Removing a core of a cable

Abstract

A method of removing a core of a cable is described. The cable comprises a sheath surrounding the core. The method comprising the step of applying a time varying tensile force to the core to extract the core from the sheath. The time varying tensile force causes a particular pattern of deformation and movement of the core within the sheath which makes it possible to remove a greater length of core.

Description

REMOVING A CORE OF A CABLE

[0001] The present disclosure relates to removing cores of cables, including but not limited to removing cores from armoured telecommunications cables underground between end user premises and footway boxes.BACKGROUND

[0002] In the United Kingdom, there are approximately 8 million domestic premises which are connected to telecommunications services using direct in ground armoured cable such as armoured copper cable. In areas where there is direct in ground armoured cable it is necessary to dig and replace the cable with a duct or tube into which a fibre cable is installed to deliver fibre to the premise which is highly labour and cost intensive. Armoured cable is not only found feeding individual premises from the main cable route (for example from a footway box to the property) but may also be used in other locations within the telecommunications access network (for example between footway boxes).

[0003] Many telecommunications networks, in the UK and elsewhere, are deploying a new optical fibre access network (e.g. Fibre to the Premises) to replace an existing copperbased access network. The new optical fibre connections are typically deployed by running new optical fibre cables to each dwelling in the network. It is desirable to reduce the cost and complexity of deploying these new optical fibre cables.

[0004] It has previously been proposed that the (copper) core of the cable could be extracted from its sheath under tension, and a new (optical) cable passed through instead. However, there are limitations to the length of core which can be extracted in this way using known techniques. Previously proposed mechanisms to reduce the static friction of the core within the cable include heating the cable and pumping in a gas or liquid.

[0005] The examples described herein are not limited to examples which solve problems mentioned in this background section.SUMMARY

[0006] Examples of preferred aspects and embodiments of the invention are as set out in the accompanying independent and dependent claims.

[0007] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0008] According to a first aspect there is a method of removing a core of a cable, the cable comprising a sheath surrounding the core, the method comprising the steps of: applying a time varying tensile force to the core to extract the core from the sheath.

[0009] The time varying tensile force causes a particular pattern of deformation and movement of the core within the sheath which makes it possible to remove a greater length of core.BT REF: A36191

[0010] The time varying tensile force may comprise a pulsed component. It may also comprise a progressively increasing component in addition to the pulsed component.

[0011] The method may comprise setting one or more parameters of the time varying tensile force.

[0012] The one or more parameters may comprise one or more of an amplitude, a frequency and a duty cycle of the pulsed component of the time varying tensile force.

[0013] The method may comprise detecting an extraction distance and / or an extraction rate of the core from the sheath, wherein one or more parameters of the time varying tensile force are set in dependence on the detection.

[0014] The method may comprise detecting a degree of correlation between changes in the detected extraction distance and / or extraction rate of the core from the sheath with changes in the amount of torque being applied, and setting the one or more parameters of the time varying tensile force in dependence on the determined degree of correlation.

[0015] The tensile force may be applied by rotation of a winch. The extraction distance and / or extraction rate may in this case detected by determining an amount or rate of rotation of the winch. The winch may comprise a stepper motor or a servo motor.

[0016] The step of extracting the core from the sheath may by application of a pulsed tensile force in a first phase, and the method may further comprise the steps of:detecting an extraction distance of the core from the sheath in the first phase; and in a second phase, subsequent to the first phase, extracting the core from the sheath by application of the pulsed tensile force, wherein a magnitude of the pulsed tensile force in the second phase is based on the detected extraction distance of the core from the sheath in the first phase

[0017] The method may further comprise the steps of:detecting a stretch of the core in the first phase,wherein the magnitude of the pulsed tensile force in the second phase is based on the detected extraction distance of the core from the sheath in the first phase and the detected stretch of the core in the first phase.

[0018] According to a second aspect there is an apparatus for removing a core of a cable, the cable comprising a sheath surrounding the core, the apparatus comprising:an extraction device for attachment to the core of the cable, and for applying a tensile force to the attached core; anda controller, for controlling the extraction device to apply a time varying tensile force to the core to extract the core from the sheath.

[0019] The extraction device may be, or comprise, a winch. The winch may comprise a stepper motor or a servo motor. Alternatively, the extraction device may be any other device capable of engaging with, or gripping, one end of the core, and of applying aBT REF: A36091 2(controlled) tensile force to the gripped end. For example, a pulley system, or a grip hoist could be used instead.

[0020] It will also be apparent to anyone of ordinary skill in the art, that some of the preferred features indicated above as preferable in the context of one of the aspects of the disclosed technology indicated may replace one or more preferred features of other ones of the preferred aspects of the disclosed technology. Such apparent combinations are not explicitly listed above under each such possible additional aspect for the sake of conciseness.

[0021] Other examples will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the disclosed technology.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic diagram of customer premises and a footway box;

[0023] FIG. 2 shows an armoured cable with an exposed core at one end;

[0024] FIG. 3 is a schematic diagram of a winch being used to extract a core from an armoured cable;

[0025] FIG. 4 is a flow diagram of a method of extracting a core from an armoured cable and optionally inserting an optic fibre;

[0026] FIG. 5 is a schematic diagram of a winch being controlled by a motor driver to extract a core from an armoured cable;

[0027] FIG. 6 is a schematic illustration of how a pulsed tensile force can be used to more effectively extract a core from an armoured cable;

[0028] FIG. 7 is a graph indicating how an electric motor can ramp up the tension with incremental pulses until the cable starts to move; and

[0029] FIG. 8 is a schematic flow diagram of a a control method for controlling the tensile force.

[0030] The accompanying drawings illustrate various examples. The skilled person will appreciate that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the drawings represent one example of the boundaries. It may be that in some examples, one element may be designed as multiple elements or that multiple elements may be designed as one element. Common reference numerals are used throughout the figures, where appropriate, to indicate similar features.DETAILED DESCRIPTION

[0031] The following description is made for the purpose of illustrating the general principles of the present technology and is not meant to limit the inventive concepts claimed herein. As will be apparent to anyone of ordinary skill in the art, one or more or all of the particular features described herein in the context of one embodiment are also present in some other embodiment(s) and / or can be used in combination with otherBT REF: A36091 3described features in various possible combinations and permutations in some other embodiment(s).

[0032] The present technology aims to reduce excavation by repurposing direct in-ground armoured copper telecommunications cable as a tube for new optic fibre cables by pulling out a cable core and leaving the rest of the cable in situ. This leaves an empty armoured tube which can be repurposed as a tube or duct which can be used to support the deployment of a fibre cable.

[0033] In various examples, an existing copper cable in a telecommunications network is partially repurposed for deploying a new optical fibre connection. An existing copper cable in a telecommunications network typically comprises a copper core, an inner sheath, metal armouring around the inner sheath and an outer sheath. Various examples provide a device configured to remove the copper core of the existing cable, such that a new optical fibre core / cable may be inserted into the hollowed sheath of the existing cable. The device comprises a housing with an aperture and a winch, the aperture having a diameter greater than the inner sheath and copper core but less than the metal armouring. The existing copper cable may be stripped to expose a copper core section, and the copper core section may be inserted through the aperture and clamped to the winch. As the winch is operated, the metal armouring pushes against the housing as the copper core is extracted through the aperture. The device therefore generates a winching force without having to clamp another section of the existing cable, enabling the device to be used in more restricted environments, such as a footway box.

[0034] FIG. 1 is a schematic diagram of customer premises 100 such as a house and a footway box 104. In the example of FIG. 1 the house is on a street where there are a plurality of houses. The street has a footway 102 or pavement in which there are one or more footway boxes 104. A footway box 104 is a rectangular pit in the ground which has a cover. Within the footway box it is possible for an engineer to access underground cables 108 that travel under the ground from the customer premises 100 to the footway box and from the footway box connect to a telecommunications network 106.

[0035] In order to replace legacy copper cables 108 between the customer premises 100 and the footway box 104 it may be necessary to dig up the copper cables where these are buried underground or dig a new trench to lay a new duct or tube within which an optic fibre cable can be installed. However, excavation is time consuming, expensive and error prone. Another option is to leave the legacy cables in place and add optic fibre cables over ground. However, this leaves the optic fibre cables exposed to the elements and damage. Therefore it is beneficial to bury the optic fibre cables although doing so is expensive.

[0036] The armoured cable of the examples described herein is as explained with reference to FIG. 2.BT REF: A36091 4

[0037] FIG. 2 shows an armoured cable with an exposed core at one end. The exposed core comprises multiple copper wires 200 where each individual copper wire is in an insulating sheath. The copper wires are held within a paper wrapping 201 in an inner sheath 206. Around the copper wires 200 within the paper wrapping 201 it is filled with lubricant such as petroleum jelly . Surrounding the inner sheath 202 are armouring wires 204 which are steel or other hard metal and run generally parallel to a longitudinal axis of the cable. The armouring wires 204 are held by an outer sheath 206 which is plastic. The outer sheath 206 may be polyethylene or poly vinyl chloride (PVC). The armouring wires 204 may be galvanised steel wire armouring. The inner sheath 202 may be polyethylene. The inner sheath 202 may be lubricant (e.g. petroleum jelly or grease) filled and hold copper core telephone wires 200. The cable comes in 2 pair, 5 pair, 10 pair, 20 pair, 50 pair, 100 pair, 200 pair and 300 pair.

[0038] FIG. 3 is a schematic diagram of a winch being used to extract a core 200 from an armoured cable. The winch has a winch body 300 having a wall 304 containing an aperture into which an inner sheath of an end of the armoured cable is press fit. Armouring wires of the cable splay away from the cable and are bent away from the winch body. The armouring wires abut the wall 304 of the winch body. An outer sheath of the armoured cable also abuts the wall 304 of the winch body 300. The diameter of the outer sheath is larger than a diameter of the aperture. The diameter of the collection of armouring wires around the inner sheath is also larger than a diameter of the aperture.

[0039] The winch comprises a spool 302 to which a core of the armoured cable is attached in any suitable manner. The winch comprises one or more gears to facilitate winding of the spool in order to pull the core 200 of the armoured cable out leaving the inner sheath 202, armouring wires 204 and outer sheath 206 in situ in the ground and / or abutting the wall 304.

[0040] Using a winch to pull the conductors from the core of an armoured cable is facilitated where they were originally manufactured to be in a lubricating jelly leaving the outer sheath, armouring and inner sheath forming a tube into which a new fibre optic cable can be inserted saving the need for digging up and replacing the copper cable with a fibre cable.

[0041] In some examples, a bundle of lubricated copper wires can be easily and tool- lessly wound in a figure of eight manner to a clamping plate that is designed to be inserted in a cut out in the winch spool. This gives sufficient grip to the cable cores to enable them to then be pulled out.

[0042] There is no need to pressurise the cable to expand it and then inject lubrication.Pressurising the cable is expensive and time consuming. It can also damage the armouring and / or inner and outer sheaths. There is no need to heat the core to helpBT REF: A36091 5remove it. Heating the core is error prone, expensive and difficult where cables are underground.

[0043] Because of the strength of the armouring wires it is possible to “pull against” these to achieve extraction of the core. The armouring wires press against a body of the winch so that there is no need for additional clamping of the outer sheath of the cable.

[0044] FIG. 4 is a flow diagram of a method of extracting a core from an armoured cable and optionally inserting an optic fibre. An engineer opens a footway box and locates a legacy armoured cable entering the footway box from a domestic or other customer premises. The engineer strips back 400 an end of the legacy cable to expose armouring and to expose a core of the legacy cable comprising, for example, copper pairs. The engineer places 402 an inner sheath of the exposed end of the legacy cable into an aperture of a winch. The inner sheath is press fit into the aperture in some cases. Armouring wires and an outer sheath of the cable remain outside the body of the winch as explained with reference to FIG. 3. The armouring wires and outer sheath abut against an outer wall 304 of the winch body so there is no need for a tool or clamp to hold the armouring wires and outer sheath. The aperture is large enough for the inner sheath to pass through but small enough to stop the armouring and outer sheath to pass through so that they can be used to apply the winching force against so that the outer of the cable does not have to be held or clamped in any other way.

[0045] The engineer winds 404 the exposed core of the end of the legacy cable around a plate and presses the plate into a recess in a spool of the winch. The spool may be serrated in order to provide additional grip of the core of the cable. In some cases the core is wound around the plate.

[0046] The winch mechanism is suspended from above (or below) within a footway box at the same height that the armoured cable enters the footway box so as not to cause any ‘lift’ to the box frame or ground whilst the core is being extracted.

[0047] The spool of the winch is rotated 406, either manually or using a motor or a hybrid of manual and motor. As the spool rotates the core of the legacy armoured cable is drawn out of the outer sheath, armouring and inner sheath. Where the core is surrounded by petroleum jelly or grease, pulling out of the core is facilitated since friction between the core and the rest of the cable is reduced. The core winds onto the spool and the engineer is able to judge, by assessing the amount of core on the spool, when to stop winding. In some cases the engineer continues winding until a second end of the core becomes visible or until the core becomes slack.

[0048] The engineer is optionally able to insert an optic fibre into the inner sheath that remains in situ. The empty armoured sheath can be repurposed as a tube or duct and fibre placed 408 through the coreless centre. In some examples optic fibre is pushed into the inner sheath, after the core has been removed, from the footway box to the customerBT REF: A36091 6premises or vice versa. The optical fibre at the customer premises is spliced 410 into a customer splice point. At the footway box the other end of the optic fibre is connected to the optic fibre network, this may be via a connectorised block terminal CBT.

[0049] In other examples, the optical fibre is connected to the legacy cable core in the customer premises. As the legacy core is drawn out of the armoured cable into the footway box, the optic fibre is pulled into the inner sheath of the armoured cable until eventually the optic fibre reaches the footway box. The optic fibre is joined to a customer splice point at the customer premises and to the optic fibre network in the footway box.

[0050] The technique described with reference to Figures 1 to 4 seeks to remove the cores of armoured cables (i.e. the bundles of twisted plastic-coated copper pairs which are encased in a reinforced sheath) which have been directly buried underground between end user premises and footway boxes. Smaller optical fibre cables can be attached to the copper bundles as they are removed, thereby installing the new technology of broadband fibre access whilst removing the old copper technology. This will incur lower cost, delay and disruption than a new dig. The reinforced sheath is fixed with a clamp and uses a winch to draw out the bundle of twisted copper pairs under tension. Using this technique, more force is required to pull out a greater length of wire bundle, which puts the wires under greater tension. When attempting to extract longer lengths of wire bundle, the contact area between the wire bundle and the sheath increases proportionally and so does the force needed to overcome the static friction. Experiments with armoured cables have shown that over 4 metres can reliably be pulled out and there have been successful tests up to 7m, but beyond that the bundled wires tend to snap. If the cable was originally laid with bends and twists and was then backfilled with soil and aggregate, then pulling on the cable causes kinks and it will break at a shorter length. When individual pairs or single wires are pulled, the critical force to overcome static friction is greater than the tensile strength of the wires and they break before sufficient tension can be applied to extract the wires. Typical cables can be 5-pair or 2-pair. 5-pair cable construction is different to the 2- pair: The 5-pair is grease-filled whereas the 2-pair is not and is wrapped in a wax paper. Overall, the 5-pair has higher copper content whereas 2 pair has less which means the collective tensile strength is more. When pulling 2-pair bundles versus 5-pair bundles, the 2-pair bundle is weaker and so only shorter lengths can be pulled with smaller wire bundles.

[0051] The present technique described below builds on the baseline methodology described above to increase the length of wire bundle that can be pulled out of the buried armoured cable. The wires within the sheath have multiple distributed resistive points of contact with the sheath along the whole length. This means that when applying a slowly increasing tension, the tension applied to the wire bundle at the winch is also the tension on the wires at the clamp point, but the tension on the wires within the sheath decreasesBT REF: A36091 7further back from the clamp point due to the distributed resistance of the sheath. This is the reason that the wires tend to break at the clamp point, since that is the point of maximum tension where wire deformation is the greatest. This is also the reason that the free end of the wire bundle at the far end of the sheath does not initially move, since it does not experience any tension from the winch.

[0052] The following technique exploits the elasticity of the wire bundle by pulsing the tension applied by the winch to progressively stretch small sections of the wire bundle. The wires take time to deform in response to a time-varying applied tension, so applying high tension for a short duration locally only causes a small short-lived deformation. At the point of maximum tension (initially around the clamp point), each short section of wire bundle will briefly thin and stretch forward, moving outwards and over the local points of contact with the sheath, before returning to its normal length and thickness. By returning to its normal length, a short section of the bundle further back within the sheath will now be the new point of maximum tension and the thin-and-stretch process will repeat. In this way, applying short duration pulses of high tension to the wire bundle at the winch will send microscopic deformations backwards along the wires within the sheath, overcoming local points of contact and then making new ones. In this way, a time-varying tension with suitable frequency / amplitude / pulse width can extract a longer length of wire bundle from a buried armoured cable than by using a steady increase of tension.

[0053] Microscopic forces cause surfaces to stick together and friction is the force necessary to tear the adhering surfaces apart. Amontons’ three laws of dry friction were published in 1699. Amontons presented the nature of friction in terms of surface irregularities and the force required to oppose the force pressing the surfaces together. Coulomb found that Amontons’ laws, as well as the independence of the coefficient of friction on velocity, normal force, contact area and roughness are only a very rough approximation. Due to the messy and variable manufacture of Direct-In-Ground (DIG) telecoms cables, there is limited value in considering idealised models of friction in this use-case.

[0054] The modern engineering discipline of tribology considers the friction and wear of materials. Contact between surfaces occurs only at certain points, called asperities. Frictional force originates at these asperities. These only cover a very small fraction of the total surface area. Frictional forces originate due to the interlocking of asperities because, in order for the surfaces to move relative to each other, asperities must deform and / or fracture, and adhesive forces must be overcome. Adhesive forces which develop at asperity contacts and deformation forces which are needed to plough the asperities of the harder surface through the softer surface are both important. Adhesion arises from the attractive forces which are assumed to operate at asperities. Ploughing forces arise since asperities will deform when the surfaces move relative to one another.BT REF: A36091 8

[0055] Ductile materials are easily stretched into wires and deform under tension. Brittle materials break rather than stretch and fracture under tension. Both the metal and the polyethylene of a twisted pair are clearly ductile materials so will stretch under tension until they thin and break. When a material is deformed under tension, it undergoes internal changes. The elasticity of a material refers to its ability to return to its original shape after deformation when the tension causing it is removed. Similar to a spring, a polyethylene- coated copper wire will be elastic at a low tension, but will be permanently deformed at a medium tension and will break at a high tension. The relative terms “low”, “medium” and “high” in this case refer to the tensions under the wire bundle are elastically deformed, inelastically deformed and break, so the values will be specific to each different cable.

[0056] The wire bundle within the sheath has multiple distributed points of contact (asperities) with the sheath throughout its length. Each point of contact will resist the motion of the wires at that point, so there is a distributed resistance to motion along the cable. If the wire bundle is under very low tension and no part of it deforms, then the whole wire bundle can only move as a single undeformed mass relative to the sheath. This means the wire bundle will experience the maximum cumulative frictional force from the whole sheath. So a very low tension can only overcome the frictional forces from a very short length of sheath.

[0057] If the wire bundle were only held fixed at one end and nowhere else, applying a tension at the free end would place the whole wire bundle under the same tension and all parts of the wire bundle would deform in the same way. However a wire bundle within a sheath is being held fixed in a distributed manner along its whole length, so the tension on the wires applied at the free end is progressively reduced further back along the sheath. Under medium applied tension, the wires at the clamp point will start to deform while the wires at the far end of the sheath only experience low tension. The limiting length of sheath from which the wire bundle can be pulled occurs when the near-end tension reaches breaking point before the reduced far-end tension is sufficiently high to overcome the remaining frictional forces.

[0058] The manner in which the present technique addresses these frictional considerations is described with reference to Figure 5. Consider a helical spring (analogous to the core) disposed within a tight-fitting rough pipe (analogous to the sheath). This is represented as instance A in Figure 5. When a low tension is applied to one end of the spring, the first few rings near the pipe exit will deform and extend, moving over the roughness of the exit and popping out. This is represented as instance B in Figure 5. As those first few rings pop out, they compress forward and tension is then applied to the next few rings within the pipe. This is represented as instance C in Figure 5. These next few rings may then also deform and extend outwards themselves, but with slightly less force. This is represented as instance D in Figure 5. In this way, the spring will deformBT REF: A36091 9under tension for some distance into the pipe. Pulling too hard will permanently deform the spring and may break it. If instead of simply pulling harder, the applied tension is rapidly changed from low to medium, pulses of deformation (longitudinal waves) will travel back along the spring and these will attenuate with distance inside the pipe due to the distributed friction. No one part of the spring is then under tension for much time, but a significant length of spring is being deformed over time and moving over the internal roughness of the enclosing pipe.

[0059] In terms of its mechanical properties, the wire bundle with an armoured sheath is somewhat similar to the spring, and behaves similarly to that shown in Figure 5. Elasticity refers to deformation that springs back. Ductility refers to deformation that does not spring back. Ideally the wires should only be deformed elastically, since any permanent deformation will weaken the wires and this could result in the wire snapping.

[0060] The objective is to overcome the distributed friction inside the sheath by only elastically deforming a part of the wire bundle at any one moment. Pulsing the applied tension results in the point of maximum tension / deformation moving back along the wire bundle within the sheath, slightly stretching then compressing the wires, overcoming the resistance at each point and microscopically moving that part of wire forward.

[0061] Referring to Figure 6, a 12V stepper (or servo) motor 520 and controller 540 drive a winch 510 (powered by a 12V battery 530). Together, these elements are able to overlay a time-varying tension pulse with suitable frequency, amplitude and pulse width on to the free end of the wire bundle. In particular, the controller 540 is able to generate a control signal to ramp up the tension applied by the winch 510 to the bundle and overlay incremental pulses, while monitoring the motor rotation (as feedback from the stepper motor 520) as being indicative of an amount and / or rate of extraction and / or deformation of the core. Extraction may be distinguished from deformation based on a comparison of changes in applied torque with changes in rotational movement of the winch 510. That is, for a given amount or rate of rotation, an applied torque (or change in applied torque) above a predetermined threshold may be indicative of deformation, whereas an applied torque (or change in applied torque) below the predetermined threshold may be indicative of extraction. In some cases multiple thresholds may be used to cater for the fact that a combination of extraction and deformation may be occurring at the same time. In any case, it will be appreciated that deformation is undesirable, and so a determination that this is occurring preferably results in the applied tension being reduced (and / or increased more slowly).

[0062] The stepper motor 520 is able to move in precise discrete steps. The controller system (in this case embodied in the motor driver 540, but may be a separate controller, such as a suitably programmed data processing apparatus such as a computer, tablet, smartphone or dedicated device that sends electrical pulses to the motor driver 540, whichBT REF: A36091 10interprets these pulses and) sends a proportional voltage to the moto 520. The motor then moves in accurate and fixed angle increments. Stepper motors have maximum torque at low speeds. A servo motor could also be used.

[0063] The motor 520 does not need to rotate quickly since there is no need to pull out the wires rapidly, but it is preferably easy to control accurately and to deliver high torque at low speeds. Stepper motor controllers provide precise control over the position, speed, and torque of stepper motors in various applications.

[0064] Separately from the motor itself, gearing 515 provided in the winch 510 is used to set the size of step. Increasing the current applied to the motor 520 will increase the torque. The controller 540 can cause the motor to move forward and backward by a different amount of steps (e.g. 2 steps forward and 1 step back). The controller will also set the step frequency. Wire bundles have been shown to guide acoustic waves in the range 10kHz to 20kHz.

[0065] Stepper motors have a relatively long lifetime because they do not have brushes, which can be subject to wear and tear. However, stepper motors have a high current consumption which reduces energy efficiency and increases heat losses. The winch motor can therefore be powered from an engineer’s 12V car battery while on site to carry out the extraction.

[0066] Referring to Figure 7, it is shown here how the electric motor ramps up the tension with incremental pulses until the cable starts to move. Two lines are shown on the graph of Figure 7. The first “torque” indicates (right hand Y axis) the amount of torque being applied by the winch. As can be seen, this defines a constantly increasing baseline torque, superimposed on which are a large number of individual torque pulses (which cause the applied torque to be higher and / or lower than the baseline torque as a function of time). The applied torque may therefore be considered a time varying tensile force, with a first, gradually increasing component, and a second, pulsed component. The second line shown on Figure 7 is the wire position - in particular (as indicated on the left hand Y axis) the position of the end of the wire core. Four “stages” are represented on Figure 7: a first phase in which the pulsed tensile force is applied and there is no significant movement of the core, a second phase in which the pulsed tensile force continues to increase and there is elastic stretching of the core, but no extraction, a third phase in which the pulsed tensile force continues to increase, providing a “slip and stick” extraction effect as will be explained below, and a fourth phase in which the core moves freely from its sheath and the pulses in the force are discontinued and a static tensile force maintained. The X axis of Figure 7 is time. As can be seen, in the first phase the position of the core does not change (no movement), while in the second phase there is a small amount of movement due to stretching of the core. In the third phase, there is significant movement of the core (accelerated with respect to the second phase), due (preferably) to the core being pulledBT REF: A36091 11out of its sheath rather than being stretched, and in the fourth phase the rate of extraction increases again, as the core moves freely. As mentioned, feedback from the motor can be used to detect if the motor is rotating (yet), and hence deduce how the free end of the wire bundle is now moving.

[0067] When the motor current is increased briefly, the torque delivered by the motor will briefly increase. The wire will then stretch (somewhere along its length, ideally just a small amount, and far from breaking) and may also move as a whole a little out from the sheath. This is the second phase. The motor will rotate a little as the end of the wire wrapped around the winch moves forward.

[0068] Ideally the (slowly increasing) torque applied by the motor will reach a level where it is sufficient to slip the wire out as a whole, just occasionally being halted by sticking points which are then overcome by the regular incremental torque pulses producing small deformations (this is the third phase). In this case, the end of the wire will slip out a variable (small) distance during the lower torque period, stop at a sticking point, deform during the higher torque period until the sticking point is overcome, then the whole wire slips forward a little more during the lower torque period, and so on. Hence there will be a lurching movement, roughly synchronised with the torque pulses.

[0069] However, the regular incremental torque pulses may not be able to overcome the sticking points, so as the lower torque level keeps increasing the wire is only deforming in one place. There would be no lurching forward in position due to slippage, just the (tiny) stretching of the wire in direct proportion to the torque as it goes past the point it can recover elastically.

[0070] Correlating wire slippage with the pulse parameters can be used to identify the parameters that are most effective at slipping the wire bundle out of the cable.

[0071] There are a number of scenarios for which there may be distinct actions applied:

[0072] Firstly, a torque is applied to the motor but the motor does not rotate (such as in the first phase of Figure 7). The torque in this case does not exceed friction and does not stretch wire appreciably. As such, the torque needs to be increased.

[0073] Secondly, a torque is applied to the motor, the motor rotates, but the wire is not extracted from the sheath (i.e. the “extraction distance” is zero) such that the exposed wire is stretched (as in the second phase of Figure 7). Again, the torque does not exceed friction but does stretch wire. So, the torque needs to be raised, but in this case carefully (for example more slowly) as there is now a risk of breaking the wires.

[0074] Thirdly, a torque is applied to the motor, the motor rotates, and the wire’s extraction distance is less than an arc length of the motor’s rotation. Here, the applied torque does exceed friction briefly then wire hits another sticking point. Torque is now adequate to remove the wire in a “slip and stick” fashion, as per the third phase of Figure 7.BT REF: A36091 12

[0075] Fourthly, a torque is applied to the motor, the motor rotates, and the wire’s extraction distance is equal to the arc length of the motor’s rotation. Torque does exceed friction so then wire moves freely with motor, as per the fourth phase of Figure 7. Torque is adequate for smooth extraction and should not be increased

[0076] Referring to Figure 8, an example operational flow is shown. At a step 810 an initial torque is applied to the end of the core, to provide a tensile force to attempt to extract it. At steps 820 and 830, the torque and rotation of the motor are both measured, using feedback from the motor. At a step 840 it is determined whether or not, or how much, the motor has rotated (for example by comparison with a threshold). If the motor has not rotated at all (corresponding to phase 1 of Figure 7), the torque is increased at the step 850. If rotation is occurring, then at a step 860 it is determined whether the rotation corresponds to extraction or deformation (based, as indicated above, on the rate or amount of rotation compared with changes in torque). If the rotation is determined to corresponding to deformation, then the torque is increased at the step 850, but slowly, whereas if the rotation is determined to correspond to extraction, then the torque is maintained (to stabilise as per phase 4 of Figure 7). It will be appreciated that the movement of the cable may not always vary as consistently as shown in Figure 7. For example, sometimes the free movement may discontinue, and the core stick, returning the process to phase 3 of Figure 7, where the tension may be gradually increased further.

[0077] It will be appreciated that various parameters of the time varying tensile force may be specified. They may be specified once, based for example on known characteristics of the cable (such as its length, diameter, age, construction, whether lubricated), or may be specified dynamically based on feedback from the motor. Settable parameters may include amplitude, a frequency and a duty cycle / pulse length of the pulsed component of the time varying tensile force, or they may include a rate of increase (with respect to time for example) of the gradually increasing component of the tensile force. For example, the amplitude of the pulses, or the duration or frequency of the pulses, may be reduced where deformation of the core is detected. Alternatively, different parameters may be used for different phases of Figure 7.

[0001] Any reference to 'an' item refers to one or more of those items. The term 'comprising' is used herein to mean including the method blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and an apparatus may contain additional blocks or elements and a method may contain additional operations or elements. Furthermore, the blocks, elements and operations are themselves not impliedly closed.

[0002] The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. The arrows between boxes in the figures show one example sequence of method steps but are not intended to exclude otherBT REF: A36091 13sequences or the performance of multiple steps in parallel. Additionally, individual blocks may be deleted from any of the methods without departing from the spirit and scope of the subject matter described herein. Aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples without losing the effect sought. Where elements of the figures are shown connected by arrows, it will be appreciated that these arrows show just one example flow of communications (including data and control messages) between elements. The flow between elements may be in either direction or in both directions.

[0003] Where the description has explicitly disclosed in isolation some individual features, any apparent combination of two or more such features is considered also to be disclosed, to the extent that such features or combinations are apparent and capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.BT REF: A36091 14

Claims

CLAIMS1. A method of removing a core of a cable, the cable comprising a sheath surrounding the core, the method comprising the steps of:applying a time varying tensile force to the core to extract the core from the sheath.

2. A method as claimed in claim 1 , wherein the time varying tensile force comprises a pulsed component.

3. A method as claimed in claim 2, wherein the time varying tensile force comprises a progressively increasing component in addition to the pulsed component.

4. A method as claimed in any preceding claim, comprising setting one or more parameters of the time varying tensile force.

5. A method according to claim 4 as appendant on claim 2 or claim 3, wherein the one or more parameters comprise one or more of an amplitude, a frequency and a duty cycle of the pulsed component of the time varying tensile force.

6. A method as claimed in any preceding claim, comprising detecting an extraction distance and / or an extraction rate of the core from the sheath, wherein one or more parameters of the time varying tensile force are set in dependence on the detection.

7. A method as claimed in any claim 6, comprising detecting a degree of correlation between changes in the detected extraction distance and / or extraction rate of the core from the sheath with changes in the amount of torque being applied, and setting the one or more parameters of the time varying tensile force in dependence on the determined degree of correlation.

8. A method as claimed in any preceding claim, wherein the tensile force is applied by rotation of a winch.

9. A method as claimed in claim 8, wherein the winch comprises a stepper motor or a servo motor.

10. A method as claimed in claim 8 or 9 as appendant on claim 5 or claim 7, wherein the extraction distance and / or extraction rate are detected by determining an amount or rate of rotation of the winch.BT REF: A36091 1511. A method as claimed in any preceding claim, wherein the step of extracting the core from the sheath is by application of a pulsed tensile force in a first phase, and the method further comprises the steps of:detecting an extraction distance of the core from the sheath in the first phase; and in a second phase, subsequent to the first phase, extracting the core from the sheath by application of the pulsed tensile force, wherein a magnitude of the pulsed tensile force in the second phase is based on the detected extraction distance of the core from the sheath in the first phase.

12. A method as claimed in claim 11 , further comprising the steps of:detecting a stretch of the core in the first phase,wherein the magnitude of the pulsed tensile force in the second phase is based on the detected extraction distance of the core from the sheath in the first phase and the detected stretch of the core in the first phase.

13. An apparatus for removing a core of a cable, the cable comprising a sheath surrounding the core, the apparatus comprising:an extraction device for attachment to the core of the cable, and for applying a tensile force to the attached core; anda controller, for controlling the extraction device to apply a time varying tensile force to the core to extract the core from the sheath.

14. An apparatus as claimed in claim 13, wherein the extraction device is a winch.

15. An apparatus as claimed in claim 14, wherein the winch comprises a stepper motor or a servo motor.BT REF: A36091 16

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