Abstract:
An elongate, elastomeric fastener ( 13, 19 ) includes a head ( 13 ) and barrel section ( 19 ). The fastener may be installed into a hole ( 12 ) in a panel ( 11 ) by stretching by the elastomeric, elongated portion reducing diameter so that it passes through the hole ( 12 ) and fastens by releasing the force on the fastener ( 13, 19 ) allowing gripping around the hole ( 12 ). In yet a further embodiment, a central push-pin ( 35 ) may be used to apply an axial force on the fastener which is required to operate the fastener ( 13, 19 ).

Description:
[0001]    Priority based upon provisional application serial No. 60/255,374 filed on Dec. 15, 2000, entitled “RESILIENT STANDOFF FASTENER” is hereby claimed. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to a resilient fastener including standoff-type fasteners that assemble two flat panels a spaced distance apart. More specifically, it relates to an elastomeric fastener that provides panel grasping and spacing functions solely by its resilience.  
         BACKGROUND OF THE INVENTION AND PRIOR ART  
         [0003]    A standoff fastener is an element that attaches two panels a spaced distance apart. The panels are generally attached through some type of clipping mechanism, or clamping by threaded fasteners or screws and generally include two types: those that are machined or formed from metal, and those made from plastic. However, whether the fasteners are metal or plastic, the various types of standoffs presently available pose problems. Problem areas include the use of metal standoffs to separate two printed circuit boards. When a printed circuit board is standing off from a metal chassis, the fastener is usually attached to the chassis using methods such as self-clinching or riveting which require tools. The attachment of threaded fasteners is also time consuming, requires a loose mating component such as a screw, and increases the time required to repair items in the field.  
           [0004]    When self-clinching fasteners are used, several other problems can also be encountered. The chassis metal must be ductile, limiting the choice of materials used in the chassis, and removal of these fasteners is a destructive process leaving either the chassis or the fastener unusable after removal. Also, the installation or removal of the fastener requires specific tooling which is relatively expensive, or not readily available in the field. And finally, when the fastener is required to make grounding contact between a printed circuit board and the chassis, metal fasteners must be used but have other disadvantages noted above with regard to mounting circuit boards.  
           [0005]    The use of plastic fasteners does not solve many of the problems encountered with metal fasteners. When a plastic standoff utilizes threads, debris can fall into the assembly and the plastic standoffs that do not utilize threads are often not resistant to shock, heat, and vibration. Plastic fasteners that do not require special installation tooling are often damaged upon removal so the fastener becomes unusable for re-assembly. Plastic fasteners are also unable to provide electrical conductivity in the event a grounding contact is needed.  
           [0006]    Debris or accidental screw contact on sensitive equipment during the manufacturing process is also a problem. Another disadvantage is that if the threaded hole is stripped, the entire panel becomes useless. Furthermore, the location of the holes in the panels to be separated in the assembly can be critical and the tolerance between the holes of the first panel and second panel can be cumulative causing misalignment of the holes so the panels cannot be assembled.  
           [0007]    While there have been many attempts in the art to solve the problems above, none to date have been successful. There is therefore a need in the art of panel fastening systems for a fastener that provides new advantages and solves the problems in the art stated above.  
         SUMMARY OF THE INVENTION  
         [0008]    The present resilient standoff invention addresses and solves many of the problems with the various types of standoffs mentioned above. This fastener has an elastomeric portion, hereinafter the “tail,” that provides retention of the attached panel by the compressive radial grip of displaced tail material. A base of the fastener, which in some embodiments includes a head and a barrel section, provides a positive stop against the further insertion of the tail into the hole of a panel. The base can also function to positively space two panels apart, providing a standoff function. A third embodiment allows the tail-elongation to occur from the opposite side of the fastener by the use of a push-pin extending through the base. All three embodiments as well as other modifications are independent but will also work in conjunction with each other.  
           [0009]    Given a panel with a hole having a diameter less than the relaxed diameter of the tail, the tail can fit into the hole of the panel when the tail is stretched to a reduced diameter. When the stretching force is released, the tail grips the interior surface of the hole as well as the surfaces of the panel around it. This occurs because when the tail is released it attempts to return to its original diameter, however the material of the tail restricted by the panel causes the tail to expand or bulge on either side of the panel. This bulge retains the panel at the location along the tail when the stretching was relaxed. The expansion or bulging is also assisted by the tendency for the tail to return to its free length. To remove the panel, the tail is stretched again until the diameter reduces to an amount sufficient to pass the panel back over the tail.  
           [0010]    Although useful as a standoff, the simplest form of the fastener invention is its application to a single panel where the protruding base on one side of the panel may serve a useful function such as a support foot commonly found on household or electronic appliances. In this embodiment, the majority of the tail expansion (i.e. bulge) occurs on the side of the panel opposite the annular underside surface of the fastener base which abuts the panel. In more complex embodiments, the base can also include various other structures such as a retainer or a sleeve to achieve additional functions of electrical conductivity, rigid spacing, or other functional characteristics as mentioned further herein.  
           [0011]    More specifically, the applicant has invented a new elastomeric fastener which provides an assembly of panels without the use of threaded structures. The fastener includes a base of enlarged diameter and an elongate elastomeric shank extending from the base providing two states of dimension. The first is a relaxed state wherein the shank is substantially free of all external forces. The second state is tensile, wherein an axial tensile force applied to the shank stretches the shank into a condition of reduced diameter. In addition, there may be attachment means adjacent the base of the fastener securing it to a first panel.  
           [0012]    A second panel has an aperture with a diameter greater than the second tensile state of the shank, but less than the diameter of the shank at the first relaxed state. During assembly, a bulge in the shank forceably contacting a backside of the second panel in the direction of the first panel is formed by first passing the shank through the aperture in the second panel while in the second tensile state, and then releasing the applied tensile force. The bulge provides a clamp force to the second panel so that the panels become secured together.  
           [0013]    The fastener may further include an internal axial blind bore having an endwall proximate the distal end of a pin slidable within the bore and extending through to the outside of the opposite end of the fastener. Pushing the pin into the bore causes the longitudinal extension of the tail. This provides the above-described tail-stretching function and allows use of the fastener from one side of a panel only. Other aspects of the present invention will be more clearly shown from the following drawings and description of the preferred embodiment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    FIGS.  1 - 3  are a series of side partial sectional views showing, step-wise, the process of assembling panels utilizing the fastener of the invention.  
         [0015]    [0015]FIG. 4 is a side partial sectional view showing an alternate embodiment of the invention.  
         [0016]    FIGS.  5 - 7  are a series of side sectional views showing step-wise the application of the attachment of a panel to an alternate embodiment of the invention.  
         [0017]    [0017]FIG. 8 is a side sectional view of an alternate embodiment of the invention.  
         [0018]    [0018]FIG. 9 is a side sectional view of an alternate embodiment.  
     
    
       [0019]    The preferred embodiments shown in the drawings depict fasteners which are substantially circular in lateral cross-section at all points along their length. Because they have axial symmetry, the side views shown in the above-described figures of drawing are sufficient to convey an understanding of the invention.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring now to FIGS.  1 - 3 , a simplistic embodiment of the invention is shown. The resilient standoff in these figures depicts a fastener with a head  13  that has an adhesive  15  applied to its end surface. Thus, no holes are required in panel  17  for assembly, thereby eliminating location tolerance requirements with the holes in either of the attached panels. The standoff can be assembled to panel  17  before or after it is attached to panel  11 .  
         [0021]    Assembly then proceeds as follows. First, the lead  10  is aligned and inserted into the hole  12  in panel  11 . Once the tip of the tail  19  protrudes through the hole  12  in the panel  11 , the tail can be stretched by manually pulling the lead  10 . As the diameter of the tail  19  reduces to less than the diameter of the hole  12 , the panel  11  will be able to slide freely over the tail  19  as shown in FIG. 2. If attached to panel  11  first, the first panel and fastener may be set onto panel  17  using the adhesive and the panels will be precisely located. The adhesive bond should be strong enough to withstand the repeated stretching force of the tail portion  19 .  
         [0022]    As shown in FIG. 3, once the desired position of the panel  11  is achieved, the tail  19  is relaxed and the diameter and length of the tail  19  will attempt to return to its original size, creating a gripping, bulged condition of the tail against the panel. The surface of the tail is preferably entirely smooth so that the gripped panel may be attached at any point along the length of the tail such as the location shown by the alternate location of panel  11  depicted in phantom lines. The result is bulges  14  and  16  formed on both sides of the panel  11  holding the panel firmly where it was located when the tail  19  was relaxed. The ability to vary the location of the attachment point along the tail may be utilized to achieve different spacing or degree of lateral resilience between the panels. To remove the panel  11 , the tail  19  is stretched again thus eliminating the bulges  14  and  16  and allowing the panel to slide over the tail in either direction. If the tail is relaxed when the panel  11  is in the position depicted in solid lines, bulge  18  retains the panel against the base  13  which firmly determines the amount of space between the panels  11  and  17 . This procedure described with regard to this form of the invention is applicable to the other embodiments which all function on the same elastomeric grip principle.  
         [0023]    Refering now to FIG. 4, an additional embodiment is similar to the fastener shown in FIGS.  1 - 3 , however another tail  21  has been added to the opposite side of the base  13 . After following the procedures described regarding FIGS.  1 - 3  on one side, the procedure is repeated on the other side of the base  13  providing the positive separation of two panels  11  and  17  equal to the height of the base  13  held between them. With this panel placement, when the tails  19  and  21  are relaxed, two bulges  23  and  25  are formed holding the panels in place.  
         [0024]    Referring now to FIG. 5, a more complex embodiment of the invention is depicted in which the base  31  of the fastener includes a head  33  and a push-pin actuator  35 . The headed base of the fastener is first inserted through a hole in a first panel to which it is retained by groove  34  adjacent the underside of the head.  
         [0025]    Referring to FIGS. 6 and 7, a second panel is then attached by the stretching and bulging of the elastomeric tail portion of the shank as described in the previous embodiments, however a push-pin provides means of stretching the fastener with access to only one side of the panel  17 . The push-pin can be either molded-over by the resilient material or assembled in a later operation. The pin preferably has a shank  38 , head  36 , and the end of the pin may have a retention groove  41  that corresponds to a narrowed retention sleeve in the bore of the fastener to captivate the pin.  
         [0026]    As shown in FIG. 6, pressing the head  36  of the push-pin at the base of the fastener stretches the tail  37  at the opposite end allowing the fitting-over of panel  11 . When force against the push-pin  35  is relaxed as shown in FIG. 7, the bulge  39  retains and presses panel  11  against the annular underside of base  40 . To remove the panel  11 , the push-pin  35  is pressed again, eliminating the bulge  39  and allowing the panel  11  to slide back over the tail  37 . In this embodiment, a barrel portion of the base  40  provides spacing means between the panels.  
         [0027]    Referring now to FIG. 8, an alternate embodiment is shown in which electrical contact is provided between two spaced panels by using the resilient standoff in combination with a metal retainer  51 . The metal retainer  51  may be permanently attached to a first ductile panel  53  by clinch means  55 . In addition to the self-clinching feature  55 , the retainer has a counterbore  57 , and through-hole  59 . The resilient portion of the standoff may be assembled either before or after the self-clinching retainer  51  is installed into ductile panel  53 . It can attach itself to the retainer by gripping bulge  52  prior to assembly with panel  54  since the retainer through-hole, like the panel hole, is undersized with respect to the relaxed diameter of the tail  50 . By assembling the panel as described above with regard to FIGS.  1 - 3 , the panel  54  will make firm contact with the retainer  51 , providing electrical contact between panels  53  and  54  if desired. Electrical conductivity can also be achieved by molding conductive material directly in the material of resilient standoff eliminating the need for the retainer. A simple metal sleeve or compression bushing inserted over the base  56  of the resilient standoff can also be used.  
         [0028]    Referring now to FIG. 9, another insert configuration utilizes a snap-in retainer rather than the self-clinching retainer shown in FIG. 8. This retainer  61  can be temporarily inserted into any panel which therefore is not required to be ductile like the self-clinching embodiment of FIG. 8. The retainer  61  has a counterbore and a through-hole much the same as the retainer of FIG. 8 except that a snap protrusion  63  and a head  65  combine to provide snap-in attachment means which replaces the clinch feature. This embodiment can be employed to assembly panels much the same as described above with regard to the embodiment in FIG. 8.  
         [0029]    In considering the above preferred embodiments, it will be realized that the many objectives and advantages of the invention have been achieved. The resilient standoff of the invention is not limited to use with any specific material. The resilient standoffs will not introduce metal chips or debris that can be damaging to electronics. There is no screw to accidentally drop onto sensitive equipment. No special tooling is required to assemble or disassemble the panels. The ease of assembly and disassembly reduces the time to repair an item by eliminating a loose screw. The fastener can be easily removed and re-assembled without damaging either the panels or the fastener. Also, the resilient material of the fastener can serve as an electrical insulator or conductor. Metal components can be over-molded or later assembled to the fastener in order to provide electrical contact or a ground. An adhesive can be added to part of the fastener thus eliminating the need to punch holes in one of the panels. The means by which this fastener retains components also makes this fastener resistant to loosening due to shock and vibration, unlike known plastic snap-in fasteners. Thus, it will be apparent that many of the problems in the prior art of panel fastening systems have been overcome.  
         [0030]    It should be understood that there may be other modifications and changes to the present invention that will be obvious to those of skill in the art from the foregoing description, however, the present invention should be limited only by the following claims and their legal equivalents.