Stripping tool for coaxial cable

[0002] This application claims the benefit of priority under 35 U.S.C. §119(e) for European Patent Application 01109855.5 filed on Apr. 23, 2001, the content of which is relied upon and incorporated herein by reference in its entirety.

[0003] The present invention relates to stripping tools for coaxial cables and more particularly to such tools for coaxial cables with a corrugated outer conductor and a hollow inner conductor.

[0004] A coaxial cable of the above mentioned kind comprises a hollow inner conductor with a longitudinal axis and coaxially with said inner conductor a tubular layer of insulating material between said inner conductor and an outer conductor which is corrugated in a non-helical manner in order to improve flexibility of the cable, said outer conductor thereby comprising a repeated axial pattern of crests and valleys, and finally provided with an outer insulating jacket.

[0005] It is an object of the present invention to provide a stripping tool for a coaxial cable with said kind of corrugated outer conductor and a hollow inner conductor, which tool is capable of performing all stripping steps required in order to prepare the cable for insertion into a coaxial connector.

[0006] More specifically said tool must be capable of providing the correct relative axial locations of the end of the inner conductor, the end of said insulating material provided between the inner and outer conductor, the end of the corrugated outer conductor and the end of the jacket. Furthermore, said correct relative axial locations must be obtained with the tool no matter at what axial location the cable is initially cut off.

[0007] According to the present invention there is thus provided a stripping tool comprising the following main means:

[0008] A jacket cutting means for stripping the appropriate axial length of the jacket, thereby exposing the corresponding axial length of said outer conductor.

[0009] A guide means to be placed coaxially around the coaxial cable after said appropriate axial length of the jacket has been removed as described above, where said guide means during operation of the stripping tool guides a second cutting means and provides a well defined axial abutment surface for this means. The guide means is furthermore provided with position determining means so that it can be located at a well-defined axial position relative to said repeated pattern of crests and valleys thereby positioning said abutment surface at a well-defined axial position relative to said pattern of crests and valleys.

[0010] A second cutting means for providing the required relative axial positions of the end of the outer conductor, the corresponding end of the insulating material between the inner conductor and the outer conductor and the end of the inner conductor, said second cutting means being guided by said guide means and being provided with cutters, blades or similar means operating while the second means is being displaced axially relative to the cable along said guide means until said abutment between the second cutting means and said guide means is obtained.

[0011] The invention will now be described in more detail with reference to the accompanying drawings, in which

[0012] FIG. 1 is an end view of a jacket cutting means according to the invention.

[0013] FIG. 1ais a schematic view of a jacket cutting means according to the invention,

[0014] FIG. 1bis a schematic view of the end of a coaxial cable inserted in the jacket cutting means in an initial position prior to stripping of the jacket;

[0015] FIG. 1cis a schematic view corresponding to FIG. 1bwith the coaxial cable in the final position with an appropriate length of the outer conductor exposed.

[0016] FIG. 1dis a schematic view of the jacket cutting means according to the preceding Figures provided with a handgrip.

[0017] FIG. 2ais a schematic perspective view of a guide part according to the invention,

[0018] FIG. 2bis a longitudinal sectional view of the guide part shown in FIG. 2a,

[0019] FIG. 2cis a longitudinal sectional view corresponding to FIG. 2bbut with a cable prepared with the aid of the jacket cutting means inserted into the operative position in the guide part;

[0020] FIG. 2dis a longitudinal sectional view of an alternative embodiment of the guide part,

[0021] FIG. 3ais a longitudinal partly sectional view of the second cutting means according to the invention,

[0022] FIG. 3bis a schematic view of the second cutting means shown in FIG. 3aseen from the direction of the arrow A; and

[0023] FIG. 4 is a schematic partly sectional view of the finished coaxial cable.

[0024] In the following, a detailed description of a preferred embodiment of the invention is given, but it is understood that other designs of the various details in the stripping tool may be made by a person skilled in the art without departing from the scope of the invention as defined by the following claims. One such alternative embodiment, differing from the first embodiment only with respect to one particular feature is also briefly described.

[0025] The stripping tool according to the preferred embodiment of the invention consists of three main parts: a jacket cutting means 1 for exposing an appropriate length of the outer conductor of the cable as a necessary preparation for the following steps in the stripping procedure, a guide part 10 to be placed coaxially over the end of the cable prepared by the jacket cutting means 1 in the preceding step and serving as a guide- and abutment means for a second cutting means 18 for providing the correct relative longitudinal extension of exposed outer conductor, inner conductor and insulating material placed between the inner and outer conductors.

[0026] FIG. 1ashows a schematic view of the jacket cutting means 1 of the stripping tool in longitudinal cross section and seen from that end of the jacket cutting means 1 into which the end of a coaxial cable to be prepared for insertion in a connector is to be inserted. The jacket cutting means 1 essentially comprises a tubular body 2, the inner diameter of which corresponds to the outer diameter of the jacket of the coaxial cable. The tubular body 2 is open at one end 3 where the cable is to be inserted and closed at the other end by a wall 4 substantially perpendicular to the longitudinal axis through the tubular body 2. A certain length of cable can thus be inserted into the tubular body. At the inner circumferential wall of the tubular body 2 there is provided a cutting means 5 in the form of a knife blade with a cutting edge 6 facing the longitudinal axis. The cutting edge 6 starts at a longitudinal distance 1 from the end wall 4 of the tubular body 2, this distance 1 corresponding to the longitudinal length of cable jacket to be removed.

[0027] The operation of the cutting means 1 is depicted in FIGS. 1band 1c. FIG. 1bshows an end of the coaxial cable 7 inserted into the tubular body 2 to an initial position where the end of the cable just touches the end of the cutting edge located the distance 1 from the end wall 4. After insertion of the cable to this point, the cable is further advanced towards the end wall 4, the tubular body 2 simultaneously being rotated about its longitudinal axis. The resultant relative movement of the cutting edge 6 and the jacket of the cable results in the jacket being cut off helically over the longitudinal distance l, thereby exposing a corresponding length of the corrugated outer conductor 9.

[0028] FIG. 2ashows a schematic view of the above mentioned guide part 10 to be placed on that end of the coaxial cable which has been prepared as described above. More specifically the guide part 10 comprises a rotationally symmetrical body composed of two sections: a tubular section 11 made of a resilient material such as hard rubber, to which section is attached a second section 12, 13, 14 made of a substantially rigid material and longitudinally cut into a number of subsections by a number of slits 15 through the wall of the second section, in this embodiment 4 subsections of equal circumferential dimensions, although other numbers of subsections could of cause also be used. By cutting up the wall of the second section longitudinally in the manner described, it is made possible for this section to undergo radial displacements except al that end of the second section where it is attached to said resilient first section. As shown in FIGS. 2band 2c, a through bore is provided through the coaxially placed first and second sections, the diameter of this through bore substantially corresponding to the outer diameter of the jacket of the cable. It is thus possible to insert the cable into the guide part 10 from the side of the resilient first section. Furthermore, the second section is at the end hereof facing away from the first section provided with inwardly directed tongues 16.

[0029] FIG. 2cshows the guide part with a cable prepared by means of the jacket cutting means 1 inserted. Due to the radially resilient construction of the guide part, as provided by the resilient first section and the longitudinal slits 15 in the second section, it is possible to insert the end 8 of the cable to a point beyond said inwardly directed tongues 16, so that these tongues 16 thereby fit into the corrugation of the outer conductor 9 at those places 17 where the diameter of the outer conductor 9 is smallest, i.e. Into the “valleys” of the corrugation. During operation of the stripping tool the prepared cable is inserted in the guide part 10 so that said tongues 16 fit into that valley of the corrugation which is located closest to the end of the jacket 7 of the cable. In this manner a well-defined longitudinal placement of the guide part 10 on the cable is obtained, which is essential for the further operations of the stripping tool.

[0030] Referring to FIG. 2dthere is shown an alternative embodiment of the position determining means, which in the embodiment described above was implemented in the form of the tongues 16 according to FIGS. 2band 2c. In this alternative embodiment of the position determining means, radially inwardly directed tongues 16′ are provided, where the surface of the tongues to be brought into contact with the corrugated outer conductor is provided with a recess to enable it to grip over the top of the crests 33 of the corrugation instead of fitting into the valleys as in the previously described embodiment. Otherwise the construction of the guide part does not differ from the guide part 10 according to the first embodiment.

[0031] It is understood that the construction of the guide part 10 based on the radially resilient section 11 and the split up second section 12, 13, 14, 16 is chosen in order to provide the end of the guide part 10 which is provided with said tongues 16 with sufficient radial resiliency to make it possible to pass the end of the cable through the through hole in the guide part 10 despite the presence of the radially inwardly directed tongue 16, 16′ and furthermore to obtain a fixed and reliable positioning of these tongues in the appropriate valley of the corrugation of the outer conductor. The required radial resiliency of the portion of the guide part comprising the tongues 16, 16′ could, however, also be achieved in other manners without the necessity to split up the second section of the guide part by the longitudinal slits 15. For this purpose either the end of the guide part 10 comprising the tongues 16, 16′ could be made of a suitable resilient material with the remaining longitudinal extension of the guide

[0032] part, including the tubular section 11, being made of a rigid material, or the whole guide part 10 could be made of a material with sufficient radial resiliency, provided a well-defined abutment surface 13 and a well-defined longitudinal distance s (see FIG. 2c) or distance s (see FIG. 2d) were still obtained.

[0033] The outer surface of the second section of the guide part 10 is subdivided into three regions 12, 13, 14. In this manner, an abutment surface 13 for the second cutting means 18 mentioned initially is provided, said abutment surface 13 in this manner being located longitudinally at a well defined distance from said tongues 16, and thereby from the valley 17 in the corrugation of the outer conductor located closest to the end of the jacket (or from a corresponding crest 33 in case of the above second embodiment).

[0034] The last of the abovementioned three parts of the stripping tool according to the invention, i.e. the second cutting means 18, is shown schematically in FIGS. 3aand 3b. In FIG. 3a, a schematic longitudinal partly sectional view of the second cutting means generally indicated by 18 is shown. The second cutting means basically comprises a tubular house 20 to be placed coaxially over the previously described guide part 10, in such a manner that during operation hereof the circumferential inner surface 21 at one end of the second cutting means 18 fits on the corresponding region 12 of the guide part 10. Thus, when the guide part 10 is placed on the end of the cable as described in connection with FIGS. 2athrough 2d, the second cutting means 18 can during rotation hereof be displaced longitudinally in a well defined manner relative to the end of the cable over a longitudinal distance ultimately determined by the end face 29 during said displacement being brought into contact with the abutment surface 13 on the guide part 10. In this final position of the second cutting means 18 a well-defined longitudinal relationship between the second cutting means 18 and the various structures of the coaxial cable (i.e. the jacket 7, the outer conductor 9, the insulating layer 32 between outer and inner conductor and the hollow inner conductor 31 disposed about hollow interior 30) are thus established.

[0035] As mentioned in the disclosure of the invention the purpose of the stripping tool is to prepare the end of the cable in such a manner that the required longitudinal relationships between said structures of the cable are obtained. This is indicated in FIG. 4. Specifically the following requirements must be fulfilled: (1) The jacket 7 must be removed over the appropriate length of the outer conductor 9 as indicated by X2 in FIG. 4; (2) The end of the hollow inner conductor 31 and the insulating material 32 must be located at a distance of X1 from the end of the jacket; and (3) in order to achieve a proper fitting of a connector on the cable it is essential that the end of the outer conductor is located substantially at a “valley” of the corrugation, i.e. substantially at a part of the corrugation where this resumes the least diameter, as indicated by B in FIG. 4.

[0036] Returning to the detailed description of the second cutting means 18, said tubular house 20 comprises a first longitudinal section 21 of an inner diameter which fits the outer diameter of the corresponding section 12 on the guide part 10. In a second longitudinal section of the second cutting means 18 there is provided the cutting means 26 as such, which means 26 comprises guide tracks 24 and 25 and comprises a central longitudinal guide shaft 19 to be inserted into the end of the hollow inner conductor 31. Coaxially with the guide shaft 19 there is provided a cylindrical cutter means generally indicated by 26 in FIG. 3acomprising a first longitudinal portion containing a first cutting edge 22 and having a diameter corresponding to the smallest inner diameter of the outer conductor, so that this portion during operation can operate within the outer conductor without affecting this. When during operation the second cutting means 18 is rotated above its longitudinal axis about drive shaft 27, and hence relative to the cable, and simultaneously advanced longitudinally relative to the guide part 10, said cutting edge 22 cuts off the inner conductor 31 and the intermediate insulating material 32 to the appropriate longitudinal distance from the end of the jacket indicated by X1 in FIG. 4. The cutter means 26 is furthermore provided with a second cutting edge 23 located at one longitudinal end of a larger diameter second portion of the cutter means 26 and at a longitudinal distance d from the first cutting edge 22. During operation of the second cutting means 18 this second cutting edge 23 cut off the outer conductor 9 to its appropriate longitudinal length relative to the end of the jacket as indicated by X2 in FIG. 4. Thus the first two of the above-mentioned three requirements are achieved. The last of these requirements, i.e. that the end of the outer conductor be located substantially at a valley of the corrugation, is fulfilled for the following reason: As previously described when the guide part 10 is correctly positioned on the end of the cable as shown in FIG. 2c, the radial tongues 16 fits into that valley of the corrugation of the outer conductor 9 which is located closest to the end of the jacket. A well-established longitudinal relationship is thereby established between the position of that valley and the abutment surface 13 of the guide part 10. When hereafter during operation of the second cutting means 18 the end of this means 18 is brought into contact with the abutment surface 13, the second cutting edge 23 will be located at the appropriate longitudinal position S relative to the abutment surface 13 and hence to said first valley of the corrugation. Provided the longitudinal dimensions of the cutter means 26 are properly chosen, corresponding to the actual longitudinal distance between the valleys of the corrugation, the outer conductor will be cut off substantially at the valley adjacent said first valley, whereby the third requirement mentioned above will be fulfilled.

[0037] For the sake of clarity the second cutting means 18 according to this embodiment of the invention is shown in FIG. 3bseen from the end indicated by A in FIG. 3a, i.e. from that end into which the cable during operation of the tool is inserted. The relative radial positions of the cutting edges 22 and 23 can be seen from this Figure.