Abstract:
An EMI transfer fitting suitable for use in submarines and other harsh environments is provided. In one embodiment, the EMI transfer fitting has two couplers, that collectively provide a mechanically robust interconnection between a flexible conduit (through which a bundle of data cables is encased by a wire mesh sheath that provides EMI shielding), and a rigid conduit made from a metallic material that requires no separate wire mesh sheath to provide EMI shielding. In addition to providing a robust mechanical interconnection, the transfer fitting provides a robust and seamless EMI shielding between the flexible conduit and the rigid conduit.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to fittings, such as fittings for interconnecting sections of conduit, and more particularly relates to transfer fittings that are shielded from electromagnetic interference (“EMI”). 
     BACKGROUND OF THE INVENTION 
     Fittings are well known. One particular application for various types of fittings is to interconnect sections of conduit that carryelectrical wires or cables, such as power cables and/or bundles of data cables. (It is to be understood by those of skill in the art that, in the present application, the terms “wires” and “cables” can generally refer to any type of conductor, suitable for a particular application, that is carried through a section of conduit). With society&#39;s greater reliance on dependable electronic data exchange, bundles of data cables that form the backbone of networks are now ubiquitous, and electromagnetic compatibility can be an important requirement in the design of the cables and the conduits that carry them. Bundles of data cables are now frequently run through fixed structures, such as houses, skyscrapers, and through vehicles such as cars, trucks, aircraft, naval ships, submarines or any other type of like-installation. 
     When running data cables through structures, vehicles and other locations it is important to provide adequate mechanical protection and/or EMI protection, depending on the particular needs of the data cable and the types of environmental hazards to which the cable may be exposed. Whereas prior art conduits used for power cables were primarily designed to provide mechanical protection, more modem data cables can be greatly suceptible to EMI, which can greatly degrade and/or otherwise impair proper functioning of the computer network that the data cable supports. 
     In submarines, data cables can be succeptible to a wide variety of mechanical and EMI stresses that are particularly unique to the submarine environment, and thus, prior art fittings for interconnecting sections of conduit, either of the same or different types, have proven to be unsuccesful in providing the desired and/or necessary robustness, thereby resulting in failure of the onboard computer networks. As will be well understood by any sailor in a combat situation, such failure could cost the sailor his or her life. Mechanical stresses peculiar to submarines can include torsional stresses on the hull of the ship, which thereby stresses any conduit runs, and fittings interconnecting such conduit. Further mechanical stresses can include exposure to water, particularly when, as in the case of a naval vessel, conduits are being cleaned using high-pressure water spray. Conduits must thus be able to withstand the pressure of the waterspray while protecting the cable and the sheathing running through the inside the conduit. EMI stresses on submarines can also be unique, such as the need to protect the data cables running through the submarine from external EMI caused by floating ground connections, and from the movement of the submarine through external magnetic fields. Additionally, it is considered important to shield data cables from emitting their own EMI, which could interfere with SONAR readings and/or adjacent data cables. 
     An additional problem with prior art transfer fittings arises when retrofitting older structures or installations, such as submarines, with modem bundles of data cables. During such retrofits, it is often necessary to affix a transfer fitting to the end of a piece of unthreaded conduit. Such unthreaded conduit can be found in portions of the vessel where a continuous piece of conduit must be cut in order to feed the cable through the conduit, thus leaving an exposed piece of conduit with an unthreaded end, making conventional, complementary threaded transfer fittings unusable. Thus, the aforementioned disadvantages of the prior art are compounded when attaching a transfer fitting to an unthreaded piece of conduit. 
     It is therefore desirable to have a robust transfer fitting for interconnecting conduits that can withstand high stress environments, including both mechanical and EMI stresses. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a novel EMI transfer fitting that obviates or mitigates at least one of the disadvantages of the prior art. 
     In an aspect of the invention, there is provided an EMI transfer fitting comprising a first coupler for connection to an unthreaded rigid conduit for carrying a cable bundle. The EMI transfer fitting also has a second coupler for connection to a second piece of conduit. The first coupler has a first male fastener, a compression ring and a first female fastener for receiving the rigid conduit therethrough. One of the fasteners is at a distal end adjacent to the rigid conduit and the other of the fasteners is at a proximal end that is opposite the distal end. The first male fastener and the first female fastener have a first cooperating tightening means for urging the first male fastener towards the second female fastener, such that when said first fasteners are tightened, the compression ring has external pressure applied thereto and thereby securely grasping the rigid conduit within the first coupler. 
     In a second aspect of the invention, there is provided an EMI transfer fitting comprising a first coupler for connection to a first piece of conduit. The first coupler has a distal end that connects with the first piece of conduit, and a proximal end opposite from the distal end. The EMI transfer fitting of the second aspect has a second coupler attached to the proximal end, the second coupler having an attachment means for connecting to a flexible conduit for carrying a sheathed cable therein, the second coupler further having a second male fastener, a hollow insert for passing the cable therethrough and passing said sheath thereover, and a second female fastener, the second male fastener and the second female fastener having a second cooperating tightening means for urging the second male fastener towards the second female fastener, such that when the second fasteners are tightened the sheath is impinged between an exterior of the insert and an interior of the second coupler. 
     In a third aspect of the invention, the first two aspects are combined into a single transfer fitting. 
     An EMI transfer fitting suitable for use in submarines and other harsh environments is provided. In one embodiment, the EMI transfer fitting has two couplers, that collectively provide a mechanically robust interconnection between a flexible conduit (through which a bundle of data cables is encased by a wire mesh sheath that provides EMI shielding), and a rigid conduit made from a metallic material that requires no separate wire mesh sheath to provide EMI shielding. In addition to providing a robust mechanical interconnection, the transfer fitting provides a robust and seamless EMI shielding between the flexible conduit and the rigid conduit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Certain preferred embodiments of the present invention will now be discussed, by way of example only, with reference to the attached Figures in which: 
     FIG. 1 is a side elevational view, in partial cross-section, showing a transfer fitting in accordance with an embodiment of the invention; 
     FIG. 2 is an exploded view of selected components of the transfer fitting shown in FIG. 1; and, 
     FIG. 3 is an end view of the compression ring shown in FIGS.  1  and  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, a transfer fitting in accordance with an embodiment of the invention is indicated generally at  20 . Transfer fitting  20  comprises a first coupler  24  for connection to a first piece of conduit  28  and a second coupler  32  for connection a second piece of conduit  36 . In the present embodiment, first piece of conduit  28  is rigid, while second piece of conduit  36  is flexible. Collectively, conduit  28  and transfer fitting  20  and conduit  36  form a mechanically robust and EMI shielded passage for electrical cabling, such as a data cables. 
     First coupler  24  also includes a compression ring  48  that is made from a suitable mechanically robust and EMI shielding material, such as the same material as used for fastener  40 . Compression ring  48  is characterized by a substantially circular band. When viewed from the end, as shown in FIG. 3, the band of ring  48  is discontinuous, having a small gap  50  removed from the circumference of the circular shape of the band. The band is thus reliently deformable, and, in a resting position, has a substantially circular shape. In a compressed position, the gap  50  closes thus reducing the diameter of the circular shape, and thereby grasping a piece of conduit (such as conduit  28 ) passing therethrough. Thus, the material and band-formation of ring  48  cooperate such that its diameter will decrease by applying external pressure to its circumference. As best seen in FIG. 2, ring  48  has a squared-end  52  and a tapered-end  56 . As best seen in FIG. 1, squared-end  52  abuts against the end of exterior thread  44  of fastener  48  when first coupler  48  is assembled. 
     As viewed in either FIG. 1 or FIG. 2, first coupler  24  includes a distal male fastener  40  having a substantially hollow cylindrical body that is large enough for conduit  28  to pass through the body. The larger extremity of fastener  40  (i.e. farthest from second coupler  32  as viewed in FIGS.  1  and  2 ), is hexagonally shaped for grasping and/or rotating fastener  40  by hand, or with a wrench or the like. By the same token, the smaller extremity of ring  40  (i.e. closest to second coupler  32  as viewed in FIGS. 1 and 2) is characterized by exterior threads  44 . Male fastener  40  is preferably made from aluminum that is electroless nickel plated, in order to provide corrosion resistance while serving as EMI shielding for cabling that passes through fastener  40 . Other type of corrosion resistant materials can also be used, such as an anodized material. Other materials can include brass, gold plated, titanium. Other types materials and alloys will occur to those of skill in the art. 
     First coupler  24  also includes a female fastener  60  that has a substantially hollow cylindrical body that is characterized by a set of interior threads  64  that are complementary to exterior threads  44 . Female fastener  60  is thus operable to securely receive the set of exterior threads  44  of male fastener  40  within the cavity that is defined by the set of interior threads  64 . Female fastener  60  is also characterized by a tapered-wall  68 , which has an angle that is substantially the same angle as tapered-end  56  of ring  48 . 
     Thus, as best seen in FIG. 1, when ring  48  is inserted into the cavity defined by interior threads  64  of female fastener  60 , and exterior threads  44  of male fastener  40  are threaded within interior threads  64  of female fastener  60 , squared-end  52  of ring  48  abuts the end of exterior thread  44  of fastener  48  while tapered-end  56  of ring  48  abuts with tapered-wall  68 . Further, due to the gap within the band of ring  48 , by continuing to tighten male fastener  40  within female fastener  60 , tapered-end  56  will be driven against tapered-wall  68 , thereby applying external pressure to the circumference of ring  48  and cause ring  48  to decrease in diameter. Accordingly, when first conduit  28  is assembled therewith by inserting the end of conduit  28  within the passageway defined by the components of coupler  24 , continual tightening of male fastener  40  and the ensuing closure of ring  48  will cause ring  48  to grasp first conduit  28  securely within first coupler  24 . It should now be apparent to those of skill in the art that first conduit  28  is thus preferably made from a rigid, non-deformable material, such as steel or aluminum, in order to ensure that tightening of male fastener  40  will not crush or otherwise deform conduit  28 , but will instead form a strong frictional attachment of first coupler  24  with conduit  28 . In a further characteristic of the present embodiment, conduit  28  is not threaded, thus making coupler  24  particularly suitable for connection to a rigid, unthreaded piece of conduit. 
     While optional, further mechanical protection from moisture exposure of the interior passage of male fastener  40  is provided by an O-ring  72 , (or other appropriate type of gasket or sealing-member), which resides within a suitably dimensioned channel  76  located within the interior of female fastener  60 . Additional mechanical grasping of conduit  28  can be achieved by sizing O-ring  72  to be slightly smaller in diameter than the exterior of conduit  28 . 
     As variously described herein, male fastener  40  can be considered to be located at the distal end of first coupler  24 , while the opposite end of coupler  24 , located at female fastener  60 , can be considered to be the proximal end of first coupler  24 . 
     Second coupler  28  includes a distal male fastener  100  having a substantially cylindrical body having a hollow passageway of a desired size to allow a bundle of data cables, (or the like), to pass through therethrough. In a presently preferred embodiment, such a bundle of data cables is sheathed within a flexible wire mesh (not shown) that provides EMI shielding, and conduit  36  is formed from a flexible tubing, such as a corrogated plastic or the like. Male fastener  100  is characterized by a wide end  104  (i.e. the end distal to first coupler  28  as viewed in FIGS.  1  and  2 ). Wide end  104  has a set of exterior threads  108  for complementary engagement with a set of interior threads  112  located on the end of conduit  36 . Male fastener  100  is further characterized by a narrow end  116  which has its own set of exterior threads  120  and an outwardly flared opening  122  that slightly widens the passageway of male fastener  100  at narrow end  116 . (It will be understood that, in one variation of the present embodiment, male fastener  100  can be modified to work with a complementary varied conduit  36 , wherein such a variation male fastener  100  is provided with interior threads, and conduit  36  is provided with exterior threads.) 
     Second coupler  28  also includes a female fastener  124  that is characterized by a hollow passageway having its own set of interior threads  128 , which are complementary to exterior threads  120 . The passageway of female fastener  124  terminates with a lip  132 , the details of which will be discussed in greater detail below. 
     Second coupler  28  further includes an insert  136 , which is also hollow to allow the bundle of data cables to pass therethrough, but is also formed to have the flexible wire mesh sheathing (i.e. the aforementioned sheathing that encases the bundle of data cables as it passes through conduit  36 ) to pass over the exterior of insert  136  in the space between insert  136  and male fastener  100 , as shown at  150  in FIG.  1 . Insert  136  is characterized by a flared portion  140  and a cylindrical portion  144 . 
     Thus, as best seen in FIG. 1, the taper of flared portion  140  is complementary to the taper of outwardly flared opening  122  of male fastener  100  such that the wire mesh sheathing is impinged therebetween when second coupler  28  is assembled. The impingement of the wire mesh sheathing is further improved by additional tightening of male fastener  100  within female fastener  124 , as the terminal end of flared portion  140  abuts lip  132  and thereby urges flared portion  140  against flared opening  122 . The result is not only a secure mechanical connection of conduit  36  to second coupler  28 , but also a continuous EMI sheathing for the entire bundle of cables, as the sheathing transitions from a wire mesh sheathing within conduit  36  to a sheathing that is accomplished by the metalic material of transfer fitting  20  and conduit  28 . 
     While optional, further mechanical protection from moisture exposure of the interior passage of male fastener  40  is provided by an O-ring  148 , (or other appropriate type of gasket or sealing-member), which resides within a suitably dimensioned channel  152  located on the exterior of male fastener  100 . 
     It will now be apparent to those of skill in the art that, at least in the present embodiment, female fastener  60  and female fastener  124  are formed in a single junction unit  152 , which in the present embodiment is characterized by a hexagonal housing  154  that includes at least one receptacle  156  (or the like) for attaching a ground terminal. Such a ground terminal is particularly desirable in an environment such as a submarine, where a plurality of conduits may need to have their sheathings electrically interconnected to ensure that a common ground potential exists for all conduits within the submarine. Such ground terminals can also be desirable in other installations, other than submarines, as will occur to those of skill in the art. 
     While the foregoing discussion describes certain presently preferred embodiments of the invention, it is to be understood the combinations, subsets, and variations of those embodiments are also within the scope of the invention. For example, it is contemplated that a transfer fitting in accordance with another embodiment of the invention could be characterized by a symmetric pair of couplers, wherein each coupler was either coupler  24  or coupler  32 , as discussed above. As another example, it is contemplated that in another transfer fitting according to another embodiment the invention, the transfer fitting could be characterized by a single coupler, of the form shown in either coupler  24  or coupler  32 , and wherein the opposite end of the transfer fitting was attached directly to a bulkhead, or other fixture, such that the transfer fitting in this embodiment would appear as a nipple on the fixture. Other variations will occur to those of skill in the art. 
     It will also be understood that in other embodiments of the invention, the EMI transfer fitting can be configured to adjoin two different pieces of conduit oriented at different angles—such as a ninety degree elbow. 
     The present invention provides a novel transfer fitting that provides a robust mechanical connection while providing continuous EMI shielding from one type of conduit to another, and is thus particularly useful in submarines and other harsh environments where mechanical protection and EMI shielding of sensitive data cables is required or otherwise desired. A further advantage of certain embodiments of the present invention is that connections to unthreaded pieces of rigid conduit are possible, as can be found on older naval vessels that are retrofitted with modem communication networks, particularly in locations where transfer fittings are attached to cut sections of conduit within existing conduit runs—making the threading of such conduit runs difficult or impractical. 
     The foregoing discussion provides certain exemplary embodiments of the invention and is not to be construed as limiting the scope of the invention, which is solely defined by the claims appended hereto.