Patent Publication Number: US-4545636-A

Title: Methods of and assemblies for strain relieving connectorized flat cable

Description:
FIELD OF THE INVENTION 
     This invention relates to methods of and assemblies for providing strain relief for flat cable and, in particular, to methods of and assemblies for providing strain relief for flat cable terminated in a connector assembly without using auxiliary parts. 
     BACKGROUND OF THE INVENTION 
     In connectorizing flat cable having a plurality of laterally disposed conductors arranged in either a single parallel array or multiple parallel arrays, it is imperative that ends of conductors which are terminated in a connector be isolated from any detrimental tension forces. Such forces can lead to impaired cable conductor-connector contact connections or open-circuits. These forces may be imparted on a connectorized length of cable during the reeling or de-reeling thereof and in the installation in electrical equipment or in buildings. Thus, some form of strain relief must be employed in order to insure the integrity of established interconnections. 
     One technique for providing strain relief for flat cable is to thread an end portion through two or more openings or slots formed in an auxiliary plate projecting from a connector housing. The cable is threaded in a serpentine path through the slots so that, when the cable is pulled, edges of the slots bite into the cable and exert forces on the cable anchoring it therein preventing longitudinal movement thereof. This form of strain relief isolates electrical connections between ends of cable conductors and the connector from detrimental tension forces during normal handling of the connectorized cable. One form of this type of cable strain relief is disclosed in U.S. Pat. No. 3,997,234 which issued to J. N. Worman. 
     A disadvantage of the serpentine-path type of strain relief is that it is often difficult to thread an end portion of the cable through the slots due to the degree of stiffness and thickness of the cable. Additionally, it is difficult to determine initially how much of a terminated-end portion of the cable should be threaded through the slots so that the normally stripped ends of the conductors may be brought into an aligned relationship with the respective connector receptacles or contacts. 
     SUMMARY OF THE INVENTION 
     The present invention contemplates, among other things, assemblies for and methods of providing an electrical device with a strain relief arrangement for terminated flat cable which contemplates folding the cable in a manner such that when a force is applied to a free end thereof, the cable binds itself within the arrangement without imparting any of the applied force to the terminated end portions of the cable. 
     More particularly, a base housing unit supports a connector orthogonally on a bottom wall thereof. The base housing further includes a vertical boss formed therewith which is spaced from said connector to provide a cable receiving recess. An elongated slot is formed through the bottom wall between said connector and opens into the recess. A first end section of said cable is threaded through the elongated slot. The threaded section of the cable is deformed to form a pair of spaced permanent creases to provide three accordion pleat sections. A plurality of conductor end portions of the cable are terminated on the connector. The pleat sections are positioned within the recess and a cover is secured to said base housing unit. In response to the application of tension to said free end of said cable, first and second pleat sections flex to move a first crease positioned between first and second pleat sections into binding engagement with said connector and a second crease into binding engagement with a wall of said cover. This binding action of said cable prevents the transmission of the tension to the terminated conductor end portions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and features of the invention will be apparent upon consideration of the following detailed description in conjunction with drawings wherein: 
     FIG. 1 is a perspective view of a section of flat cable; 
     FIG. 2 is a sectional view of a station-end connector assembly and a strain relieved flat cable embodying certain principles of the invention; 
     FIG. 3 is an enlarged view of a portion of FIG. 2 illustrating a folded cable section interposed between a connector and a wall of a cover; 
     FIG. 4 is similar to FIG. 3 and illustrates the cable flexed to engage the connector and the wall of the cover; and 
     FIG. 5 is a sectional top view of the assembly of FIG. 2. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, there is shown a portion of a flat cable designated generally by the numeral 10. Cable 10 includes a planar array of pairs of insulated conductors 12 which are positioned and laminated between two outer layers 14 and 16 of plastic material. The flat cable 10 is constructed of plastic material, e.g. polyetheyelene terephthalate, one form sold under the trademark MYLAR plastic film (registered trademark of the E. I. duPont de Nemours Co.), that is relatively stiff but possesses a degree of flexibility and is deformable to permit permanent creases to be imparted to the cable. Moreover, cable 10 has portions of the outer layers 14 and 16 stripped away which exposes end portions 18 of the insulated conductors 12 in order to enable the subsequent termination of the cable. 
     Referring to FIGS. 2 and 5, there are shown sectional views of a telephone station-end connector assembly designated generally by the numeral 20. The connector assembly 20 includes a base member or floor plate 22 having a first major surface 24 which may be attached to a floor surface 26 by an adhesive medium such as a first pair of spaced parallel strips of foam tapes 28 that are adhesive coated on both major surfaces. A transversely extending slot 30 is formed through the base member 22. The slot opens into the space between the parallel strips of adhesive coated foam tape 28. 
     A base housing unit, designated by the numeral 32, is attached to the base member 22 by a second pair of spaced parallel strips of adhesive coated foam tape 34. An index or slotted fanning strip 36, which enables the termination of a plurality of conductors 38 coupled to a standard telephone modular jack 44, is mounted on an upper surface 40 of the base housing unit 32. An elongated slot 42 is formed through a vertical boss 46 which extends the base housing unit 32 and is spaced from the slotted fanning strip 36. Moreover, the elongated slot 42 is located above and aligned with the elongated slot 30 formed in the base member 22. An insulation piercing connector 48 is mounted on the fanning strip 36 and enables the termination of the end portions 18 of the conductors 12. 
     A cover, designated generally by numeral 50, is positioned onto and removably secured to the base housing unit 32. The cover 50 includes an opening 52 formed therein which is aligned with and allows access to the telephone modular jack 44. The cover 50 is secured to the base housing unit 32 by a screw 54 which is seated within a tapped bore 56 formed in a post 58 extending upwardly from the base member 22. 
     In use, with the cover 50 removed and referring to FIGS. 2, 3 and 4, an operator threads a first or leading end section of cable 10 through the transverse elongated slots 30 and 42 of the assembly 20. The operator then deforms the first end portion of the cable 10 using a plier-like tool (not shown) or by hand to form a pair of permanent creases 60 and 62 across the width thereof and first, second and third successive flexible accordion pleat sections 64, 66 and 68, respectively. The pleat sections 64 and 66 are positioned within a recess 70 which is formed between the fanning strip 36 and the boss 46 of the base housing unit 32 so that crease 60 is positioned adjacent to the upper surface 40 of the base housing unit. The length of the first pleat section 64 must be such that end portions 18 of the conductors 12 are positioned adjacent to and aligned with the insulation piercing connector contacts 72 of the connector 48 when crease 60 is positioned adjacent to the upper surface 40 of the base housing unit 32. The end portions 18 are then pressed and terminated into the insulation piercing connector contacts 72. The assembly 20 is adhesively secured to a selected position on the floor surface 26 such that the portion of the cable 10 which extends from the elongated slot 30 is positioned between the parallel strips of the adhesive coated foam tapes 28. 
     As noted above, cable 10 is relatively stiff but possesses a degree of flexibility. Thus, when tension is applied to a second or unterminated end portion 76 of cable 10, the second and third pleat sections 66 and 68, respectively, flex to move crease 60 downwardly into sliding engagement along the bottom surface 40 of recess 70 and ultimately into binding engagement against a bottom section of a side wall of the connector 48. As tension continues to be applied to the second end portion 76 of cable 10, the third pleat section 68 continues to move in a downward direction through the elongated slot 42 while the second pleat section 66 pivots about crease 60 and moves crease 62 in a direction away from the connector 48 and into binding engagement with an internal wall surface 73 of the cover 50. The movement of crease 62 moves a lower section of the third pleat section 68 into binding engagement with an edge 74 of the elongated slot 42. The stiffness of the second pleat section 66 enables this section to be placed in longitudinal compression due to the binding engagements of creases 60 and 62 and, thus, acts as a bridging wedge between first and third pleat sections 64 and 68, respectively, as long as the tension is being applied to the second end portion 76 of cable 10. Ultimately, the wedging action of the second pleat section 66 prevents the transmission of the tension, which is being applied to the second end 76 of cable 10, to the end portions 18 terminated within connector 48. Thus, the binding of cable 10 within the assembly 20 isolates the end portions 18 from the tension being applied to the second end 76 of the cable. 
     Another important feature of assembly 20 is that strain relief is maintained for the connected end of the cable 10 when the cover 50 is removed for servicing of the assembly. As noted above, when a pulling force is applied to the second end portion 76 of cable 10, the second and third pleat sections 66 and 68, respectively, flex to move crease 60 downwardly and into binding engagement against the bottom section of the side wall of the connector 48. The third pleat section 68 moves in a downward direction through the elongated slot 42 while the second pleat section 66 pivots about crease 60. The stiffness of the second pleat section 66 moves crease 62 in a direction away from the connector 48 which ultimately moves the third pleat section 68 into binding engagement with the edge 74 of the elongated slot 42. Moreover, the stiffness of the second pleat section 66 enables this section to be placed in longitudinal compression due to the binding engagement of crease 60 and the downward movement of the third pleat section 68. 
     In summary, the third pleat section 68 moves downward in response to the application of tension to the second end portion 76 of cable 10. The second pleat section 66 (1) flexes to move the first pleat section 64 toward the side wall of the connector 48 and crease 60 into binding engagement with the bottom wall section of the connector and (2) pivots about crease 60 and forces crease 62 in the direction away from the connector 48 and into binding engagement with the inner vertical wall 73 of the cover 50. Due to the stiffness of cable 10, the second pleat section 66 is placed in longitudinal compression and the lower section of the third pleat section 68 is moved into engagement with edge 74 of elongated slot 42 of the base housing unit 32 by the movement of the crease 62. Ultimately, the third pleat section 68 binds itself against edge 74 as a result of the force exerted thereon by the second pleat section 66 which is wedged between the first and third pleat sections, 64 and 68, respectively, and which thereafter prevents any further movement of the third pleat section through the elongated slot 42.