Abstract:
The present invention is directed to a connector for terminating a plurality of shielded conductors. The connector includes a conductive backshell housing, a connecting structure, one or more ground structures for grounding each of a plurality of conductive shields, and a strain relief structure. The ground structures are located inside the conductive backshell housing between the plurality of connecting elements and the passage in the housing for the cable. The connector is particularly useful in terminating a cable that includes a plurality of conductive shields surrounding one or more of the plurality of conductors.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to electrical connectors and specifically to electrical connectors for terminating to conductors of a shielded cable. 
     BACKGROUND OF THE INVENTION 
     In many applications, particularly in military and aerospace applications, shielded cable, such as cable in accordance with the M27500 cable specification, is used. Typically, the shielded cable includes not one but a plurality of conductive shields surrounding one or more conductors in the cable. Typically, a single shield surrounds at least one and no more than ten conductors. In some cases, an outer conductive shield will surround the plurality of conductive shields and shielded conductors. The shields protect the signals transmitted along the conductors from electromagnetic interference (EMI) due to electromagnetic radiation in the ambient atmosphere. The shields must be grounded to protect the conductors from EMI. Typically, the connector includes a conductive backshell that grounds the shields when the connector is plugged into a receptacle. 
     The ground to the backshell can be effectuated by a number of approaches. In one approach, one or more shields are soldered to a conductor which is connected to the backshell. The shields can be daisy chained together by soldering to utilize the same ground conductor. The daisy-chained shields and conductor are typically located inside of the backshell to protect them from EMI. As will be appreciated, exposing the daisy chained shields to electromagnetic radiation in the external environment can seriously compromise or degrade the EMI resistance of the shields. The EMI resistance is further weakened by the build up of electrical resistance from shield to shield along the daisy chain. The use of soldering and daisy chaining is not only labor intensive but also produces “brown crud” contamination from the solder flux. The “brown crud” is solder flux that wicks up underneath the jacket along the shield braid. Brown crud contamination is a type of corrosion that is unacceptable in many applications. 
     In other approaches, the shields are engaged with a clamping ring or coil spring and the ring or spring compressed between a metal seat and a tightened metal nut. Although the grounded portion of the conductive shields are well protected by the outer wall of the seat and the nut from exposure to electromagnetic interference, the nut often requires the shield to be cut to the proper length and properly positioned to permit the nut to be engaged properly with threads located on the outer wall of the seat. Otherwise, the shields could engage the threads and interfere with nut tightening and/or generate loose pieces or fragments of the conductive shield(s). In many applications, the shield must be temporarily clamped or otherwise held in position before the nut is tightened to effectuate the ground. Even when the shields are cut to the proper length, rotation of the ring or spring in the seat during rotation of the nut can cause the grounded shields to rub or abraid or otherwise frictionally contact against the seat, which can cause small fragments of the shield to be broken off. Such small fragments can later be dislodged, such as during the launch of a space vehicle, causing electrical shorts and vehicle malfunctions. The ability to remove such debris is hindered by the inaccessibility of the grounded shields after the nut is tightened. The grounded shields are generally not visible after nut tightening, complicating inspection of the integrity of the ground connection. The ground structure in such connectors is radiused, which provides a high profile for the connector, thereby creating problems where space is at a premium. 
     SUMMARY OF THE INVENTION 
     These and other needs are addressed by one or more embodiments of the present invention. Generally, the present invention provides a connector that utilizes a ground structure located inside of the backshell to provide ease of shield grounding. 
     In one embodiment, a connector for terminating a plurality of shielded conductors is provided that includes: 
     (a) a conductive backshell housing including a passage for receiving a plurality of conductors, the passage being disposed at a distal end of the conductive backshell housing; 
     (b) a connecting structure including a plurality of connecting elements for connecting to the corresponding plurality of conductors wherein each of a plurality of conductive shields surrounds one or more of the plurality of conductors, the plurality of connecting elements being disposed at a proximal end of the conductive backshell housing; 
     (c) one or more ground structures for grounding each of the plurality of conductive shields, each of the one or more ground structures being located inside the conductive backshell housing between the plurality of connecting elements and the passage; and 
     (d) a strain relief structure for restraining movement of the plurality of shielded conductors relative to the backshell housing. 
     The backshell housing can be composed of any conductive material and/or superconducting material and/or a composite of a conductive material and/or a superconducting material with a nonconducting material and/or a nonsuperconducting material. By way of example, the backshell housing can be composed of a plastic substrate with a metal coating. The backshell housing can be rectangular, circular, eliptical, or any other suitable cross-sectional shape and can be an integral or nonintegral (e.g., multipiece) assembly unit. 
     The connecting structure and connecting elements can be of any suitable configuration. Typically, the connecting structure has stacked rows of pin-type contacts. 
     The ground and strain relief structures can also be of any suitable configuration. For example, the structures can each include one or more movable clamping bars, jaws, or openings having smooth, serrated, ribbed, knurled, etc., configurations or edges that may be a part of or mounted on one or more parts of the backshell. In one configuration, the strain relief structure clamps the plurality of shielded conductors between a stationary bar (or a portion of the backshell) and a moveable bar and is located inside the backshell housing and near an opening of the passage. In one configuration, the ground structure clamps the conductive shield between a stationary bar (which is typically attached in some fashion to the backshell housing) and a surface of the conductive backshell housing (or another stationary bar). 
     In one configuration, the strain relief structure contacts an insulative cover enclosing the conductive shield and the plurality of shielded conductors. As will be appreciated, most shielded cables will have an insulated or dielectric (e.g., thermoplastic) cover. The cover is typically removed only as necessary to access the shields and the individual conductors, with the cover commonly being left in place where the cable contacts the strain relief structure. 
     The strain relief structure and ground structure can be located at any suitable location in the backshell. In one configuration, the strain relief structure is located between the ground structure and the distal end of the backshell housing. In another configuration, the ground structure is located between the ground structure and the distal end of the backshell housing. 
     The ground and strain relief structures can be formed by one or more integral or nonintegral components. In one configuration, the ground and/or strain relief structure includes a single unitary (or integral) bar for clamping or compressing a plurality of conductive shields or the cable, respectively. The bar (for either the ground and/or strain relief structure) may be moved or displaced by any suitable connector or connecting means such as one or more screws, a cam, a lever, a rivet, and a ratchet and locked or held in place by any suitable means such as one or more of a hook, a latch, a screw, a solder, a weld (e.g., a spot weld, an ultrasonic weld, etc.), a magnet, a rivet, an adhesive, and a lock washer. In another configuration, a plurality of ground structures is used, each of which includes a clamping bar, at least one end of which is secured to the conductive backshell housing, for electrically connecting at least a portion of the plurality of conductive shields with the conductive backshell housing. In the various configurations, rubbing, abrading, or other types of lateral movement of the shields is maintained at acceptable levels or substantially minimized. 
     The clamping bar in the ground and/or strain relief structures can be located in any suitable orientation relative to the backshell and/or another clamping bar. In one configuration, the clamping bar (of the ground and/or strain relief structures) is connected to the conductive backshell housing such that the bar moves in a direction that is at least substantially normal to at least a portion of a surface of the backshell housing to engage the plurality of shields but is at least substantially free of movement in a direction parallel to the surface. In one configuration, the bar moves in straight line motion relative to an adjacent surface of the backshell housing. In one configuration, the bar is at least substantially free of rotation (though the connectors connecting the bar to the backshell housing may rotate). In one configuration, the bar moves downwardly and upwardly relative to a ground surface of the backshell housing. 
     In another embodiment, a method for securing a plurality of shielded conductors to a connecting assembly is provided that includes the steps of: 
     (a) removing a portion of an insulating cover enclosing the plurality of conductors to provide access to a plurality of conductive shields enclosing the plurality of conductors; 
     (b) placing the plurality of conductively shielded conductors enclosed by the insulating cover into a strain relief structure in the connecting assembly; 
     (c) compressing the plurality of conductors in the strain relief structure to restrain movement of the plurality of conductors relative to a conductive backshell housing in the connecting assembly; 
     (d) engaging the accessible portions of the plurality of conductive shields with a ground structure in the connecting assembly, wherein at least a portion of the ground structure that contacts the plurality of conductive shields is at least substantially free of rotation in the engaging step (d); and 
     (e) connecting the plurality of shielded conductors to a plurality of connecting elements in the connecting assembly. 
     As will be appreciated, the engaging and compressing steps generally occur at different times. Typically, the compressing step will precede the engaging step to permit the strain relief structure to stabilize movement of the cable during the grounding operation. 
     In yet another embodiment, a connector for terminating a plurality of shielded conductors, includes: 
     (a) a conductive backshell housing including a passage for receiving a plurality of conductors, the passage being disposed at a distal end of the conductive backshell housing; 
     (b) a connecting structure including a plurality of connecting elements for connecting to the corresponding plurality of conductors wherein each of a plurality of conductive shields surround one or more of the plurality of conductors, the plurality of connecting elements being disposed at a proximal end of the conductive backshell housing; 
     (c) a strain relief structure for restraining movement of the plurality of shielded conductors relative to the backshell housing; and 
     (d) shield grounding means for clamping each of the plurality of conductive shields to a grounding surface of the conductive backshell housing. The shield grounding means is configured to maintain alignment with the grounding surface during engagement of the shield grounding means with the plurality of conductive shields. The shield grounding means can be any suitable clamping device, including without limitation one or more moveable or nonmoveable clamping bars or jaws, and/or a raised portion of the backshell housing that exerts a clamping force on the shields when the housing is assembled. 
     In one configuration, a grounding bar of the shield grounding means has freedom of movement in a direction at least substantially normal to the grounding surface of the backshell housing to engage the plurality of conductive shields and is at least substantially free of movement in a direction at least substantially parallel to the grounding surface. 
     In yet another embodiment, a method for grounding a plurality of shielded conductors is provided that includes the steps of: 
     (a) providing a plurality of conductive shields enclosing a plurality of conductors; 
     (b) passing the plurality of conductively shielded conductors through a passage in a backshell housing of a connecting assembly; 
     (c) engaging the plurality of conductively shielded conductors with a strain relief structure in the connecting assembly; 
     (d) after the passing step, engaging portions of the plurality of conductive shields with a ground structure in the connecting assembly; and 
     (e) connecting the plurality of shielded conductors to a plurality of connecting elements in the connecting assembly. 
     The various steps can include one or more substeps. For example, the engaging step (c) can include the step of compressing the plurality of conductors in the strain relief structure to restrain movement of the plurality of conductors relative to a conductive backshell housing in the connecting assembly. In one configuration, the engaging step (d) occurs interiorly of the passage. 
     The various embodiments can have one or more advantages relative to conventional devices. The grounded conductive shields can be externally accessible via a removable plate in the backshell housing. This permits the integrity of the grounding to be checked by quality control personnel, periodically during operation, and/or during routine maintenance functions. The accessibility further permits fragments or shards of the conductive shields to be removed by suitable techniques such as with an inert gas. The location of the grounding structure within the backshell can significantly enhance the EMI protection or resistance afforded by the shields. The moveable clamping member or bar can provide ease of use or installation and therefore significant labor savings. The shield does not have to be trimmed to any particular length for the ground to be realized. The ability to use shields of varying lengths provides labor savings and reduces (relative to existing designs) the generation of fines or shards from cutting of the shields. The moveable clamping member or bar can be secured by solderless techniques, thereby eliminating “brown crud” and other types of solder-related contamination. The use of a clamping member or bar that has straight-line motion can prevent rubbing or abrading of the shields against the backshell or other clamping surface during clamping, thereby reducing, relative to conventional systems, the incidence of loose fragments or shards of conductive shield located in the backshell. This reduction further reduces, relative to conventional systems, malfunctions (e.g., electrical short circuits) attributable to such fragments, thereby increasing system reliability. The backshell can have a low profile (a height that is typically no more than about 0.060 inches greater than the maximum face height of the connector), which permits more connectors to be located or stacked in a given space. This small size can be especially important in applications where space is at a premium. The strain relief and ground structures can be located at discrete or spaced apart locations. The use of the same structure to perform both functions is poor practice and can lead to a loss of system integrity. 
     The foregoing summary is intended to be neither exhaustive nor complete. As will be appreciated by one of ordinary skill in the art, the above-noted features may be used alone or in combination to form other embodiments of the invention. Such other embodiments are considered to be a part of the invention(s) set forth and/or claimed herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a backshell assembly according to a first embodiment of the present invention; 
     FIG. 2 is a front view of the backshell assembly of FIG. 1; 
     FIG. 3 is a side cross-sectional view of the backshell assembly of FIG. 1 along line  3 — 3  of FIG. 1; 
     FIG. 4 is cross-sectional view of the lower half of the backshell assembly of FIG. 1 taken along line  4 — 4  of FIG. 3 with the shields and conductors removed; 
     FIG. 5A is a cross-sectional view of the lower half of the backshell assembly of FIG. 1 taken along line  5 — 5  of FIG. 3 with the shields and conductors removed; 
     FIG. 5B is a bottom view of the grounding bar; 
     FIG. 6 is a perspective view of the ground structure engaging a portion of the lower backshell housing; 
     FIG. 7 is a rear perspective view of a backshell assembly according to another embodiment of the present invention; 
     FIG. 8 is a plan view of the backshell assembly of FIG. 7; 
     FIG. 9 is a cross-sectional view of the backshell assembly of FIG. 7 taken along line  9 — 9  of FIG. 8; 
     FIG. 10 is a rear view of the backshell assembly of FIG. 7 without the neck insert; 
     FIG. 11 is a rear view of the backshell assembly of FIG. 7 with the neck insert; 
     FIG. 12 is a side view of the backshell assembly of FIG. 7; 
     FIG. 13 is an exploded perspective view of the backshell assembly of FIG. 7; 
     FIG. 14 is a plan view of the various parts of the cable installed in the backshell assembly with the top cover removed; 
     FIGS. 15A and B are respectively an electrical circuit diagram showing the grounding of the shield of one cable configuration and a cross-sectional view of the cable; and 
     FIGS. 16A and B are respectively an electrical circuit diagram showing the grounding of shield(s) of second and third cable configurations and a cross-sectional view of the cable. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1-5 depict a first embodiment of a connector assembly according to a first embodiment of the present invention. The connector assembly  100  includes a connecting structure or plug  104  engaged with a backshell assembly  108 . The connecting structure  104  and backshell assembly  108  are typically removably connected using one or more suitable connectors such as screws  112   a,b . The backshell assembly  108  includes upper and lower housing members  116  and  120 , a strain relief structure  128  and a ground structure  124 . The upper and lower housing members  116  and  120  are typically removably connected using one or more suitable connectors such as screws  310 . 
     FIGS. 15B and 16B depict possible cable configurations which may be employed with the backshell assembly. Referring to FIG. 15B, the cable  132  in one configuration includes an outer insulative layer  136  and a conductive shield  140  both of which surround a plurality of conductors  144 . Each of the plurality of conductors  144  each includes an insulative coating  148  and a conducting element  152 . Referring to FIG. 16B, the cable  156  in other configurations includes an outer insulative layer  160  and an outer conductive shield  164  both of which surround a plurality of conductors  168  and a plurality of inner conductive shields  172 . As will be appreciated, in some cable designs each inner conductive shield is also covered by an insulative cover or layer. Each inner conductive shield  172  in turn surrounds one or more (but not all) of the conductors  168  contained in the cable  156 . A plurality of inner conductive shields  172  is therefore utilized to protect further the conductors  168  in the cable  156 . The outer conductive shield  164  is optional in many applications and therefore may be absent from the cable depending on the application. As shown in FIG. 2, connecting elements  180  in the connecting structure  104  connect to each of the conducting elements  152  in either of the cable configurations. 
     The strain relief structure  128  includes a strain relief bar  184  connected to the lower housing member  120  by means of screws  188   a,b . As will be appreciated, the strain relief bar  184  is moved downwardly and upwardly by tightening or loosening, respectively, the screws  188   a,b . The strain relief bar  184  at least substantially inhibits movement of the cable  192  relative to the backshell assembly to prevent the cable  192  from being pulled out of or pushed into the backshell assembly  108  during use. The strain relief bar  184  typically contacts the outer insulative layer  136  and compresses the cable. The outer insulative layer  136  is left in place adjacent to the strain relief bar  184  to protect the various shields and conductors from damage due to direct contact with the bar  184 . The strain relief bar  184  can be modified to include serrations or another configuration of uneven surface to enhance the gripping strength of the bar  184 . As will be appreciated, any such feature should be relatively shallow in relief to avoid shorting or otherwise damaging a shield or a conductor. 
     Referring to FIGS. 3-6, the ground structure  124  will be discussed. The ground structure  124  includes a grounding bar  200  connected to the lower housing member  120  by means of screws  204   a,b . As will be appreciated, the grounding bar  200  is moved in downwardly and upwardly by tightening or loosening, respectively, the screws  204   a,b . The bar  200  includes a plurality of teeth or serrations  208   a-d  which engage complementary teeth  212   a-c  located on the lower housing member  120 . As depicted, the teeth are positioned so as to mesh together; that is, each tooth on the lower housing member is received between adjacent teeth on the bar  200  and vice versa. The enmeshed teeth provide a contact of high electrical integrity and strength with the conductive shields in the cable. 
     Referring to FIG. 6, the grounding bar  200  is configured so as to reduce (relative to conventional systems) or substantially minimize lateral movement of the shields during tightening of the screws  204   a,b . The grounding bar  200  moves in a straight-line fashion in direction  216 , which is parallel to the Z axis  220 . The X and Y axes  224 ,  228  are in the plane of the interior surface  232  of the lower housing member  120  while the Z axis  220  is substantially normal or orthogonal to the surface  232 . The tolerance between the screws  204   a,b  and the corresponding threaded hole  236   a,b  in the bar  200  that receives the screw and the corresponding hole  238   a,b  through the lower housing member  120  that receives the screw are each relatively close to at least substantially inhibit movement of the bar laterally (e.g., in the plane of the surface  232  or in the plane containing the X and Y axes  224 ,  228 ). Preferably, the tolerance (or radial distance between the outer screw periphery and adjacent hole wall(s)) is no more than about 0.020 inches and more preferably no more than about 0.010 inches. Preferably, there is at least substantially no movement of the bar  200  (and of each shield after contact with the bar  200 ) in the plane formed by the X and Y axes. 
     The assembly of the connector assembly  100  will now be described with reference to FIGS. 1 through 6. The lower housing member  120  is first connected to the connecting structure  104  by tightening screws  112   a,b . The outer insulative cover  136  or  160  of the cable is then removed to access the various shields and conductors. The braid of each shield  140 ,  164  and/or  172  is bird caged, and the insulative coating  148  around the free end of each conductive element  152  removed. Preferably, the conductive shields  140 ,  164 , and/or  172  are not cut to avoid generating shards or fragments of the shields which can cause electrical shorts. The cable  132  or  156  is passed through the strain relief structure  128 , and the strain relief bar  184  tightened (or lowered) to compress the cable and at least substantially inhibit movement of the cable  132  or  156  relative to the lower housing member  120  in the later steps. The free ends of the various shields  140 ,  164 , and/or  172  are next placed between the upper and lower teeth  208  and  212 , and the bar  200  of the ground structure  124  tightened (or lowered) to clamp or compress the shields  140 ,  164 , and/or  172  against the lower housing member  120 . The free ends of the conductive elements  152  are then connected typically by soldering or crimping to each of the connecting elements  180  in the connector assembly  104 . 
     FIGS. 15A and 16A depict the electrical grounding circuit for the differing cable configurations realized through use of the ground structure  124 . Referring to FIG. 15A, the single outer conductive shield  140  is grounded to the connector assembly  104 , which is further grounded to another connector assembly (not shown) when the two assemblies are plugged together. Referring to FIG. 16A, the individual inner conductive shields  172   a-c , each of which surrounds a pair of conducting elements  152   a,b , is grounded to the connector assembly  104 . An optional outer conductive shield  164  may also be grounded to the connector assembly  104  by being clamped between the bar  200  and the lower housing member  120  along with the inner conductive shields  172   a-c.    
     Another embodiment of a backshell assembly  300  is depicted in FIGS. 7 through 13. The backshell assembly  300  includes a body member  304 , a cover  308 , a neck insert  312  (which is optional), and strain relief and ground structures  316  and  320 . Strain relief structure  316  includes strain relief bar  324  which includes threaded holes  328  which engage screws  332 . Ground structure  320  includes grounding bar  336  which includes threaded holes  340  which engage screws  344 . Teeth  348  are located in the body member  304  engage the shields as noted above. As can be seen from FIG. 9, the height “H G ” is no more than (and is typically less than) the height “H SR ” to permit the connectors to clear the ground structure  320  and because the gap “G GB ” between the grounding bar  336  and the body member  304  is not required to be as large as the gap “G SR ” between the strain relief bar  324  and the body member  304 . Neck insert  312  is typically used to provide termination for an outer shield  144 ,  164  via a conductive band  371 . The insert  352  has peripherally disposed lips  356  that are received in slots  360  in the body member  304  and cover  308  (not shown). The slots are, of course, aligned with one another to receive upper and lower lips  356   a,b  therebetween. 
     Referring to FIG. 14, the accessibility of the cable after connection with the backshell assembly is depicted. As can be seen from FIG. 14, the outer shield  144 ,  164  is passed over the lips  356  of insert  352  and secured to insert  352  with a conductive strap  371 . The cable  370  is passed through the neck insert  312  and into the interior of the body member  304 . The strain relief bar  324  is tightened to compress the cable and thereby restrain the cable in a fixed position. The conductors  374  are passed over the grounding bar  336  (between the grounding bar and cover) and connected to the connector assembly  104  (such as by soldering). Shields  378  covering one or more conductors  374  are partially stripped from the conductor and clamped between the grounding bar  336  and the teeth  348  in the body member  304 . The cover  308  is removably fastened to the body member  304  by means of screws  310   a,b . A step  314   a,b  in each side of the body member  304  engages a similarly shaped step in the cover to provide lateral (side-to-side) rigidity. 
     The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, in the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiments described here and above are further intended to explain best modes for practicing the invention and to enable others skilled in the art to utilizing the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.