Abstract:
A shielded cable assembly contains one or more hardpoints that resist damage arising from possible collapse of the shielded cable assembly under strong compressional forces that are exerted by a clamp assembly in the form of a separable block having first and second opposed members. The hardpoint contains a conduit that protects a data transfer line or cable bundle by compressing electromagnetic shielding between the conduit and the clamp assembly. Cable electromagnetic shielding may be exposed over a selected hardpoint for use as needed in a particular application.

Description:
RELATED APPLICATIONS  
         [0001]    This application is related to copending and cofiled applications for U.S. Pat. No. ______, filed ______ and entitled CLAMP SYSTEM FOR HIGH SPEED CABLE TERMINATION (Attorney Docket No. 100110081-1); Ser. No. ______ filed ______ and entitled CABLE SHIELD TERMINATION SYSTEM USING CLAMPS AND FERRULES (Attorney Docket No. 10018053-1); and Ser. No. ______, filed ______.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention pertains to the field of shielded cables for use in high speed data transmissions and associated cable retention mechanisms. More specifically, ground receptacles are used in mounting the cables to electrical housings or chassis in a manner that minimizes electromagnetic interference (EMI).  
           [0004]    2. Discussion of the Related Art  
           [0005]    Cables for use in transmitting electronic signals are often provided with shielding in the form of foil, wire mesh or screen material that surrounds one or more central insulated leads. One common example of this type of cable is the coaxial cable that is used to carry television or data transmissions; however, in computer applications, there are often a plurality of data transfer lines in the form of a cable bundle. The shielding itself is usually covered with an external layer of insulation or a protective outer layer. The shielding protects the signal that is being transmitted on the central lead from ambient electromagnetic disturbances. The shielding also limits the amount of electromagnetic disturbance that is transmitted outwardly from the central lead. For these reasons, shielded cables are increasingly utilized in densely packed arrays of electrical equipment.  
           [0006]    A variety of connectors are used to secure and interconnect these cables. Typically, bulkhead connectors, which connect the shielding to a ground proximate the terminus of the cable, are used for shielded cables. Nevertheless, it is not always desirable or practical to connect the cable to ground solely at its terminus. For example, U.S. Pat. No. 5,975,953 to Peterson describes the difficulties and special considerations that are involved when connecting electromagnetic interference (EMI) shielded cables directly to an input/output (I/O) card and having to shunt the ground path through the I/O card.  
           [0007]    Further, in the case of bulkhead connectors, a continuing problem exists with securing the cables against unwanted motion that can, for example, cause signal degradation by torsional or translational motion of the cable. Prior systems are unable to secure the cable against unwanted motion while providing a ground for the EMI shielding. Separate structures, such as a rubber grommet that is separate from the bulkhead connector are often used to limit such motion, but constitute poor electrical conductors and may facilitate EMI leaks form an otherwise closed EMI housing.  
           [0008]    Regulatory agencies are promulgating ever stricter regulations that increasingly limit the amount of EMI which electronic equipment may generate. Additionally, stricter EMI limits are necessarily imposed by the practicalities of operating computer and telecommunications systems at increasingly faster rates of data transmission. Whenever a cable passes through the wall of an electrical housing or chassis, the opening may provide an unacceptable EMI leak. Increasingly, it is necessary to seal openings electrical housings, in order to prevent EMI leaks. At the same time, it is useful to be able establish EMI seals at multiple optional locations on a single cable construction, to reduce the number of unique cable constructions which would otherwise have to be manufactured and stocked, and to configure these as needed at the time of installation.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention overcomes the problems that are outlined above by providing a shielded cable assembly for use in conveying data signals through a chassis wall with a substantially complete EMI seal.  
           [0010]    The shielded cable comprises at least one data transfer line, which may also be part of a cable bundle. The data transfer line typically includes an electrically conductive lead for use in transmitting the signal; however, use of a data transfer line communicating optical signals is also contemplated, as are combinations of electrical and optical data transfer lines in a single cable. Electromagnetic shielding surrounds the data transfer line. The shielded cable contains a first hardpoint comprising a conduit positioned around the data transfer line over an interval at a preselected location for use in passing through the chassis wall. The conduit defines an interior passageway and has an exterior side. The data transfer line passes through the interior passageway of the conduit, and the electromagnetic shielding surrounds the exterior side of the conduit. Thus, when a clamp assembly is placed around the shielding over the conduit, a superior mechanically secure ground connection is established by compressive forces that are exerted between the exterior side of the conduit and the clamp assembly.  
           [0011]    Various other components are optionally provided in the shielded cable. For example, a protective covering may surround the data transfer line at a position within the electromagnetic shielding. The protective covering is absent over a section of the interval over the conduit. The conduit may have a first end inserted within the protective covering, a second end inserted within the protective covering, and a middle section comprising the area where the protective covering is absent. An electrically insulative material, such as adhesive-backed electrical tape, may be positioned around the conduit and within the electromagnetic shielding to secure the conduit. An outer sleeve may be placed around the data transfer line and the electromagnetic shielding, but a portion of the outer sleeve must be removed over the section of the conduit where the protective covering is also absent, in order to facilitate access to the electromagnetic shielding for purposes of establishing a ground connection.  
           [0012]    In some embodiments, a selectively detachable tube covers electromagnetic shielding over the section of the conduit where the outer sleeve is absent. The selectively detachable tube may comprise a tear-away material having a pattern of holes that are spaced apart at distances which facilitate removal of the selectively detachable tube in predetermined lengths. A shrink-wrap layer may surround at least one end of the conduit. The shrink wrap layer overlaps the outer sleeve at a position outboard of the outer sleeve and underlap the selectively detachable tube inboard of the selectively detachable tube for containment of metal fragment from the electromagnetic shielding. The provision of a selectively detachable tube expedites custom installation procedures by affording quick access to the electromagnetic shielding, which is exposed by simply peeling awaythe selectively detachable tube.  
           [0013]    The data transfer line may comprise a first end connected to a first cable coupling, a second end connected to a second cable coupling. A plurality of hardpoints may be provided including a hardpoint at any interval location where the shielded cable could pass through an electrical housing or chassis.  
           [0014]    A clamp assembly, such as a separable block, may be used to retain the shielded cable on the electrical housing or chassis and to establish a grounded connection between the electromagnetic shielding and the chassis by virtue of compressive forces over the interval between the clamp assembly and the conduit. The conduit is sufficiently rigid to withstand the compressive forces from the clamp assembly while protecting the data transfer line from damage that would, otherwise, possibly inure to the data transfer line from the compressive forces. As used herein, the term “separable block” encompasses a clamping structure that is formed of two or more pieces, as well as structures where these pieces are joined by a hinge or pivot, for example, in a bivalve configuration. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 depicts a shielded cable that contains hardpoints for use in establishing a grounded connection between the shielded cable and an electrical housing or chassis;  
         [0016]    [0016]FIG. 2 depicts a midsectional view of one of the hardpoints taken along line  2 - 2 ′ of FIG. 1;  
         [0017]    [0017]FIG. 3 depicts a separable block comprising a first member and a second member for use as a clamp assembly in attaching the hardpoint shown in FIG. 2 to the electrical housing or chassis;  
         [0018]    [0018]FIG. 4 depicts the second member of the separable block;  
         [0019]    [0019]FIG. 5 depicts the separable block within a mounting panel that forms part of the electrical housing or chassis;  
         [0020]    [0020]FIG. 6 is a midsectional view of the separable block within the receptacle taken along line  6 - 6 ′ of FIG. 5; and  
         [0021]    [0021]FIG. 7 is a rear view of the clamp assembly including the separable block with the shielded cable installed to ground.  
     
    
     DETAILED DESCRIPTION  
       [0022]    The following detailed description illustrates a preferred embodiment of a shielded cable that contains hardpoints for use in establishing grounded connections over predetermined intervals that are located, for example, where the shielded cable passes through an electrical housing or chassis. The use of a preferred example should not be construed to impart undue limitation to the concepts that are disclosed herein because the teaching is by way of example and not by limitation.  
         [0023]    [0023]FIG. 1 depicts a shielded cable  100  for use in high speed data transmission. The cable  100  includes at least one data transfer line, such as data transfer line  102 , which preferably but optionally forms part of a first cable bundle  104  comprising a plurality of such data transfer lines. Additional cable bundles, such as a second cable bundle  106 , may travel coextensively with the first cable bundle  104 . Each of the cable bundles  104  and  106  may be surrounded by a protective covering, such as an insulator or sheath  108 . The respective data transfer lines  102  are coupled at remote ends with corresponding first data couplings  110  and  112  in the case of first cable bundle  104 , and second data couplings  114  and  116  in the case of second cable bundle  106 . The protective covering  108  is optionally secured to the first cable bundle  104  through use of adhesively back electrical tape  118 .  
         [0024]    A first end  120  of shielded cable  100  may, for example, be used for coupling with an input/output bay (not shown). A conventional bulkhead mounting bracket  122  is optionally used to secure the first end  120  with a grounded connection being established between the input/output bay and shielded cable  100  through use of a clamp  124  that compresses electromagnetic shielding  126  against the bulkhead mounting bracket  122 . Shrink wrap  128  is optionally provided to cover the electromagnetic shielding  126 , which is typically formed of braided metal strands or foil, for purposes of containing metal strand of fragments that could break free from the electromagnetic shielding  126 . An elastomeric cable reinforcer  130  is also optionally provided to prevent cable motion from fatiguing the electromagnetic shielding with resultant degradation of the grounded connection between the electromagnetic shielding  126  and the bulkhead mounting bracket  122 . Labeling, such as label  132 , may optionally be used to provide indicia with descriptive information concerning the type of shielded cable  100 , as well as information concerning its use and operating characteristics.  
         [0025]    An outer sheath  134 , such as an insulator or plastic mesh, surrounds and packages the shielded cable  100 . A second end  134  of shielded cable  100  may connect, for example, with electrical components inside a cabinet that houses a central processor (not shown). Hardpoints  136  and  138  are provided on the shielded cable  100  at selected locations covering intervals where the shielded cable  100  is intended to pass through a chassis or electrical housing (not shown). By way of example, the chassis or electrical housing may be the housing for the input/output bay or the central processor cabinet that have been previously described.  
         [0026]    [0026]FIG. 2 is a midsectional view taken along line  2 - 2 ′ of FIG. 1. A conduit  200  surrounds the first cable bundle  104  and data transfer line  102 . The conduit  200  defines an interior passageway  202  through which the first cable bundle  104  passes. Conduit  200  protects the first cable bundle  104  from potential damage due to external compressive forces F. As shown in FIG. 2, conduit  200  has a circular cross-section that solely accommodates interior receipt of the first cable bundle  104 . Conduit  200  may alternatively have any other shape, such as an oblong cylindrical, or ovaloid cross-section (not shown) that accommodates both the first cable bundle  104  and the second cable bundle  106 , which may also be combined into a single cable bundle within the interior passageway  202 . Conduit  200  presents an exterior side  204  that is surrounded by the electromagnetic shielding  126 . PVC plastic is an especially preferred material for use in making conduit  200 .  
         [0027]    The protective covering  108  and the outer sheath  134  are absent, i.e., discontinuous, over a section or portion  206  radially outboard of conduit  200 . A first end  208  of conduit  200  passes beneath the protective covering  108 , as does a second end  210 , but a middle section  212  of conduit  200  is not covered by the protective covering  108  or the outer sheath  134 . An insulative material  214 , such as adhesive-backed electrical tape, is optionally wrapped around conduit  200  with mutual overlapping reinforcement against the protective covering  108  to secure conduit  200  in place.  
         [0028]    In the arrangement shown, the electromagnetic shielding  126  would be uncovered and exposed, except for the provision of a selectively detachable tube  216 , a first shrink wrap  218  segment, and a second shrink-wrap segment  220 . The first and second shrink-wrap segments  218 ,  220  respectively overlap the first and second ends  208  and  210 , extending inwardly over the middle section  212  beyond the protective layer  108  and the outer sleeve  134 . Another selectively detachable tube  217  (see FIG. 1) may be provided to cover hardpoint  138 .  
         [0029]    The selectively detachable tubes  216  and  217  comprise a tear-away material, such as a low-shear shrink-wrap or plastic coating. As shown in FIG. 1, a plurality of holes  140  are provided at distances that are selectively spaced apart from one another to facilitate removal of the selectively detachable tube  216  or  217  in lengths as needed.  
         [0030]    The first and second shrink-wrap sections  218  and  220  are optional components that contain any metal fragments which, otherwise, could devolve from the electromagnetic shielding  126 . The first and second shrink-wrap sections  218  &amp;  220  generally reinforce hardpoint  136  proximate the first and second ends  208 ,  210 . The first and second shrink-wrap sections  218  and  220  respectively overlap the outer sleeve  134 , as at portion  222 , and underlap the selectively detachable tube  216 , as at portion  224 .  
         [0031]    There will now be shown a clamp assembly for use in establishing a grounded connection between the shielded cable  100  and an electrical housing or chassis over the intervals of hardpoints  136  and  138 . Again, a variety of clamp assemblies may be used, and the demonstration of a preferred example should not be construed to impart undue limitation to the concepts that are disclosed herein because the teaching is by way of example and not by limitation.  
         [0032]    [0032]FIG. 3 illustrates the clamp assembly in the form of an electrically conductive separable block  300  defining at least one aperture  302 . The separable block  300  may in an identical manner also define additional apertures, such as aperture  304 . A first generally L-shaped member  306  defines a first portion  308  of the aperture  302 . A second generally L-shaped member  310  defines a second portion  312  of the aperture, such that the aperture  302  is completely defined when the first member  306  and the second member  310  are deployed opposite one another. The first portion  308  and the second portion  312  have respective diameters, preferably equal diameters, that accommodate the diameter of hardpoints  136  and  138  (see FIG.  1 ) after a portion of the selectively detachable tube  216  is removed. The first portion  308  and the second portion  312  of aperture  302  contain a series of continuous pressure ridges, such as ridges  314  and  316 , that oppose one another to exert compressive forces on the hardpoints  136  and  138 . Electrical contact between the separable block  300  and the electromagnetic shielding  126  is sufficient for establishing a grounded connection under the influence of these compressive forces. The first portion  308  and the second portion  312  are mirror images of one another.  
         [0033]    The separable block  300  comprises a forward face  318  and a rearward face  320 .. Holes  322 ,  324 , and  326  are provided for receipt of threaded fasteners that couple the first member  306  with the second member  310 . The first member  306  presents a first side leg  328  that contains a hole  330  which is used to accommodate a threaded fastener (not shown). The second member  310  presents a second side leg  332  that contains a hole  334  which is also used to accommodate a threaded fastener (also not shown).  
         [0034]    A gap tolerance along cut line  336  facilitates relative positioning of the first and second members  306 ,  310 , to adjust the separation of these members across aperture  302  in varying the magnitude of compressive force F (see FIG. 2) as the electromagnetic shielding  126  is compressed between the conduit  200  and aperture  302 .. This gap is closed to zero as the first and second members are assembled onto the cable hardpoint and compressed onto the cable shield as the clamp assembly fasteners are tightened.  
         [0035]    [0035]FIG. 4 depicts the second member  310  and reveals faces  400 ,  402 , and  404 , which follow cut line  336 . These faces comprise holes, such as hole  406 , in alignment with each of holes  322 - 326  for receipt of threaded fasteners.  
         [0036]    [0036]FIG. 5 depicts a front view of cable mounting panel  500 , which contains a receptacle  502  that receives the separable block  300 . The mounting panel  500  is part of an electrical housing or chassis. Mounting panel  500  contains mounting structure, such as channel bearing surfaces  504 ,  506 , and  508 , that cooperatively mate with other portions (not shown) of the electrical housing or chassis to provide an EMI enclosure.  
         [0037]    [0037]FIG. 6 is a midsectional view taken along line  6 - 6 ′ of FIG. 5. An electrically conductive mechanically compliant gasket  600  is provided within receptacle  502 , either facing forward face  318 , as shown in FIG. 6, or around the periphery of the receptacle  502  facing separable block  300 . The gasket  600  forms an EMI seal. A forward overhanging lip  602 , which may also be a separate backing plate, is threaded for receipt of threaded fasteners through, for example, holes  330  or  334  as shown in FIG. 3, and functions to retain the separable mounting block  300  in place within receptacle  502 .  
         [0038]    [0038]FIG. 7 depicts a rear view of mounting panel  500  with separable block  300  installed in receptacle  502  and shielded cable  100  installed in aperture  302 . Threaded fasteners  700  and  702  having threaded engagement with holes  330 ,  334 , are used for establishing compressive force F to compress the electromagnetic shielding  126  against the forward face  318  of separable block  300  and the adjoining face of receptacle  502  according to the instrumentalities demonstrated in FIGS.  2 - 6 , through which the electromagnetic shielding  126  is grounded to separable block  300  and mounting panel  500 . A separable block  704  is identical to separable block  300 , except a pair of plug blanks  706  and  708  are installed therein to seal an EMI enclosure  710 .  
         [0039]    In operation, the shielded cable  100  is grounded to the mounting panel  500  by separating the first and second members  306 ,  310  of separable block  300 , and removing the selectively detachable tube  216  to accommodate the thickness of aperture  302 , to create an exposed section of electromagnetic shielding  126  over hardpoint  134 . The first member  306  and the second member  310  are placed around the exposed section of electromagnetic shielding  126  such that the exposed section of electromagnetic shielding  126  resides within the aperture  126 . The first member  306  and the second member  310  are bolted together and inserted into the receptacle  502  of mounting plate  500 . Threaded fasteners  700  and  702  are then installed to retain the separable mounting block in receptacle  502 . An electrical ground contact is established between the separable block  300 , electromagnetic shielding  126 , the threaded fasteners  700 ,  702 , overhanging lip  602 , gasket  606 , and mounting plate  500 .  
         [0040]    The foregoing discussion is intended to illustrate the concepts of the invention by way of example with emphasis upon the preferred embodiments and instrumentalities. Accordingly, the disclosed embodiments and instrumentalities are not exhaustive of all options or mannerisms for practicing the disclosed principles of the invention. The inventors hereby state their intention to rely upon the Doctrine of Equivalents in protecting the full scope and spirit of the invention.