Abstract:
An automatic wire stripper comprises a knife unit ( 40 ) having a knife holder ( 41 ) and a knife carriage ( 45 ) articulated on the knife holder; A clamping arm unit ( 30 ) is pivotally mounted on a clamping arm bearing ( 30 ). A handle lever unit ( 60 ) is pivotally connected to a housing base ( 20 ) on a handle lever bearing ( 61 ). An articulated lever ( 70 ) has a first and second articulated lever arm ( 72, 75 ) connected in a pivotable manner by an articulated lever center axis ( 73 ). The first articulated lever arm ( 72 ) is guided with a first articulated lever axis ( 71 ) in a guiding connecting link ( 32 ) of the clamping arm unit ( 30 ). The second articulated lever ( 75 ) is fixed in an articulated manner to the knife unit ( 40 ) with the articulated lever center axis ( 73 ) guided in the handle ( 60 ).

Description:
This application is a 371 of PCT/EP04/10718, filed Sep. 24, 2004. 
   BACKGROUND OF THE INVENTION 
   The invention relates to automatic stripping pliers, in particular for flat cables. 
   Automatic stripping pliers that are used to strip the ends of an electrical cable from the insulating jacket are known from, for example, DE 39 22 016 C2. With it, the cable is placed between two knife elements that have their blades set against each other. The insulated cable is clamped next to the knives. By pulling the movable grip lever against the handgrip of the base housing, the knife elements are pressed into the insulation. With the continued grip movement, the knives are moved in the direction of the cable end, such that the insulation that has been severed by the knives is stripped off the electrical lead. All these processes can be accomplished with the known automatic stripping pliers in one single movement, namely the moving of the grip lever to the hand grip of the base housing. This significantly simplifies the stripping of electrical cables. 
   However, with the known stripping pliers only a certain length can be stripped from the end of the cable, because the knives are attached to arms that are connected in an articulated manner to one another, resulting in the distance from the knife to the articulated axis that is struck by the cable end as a maximum functional length. This distance is sufficient to strip the electrical lead at the end of the cable, which can then be inserted into respective terminals of electrical devices. However, it is not possible to remove the outer jacket of a multi-insulated electrical cable over a greater length, as is necessary, for example, to arrange individual wires at intact individual wire insulations in junction boxes, etc. While as a workaround, round wires can still be lead to the side out of the knife arms, kinking flat cables to the side is not possible such that with the known pliers the outer jacket cannot be removed to a greater length. 
   SUMMARY OF THE INVENTION 
   A principle objective of the invention, therefore, is to provide automatic stripping pliers which are capable of stripping any length of stripping a cable jacket, in particular of a flat cable. 
   This objective, as well as other objectives which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, by providing wire stripping pliers that comprise at least one knife unit having at least one knife holder and a knife carriage articulated on the knife holder; a clamping arm unit with at least one clamping jaw disposed on the front end thereof; a housing base having an upper clamping arm in which the knife unit is displaceably guided; at least one clamping jaw; a clamping arm bearing whereon the clamping arm unit can be pivotally mounted; a handle lever unit which is pivotally connected to a housing base on a handle lever bearing and an articulated lever having a first and a second articulated lever arm which are connected to each other in a pivotable manner by an articulated lever center axis. The first articulated lever arm is guided with the first articulated lever axis in a guiding connecting link of the clamping arm unit; the second articulated lever is fixed in an articulated manner to the knife unit; and the articulated lever center axis is guided in the handle lever unit. 
   Significant to the invention is the elbow lever unit, which controls the entire movement sequence during stripping and affects a uniform force distribution in all phases of movement. Load peaks during operation of the elbow lever unit according to the invention have the effect that certain positions of the components are assumed or abandoned. It is not possible to destroy the cable being stripped or even the stripping pliers through carelessness or by applying too much force. Thus, many components of the stripping pliers can be manufactured economically of synthetic materials. 
   Feed-through of long cables can, for example, be enabled by a knife holder that is open towards the top and a base housing that is open towards the top. Preferably, however, the knife holder and/or the knife carriage exhibit, at least in the area of the articulated axis, a U-shaped cross-section. This forms a cable feed-through channel between the knife carriage and the knife holder. 
   To reduce the friction forces, and with it the actuating forces to be applied by the user, the center axis of the elbow lever should be made rollable in the elbow lever axis guide groove via an elbow lever guide roll. 
   In preferred embodiments, the clamping arm unit exhibits at its bottom side a guide link, where the knife unit is guided via a knife unit guide roll. The guide link is provided with at least one locking notch. The guide link controls the movement of the knife unit in the clamping arm unit. In addition, the locking notch provides a fixed support for the elbow lever unit in a first phase of movement. 
   In one preferred embodiment, the knife unit&#39;s guide roll is furthermore supported at the receiving joint of the spring, such that the pressing force transferred by the spring unit presses directly onto the knife unit&#39;s guide roll and if applicable presses it into a locking notch. 
   Preferably, the end axis of the second elbow lever is located in the articulated axis of the knife unit, such that a force vector acting from the elbow lever unit onto the second elbow lever end axis affects only a translatory movement of the knife unit but not an opening or closing of the knife unit. 
   The knife carriage and/or the knife holder are preferably provided with replaceable knife elements in order to easily replace dull blades. 
   The upper clamping arm and/or the clamping arm unit can be provided with replaceable clamping jaws such that not only damaged clamping jaws can be replaced but also special clamping jaws can be employed that are matched to the respective cable type processed by the stripping pliers. 
   For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 to 3  are cross-sectional side views of the stripping pliers according to the invention at various operational positions. 
       FIG. 4  shows the stripping pliers according to  FIGS. 1 to 3  with a long cable end. 
       FIG. 5  is a side view of the stripping pliers of  FIGS. 1 to 3 . 
       FIG. 6  is a side cross-sectional view of another preferred embodiment of the stripping pliers with a cable cutter. 
       FIG. 7  is a cross-sectional side view of still another preferred embodiment of stripping pliers according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The preferred embodiments of the present invention will now be described with reference to  FIGS. 1-7  of the drawings. Identical elements in the various figures are designated with the same reference numerals. 
     FIG. 1  shows a side view of a preferred embodiment of stripping pliers  100  according to the invention. Essentially, it is comprised of:
         a base housing  20 ,   a clamping arm unit  30 ,   a knife unit  40 ,   a stop element  50 ,   a handle lever element  60 ,   an elbow lever unit  70 , and   a spring element  80 .       
   At its upper end, the base housing  20  ends with an upper clamping arm  25  with a clamping jaw  21  located at its front end. A handgrip section  24  is formed downwards. 
   Connected with the base housing  20  in a movable manner are:
         the clamping arm unit  30  via the articulated clamping arm bearing  23 , and   the handle lever unit  60  via the articulated handle lever joint  61 .       

   The length of the clamping arm unit  30  is selected such that the free end is approximately opposite to the end of the upper clamping arm  25 . Another clamping jaw  31  is located at the free end and is located opposite the clamping jaw  21  of the base housing  20 . The clamping arm unit  30  is designed such that it receives the knife carriage  45  as the lower partial element of the knife unit  40 , whereby the knife carriage  45  is supported in it across a portion of the length of the clamping arm unit  30  in a movable fashion. 
   As  FIG. 5  clearly shows, the clamping arm unit  30  exhibits at its side wall at least one elbow lever axis guide groove  34  (cf.  FIG. 5 ) that limits the travel of a first elbow lever end axis  71  in certain operational positions. At its bottom side, the clamping arm unit  30  is designed with a sliding seat for the stop element and a guide link for a knife unit guide roll. 
   The handle lever unit  60  exhibits at the articulated handle lever joint  61  a stop bolt  62 . This is a fixed stop for the stop element  50  of the elbow lever unit  70 . The stop bolt  62  can be connected to the handle lever unit  61  in a fixed manner cylindrically as a rigid axis, or it is arranged rotatably around the articulated handle lever joint  61 . 
   A handgrip section  64  is formed at the end opposite the handle lever joint  61 . Length and curvature are selected and matched to the handgrip section  64  of the base housing  20  such that the stripping pliers  100  subject to the invention can be held and operated easily by the user. 
   The handle lever unit  60  with the elbow lever axis guide groove  66 , which is advantageously surrounded by an elevated guide strip  65 , exhibits a slide guide for an elbow lever center axis  73 . 
   At the handle lever unit  60 , a spring element  80  is additionally articulated at an articulated spring element bearing  63 . The spring element  80  consists essentially of an upper and a lower spring support element  81 ,  82 , which are located on the same center axis and have a compression spring located between them. The upper spring support element  81  is articulated at the knife unit  40  via a spring element receiving axis  48 . 
   Fundamentally, the knife unit  40  is comprised of a lower knife carriage  45  and a knife holder  41  articulated on said carriage. At their free ends, the knife carriage  45  and the knife holder  41  each exhibit at least one knife element  43 ,  46 , that can, at least partially, cut through the synthetic jacket of an electrical cable  1 . The knife carriage  45  and the knife holder  41  are connected in an articulated manner via a knife unit joint  44 . In the area of the knife unit joint  44 , the knife holder  41  is designed with a U-shaped cross-section, whereby the open end of the cross-section points down in the direction of the knife carriage  45 . This creates an interim space between the upper side of the knife carriage  45  and the bottom side of the wall of the knife holder  41  shown sectionally in  FIG. 1 , where the cable  1  can be fed through. Molded onto the bottom side of the knife carriage  45  is a joint receptacle in which a knife unit guide roll  49  is supported rotably. Preferably, the axis  48  of the knife unit guide roll  49  coincides with the articulated joint of the upper spring support element  81 . 
   The knife unit guide roll  49  runs along the guide link  32  at the bottom side of the clamping arm unit  30 . The guide link  32  is provided with locking notches, run-up slopes, etc. to control the movement of the knife unit  40  in relation to the clamping arm unit  30  as will be elucidated below. 
   A core component of the stripping pliers  100  according to the invention is in addition to the knife unit  40  with cable feed-through channel, the elbow lever unit  70  together with the stop element  50 . 
   The elbow lever unit  70  is comprised of a first elbow lever  72  and a second elbow lever  75  that is articulated on the first elbow lever via an elbow lever center axis  73 . The elbow lever center axis  73  is guided in a movable fashion in the elbow lever axis guide groove  66  of the handle lever unit  60  via an elbow lever guide roll  74 . 
   The second elbow lever  75  with its second elbow lever end axis  76  is articulated at the knife unit  40 ; preferably, the second elbow lever end axis  76  and the knife unit joint  44  coincide. This has the effect that the force acting by the elbow lever  75  onto the knife unit  40  results only in a movement of the same in relation to the clamping arm unit  30 , but not to an articulating movement of the knife carriage  45  in relation to the knife holder  41 . 
   In this preferred embodiment, the first elbow lever  72  is guided with its first elbow lever end axis  71  both in the guide link  32  of the clamping arm unit  30  and in the elbow lever axis guide notch  47  of the knife unit  40 . While the guide link  32  of the clamping arm unit  30  exhibits only a certain length and limits the movement range of the first elbow lever end axis  71 , the elbow lever axis guide groove  47  of the knife unit  40  is designed with such a length that the knife unit  40  can be moved independent of the respective position of the first elbow lever end axis  71  across the entire possible travel path within the clamping arm unit  30 . 
   The stop element  50  is articulated on the first elbow lever end axis  71 . This stop element exhibits a support surface that is used to support the stop element  50  at the bottom side of the clamping arm unit  30 . In addition, the stop element  50  exhibits a stop surface  52 , which is at a slope towards the support surface and approximately vertical to the force vector of a force F applied by the user when operating the handgrips  24 ,  64 . 
   The kinematics subject to the invention is explained below based on the movement sequence when stripping an electrical cable as shown in  FIGS. 1 to 3 : 
     FIG. 1  shows a possible starting position, where the clamping arm unit  30  with its clamping jaw  31  is spread apart from the clamping arm  25  with the clamping jaw  21  of the base housing  20 , and the knife holder  41  is spread apart from the knife carriage  45 , such that the two knife elements  43 ,  46  are at a certain distance opposite each other. It is now possible to insert a cable  1  between the clamping jaws  21 ,  31  and the knife elements  43 ,  46 , and that at any length, for example, as shown in  FIG. 1 , relatively short for full stripping of the individual wires at their ends, or for removing the outer jacket of the cable at a greater distance from the cable end. 
   With the stripping pliers  100  according to the invention, it is possible to push the cable  1  through the entire knife unit  40  and past the two articulating axis joints  44  located on the outside until the cable  1  exits from the back of the base housing  20 . In this manner, the outer jacket can be cut at a great distance from the end of the cable. 
   At the starting position shown in  FIG. 1 , the hand grip  64  is also spread apart of the base housing  20  with its hand grip  24  due to the force of the spring  83 . In its most forward position, the knife unit  40  is located within the clamping arm unit  30  or the base housing  20 , respectively. At this position, the knife unit guide roll  49  engages in a locking notch  33  of the guide link  32  at the bottom side of the clamping arm unit  30 ; the locking notch  33  can be recognized in  FIG. 3 . 
   The slanted position of the elbow lever axis guide groove  66  has the effect that at a maximum spread of the grip lever unit  60  according to  FIG. 1 , the elbow lever center axis  73  is pulled into the right area of the groove  66  via the elbow lever guide roll  74  that runs in the elbow lever axis guide groove  66 . Through this, the first elbow lever end axis  71  with the stop element  50  is pulled back at the same time via the first elbow lever  72 . The stop surface  52  of the stop element  50  maintains a distance to the stop bolt  62 . 
   When operating the stripping pliers  100  according to the invention, the handle lever unit  60  is pivoted toward the base housing  20  around the handle lever joint  61 . A force is applied to the knife unit guide roll  49  via the spring element  80 , and is pressed into the locking notch  33  of the guide link  32  by this force. Via the knife unit guide roll  49 , the second elbow lever end axis  76  is at the same time temporarily fixed in the locking notch, because a fixed connection is established between the axes  44  and  48  via the knife carriage  45 . 
   At the same time, when operating the handle lever unit  60 , a force is applied to the elbow lever guide roll  74  at the elbow center axis  73  via the guide strip  65  at the elbow lever axis guide notch  66 . Because the second elbow lever axis  76  is in this phase still fixed as described above, the first elbow lever  72  makes an evasive movement to the left. Through it, the stop element  50  is pushed further forward, i.e., in the direction of the clamping jaws  21 ,  31  until the stop surface  52  rests on the stop bolt  62 . 
   This condition is shown in  FIG. 2 : The clamping jaws  21 ,  31  clamp the inserted cable  1  at its outer circumference. The blades of the knife elements  43 ,  46  have entered the jacket of the cable  1  and have cut the jacket at least partially. To this end, the position of each of the blade edges of the knife elements  43 ,  46  is selected such that they protrude only slightly past the clamping jaws  21 ,  31  toward the inside into the angle formed between the knife carriage  45  and the knife holder  41 . This ensures that even cables that are provided with a very thin jacket are not cut by the knife elements  43 ,  46 , and that only the outer jacket is removed without the copper strands being cut by the knives. Cutting into the jacket at the circumference is sufficient to tear off the jacket portion with only minimal application of force for the typical electrical cable PVC jackets, and thus achieve the full separation of the jacket. 
   Tearing off is accomplished through the backwards movement of the knife unit  40  as the third significant phase of movement, whereby the knife elements  43 ,  46  remain engaged with the jacket, and the cable  1  remains clamped next to the knife elements  43 ,  46  by the clamping jaws  21 ,  31 . 
   The third operating phase starts with the situation shown in  FIG. 2 , whereby the knife unit  40  is still located in its front most position near the clamping jaws  21 ,  31 , and whereby the stop surface  52  is supported at the stop bolt  62 . Now, a movement of the stop element  50  is no longer possible, such that the end axis of the first elbow lever  71  is fixed via the stop element  50 . 
   The force applied to the elbow lever center axis  73  also acts upon the second elbow lever  75 , and thus upon the knife unit joint  44 . In the course of the operation of the handle lever unit  60 , the force acting upon the second elbow lever  75  and the knife unit  40  rises due to the first elbow lever  72 , which is fixed via the stop element  50 , to an extent that the knife unit guide roll  49  is pressed out of the locking notch  33  and the knife unit  40  is pushed backwards in the clamping arm unit  30 . 
   The part of the jacket of the cable  1  that is to be removed is pulled backwards with the movement of the knife unit  40  and is fully torn off. This results in the situation shown in  FIG. 3 . 
   Upon release of the hand grip section  64 , the handle lever unit  60  is returned to its initial position due to the force of the compression spring  83 , whereby the clamping arm unit  30  is spread apart from the upper clamping arm  25  of the base housing  20 ; the same applies to the knife holder  41  in relation to the knife carriage  45 . The processed cable  1  can now be removed from the opened stripping pliers  100 . 
   The separated portion of the jacket has been automatically pulled off completely, if the length to be stripped is not longer than the maximum possible return path length of the knife unit  40 . Otherwise, the end of the jacket to be removed has been pulled back enough such that the user can easily grab it and pull it off the cable end. 
   A knife holder guide groove  22  can be recognized in  FIG. 3  in which a guide cam  42  runs that has been molded onto the outside of the knife holder  41 . This has the effect that the knife holder  41  moves at a pre-specified path in the base housing  20  and that the knife holder  41  does not need to be spread apart from the knife carriage  45  through additional springs, etc. 
   The specific advantage of the invention is achieved through the elbow lever unit  70 . In all operational phases, a force is transferred via the elbow levers  72 ,  75  leading to the closing of the clamping jaws  21 ,  31 , or the pressing together of the knife elements  43 ,  46 , respectively, and maintaining the clamping action also during the subsequent operational steps; i.e., a sufficient clamping force is created via the elbow lever unit  70  that the cable  1 , which is clamped between the clamping jaws  21 ,  31 , is not moved during the return movement of the knife unit  40 . Together with the clamping force, the force for the complete tearing off and pulling off of the jacket is applied via the elbow lever unit  70 . Force peaks lead to the initiation of the next phase of the movement, such that the forces acting upon the cable are limited by design. 
     FIG. 4  shows how a long cable end is fed through the stripping pliers  100 , in particular through the pliers&#39; knife unit  40 . Also recognizable is the elbow lever axis guide groove  34  in the clamping arm unit  30  (see  FIG. 5 ) by which the travel of the first elbow lever end axis  71  and with it, the travel of the stop element  50  is limited. Important is, in particular, the limiting of the forward movement of the first elbow lever end axis  71 , because this prevents too great a clamping force from acting upon the clamping jaws  21 ,  31 , which would squeeze off very thin cables. 
     FIG. 6  shows another preferred embodiment with an additional cable cut-off device. It is formed by a knife holder  91  that is positively connected to the base housing and a blade  92  that is attached to the handle lever unit  60 . When pivoting the handle lever unit  60  around the handle lever joint  61 , the blade  92  is moved toward the fixed knife holder  91 . A cable placed between these parts will be fully cut. The knife holder  91  is preferably fixed to the stop bolt  62  as well as to another point at the base housing  20 , which can be freely selected as long as it does not interfere with the operation of the user and does allow a free movement of the elbow lever unit  70  and of the spring element  80 . For the sake of clarity, the elbow lever unit  70 , the spring element  80  and the stop element  50  are not shown in  FIG. 6 . 
     FIG. 7  shows still another preferred embodiment of stripping pliers  100 ′, where the clamping arm  25 ′ of the housing  20 ′ exhibits a pressure point element  26 ′, which is located opposite the upper side of the knife unit  40  and is guided in a movable fashion in a pressure point element guide groove  27 ′. 
   Through the pressure point element  26 ′, the pressure point against which the knife unit  40  is pressed when operating the stripping pliers, can be defined and changed, in a first phase when the knife holder  41  and the knife carriage  45  as well as the clamping jaws  21 ,  31  are moved toward each other under inclusion of a cable  1  placed between them. The knife unit  40  presses, depending on the position of the pressure point element  26 ′ somewhat earlier or somewhat later in its movement against this created pressure point. In this manner, the knife unit  40  is fixed at the front at the knife elements and further back at the pressure point element  26 ′. At the same time, the clamping arm unit  30 ′ is also fixed at the front at the clamping jaws  21 ,  31  and indirectly via the knife unit  40  at the pressure point element  26 ′. 
   A further increasing force, when operating the stripping pliers  100 ′, is guided to the blocked clamping arm unit  30 ′ via the knife unit guide roll  49 , and results in the knife unit guide roll  49  being pushed out of the locking notch  33  (cf.  FIG. 4 ), which triggers, as has already been explained above, the return movement of the knife unit  40  leading to the pulling off of the cut off cable jacket. 
   To reduce the bending stress of the clamping arm unit  30 , in particular between the moment of blocking of the clamping arm unit  30 ′ by placing the knife unit  40  against the pressure point element  26 ′ and the start of the return movement of the knife unit after the knife unit guide roll  49  has been pushed out of the locking notch, the articulated clamping arm bearing  23 ′, is formed by an axis connected to the base housing  20 ′ where said axis rests on a damping element  35 ′ in the clamping arm unit  30 ′. 
   The elastomeric damping element  35 ′ is preferably located underneath the axis in an elongated hole  36 ′ in the clamping unit  30 ′ and cushions load peaks. The additional damping can be provided for both the first shown embodiment of the stripping pliers  100  and the embodiment of the stripping pliers  100 ′ with the pressure point. 
   There has thus been shown and described a novel automatic wire stripper which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.