Patent Publication Number: US-5026301-A

Title: Lead termination

Description:
BACKGROUND OF THE INVENTION 
     Factories produce a large number of terminations where the cut end of a wire is terminated to a contact device. Techniques involving soldering and crimping have disadvantages such as requiring stripping of insulation. Insulation displacement termination techniques have many advantages, but often are not useful with wires whose conductors contain multiple strands, do not provide automatic strain relief, or allow the same termination devices and tooling to be used with wires having central conductors of different diameters. An insulation displacement wire termination apparatus and method which provided low cost and reliable terminations, would be of considerable value. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a low cost and reliable insulation displacement termination is provided for connecting the conductor of a wire to a contact device. The termination includes a contact device with a penetrating portion that penetrates into one side of the wire insulation and moves the wire conductor through the opposite side of the insulation. The penetrating portion continues to press against the now-displaced wire conductor. 
     In one termination, wherein the wire and an elongated contact device extend substantially perpendicular, the cut end of a wire lies in a first bore of an insulative body. A contact device lies in a second perpendicular bore of the body. The contact device has a pin-like penetrating portion which penetrates through one side of a wire insulation and presses the wire conductor through the insulation and against an opposite wall of the first bore of the body. In a second termination, wherein an elongated contact device extends largely parallel to a wire end portion, the wire end portion lies in a rear metal tubular portion of the contact device. The metal tubular portion has a slot therein which forms a metal prong. The prong, which forms a penetrating portion of the contact device, is bent to project into the wire insulation and deflect the wire conductor through the insulation and against an opposite side of the metal tubular portion. 
     The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a multimeter test lead which has terminations at its opposite ends constructed in accordance with the present invention. 
     FIG. 2 is a sectional side view of a first termination of the test lead of FIG. 1, with the termination only partially completed. 
     FIG. 3 is a view similar to that of FIG. 2, but with the termination completed. 
     FIG. 4 is a view taken on the line 4--4 of FIG. 3. 
     FIG. 5 is a sectional view of another embodiment of the invention somewhat similar to the first termination of FIG. 2, with the termination only partially completed. 
     FIG. 6 is a view similar to that of FIG. 5, but with the termination completed. 
     FIG. 7 is a sectional view of the second termination of the test lead of FIG. 1. 
     FIG. 8 is an enlarged view of the region 8--8 of FIG. 7. 
     FIGS. 8A and 8B are respectively side elevation and front elevation views of a piercing and displacing tool useful to construct the apparatus of FIG. 8. 
     FIG. 9 is a partial top view of the rear tubular portion of the contact device of FIG. 8. 
     FIG. 10 is a view taken on the line 10--10 of FIG. 8. 
     FIG. 11 is an enlarged view of part of the termination of FIG. 10. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a test lead 10 which includes a wire 12 having opposite ends connected to contact assemblies at first and second terminations 14, 16. The first termination 14 includes an elongated banana plug contact device 20 which extends along an axis 22 that is perpendicular to the axis 24A of the adjacent wire portion, and is suitable for plugging into a contact hole of a multimeter. The second termination 16 includes an elongated test probe contact device which extends along an axis 24B that is in line with the axis of an adjacent portion of the wire. Factories that produce multimeter test leads require large numbers of low cost and reliable terminations that can be easily attached to opposite ends of the test lead. 
     FIG. 3 illustrates some details of the first termination 14 which terminates to an end portion 12A of the wire. The wire includes a metal conductor 30, which is usually formed of numerous thin wire strands for flexibility of the lead, and a wire insulation 32 that surrounds the conductor. The contact device 20 includes a banana plug 34 and a rod 36 with an insulation penetrating pin portion 38 at its upper end. The wire and contact device lie in an insulative body 40 having a pair of bores 42, 44 that extend perpendicular to one another and which intersect. 
     As shown in FIG. 2, the termination is made by first projecting a cut end 12A of the wire through the first bore 42. The first bore is a blind bore with an end at 46 that extends beyond the intersection with the second bore 44. The first bore closely receives the wire. After the wire is installed, the contact device 20 is projected upwardly, or forwardly, along the axis 22 until the front end or tip 50 of the insulation penetrating contact pin portion 38 bears against the lower side 52 of the wire, at a wire displacement location 53 along the first bore. The contact device is advanced upwardly with sufficient force to penetrate into the lower side of the wire insulation, displacing the insulation in the process, until the tip 50 of the pin portion engages the wire conductor 30. The contact device continues to be advanced upwardly to force the wire conductor 30 to press through the insulation until it emerges from an upper side 54 of the insulation, into a recess 56 in the first bore that lies in line with the second bore 44. The pin portion deflects the wire conductor into this recess, providing a press interference fit between pin portion 38 and the walls of hole 56, with the wire caught between them. 
     Although it is possible to form the recess 56 directly in the insulative material of most of the body 40, applicant prefers to use a metal insert or bushing 58 that is installed before the wire is installed. The metal insert avoids a &#34;creep effect&#34; wherein the wire conductor could creep out of the first bore 42. No sharp edges are allowed on the walls of hole 56 or at the tip so to avoid severing the wire conductor. 
     As the contact device is pushed upwardly, its shoulder 60 which lies around the rear end of the pin portion 38, presses against the lower side 52 of the wire insulation. The pressing of the shoulder 60 causes it to grip the wire insulation to help resist pullout of the wire from the insulative body 40. At full installation of the contact device, a ring-shaped projection 62 of the body insulation snaps into a groove 64 of the rod 36 of the contact device rod, to lock the contact device in place. 
     The wire insulation 32 is preferably of soft and easily displaced material such as silicone. This facilitates penetration by the pin portion of the contact device, and subsequent penetration by the wire conductor. The insulative body 40 of the termination is preferably of a harder insulative material such as Nylon. The termination can be constructed for low cost, high volume production. The contact device 20 is similar to prior art contact devices, except that it includes the narrower pin portion and the snap-in groove, which do not substantially increase its cost. The insulative body 40 is an easily molded part, especially because the contact device is not a molded-in insert. Mass production assembly is easily accomplished, because it is only necessary to insert the wire in the first bore, and then the contact device in the other bore until it snaps into place, all of which is easily accomplished. 
     The termination 14 provides a reliable termination. With the pin portion 38 pressing the wire conductor against the relatively hard insulative body 40, and with the wire conductor bent and pressed around the tip 50 of the pin portion, good contact is made. The fact that the wire conductor is bent near its location of contact with the pin portion, results in reduced possibility that the wire conductor will pull out of the body. With the shoulder 60 of the contact device pressing against the wire insulation, the wire insulation is also trapped in place. With a wire of a diameter of about 3.6 mm (0.140 inch), the shoulder 60 preferably penetrates into the insulation by at least about 8% of the diameter or about 0.3 millimeter (0.012 inch), but less than the radius of the wire. 
     FIGS. 5 and 6 illustrate another insulation displacement terminal 70 somewhat similar to that of FIGS. 2-4, in that it includes an insulative body 72 with perpendicular bores 74, 76 for respectively receiving a wire end portion 12A and a contact device 78. However, the contact device has a forward end 80 with a central hole 82 to leave a ring-shaped forward end. In addition, the body forms a protuberance 84 along the first bore 74 where it lies in line with the second bore 76. When the wire 12A is inserted, its end is deflected downwardly about the protuberance 84. When the contact device 78 is pushed upwardly, or forwardly, it bends the wire conductor 30 upwardly. It is noted that applicant originally constructed the termination as shown in FIGS. 5 and 6, and later developed the design shown in FIGS. 2-4. The design shown in FIGS. 2-4 was found to be superior in the tests that applicant performed, because it has a greater contact area, has better cable retention, is less affected by creep, and easily provides a press fit when engaged with a wire. 
     FIGS. 7-11 illustrate details of the second in-line termination 16. The second termination includes a metal contact device 24 which, in this case, is a test probe with a tip 90 that can contact one of many closely-spaced traces on a circuit board, and with the tip portion covered by an insulative cap 92. The probe has a tubular rear portion 94, shown in greater detail in FIG. 8. The tubular rear portion has an open rear end 96 for receiving a wire end portion 12B. The wire end has been cut, and is pressed into a blind hole 98 formed by the tubular portion, and extends rearwardly out from the tubular portion. The termination also includes an insulative body 100 surrounding at least the tubular rear portion of the contact device. 
     As shown in FIG. 9, the tubular rear portion 94 of the contact device has a slot 102 in a first side 104 of the tubular portion which lies opposite side 106. The slot forms a prong 110 which can be bent, as along a bend line 112 at the rear ends of the curved slot. The prong, which forms a penetrating portion of the contact device, is bent to displace a region of the wire insulation 32 and to displace a location 30B of the wire conductor so it presses against the second side 106 of the contact device rear tubular portion at the inside of the tubular portion. 
     As shown in FIG. 11, the wire conductor 30 includes multiple conductive strands 114 that initially lie within an imaginary circle 116 centered on the outside of the wire insulation 32. The tip 120 of the prong presses against the wire strands and deforms them from their original circular shape, but still presses many of them securely against the second side 106 of the tubular rear portion. In order to assure that the prong will press a large portion of the wire conductor through the wire insulation, instead of merely separating the strands, the probe tip is rounded, with a large radius of curvature R, which is more than one half the radius of the circle 116 which define the edge of the original wire conductor, with the radius of the prong tip preferably being at least about as great as the radius of the circle 116. 
     The termination is made by forming the slot 102 in the rear tubular portion of the contact device, but without bending the resulting prong 110. The wire end portion 12B is inserted into the tubular rear portion 94 at a time when the tubular rear portion is not surrounded by the insulative body 100. Then a piercing and displacing tool shown at 120 in FIGS. 8A and 8B, is pressed against one side 104 of the tubular member to pierce it and punch out the prong 110 from the rest of the tubular member and to bend the prong. As the prong is forced to bend, its tip displaces the wire insulation until the prong tip presses against the wire conductor, and then moves the wire conductor so it displaces insulation until the wire conductor presses against the second side 106 of the tubular rear portion. Then, the insulative body is slid to lie around the tubular rear portion and around the wire region projecting rearwardly from the contact device. 
     The contact device, including the tubular rear portion 94, is formed of a ductile material such as free machining brass. As a result, there is substantially no springiness which would urge the deformed prong to spring back after it has deformed the wire. Applicant prefers to have the prong or probe 110 extend at an angle A of between about 30° and 45° to the axis 24B of the wire. The probe then securely resists pull out of the conductor. As discussed above, the wire insulation is preferably of soft material such as silicone, to facilitate its displacement. The probe provides strain relief for the wire, because the probe tip resists rearward movement of the wire conductor and the probe sides resist rearward movement of the wire insulation. 
     The contact device 24 and the tool for depressing the prong, can be used with wires having conductors of different diameters. The only change that is required is the depth of depression of the probe of the tubular rear portion of the contact device. 
     Thus, the invention provides a wire or lead termination which can be made at low cost, especially in mass production, and which provides reliable connection of a contact device to a wire. The termination includes a contact device with a wire insulation penetrating portion such as a pin portion or prong, which is pressed against a side of a wire to displace the wire insulation until the displacing element engages the wire conductor, and which then moves the wire conductor to cause it to displace an additional portion of the wire insulation, preferably until the wire conductor has passed through the insulation. In one termination, a pin portion of a contact device presses the wire conductor against an inside wall of a body of material harder than that of the wire insulation. In another termination, a prong formed in a tubular rear portion of a contact device, presses the wire conductor against one side of the tubular contact portion which lies opposite the prong. 
     Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.