Method of manufacturing a low-crosstalk data cable

Abstract: A low cross-talk data cable and method of manufacturing the same, where a low-crosstalk data cable (5) includes a cable housing jacket (30) made of flexible insulating material for housing a multi-channel shielding member (20) and a plurality of conductors (10). A hollow multi-channel shielding member of the invention is formed during the cable pulling process from a single, flat, thin, self-adapting shielding tape. The multi-channel shielding member separates and prevents crosstalk between adjacent conductors. A grounded low-cross talk data cable is provided when a current drain wire is positioned down the center of the hollow multi-channel shielding member. Further, the low-crosstalk data cable may have a metallic outer shielding jacket positioned between the cable housing jacket and the combined conductor/multi-channel shielding member core. A second current drain wire may also be provided to enable grounding of the metallic outer shielding jacket.

Description: FIELD OF THE INVENTION This invention relates generally to a method of manufacturing a multi-conductor cable. In particular, the invention is directed to a method of manufacturing a data cable with a shielding member to separate conductors of a cable where the shielding member prevents cross-talk between the conductors. BACKGROUND Multi-conductor cables are common for transferring multiple currents to and from electronic systems and devices. For example, multi-conductor cables are frequently used for audio, video and data transmission between components in communication networks, computer systems, and other similar bi-directional data transmission systems. In these types of multi-conductor cables, it is essential to reduce or prevent cross-talk due to the electromagnetic fields of current flowing in adjacent conductors. It is also important to properly insulate the conductors from each other and to provide an overall cable that is flexible, lightweight and free of moisture. Due to the potential length of this type of multi-conductor cable, it is desirable to produce a high quality cable which is easily manufactured at a low cost. It is well known in the art to provide floating or grounded metallic shielding in multi-conductor cables to prevent cross-talk between adjacent conductors or conductor pairs in a cable. For example, U.S. Patent 3,911,200 discloses a cable assembly having an encapsulated shielding tape made of a laminate metal foil and plastic film bonded together. This shielding tape is folded into an L- shape to form a channel and then laminated to another piece of similarly shaped shielding tape to result in a multi-channel shielding tape, wherein a conductor resides in each channel. Furthermore, International Patent WO 98/48430 discloses a shielding core formed of a cross-talk reducing conductive material. The core is formed of conductive material and has multiple fins extruding in an outward direction from the core in order to isolate conductors in respective channels. These prior art shielding techniques have problems in that they require complex pre-assembly or intricate formation of shielding members prior to cable construction. Therefore, it is desired to have a self adapting shielding member that can be formed at the same time the cable is pulled together in a cabling production device. Methods of manufacturing low-crosstalk data cables comprising a multi-channel shielding member are also known from US-4920234 and EP-0964408. the latter belonging to the state of the art according Art. 54.3 EPC. US-2538019 discloses a method of manufacturing a data cable wherein a multi-channel shielding member is formed of a plurality of superposed paper stripes. This plurality of superposed paper stripes is folded by means of passing the pile of stripes through suitable guides. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method of manufacturing a low cost, low-crosstalk data cable that is easily manufactured using a self-adapting shielding tape. It is thus an object of the invention to provide a method of manufacturing a low-crosstalk data cable that eliminates the need and expense of pre-formed or complicated formation of a shielding member by forming a channeled shielding member during the cable pulling process. Therefore, there is provided a method of manufacturing a low-crosstalk data cable according to claim 1. These and other objects are achieved in accordance with a preferred embodiment of the invention as discussed below. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 illustrates a cross-sectional view of the low-crosstalk data cable according to a first preferred embodiment of the invention; FIGURES 2(a) and (b) illustrate a cross-sectional view of a low-crosstalk data cable according to a second embodiment of the invention; FIGURES 3(a) and (b) illustrate a cross-sectional view of a low-crosstalk data cable according to a third embodiment of the invention; FIGURE 4 illustrates a manufacturing setup and process for forming the low-crosstalk data cable of the invention; FIGURES 5a-5d illustrate the "+"-shaped die used to form the multi-channel shielding member for the low-crosstalk data cable of the preferred embodiment; FIGURES 6a-6c illustrate individual die of a 3-die setup for forming a low-crosstalk data cable of the preferred embodiment; and FIGURES 7a-7d illustrate the shape progression of forming a multi-channel shielding member and cable core of a low-crosstalk data cable of the preferred embodiment. DETAILED DESCRIPTION OF THE DRAWINGS According to a preferred embodiment shown in Figure 1, a low-crosstalk data cable 5 is preferably manufactured such to include four insulated conductor pairs 10 separated by a multi-channel shielding member 20 . The multi-channel shielding member 20 is formed from a thin flat shielding tape which is folded into a tube and collapsed or indented to have a cross section resembling a plus-shape (see Figs. 7a-7c). The conductor pairs 10 reside in the channels 25 of the multi-channel shielding member 20 . It is preferable that the conductor pairs 10 are twisted in channels 25 . The dashed lines represent the circumference of the twisted conductor pairs 10 . The combination of the conductor pairs 10 and the multi-channel shielding member 20 is referred to as a "cable core." This cable core is then covered by a cable housing jacket 30 made of insulating flexible material such as rubber, plastic or polymer. The multi-channel shielding member 20 is typically made from a flexible conductive material such as aluminum. As shown in Fig. 1, the multi-channel shielding member 20 has a substantially hollow center. In a second embodiment of the invention, a grounded low-crosstalk data cable 5 is manufactured as shown in Figure 2a. The second embodiment has the same structure of the first embodiment except that a shielding drain wire 40 resides in the substantially hollow center of the multi-channel shielding member 20 . The shielding drain wire 40 provides a ground for currents that may accumulate in the multi-channel shielding member 20 . The shielding drain wire 40 is made of a flexible conductive material such as copper. Additionally in this embodiment, as shown by the exploded view of Fig. 2b, the multi-channel shielding member 20 is made from an aluminum/mylar shielding tape. While the shielding tape for the multi-channel shielding member 20 can be made from numerous types of materials, the inventor has found that it is preferable that it be made from a shielding tape formed with two layers, an aluminum layer 21 and a mylar layer 22 . The multi-channel shielding member 20 is then formed with the aluminum layer 21 on an interior surface of the multi-channel shielding member 20, and the mylar layer 22 outwardly facing the twisted pair conductors 10. The mylar layer 22 primarily serves as a bonding or strengthening material for the aluminum so that the aluminum does not tear or rip during cable fabrication (as discussed below). However, the mylar layer 22 also serves as an additional insulator between the aluminum layer 21 and the conductor pairs 10 . In fact, when the mylar layer 22 is thick enough, conductor wires located in channels 25 are not required to be independently insulated. Of course, with conductor pairs 10 independent insulation of conductor wires is essential. A third embodiment of the invention, as shown in Figs. 3a and 3b, includes the manufacturing steps of the grounded low-crosstalk data cable 5 of the second embodiment except that the cable core further includes an outer shielding jacket 50 which encapsulates the conductor pairs 10 and the multi-channel shielding member 20 . The outer shielding jacket 50 provides additional shielding from electromagnetic fields that may be present from other sources such as adjacent cables. In this embodiment, a second shielding drain wire 60 is provided to allow grounding of potential currents that accumulate in the outer shielding jacket 50 . While the outer shielding jacket can be made from many different materials, it is preferable to provide a two-layer tape having a layer of aluminum 51 and a layer of mylar 52 . The layer of mylar 52 provides additional strength for the aluminum layer 51 to avoid tearing during the fabrication process. The aluminum/mylar outer shielding jacket 50 of the preferred embodiment is positioned such that the aluminum layer 51 is on an interior surface of the outer shielding jacket 50 , while the mylar layer 52 faces outwardly toward the cable housing jacket 30 . However, because of the potential for shorting between the outer shielding jacket 50 and the twisted pair conductors 10 , it is also preferable to place a thin layer of mylar 53 between the twisted pair conductors 10 and the outer shielding jacket 50 . In the method of manufacturing a low-crosstalk data cable of the invention, four twisted pair conductors are discussed and shown. However, the multi-channel shielding member can be adapted for any number of conductors desired. Furthermore, it is not necessary that the conductors be insulated twisted pairs. The low-crosstalk data cable of the invention works equally as well with insulated or non-insulated single conductors. A preferred method of manufacturing the low-crosstalk data cable detailed above will now be described with reference to Figures 4-7. Figure 4 shows the basic setup for manufacturing the low-crosstalk data cable. For simplicity, reference numerals are used that correspond to the cable components previously described. Here, a low-crosstalk data cable 5 is formed by pulling four twisted pair conductors 10 from two dual twisted pair payoffs 100 . The dual twisted pair payoffs 100 are preferably self-driven. The four twisted pair conductors 10 are pulled through a series of box rollers 110 which are attached to a cable tool table 120 . The box rollers 110 straighten and guide the twisted pair conductors as they are pulled from the dual twisted pair payoffs 100 . A lay control 130 , positioned between the dual twisted pair payoffs 100 and the box rollers 110 , is used to control the lay length of the cable and count the cable footage. Additionally, a thin, flat, self-adapting shielding tape is pulled from a tape let-off roll 140 through a series of horizontal and vertical tape rollers 145 into a tape folding tool 150 which is attached to the cable tool table 120 . The tape folding tool 150 folds the shielding tape into a substantially tubular shape (see Fig. 7b, discussed in detail below). The tubular-shaped shielding tape is then fed through a "+"-shaped die 160 for collapsing or indenting the tubular shaped shielding tape into a "+"-like shape (see Fig. 7c), to form the multi-channel shielding member 20 . Next, the multi-channel shielding member 20 and four twisted pair conductors 10 are combined through a 3-die setup 170 to form a cable core (Fig 7d). The 3-die setup 170 guides each twisted pair conductor 10 into separate channels 25 of the multi-channel shielding member 20 and compresses them into a tight formation to form the cable core. The cable core is then fed into a cabler 180 where the cable core is tightly twisted. After the cabler 180 , the resulting twisted cable core is processed through an extruder (not shown) for applying a polymer cable housing jacket 30 . The cabler 180 and extruder (not shown) are well known in the industry and therefore have not been described in detail. For the method of manufacturing a grounded shielded cable of the second embodiment, a shielding drain wire 40 is inserted into the center of the multi-channel shielding member 20 . Here, a shielding drain wire 40 made of a flexible conductive material such as copper, is drawn from a drain wire pay-off 190 . The shielding drain wire 40 is fed through the tape folding tool 150 and is surrounded by the shielding tape as it is bent into a tubular shape. The shielding drain wire 40 is secured in the center of the muli-channel shielding member 20 when the tubular-shaped shielding tape is collapsed by the "+"-shaped die 160 . As method to produce a low-crosstalk data cable according to the third embodiment, the same method is used as in the second embodiment, but an additional jacketing process is performed between the cabler 180 and the extruder (not shown). Here the cable core from the cabler 180 is run through a series of die (not shown) where the cable core is coated with a thin layer of mylar 53 and a second shielding drain wire 60 is strung along the cable core. The outer shielding jacket 50 is then applied through the series of die with an aluminum side facing inward toward the second shielding drain wire 60 . The completed cable core is then run through the extruder to apply the cable housing jacket 30 , as previously discussed. The "+"-shaped die 160 , according to this manufacturing process, can be viewed in greater detail in Figures 5a-5d. Figure 5a shows the "+"-shaped die 160 from a side view. Figure 5b shows a rear view of the "+"-shaped die 160 where the multi-channel shielding member 20 exits. Figure 5c shows a side view cross section of the die.As shown, the die has a funnel-shaped input 161 where the tubular-shaped shielding tape enters. The funnel-shaped input 161 collapses the tubular shielding tape and presses the shielding tape through a "+" shape exit hole 162 of the die detail shown in Figure 5d, to form the multi-channel shielding member 20 . Figures 6a-6c show the respective dies in the 3-die setup 170 . Figure 6a shows a front and side view of a first die 171 that receives the multi-channel shielding member 20 and the four twisted pair conductors 10 . This first die 171 aligns and guides the twisted pair conductors 10 into the channels 25 of the multi-channel shielding member 20 . Fig. 6b illustrates the front and side views of a second closing die 172 which compresses the conductor pairs 10 and multi-channel shielding member 20 (cable core) into a circular diameter. Fig. 6c illustrates the front and side views of a third closing die 173 where the cable core is further compressed into a smaller diameter. The result of the 3-die setup is a cable core, which includes the conductor pairs 10 and the multi-channel shielding member 20 , having a fixed diameter. Figures 7a-7d illustrate the progression of the self-adapting shielding tape and cable core during the cable manufacturing process described above. Fig. 7a depicts the thin, flat, self-adapting shielding tape as it is received from the tape let off roll 140 . Fig. 7b illustrates the tubular shape that results from the folding tool 150 . Fig. 7c illustrates the "+" shape of the multi-channel shielding member 20 as it exits from the "+" plus-shape die 160 . Fig. 7d illustrates the cable core corresponding to the first embodiment as it exits the first die 171 of the 3-die setup 170 . As described and shown by the foregoing process, a high-quality low-crosstalk data cable is manufactured according to the objects of the invention. Although there have been described preferred embodiments of this novel invention, many variation and modifications are possible and the embodiments described herein are not limited by the specific disclosure above but only by the scope of the apprended claims. In particular, the multi-channel shielding member 20 described herein, is not intended to be limited to only a cross-talk shielding device. For example, the multi-channel shielding member 20 can be used as an insulating member or for any other purpose requiring channels formed inside a low-crosstalk data cable.

Claims: A method of manufacturing a low-crosstalk data cable comprising: pulling a plurality of conductor wires (10) into a cable forming device; pulling a single flat self-adaptingshielding tape into a tape folding tool (150) of the cable forming device so as to form a self-adapting mulfi-channel shielding member (20); forming a cable core by combining the self-adapting multi-channel shielding member with said plurality of conductor wires (10), wherein said self-adapting multi-channel shielding member is formed at the same time said plurality of conductor wires (10) and said single flat self-adapting shielding tape are pulled in said cable forming device, and wherein said plurality of conductor wires (10) are placed individually into channels of said self-adapting multi-channel shielding member; and encapsulating said cable core in a flexible insulating cable housing jacket (30). The method of manufacturing a low-crosstalk data cable according to claim 1, wherein forming said cable core further comprises coating the combined self-adapting multi-channel shielding member and plurality of conductive wires with a substantially metallic outer shielding jacket (50). The method of manufacturing a low-crosstalk data cable according to claim 2, wherein four twisted pair conductor wires are combined with said self-adapting multi-channel shielding member, and wherein said self-adapting multi-channel shielding member and said outer metallic shielding jacket are made from a flexible, substantially aluminum material. The method of manufacturing a low-crosstalk data cable according to anyone of claims 1 to 3, wherein: said conductor wires are acquired from their respective payoff rolls (100); said shielding tape is acquired from a tape let-off roll (140); and wherein said method further comprises folding said flat self-adapting shielding tape into a substantially tubular-shaped shielding tape via said tape folding tool, and pulling the tubular-shaped shielding tape through an indentation die (160) to form a self-adapting multi-channel shielding member (20) having a plurality of longitudinal channels. The method of manufacturing a low-crosstalk data cable according to claim 4, wherein said self-adapting multi-channel shielding member has four channels such that a cross-section of said channeled shielding member resembles a plus-shape, and wherein four insulated, twisted pair, conductor wires are placed into respective channels. The method of manufacturing a low-crosstalk data cable according to claim 5, wherein forming said cable core further comprises inserting a shielding drain wire (40) longitudinally through an interior of said self-adapting multi-channel shielding member. The method of manufacturing a low-crosstalk data cable according to claim 6, wherein forming said cable core further comprises encapsulating a second shielding drain wire (60) and the combined self-adapting multi-channel shielding member and conductor wires with a metallic outer shielding jacket (50). The method of manufacturing a low-crosstalk data cable according to claim 7, wherein said flat self-adapting shielding tape and said metallic outer shielding jacket are made of flexible, substantially aluminum material.

Inventors: DESPARD BOYD V, DESPARD, BOYD V.
Applicants: CIT ALCATEL, ALCATEL
Application year: 2000
Main classification: H01B11
IPC codes: H01B11