical fibre duct is enclosed in the cable jacket (13.124) with low or zero twist.

18. An electrical cable as claimed in claim 17, characterized in that the duct (13.020) is disposed between the outer jacket (13.124) and an inner insulation (13.122).