WO2001024334A1

WO2001024334A1 - Cable laying device

Info

Publication number: WO2001024334A1
Application number: PCT/AU2000/001194
Authority: WO
Inventors: Gary Douglas Osborn
Original assignee: Ozweld Engineering Pty Ltd
Priority date: 1999-09-29
Filing date: 2000-09-29
Publication date: 2001-04-05
Also published as: AUPQ315099A0

Abstract

A cable laying device (10) for laying fibre optic cable (20) between a paire of cable conduits (23, 24) which open into a below ground pit (39). The device (10) includes roller means (11) having a rotatable roller (12) of a readius which is greater than the radius of a bend that would cause damage to a fibre optic cable (20) being laid and mounting means (14, 16) for mounting the device (10) within the pit (39). The mounting means (14, 16) being so arranged that in use, the roller (12) is positioned adjacent the opening into the pit (39) of a first of the pair of conduits (23, 24) from which the cable (20) is pulled during cable laying. The cable (20) in use being guided about a portion of the roller (12) and toward the opening of a second of the pair of conduits (23, 24) and into which the fibre optic cable (20) is to be inserted.

Description

CABLE LAYING DEVICE

The present invention relates to a device for use in laying underground optical fibre cable. Optical fibre is used in the telecommunications industry, for transmitting optical signals, and vast quantities of that type of cable are laid underground. The cables include a bunch of longitudinally extending optical fibres that are encased within a tubular plastic covering and when the cables are laid underground, they are laid within protective plastic conduits that can house a plurality of cables. The cable is supplied on large reels and is normally pulled through the conduit by rope. The cable is generally laid in straight lines and where a change in cable direction is necessary, the conduit opens into a below ground pit, which is normally square or rectangular, and the cable is bent to enter another conduit that extends away from the pit in the desired direction. Applying bends to optical fibre needs to be conducted very carefully, as a bend of too small a radius can damage the fibres of the cable. As such, it is common practice when laying a cable, that the length of cable is pulled entirely through a first conduit and laid on the ground above the pit, before being inserted in and pulled through the second conduit. Thus, in such a cable layout, say for example where each of the first and second conduits are 500m long, the entire 500m length of cable that is to be accommodated within the second conduit must first be pulled through the first conduit prior to insertion in and pulling through the second conduit. In this accepted cable laying method, the cable which has been pulled through the first conduit is simply laid on the ground in the vicinity of the pit, ready for insertion in and pulling through the second conduit. The adoption of this method is simply to ensure that damaging cable bends do not occur. Instead, the cable which is laid on the ground can be inserted into the second conduit in a very wide arc, so that the cable only experiences gentle curves. It can be easily appreciated, that long lengths of cable are awkward to handle, but regardless, the cable must nevertheless be handled carefully, to avoid the cable kinking in a damaging manner. A 500m length of cable is very awkward to handle, but it is not uncommon for much larger lengths of cable to be involved. The cable could in fact be in the order of kilometres or miles in length and the very early bends in such a cable lay would require significant cable handling. The above method is employed to ensure that abrupt bends in the cable are avoided. However, this method is extremely time consuming, because of the large lengths of cable that have to be handled at each cable bend, and also because of the care that needs to be taken in handling the cable. As an example, it is necessary in some areas, that the cable only be laid on soft or non-abrasive surfaces prior to insertion into a second or subsequent conduit extending from a pit, because any abrasion to the outer coating of the cable may remove protective layers, such as anti-termite coatings. It follows, that the present cable laying method disclosed above is extremely time consuming and therefore costly. It is an object of the present invention to provide a device for use in the laying of fibre optic cables, that permits a bend of a non-damaging radius to be made in a cable that extends from the outlet of a first conduit that opens into a cable pit, for direct insertion of the cable into the inlet of a second conduit that opens into the pit. It is a further object of the invention to provide a method of laying cables that embodies the above device.

According to the present invention there is provided a cable laying device for laying fibre optic cable between a pair of cable conduits which open into a below ground pit, said device including roller means having a rotatable roller of a radius which is greater than the radius of a bend that would cause damage to a fibre optic cable being laid and mounting means for mounting said device within said pit, said mounting means being so arranged that in use, said roller is positioned adjacent the opening into the pit of a first of the pair of conduits from which the cable is pulled during cable laying, said cable in use being guided about a portion of said roller and toward the opening of a second of the pair of conduits and into which the fibre optic cable is to be inserted. The above device is advantageous, because the roller means permits cable that egresses from the first conduit to be bent in a non-damaging manner toward and into the opening of the second conduit and to be pulled therethrough, so that the normal method of pulling the cable fully through the first conduit prior to inserting it into and pulling it through the second conduit, is unnecessary. This simplifies immensely the cable laying process and in particular, is expected to reduce considerably, the hours spent laying fibre optic cable and the number of personnel needed for that purpose. As an example, the time spent laying fibre optic cable has been reduced in some installations by 25%, while the number of personnel needed to lay a cable of some 1.5 km in length, can be reduced from 6 to 2.

The roller means of the invention can include a single roller, but in a preferred arrangement, two rollers are provided. In the single roller arrangement, it is preferred that the maximum bend applied to the cable is of approximately 45° and therefore, for a 90° bend, a second of the single roller devices is preferable, positioned adjacent the inlet of the second conduit, so that the cable can engage and be guided by the roller of the second device a further 45°. The use of two of these single roller devices is appropriate for relatively large pits, such as those formed in concrete and measuring approximately 1200mm x 450mm in plan cross-section. However, the invention also extends to a twin roller device in which a first roller is positioned in use adjacent the outlet of a conduit and the second roller is spaced forward of the first roller, away from the conduit outlet, but with its axis of rotation displaced toward the inlet of the second conduit. In this latter arrangement, cable egressing from the first conduit first engages and is guided by the first roller and then engages and is guided by the second roller. The cable is thus bent the amount required for insertion into the inlet of the second conduit.

The invention is not limited to roller means having single or twin roller arrangements, but can have any suitable number of rollers appropriate to create the angular cable bend required, in a manner that will not damage the cable. The invention is moreover not limited to bends of 90°, but can be applied as desirable to bends of lesser or greater degree, as long as the bend is greater than that which would damage the cable as hereinbefore described.

The attached drawings show example embodiments of the invention of the foregoing kind. The particularity of those drawings and the associated description does not supersede the generality of the preceding broad description of the invention.

Figure 1 shows a side cross-sectional view of a fibre optic cable laying device according to one embodiment of the present invention. Figure 2 shows an end view of the device of Figure 1. Figure 3 shows a side view of the device of Figure 1.

Figure 4 illustrates the use of the device of Figure 1 in a below ground pit. Figure 5 shows a side cross-sectional view of a fibre optic cable laying device according to a second embodiment of the present invention. Figure 6 shows a side view of the device of Figure 5. Figure 7 shows an end view of the device of Figure 5.

Figure 8 illustrates the use of the device of Figure 5 in a below ground pit. Figure 9 shows a side cross-sectional view of a fibre optic cable laying device according to a third embodiment of the present invention.

Figure 10 shows a side cross-sectional view of a fibre optic cable laying device according to a fourth embodiment of the present invention.

Figures 1 to 3 show side, end and plan views respectively of a device 10 according to the invention.

The device 10 includes roller means 11 comprising a roller 12 which is rotatably mounted on a shaft 13 that extends in engagement with a pair of arms 14. The roller 12 is preferably mounted to the shaft 13 through a needle roller bearing, although other suitable bearings may be appropriate. Preferably, however, the bearing is such as to permit free rotation of the roller 12.

The roller 12 is symmetrical about a central axis perpendicular to the axis of rotation AA, and defines a central channel 15. The channel 15 can have any suitable dimensions and is preferably of a depth suitable to locate a fibre optic cable therewithin for guiding purposes. The arms 14 are attached in any suitable manner to a tube 16. That attachment can be made by welding, particularly if both the arms 14 and the tube 16 are metallic, although if other materials such as plastic are employed for these components, the arms 14 may be otherwise connected to the tube, such as by an adhesive. The tube 16 is formed of an external diameter to be a snug friction fit within the end of a cable conduit through which a cable is to be pulled.

Cable conduits can vary in diameter and therefore the tube 16 can be of any suitable diameter to fit a particular conduit. In one arrangement, the tube 16 may be releasably fixed to the arms 14, so that the tube can be replaced as necessary with a tube of different diameter to suit a different conduit.

Alternatively, the tube 16 may be arranged to accept a collar or range of collars, which are either of greater or smaller radius. Thus, if the tube 16 was not of a radius suitable to be accepted in a friction fit within the end of the cable conduit, a collar may be fitted to the tube 16 so as to adapt the device to the particular conduit involved in the cable pull.

The tube 16 may be pushed into the open end of a conduit and by friction engagement, position the roller means 11 adjacent that open end. This is a convenient and quick method of aligning the roller means 11 , although clearly other arrangements could be adopted to achieve the same result. For example, the tube 16 may be of an internal diameter approximately equal to the external diameter of the conduit, so that the tube may be fitted to the outside surface of the conduit. Still alternatively, suitable clamping means may be employed to clamp the roller means 11 into position, or the device may be otherwise fitted, such as by suitable fasteners or brackets, and each of these arrangements is within the scope of the present invention.

The tube 16 includes a lengthwise slot 17 that extends from one open end thereof to the other. The slot 17 is provided, so that cables within a conduit can be received within the tube while the tube is fixed within the conduit and can thereafter be removed from the tube 16 when the cable laying operation is complete. The slot 17 also permits the rope which is used to pull a cable through the conduit, to be received within the tube 16. Figure 1 shows in cross- section, the open end of a conduit 18 within which the tube 16 has been fitted. The device 10 further includes guide means in the form of a guide 19 that is fixed by any suitable means to one of the pair of arms 14. The guide 19 extends from the respective arm 14 and across the roller 12 to a position adjacent the other of the arms 14. The guide 19 is arranged to extend over the path of a cable which extends through the conduit 18 and into engagement with the roller 12, so that movement of the cable away from the roller 12 is resisted. This arrangement is most clearly shown in Figure 1 in which a length of cable 20 is shown extending through the tube 16 and the conduit 18, within the guide 19 and into engagement with the channel 15 of the roller 12. In Figure 1 , the cable 20 extends at an approximate angle 45° away from the roller 12 and toward a second conduit which is fitted into a cable pit. The guide 19 is fixed only to one of the arms 14, so that a cable which passes between the guide 19 and the roller 12, can be removed through the gap existing between those two components when the cable pulling operation is complete. Therefore, the floating free end 21 of the guide 19 permits such removal.

Figure 4 illustrates the use of the invention in a cable pit 22. Cable pits can be of any particular dimension, although a common size of pit in Australia measures 1200mm long x 450 mm wide x 900 mm deep. As shown in Figure 4, the cable pit 22 includes conduits 23 and 24 opening into the pit 22 at an angle of 90° to each other. In normal circumstances, the cable 25 would be pulled to its maximum extent through the conduit 23 and the length of cable 25 to be inserted and pulled through the cable 24 would be laid upon the ground above the pit 22. By employing devices 10 according to the invention, the cable 25 can be gradually bent in two angles of 45° without any damage occurring to the cable 25, so that the cable can be inserted directly into the conduit 24 and pulled therethrough.

An alternative embodiment of the invention is shown in Figures 5 to 7. Several of the parts of the device 30 correspond with parts of the device 10 and for those parts, like numerals are maintained. In the device 30, the roller means 31 , includes a pair of rollers 32 and 33. The rollers can have any suitable form and in Figures 5 to 7, they have an identical form to the roller 12 shown in Figures 1 to 3. Thus, each of the rollers 32 and 33 includes a roller needle bearing mounted on a respective shaft 32a and 33a each of which is attached between a pair of arms 34 that are attached in any suitable manner to the tube 16. As shown, each of the arms 34 is comprised of a first section 35 which extends substantially in a longitudinal direction of the tube 16, and a second section 36 depending from the first section 35 which extends at an approximate angle of 45° relative to the first section 35. As shown in Figure 5, the first and second arm sections 35 and 36 are fixed at the 45° angle to each other. In an alternative embodiment, the second arm section 36 may be adjustably fixed to the first arm section 35, so that the angle between the first and second sections is adjustable in the direction A. Advantageously, this facilitates optimum placement of the rollers of the device 30 within a pit relative to the position of the conduits of the pit. Thus, in the event that the first and second conduits are disposed at an angle less or greater than 90°, the arms 34 can be adjusted as necessary to provide the most appropriate support for the fibre optic cable. Associated with each of the rollers 32 and 33 are guide means in the form of guides 37 and 38 through which a cable 20 extends in a cable laying operation. As with the guide 19 of Figures 1 to 3, each of the guides 37 and 38 is attached to only one of the pair of arms 34 and extends across the path of the cable 20 to a position spaced from the other of the arms 34. In the same manner as that shown in Figures 1 to 3, the cable 20 is guided by the guides 37 and 38 about the rollers 32 and 33 but can be released therefrom past the floating free end thereof.

As shown in Figure 5, the cable 20 experiences a full 90° bend about the pair of rollers 32 and 33. This is also shown in Figure 8 in which a pit 39, which is of smaller dimensions than the pit 22 shown in Figure 4, includes a device 30 for bending a cable between a pair of conduits 40 and 41. In the Figure 8 illustration, a cable 42 extends through the conduit 40 and into engagement successively with the rollers 32 and 33 before entering the opening of the conduit 41 and extending therethrough. In the Figure 8 arrangement, a pair of single roller devices 10 could equally have been employed in the open end of each of the conduits 40 and 41 , but the Figure 8 illustration shows that the alternative embodiment of the device 30 has the same effect as the deployment of two single roller devices 10. The device 30 has particular application in pits which are smaller to that of the pit 22.

Referring back to Figure 6, the tube 16 can include one or more (two are shown) openings 43, which facilitate the use of ties to tie back existing cables within a conduit to which the device 30 is fitted, when a new cable is being pulled through that conduit. The ties can have any suitable form and are looped around the existing cables and fixed through one or both of the openings 43, to clear a path for the new cable being pulled through the conduit. The openings can equally be applied to the tube 16 shown in Figures 1 to 3. Figure 9 is a substantially identical drawing to Figure 1 with the exception that the arm 14 of the device 100, includes an additional right-angle portion 43 which permits adjustment of the position of the roller 12. Thus, the roller 12 can be moved from the position shown, outwardly toward the free end of the right angle portion 43 by removal of the shaft 13 and reinsertion of the shaft 13 into one of the other openings 44, 45 or 46. This permits the cable 20 to be drawn through the conduit 18 closer to the side wall, than the position shown in Figure 1. This is an advantage, when the conduit starts to become full of fibre optic cable.

Figure 10 shows still a further arrangement and again, parts of this arrangement which are identical to those shown in Figure 1 , retain the same reference numerals. In Figure 9, the arm 47 is pivotably attached to the tube 16, by a pivot bracket 48. This permits the arm to rotate in the direction B when the cable 20 is being pulled through the conduit 18 and tension in the cable increases. Thus, by rotation of the arm 47, the cable tension can be alleviated. Biasing means in the form of a spring steel biasing plate 49 resist the arm 47 rotating, while a meter 50 indicates the increase in tension in the cable as the arm 47 rotates. Accordingly, when a cable is being pulled through the conduit 18, a person positioned in the pit in which the device 10 is installed, can monitor the cable tension by the meter 50 and by communicating with the cable winch operators can holt cable pulling when the tension reaches a dangerous level. Alternatively, the meter 50 may be electronically monitored by the cable winch operator or by other appropriate personnel to ensure that the cable 20 is not subject to excessive tension.

The devices according to the invention are advantageous in use in the field as they permit a cable to be pulled through a first conduit and fed directly into and pulled through a second conduit without damaging the cable. This is achieved, by carefully choosing the radius of the rollers of the device so that a gradual change in direction of the cable occurs. Use of the device results in substantial cost savings, by virtue of reduced cable laying time and personnel requirements. The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description.

Claims

CLAIMS:

1. A cable laying device for laying fibre optic cable between a pair of cable conduits which open into a below ground pit, said device including roller means having a rotatable roller of a radius which is greater than the radius of a bend that would cause damage to a fibre optic cable being laid and mounting means for mounting said device within said pit, said mounting means being so arranged that in use, said roller is positioned adjacent the opening into the pit of a first of the pair of conduits from which the cable is pulled during cable laying, said cable in use being guided about a portion of said roller and toward the opening of a second of the pair of conduits and into which the fibre optic cable is to be inserted.

2. A device according to claim 1 , said first and second conduits being disposed at an angle of about 90°.

3. A device according to claim 1 or 2, said roller means including two rollers which are spaced apart in substantially the same plane and rotate about substantially parallel axes, such that in use, a cable being laid extends about a portion of a first of said rollers and then about a portion of a second of said rollers prior to entry of said cable into said second conduit.

4. A device according to claim 3, such that said cable is bent about 45° about each of said rollers.

5. A device according to claim 3 or 4, said second roller being disposed adjacent the opening of said second conduit.

6. A device according to any one of claims 1 to 5, said mounting means including clamping means for clamping engagement with said first conduit.

7. A device according to any one of claims 1 to 5, said device being attached to a wall of said pit.

8. A device according to any one of claims 1 to 5, said mounting means including an arm or arms extending from a shaft about which said roller is rotatable and being connected to a tube which facilitates mounting of said device within said pit by receipt of an end of said tube in frictional engagement within said first conduit.

9. A device according to claim 8, said tube being releasably connected to the or each said arm.

10. A device according to claims 8 or 9, said tube including a lengthwise slot which permits insertion and removal of the tube from about the cable being laid.

11. A device according to any one of claims 8 to 10, and including cable guide means fixed to one of the or each said arm and extending across said roller, said guide means being spaced from said roller to permit a cable being laid to extend between said roller and said guide means, but said guide means in use resisting movement of said cable away from said roller.

12. A device according to any one of claims 8 to 11 when dependent on claim 3, each of said rollers being rotatable about a respective shaft and the or each said arm extending from each of said shafts, the or each said arm being formed in two arm sections, a first arm section extending between said tube and the shaft of said first roller, and a second arm section extending between said shaft of said first roller and said shaft of said second roller, said respective arm sections being disposed at angle to each other.

13. A device according to claim 12, said arm sections being disposed at 45° to each other.

14. A device according to claim 12, said arm sections being angularly adjustable relative to one another.

15. A device according to any one of claims 12 to 14, cable guide means being associated with each of said rollers, each of said guide means being fixed to a respective arm section and extending across said roller, said guide means being spaced from said roller to permit a cable being laid to extend between said roller and said guide means, but said guide means in use resisting movement of said cable away from said respective roller.

16. A device according to any preceding claim, said roller being adjustable on an arm laterally to the longitudinal axis of said conduit.

17. A device according to any preceding claim, said roller means being mounted for pivotal movement to pivot as tension increases in said cable, and so reduce said cable tension, biasing means being associated with said roller means to resist pivotal movement, a tension measuring meter being provided to measure tension in said cable so that said cable tension can be maintained below a maximum level.

18. A method of laying a cable which employs a fibre optic cable laying device of any preceding claim, said method including mounting said device within a below ground pit which includes a pair of cable conduits opening thereinto, pulling a cable through a first conduit, about said roller or rollers of said cable laying device connected adjacent to said first conduit and inserting said cable into said second conduit.

19. A method according to claim 18, said method including connecting a second cable laying device according to any one of claims 1 to 17 to said second conduit, and extending said cable about said second cable laying device prior to inserting said cable into said second conduit.