Abstract:
In a method of stripping and removing shielding from a cable, an end of the cable is stripped from an outer insulating sheath to expose a portion of the shielding which envelopes an inner electrical conductor. The exposed shielding portion is compressed in axial direction of the cable to so deform the shielding portion as to assume a donut shape which exceeds an outer dimension of the insulating sheath. A cutting unit is movable approximately transversely to a longitudinal orientation of the cable to shear off a circular section of the shielding portion.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of European Patent Application, Ser. No. 99 810 990.4, filed Nov. 1, 1999, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method and apparatus for stripping and removing the shielding from a cable. 
     U.S. Pat. No. 3,153,358 describes a shielded wire stripper by which, after removal of the outer sheath, the exposed cable end with shielding is placed into respective bores of first and second casings and so retained that the metallic shielding is compressed, when the second casing moves relative thereto in axial direction of the cable, and pushed by the second casing, which is provided with a counterbore, against a circular shoulder of the first casing, thereby shearing off the shielding. The separation process is thus implemented substantially through a shearing action which acts in axial direction of the cable. This is disadvantageous because the cable end and in particular the sheath in the area of the cable will fray and the shielding will expand out, thereby adversely affecting the electric connection. 
     SUMMARY OF THE INVENTION 
     It is thus an object of the present invention to provide an improved method for stripping and removing shielding from a cable, obviating the afore-stated drawbacks. 
     In particular, it is an object of the present invention to provide an improved method for stripping and removing shielding from a cable, by which the cable end of an electric conductor, after trimming away the insulating sheath, can be stripped of the enveloping shielding in a simple and cost-efficient manner to realize a reliable connection, without altering a relative geometric disposition in particular of two, three or more electric conductors, whereby this requirement is also ensured in relatively thin cables. 
     These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by stripping away the insulating sheath from an end of the cable to expose a portion of shielding, which envelopes an inner electrical conductor; compressing the exposed shielding portion in axial direction of the cable to so deform the shielding portion as to assume a donut shape which exceeds an outer dimension of the insulating sheath; and severing a circular section of the bunched shielding portion by a cutting unit which is movable approximately transversely to a longitudinal orientation of the cable. 
     According to another feature of the present invention, the exposed shielding portion is held between two clamping devices which are spaced-apart in axial direction of the cable and movable relative to one another, with the compression being implemented by moving the clamping devices relative to one another to thereby push together and bunch up the shielding portion until the donut-shape is realized. 
     Suitably, the circular section of the bunched shielding portion is positioned above the insulating sheath and has a substantially triangular-shaped configuration, whereby the triangular-shaped circular section has walls extending at an acute angle. 
     According to another feature of the present invention, the cutting unit can be moved from an idle position, in which the cutting unit extends transversely to a longitudinal axis of the cable, to an operative position, in which the cutting unit orbits around the bunched shielding portion for shearing off the circular section. Suitably, the bunched shielding portion is sheared off directly at an outer periphery of the insulation by the cutting unit orbiting around the bunched shielding portion. Of course, it is also possible to turn the cable and the bunched shielding portion relative to the cutting unit in the operative position for shearing off the circular section. 
     It is still another object of the present invention to provide an improved apparatus for carrying out the novel and inventive method of stripping and removing shielding from a cable, in accordance with the present invention. 
     This object is attained in accordance with the present invention by providing a pair of clamping devices for insertion of a cable which has been stripped of its insulating sheath to thereby expose a portion of a shielding, with the clamping devices so positioned at a distance to one another as to confine the exposed shielding portion therebetween, wherein the clamping devices are movable relative to one another to compress and bunch up the shielding portion to assume a donut shape; and by providing a cutting device movable in a direction transversely to a longitudinal direction of the cable for shearing off the bunched shielding portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects, features and advantages of the present invention will be more readily apparent upon reading the following description of a preferred exemplified embodiment of the invention with reference to the accompanying drawing, in which: 
     FIGS. 1A to  1 I show schematic illustration s of various process stages of the method for stripping and removing an exposed shielding portion from a cable, in accordance with the present invention; 
     FIGS. 2A to  2 D show partially sectional views, on an enlarged scale, of process steps for separating a circular section of the bunched shielding portion; 
     FIG. 3 is partial sectional view of an apparatus for stripping and removing an exposed shielding portion from a cable in accordance with the present invention; 
     FIG. 4 is a sectional view of the apparatus of FIG. 3, taken along the line IV—IV in FIG. 3; 
     FIG. 5 is a schematic illustration of a clamping device for use in the apparatus of FIG. 3; 
     FIG. 5A is a schematic illustration of a variation of a clamp piece of a clamping device, having fluted clamping surface; and 
     FIG. 5B is a schematic illustration of another variation of a clamp piece of a clamping device, having a clamping surface lined with a rubber coating. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. 
     Turning now to the drawing, and in particular to FIGS. 1A to  1 I, there are shown schematic illustrations of various process stages of the method for stripping and removing an exposed shielding portion  12  from a cable  10 , in accordance with the present invention. The cable  10  may be any commercially available jacketed cable comprised of two or more electric conductors  15 , which are held together in the form of a bundle by a transparent envelope (not shown), a shielding  120  (only exposed shielding portion  12  is shown here), which envelopes the conductors  15  and a stranded wire (not shown) and may be formed as a wire braid shielding, and an outer insulating sheath  11  which envelopes the shielding  120 . 
     FIG. 1A shows the cable  10  having a cable end  10 ′ which is stripped from the insulating sheath  11  by a suitable tool to thereby expose the shielding portion  12 . In order to realize a reliable connection of the electric conductors  15 , the shielding portion  12  should be stripped away precisely and as closely as possible to the circular end face  11 ′ of the insulating s heath  1 . 
     In a first phase of the novel and inventive method according to the present invention, as shown in FIG. 1B, the cable  10  with the exposed shielding portion  12  is guided in a direction, indicated by arrow  1 , through a throughboreof a first fixed clamping device  35  and pushed into a second clamping device  45 , which is movable along the cable  10  relative to the clamping device  35 , until impacting against a stop (not shown here, cf. adjustment member  66  in FIG.  3 ). For sake of simplicity, the clamping devices  35 ,  45  are each shown schematically in FIGS. 1B to  1 I by way of example only in the form of two interacting clamping pieces that are movable relative to one another for opening and closing the clamping device, as indicated in FIG. 1B by the arrows so as to set forth the principle of the present invention. Structure and operation of the clamping devices  35 ,  45  will be described in more detail with reference to FIGS. 3 to  5 . 
     After positioning the cable  10  with the exposed shielding portion  12  in a manner described above, the clamping devices  35 ,  45  are closed. The closing force applied by the clamping devices  35 ,  45  is such that the clamping device  35  holds the cable  10  in place via the insulating sheath  11 , without damaging the insulating sheath  11 , and the clamping device  45  engages the exposed shielding portion  12  at slight enough contact pressure that the shielding portion  12  can still be shifted relative to the conductors  15  in the direction of the clamping device  35 . 
     After clamping the cable  10  in the manner described, the clamping device  45  which is in engagement with the shielding portion  12  is moved in a direction of arrow  4  toward the stationary, closed clamping device  35 , as shown in FIG. 1C, thereby compressing and bunching the shielding portion  12  between the two clamping devices  35 ,  45  in circumferential direction radially outwards. In this phase, the conductors  15 , held together by the transparent envelope (not shown), remain in substantially stretched disposition and become exposed as well. The transparent envelope is later removed by suitable means, when the cable  10  is electrically connected. 
     Subsequently, as shown in FIG. 1D, the clamping device  45  is further shifted in the direction of arrow  4  until the shielding portion  12  between the confronting clamping devices  35 ,  45  is so bunched up as to form a ring-shaped bead or assume a donut shape which is substantially wedge-shaped in the outer zone. In this phase, both radially outwardly oriented walls of the shielding portion  12  are pressed together, and the conductors  15  are exposed and jut out from the clamping device  45  in substantially stretched disposition. 
     Next, as shown in FIG. 1E, the clamping device  35  is opened again whereas the clamping device  45  still clamps an end piece  12 ′ (FIG. 1F, not visible in FIG. 1E) of the shielding portion  12  and thus the cable  10 . The cable  10  is now pulled relative to the clamping device  35  in a direction of arrow  1 , thereby conjointly moving the clamping device  45 . The movement of the clamping device  45  in the direction of arrow  1  together with the cable  10  is restricted by an adjustable stop member (not shown here, cf. stop cylinder  78  in FIG.  3 ). 
     Next, as shown in FIG. 1F, the clamping device  35  is closed again for clamped engagement with the insulating sheath  11  of the cable  10 . The clamping device  45  is then opened and pulled, together with the cable  10 , in the direction of arrow  1  relative to the clamping device  35 . In the end position, the circular bunched shielding portion  12  bears against a confronting circular ring shaped end face  11 ′ of the insulating sheath  11  and is arranged between the two clamping devices  35 ,  45 , normally in a midsection between the clamping devices  35 ,  45 , and the conductors  15 , enveloped by the end piece  12 ′ of the shielding portion  12 , partially jut out from the clamping device  45 . 
     While the clamping device  35  is still closed and in clamped engagement with the insulating sheath  11 , the clamping device  45  is now closed as well, as shown in FIG.  1 G. In this position, the shielding portion  12  is held in the clamping device  45  via the end piece  12 ′ at slight contact pressure, with the conductors  15  jutting out of the clamping device  45 . The shielding portion  12  is securely held in place at this stage by the clamping devices  35 ,  45 . 
     As the spaced-apart clamping devices  35 ,  45  are closed and engaged with the insulating sheath  11  and the end piece  12 ′ of the shielding portion  12 , respectively, at least one cutting unit  20  is activated to orbit, e.g. in clockwise direction, as indicated by arrow Y, in circumferential direction about the theoretical longitudinal axis X of the cable  10  to thereby sever a peripheral circular section  12 ″ (cf. FIG. 2B) of the shielding portion  12  approximately flush with the outer diameter of the insulating sheath  11 . As shown in FIG. 1H, the peripheral circular section  12 ″ has a substantially triangular-shaped configuration. For sake of simplicity and ease of illustration, the cutting unit  20  is shown schematically in FIG. 1H merely by way of example in the form of two interacting blades that are movable relative to one another in order to set forth the principle of the present invention. Structure and operation of the cutting unit  20  will be described in more detail with reference to FIGS. 4 and 5. 
     Of course, it is certainly within the scope of the present invention to also move the cutting unit  20  from an idle position in a direction transversely to the elongation of the cable  10  toward the shielding portion  12 , and then lock the cutting unit  20  in place whereupon the cable  10  is rotated about its longitudinal axis in the direction of arrow Y to orbit around the cutting unit  20 , while the fixed cutting unit  20  is activated to sever the circular section  12 ″ of the shielding portion  12 . 
     After severing the circular portion  12 ″, both clamping devices  35 ,  45  are opened again, either simultaneously or sequentially, and the cable  10  is pulled out of the clamping devices  35 ,  45  in the direction of arrow  4 , as shown in FIG.  1 I. The end piece  12 ′ of the shielding portion  12 , which is left of the shielding portion  12  and still envelopes the conductors  15 , may be removed either automatically as a result of a slight contact pressure applied by the clamping device  45  against the end piece  12 ′ when withdrawing the cable  10  in the direction of arrow  4 , or manually stripped from the conductors  15 , after the cable  10  is pulled out. 
     Turning now to FIGS. 2A to  2 D, there are shown partially sectional views, on an enlarged scale, of the process steps for separating the peripheral circular section  12 ″ of the bunched shielding portion  12 . FIG. 2A shows the cable  10 , the insulating sheath  11 , the shielding  120 , which envelopes the conductors  15 , and the shielding portion  12 , which is bunched up after compressing the shielding  120  and slightly spread as a consequence of the own elasticity (cf. FIGS.  1 D and  1 E), after removal of the clamping devices  35 ,  45 . The shielding portion  12  of substantially triangular-shaped configuration bears with one sidewall against the circular end face  11 ′ of the insulating sheath  11  and has an opposite sidewall whereby the sidewalls define an acute angle γ relative to one another so that the circular section  12 ″ can be grasped by the cutting unit  20  in an optimum manner and severed at a cutting line S—S above the insulating sheath  11  or flush with the outer diameter of the insulating sheath  11 , as illustrated in FIG.  2 B. Suitably, the distance between the sidewalls should be as small as possible to attain an optimal cutting operation. Once the circular section  12 ″ is separated and removed, only stubs  13 ′,  13 ″ of the sidewalls of the shielding portion  12  as well as the end piece  12 ′ remain, whereby the sidewall stubs  13 ′,  13 ″ are separated from one another in spaced-apart disposition, with the sidewall stub  13 ″ being attached to the end piece  12 ′ and the sidewall stub  13 ′ being attached to the shielding  120 , as shown in FIG.  2 C. The end piece  12 ′ with attached sidewall stub  13 ″ can now be stripped away from the conductors  15  by pulling it in the direction of arrow  1 . 
     Turning now to FIG. 3, there is shown a partial sectional view of a shielding removal apparatus for carrying out the method as described above, generally designated by reference numeral  100 . The apparatus  100  includes a first assembly  50 , which combines the clamping device  35  with the cutting unit  20 , and a second assembly  80 , which combines the clamping device  45  with a drive mechanism for moving the clamping device  45  relative to the clamping device  35 . The first assembly  50  includes a fixed bearing block  25  mounted on a base plate  40 . Fitted in the bearing block  25  is a clamping sleeve  26  and, coaxial thereto, an outer bearing sleeve  27 . Secured to the bearing sleeve  27  is a disk  32  which, in the non-limiting example illustrated here, is rotatable clockwise about pivot axis X and carries the cutting unit  20 . Placed on the bearing sleeve  27  adjacent to and interacting with the disk  32  is a drive disk  33 , which has external teeth, and a slip ring  34  formed with sliding contacts (not shown). The slip ring  34  forms part of a generally known electric motor (slip ring motor) and supplies electric current to the drive motor  24  (FIG. 4) of the cutting unit  20 . 
     A pivot lever  28  has one end in cooperating relation with the bearing sleeve  27  and another end articulated to a head piece  31 , which forms part of an actuating mechanism for opening and closing the clamping device  35 . The actuating mechanism further includes a pneumatic or hydraulic cylinder  30  which accommodates a piston rod  29  whose free end is connected to the headpiece  31 . Activation of the cylinder  30  results in a swinging motion of the pivot lever  28  via the piston rod  29 , thereby pivoting the bearing sleeve  27  relative to the inner clamping sleeve  26  about the axis X to close and open the clamping device  35 . 
     The cutting unit  20  has a mounting  22  for support of two blades  21 , which are pivotally connected together by a pivot so as to be movable relative to one another, and a drive motor  24  which has an output journal  24 ′ (FIG. 4) for connection to the disk  32  and is operatively connected to a gear mechanism  23 . The gear mechanism  23  provides, on the one hand, a transmission of the speed of the drive motor  24  and, on the other hand an operation of the blades  21  in dependence on the speed. Thus, activation of the drive motor  24  results in a swinging of the cutting unit  20  from an idle position (FIG. 4) to an operative position about the journal  24 ′ and movement in the direction of the theoretical axis X of the shielding removal apparatus  100  to sever the circular section  12 ″ of the shielding portion  12 . After separation, the circular section  12 ″ drops in a container  85  through an opening  16  in the base plate  40 . 
     The second assembly  80  includes a carrier  55 , which is guided along two guide rods  41  for movement relative to the first assembly  50 , and a fixed bearing block  42 , which is mounted on the base plate  40  for support of the guide rods  41 . A hydraulic or pneumatic cylinder  75  includes a piston rod  74  whose free end is received in the carrier  55  so that an activation of the cylinder  75  results in a displacement of the carrier  55  in a direction of double arrow  6  relative to the fixed bearing block  25 . A bracket  73  secures to the base plate  40  a stop cylinder  78  whose piston rod  77  extends through the bearing block  42  for interaction with the carrier  55 . Fitted in the carrier  55  are a clamping sleeve  56  and an outer bearing sleeve  57 . Secured to the outer bearing sleeve  57  is one end of a pivot lever  58  whose other end is articulated to a headpiece  61 , which forms part of an actuating mechanism for opening and closing the clamping device  45 . The actuating mechanism further includes a pneumatic or hydraulic cylinder  60  which accommodates a piston rod  59  whose free end is connected to the headpiece  61 . The cylinder  60  is connected at its lower end to a journal  53  which is received in a mounting  54  secured to the carrier  55 . Activation of the cylinder  60  results in a swinging of the pivot lever  58 , thereby pivoting the bearing sleeve  57  relative to the inner clamping sleeve  56  about the axis X to close and open the clamping device  45 . For example, when the piston rod  59  occupies the retracted position in the cylinder  60 , the clamping device  45  is opened. 
     Extending interiorly of the clamping sleeve  56  is a pickup pipe  65  for receipt of the cable  10 . The pickup pipe  65  is secured at its end distal to the clamping device  45  in a mounting  64  which supports a pneumatic or hydraulic cylinder  62  which accommodates a piston rod  63  received in the carrier  55 . Activation of the cylinder  62  conjointly shifts the mounting  64  and the pickup pipe  65  in axial direction relative to the clamping device  35  for capturing the inserted cable  10 , when the clamping device  45  is open. 
     Accommodated in the pickup pipe  65  is an adjustment member  66  which forms a stop member for the cable  10  and is secured to a carrier frame  68 . A drive  44  is connected to the carrier frame  68  via a piston rod  43  to thereby effect a displacement of the adjustment member  66 . A set screw  69  is provided on the carrier frame  68  to secure the adjustment member  66  against axial displacement. Securely fixed to the rear free end of the adjustment member  66  is a retention member  67  which supports an elongate adjusting rail  70  extending through the carrier frame  68 . The adjusting rail  70  is movable in the direction of arrow  6  relative to a graduation  71 , e.g. a millimeter graduation, formed on the carrier  55 . Through operation of the drive  44  via the piston rod  43  is it possible to adjust the position of the stop-forming adjustment member  66  in the pickup pipe  64  in dependence on the extent of the shielding portion  12  to be stripped away from the cable  10 . 
     FIG. 4 shows an illustration of the first assembly  50 , taken along the line IV—IV in FIG.  3 . The clamping device  35  has a plurality of clamp pieces  36  which are movably secured about the circumference of the bearing sleeve  27 . As illustrated in FIG. 4, a platform  17  is mounted onto the base plate  40  for support of a bearing member  49  for receiving a drive assembly  46  having an output gear  47  which is operatively connected via a toothed belt  48  with the toothed drive disk  33  upon the bearing sleeve  27 . As shown in broken line, a second cutting unit  20  may be, optionally, secured to the disk  32 . When providing only one cutting unit  20 , the disk  32  with attached cutting unit  20  is rotated, e.g. clockwise as indicated, about an angle of 360° for separating the circular section  12 ″ from the shielding portion  12 . When mounting two cutting units  20  to the disk  32 , each cutting unit  20  is rotated in increments about an angle of 180°. Of course, the cutting units  20  may also be so operated that each cutting unit  20  rotates about an angle of 180° in one direction of rotation and then is returned to its idle position by rotating in the opposite direction. Double arrow  5  indicates the direction of displacement of the cutting unit  20  with respect to the cable  10 . 
     FIG. 5 shows, on an enlarged scale, the structure of the clamping device  35 . As the clamping devices  35 ,  45  are of an identical construction, it will be understood by persons skilled in the art that the following description of the clamping device  35  is equally applicable to the other clamping device  45 . The clamp pieces  36  are each provided with an oblong hole  38  and secured by a screw  37  to the outer bearing sleeve  27  and a further screw  39  to the clamping sleeve  26 . Each clamp piece  36  has a slanted end clamping surface  36 ′ which defines an angle α, e.g. of about 45°, and is so configured that the insulating sheath  11  of the cable  10  will not be damaged during clamping action while still securely positioning the cable  10  in place during the cutting operation. FIG. 5 shows the clamp pieces  36  in substantially closed disposition. FIGS. 5A and 5B show variation of clamp pieces  36 , with FIG. 5A showing the clamp piece  36  having a fluted clamping surface  36 . 1 , and FIG. 5B showing the clamp piece  36  having a clamping surface  36 . 2  which is lined with a rubber coating. 
     While the invention has been illustrated and described as embodied in a method and apparatus for stripping and removing the shielding from a cable, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.