GB2273970A - Rope-gripping device for pulley assembly - Google Patents

Abstract

A rope-gripping device without moving parts comprises: a pair of side-entry guides 2, 3 for entry and egress of a rope 5; between the said guides a pair of jamming cleats 4; and between said cleats a guide comprising a body 6 providing a surface having two grooves 8, 9 separated by a ridge 10, the shape of the ridge being such that a rope of suitably chosen size can be rolled over the ridge to pass from one of the said grooves to the other and the positions of the grooves being such that when the rope is taut between the said guides 2, 3 it is engaged with the said jamming cleats 4 when in one 9 of the said grooves and disengaged from them when in the other 8. The device is especially useful for incorporation in pulley assemblies for use in work on electric overhead lines, especially the replacement of earth wires (for example with earth wires incorporating optical fibres). <IMAGE>

Description

A Gripping Device for Ropes and the Like, Pulley Assemblies Incorporating it and the Use Thereof This invention relates firstly to a gripping device for ropes, cords, strings and other elongate members having a degree of compressibility (all hereinafter, where the context admits, included in the term "rope") that can be easily and quickly transferered between a condition in which the rope is guided but slides freely in the direction of its length and another condition in which the rope is gripped to inhibit such sliding.

Secondly, the invention includes pulley assemblies incorporating the gripping device, especially pulley assemblies suitable for use in installation or replacement of earth conductors or other lines in an overhead line installation for transmission of electric power and/or optical and/or electrical signals.

Thirdly, the invention icludes a method of installing or replacing such a line in which the said assembly is used.

In certain methods of installing or replacing such lines, it is a requirement to suspend from the existing line (in the case of replacement) or some kind of preinstalled catenary support (in the case of a new installation) a plurality of pulley assemblies through which the new or replacement line may be drawn into place before being finally positioned and secured at each of the towers or other supports of the installation.

To prevent such pulley assemblies from running to the lowest point of the existing line or catenary support, they must be appropriately spaced apart by a tension member, which is normally a rope. It is not practicable to affix the pulley assemblies to the rope at any time except when the rope is being payed out along the line from one of the supports of the installation. Since the rope may be several kilometres long and weigh a few tonnes and the pulley assemblies may be needed every 5-10 metres, it is highly desirable to be able to affix the pulley assemblies on the rope without stopping the movement of the rope.Given the working conditions that exist on such supports, this cannot reasonably be achieved with conventional affixing techniques involving knotting of the rope, and gripping devices using moving parts are generally too delicate to withstand the rough handling to which they will inevitably be exposed.

It is therefore an object of the invention to provide a rope-gripping device without moving parts that can be applied to an advancing rope without inhibiting the advance of the rope and then, when the rope reaches a chosen position, can be quickly and easily secured to the rope so as to advance with it thereafter.

In accordance with the invention, a rope-gripping device comprises: a pair of side-entry guides for enty and egress of a rope; between the said guides a pair of jamming cleats; and between said cleats a guide comprising a body providing a surface having two grooves separated by a ridge, the shape of the ridge being such that a rope of suitably chosen size can be rolled over the ridge to pass from one of the said grooves to the other and the positions of the grooves being such that when the rope is taut between the said guides it is engaged with the said jamming cleats when in one of the said grooves and disengaged from them when in the other.

Preferably the jamming cleats are of the kind in which the rope is gripped by being urged into engagement with jaws that taper in the longitudinal direction of the rope, and in such cases the two jamming cleats should face in opposite directions, so that any tendency for the rope to slip in either direction tightens the grip of one of them.

Preferably the surface forming the grooves and the rib is a generally convex surface; apart from the grooves and the rib, it is conveniently a part of a cylinder.

The pulley assembly in accordance with the invention will normally include at least a pair of pulleys, one pulley at the top for suspending the assembly from a first line and one at the bottom for suspending a second line from the assembly. Preferably, however, it includes two such pairs of pulleys so that the functions of the first and second lines may be exchanged by adjusting the relative tensions in the lines without turning the assembly over and without requiring a pulley to perform two functions. Preferably the assembly has a frame shaped to define two openings, one for passage of each of the two lines referred to, each opening having one pulley at the top and one at the bottom. Preferably the rope grip is located on the member separating the two openings, and preferably each opening is formed with a gate to allow side entry/exit of its line.

The pulley assembly in accordance with the invention may be used in a variety of different installation techniques, but is primarily intended for use in a process (the main procedural steps of which are known per se) for replacement of an existing line, more especially for replacing an existing earth conductor, for example with one incorporating optical fibres for communication purposes. When the dimensions and geometry of the overhead line installation permit, the work may be done with the power circuits live.

In this preferred process, a rope is gradually advanced along the earth wire by a pulling device (hereinafter a "tug") suspended from and gripping the earth wire, and as it advances, a plurality of pulley assemblies in accordance with the invention are suspended from the earth wire and secured to the rope at spaced intervals; a second rope is attached at its leading end to the tug (or to the first of the pulley assemblies) and is suspended from each of the pulley assemblies.After at least one complete span has been provided with pulley asemblies and ropes in this way, the second rope is used to pull a new length of earth wire into a position where it can be secured and electrically connected to the towers or other supports at each end of the span; the old earth wire can then be disconnected and its tension reduced so that (if it has not already done so) the new earth wire moves to its upper pulley in each pulley assembly, taking over the support function from the old earth wire which falls to its lower pulley and can subsequently be withdrawn against any suitable braking means.

The invention will be further described, by way of example, with reference to the accompanying drawings in which: Figures 1 and 2 are sketches of one form of gripping device in accordance with the invention, showing it respectively with a rope in disengaged and engaged positions; Figure 3 is a plan view of the device; and Figure4 is a sketch of a pulley assembly incorporating this device.

The device 1 comprises two side-entry rope guides 2,3 at its opposite ends, and between them two jamming cleats 4,4 of the kind comprising rigid jaws which taper in opposite directions, the narrow ends of the tapers being (in this case) towards respective ends of the device. Between the two cleats, the rope 5 engages a convex surface 6 which may form part of a structural tube 7. This surface 6 is shaped to form a first groove 8 and a second groove 9 in positions such that when the rope 5 (assumed pulled taut between the two guides 2,3) is in the first groove 8 it is disengaged from and above both of the cleats 4,4; whereas when it is in the second groove 9 it is drawn into the cleats and gripped by at least one of them.

Between the grooves 8,9 is a rib 10 which is smoothly rounded and so dimensioned that the rope may be rolled over it to transfer it from one groove to the other.

The preferred manual technique for so rolling it comprises gripping the device in the fingers of one hand and using the thumb of that hand to roll the rope into the required position.

Figure 4 shows a complete pulley block assembly in which the rope gripping device 1 of Figures 1-3 is mounted so that the structural tube 7 forms the upright structural dividing member between two openings 11,12.

These openings are otherwise defined by respective upper pulleys 13 and lower pulleys 14, supported by frame castings 15,15, and hinged side members 16,16 (one seen in an open position and the other in a closed position).

As seen in the drawing, the assembly is supported from a line 17 and supports a line 18; these may be of various kinds depending not only on the application but also on the stage of operation that has been reached.

In one particular application, the invention may be applied to the replacement of an overhead line earth wire by a new one containing optical fibres (or a duct into which they may be subsequently introduced). As a preliminary operation, the earth wire is bonded to each of the towers affected by the operation by a length of bonding conductor and transferred from its existing attachments (which are needed for the new wire to be installed) to temporary ones in convenient positions.

At a tower at the starting end of the operation, payingout apparatus for two ropes and one new conductor are provided, together with a sufficient supply of the pulley asemblies in accordance with the invention to supply one such assembly per ten metres of the adjoining span. A motorised tug is raised and suspended from the earth wire, using appropriate scaffolding and lifting gear if required. The leading ends of a spacing rope (5 in Figure 4) and a pulling rope (18) are both attached to the tug, one of them in such a way that it controls a clutch in the drive of the tug, so that the tug will stop automatically if the ropes should become entangled and can be stopped at any time by pulling on that rope.

The spacing rope 5 is marked at lOm intervals.

When the pulley assemblies are in ready position at the top of the tower, the tug is started and slowly advances from the tower into the span. Immediately, the lineman takes the first pulley assembly, with both of its hinged sides open, suspends it from the earth wire 17, suspends the pulling rope 18 from it, and inserts the spacer rope 5 in the guides 2,3 and the upper groove 8. Still holding the assembly, he closes the hinged sides 16,16 (since they are pivotted at the bottom, they will not stay closed unless latched), and waits for the first mark on the spacer rope to arrive at the position of the gripper. He then rolls the rope 5 over the rib 10 (figures 1-3) to engage it in the gripping device and releases the assembly which moves out into the span.This is repeated until the tug reaches the other end of the span where (if more than one span is to be replaced) it is transferred to the next span and the process continues using a new spacer rope introduced at the next tower and pulley assemblies applied there, but still using the same pulling rope.

When this process is complete, the new earth wire is attached to the trailing end of the pulling rope and by this means pulled into place. It is tensioned and attached machanically and electrically to each tower, and during tensioning, since it will be drawn tighter than the old earth wire, it is lifted from the pulleys at the bottom of the pulley assemblies and engaged with the corresponding ones at the top; further it lifts the pulley assemblies so that the old earth wire is transferred to its pulley at the lower end of each assembly. Thus once the bonding conductors have been removed from the old earth wire, it can be pulled out and replaced by a tensioned rope, and then the ropes and pulley assemblies can be removed using a friction brake device at the trailing end and otherwise essentially reversing the process by which the pulling rope and spacer rope were first put in place.

Claims (13)

1 A rope-gripping device comprising: a pair of sideentry guides for enty and egress of a rope; between the said guides a pair of jamming cleats; and between said cleats a guide comprising a body providing a surface having two grooves separated by a ridge, the shape of the ridge being such that a rope of suitably chosen size can be rolled over the ridge to pass from one of the said grooves to the other and the positions of the grooves being such that when the rope is taut between the said guides it is engaged with the said jamming cleats when in one of the said grooves and disengaged from them when in the other.

2 A gripping device as claimed in Claim 1 in which the jamming cleats are of the kind in which the rope is gripped by being urged into engagement with jaws that taper in the longitudinal direction of the rope, and in which the two jamming cleats face in opposite directions, so that any tendency for the rope to slip in either direction tightens the grip of one of them.

3 A gripping device as claimed in Claim 1 or claim 2 in which the surface forming the grooves and the rib is a generally convex surface.

4 A gripping device as claimed in claim 3 in which apart from the grooves and the rib, the said surface is a part of a cylinder.

5 A gripping device substantially as described with reference to figures 1-3 of the drawings.

6 A pulley assembly comprising at least a pair of pulleys and a gripping device as claimed in any one of claims 1-5.

7 A pulley assembly as claimed in Claim 6 comprising two pairs of pulleys.

8 A pulley assembly as claimed in Claim 6 or claim 7 having a frame shaped to define two openings, each opening having one pulley at the top and one at the bottom.

9 A pulley assembly as claimed in claim 8 in which the rope grip is located on the member separating the two openings.

10 A pulley assembly as claimed in claim 8 or claim 9 in which each opening is formed with a gate.

11 A pulley assembly substantially as described with reference to the drawings.

12 A method of installing or replacing a line in an overhead line installation in which a pulley assembly as claimed in any one of claims 6-11.

13 A method of replacing an earth wire in an overhead line for transmission of electric power substantially as described by way of example.