GB2052887A - Apparatus for preparing the ends of coaxial cables - Google Patents

Abstract

Apparatus for stripping coaxial cables comprises alignment sleeve 13, and pointed double edged blades for cutting into the inner and outer conductors respectively. Sleeve 13 may have a low coefficient of friction w.r.t. the sheath, and a support may be a diametrically opposite blade, an extension of sleeve 13 (Fig. 4, not shown), or a roller. The sleeve may be hinged (also Fig. 5, not shown), or retractable blades provided, the retracting levers also effecting rotation. In Fig. 3, guide means include grooves formed by half-moon blades. Penetration depth may be such as to leave a thin uncut layer, and cylindrical passages (eg '30') facilitate removal of any remaining insulant. A separator facilitating connector mounting is described w.r.t. Fig. 6 (not shown). Applications are exemplified. <IMAGE>

Description

SPECIFICATION Apparatus for preparing the ends of coaxial cables The present invention relates to a device intended for preparing the ends or heads of coaxial electric cables so as to accomplish their subsequent connection to other conductors (standard connectors for example) which do not form part of the present invention.

Preparation with a view to ensuring the desired connection essentially comprises a stripping operation, over a predetermined length, for each of the inner and outer conductors. The geometry of the cable end thus obtained has to be accurately observed, without crushing or ovalisation of the outer conductor, without cuttings or burrs, and with cutting surfaces which are perfectly plane and perpendicular to the axis of the cable. Observance of this geometry, which is the key aspect of the problem to be solved, makes it possible to fit connectors rapidly and accurately, with good electrical contact, which itself ensures the absence of subsequent repair operations which are always expensive.

Furthermore, the device according to the present invention has to make possible rapid working carried out on site, if necessary, using a light and compact apparatus.

At the present time, the operation of preparing cable ends can only be carried out, in compliance with the requirements described above, provided that a knife, a file and a lot of time are used, while also accepting the risks attached to the use of a knife. Certain devices are available on the market which are designed to effect this operation more easily and more rapidly, but the quality of stripping and cutting, therefore observance of the geomoetry of the cable end, leaves so much to be desired that the disappointed user more often than not returns to the use of a knife and file.

These devices usually take the form of pliers having the width of the piece of outer conductor to be stripped and of which the sides are provided with blades which penetrate to different depths into the material of the cable; one of the blades has to be at a tangent to the outer conductor, i.e. only cut the insulation or outer sheath, the other blade has to be at a tangent to the inner conductor, i.e. cut the outer insulation, the outer conductor and the inner insulation. As already stated above, these appliances are unsatisfactory, since they do not make it possible to observe the geometry of the cable end (thus giving rise to difficulties in fitting connectors), whilst they are not after all very practical in use.

The apparatus according to the present invention perfectly solves the problem set, in an accurate and rapid manner. This apparatus is notable for the combination of the following means: a sleeve or socket enclosing the cable to be stripped so as to impart rectilinear alignment thereto but at the same time allowing movement of the cable;; -two cutting systems, comprising at least one plane blade directed so as to cut in a plane perpendicular to the common axis of the coaxial cable and of the sleeve, which are spaced apart by a distance equal to the desired length of stripping of the outer conductor and arranged so as to penetrate into the cable as far as the vicinity of the outer conductor for one system, and as far as the vicinity of the inner conductor for the other system, the blade or blades of which is or are sharp-pointed and double-edged; means for guiding the blades so that they move only in their own plane; means designed to drive the blades into the material of said cable and to cause them to rotate in their own plane.

The invention will be understood more clearly with reference to the accompanying drawings, in which the same reference numerals are used to designate identical parts.

Figure 1 illustrates a section in an axial plane through an end of a coaxial cable prepared with the apparatus according to the present invention.

Figure 2 illustrates a side view of an apparatusl according to state of known art.

Figure 3 illustrates a side view of one of the variants of the apparatus according to the invention.

Figure 4 illustrates a section in an axial plane of another variant of the apparatus according to the invention.

Figure 5 illustrates a front view of the variant according to Fig. 4 of the apparatus according to the invention.

Figure 6 illustrates a section through a spacer or separator optionally fitted to the apparatus, the section being taken along an axial plane.

With reference to Fig. 1, it is evident that the coaxial cable comprises an inner conductor 1, a layer of insulating material 2, an outer conductor 3 and an outer insulation or sheath 4. The preparation of the cable end such as that desired for connecting a connector should result in an end such as the one illustrated at the right-hand extremity of the cable in Fig. 1, having well-defined faces 5 and 6, without ovalisation, without cuttings or burrs.

Fig. 2 shows a pair of pliers according to the state of the art. It essentially comprises, in the cutting zone, a recess 7 designed to receive the cable to be stripped. Two blades 8 and 9, either with a straight end or a rounded end, are arranged along the sides of the pliers. One blade, for example the blade 8, is arranged along the front side and is adjusted in height so as to be able to be at a tangent to the inner conductor 1 (and thus so as to notch or cut the outer insulation 4, the outer conductor 3 and the inner insulation 2). The other blade, for example the blade 9, is arranged along the rear side and is adjusted in height so that it can be at a tangent to the outer conductor 3 (and thus cut the outer insulation 4). The width of the pliers, i.e. the spacing between the front and rear sides, is equal to the length 10 of the outer conductor to be stripped.The cutting of those portions of the cable to be removed, so as to endeavour to arrive at the desired cable end, is effected by closing the handles 11 and 1 2 and by causing them to rotate in a plane perpendicular to the axis of the cable.

The cutting achieved with such an apparatus may be considered to be relatively rapid.

However, the result obtained is totally unsatisfactory. The major difficulty with such a system lies in the deep-cutting operation, i.e. that which should be tangential to the outer conductor and thus notch three layers of material.

Whatever precautions are taken while cutting through the outer metal conductor, such a system necessarily results in the crushing of this conductor and in irregular cutting thereof, at the expense of considerable frictional stress which leads to flattening, ovalisation, cuttings and burrs. In fact, the cutting effort takes place with a line of contact between the cutting edge of the blade and the cable which is much too great, this effect is accompanied by inaccurate positioning of the cable which is unsatisfactorily held in place radially and which can easily twist under the action of the forces applied by the cutting operation.The crushing and ovalisation of the end of the cable are caused by the excessively large contact area between the cable and the deepcutting blade (no matter how sharp the latter may be) and by the fact that, under the effort of driving in the blade and the inherent deformability of the cable, the latter is formed to a greater or lesser extent into the recess 7. The deformation of the cable during the rotation of the implement and the absence of precise positioning of the latter lead, moreover, to irregular cutting of the faces 5 and 6. The end of the cable becomes so deformed and irregular, thus difficult to connect, that the user finally abandons using such instruments, as described in connection with Fig. 2.

The device according to the present invention eliminates these serious disadvantages by way of the combination of four means, the overall result of which is to accomplish a clean and precise penetration of the outer conductor 3, followed by a clean circular cut through all the material surrounding the inner conductor 1. These four means will be readily apparent from the description which follows, with reference to Figs. 3, 4 and 5.

Referring now to these Figures, there is shown a circular sleeve 1 3 which encloses the cable to be stripped and which, advantageously, may be made of material having a low coefficient of friction with the sheath. It has the purpose of ensuring accurate positioning of the cable, so as to keep each of its components (conductors and insulations) in its ideal radial position, even during the cutting stresses, so that the blades, which themselves are well positioned as will be seen later, do in fact cut at the desired location. The sleeve 1 3 should thus enclose the cable as closely as possible, while retaining the possibility of moving longitudinally in relation to the latter (inter alia for putting it into position), and also of rotating (for cutting).The sleeve thus imparts rectilinear alignment to the cable under all conditions, which enabies it to be always presented to the cutter at the same angle.

The device according to the invention also comprises two cutting systems, each consisting of at least one deep-cut blade 14 or shallow-cut blade 1 5 or 15", which blade is plane and directed to cut in plane perpendicular to the common axis of the cable and of the sleeve.

According to the invention, the blade 14 is sharp-pointed and with twin cutting edges 1 7 and 18.

The cutting systems are also arranged so that one of them, in penetrating to its full depth into the cable, can be tangential to the outer conductor (here the blade 15) whereas the other one should be able (while still penetrating to its full depth into the cable) to be tangential to the inner conductor (here the blade 14). When in this text the expression "blades which are tangential" or else the expression "blades reaching into the vicinity" of a conductor is used, it should be understood that they can be driven into the material of the cable to such a depth that they cut around said conductor, without ever notching this latter, the material surrounding it, and they leave a thickness thereof possibly uncut but sufficiently thin (in order of 0.1 mm for example) which may be broken by simply applying a muscular effort on the severed fragments upon removing them. This aim of effecting a precise cut, which is conventional per se, has actually been accomplished, as far as the inventor knows, only by the present design.

The apparatus according to the invention should also comprise a system for guiding the sharp-pointed deep-penetration blades so that, when they are being driven in and when they are rotating about the cable axis, they can only move in their own plane.

The apparatus according to the invention also comprises means designed to drive said blades into the material of said cable and to cause them to rotate. As a result of the aforementioned guidance, this rotation can only take place in the plane of the blades.

By cutting system there is meant not only a blade, sharp-pointed or not, but also a blade/ cable-support assembly, in which the support is diametrically opposite the blade and supports the cable so that it remains axially centred and rectilinear under the action of the forces applied thereto by the blade. This support may be a blade which is identical and diametrically opposite to the first blade, like the blades 14' or 15"' (see Fig. 3).

Similarly, it may be a simple extension 1 9 of the sleeve 1 3 (see Fig. 4) or else a roller (not shown), or any other device serving the same purpose.

The system designed to drive the blades into the cable and to cause them to rotate consists in making the sleeve 13, to which the blades are rigidly fixed, so that it can be opened by dividing it into two parts articulated about a hinge parallel to its axis (see Figs. 3 and 5). A handle or lever 21 or 21' (see Figs. 3 and 5) is attached to each of the two portions of the sleeve. A variant of this system (not shown in the drawings) lies in providing the non-opening sleeve with retractable blades. According to this variant, the blade-retracting levers also serve to force them in and to rotate them in their plane about the axis of the sleeve.

The system for guiding the blades to ensure that their movement can only take place in planes per pendicular to the common axis of the sleeve and of the cable may be provided in several variants.

The variant of the apparatus according to the present invention shown in Fig. 3 comprises a simple device which takes the form of pliers and lies in using as shallow-penetration cutting system two half-moon shaped blades 15" and 15"'. In fact, by closing the levers 21 and 21' the half-moon shaped blades 15" and 15"' are forced into the cable, thus cutting in said insulation a groove in which they can easily rotate under the action of a simultaneous rotation of the levers 21 and 21', which are held together in the closed position by the operator's hand, in the direction of arrow 22 in a plane perpendicular to the axis of the cable.It is thus the half-moon shaped blades 15" and 15"' which, together with the sleeve 1 3 and the groove which they have cut into the outer sheath upon being forced in, serve as guide means for the whole apparatus during its rotation in the direction of the arrow 22 and thus also for the blades 14 and 14' during the same rotation.

Another variant for guidance of the apparatus according to this invention is visible on the device shown in Figs. 4 and 5. The openable sleeve 1 3 is securely connected to a non-opening extension 23 which itself is attached, in a manner solely rotationally movable by means of, for example, a ball-bearing, to a device 25 for fastening on to the cable.

This device 25 may be provided, by way of non-exclusive example, in the form of a hollow cylinder, through which passes radially a screw 26 which is driven in by turning a knob 27 so as to press an inner tightening flat 28 against the cable.

In the device according to Figs. 4 and 5, the cutting systems comprise a single blade 14 or 15 and an extension 1 9 or 29 of the sleeve 1 3. In this same device it is possible to use, without departing from the scope of the invention, a system for imparting rotational movement to cutting systems based on the principle known as "racagnac" Such a system, known per se, has the advantage of being of compact dimensions.

The device according to the present invention, which is designed to be used solely for preparing cable ends, may also be provided with two systems which, for the sake of clarity, are only illustrated in Fig. 3.

The first system serves to extract or carry along end portions of the cable severed by the blades but remaining in place as a result of shreds of insulation not cut level with the conductor and as a result of the rubbing or adhesion of the insulation on the conductor all along their common lateral surface. This system essentially comprises an openable cylindrical passage 30 with toothed inner walls and of a diameter substantially equal to that of the outer sheath 6 of the cable. By closing the levers 21 and 21", the extremity of the cable to be removed is secured and it is only necessary to pull it laterally to extract it.

The second system comprises another openable cylindrical passage 31 substantially equal in diameter to the inner conductor and whose side walls are abrasive. This system makes it possible, in fact, to scrape the inner conductor after stripping so as to remove therefrom the small fragments of insulation which, in the case of certain flexible and adhesive materials used sometimes for the inner insulation, remain attached to the inner conductor after the piece of severed cable has been removed by means of the system 30.

Some connectors to be fitted on the end of a cable prepared in accordance with the illustration in Fig. 1 have a tubular portion which has to be inserted between the outer insulation 4 and the inner conductor 3 into the extension 32 of the lateral surface 10. In this case the apparatus according to the present invention to be complete has still to be provided with a spacer or separator, the purpose of which is, without notching either the insulator 4 or the conductor 3, to separate these latter from one another along the common cylindrical surface 32.

An example of a separator designed for this purpose will now be described with reference to Fig. 6, it being understood that said separator forms the subject matter of this separate Fig. 6 so as not to complicate Figs. 3 to 5.

This separator comprises two coaxial metal tubes 32 and 33 fixed, for example, on the apparatus of the invention at a point 34 (see also this point 34 in Figs. 3 and 5). The inner tube 32 has its free end 35 pointed so as to form a cutting edge. Its inner diameter is substantially equal to that of the outer conductor 3 so that it can be inserted therein.

The outer tube 33 has an internal diameter slightly greater than the external diameter of the conductor 3 and its free end 36 is not sharpened.

By forcing the above-described separator into the extremity of the cable prepared using the apparatus according to Figs. 3 to 5, the outer conductor 3 is fitted into the tube 32 thus providing a satisfactory guide allowing the sharpened end 35 to gradually cut and separate the conductor 3 from the insulation 4 as a result of helical movements of the separator, while the latter is expanded as a result of the deformability of its material. A circular slot 37 is, thus provided, in which the corresponding part of the connector is fitted.

The outer tube 34 prevents the outer sheath 4 from opening too much. Fig. 6 illustrates the cable head emerging from the separator.

It is evident from the foregoing description that the apparatus according to the invention is able by itself to prepare fully a coaxial cable end for effecting a connection. The apparatus is light and, above all in the version according to Figs. 4 and 5, of compact dimensions. This enables it to be empioyed both for underground cables (around which it is advantageous not to excavate excessively large trenches) and for aerial or overhead cables (where the operator has to be able to carry it in his pocket and handle it easily, as in the case of telecommunication cables fixed against a wall). It permits a high operating speed and provides a high quality of cutting and geometry of the cable head, as a result of the fact that it combines various means enabling the cable to be cut without distorting it.To summarise what has been stated above, these means are: -at least for the deep cut, a cutting system provided with one or more sharp-pointed double-edged blades which penetrate readily through all materials, including the outer metal conductor; -accurate positioning of the cable in all circumstances, as a result of the sleeve and the selected cutting system; -accurate and reproducible positioning of the blade or blades as a result of good guidance; -the driving in and setting into motion of the blade or blades as a result of levers or mechanisms which are compatible with the types of guide chosen.

It is evident that the invention is not restricted to the examples of embodiment described but it covers any variant.

Thus, without departing from the scope of the present invention, it is possibe to combine in various ways the cutting and guide systems described. Similarly, the number of blades per cutting system may be greater than two.

Claims (14)

1. Apparatus for the stripping of the inner and outer conductors of a coaxial electrical cable, comprising of: a sleeve for the cable to be stripped, two cutters capable of cutting in respective spaced apart planes perpendicular to the common axis of the coaxial cable and of the sleeve, and of penetrating into the cable as far as the vicinity of the outer conductor and of the inner conductor respectively, the blade or blades of which is, or are, sharp-pointed and double-edged, and means for driving the blades of the cutters into the material of said cable and for guiding the blades so that each rotates in its plane.

2. Apparatus according to Claim 1, characterised in that said cutters are formed by at least one plane blade and by a support diametrically opposite thereto, thus making it possible to keep the cable axially centred and rectilinear even under the forces applied thereto by the blade.

3. Apparatus according to any one of the preceding Claims, characterised in that said support is a blade identical to the first blade.

4. Apparatus according to either of Claims 1 and 2, characterised in that said support is an extension of the interior profile of said sleeve.

5. Apparatus according to either of Claims 1 and 2, characterised in that said support is a roller, of which the generatrix in contact with the cable is located in the extension of the interior profile of said sleeve.

6. Apparatus according to any one of the preceding Claims, characterised in that said sleeve can be opened in accordance with a hinge parallel to its axis, and in that the cutters are attached in fixed manner to the extremity of said hollow body.

7. Apparatus according to any one of Claims 1 to 5, characterised in that said sleeve cannot be opened, and in that cutting systems comprise retractable blades.

8. Apparatus according to any one of the preceding Claims, characterised in that said sleeve is provided with levers which ensure not only its closure or driving in of the retractable blades, but also its rotation about the axis of the cable.

9. Apparatus according to any one of the preceding Claims, characterised in that said guidance is ensured by the shallow-penetration cutting system formed by two identical blades of half-moon shape.

10. Apparatus according to any one of Claims 1 to 8, characterised in that said guidance of the blades is ensured by securing said sleeve, in such a way that it can move about its own axis, to a device for fastening on to the cable to be stripped.

11. Apparatus according to any one of Claims 1 to 8 and 10, characterised in that said immobilising device is a tube, which can or cannot be opened, surrounding said cable to be stripped and provided with internal means for fastening on to the cable.

1 2. Apparatus according to any one of the preceding Claims, characterised in that it comprises an openable cylindrical passage with toothed inner walls and of a diameter substantially equal to that of the outer sheath of the cable, said passage serving to remove the severed portions of sheath.

1 3. Apparatus according to any one of the preceding Claims, characterised in that it comprises an openable cylindrical passage of a diameter substantially equal to that of the inner conductor and the walls of which are abrasive.

14. Apparatus according to any one of the preceding Claims, characterised in that its outer surface is fastened to a separator consisting of two coaxial tubes, the inner tube of which has an internal diameter substantially equal to the external diameter of the outer conductor and a sharpened extremity, and whose outer cylinder has an internal diameter slightly greater than the diameter of the cable.