Patent Publication Number: US-6704972-B2

Title: Fastener assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of invention relates to fastener structures and more particularly for a lightweight plastic fastener utilized in the aircraft industry which replaces a conventional bolt/screw-and-nut combination. Typically fasteners retain two or more elements together with a varying grip range. In aircraft applications it can be used to attach small diameter tube-clamps, guide blocks and cushion clamps. There are many applications where steel bolts/screws are structurally excessive and therefore overweight. The fastener of the present invention is installed with a squeezing or a push-pull motion rather than torsional rotation as used with conventional screws and bolts. 
     2. Description of the Prior Art 
     Plastic fasteners of various types have been well known in the prior art for a variety of different uses, such as binding a series of pages in a book-like form in a rapid manner, as typified in Tanaka, U.S. Pat. No. 5,074,696 which teaches a fastener used in binding pages: 
     Plastic wire tie fasteners are well known in the art which utilize a somewhat similar structure to the present invention to bind a bundle of wires. The flexible stem of the wire tie includes a longitudinal rack of serrated teeth that are pulled through an aperture having a deflectable locking tab which ratchets the teeth on the flexible stem to retain a bundle of wires together. 
     The patent to Vian, U.S. Pat. No. 3,938,587, illustrates a plastic tension fastener with a conventional male/female relationship between a bolt and nut which has a limited contact area between the latching teeth  26  on the nut and the cogs  30  on the bolt. 
     The patent to Sun et al, U.S. Pat. No. 4,730,972 teaches another fastener assembly for binding paper sheets in a conventional male/female relationship between the two binding parts  20  and  12  having mating teeth thereon which ratchet together. 
     SUMMARY OF THE INVENTION 
     The fastener of the present invention joins two or more elements together in a bolt like fashion whereby a pair of identical fasteners in opposed relationship are engaged together wherein the stem of one, which is semicircular in cross-section, is inserted through an aperture in the head of the other whereby a rack of serrated teeth on the inside flat surface of each stem is engaged by deflectable locking tabs attached to the opposite fastener. A dual ratcheting function is provided so each fastener engages and holds the stem of the other fastener so if one locking tab failed the fasteners would remain engaged to each other by reason of the locking tabs on the other fastener. 
     Once applicant&#39;s fastener has engaged what it is attempting to hold, the extending portions of the stem are cut off leaving a bolt like fastener custom sized to grip length with similar heads on opposite ends of the bolt. Due to the original length of the stem portions, the fastener has a variable grip length with a range between 0.05 inches and 1.75 inches. Larger sized fasteners could have greater grip lengths. The installation time with this fastener is very short due to the strictly lineal movement of the mating fasteners which can be engaged by either tensile action pulling the extending stems with a modified Panduit type wire tie gun. Also a compression action can be used by forcing the two heads together A whereby the locking tabs on each fastener ratchet along the rack of serrated teeth of the opposing fastener so as to firmly grip the items being joined. 
     The plastic fasteners of the present invention are substantially lighter than conventional bolts or screws. Removal of the fastener of the present invention is quickly removed by merely cutting off one of the heads through the center of the head. 
     The fastener of the present invention is used in pairs which are engaged in opposite juxtaposed orientation to each other wherein the stems of each fastener are inserted through a semi-circular aperture in the head of the opposing fastener whereby locking tabs within each head engage the serrated teeth positioned longitudinally along the flat diameter surface of the stem of the other in a ratcheting manner with each fastener providing an engagement means with the other. 
     The previously mentioned patent to Tanaka is similar to the present invention in that it utilizes a pair of fasteners placed in opposite orientation to each other wherein a rack of serrated teeth positioned on the diameter surface of each fastener engages a similar series of serrated teeth on the opposite fastener to provide a bolt-like tension fastener assembly. The two identical fasteners are held in juxtaposed coaxial relation by means of a pair of rigid plates  18  and  19  which are separate and apart from the fasteners. The Tanaka fasteners can accommodate a varying grip range. However, it is limited in that the pair of fasteners cannon overlap past the head of the fastener, which is contrary to the present invention. Also, the two plates, which the Tanaka fasteners pass through, must have a relatively large tolerance fit since the unmeshed depth of the serrated teeth require a larger diameter hole. 
     It is therefore the principal object of the present invention to provide a variable grip range fastener used in pairs having a dual set of locking teeth. 
     A further object of the present invention is to provide a fastener with a smooth circular shank once assembled with its clearance hole. 
     Another object of the present invention is to provide a single size fastener which provides a variable grip length which can be trimmed to a tailored configuration: 
     Another object of the present invention is to provide a fastener with a quick installation time wherein the manner of engagement is either tensile action or compression of the heads of the two fasteners. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of two of the fasteners engaging each other with their respective heads in contacting relation; 
     FIG. 2 is a side elevational view in longitudinal section of a single fastener; 
     FIG. 3 is a side elevational view of the fastener; 
     FIG. 4 is a stem end view of a single fastener taken along line  4 — 4  of FIG. 2; 
     FIG. 5 is a longitudinal sectional view to an enlarged scale of a pair of fasteners tensionally gripping together two sheets of material with portions of the fastener stems broken away; 
     FIG. 6 is a head end view of a single fastener taken along line  6 — 6  of FIG. 2; and 
     FIG. 7 is a sectional view taken along line  7 — 7  of FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the drawings, and in particular FIGS. 2,  3  and  4 , the fastener of the present invention is generally designated by reference numeral  10 . 
     Each fastener  10  comprises a semi-cylindrical stem  14  connected to a head  12 . Each head  12  contains a semi-circular opening  16  for receipt of the stem  14  of a companion fastener. The opening  16  is coaxially aligned with the stem portion of its fastener whereby a pair of fasteners oppositely positioned to each other, each stem  14  can engage the opening  16  of the opposite fastener. 
     Located on the flat or diameter side  15  of each stem  14 , is a channel  17  which has a recessed rack of serrated teeth  18  contained therein. The ends of the teeth  18  lie in the plane of the diameter side  15  of the stem. 
     Located on the back side of head  12 , as shown in FIGS. 5 and 6, is a circular opening  26  sized to receive the stem  14  of the opposing fastener  10  in juxtaposed contacting relation. Located within cylindrical opening  26  is an extension  22  of stem  14  which carries at least one locking tab  20 , as best seen in FIG. 5, which extend past the diameter side  15  of its stem into engagement with the serrated teeth  18  recessed in juxtaposed stem  14 . Extension  22  is cantilevered over an undercut area  28  thereby providing a degree of flexing so that tabs  20  can ratchet along rack  18 . The free end of stem  14  includes a taper  24 , as shown in FIG. 1, to assist in engaging opening  16  in its opposing fastener. 
     OPERATION 
     The tension fastener  10  of the present invention can be used to join two parts  30  and  32 , as shown in FIG. 5, or any other multitude of objects. The stem of the first fastener  10   a  is inserted through a clearance hole of mating parts whereupon the second fastener  10   b  is aligned for receipt of its stem  14  in the opening  16  of stem  10   a  and similar receipt of stem  14  of fastener  10   b  in its semi-circular opening  16 . Once one of the stems  14  of a fastener extends through the head of the opposing fastener, the locking tabs  20  will engage the rack of serrated teeth  18  on the opposing fastener and permit the fasteners  10   a  and  10   b  to be drawn together in a dual ratcheting fashion by the locking tabs  20  of both fasteners,  10   a  and  10   b . The free ends of stems  14 , as seen in FIG. 1, can be engaged and placed under tension to draw the pair of fasteners into tightened engagement. Since one side of the locking tab  20  is sloped at an angle while the opposing tooth surface is normal to the length of the stem, the engaging tabs  20  will ratchet in one direction and lock in the other. By reason of the undercut area  28  behind locking tabs  20 , the tabs are free to deflect behind the diameter side  15  of its stem and ratchet along the rack of teeth  18 . Once the pair of fasteners has engaged, whatever parts or surfaces they are joining, the racks of serrated teeth are blocked from view with the stems of the two fasteners in juxtaposed contacting relation with each other, providing a smooth surface round shank for its clearance hole. Once the fasteners have joined two elements together, the extending portions of each stem  14  from its opposing head can be cut off flush so as to provide a cylindrical head on both ends of the fastener assembly. 
     To remove the fasteners once engaged, a head  12  at one end is cut off which thereby releases the two joined stems  14  to pass through the clearance hole of the parts  30  and  32 . Removal can also be accomplished by running a #40 drill bit down through the center of the fastener destroying the locking tabs  20  on both fasteners. 
     The foregoing is considered as illustrative only of the principals of the invention. Further, since numerous modifications and changes will readily occur, to those skilled in the art it is not desired to limit the invention to the exact construction as shown and described, and accordingly, all suitable modifications and equivalents may be resorted to which follows within the scope of the invention.