Patent Publication Number: US-5159154-A

Title: Multiple conductor dielectric cable assembly and method of manufacture

Description:
FIELD OF THE INVENTION 
     The present invention relates to electrical cables and more particularly to multiple conductor cables in which a desired dielectric medium may be provided around the conductors. 
     BACKGROUND OF THE INVENTION 
     Cables of electrical conductors in data transmission or computer applications are typically formed of many wires running between the same terminations and are insulated from each other by embedding each conductor in a dielectric medium having an average dielectric constant. In cables having multiple conductors, the conductors are typically individually embedded in a solid dielectric material which also separates the conductors from each other to prevent short circuits. The individual cables may also be shielded and further surrounded by a common insulating sheath. Such cables are complex to construct and thus expensive. Moreover, faults such as open or short circuits may be invisible until start-up of the associated circuitry reveals them. 
     SUMMARY OF THE INVENTION 
     The present invention provides a multiple conductor cable which is readily manufacturable. The present invention comprises an elongated housing which is substantially rigid and comprises an elongated channel, enclosed at each end, and a lid. The electrical conductors or wires run along the length of the channel. U-shaped support members are placed at intervals within the channel. Grooved damper elements are mounted in a stacked relationship in each U-shaped support member. The electrical conductors pass over and under the damper elements along a path between connections in the walls of the housing. The grooves of adjacent damper elements are oppositely oriented and offset to provide deviations of the conductors from a straight line path. In this manner, the damper elements hold the conductors under tension and spaced from other conductors and the walls of the housing and dampen vibrations in the conductors. A dielectric medium fills the interior of the housing to surround each conductor. The wires inside the housing may be connected to a printed circuit board, another cable, or any other desired connection outside the housing via suitable connections in the housing walls. 
     In the manufacture of the cable assembly, the U-shaped support members are fastened to the channel. A first set of damper elements, with the grooves facing upwardly, is dropped into slots in alternate U-shaped support members. The conductors or wires, which are provided on reels, are unrolled and fastened to a header mounted on one end of a jig. The wires are cut to the appropriate length and fastened to a further header mounted on the opposite end of the jig. The wires are then laid into the upwardly-facing grooves of the first set of damper elements. A second set of damper elements, with the grooves facing downwardly, is dropped into the remaining U-shaped supports, locking the conductors between the first and second sets of damper elements and holding the conductors under tension. The process may be repeated for as many levels of conductors as desired. 
     The conductors are then attached to the walls of the housing, generally at the ends, with any suitable connection. The interior chamber of the housing is filled, such as by injection, with a dielectric. The dielectric may be any suitable dielectric fluid, such as air, oil, or N 2 , or a suitable dielectric solid. The lid is placed on the channel to close the chamber. If a vacuum is to be the dielectric, the housing is evacuated and sealed. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is an exploded perspective view of the preferred embodiment of the present invention; 
     FIG. 2 is a top plan view of the invention of FIG. 1; 
     FIG. 3 is a cross-sectional elevational view along line III--III of FIG. 2; 
     FIG. 4 is a cross-sectional view along line IV--IV of FIG. 2; 
     FIG. 5 is a cross-sectional view along line V--V of FIG. 2: 
     FIG. 6 is a view of a damper element of the present invention; 
     FIG. 7 is cross-sectional side view of an alternative embodiment of the present invention; 
     FIG. 8 is a cross-sectional side view of a further embodiment of the present invention; and 
     FIG. 9 is a diagram illustrative of the manufacture of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiment of the cable assembly of the present invention is shown generally at 10 in FIG. 1. The cable assembly 10 comprises a housing 12 having an elongated channel 14. End pieces 16, 18 are provided on each end of the channel 14. A lid 20 is provided to close the top of the channel. 
     U-shaped support members 30 are mounted at intervals within the channel 14 and fastened to the housing with bolts 32 inserted through holes in the lid 20, support members 30, and the floor of the channel 14. Alternatively, any other suitable manner of fastening the support members to the housing may be used. Each U-shaped support member 30 has two upstanding arms 36. Opposed slots 40 are provided in the interiorly-facing surfaces 42 of the arms 36. 
     Damper elements 50 are stackably mounted within each U-shaped support member 30. As best seen in FIG. 6, each damper element 50 is generally planar and rectangular, having three edges 52, 54, 56 that are substantially straight. A fourth edge 58 has grooves or recesses 60 formed therein. Each damper element 50 fits slidably within a pair of opposed slots 40 by inserting the edges 52 and 54 within the slots 40. 
     Each damper element 50 may fit within a U-shaped support member 30 either with the grooves 60 oriented to open upwardly or to open downwardly. As best seen in FIG. 1, the damper elements are inserted into the U-shaped support members such that all damper elements within one U-shaped support member are oriented in the same direction, i.e., with the grooves all facing upwardly or all facing downwardly. In addition, the damper elements in alternating U-shaped support members are oriented in the same direction. Therefore, damper elements in adjacent U-shaped support members are oriented in the opposite direction. 
     Electrical conductors or wires 70 are carried within the channel 14 of the housing 12. The wires 70 may be connected to the end pieces 16, 18 of the housing 12 in any suitable manner to provide a good mechanical and electrical connection. For example, they may be soldered, crimped, or welded to suitable connections in the end pieces. The end pieces may provide connections directly to a printed circuit board (not shown) or to ribbon cables 76. Alternatively, the wires may extend through openings in the end pieces to a wire wrap or other termination. 
     Referring to FIGS. 1 and 3, the wires 70 pass over and under the grooves 60 of the damper elements 50. The damper elements are stacked or placed in levels in the U-shaped support members. Each level of damper elements supports a separate level of conductors. Any desired number of levels of damper elements and conductors may be provided. 
     The grooves 60 of the damper elements 50 generally are formed to have a pair of rounded wells 82, 84 so that the wires 70 may conveniently be provided in pairs for differential signal transmission if desired. Differential signal transmission aids in reducing common-mode interference, if the wires are close enough so that substantially the same interference signal is induced in the two wires by the common-mode interference source. The spacing and depth of the wells 82, 84 and of the grooves 60 may be varied to achieve a desired impedance. The damper elements are formed from a non-conductive material with a high damping constant, such as TEFLON. The damping elements thereby do not support vibrations themselves and aid in suppressing or damping vibrations of the conductors. 
     The grooves 60 extend to a depth which is less than half the distance across the width of the damper element 50, as indicated by the dotted line 86 in FIG. 6. Accordingly, when the damper elements 50 are slipped within the U-shaped support members 30, the bottom of the upwardly-facing grooves do not fall at the same vertical level as the top of the downwardly-facing grooves of damper elements in the same level in the adjacent U-shaped support members. When a wire is placed over upwardly-facing grooves and beneath downwardly-facing grooves, it deviates slightly from a straight line path, as best shown in FIG. 3. In this manner, the damper elements 50 maintain tension on the wires. 
     The housing 12 forms a chamber for containing a dielectric medium. Any fluid or solid medium having an appropriate dielectric constant for a particular application may be used. For example, for high speed data transmission applications, air is a desirable dielectric. Other dielectrics include oil or N 2 . Suitable sealing of the housing may be provided if necessary. The housing may also be evacuated and sealed to provide a vacuum as a dielectric if desired. 
     Alternative embodiments in which the electrical conductors take different paths through the housing and access is provided to the conductors at intermediate locations in the housing are contemplated by the invention. For example, as shown in FIG. 7, the housing 112 may have openings 114, 116 in the lid 118. An electrical conductor 120 may enter housing 112 through the opening 114 and pass around a pin 122, through damper elements 124, around a second pin 126, and out through opening 116. Pins 122 and 126 may be fastened in any suitable manner to the side walls of the channel 113 of the housing 112. Alternatively, an electrical conductor 130 may enter the housing 112 through an opening 132 in end piece 134 and pass through the damper elements 124, around pin 136 fastened to the floor of the channel 113, and out through opening 138 in the side wall of the channel. Similarly, an electrical conductor 140 may enter the housing 112 through an opening 142 in end piece 144 and pass through one or more damper elements 124, around pin 146 fastened to the side walls of the channel 113, and out through opening 148 in the floor of the channel 113. 
     It will be apparent that the electrical conductors may take any desired path through the housing simply by placement of pins as necessary and the provision of openings in the ends, sides, floor, or lid of the housing. Alternatively, connections, rather than openings, may be provided in the ends, sides, floor, or lid of the housing to which the electrical conductors may be appropriately connected. In a further alternative, conductors may be interleaved such that a conductor may pass from one level to another level as shown in FIG. 8. Also, while multiple conductors have been shown, a single conductor also may be provided. 
     Referring to FIG. 9, the cable assembly of the present invention is manufactured with the use of a jig 212. A header 216 is placed at one end of the jig 212. The electrical conductors are generally supplied on reels 214. The free end of the conductors are attached to the header 216. Grippers 218 at the opposite end of the jig 212 grip the conductors and pull them to a desired tautness. The conductors are cut by a cutter 220 to a suitable length, to which the jig may be set. Next, the conductors are attached to a further header 222 placed at the opposite end of the jig 212. The headers may include connector pins to be wire wrapped or any other termination. 
     The U-shaped support members are placed into the channel and fastened. A first set of damper elements, having the grooves oriented to face upwardly, are slipped into the slots of alternate U-shaped support members. The conductors, attached to the headers, are dropped into the grooves of the dampers. A second set of damper elements, having the grooves oriented to face downwardly, are slipped into the slots of the remaining U-shaped support members and over the conductors. 
     This process is repeated for as many levels of conductors as desired. When the last level of conductors is in place, the lid of the housing is placed on top of the channel and fastened in any suitable manner. The conductors are tensioned and fastened in any suitable manner to the housing, as discussed above. If desired, the headers may comprise the end pieces of the housing with connections to printed circuit boards, cables, or other devices. 
     The channel of the housing may be of any desired dimensions. Similarly, there may be any desired number of U-shaped support members within the housing and any desired number of levels of damper elements and conductors. Alternatively, in lieu of separately installable U-shaped support members, the inner surfaces of the housing may have grooves or slots into which the damper elements fit directly rather than fitting the damper elements into the U-shaped support members. The housing is preferably formed of a material having a thermal expansion within the elastic range of the wire. Aluminum and copper are generally suitable materials. The damper elements may be formed of any polymer. TEFLON is generally suitable. 
     The cable assembly of the present invention is suitable for the transmission of signals at high propagation rates with low levels of cross talk between transmission lines for a wide range of impedances. The assembly has a low material cost. It may be readily mass produced and integrates the manufacture of the cable housing with the cable conductors. 
     The invention is not to be limited by what has been particularly shown and described, except as indicated in the appended claims.