Abstract:
A quarter-turn latch for fastening a first panel to a second panel includes a bolt with a bayonet key that rotationally engages a keyhole in the second panel, and a capture key that engages with the first panel to prevent loss of the bolt. A track on the underside of the second panel, surrounding a portion of the keyhole, secures the bolt in the closed position. Bump stops engageable with the bayonet key define open and closed positions. A spring integrated with the bolt prevents rattles, overcomes misalignment and/or assists disengagement of the latch. The system may be used, for example, in network interface devices (NIDs), plastic enclosures, and other devices.

Description:
FIELD OF THE INVENTION 
     The present invention relates to fasteners for removably securing together two panels or other objects. More particularly, the present invention relates to a quarter-turn panel fastener having a spring. 
     BACKGROUND OF THE INVENTION 
     Many types of fasteners are used to removably attach one panel to another. Often, sheet metal screws or machine screws, with or without nuts, are used for these tasks. Although these screw type fasteners will securely fasten one panel to another and are readily unfastened, they are inadequate for many applications. For instance, screw type fasteners take too long to assemble and disassemble, require relatively precise tolerances in panel fit, and are subject to cross-threading, stripping, and under- or over-tightening. There is a need for fasteners that are quick and easy to use, and that positively engage. This is particularly true in light industrial applications such as the computer industry, where it is desired to attach various loose-fitting components and covers in a positive secure fashion that allows such covers and components to be easily installed and removed. 
     Quarter-turn latches are used for latching a variety of cabinets, doors and other enclosures. It has been suggested to construct a quarter-turn fastener as shown in FIG. 1. A bolt  1  has a disk-shaped head  2  and a cylindrical shank  3 . Two projecting keys  4 ,  5  project radially outward from the shank  3  opposite one another. A keyhole  6 , shown in FIG. 2, is made in each panel  10 ,  11  to be adjoined. The keyhole  6  consists of a circular hole  7  with two radially extending rectangular slots  8 ,  9  opposite one another. In operation, the top panel  10  is placed over the bottom panel  11  with the keyhole in each panel aligned. The bolt  1  is guided through the panels  10 ,  11  and the keys  4 ,  5  simultaneously pass through the slots  8 ,  9 . 
     The bolt is twisted 90°, placing the keys  4 ,  5  in the positions  12 ,  13  shown by dotted lines in FIG. 2, effectively locking the panels  10 ,  11  together. A coil spring  14  coaxially surrounds the shank  3  and is compressed between the bolt head  2  and the top panel  10 . The compressed spring  14  pulls the keys  4 ,  5  against the underside of the bottom panel  11 , holding the bolt  1  in position by friction. Thus, the spring  14  provides a compressive biasing force that pulls the panels  10 ,  11  together for positive engagement and to avoid rattles. 
     Drawbacks exist with many quarter-turn latches. For instance, they can be susceptible to operator error. Without positive engagement, the operator can turn the bolt too far, or not far enough. The bolt can rotate to the unlocked position due to vibration. In addition, the coil spring adds purchase and assembly costs, and can be lost. Consequently, there is a need for a quarter-turn fastener which is simple, inexpensive, requires a minimum number of parts, and provides positive engagement. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a fastener system for fastening a first panel in which is formed a first keyhole to a second panel in which is formed a second keyhole. According to one aspect of the invention, the fastener system includes a bolt with a head, a spring member integrally formed with the head, a shank, and a first key attached to the shank opposite the head. The bolt passes through the first keyhole and the second keyhole, when the first key is aligned with a first slot in the first keyhole and a second slot in the second keyhole. The bolt is rotatable from an open position where the first key is aligned with the first slot and the second slot, to a closed position where the first key bears against a back surface of the second panel. The spring cooperates with the first key to bias the first panel to the second panel. 
     In a preferred embodiment of the invention, an annular track is located on the back surface of the second panel and slopes to a crest and recedes to a landing area. The first key is retained in the landing area by the biasing force of the spring member. An open bump stop is located on the back surface of the second panel adjacent the first slot portion and is engageable with the first key when the bolt is in the open position. A closed bump stop is located on the back surface of the second panel adjacent the landing area and is engageable with the first key when the bolt is in the closed position. 
     The bolt may have a second key located on its shank between the head and the first key. In a preferred embodiment of the present invention, the second key fits through the first slot in the first panel and engages a back surface of the first panel when the bolt is rotated away from the entry position of the second key in the first slot. The second panel may be recessed away from the first panel to provide room for the second key. 
     The present invention should not be limited to the preferred embodiments shown and described in detail herein. The above and other advantages and features of the invention will be more readily understood from the following detailed description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is sectional side view of a quarter-turn latch system. 
     FIG. 2 is a plan view of a portion of a panel illustrating the keyhole of the quarter-turn latch system of FIG.  1 . 
     FlG.  3  is sectional side view of a quarter-turn latch system constructed in accordance with the present invention. 
     FIG. 4 is a front view of the bolt of the quarter-turn latch system of FIG.  3 . 
     FIG. 5 is an axial sectional view of the underside of the head of the bolt of FIG.  4 . 
     FIG. 6 is a plan view of the keyhole in the top panel of the system of FIG.  3 . 
     FIG. 7 is a bottom view of the bottom panel of the quarter-turn latch system of FIG.  3 . 
     FIG. 8 is a profile projection view of the track and bump stops of FIG.  7 . 
     FIG. 9 is a sectional side view of another quarter-turn latch system constructed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 3 shows a quarter-turn latch system  100  that has a rotatable bolt  102  for locking a top panel  104  to a bottom panel  106 . The panels  104 ,  106  are referred to as top and bottom for ease in exposition. It should be understood, however, that the invention can be employed in many different orientations. The bolt  102  is preferably integrally formed in one piece. In a preferred embodiment of the invention, the bolt  102  is integrally molded from plastic resin. The bolt  102  consists of a cylindrical shank  108  with a disk-shaped head  110 . The head  110  is coaxially located at one end of the shank  108 . 
     The head  110  consists of a hexagon-shaped portion  112  and a circular shoulder  114 . The hexagon-shaped portion  112  may be engaged by a wrench (not shown). The shoulder  114  is located between the hexagon-shaped portion  112  and the shank  108 . The shoulder  114  may be used to promote positive wrench engagement and to prevent the wrench from marring the top panel  104 . Alternatively, other types of heads may be used, including those incorporating screwdriver slots, thumb screws and other suitable torque transmitting means. 
     The end  103  of the shank  108  opposite the head  110  has a chamfered shoulder  109 . Near the end  103  of the shank  108  is a rectilinear bayonet key  116 , extending radially away from the shank  108 . The key  116  has rounded surfaces  118 ,  119  facing towards and away from the head  110 . A capture key  125  also extends radially from the shank  108  between the head  110  and the bayonet key  116 . The capture key  125  is out of phase with the bayonet key by 90°. Two integral, resilient, flexible, curved spring members  120 ,  122  emanate from the head  110  of the bolt  102  facing the top panel  104 . As shown in FIG. 4, each spring member  120 ,  122  defines a gentle, S-shaped curve, with one end of the “S” being integrally attached in one piece to the head  110 . Viewed in the axial direction of the bolt  102 , as shown in FIG. 5, each spring member  120 ,  122  defines a curved arc (a portion of a circle). Alternatively, each spring member could define a straight section when viewed in the axial direction. When compressed between the head  110  and the top panel  104 , the spring members  120 ,  122  store elastic energy. 
     Referring now to FIG. 6, the top panel  104  has a keyhole  124 . The keyhole  124  extends through the top panel  104 . The keyhole  124  consists of a circular hole  126  with a rectangular slot  128 . The slot  128  projects radially away from the center of the hole  126 . Referring back to FIG. 3, the bottom panel  106  has a recessed portion  130  dimpled away from the top panel  104 . As shown in FIG. 7, the recessed portion  130  has a keyhole  132  through it, of identical shape to the keyhole  124  of the top panel  104 . The bottom panel keyhole  132  consists of a circular hole  134  with a rectangular slot  136  projecting radially from the center of the hole  134 . As noted above, the present invention should not be limited to the specific structures and instrumentalities described herein. 
     The underside  138  of the bottom panel  106  (the side  138  facing away from the top panel  104 ) has a rectilinear open bump stop  140 . The open bump stop  140  projects downwardly from the bottom panel  106  (away from the top panel  104 ). In the illustrated embodiment, the open bump stop  140  is located immediately and rotationally adjacent to the rectangular slot  136  of the keyhole  132 . A rectilinear closed bump stop  142  also projects from the underside  138  of the bottom panel  106 . The closed bump stop  142  is located in a position that would be immediately and rotationally adjacent to the rectangular slot  136  opposite the open bump stop  140 , if the keyhole  132  were rotated 90° counterclockwise (as viewed in FIG.  7 ). As discussed in more detail below, the open bump stop  140  and the closed bump stop  142  prevent rotation of the bolt  102  past its fully open or fully closed positions. 
     Located between the rectangular slot  136  and the closed bump stop  142  on the underside  138  of the bottom panel  106  is a raised, annular (curved) track  144 . The track  144  is straightened out in the projection of FIG. 8 to illustrate its profile. Starting at the rectangular slot  136 , the track  144  gently projects away from the underside  138  of the bottom panel  106  forming a first sloped portion  146 . The sloped portion  146  may form an angle of about 35° with respect to the underside  138  of the panel  106 . The track  144  then gently curves back towards the underside  138 , forming a crest  148  and then a second sloped portion  150  returns to the underside  138  of the bottom panel  106 . 
     The second sloped portion  150  may form, for example, an angle of approximately 60° with respect to the panel underside  138 . The track  144  ends prior to reaching the closed bump stop  142 , such that a landing area  152  is defined adjacent to the closed bump stop  142 . In a preferred embodiment of the invention, the depth of the crest  148  above the underside  138  is approximately equal to the thickness of the key  116 . The length of the landing area  152 , measured from the closed bump stop  142  to the transition from the slope  150  to the crest  148 , may be about one and one-half the thickness of the key  116 . 
     In operation, the bolt  102  is axially guided through the keyhole  124  so that the bayonet key  116  passes through the rectangular slot  128 . The bolt  102  is then twisted 90° so that the capture key  125  also passes through the rectangular slot  128 . The chamfered shoulder  109  of the bolt  102  and the rounded surface  119  of the key  116  promote entry of the bolt  102  through the keyhole  124 . The bolt  102  is then twisted further, loosely locking it into engagement with the top panel  104 . The capture key  125  is axially located along the bolt shank  108  so that the spring members  120 ,  122  are either lightly compressed or uncompressed. In this manner, the bolt  102  can be easily engaged or disengaged with the top panel  104 , but is unlikely to accidentally disengage. Accidental disengagement would require the bolt  102  to randomly move until both the capture key  125  and the bayonet key  116  are sequentially aligned with and pass through the rectangular slot  128 . 
     To fasten the top panel  104  to the bottom panel  106 , the top panel  104  is brought into engagement with the bottom panel  106 . The chamfered point  109  of the bolt  102  engages with the keyhole  134 . The operator (not shown) then simultaneously pushes the bolt  102  against the resisting force of the spring members  120 ,  122 , and twists the bolt  102  until the key  116  engages with the rectangular slot  136 . At this point, the key  116  will pass through the keyhole  134  and the quarter-turn latch will be ready for engagement. 
     The operator then twists the bolt  102  clockwise 90°. During this twisting movement, mild resistance will be felt by the operator as the key  116  travels over the sloped portion  146  and the crest  148 . The key  116  then settles into the landing area  152  and is stopped by the closed bump stop  142 . The rounded surface  118  promotes a smooth cam operation between the key  116  and the track  144 . The arrest of angular motion effected by the closed bump stop  142  is a positive indicator to the operator that the quarter-turn latch system  100  is in the closed position. 
     In the closed position, the force provided by the compressed spring members  120 ,  122  keeps the key  116  in the landing area  152  by resisting movement of the key  116  over the sloped portion  150 . The spring force also prevents rattles and other movements by drawing the top panel tightly against the bottom panel  106 . The spring members  120 ,  122  also compensate for any minor misalignment of the latch system  100 . 
     To unfasten the top panel  104  from the bottom panel  106 , the operator twists the bolt  102  counterclockwise, overcoming the resistance required to pass the key  116  over the sloped portion  150  and the crest  148  of the track  144 . The bolt  102  is twisted until the key  116  is stopped by the open bump stop  140 . The arrest of angular motion effected by the open bump stop  140  is a positive indication that the bolt  102  is in the open position. When the operator releases the bolt  102  in the open position, the bolt  102  pops up through the keyhole  134  as the integral springs  120 ,  122  decompress. Thus, release of the bolt  102  in the open position causes the key  116  to move into the space between the two panels  104 ,  106 . 
     In an alternative embodiment of the invention shown in FIG. 9, the capture key  125  is omitted and the bottom panel  106  is not dimpled. The embodiment of FIG. 9 is otherwise essentially the same as the embodiment shown in FIGS. 3-8. 
     The present invention provides an economical quarter-turn latch system that easily and positively fastens panels together and that features one or more integral springs. Variations of the disclosed embodiments will be apparent to those skilled in the art. For instance, the invention could be practiced with different shaped springs, different numbers of springs, or with two bayonet keys. Accordingly, it is to be understood that although the present invention has been described with reference to exemplary embodiments, various modifications may be made without departing from the spirit or scope of the invention which is defined by the claims appended hereto.