Patent Publication Number: US-2005129461-A1

Title: Two-part snap-together panel fastener

Description:
The present application is related to provisional patent application Ser. No. 60/354,920 entitled “Two-Part Snap-Together Panel Fastener” filed on Feb. 11, 2002, priority from which is hereby claimed. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to captive panel fasteners of the type having a retractable screw which is captive and extendable within a ferrule that attaches to a first panel. In fasteners of this type, the screw is usually held in its extended position by a spring but when depressed may be threaded into a second panel thereby joining the two panels.  
     BACKGROUND OF THE INVENTION AND PRIOR ART  
      Panel fasteners are well known in the art and include different means of attaching the ferrule to the first panel. Both snap-in and clinch-fit means of attachment are employed. The screw may be captivated in the ferrule by different means, but the captivation means are usually permanent and thus the screw and spring assembly is not detachable once the assembly of parts is completed. Thus, all elements of the fastener assembly must be fixed to the panel at the same time and therefore all elements will experience the same environment in subsequent steps of the manufacturing process to which the greater assembly is subjected.  
      A problem exists, however, because this may not be desirable. The panel may be subjected to manufacturing environments such as excessive heat that is not compatible with the materials of the screw/spring assembly. By nature, the screw/spring sub-assembly of these fasteners includes more delicate structures which cannot survive many harsh manufacturing environments such as those experienced during circuit board manufacture. However, there is a need to have the panel fastener attachment occur during or prior to manufacturing steps such as wave soldering. Therefore, while a permanently assembled panel fastener has the advantage of the permanent retention of all components, it may not be suitable in all applications. There may also be other applications in which the panel fastener not only unites two panels, but is also required to support other structures. In these cases, some means for the attachment/detachment of those structures to the body of the panel fastener is also needed. In yet other applications, it may be desirable to have the panel fastener installed on the panel in stages where the ferrule is attached first and then the spring and screw assembly assembled at a later time at another location.  
      There is therefore a need in the art for a panel fastener assembly which will permit the ferrule portion to be attached to the base panel in a step separate from assembling the other components of the captive panel fastener. There is a further need for having the final assembly of parts to be quick and efficient without the need for special tools. And finally, there is a need for a captive panel fastener assembly which will accommodate the attachment of other structures to the panel without additional cost or complexity.  
     SUMMARY OF THE INVENTION  
      The present invention has been devised to meet the needs in the art described above. The invention consists of a two-component, snap-together captive panel fastener in which the two components are individual sub-assemblies kept separate during different phases of the manufacturing operation. This is accomplished by a unique configuration of snap-together elements which includes a detachable ferrule portion and a snap-in screw/spring/retainer sub-assembly. The present invention&#39;s two-part system permits, for example, a separate ferrule of very hard and durable metal to be first wave-soldered to a printed circuit board with other elements of the board. Later, the screw sub-assembly can be snapped into the ferrule mounted on the circuit board when desired away from the harsh wave-soldering environment.  
      In another embodiment of the invention, the ferrule and the screw retainer include cooperating outer flanges which captivate a pivoting structure such as a lever so that the panel fastener may not only be used to secure the panel to a sub-structure, but may also be employed to affix other hardware. In one embodiment, a lever is fitted over the barrel of the ferrule and is retained against a bottom flange of the ferrule by a top flange of the screw/spring sub-assembly retainer. Sufficient snap force holding the two parts together is provided to withstand the forces of normal lever actuation.  
      More specifically, the applicant has invented a captive panel fastener assembly comprising a screw having an enlarged head, a shank, and a threaded portion of greater diameter than the shank. The fastener includes a retainer having a flange at the top, a bore receiving the screw, and a plurality of axially-extending resilient fingers at the bottom, the fingers each include an outward-facing barb and an inward-facing fingertip adjacent the shank when assembled. The diametric distance between the fingertips at rest is less than the diameter of the threaded portion of the screw but greater than the diameter of the shank. Spring means is operative between the screw head and the retainer flange to bias the screw in a retracted position. A ferrule includes a bore with an internal annular flange dimensioned to cooperate with the resilient retainer fingers by snap action whereby the barbs are forceably engaged with the internal flange to join the ferrule and the retainer. The ferrule further includes panel attachment means adjacent a bottom end and a second radially extending outer flange proximate the bottom end thereof. When applied, snap fingers and a solder joint rigidly attaches the ferrule to an aperture in the circuit board panel. The ferrule further includes a barrel portion located between the retainer flange and the second outer flange proximate the bottom end thereof. The fastener may also include a device that is captivated by the retainer flange and the ferrule outer flange whereby the device is attached to the panel. In one embodiment, the device is a lever rotatable about an outside surface of the barrel of the ferrule. Preferably, the retainer also includes a bottom-facing bevel on the inside surface of each fingertip. This provides a locking function since the threaded portion of the screw includes a downwardly-angled top land which engages the bevel upon upward retraction of the screw from the ferrule. Thus, if the screw is pulled away from the panel, the retainer fingers are forced outwardly against the internal flange of the ferrule preventing further retraction. The screw sub-assembly can only be released from the ferrule by first pushing in the screw while pulling on the retainer. Since this operation requires the application of forces to different parts of the assembly in different directions, inadvertent removal of the spring sub-assembly from the ferrule is avoided.  
      It is therefore an object of the invention to provide a panel fastener with a separatable spring/screw sub-assembly that may be pre-assembled away from the final assembly site. It is another object of the invention to provide an assembled panel fastener that may be accomplished quickly and efficiently without the need for special tools. It is yet another object of the present invention to provide a captive panel fastener assembly which will also secure other structures to the primary panel without additional cost or complexity. Other objects and advantages will become apparent from the following drawings and description of the preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exploded assembly view of the present invention.  
       FIG. 2  is an exploded assembly view of the screw/spring sub-assembly.  
       FIG. 3  is a side sectional view of the retainer of the spring screw sub-assembly.  
       FIG. 4  is a side sectional assembly view of the present invention.  
       FIG. 5  is a side sectional view of the ferrule element of the invention shown in isolation.  
       FIG. 6  is a side sectional view of the present invention in its fully assembled condition. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring now to  FIG. 1 , the present invention includes two major fastener sub-assemblies  11  and  13  snapped together to captivate lever  15  between cooperating flanges, one on each of the two inner fitting snap-together parts. The top part is a screw/spring sub-assembly  21  which includes a retainer  12  that snaps into the bore of the ferrule  23  that is pre-assembled to panel  25  in a separate assembly step. This sequence of assembly may take place as different events separated by time and distance as desired. For example, the assembly of the ferrule to the panel may take place during a wave-soldering process where it is not desirable to expose the other components to the heat and hazardous conditions in that manufacturing environment. As described further herein, the assembly of parts may support a rotatable element such as lever  15 .  
      Referring now to  FIGS. 2 and 3 , an assembly view of the screw/spring sub-assembly is shown with screw  31  fitted inside of spring  33  and both parts fitted within the bore of retainer  35 . The screw includes a head  30 , a shank  32 , and a threaded portion  34  of greater diameter than the shank. Snap fingers  43  extend axially from the base of the retainer. As more clearly shown in  FIG. 3 , the retainer includes a flange  41  with snap fingers  43  extending axially around the circumference of an internal bore  45 . The ends of the snap fingers include external, outward-facing barbs  47  for snap-in engagement with an internal flange of the ferrule. Fingertips  49  are inward-facing to provide a bottom opening of reduced diameter about the central axis so that the smallest diameter between the snap fingers  42  is less than the major diameter of the threaded portion  34  of the screw but greater than the diameter of the screw shank  32 . Therefore, when the screw is first pressed into the retainer, the fingertips  49  spread to allow passage of the threaded portion  34  and then they contract about shank  32 . This operation slidably captivates the screw in the retainer by the inward-facing surfaces of the retainer snap fingers as shown in  FIGS. 4 and 6 . A bevel  48  is located around the inside edge of each of the fingertips  49 . Bevel  48  contributes to a locking function of the fastener that will be more fully explained with regard to  FIG. 6 .  
      Referring now to  FIG. 4 , the assembly of parts of  FIG. 1  is shown from a side view. The screw sub-assembly  21  is shown in alignment with lever  15 , ferrule  23 , and panel  25 . The lever includes an aperture  50  having an inside wall  52  which is compatible with the outside diameter of the ferrule barrel  54  to provide an axle for the lever to pivot. Referring now to  FIG. 5 , the ferrule  23  further includes an area  56  of increased diameter along the bottom portion of its bore forming an internal annular flange  58 . As more clearly shown in  FIG. 6 , the external barbs of the retainer snap fingers expand into this area against the flange  58  to form the snap-fit connection of the retainer into the ferrule. Outer flange  59  acts as a stop against the top side of the attached panel and also provides an abutment for the lever to space it away from the panel. The ferrule further includes snap-arms  55  to provide means for panel attachment.  
      Referring now to  FIG. 6 , all elements of the present invention are shown in their fully assembled condition. The lever  15  is comfortably received about the barrel of the ferrule and between the retainer flange  41  and the ferrule flange  59  so that the united parts form a rotatable attachment of the lever to panel  25 . From this figure the importance of the radial bevel on the inside surface of the retainer snap fingertips can be appreciated. Since the screw in its retracted position places the screw threads against bevel  48 , further retraction of the screw creates a wedge force between the land of the top thread and the face of the bevel pushing the snap fingers outwardly against the internal flange of the ferrule thus locking the retainer to the ferrule. Therefore, pulling on the head of the screw in a completed assembly as shown in this figure will not separate the parts until the pull-out force exceeds the pull-out limit of the ferrule/panel connection. It should also be understood by these mechanical relations that the same locking function provided by the screw, the retainer, and the ferrule is operative whether or not the panel fastener assembly stands alone or is fitted into other parts as shown in  FIG. 6 . For the sub-assembly to be removed from the ferrule, the screw must first be depressed downward until the smaller diameter of the screw shank  32  resides between the tips of the retainer snap fingers. When the screw is held in, the fingers are able to contract as the retainer is then pulled axially upward out of the ferrule. Because opposing dual actions are required, accidental or inadvertent disassembly of the parts is prevented. The assembly of parts shown in  FIG. 6  may then, as a self-contained unit, be fastened to a chassis or other sub-structure (not shown) by depressing the screw downwardly and threading it into the sub-structure.  
      In this preferred embodiment, the panel is attached to the ferrule by snap-fit provided by snap-in fingers  55  which axially extend from the bottom of the ferrule. It should be understood, however, that other panel attachment means at the base of the ferrule may be employed. Furthermore, there may be other modifications, enhancements, or improvements to the described preferred embodiment without departing from the nature and scope of the invention which is to be determined only by the following claims and their legal equivalents.