Patent Publication Number: US-6706970-B2

Title: Strain relief for electrical cable

Description:
BACKGROUND OF THE INVENTION 
     Certain embodiments of the present invention generally relate to a strain relief for maintaining a secure connection between separate structures, such as between electrical cables, coaxial cables, connectors, circuit boards and the like, with little or no compressive force. 
     In the past, connectors have been proposed for connecting electrical cables that carry power and/or data signals with other cables or other structures. Generally, electrical cables have a particular cross-sectional geometry such as the circular geometry of a coaxial cable formed with a central conductor (of one or more conductive wires) surrounded by insulation or a cable dielectric material. In coaxial cables, the dielectric material is surrounded by a circular, ring-shaped outer conductor, such as a cable braid (of one or more conductive wires). The outer conductor is surrounded by a jacket. 
     In certain applications using coaxial cables, a connector is mounted on at least one end of the coaxial cable. The connector includes contacts that are electrically secured to center and outer conductors of the coaxial cable through various contact mounting means. The contact mounting means may include, among other things, a crimp, solder, set screws and the like. The connector mounted on the coaxial cable is typically plugged into a mating connector that is housed on an electrical system. The electrical system, into which the coaxial cable is plugged, may be moved with little concern for the attached coaxial cable. During installation and throughout use, coaxial cables are repeatedly bent and pulled. The bending and pulling forces tend to cause relative motion at the electrical interface between the connector and the cable conductor(s). It is desirable to limit the bending and pulling forces induced on the electrical interface in order to prevent relative movement between the connector and the cable and to prevent relative movement at a separable interface between mating contacts. 
     Strain reliefs have been proposed to limit the amount of movement within, and forces experienced on, the electrical interface between the connector and the cable. For example, conventional strain reliefs have been mounted to, or formed integral with, the connector. The strain relief extends outward from the connector along the cable proximate the point at which the coaxial cable joins the connector. The strain relief includes an arc-shaped section that receives the jacket of the coaxial cable. One or both ends of the arc-shaped section include crimp beams that fold over or wrap around the coaxial cable. The crimp beams are compressed to securely grip the jacket of the coaxial cable between the crimp beams and the arc-shaped section of the strain relief. 
     However, these conventional strain reliefs have experienced certain drawbacks. For example, when the strain relief compresses the jacket of a coaxial cable, the strain relief deforms the shape of the coaxial cable. Coaxial cables normally have a circular cross-section with a central conductor positioned at the center of the outer conductor which has a ring-shaped circular cross-section. The circular shape of the outer conductor and the relation between the center and outer conductors is maintained by the dielectric material that separates the center and outer conductors. It is preferable to maintain the circular shape for the outer conductor in order to maintain an even radial distance between the center and outer conductors. This even radial distance, in turn, maintains symmetric electromagnetic field distribution about the coaxial cable. 
     The conventional strain relief deforms the shape of the outer conductor and the dielectric material from their original geometry. When the dielectric material and outer conductor are deformed from their original geometry, the electromagnetic field distribution surrounding the coaxial cable is also changed. The modified electromagnetic field distribution created by the strain relief affects the coaxial cable&#39;s impedance characteristics and may degrade signal performance. For example, the modified electromagnetic field distribution may increase the impedance exhibited by the coaxial cable and\or may affect the voltage standing wave ratio (VSWR), shield effectiveness and the like. 
     An improved strain relief is needed that avoids the above noted problems and other disadvantages experienced heretofore. 
    
    
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with at least one embodiment, a cable strain relief is provided that comprises a cable retention member and a cable support member matable with one another to define a cable retention passage therethrough. The cable support and retention members are configured to receive a cable along the cable retention passage. The cable retention member has a retention body and at least one arm. The cable retention member also includes a cable grip configured to engage a cable. The cable support member has a support body that is secured to the arm on the cable retention member when the cable retention and support members are joined with one another. The cable grip is configured to securely engage at least a jacket of the cable to resist movement of the cable with respect to the cable support and retention members. 
     Alternative embodiments of the present invention include cable grips having different structures that are located in different positions. The cable grip may include a punch-out pattern of teeth centered in the retention body of the cable retention member and bent inward to face the cable retention passage. The cable grip may include one or more barbs provided on one or both ends of the retention body and bent inward to face the cable retention passage. The cable grip may include one or more grooves and ridges extending transverse to the cable retention passage to depress the outer surface of the cable in a rippled manner. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 illustrates an isometric view of a cable retention member formed in accordance with an embodiment of the present invention. 
     FIG. 2 illustrates an isometric view of a cable support member formed in accordance with an embodiment of the present invention. 
     FIG. 3 illustrates a reverse isometric view of the cable support member of FIG.  2 . 
     FIG. 4 illustrates an isometric view of a cable retention member formed in accordance with an alternative embodiment of the present invention. 
     FIG. 5 illustrates an isometric view of a cable retention member formed in accordance with an alternative embodiment of the present invention. 
     FIG. 6 illustrates an isometric view of a contact shell and cable retention member joined in accordance with one embodiment of the present invention. 
     FIG. 7 illustrates a reverse isometric view of the contact shell and cable support member of FIG.  6 . 
     FIG. 8 illustrates an insulated housing joined with a cable support member formed in accordance with an embodiment of the present invention. 
     FIG. 9 illustrates a reverse isometric view of the insulated housing and cable support member of FIG.  8 . 
     FIG. 10 illustrates a strain relief joined to a cable in accordance with an embodiment of the present invention. 
     FIG. 11, illustrates a top plan view of a contact shell and cable retention member formed in accordance with an alternative embodiment of the present invention. 
     FIG. 12 illustrates a side view of the contact shell and cable retention member of FIG.  11 . 
     FIG. 13 illustrates a top plan view of a cable retention member and contact joined to a carrier strip. 
     FIG. 14 illustrates an end view of cable retention and support members joined with one another in accordance with an alternative embodiment of the present invention. 
     The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, certain embodiments. It should be understood, however, that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a cable retention member  10  formed in accordance with an embodiment of the present invention. The cable retention member  10  includes a cable retention body  12  having opposite sides  14  that are formed with arms  16  extending upward in a direction substantially parallel to one another and perpendicular to the cable retention body  12 . The arms  16  include beveled upper edges  18 . Opposite lateral edges of each arm  16  include ribs  20  projecting outward to securely engage a cable support member  40  (FIG.  2 ). The cable retention body  12  and arms  16  when joined with the cable support member  40  define therebetween a cable retention passage  24 , in which a cable is placed and firmly held. 
     Rounded portions  26  are formed with opposite sides  14  and join the cable retention body  12  with the arms  16 . Lateral indentations  28  are stamped into the cable retention body  12 , rounded portions  26  and arms  16  to strengthen the overall structure of the cable retention member  10  and to provide a cable gripping feature that resists light stresses. In more detail, when a cable is firmly held within the cable retention passage  24 , the outer surface of the cable is slightly depressed to fill the lateral indentations  28 , thereby gripping the cable surface. In the embodiment of FIG. 1, lateral indentations  28  are provided on opposite sides of the cable retention body  12 . A lead end  30  of the cable retention member  10  is formed integral with a separation strip  32 . The separation strip  32  is initially formed with or mounted to another structure and later separated during assembly (as explained below in more detail). 
     The cable retention body  12  also includes a cable grip  34  centered between the arms  16 . The cable grip  34  includes teeth  36  directed inward to face the cable retention passage  24 . The teeth  36  pierce the jacket of the cable when the cable retention member  10  is secured to the cable. In applications in which the cable constitutes a coaxial cable, the teeth  36  may also pierce the outer conductor of the coaxial cable to afford added resistance to movement between the cable retention member  10  and the coaxial cable. The teeth  36  afford a cable gripping feature that resists heavy stresses. 
     FIG. 2 illustrates a cable support member  40  formed in accordance with an embodiment of the present invention. The cable support member  40  includes a cable support body  42  having opposite sides formed with sidewalls  44 . The cable support body  42  and sidewalls  44  cooperate to define U-shaped notch  46  extending along the cable retention passage  24 . Opposite sides of the notch  46  include ledges  54  proximate the side walls  44 . The sidewalls  44  extent upward beyond the ledges  54  along opposite sides of the notch  46 . Channels  56  are formed in each ledge  54  and extend through the cable support member  40  to a rear side  58  (FIG. 3) thereof. The channels  56  are spaced apart from one another to align with and receive the arms  16  of the cable retention member  10  when the cable retention member  10  and cable support member  40  are matably joined with one another to sandwich a cable therebetween. The arms  16  are inserted through the channels  56  in the direction of arrow  60  to function as a locking member that holds the cable retention and support members  10  and  40  together. 
     The notch  46  includes an arc-shaped inner surface  50  having transverse grooves  52 . The grooves  52  are separated by a series of transversely extending ridges  53 . The ridges  53  press into the outer surface of the cable, while the grooves  52  are filled by displaced surface material from the cable. The grooves  52  and ridges  53  enable the cable support member  40  to firmly engage the surface of the cable without exerting sufficient force on the cable as to deform the overall shape of the cable. In an application using a coaxial cable, the grooves  52  and ridges  53  enable the coaxial cable to be gripped adequately to resist light stresses that might otherwise cause movement between the cable support member  40  and the coaxial cable without deforming the circular ring shape of the outer conductor of the coaxial cable. 
     Optionally, the shape may be varied for cable retention passage  24  by changing the shape of the notch  46  in the cable support member  40  and/or the cable retention body  12  and arms  16  of the cable retention member  10  to accommodate other cable geometries. For example, the cable retention passage  24  may be rectangular, oval, triangular, square or otherwise shaped to accommodate cables having similar shapes. 
     FIG. 4 illustrates an alternative embodiment for the cable retention member. A cable retention member  70  includes a cable retention body  72  having side edges  74  formed with arms  76  at rounded portions  78 . The arms  76  include ribs  80  along opposite lateral edges thereof and include beveled outer ends  82  to facilitate entry into channels  56  of the cable support member  40  (FIGS.  2  and  3 ). A rear end  84  of the cable retention body  72  is formed integral with a lateral beam  86  that extends in a direction transverse to a cable retention passage  88 . The lateral beam  86  includes an upper edge  90  configured to securely and firmly engage the cable once located in the cable retention member  70 . The cable retention body  72  further includes lateral indentations  92  that span an entire width of the cable retention body  72 , rounded portions  78  and a portion of the arms  76 . The lateral indentations  92  afford added support and facilitate gripping of the cable when a portion of the cable&#39;s surface is forced into the lateral indentations  92 . The cable retention member  70  may be joined with the cable support member  40  (FIGS. 2 and 3) to firmly engaged a cable without deforming a normal cross-section of the cable. 
     FIG. 5 illustrates an alternative embodiment for the cable retention member. A cable retention member  100  includes a cable retention body  102  with side edges  104  joined with arms  106 . The arms  106  are spaced apart with a cable retention passage  116  therebetween. The arms  106  are configured to be inserted into the channels  56  in the cable support member  40  (FIGS.  2  and  3 ). The arms  106  include ribs  108  on opposite lateral edges thereof to securely retain the cable retention member  100  at a desired position with respect to the cable support member  40 . 
     Opposite ends  110  of the cable retention body  102  include forked sections  112 . Each forked section  112  includes a pair of pointed prongs  114  oriented in a plane transverse to the cable retention passage  116 . The prongs  114  are separated by a gap  118  having a width based on the dimensions of the cable. When used with a coaxial cable, the gap  118  may be greater than the diameter of the center conductor of the coaxial cable and smaller than the outer diameter of the dielectric material that separates the center and outer conductors. The prongs  114  cut the jacket and outer conductor of the coaxial cable and partially pierce the dielectric material separating the center and outer conductors. 
     The cable retention body  102  also includes a punch out  120  having a series of teeth  122  extending inward to face the cable retention passage  116 . The prongs  114  and punch out  120  securely grip the cable thereby avoiding the need for the cable retention member  100  and cable support member  40  to squeeze the cable with such force as to deform the normal shape of the cable. 
     Optionally, any number or combination of the cable gripping features, such as the teeth  36 , lateral indentations  28 , grooves  52 , ridges  53 , lateral beam  86 , lateral indentations  92 , teeth  122 , and prongs  114 , may be used depending upon an anticipated amount of stress for a particular application. 
     FIGS. 6 and 7 illustrate opposite views of one example of a contact shell  340  that may be joined to a cable retention member. Two contact shells  340  are joined with one another when they are assembled in a connector. Each contact shell  340  includes side walls  344  and a connecting wall  348 . The side walls  344  include, on one end, coaxial cable displacement contacts  368  and an open opposite end. A projection  352  is provided on at least one side wall  344  to ensure a proper electrical connection between mating contact shells  340 . 
     The connecting walls  348  include a transition region  356  at a rear end thereof that is formed integrally with a laterally extending separation plate  360 . The separation plate  360  includes a slot  363  to facilitate cutting of the separation plate  360  during assembly. The separation plate  360  may be formed integrally with the cable retention member  364 . During assembly, the cable retention member  364  is physically separated from the transition region  356 , such as through a stamping operation, and then secured to the coaxial cable. 
     The cable retention member  364  includes a cable retention body  361  joining the separation plate  360 . The cable retention body  361  is secured at opposite lateral edges to arms  365  that extend parallel to one another and in a direction perpendicular to the cable retention body  361 . The arms  365  include ribs  367  along both lateral edges thereof. The cable retention body  361  includes a cable grip  369  between the arms  365 . The cable grip  369  includes teeth  371  directed inward to face the coaxial cable. The teeth  371  pierce the jacket of the coaxial cable and engage the outer conductor of the coaxial cable when the cable retention member  364  is secured to the coaxial cable. The cable grip  369  may be formed in a punched star pattern with a plurality of teeth  371  being stamped, and bent to face inward. Alternatively, the teeth  371  may be replaced with a single tooth. Optionally, the cable grip  369  need not engage the outer conductor, but instead may only pierce a surface of the jacket sufficiently to resist any anticipated cable stresses. 
     FIGS. 8 and 9 illustrate opposite views of one example of an insulated housing  400  that may be joined to a cable support member. The insulated housing  400  includes a mating face  402  on a front end of a rectangular body section  404 . A rear end of the body section  404  is formed with a shroud  406  through a joining section  408 . The shroud  406  includes opposed side walls  410  and  412  cooperating to define a U-shaped chamber  414  therebetween that receives the coaxial cable. Interior surfaces of the side walls  410  and  412  include notches  416  and  418  facing one another and extending vertically in a direction transverse to a length of the insulated housing  400 . At least one of the notches  416  and  418  includes a pair of parallel ribs  420  that extend along the length of the corresponding notch  416  or  418 . 
     The body section  404  includes a chamber  405  adapted to receive a leading end of the coaxial cable and a crimp on a blade or receptacle contact attached thereto. A front end of the body section  402  includes a slot  407  that accepts an associated one of the blade and receptacle contacts. 
     A rear end  424  of the shroud  406  is joined with a cable support member  426  having a cable support body  419  with a U-shaped notch  428  therein. The notch  428  in the cable support member  426  includes an inner surface  421  having transverse grooves  423 . Opposite sides of the notch  428  form ledges  425 . Side walls  427  extend upward from the ledges  425  along opposite sides of the notch  428 . Channels  430  are formed in each ledge  425  and extend through the cable support member  426  to a rear side  431 . The channels  430  are spaced apart to align with and receive the arms  365  when the contact shell  340  is laterally joined with insulated housing  400  in the direction of arrow  434  (FIG.  9 ). The length of each channel  430  is slightly less than an outer dimension of the ribs  367  such that, as the arms  365  are pressed into channels  430 , the ribs  367  engage the ends of channels  430  to hold the cable retention member  364  and cable support member  426 . 
     As the cable retention member  364  and cable support member  426  are pressed together, the teeth  371  of the cable grip  369  pierce the jacket and engages the outer conductor of the coaxial cable. The cable grip  369  secures the cable retention member  364  to the coaxial cable and prevents relative axial motion therebetween. 
     The cable grip  369  resists axial movement between the coaxial cable and the insulated housing  400  without deforming the circular cross-section of the coaxial cable. The cable retention member  364  and cable support member  426  minimize compression of the coaxial cable into a compressed geometry which may otherwise interfere with the impedance and signal performance. The channels  430  and arms  365  need not have a rectangular cross-section, but instead may be circular, square, arcuate, triangular and the like. Optionally, the number of channels  430  and arms  365  may be fewer or greater than two. 
     FIG. 10 illustrates the contact shell  340  mated to a corresponding insulated housing  400 . The cable retention member  364  is separated from the contact shell  340  at the separation plate  360 . The cable retention and support members  364  and  426  are pressed toward one another until the cable grip  369  pierces the cable  432  by a desired amount to form a strain relief. 
     FIGS. 11 and 12 illustrate an alternative embodiment for a contact shell and cable retention member. The contact shell  560  includes side walls  562  and a connecting wall  564 . A contact retention end  566  of the side walls  562  includes coaxial cable displacement contacts  568 . The connecting wall  564  is joined with a separation plate  570  through a transition region  572 . The separation plate  570  is in turn connected to a cable retention member  574  through a transition region  590 . The separation plate  570  includes a slot  576  to facilitate cutting of the separation plate  570 . 
     The cable retention member  574  is U-shaped and includes a cable retention body  577  having arms  578  on opposite sides thereof and extending upward therefrom. The arms  578  include ribs  580  on opposite sides thereof. The cable retention member  574  operates in the same manner as the cable retention members  364  discussed above to frictionally engage channels in a mating cable support member (such as channels  430  in cable support member  426  in FIGS.  8  and  9 ). 
     The cable retention member  574  includes multiple cable gripping features, such as cable grips  582  and  584  and barbs  586 - 588 . Cable grips  582  and  584  are provided along the length of the cable retention body  577  and are formed by punching a star pattern in the cable retention body  577  and bending the star pattern to provide a circular ring of teeth extending upward from the cable retention body  577 . The barbs  586 - 588  are provided on opposite ends of the cable retention body  577 . In the example of FIGS. 11 and 12, a barb  586  is stamped in, and bent upward proximate, the lead edge of the cable retention body  577  within the transition region  590  connecting the cable retention member  574  to the separation plate  570 . A pair of barbs  587  and  588  are provided proximate the rear edge of the cable retention body  577  next to one another. The cable grips  582  and  584 , and barbs  586 - 588  pierce the coaxial cable when the cable retention member  574  is securely joined with a corresponding cable support member  426 . The cable grips  582  and  584 , and barbs  586 - 588  may extend so far into the coaxial cable as to completely pierce the outer jacket and engage and/or also pierce the outer conductor to afford a secure connection between the cable retention member  574  and the coaxial cable. 
     FIG. 13 illustrates a cable retention member  600  joined with a portion of a contact shell  602  through a carrier strip  604 . The cable retention member includes a cable retention body  606  having a lead edge  608  stamped integral with two linking straps  610 . The linking straps  610  are also stamped integral with one side of the carrier strip  604 . The linking straps  610  are separated by an opening  612 . 
     The carrier strip  604  is stamped integrally on an opposite side to the contact shell  602  through linking straps  616 . The linking straps  616  are separated by a space  618 . The carrier strip  604  includes pilot holes  614  that are mated with a tool die that pulls the carrier strip  604  and cable retention member  600  along an assembly process. Once the contact shell  602  and cable retention member  600  are located proximate a corresponding insulated housing and cable support member (not shown), the linking straps  610  and  616  are cut and the cable retention member  600  is pressed into a mating cable support member (not shown). 
     FIG. 14 illustrates an alternative embodiment for the cable retention and support members. A cable retention member  650  includes a cable retention body  652  with arms  654  provided on opposite sides of the cable retention body  652 . The cable retention body  652  and arms  654  enclose the cable support member  656  which includes a cable support body  658  and opposed side walls  660 . The cable support body  658  does not include channels, nor do the arms  654  include ribs. Instead, the arms  654  are spaced apart sufficient to receive the side walls  660  therebetween. Outer ends  662  on the arms  654  are crimped to wrap around a back side  664  of the cable support body  656 . The outer ends  662  are crimped until teeth  668  on the cable retention body  652  pierce at least one of the jacket  670  and outer conductor  672  without entirely piercing the dielectric layer  674  of a coaxial cable. 
     Optionally, the arms  654  and/or side walls  660  may be modified to include ridges and valleys (not shown) on an inner side of the arms  654  and on the outer side of the side walls  660 . The ridges and valleys engage one another as the arms  654  are slid over the side walls  660  to secure the cable retention and support members  650  and  652  to one another. In this alternative configuration, the outer ends  662  may remain or be removed. 
     Optionally, the cable retention and support members may be modified to remove the arms from the cable retention body entirely and instead provide the arms on the cable support body. Similarly, the channels through the cable support body may be removed and instead provided on the cable retention body. 
     Optionally, the arms on the cable retention body and the side walls on the cable support body may be removed entirely. Instead, a separate locking collar may be placed entirely or partially around the cable retention and support bodies to secure them to one another. 
     Optionally, teeth may be provided on the cable support member in place of, or in addition to the teeth and/or other retention features on the cable retention member. 
     Optionally, the cable support and retention members need not be used with coaxial cable, but instead may be adapted to be connected to discrete components, a printed circuit board, a circuit board, a flex circuit, a differential pair, a twisted pair of wires, two wires, a back plane, and the like. Accordingly, the end of the cable support and retention members need not include a shell or coaxial cable displacement crimp as discussed above. 
     Optionally, the cable retention and support members may be used with an insulated conductor other than a coaxial cable. For instance, the insulated conductor may include one or more individual conductors surrounded with insulation. If more than one conductor (braided or single strand) exist, the conductors may be arranged side by side, in a helix, in a circular pattern and the like. The cable gripping features need not entirely pierce the insulation, but instead may only grip or partially pierce the insulation without directly contacting the conductor(s). 
     Optionally, the cable retention and support members need not be attached to an end of an electrical cable, but instead may be mounted at an intermediate point along the length of the electrical cable. The cable retention and support members may be attached anywhere along an electrical cable, at which it is desirable to fasten the electrical cable to another structure, such as other electrical cables, a panel, the wall or floor, a circuit board, a computer housing and the like. 
     While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. It is therefore contemplated by the appended claims to cover such modifications that incorporate those features which come within the spirit and scope of the invention.