GB2289577A

GB2289577A - Cable bend limiter

Info

Publication number: GB2289577A
Application number: GB9409703A
Authority: GB
Inventors: Henry Kirby
Original assignee: Northern Telecom Ltd
Current assignee: Nortel Networks Ltd
Priority date: 1994-05-14
Filing date: 1994-05-14
Publication date: 1995-11-22
Anticipated expiration: 2014-05-14
Also published as: GB9409703D0; GB2289577B

Abstract

A cable bend limiter for use with optical patchcords comprises a set of links (21, 20a and 20b) which can be snap-fastened together end-to-end by ball (14) and socket (15) snap fastenings. Individual ones of the links carry grips (11) on their sides into which a patchcord cable (12a, 12b) can be introduced. In another embodiment (Figure 3) the ball and socket joints are replaced by cuboid protrusions (34) and complementary cuboid recesses (35) which allow limited movement between adjacent links. Resilient prongs (23) allow the bend limiter to be mounted on an equipment rack. The links may be coated with an adhesive which melts on heating so that the bend limiter takes a set shape on cooling. <IMAGE>

Description

Cable Bend Limiter This invention relates to cable bend limiters. Cable bend limiters are employed in a variety of situations, including for instance to limit the bending that can occur where a submarine telecommunications cable is about to enter a submerged repeater house, and to limit the bending that can occur where electricity mains cable is about to enter a portable domestic appliance such as an iron or foodmixer.

In each case the bend limiter is provided around the cable in order to limit the tightness of the bending which can occur, and so preclude damage occurring to the cable as the direct result of an excessively tight bend occurring.

It is not only electrical cables, but also optical cables, that are susceptible to damage through excessively tight bending. Bend limitation may be required, not just in the neighbourhood of the extremities of the cable, but over the whole of its length. If a bendlimiter can be fitted to a length of cable before at least one of its ends is terminated, or if one of the terminations is not significantly larger in diameter than the cable itself, then the bend limiter can take the form of a generally tubular device through whose central aperture that end of the cable is threaded. A tubular format of this kind is however not suitable in instances where it is desired to fit the bend limiter to a length of cable after both ends have been terminated in terminations of significantly greater diameter than that of the cable itself. An example of such a cable is an optical fibre patch cord whose ends are terminated in terminations that are required to be fitted in the factory rather than in the field. In optical equipment practice such a patchcord may be required to take a curved path that has curvature in all three orthogonal planes.

The present invention relates to a form of cable bend limiter which can be applied to a cable without the requirement of being introduced over either end of the cable.

According to the present invention there is provided a cable bend limiter composed of a plurality of links that have been or can be snap-fastened together end-to-end.

There followings a description of cable bend limiters embodying the present invention in preferred forms. The description refers to the accompanying drawings in which Figure 1 depicts a perspective view of two separated links of a cable band limiter, Figure 2 depicts variants of the links of Figure 1, including one variant on its own and another connected in a chain of four links, and Figure 3 depicts a perspective view of the separated links of a cable bend limiter of alternative design.

Referring to the drawings, Figure 1 depicts a perspective view of two identical links of a first preferred form of cable bend limiter. These links are preferably moulded parts made of a tough resilient plastics material, such as acrylonitrile butadiene styrene (A.B.S.), and are illustrated before they have been snap-fastened together. Each link has a generally cylindrical elongate body portion 10 on one side of which is formed a pair of resilient arms 11 of a cable grip. In this particular example the arms are of a length designed for the grip to accommodate two cables 12a, 12b. The arms 11 are provided at their extremities with inwardly projecting shoulders 13 to provide a separation just less than the diameter of either cable so that the arms have to be sprung apart to effect lateral insertion or removal of a cable from the cable grip, but so that, once inserted, the cables are freely accommodated within the grip.

At one end of this body portion 10 of each link is a ball 14, while the other end is provided with a socket 15 of complementary shape designed to be a snap-fit around the ball 14 of another link. When the two links are snap-fastened together, articulation of one link with respect to the other is limited by a rearward facing shoulder 16 to the rear of the socket 15 of the forward link coming into abutment with a forward facing should 17 to the rear of the ball 14 of the rear link. At least one of the shoulders 16, 17 may be of generally conical shape with a large, near 90 , semi-vertical angle. Because the cable or cables retained by the cable grips 11 are displaced form the axis of the body portion, it may be desirable to limit articulation that leaves the cable grips on the inside of the bend to a rather greater extent than articulation that leaves them on the outside of the bend, in which case the magnitude of the semi-vertical angle will be a function of azimuth.

In addition to limiting the articulation of the two links by means of the shoulders 16 and 17, it is necessary to provide some means to limit the rotation of either link with respect to the other. In this instance rotational freedom of movement is limited by providing the links with co-operating keys 18 and keyways 19. The looseness of the fit of a key 18 of one link into the keyway of the next provides the desired limitation upon the amount of rotation permitted.

If the ball and socket snap fastening arrangement is replaced by a modified geometry using a non-spherical boss engaged in a recess of co-operating configuration, for instance a boss of generally cuboid shape with rounded corners, or a boss in the form of a truncated sphere having a flat face on one side, then it may be possible to dispense with the separate key and keyway arrangement, and rely instead upon keying provided by the boss itself.

For use with a pair of optical fibre cables 3.4mm in diameter, the total lengths of one of the links of Figure 1, including its ball 14 but excluding its key 18, may be about 15mm, the ball 14 being about 4mm in diameter, and the diameter of the body portion being about 5.5mm. For use with optical patchcord fibres for which it is known that portions of their length will never be required to be anything but straight, it may be found convenient to use longer links (not shown) for these straight portions. The ends of the longer links would have the same fastening and key and keyway configurations as their short link counterparts, but would be provided with two or more cable clamps distributed in line along the side of their longer body portions.

Two other variants of longer link, which may be found useful in certain applications are illustrated in Figure 2 these variants incorporating a form of staking arrangement for securing the cable bend limiter in position, for instance to some component of an equipment rack. One of these variants, 20a, is depicted in isolation while the other, 20b, is depicted attached to a chain of three short links 21 of the type illustrated in Figure 1. Both variants have the same staking arrangement that comprises, integral with the body portion 10, a block 22 from the base of which protrudes a pair of resilient barbed prongs 23. The difference between the two variants is that variant 20a includes cable grip arms 11, whereas variant 20b does not. The latter variant may find particular use when employed near an end of a patchcord, where the absence of the cable grip may facilitate access to the patch cord termination and the engagement and disengagement of that termination with an optical connector.

Optionally the balls 14 of the individual links of a bend limiter may be provided with a solid polymer layer of material that becomes adhesive when heated. Under these circumstances the bend limiter can be applied to a cable or group of cables before installation. The bend limiter retains its limited flexibility during that installation, after which it is heated, for instance with a hot air blower, to convert it to a rigid structure.

Previous reference has been made to modified geometries of nonspherical boss engaged in a recess of co-operating configuration to replace the ball and co-operating socket arrangement of snapfastening. A specific example of such a modified geometry is illustrated in Figure 3 which depicts a separated pair of links. Each of these links has a body portion 30 on one side of which is formed a pair of resilient arms 31 of a cable grip. (These arms 31 are of the same general shape and function as the corresponding arms 11 of the links of Figure 1.) At one end of the body portion 30 of each link is a boss 34 of rounded generally cuboid shape joined to the body portion by a neck 32. The opposite end of the body portion 30 is formed with a slot 33 in one side whose size and shape is such that the neck 32 of an identical link can be snap-fastened therein. The slot 33 has jaws 33a defining the mouth that needs to be sprung apart to permit entry of the neck, but opens out at a greater depth into a region 33b in which the neck 32 is freely accommodated. The slot 33 communicates with a recess 35 whose size and shape generally complements that of a boss 34 to provide restricted rotational freedom of the boss 34 of one link about the axis of its neck with respect to that of another link in whose recess 35 that boss 34 has been engaged. Articulation of these two joined links is similarly restricted by the contact between the boss of one link and the walls of the recess of the other, or by contact between the face 37 from which the neck 33 of the one link protrudes and the opposite face 36 of the other link. Typically the face 37 will be of generally frusta-conical shape.

Claims

CLAIMS:

1. A cable bend limiter composed of a plurality of links that have been or can be snap-fastened together end-to-end.

2. A cable bend limiter as claimed in claim 1, wherein individual ones of the links carry cable grips on their sides into which a cable can be laterally introduced, and wherein the snap-fastenings by which pairs of the links are fastened end-to-end include means for limiting both the articulation and the rotational freedom of movement of either member of the pair with respect to the other.

3. A cable bend limiter as claimed in claim 2, wherein the endto-end snap fastenings of the links are of boss and complementary socket configuration.

4. A cable bend limiter as claimed in claim 2, wherein the endto-end snap fastenings of the links are of ball and complementary socket configuration.

5. A cable bend limiter as claimed in claim 2, 3 or 4, wherein the means for limiting the rotational freedom of movement consists of a key and complementary keyway configuration.

6. A cable bend limiter as claimed in claim 2, 3, 4 or 5, wherein each snap fastening includes an element coated with a solid layer which becomes adhesive upon heating, whereby heating of the cable bend limiter converts it from a structure of restricted flexibility into a substantially rigid structure.

7. A cable bend limiter substantially as hereinbefore described with reference to the accompanying drawings.