GB2212341A

GB2212341A - Cable stripper

Info

Publication number: GB2212341A
Application number: GB8829683A
Authority: GB
Inventors: Jiri Stepan
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-12-23
Filing date: 1988-12-20
Publication date: 1989-07-19
Also published as: JPH01209909A; GB8829683D0; FR2625379A1; DE3842754A1

Description

V k- 871218 1 221234 1 Cutting apparatus for selectively cutting the

multilaver sheath of a cable The invention relates to a cutting apparatus according to the preamble of claim 1.

Since the beginning of the age of electrical engineering and electronics, the stripping of cables has been of industrial importance and has recently become a problem in connection with the attempted automation of all work sequences:

On the one hand, conductors or certain insulation or sheath layers of a cable should not be damaged, while on the other hand other sheath layers should be reliably cut and stripped off. A large number of different materials set very high requirements for the tools. This circumstance was further complicated in some cases by the technology of optical waveguides, with many novel tough materials.

European Patent Application No. 0195932 of the Applicant describes an apparatus for mechanical stripping which has to date met the highest requirements and is capable of readily cutting through both soft and hard sheath layers, such as, for example, braided steel shielding.

The best cutting effect of this known stripping apparatus is of course always achieved when that layer of the sheath which is underneath the layer to be cut through is harder than the layer to be cut through. Problems may therefore arise if the layer to be cut through is substantially harder or tougher. In such a case, the layer to be cut through may not be completely cut through, or the soft layer underneath may be damaged. Such disadvantages were observed, for example, in the recently used optical waveguide cables with a relatively soft dielectric and an extremely tough fiber network, for example consisting of Kevlar.

1 871218 (Kevlar or similar fibers absorb tension in the provide substances which the extension properties optical waveguide.) Ke-v6s 2 are used because, in order to cables, it is necessary to are most closely similar to of the glass fibers for the A: C, Ab'.V+_zz"_"L TrAe- K(Xr k, When stripping in practice, scissors are frequently relied upon in the case of such cables, and stripping is carried out manually.

Another tool for cutting sheaths of optical waveguide f ibers is described in German Offenlegungsschrift 3,529,141. It is true that relatively soft sheath layers can be easily cut through with this tool; however, in the case of the situation described at the outset, with a soft under-layer and a tough layer on top, which is to be cut through, the difficulties mentioned, such as, for example, those observed in the case of Kevlar, can also easily arise. The fibers are simply so tough and hard that it may not be possible to cut through them even with a sharpened blade, especially since the pressure of the blade on the fibers must not be excessively high in view of the soft lower layer of the sheath.

Hence, despite the use of the tool according to the German Offenlegungsschrift, scissors are still often used in 6rder subsequently to cut through fibers which have not been cuti This involves subsequent work and is very time-consuming.

Furthermore, the precision of the scissors themselves must be very high, since otherwise the tough fibers will bend and jam between the blades of the scissors or knife blades and once again will not be cut.

The problems are also not solved by the apparatus according to U.S. Patent 3,280,420, which, for example, shows a type of scissors in Fig. 6 and 7 v 871218 0 3 and shows a small cutting wheel in Fig. 13-17. Although attempts have been made to strip dielectric protective sheaths using this arrangement, the attempts were not successful in the case of certain types of cable, for example those having hard Kevlar fiber layers. The inventor studied the problem in many experiments and found that the source of error was the arrangement of the small cutting wheel relative to the knife blade.

U.S. Patent 3,965,570 likewise disclosed a rotating knife together with a stationary one. However, the blade of the stationary knife had a peeling effect there, so that it did not provide any support during cutting of hard layers.

It is thus the object of the invention to provide a cutting apparatus for selectively cutting the multilayer sheath of a cable, which permits reliable cutting of individual layers, or a plurality of lavers, of the sheath of a cable, either manually or mechanically, without damaging any softer layers underneath. At the same time, the time required for cutting and stripping should be minimized.

The object set is achieved for the first time in an outstanding manner by the features of the defining clause of claim 1.

The knife blade holds the layer or layers to be cut through, just like the lower blade of a conventional pair of scissors, while the rotating knife initially alone, like a conventional circular saw - begins to cut into the layer and subsequently, because of the shearing arrangement, cuts through the layers simultaneously with the knife blade, as in the case of a conventional pair of scissors. Even the finest fibrous constituents of a sheath are cut through just as readily as hard plastics or metal layers.

871218 4 Particular embodiments of the invention are described in the defining clauses of the subclaims. The advantages of each of these embodiments are described below:

The feature of claim 2 permits easier penetration of the cutting apparatus into the sheath. The rotating knife need not necessarily be driven by a motor. In the case of hand-operated tools, it can, in particular, also be designed without a drive, since the rotating knife is automatically caused to rotate by the cutting movement itself or by the advance of the cable relative to the cutting apparatus. The feature of claim 3, which facilitates initial cutting into the outermost layer of the sheath and simultaneously ensures that the rotating knife is subjected to a uniform load or uniform wear over its circumference.

On the one hand, this increases the lif e and, on the other hand, ensures high cutting quality over a long period.

The arrangement of the knif e blade and of the rotating knife according to claim 4 is very suitable for mechanical stripping and permits complete automation of the stripping Process.

The arrangement according to claim 5 essentially corresponds to a technical reversal, which can particularly advantageously be used where only short pieces of cable or very long pieces of cable have to be stripped, since in both cases rotation or consequent twisting of the cable plays scarcely any role.

The embodiment according to claim 6 increases the cutting quality and the cutting force for particularly tough materials. As a result, the cutting speed can be increased. The preferred embodiment of the teeth ensures that all sheath layer material to be 1 1 t 871218 J cut through is included and furthermore improves the shearing effect between the rotating knife and the knife blade. The slope of the tooth flank is understood as the angle which the flank of a tooth makes with the normal to the connecting line between the tooth points - or, in the case of a rotating knife, with the radius.

It is optimal if, according to claim 7, the angle is chosen so that, in the position of the shearing cut, between a tooth of the rotating knife and the cutting edge of the knife blade, the latter makes contact from the tip of the knife blade continuously in a backward direction. This essentially corresponds to an embodiment of the cutting area which is diametrically opposed to that of a pair of scissors, since in a pair of scissors contact of the blades of the scissors in the cutting area takes place from back to front. As a result of the embodiment according to the invention, even the finest constituents of the layers of the sheath are forced into the cutting area, where they are cut through. Escape toward the front, as may occur in the case of a commercial pair of scissors, is prevented. The embodiment according to claim 8 also improves the gripping of the finest sheath constituents, in that the soft layer which is not to be cut through is temporarily slightly deformed and the cutting edge of the knife blade thus grips underneath the layers to be cut through. 30 The features of claim 9 permit, on the one hand, reliable and complete inclusion of all layers to be cut through and, on the other hand, the controlled inclusion of the cutting position advantageously to be chosen for this purpose. it is of course also possible to cut in the 871218 6 form of a continuous spiral line, but the arrangement according to the first part of the features of claim 9 is preferred.

Claims

Claim 10 describes the preferred method of cutting which, as various tests have shown, can be used in all cases for trouble-free and reliable cutting of even the most difficult sheath layers. The invention is illustrated in more detail below with reference to diagrams. Fig. 1 to 3 show a vertical section, a side view and an outline plan of a knife blade and a rotating knife in the cutting position on a cable, Fig. 4 and 5 show a cut-away detailed picture of the cutting area, in side view and vertical section, and Fig. 6 and 7 show a cut-away side view and vertical section of a mechanically operated means having a cutting apparatus according to the invention, in the cutting position. The Figures are restricted to a diagramatic representation of the essential components of the invention, without any details which are familiar to an average skilled worker and can also be varied within the framework of the invention. identical parts are provided with the same reference symbols. The description of the Figures overlap. The essential feature of the invention consists of a rotating knife 1 and a knife blade 2 which have a shearing interaction with one another along their cutting edges 10 and 5, respectively, and can be made to engage a cable 3 or its sheath and can be caused to perform a relative rotary movement with respect to one another. in all embodiments shown, the cutting edge 10 1 2 871218 X 7 of the rotating knife 1 is provided with teeth. The slope of the tooth flanks in the embodiments shown is about 40 degrees, measured in both directions, with respect to a tangent 15 to the cutting edge 10 of the 5 rotating knife 1. The cutting edge 5 of the knife blade 2 is not toothed but, within the scope of the invention, could have teeth or, for example, be cylindrically ground. In the front area, the knife blade 2 has a point 17. The cutting edge 5 shears against the rotating knife 1, since the said cutting edge is ranged in a plane parallel to the rotating knife 1. Fig. 1 indicates the rotary movement of the cable (3) relative to the rotating knife or to the knife blade 2, by means of the arrow C. It is practical if the direction of rotation (arrow C) opposes the knif e blade 2, so that the point 17 has a sort of lifting effect for the layers of the cable 3 which are to be cut through. The rotating knife 1 can be mounted so that it is freely rotatable, or can be driven by a motor 11, as in Fig. 6 and 7.. In both cases, the rotating knif e 1 rotates in the direction of the arrow d (Fig. 1) on cutting into the sheath of the cable 3. In the case of a motor drive. this results in cutting into the sheath in the manner of a circular saw, while in the case of a non-driven rotating knife the advance of the knife blade 2 and the associated engagement of the cutting edge 10 of the rotating knife 1 with the sheath forces the rotating knife to perform a rotation, which simultaneously results in the relevant section of the sheath being sheared off between the cutting edge 5 of the knife blade 2 and the cutting edge 10. Corresponding to the coordinate arrows a and b, and as indicated in Fig. 1, a feed means (not shown) 871218 8 for cable 3 is provided, in which the direction a represents the feed of the cable 3 to the cutting apparatus, while the distance in direction b determines the cutting depth. in the case of a rigidly mounted or fixed cutting apparatus, as shown in Fig. 1, the rotation (arrow c) of the cable 3 is produced by a separate apparatus, as is familiar to an average skilled worker, for example by a driven jaw chuck or an apparatus similar to the centering jaws, as described in European Patent Application No. 0195932. The rotation must take place exactly about the axis 19 of the cable 3. The best cutting position for continuous cutting of a plurality of layers of the sheath of cable 3, for example including a layer 4 consisting of Kevlar, is obtained in this case when the point 17 of the knife blade 2 lies in the region of a plane through the axis of rotation 18 of the rotating knife 1 and through the axis 19 of the cable 3. if the rotation of the cable 3 relative to the cutting apparatus or that of the cutting apparatus relative to the cable 3 takes place starting from this position, the relevant. layer is. reliably cut through in one operation. The slope of the tooth flanks of the teeth 14 is such that a cutting space 6 is formed in the cutting region for the cutting edge 5 of the knife blade 2, as can be most readily seen in Fig. 5. The cutting space 6 takes the form of an area which has a triangular cross-section and has a very acute angle whenever that side of a tooth 14 which faces the knife blade 2 begins the shearing movement against the knife blade 2. At this time, the point of the tooth 14 first touches the point 17 of the knife blade 2; as a result of continued rotation of the rotating knife 1, this shearing point 1 2 1 1 1 1 871218 9 then migrates along the cutting edge 5 of the ' knife blade 2, away from the point 17. Consequently, any fine fibers present cannot escape from the cutting region and are reliably cut through by the shearing 5 effect. The front part of side 16 of the knife-blade 2, which is opposite the cutting edge 5, is in the form of a pressure area 7. As can be seen in particular in Fig. 5, this pressure area is convex. However, it could also be merely beveled. The object of the pressure area 7 is to press the generally very soft resilient layer 25 underneath the Xevlar layer 4, which is still to be cut through, slightly in the direction of the axis 19 of the cable 3, in order to permit the cutting edge 5 of the knife blade 2 to grip underneath the layer 4. As a result, all fibers of this layer 4 are reliably included and cut through. The concentric structure of the cable 3 is not described in detail since it is familiar to any average skilled worker. Control of the cutting apparatus - as shown in Fig. 5 - is based on a tangent 24 to the layer 25 or on a plane 23 at right angles to this tangent 24. During cutting, the point 17 of the cutting knife 2 and at the same time the rotating knife 1 - a distance away from the cable - are first transported towards the tangent 24 and then pushed along the latter as far as the plane 23 which is at right angles to the tangent 24 and passes through the axis 19 of the cable 3. As a result, the outermost layer 8 of the sheath is first cut into, followed by the layer 4. The relative rotary movement between the cutting apparatus and the cable 3 must begin no later than when the position shown in Fig. S is reached, in order to cut through the layers 8 and 4 in the desired manner. This relative rotary 871218 movement can of course also be effected during transport of the cutting apparatus along the tangent 24. Consequently, a spiral cutting line is formed. The- sheath layer currently being cut is relatively thin, permitting very high cutting speeds. The example of a mechanized cutting apparatus according to the invention, illustrated diagramatically in Fig. 6 and 7, shows a stand 21 which carries a rotatably mounted drum 26. A motor 27 ensures the 10 rotary movement of the cutting apparatus relative to the cable via a synchronous belt drive 28 or the like, in that the said motor rotates the drum 26 while the cutting apparatus is mounted or fixed in a bearing block 12 and the motor 27 is rigidly connected to the 15 drum 26. A feed means 20, which comprises gears and advance motors (Mot. 1 and Mot. 2), which are not shown in detail, is also connected to the drum 26 and to the bearing block 12. Drives of this type may be 20 conventional drives, as used, for example, in machine tools. The stand 21 furthermore carries clamping jaws 22 (not shown in detail) for clamping the cable 3. The drum 26 carries, concentrically in its middle, a central holding apparatus 13 in the form of a tube, 25 which carries the cable 3. The holding apparatus 13 is closed in the region facing away from the knife blade and cut away in its region f acing the knif e blade 2. Consequently, the cable 3 is supported against the rotating knife 1 and the knife blade 2, and it 30 therefore cannot escape downward under pressure from the rotating knife 1 or from the knife blade 2. With the aid of the apparatus described above, the cable 3 can be stripped by the process acccording to claim 10. The invention is not restricted by the Figures 1 7! 7 1 871218 11 1 shown. In particular, it is also possible for the cutting edge 5 of the knife blade 2 to possess teeth. In addition, the knife edge 10 of the rotating knife 1 may also be smooth or merely roughened or, for example, covered with precious stones or hard materials. Moreover, an oblique position of the knife blade 2 with respect to the rotating knife 1 is also possible within the scope of the invention and, in this case, the cutting edges 5 or 10 should additionally be beveled. European Patent Application No. 0195932 and the Applicant's still unpublished Swiss Patent Application No. 2494/87 are also herewith incorporated by reference in the present disclosure.

1 871218 12 LIST OF PARTS 1. Rotating knife

2. Knife blade 3. Cable 4. Kevlar layer 5. Cutting edge 6. Cutting space 7. Pressure area 8. Outer sheath layer 9. Indentation 10. Cutting edge of the rotating knife 11. Drive of the rotating knife 12. Bearing block 13. Central holding apparatus 14. Teeth 15. Second tangent 16. Side 17. Point 18. Axis of rotation 19. Axis 20. Feed means 21. Stand 22. Clamping jaws 23. Plane 24. Tangent 25. Layer 26. Drum 27. motor -j 1 a 871218 13 CLAIMS Cutting apparatus for selectively cutting the multilayer sheath of a cable, having at least one knife blade and at least one rotatably mounted rotating knife coordinated with this knife blade, the cutting edges of the knife blade and of the rotating knife making shearing contact with one another, wherein the rotating knife is arranged in a plane parallel to the cutting edge of the knife blade, the knife blade being pointed in the region of the rotating knife, and wherein the rotating knife projects beyond the point of the knife blade with respect to a cable sheath to be cut through. 2. Cutting apparatus as claimed in claim 1, wherein the rotating knife is lamellar.

3. Cutting apparatus as claimed in claim 1 or 2, wherein the rotating knife can be driven by means of a drive, preferably a motor drive.

4. Cutting apparatus as claimed in any of the. preceding claims, wherein the rotating knife and the knife blade are fastened or mounted on a bearing block which is mounted in such a way that it is rotatable about the cable and/or displaceable in the axial direction of the cable.

5. Cutting apparatus as claimed in any of claims 1 to 3, wherein the rotating knife and the knife blade are rigidly fastened or mounted, and wherein an apparatus for rotation and/or radial displacement is provided for the cable.

6. Cutting apparatus as claimed in any of the preceding claims, wherein the knife blade and/or the rotating knife has or have teeth, the teeth preferably having a flank slope of 20 to 80, in particular 30 to 50, degrees.

7. Cutting apparatus as claimed in claim 6, wherein, when their points make contact, the two 871218 14 cutting edges together form an angle which opens in a backward direction.

8. Cutting apparatus as claimed in any of the preceding claims, wherein that side of the knife blade which is opposite the cutting edge is in the form of a pressure area, which is preferably rounded or beveled in a backward direction from the point.

9. Cutting apparatus as claimed in any of the preceding claims, wherein, at least during cutting of one layer of the sheath of the cable, the point of the knife blade lies in the region of a plane which passes through the axis of rotation of the rotating knife and through the axis of the cable or preferably projects somewhat beyond the said plane, and/or wherein a feed apparatus, which may or may not be motor-driven, is provided for adjusting and advancing the bearing block or the knife blade and the rotating knife to this position.

10. A method for cutting a multilayer sheath of a cable using an apparatus as claimed in one or more of the preceding claims, which comprises the following steps:

- The cable is inserted into a holding apparatus which is concentric with respect to the axis of the cable and is fixed there, if necessary by means of clamping jaws; The bearing block is brought into a position in which the point of the knif e blade is a distance away from the cable and on a tangent or slightly lower - with respect to the axis of the cable - than a tangent to the sheath layer which is not to be cut through; The bearing block is then moved along the second tangent to a cutting position in which the point of the knife blade reaches or just passes through a 3563 plane which runs through the axis and is at right angles to the second tangent:

- The bearing block is then rotated along a circular path along the axis of the cable and - The rotating knife is preferably caused to rotate by its drive no later than the time when it has reached the cutting position, the rotation advantageously being in the same direction as that of the bearing block.

11. Cutting apparatus as claimed in any one of claims 1 to 9 constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in, the accompanying diagrammatic drawings.

12. A method as claimed in claim 10 substantially as herein described with reference to the accompanying diagrammatic drawings.

13. A cable cut with the use of an apparatus as claimed in any one of claims 1 to 9 or 11.

14. A cable cut using a method as claimed in claim 10 or 12.

Published 1989 at The Patent 0Mce, State House,68171 Eligh Holborn, London WC1R 4TP. Further copies maybe obtainedfrom The Patent Office.