Abstract:
A coaxial connector includes a clamp nut dimensioned to fit over the outer conductor, the clamp nut having threads that mate with corresponding threads on the connector body. A clamp element is positioned between the clamp nut and a leading edge of the outer conductor. The connector body having an annular wedge surface dimensioned to mate with the leading edge of the outer conductor. The threads draw the clamp nut towards the connector body, to clamp the leading edge between the clamp element and the annular wedge surface. A surface-to-surface positive stop between the clamp nut and the connector body limits the compression force to a predetermined maximum by preventing further movement of the clamp nut towards the connector body. A thread lock is engaged as the positive stop is reached; the thread lock inhibiting unthreading of the clamp nut from the connector body.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/022,808, “LOCKING THREADED CONNECTION COAXIAL CONNECTOR”, by Norman S. McMullen, filed Jan. 22, 2008—currently pending and hereby incorporated by reference in the entirety. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention relates to electrical cable connectors. More particularly, the invention relates to a coaxial cable connector having a locking threaded connection for the prevention of undesired loosening of the threaded connection after assembly. 
     2. Description of Related Art 
     Coaxial cable connectors are used, for example, in communication systems requiring a high level of reliability and precision. 
     To create a secure mechanical and optimized electrical interconnection between the cable and the connector, it is desirable to have uniform, circumferential contact between a leading edge of the coaxial cable outer conductor and the connector body. A flared end of the outer conductor may be clamped against an annular wedge surface of the connector body, using a coupling nut. Representative of this technology is commonly owned U.S. Pat. No. 5,795,188 issued Aug. 18, 1998 to Harwath. 
     To minimize twisting forces upon the outer conductor as the coupling nut is tightened, an opposing thrust collar may be placed between the back side of the flared end of the outer conductor and the coupling nut. To allow the wedge ring to fit over the flared end of the outer conductor, a circular coil spring or the like may be used between the thrust collar and the flared end of the outer conductor. Rotation of the coupling nut urges the thrust collar, if present, against the spring and the spring against the backside of the flared end of the outer conductor. Thereby, the flared end of the outer conductor is securely sandwiched between the annular wedge surface and the spring. 
     A connector that is poorly installed may damage equipment, significantly degrade system performance and/or lead to premature system failure. Therefore, prior connectors typically include extensive installation instructions that require costly specialized tools. 
     Threaded connections on and between connectors are typically tightened using wrenches having the potential for large moment arm force generation that may damage the connector and/or associated cable(s). Commonly owned U.S. Pat. No. 6,793,529 issued Sep. 21, 2004 to Buenz discloses a positive stop for threaded surfaces between the coupling nut and connector body located at the position along the threads at which a specific desired clamping force is applied upon the leading edge of the outer conductor of the attached cable, eliminating the need for torque wrenches and greatly simplifying connector assembly. 
     Competition in the coaxial cable connector market has focused attention on minimization of overall costs, including materials costs, training requirements for installation personnel, reduction of dedicated installation tooling and the total number of required installation steps and/or operations. 
     Therefore, it is an object of the invention to provide a connector that overcomes deficiencies in the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a partial cut-away side view of a coaxial connector according to one prior art embodiment, installed upon a coaxial cable, prior to final tightening of the coupling nut. 
         FIG. 2  is a partial cut-away side view of the coaxial connector of  FIG. 1 , with the coupling nut fully tightened, seated against the positive stop. 
         FIG. 3  is a schematic isometric external view of a first exemplary embodiment of the invention. 
         FIG. 4  is a cable end external view of the exemplary embodiment of  FIG. 3 . 
         FIG. 5  is a side partial cutaway view along line A-A of  FIG. 4 . 
         FIG. 6  is a close-up view of area A of  FIG. 5 . 
         FIG. 7  is a schematic isometric view of a connector body of a second exemplary embodiment. 
         FIG. 8  is a schematic isometric view of a clamp nut of the second exemplary embodiment. 
         FIG. 9  is a schematic isometric view of a connector body of a third exemplary embodiment. 
         FIG. 10  is a close-up view of area B of  FIG. 9 . 
         FIG. 11  is a schematic isometric view of a clamp nut of the third exemplary embodiment. 
         FIG. 12  is a close-up view of area C of  FIG. 11 . 
         FIG. 13  is a schematic isometric view of a connector body of a fourth exemplary embodiment. 
         FIG. 14  is a schematic isometric view of a clamp nut of the fourth exemplary embodiment. 
         FIG. 15  is a close-up view of area D of  FIG. 14 . 
         FIG. 16  is a schematic side view of a connector body with attached clamp nut of the fourth exemplary embodiment. 
         FIG. 17  is a close-up view of area E of  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1 and 2 , a connector  1  according to U.S. Pat. No. 6,793,529 for use with a coaxial cable  5  has a coupling nut  10  adapted to fit over an end portion of the cable  5 . A sheath  15  of the cable  5  is removed from the end of the cable  5  to expose the outer conductor  20 . Threads  25  between the coupling nut  10  and the connector body  35  operate to drive a thrust collar  27  into a clamp element, here a circular coil spring  30  to clamp a leading edge  26  of the outer conductor  20  between the circular coil spring  30  and an annular wedge surface  33  of the connector body  35 , to secure the connector  1  to the cable  5 . The clamping action creates a compression force that is distributed evenly around the annular wedge surface  33  to create a uniform electrical and mechanical interconnection between the connector body  35  and the outer conductor  20 . 
     The connector  1  may be supplied with environmental seals to prevent fouling and/or moisture infiltration into the connector  1  and/or coaxial cable  5 . A stop o-ring  37  seals between the outer radius of the coupling nut  10  and the connector body  35 ; an outer conductor o-ring  39  seals between the coupling nut  10  and the outer conductor  20 . Further, an inner conductor o-ring  41  seals between the inner conductor  45  and an inner contact  47  coaxially located within the connector  1  by an insulator  49 . 
     Over-tightening of the coupling nut  10  onto the connector body  35 , which may generate compression and/or shearing forces at damaging levels, is prevented by a surface-to-surface positive stop contact, for example, between an end  50  of the connector body  35  and a shoulder  52  of the coupling nut  10 . One skilled in the art will recognize that other variations of the positive stop are possible: for example shoulder to shoulder and reversal of the end to stop, etc., with the limitation that when reached, the positive stop prevents further threading between the connector body  35  and the coupling nut  10 . The specific location upon the connector  1  of the positive stop is adapted to a position where the coupling nut  10  is threaded to the connector body  35  to clamp the leading edge  26  of the outer conductor  15  at a desired maximum compression force level. The circular coil spring  30  may be configured to have an acceptable range of deformation prior to collapse to accommodate manufacturing tolerances of the associated connector  1  components and an expected thickness range of the outer conductor leading edge  26 . 
     Alternative clamp elements may be applied. For example, U.S. Pat. No. 5,795,188 discloses embodiments replacing the circular coil spring  30  with a clamping ring having a plurality of beads or wedge segments. Further alternatives include a thrust collar or separate ring with a plurality of spring fingers capable of bending to allow initial placement over the leading edge  26  but which then either spring down or are forced down by either the coupling nut  10  or connector body  35  to allow the fingers to be compressed against the back side of the leading edge  26 . One skilled in the art will appreciate that any clamp element configured to seat against the back side of the leading edge  26  may be applied, the clamp element retaining the leading edge  26  against the annular wedge surface  27  of connector body  30  as the coupling nut  10  is tightened. 
     Preferably, the selected clamp element has a limited deformation characteristic short of a collapse and/or crush force level to allow for an increased range of associated component manufacturing tolerances. The limited deformation characteristic may be varied to adapt for observed manufacturing tolerances, for example, by varying the selected material, the configuration of the compression arrangement and/or the thickness of the selected material. The selected limited deformation characteristic may be adapted to provide a desired range of additional compression “slack” before the positive stop is reached, allowing use of overall manufacturing cost saving decreased precision in the manufacturing process but still ensuring that each connector assembly will reach the desired compression force when the positive stop is reached, even if the components of an individual connector each happen to be on the short side of the allowable manufacturing tolerance. The selected clamp element, here the circular coil spring  30 , may be adapted to have the desired limited deformation characteristic by selecting a material, such as steel, and a desired material thickness wherein the circular coil spring  30  will partially deform over a desired compression force range before either collapsing or transmitting a damaging out of range compression force to the leading edge  26  of the outer conductor  20 . 
     In further embodiments, the overlap between the coupling nut  10  and the connector body  35  may be reversed. That is, rather than the connector body overlapping the coupling nut  10  as shown in  FIG. 1 , the relative positions of the components may be reversed, for example as shown in U.S. Pat. No. 5,795,188. The compression force generation between the components remains the same in either configuration. 
     In use, the cable  5  end is prepared and the coupling nut  10  placed over the cable end along with any applicable outer conductor o-ring  39  and thrust collar  27 . The circular coil spring  31  or other clamp element is then stretched over the leading edge  26  into position behind the leading edge  26 . If used, the stop o-ring  39  is placed upon the coupling nut  10  proximate the shoulder  52 . The connector body  35  is then located so that the inner contact  47  engages the inner conductor  45  and the annular wedge surface  33  is pressed against the front side of the leading edge  26 . The coupling nut  10  is then moved toward the connector body  30  and threaded into the threads  25  as shown in  FIG. 1 . The coupling nut  10  is threaded until the end  50  of the connector body  30  reaches the positive stop at the shoulder  52  of the coupling nut  10  as shown in  FIG. 2 . Reaching the positive stop signifies to the installation personnel that the desired compression force has been reached without requiring use of a torque wrench and prevents further tightening of the coupling nut  10  which would increase the compression force beyond the desired maximum level. 
     One skilled in the art will appreciate that the connector  1  may be adapted to mate with the dimensions and configuration of a specific coaxial cable  5 , for example a coaxial cable  5  with annular or helical corrugations in the inner and/or outer conductors  47 ,  20 . To mate with a circular coil spring  30  or the like adapted for use with outer conductor(s)  20  having helical corrugations, the thrust collar  27  may be formed with a step located at a point where the circular coil spring  30  bridges across the corrugations. Further, the connector end  55  of the connector  1  may be adapted to mate according to male and/or female embodiments of a proprietary or standardized connector interface, such as BNC, Type-N, SMA or DIN. 
     The inventor(s) have analyzed the long term performance of connectors configured with a positive stop according to U.S. Pat. No. 6,793,529. The friction between smooth co-planar surfaces of the positive stop threaded connection, when installed in environments with extreme levels of vibration, temperature variation and/or moisture penetration, provides less than desired resistance to undesired loosening of the threaded connection, especially where each of the surfaces are metallic. Also, the metal coupling nut adds a significant weight, materials and manufacturing cost to the connector. 
     Also, the inventor&#39;s analysis of previous attempts to apply polymeric materials to clamp nuts has revealed that polymeric material typically has a creep characteristic that further reduces the long-term retention characteristic of threaded interconnections. 
     Connectors according to the invention incorporate a thread locking feature and optionally use a polymeric material for the coupling nut, instead of metal. 
     As shown in  FIGS. 3-6 , a connector according to a first exemplary embodiment of the invention has a thread lock created by an interference fit between the connector body  35  and the coupling nut  10 . A body locking surface  57  is located on an inner diameter surface of a cable end of the connector body  35 . A corresponding coupling nut locking surface  59  is formed on an outer diameter area of the coupling nut  10 , preferably between the shoulder  52  and the threads  25 . To form an interference fit between the body locking surface  57  and the coupling nut locking surface  59 , the inner diameter of the body locking surface  57  is formed smaller than an outer diameter of the coupling nut locking surface  59 . Thereby, as the coupling nut  10  is threaded onto the connector body  35  an interference fit occurs between the body locking surface  57  and the corresponding coupling nut locking surface  59 . 
     The degree of interference fit, that is, the magnitude of mismatch between the opposing locking surface dimensions, may be selected to create a resistance to threading that is not so great that it causes undue effort to thread the elements together up to the positive stop, but alternatively once at the positive stop secures the assembly from undesired unthreading. To assist with the alignment and initial mating of the interference fit between the body locking surface  57  and the coupling nut locking surface  59 , an angled guide edge  61  may be applied to one or both of the respective locking surfaces. Further, an annular deflection groove  63  may be applied to the connector body  35  exterior surface at a longitudinal position corresponding to the position of the threads  25 . The deflection groove  63  provides a flexure point for the connector body  35  enabling a slight stress relief as the interference fit between the respective locking surfaces is made, until the coupling nut  10  and connector body  35  contact one another at the positive stop. 
     The coupling nut  10  is preferably formed from a polymeric material such as polybutylene terephthalate (PBT) plastic resin. The PBT or other selected polymeric material may be injection molded and/or machined. Carbon black or the like may be added to the PBT or other selected polymeric material to improve a UV radiation resistance characteristic of the polymeric material. The connector body  35  is preferably formed from a metallic material having suitable strength and conductivity characteristics, such as coated or uncoated brass or a copper alloy. 
     A slight elasticity characteristic of the polymeric material may aid in permitting the initial threading that engages the interference fit and also then aids in retention of the interference fit once threading is complete, as the polymeric material returns to a static position, sealing securely at the interference fit. 
     In the present embodiment, a polymeric coupling nut  10  is demonstrated acting directly upon the clamp element, here demonstrated as a circular coil spring  30 . One skilled in the art will appreciate other clamp elements and/or additional elements such as a thrust collar  27  may be applied. 
     In further embodiments, textures, corrugations, ribs, protrusions or the like may be applied to the locking surfaces to provide a positive interlock and/or higher levels of retention/resistance to unthreading. For example, the thread lock may be a plurality of interlocking corrugations and/or ramp features which allow threading in a direction across the ramp faces but which present shoulders or other stops in the direction of unthreading. The thread lock may be applied to create a connector embodiment that is not removable without destroying the connector, once secured upon the coaxial cable  5 . 
     As described herein above, the arrangement of the overlapping portions containing the threads  25  between the coupling nut  10  and the connector body  35  may be exchanged. A second exemplary embodiment, as shown in  FIGS. 7 and 8 , demonstrates a threaded interconnection between the coupling nut  10  and connector body  35  in which the coupling nut  10  overlaps the connector body  35 . Further, the thread lock is demonstrated as a friction surface formed as corrugation(s)  65  applied to the surfaces of the positive stop contact between the end  50 , now of the clamp nut  10 , and the shoulder  52 , now of the connector body  35 . One skilled in the art will recognize that once interlocked with each other, the corrugation(s)  65 , alone, provide a significant resistance to unthreading. Depending upon the degree of resistance to unthreading that is desired, the corrugation(s)  65  may be applied with or without also configuring an additional thread lock in the form of, for example, an interference fit between the body locking surface  57  and the coupling nut locking surface  59 , as described herein above. 
     As demonstrated in  FIGS. 9-12 , in a third exemplary embodiment the thread interlock is a radial ramp protrusion  67  of the connector body  35  that interlocks with an inner diameter ramp groove  69  of the clamp nut  10  as the threading between the clamp nut  10  and connector body  35  reaches the positive stop. Again, depending upon the degree of positive interlock resistance to unthreading that is desired, the ramp protrusion  67  to ramp groove  69  thread interlock may be applied with or without also configuring an additional thread interlock such as an interference fit between the body locking surface  57  and the clamp nut locking surface  59 . The interference fit is demonstrated in the present embodiment with a contact area that is a plurality of arc segment(s) that are less than the entire circumference of the clamp nut  10  and/or connector body  35 . The length of the arc segments selected for the interference fit surfaces may be used to configure the resistance to threading presented by the interference fit surfaces and also the degree of thread lock function obtained therefrom. 
     A fourth exemplary embodiment, as shown in  FIGS. 13-17 , demonstrates a releasable thread lock that enables disassembly of the connector  1  without damage to the thread lock. One or more deflectable tab(s)  71  are positioned to engage and interlock with respective socket(s)  73  against rotation in an unthreading direction as the coupling nut  10  and connector body  35  are threaded together along the corresponding thread(s)  25  to the positive stop. 
     The interlock between the deflectable tab(s)  71  and socket(s)  73 , if configured to be on the exterior surface of the connector, for example as best shown in  FIGS. 16 and 17 , provides a visual indicia to the assembler that the positive stop has been reached. Alternatively, visual indicia such as alignment marks or the like may be applied the connector exterior to indicate the rotational positions between the connector body  35  and clamp nut  10  that indicate that the positive stop is being approached and/or has been reached. 
     To disassemble the connector  1  for inspection and/or re-use, the deflectable tab  71  may be manually deflected away from engagement with the socket  73  to enable unthreading of the coupling nut  10  from the connector body  35 . 
     One skilled in the art will appreciate that the addition of thread interlock(s) according to the invention to a coaxial connector with a positive stop configuration significantly improves the connector&#39;s resistance to unthreading due to vibration, thermal expansion and/or tampering. The addition of thread interlock(s) also enables the clamp nut  10  to be formed with cost efficient and light weight polymeric materials that may otherwise exhibit an unacceptable threaded connection stability due to a polymeric material creep characteristic. 
     The various thread lock embodiments of the invention may also be applied to connector configurations that do not include a positive stop configuration and also to threaded connections other than between the connector body and the clamp nut, such as the coupling nut of a connector interface. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 Table of Parts 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 connector 
               
               
                 5 
                 coaxial cable 
               
               
                 10 
                 clamp nut 
               
               
                 15 
                 sheath 
               
               
                 20 
                 outer conductor 
               
               
                 25 
                 threads 
               
               
                 26 
                 leading edge 
               
               
                 27 
                 thrust collar 
               
               
                 30 
                 circular coil spring 
               
               
                 33 
                 annular wedge surface 
               
               
                 35 
                 connector body 
               
               
                 37 
                 stop o-ring 
               
               
                 39 
                 outer-conductor o-ring 
               
               
                 41 
                 inner-conductor o-ring 
               
               
                 45 
                 inner conductor 
               
               
                 47 
                 inner contact 
               
               
                 49 
                 insulator 
               
               
                 50 
                 end 
               
               
                 52 
                 shoulder 
               
               
                 55 
                 end 
               
               
                 57 
                 body locking surface 
               
               
                 59 
                 clamp nut locking surface 
               
               
                 61 
                 guide edge 
               
               
                 63 
                 deflection groove 
               
               
                 65 
                 corrugation(s) 
               
               
                 67 
                 ramp protrusion 
               
               
                 69 
                 ramp groove 
               
               
                 71 
                 deflectable tab 
               
               
                 73 
                 socket 
               
               
                   
               
             
          
         
       
     
     Where in the foregoing description reference has been made to materials, ratios, integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth. 
     While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus, methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant&#39;s general inventive concept. Further, it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope or spirit of the present invention as defined by the following claims.