Abstract:
Apparatus for severing and stripping a portion of a coating material from an elongated member such as an insulated electrical conductor, or the like, utilizing a pair of overlapping blades having cutting edges formed at the junction of two planar surfaces meeting at an acute angle. The blades are moved relative to one another, radially of the conductor, to cause the cutting edges to move radially partially through the layer of insulation. Relative movement of the blades and conductor axially of the conductor completes the severing of a slug of insulation, all in accordance with the prior art. The present apparatus is distinguished by making the planar surface portions immediately adjacent the cutting edges of the overlapping blades and engaged with the portion of the insulation to be stripped, i.e., the portions of the blades which apply the axial severing force, at equal angles, either 90° or an acute angle, to the direction of relative movement. The disclosure is also embodied in the method of cutting and severing a slug of coating material in the foregoing manner.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to apparatus having a pair of overlapping blades for cutting partially through one or more layers of material surrounding an elongated, filamentary member, and then severing the material at the position of the cuts by moving the blades axially of the member while restraining the latter against axial movement, or by maintaining the blades stationary and moving the member axially with respect thereto. More specifically, the invention relates to novel configurations and arrangements of the blades used in apparatus of the foregoing type to provide improved operation, particularly when operating upon members of relatively large diameter. 
     The prior art contains many examples of manually, semi-automatically and automatically operated apparatus for severing layers of material which cover elongated, filamentary members for the purpose of exposing an end portion or intermediate part of such member. In one widely used application, a layer of insulation is cut, severed and stripped from a free end of an electrical wire. Such apparatus is also used for removing coating layers from selected portions of optical fibers, coaxial cable, flat ribbon cable, etc. Although it will be understood that the present invention is suitable for use in all analogous operations, it will be explained and hereinafter referred to in the context of severing and stripping a single layer of insulating material from a free end portion of an electrical wire. 
     While some severing and stripping apparatus has used only a single cutting blade which is moved around the wire, it is far more common to employ a plurality of blades to cut the insulation. In any case, the blade or blades are mounted for reciprocating movement of the cutting edge(s) radially of the wire or other elongated member. When two or more blades are used in such operations, they may be mounted with the cutting edges in direct opposition, i.e., in the same plane perpendicular to the axis of the wire, such as in the various embodiments of cutting and stripping apparatus disclosed in U.S. Pat. Nos. 4,993,147 and 4,993,287, both issued Feb. 19, 1991 and assigned to applicants&#39; assignee. Since at least portions of the opposing edges of blades mounted in this manner are in mutual, abutting relation when the blades are moved toward one another to the limit of their movement, they will be termed &#34;abutting blades.&#34; 
     In some apparatus of this type, it has been found convenient to mount the blades with opposing surface portions in superposed, sliding contact as the blades are moved reciprocally relative to one another and radially of a wire positioned therebetween with its axis perpendicular to the blade cutting edges. The prior art includes numerous examples of cutting and stripping apparatus with blades arranged in this manner. Since portions of such blades are in mutually overlapping relation, they are termed &#34;overlapping blades, &#34; as distinguished from abutting blades The cutting edges of overlapping blades are usually formed along the edges of notches, e.g., of V-shaped configuration, in one side of the blades. 
     The cutting edges of both types of blades are normally formed at the juncture of two essentially planar surface portions meeting at an acute angle to form a sharp edge. The plane of at least one of the planar surfaces forming the cutting edge(s) also intersects the axis of the wire at an acute angle, the other planar portion commonly being perpendicular to the wire axis; the planar portion(s) adjacent the cutting edge(s) arranged at an acute angle to the wire axis are herein termed &#34;bevel surface(s).&#34; 
     After the blade cutting edges are moved toward one another to cut at least partially through the insulation, the blades and wire are moved relative to one another in a direction axially of the wire to complete the severing of a slug of insulation and strip it fully or partially from the conductor. The slug may be stripped in one of two ways: 1. the wire may be firmly clamped at a position on the side of the blades opposite the slug to be stripped and the blades, while engaged with the insulation, moved simultaneously in the direction of the slug, or 2. the wire may be grasped mechanically or manually on the side of the blades opposite the slug to be removed and moved axially as the engaged blades remain stationary. 
     Although blades of the abutting type have been arranged with the planar surface portions adjacent the cutting edges and facing the slug to be stripped disposed at the same angle to the axis of the wire, conventional wisdom dictates that, when employing a pair of overlapping blades, the bevel surfaces face in opposite directions from the surfaces in sliding contact. This is because such an arrangement places the sharp, cutting edges as closely as possible to the same plane, i.e., the planes of the blade surfaces which are in sliding contact. This may be, and normally is, achieved by employing two identically formed blades placed in front-to-rear surface contact with the cutting edges facing in opposite directions. That is, when identical blades are placed side by side, with the cutting edges facing in the same direction, both bevels extend from blade surfaces facing in the same direction. When one blade is turned over onto its opposite surface and turned end-for-end to place the cutting edges in opposed relation, the bevel surfaces are then on opposite sides of the blades, i.e., on the front surface of one blade and the rear surface of the other. 
     When overlapping blades with cutting edges in opposed notches are used to cut the insulation on wires of various diameters, the cuts are necessarily incomplete. For example, when a pair of V-shaped cutting edges are employed, the insulation will be cut from four, linear sides, and since the wire is round in cross section and cannot be contacted by the blades, portions of the insulation will remain uncut, assuming neither the blades nor the wire is rotated. Severing of the insulation is completed by relative movement of the blades and the wire in one of the two previously described ways. A slug of insulation is thus severed and moved axially on the wire to be stripped either fully or partly, depending on the distance of blade travel, from the free end of the wire. 
     When such apparatus, having overlapping, non-rotating blades, is used to cut partially through the insulation and complete the severing thereof by moving the blades to break the uncut portions, the wire is sometimes nicked or scraped by the blades. This problem is generally amplified as the diameter or gauge of the wire increases, with corresponding increase in the axial force exerted by the blades on the slug of insulation being stripped. With common types of insulation, the problem of nicking, etc., requiring scrapping of the wire, is most prevalent in wires of 10 gauge or larger. However, when severing insulation or other coating materials having relatively high tensile strengths, the problem may also arise with smaller gauge wires. 
     The principal object of the present invention is to provide apparatus and methods utilizing overlapping blades to cut partially through one or more layers of coating material on a filamentary member and severing the material by relative movement of the engaged cutting blades and the member in a manner which greatly reduces or eliminates the tendency of the blades to nick or score the member during the severing and/or stripping operation. 
     Another object is to provide apparatus for and methods of severing and stripping insulation from an electrical wire, or the like, including configuring and relatively positioning a pair of overlapping blades in a novel manner to improve operation and reduce scrap. 
     Other objects will in part be obvious and will in part appear hereinafter. 
     SUMMARY OF THE INVENTION 
     The present invention is based upon recognition of the source of the aforementioned problem as related to the angular force exerted by the surface portions of the blades adjacent the cutting edges on the wire as the insulation is being severed. In conventional arrangements of blades of the overlapping type, the surface portion of one blade which engages the insulation and faces in the direction of the slug being severed is perpendicular, while the bevel surface of the other blade facing in the same direction is angularly disposed, with respect to the axis of the wire. Hence, a component of the severing force applied by the bevel surface to the insulation is in the direction of the other blade; when this force component, which increases commensurately with the tensile strength of the insulation being severed, becomes great enough the wire is pushed against and damaged by the sharp edge of the other blade. 
     The present invention essentially eliminates the aforementioned problem, while retaining the advantages associated with overlapping blades, by positioning the bevels forming the blade cutting edges to equalize the force components exerted on the wire as the insulation is severed by movement of the engaged blades axially of the wire. In a first embodiment, the cutting edges of both blades are formed at the junction of a plane surface and a bevel surface, and the blades are positioned with the planar surfaces of each facing in the direction of the portion being severed. In a second embodiment, the blades are formed in the same manner, with the bevels at equal angles to the planar surfaces, and the blades are positioned with the bevels of both blades facing in the direction of the portion being severed. In a third embodiment, the cutting edges of both blades are formed by bevels extending at equal angles from both planar surfaces; that is, bevels on both sides of both blades meet to form the cutting edges, whereby the blades are necessarily positioned with bevels on both blades facing the portion being severed, as well as in the opposite direction. In all embodiments, the cutting edges are formed in notches of V-shape or other appropriate configuration in opposing edges of the overlapping blades. 
     The foregoing and other features of the invention will be more readily understood and fully appreciated from the following detailed description, taken in conjunction with the accompanying drawings, wherein: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a pair of blades of the overlapping type, formed and positioned according to the prior art, for use in insulation cutting and stripping apparatus; 
     FIG. 2 is a fragmentary, side elevational view in section on the line 2--2 of FIG. 1, also showing an insulated wire positioned between the cutting edges of the blades; 
     FIG. 2a is a fragmentary, front elevational view as seen from the line 2a--2a of FIG. 2; 
     FIG. 3 perspective view of a pair of blades formed and positioned according to a first embodiment of the present invention; 
     FIG. 4 is a fragmentary, elevational view in section on the line 4--4 of FIG. 3, also showing an insulated wire positioned between the cutting edges of the blades; 
     FIGS. 5 and 6 fragmentary, elevational, sectional views, as in FIG. 4, showing blades formed and positioned according to second and third embodiments of the invention; and 
     FIGS. 7 and 8 are diagrammatic, plan views of cutting and stripping apparatus illustrating the manner of operation of the invention. 
    
    
     DETAILED DESCRIPTION 
     In FIGS. 1 and 2 are shown a pair of identical blades 10 and 10&#39;, formed and positioned in accordance with the prior art, and so labeled, for cutting partially through one of more layers of coating material on a filamentary member, and then severing the material by movement of the engaged blades relative to and axially of the member. Blade 10 is formed with side edges 14 and 16 parallel to one another and perpendicular to outer edge 18, and an inner edge configured as an essentially V-shaped notch 20. Likewise, blade 10&#39; includes parallel side edges 14&#39; and 16&#39;, perpendicular outer edge 18&#39; and V-shaped notch 20&#39; at its inner edge. Each of blades 10 and 10&#39; includes a pair of openings 22, 24 and 22&#39;, 24&#39; adjacent outer edges 18, 18&#39;, respectively, for passage of screws mounting the blades upon conventional moveable support means. 
     The thickness of blades 10 and 10&#39; is adequate to provide the degree of rigidity necessary for the intended application of the blades. As previously indicated and discussed in more detail hereinafter, the blades are mounted and moved in a cooperative manner to make radial cuts in a layer of insulating material, or the like, on a filamentary member such as an electrical conductor. The cuts made by the blades, due to the linear and circular configurations of the blade cutting edges and the conductor, respectively, pass partially but not completely through the insulation. Severing is completed by relative movement of the blades and the conductor, e.g., by moving the blades in unison axially of the insulated conductor in a direction away from a position where the insulated conductor is securely clamped. Thus, the blades must be rigid enough to withstand the forces imposed thereon as severing of the insulation is completed by movement of the blades axially of the insulated conductor. This will be a function not only of the material and dimensions of the blades, but also the tensile strength and cross-sectional area of the insulation or other coating material to be severed and its adherence to the conductor or other underlying layer. 
     The sharp cutting edges are provided in the usual manner along the inner edges of each of blades 10 and 10&#39; i.e., in V-shaped notches 20 and 20&#39;. A planar bevel surface meets one of the opposite, planar blade surfaces at an acute angle, providing the sharp cutting edge, and the other at an obtuse angle. In the prior art arrangement of FIGS. 1, 2 and 2a, bevel surface 23 meets opposite, planar surfaces 25 and 26 of blade 10 at acute and obtuse angles, respectively, forming sharp cutting edge 28 along both sides of notch 20. Likewise, cutting edge 28&#39; is formed at the juncture of bevel surface 23&#39; and planar surface 25&#39; of blade 10&#39;, the bevel surface meeting planar surface 26&#39; at an obtuse angle. 
     Blades 10 and 10&#39; are mounted on any conventional support structure (not shown) with bevels 23 and 23&#39; facing in opposite directions. It will be noted that this is accomplished with two identically formed blades, with one blade turned over, placing surfaces 25 and 25&#39; in overlapping contact and notches 20, 20&#39; in opposing relation. Cutting edges 28, 28&#39; are thus in essentially the same plane when blades 10, 10&#39; are in overlapping relation with surfaces 25, 25&#39; in sliding engagement. As shown in FIGS. 2 and 2a, blades 10, 10&#39; have been moved to bring the two sides of each of cutting edges 28, 28&#39; into closely spaced relation to conductor 30, passing partially through insulation 32. For greater clarity of the features under consideration, the size of conductor 30 and insulation 32 relative to blades 10 and 10&#39; has been exaggerated as compared to typical wires operated upon by such blades. 
     As blades 10, 10&#39; are moved in unison in the direction of arrow 33 (FIG. 2) to complete severing of the insulation, the severing force is applied to the portion of the insulation to be stripped (the upper portion in FIG. 2) by planar surface 25 and bevel surface 23&#39;. If severing and stripping were effected by moving the conductor in an axial direction opposite to arrow 33 while maintaining the blades stationary, the force would still be applied by the same surfaces 25 and 23&#39;. In any case, with blades formed and positioned as dictated by the prior art severing forces are applied to the insulation with one of the force-applying surfaces normal to the direction of relative blade and conductor movement, and the other at an acute angle. Thus, as the blades are moved in the direction of arrow 33, a component of the force applied to insulation 32 will be in the direction of arrow 35 (normal to bevel surface 23&#39;), thereby urging conductor 30 in the direction of cutting edge 28. 
     Turning now to the illustrated embodiments of the present invention, in FIGS. 3 and 4 are shown a pair of blades 34 and 36 which are formed and arranged to have bevels facing in the same direction when the blades are placed in front-to-rear surface contact with the cutting edges opposed. Blade 34 includes side edges 38 and 40, parallel to one another and perpendicular to outer edge 42, with V-shaped notch 44 on the inner edge. Likewise, blade 36 has side edges 46 and 48, outer edge 50 and V-shaped notch 52. Both blades have a pair of openings 54 and 56 for mounting purposes. 
     As with some blades of the prior art, blades 34 and 36 include portions of reduced thickness adjacent their inner edges. This configuration is sometimes used in blades intended for relatively heavy duty applications, i.e., when the layers to be severed by the blades are relatively thick and/or of high tensile strength. Thus, in addition to opposite, planar, parallel surfaces 58 and 60, blade 34 has intermediate planar surface 62, and blade 36, in addition to planar surfaces 64 and 66, has intermediate planar surface 68. Intermediate planar surfaces 62 and 68 are, of course, parallel to outer surfaces 58 and 60, and 64 and 66, respectively. 
     Bevel surface 70 meets planar, parallel surfaces 58 and 62 at acute and obtuse angles, respectively, forming sharp cutting edge 72 along V-shaped notch 44 of blade 34. Bevel surface 74 is formed along notch 52 of blade 36 to meet surface 68 at an acute angle and surface 66 at an obtuse angle, providing cutting edge 76. Blades 34 and 36 are supported with notches 44 and 52, and thus cutting edges 72 and 76, opposing one another, and with surfaces 58 and 66 in the same plane; thus, portions of surfaces 58 and 66 are in sliding engagement as the blades are reciprocally moved in the directions of arrows 78, in the course of the cutting operation. 
     After blades 34 and 36 are moved to bring portions of cutting edges 72 and 76 into close proximity to conductor 80, thereby passing partially through insulation layer 82, as shown in FIG. 4, the blades are moved in unison in the direction of arrow 84. The insulated conductor is clamped firmly on the side of the blades opposite the direction of blade movement, thereby completing severing of the insulating layer at the position of the cuts. The severing force applied to the portion of insulation to be stripped by the blades is by planar surfaces 58 and 68, i.e., the portions of the blades adjoining the cutting edges which face in the direction of severing movement of the blades, both of which are at the same angle (90°) to the axis of conductor 80. 
     In the embodiment of FIG. 5, overlapping blades 86 and 88 have bevel surfaces 90 and 92, respectively, adjoining the cutting edges. Insulating layer 94, after being partially cut, is severed by movement of blades 86 and 88 in unison in the direction of arrow 96. The severing force is thus applied to the portion of insulating layer 94 to be stripped by bevel surfaces 90 and 92 which both face in the direction of blade movement (i.e., to the axis of conductor 97) and are disposed at equal angles (e.g., 45°) thereto. 
     Blades 98 and 98&#39; of the FIG. 6 embodiment have cutting edges formed by the juncture of bevels on both sides, whereby the two blades may be identical. Bevel surfaces 102 and 104 extend from a common juncture at the cutting edge to opposite, parallel surfaces 106 and 108, respectively, of blade 98. Likewise, bevels 102&#39; and 104&#39; meet one another to form a sharp cutting edge, and adjoin parallel surfaces 106&#39; and 108&#39; respectively, at obtuse angles in blade 98&#39;. Thus, regardless of the direction of relative movement of the blades and conductor to sever partially cut insulation 110, the surfaces which apply the severing force are disposed at the same angle with respect to the axis of the conductor. 
     Means for clamping or otherwise restraining axial movement of the insulated conductor, as well as means for mounting and moving the blades are well known in many forms in the prior art. For purposes of the present invention, any conventional clamping means and support and movement means for overlapping blades may be used, whereby such elements are shown entirely diagrammatically in FIGS. 7 and 8. Insulated conductor 112 is inserted axially between spaced clamping jaws 114 and blades 116, as shown in FIG. 7. Jaws 114 are then moved toward one another, in the directions indicated by arrows 120 in FIG. 7, to firmly engage the insulated conductor therebetween, as shown in FIG. 8. Blade support means 122, upon which blades 116 are fixedly mounted, are moved in the directions of arrows 118, to the position of FIG. 8, wherein the blade cutting edges make partial radial cuts through the insulating layer and are in close proximity to the conductor. The depth of cut is controlled by any of a number of well-known means. The blade supports and engaged blades are then moved in the direction of arrow 124 to complete the severing of the insulation and strip the severed slug fully or partially from the end portion of the conductor. 
     It should be noted, as previously suggested, that rather than clamping the conductor and moving the blades in a direction away from the clamping means, i.e., toward the portion of insulation to be fully or partially stripped, the conductor may be moved axially in the opposite direction, i.e., away from the portion to be stripped. In either case, the forces applied by the blades to the portion to be stripped as such portion is severed from the remainder of the insulation are at equal angles to the direction of relative blade/conductor movement, i.e., to the axis of the conductor. Experimental data indicates that the best and most consistent performance is achieved when the blade surfaces which apply the severing force to the insulation are at equal, acute angles to the axis of the conductor, as in FIG. 5, which represents the preferred embodiment. Making the planar surface portions immediately adjacent the cutting edges of the blades which apply the axial severing and stripping force to the slug of insulation at equal angles to the axis of relative blade/conductor movement in overlapping blades means, of course, that the cutting edges of the two blades are moved radially of the conductor in parallel planes which are axially spaced with respect to the conductor.