Abstract:
A fastener for coupling two members together is provided with a rotatable core carried by a first member and a protruding elbow for insertion through an elongated slot in the second member. By rotating the core, the elbow is caused to swing over the outer surface of the second member, adjacent the slot, coupling the two members together. The inner, member-engaging surface of the elbow is tapered to form a ramp-like surface that, with rotation, draws the two members together and frictionally fixes the elbow in its engaged position. The latch core when installed in a tubular first member may be provided with resiliently based, expanding locking members positioned adjacent to the core to secure the latch within the hollow core of the tubular first member.

Description:
FIELD OF THE INVENTION 
     This invention relates to a fastener used to hold together thin sheets or panels of metal or plastic. More particularly, it relates to a simplified form of connector for ready installation that provides a disengageable clamping action between the parts being held together. 
     BACKGROUND TO THE INVENTION 
     In previous art, disengageable fasteners or latches used to clamp two members, such as pieces of sheet metal together have included a simple handle coupled to a rotating arm that can be swung into a wedge-shaped receptacle to effect a latching engagement. Kitchen cupboard doors have been provided with latches of this type. Such a latching mechanism is externally mounted and has parts that extend outwardly from the pieces being fastened together. 
     An existing electronic air filter design comprises two outer frames of sheet metal which are closed to enclose trapping media. External clips are presently used as latches to hold the frame together. These clips protrude outwardly from the filter&#39;s frame and interfere with the insertion and extraction of the filter from a slot in an air handling unit. 
     A need exists for a fastener which is substantially non-protruding, or minimally protruding, from surfaces to be coupled together. The fastener should be readily installable and, once installed, should be easily manipulated to effect engagement and disengagement with respect to the members being coupled together. This invention addresses such a need. 
     The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification. 
     SUMMARY OF THE INVENTION 
     According to one feature of the invention described herein a first carrier member supports a latch core from which protrudes a rotatable elbow. This protruding elbow is dimensioned to fit in one orientation through a perforation in the form of an elongated slot present in a second member that is to be latched to the first member. Upon rotation of the latch core the protruding elbow swings laterally to overlie the side of the slot formed in the second member. The inside surface of the elbow which is positioned for engaging the second member is ramp-like in form so that when the elbow is operated by turning it to overlie the second member, the second member slides up the ramped inside surface of the elbow drawing the second member to press against the first member. The core is provided with a head or flange located on the other side of the first member from the elbow which prevents the core from being pulled-through the opening in the first member. This head, or the end of the core, may also be slotted to enable the core to be turned. 
     By a further feature of the invention, the first member is of a box-tube construction having perforated outer and inner walls with a cavity formed therebetween. The outer wall is the wall which is more remote from the second member to be coupled to the first member by the latch. Preferable, the latch core lies within the cavity without protruding significantly on the outward side of the outer wall of the first member. The core carries a head or flange that prevents it from being pulled fully through the first member. The latch core in this embodiment is provided with engagement means, preferably in the form of a slot, by which it may be engaged to effect its rotation. 
     The core may be retained within the first member by a retention means such as a conventional, expandable, C-shaped split lock washer. It may also be retained by interior, resilient retention means, contained within the cavity, that, once inserted into the core-receiving cavity in the first member, expands within the cavity and engages the inner side of the outer wall of the first member. This retention means may optionally be in the form of a split cylindrical sleeve, or may comprise one or more longitudinally extending locking arms that are carried by the core and spring outwardly into the cavity to fix the core in place once the core is inserted within the cavity. These arms may nest against the core within the diameter of the head or flange for ready insertion into the cavity. 
     In a further variant, the free ends of the arms have protruding tab&#39;s that extend beyond the ends of the arms. These tabs extend into the hole through which the core has been passed, and provide access to displace the arms towards the core for removal of the latch in cases where replacement is required. 
     The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow. These and other features of the invention will be more apparent in view of the drawings and description which follows: 
    
    
     SUMMARY OF THE FIGURES 
     FIG. 1 shows a pictorial view of the latch according to the invention and two pieces of sheet material being latched together; 
     FIG. 2 a  and FIG. 2 b  are partially cross-sectioned side views showing the latch of FIG. 1 in open and closed positions respectively without use of a retaining clip; 
     FIGS. 2 c  and  2   d  show the latch of FIGS. 2 a  and  2   b  with a C-shaped, split washer retaining clip present to secure the latch to the upper of the two sheets; 
     FIG. 3 a  is a pictorial view showing an alternative construction of the latch carrying elastically biased locking arms for installation in a hollow, tubular frame member; 
     FIG. 3 b  is a cross-sectional side view of a variant of the latch of FIG. 3 a  showing details including a release tab on the locking arms; 
     FIG. 3 c  shows the construction of FIG. 3 a  but using an elastically compressible split cylinder in place of the locking arms; 
     FIGS. 4 a  and  5   a  show close-up detailed cross-sectional side views of the latch of FIG. 3 a  installed in a tubular frame that is to be latched to a second tubular member; 
     FIGS. 4 b  and  5   b  close-up detailed cross sections of the latch of FIGS. 4 a  and  5   a  before and after engagement; 
     FIGS. 6,  7 , and  8  are pictorial views of the latch of FIG. 1 depicting variants in the shape of the dual locking elbows; 
     FIG. 9 shows how the latch of FIG. 6 is used with sheet material which has extra smaller transversely extending slots oriented perpendicularly to the main slot to produce an indent effect when the latch is rotated through a ¼ turn; 
     FIG. 10 shows a similar arrangement to that of FIG. 9 but with the latch of FIG.  8  and holes substituted for the smaller slots; 
     FIG. 11 depicts an air filter frame with prior art hook latches; 
     FIG. 12 is a pictorial depiction of an air filter frame incorporating the latch of the invention; 
     FIGS. 13 and 14 contrast a latch as in FIG. 5 b  with a latch held in place by a split locking washer as in FIG. 2 d.    
     FIG. 14 a  shows a C-shaped, split locking washer in plan view. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, the latch  1  comprises a head  2  with a slot  3  for operating the latch  1  with a screwdriver or a coin. A shaft  4  connects head  1  to dual elbows  5 . Elbows  5  are provided by a transversely oriented rectangular bar featuring two sloping, ramp-like surfaces  6  and  7  on each inner surface of the elbows  5 . Two sheet members  8 , 9  to be latched together, are provided with slots  10  and  11  formed through their bodies. Slots  10  and  11  have a width such that dual elbow  5 , when aligned with the slots  10 ,  11 , can just pass through the slots  10 ,  11 . A retainer C-clip, split washer  4 a of resilient material holds the latch  1  from coming back out of the first sheet  8  by engaging with a groove  30  formed around shaft  4 . The head  2  in seating on the first member  8  serves as a seating collar which prevents the latch  1  from pulling through the first sheet  8 . 
     While two slots  10 , 11  are shown, only the second sheet remote from the latch need be slotted. The first sheet  8  may have a more circular opening wide enough to allow the dual elbows  5  to pass through. In such case the diameter of the head  2 , or other means, should limit the complete passage of the latch  1  through the opening in the first sheet  8 . 
     FIGS. 2 a  and  2   b  depict progressive stages in the engagement of the latch  1  in clamping the two pieces of sheet material  8 , 9  together. In FIG. 2 a , the latch  1  with its dual elbows  5  is passed through the rectangular slots  10 ,  11  of both sheets  8 , 9 . In FIG. 2 b  the latch  1  has been turned one quarter turn. When the latch  1  is turned, the bordering edges of the bottom slot  11  are drawn against the ramped surfaces  6  and  7  and sheet  9  is pressed against sheet  10  thus providing a clamping action. Because of the sloping orientation of the upper surfaces  6 , 7  on the elbows  5 , the elbows  5  engage the lower sheet  9  while the sheets  8 , 9  are not fully pressed together. The position of the ramped surfaces  6 , 7  along shaft  4  below the head  2  can be selected to ensure that, at the final clamped position of FIG. 2 b , these surfaces  6 , 7  positively press the two sheets  8 , 9  together. 
     FIGS. 2 c  and  2   d  correspond to FIGS. 2 a  and  2   b  respectively, but with the added pressure of an optional C-shaped, split retainer clip  4   a  which prevents latch  1  from falling out of sheet  8  when the latch is disengaged. To accommodate the clip  4   a , a groove  30  is formed around the shaft  4 . 
     FIG. 3 shows another version of a self-retaining latch  12  having a lower, flanged, seating collar or flange  16 , a central shaft or core  13  and spring-mounted locking arms  14  or resilient split/cylinders connected to the core  13 . This arrangement allows this self retaining latch  12  to be installed in a hollow, tubular frame as shown in FIGS. 4 a  through  5   b . The collar  16  serves the function of the head  2  in limiting the latch  12  from passing fully through the first member. With the collar  16  present, the head  2  is optional. 
     Latch  12  is installed in a hole formed in a hollow frame  18  as in FIG. 4 b  having a cavity  31  present in its interior defined by upper  32   a  and lower walls  32   b.  When latch  12  is inserted in upper hole  20 , formed in upper wall  32   a,  locking arms  14  are initially pressed against the core  13  to permit the arms  14  to fit through the hole  20  preferably, with the arms nested against the core, they occupy a diameter that is less than of the head or flange. After passing through hole  20  the arms  14  are elastically biased at their base end connection  34  to the core  13  to spring away from the core  13 . The arms  14  engage by locking at surface  40  their upper, free ends with the underside of the upper wall  32   a  adjacent the upper hole  20 . This prevents the latch  12  from coming out of frame  18 . To operate the latch  12 , the latch  12  is turned by one quarter turn and the clamping action is as described above. Small optional tabs  35  extend beyond the locking surfaces  40  on the ends of the arms  14 . These tabs  35  protrude through hole  20 , as shown in FIG. 3 b , and allow the arms  14  to be displaced inwardly for removal of the latch  12  from the hole  20 . 
     FIG. 3 c  shows the same latch as that of FIG. 3 a  but without locking arms  14 . Instead, a retainer clip  15  in the form of an elastically compressible split cylinder extending from collar  16  to the underside of the upper wall  32   a  prevents the latch from coming out of the hollow frame  18 . Thus the self-retaining latch  12  operates on the basis of resilient retaining means, positioned adjacent the core  13  and dimensioned to spring outwardly into the cavity  31  and engage the surface of an upper wall  32   a  after insertion through a hole  20  formed therein. 
     FIGS. 4 a  through  5   b  show the cross-sectional view of a hinged box with hollow peripheral frame members  18 ,  19 . The upper wall  32   a  of the hollow frame  18  has a hole  20  just large enough to allow latch  12  to go through. Within the lower wall  32   b  of the hollow frame  18 , and within the upper wall of hollow frame  19 , there are rectangular slots  21  and  22  similar to slots  10  and  11  of FIG.  1 . As described previously, rotation of the elbows  5  to a position transverse to the slot  21  draws the parts  18 ,  19  into locking engagement—See FIG. 5 b.    
     FIG. 14 shows an alternate retaining means for a latch with a core  13 , based on use of a C-shaped split washer clip  4   a  as shown in FIG. 14 a.  All of these latch designs operate on the basis of the presence of the elbowed engagement mechanism. The dual elbows  5  of the latch  12  are rotated  90  degrees to provide the clamping action as described with respect to FIGS. 2 a  and  2   b.    
     While the latch  1  of FIGS. 1-3 c  is shown as having flat, angled, ramped surfaces  6 , 7 , such surfaces may be angled so as to be ramped in differing directions. In FIG. 6, the upper surface  31 ,  32  of the dual elbows  5  are not only downwardly inclined, but are also cylindrical in cross section. This makes the operation of the latch easier because the bottom sheet  9 , when the latch  1  is rotated, does not encounter the edge of the sheet  9  with a sharp corner but with a smoother, rounded surface  31 , 32 . 
     Another alternative way of constructing the upper surfaces of the dual elbows  5  is as shown in FIG.  7 . This is a similar configuration to that of FIG. 6 but surfaces  23  and  24  are not downwardly sloping but are horizontal. Nevertheless, the curvature of the surfaces  23 , 24  makes them ramped in a different orientation. The operation of this arrangement is the same as that of FIG.  1 . The inclined angle of the surfaces  23 , 24  is chosen to tend to draw the sheets  8 , 9  being coupled more closely together. 
     Yet another alternative for the construction of the upper surfaces of the dual elbows  5  is shown in FIG.  8 . In this case, the entire upper surfaces of the elbows  5  are not sloping. Instead they are, for their greater part, flat and horizontal but they feature semispherical protrusions  25  and  26  that provide ramped surface portions. The operation of this arrangement is the same as that of FIG.  1 . In this case, when the latch is turned, the edges of the upper slot  10  climb up the spherical protrusions  25 ,  26  and thus these protrusions  25 , 26  serve to clamp the two sheets  8 , 9  together. 
     The arrangements of FIGS. 2,  6 ,  7  and  8  can be used with a detent in the lower surface  9  to provide an indexing effect for the position of the latch  1  in the locked position. Indents may be provided by a second set of smaller transversely oriented slots  27 , 28  formed on the sides of the slot  11  in the bottom sheet  9  (FIG.  9 ). These transverse indexing slots  27  allow an operator to “feel” when he has turned the latch exactly ¼ turn. To accommodate a latch as in FIG. 8, two adjacent holes  29  and  30 , as shown in FIG. 10, may alternately be provided. This arrangement also provides an indexing effect upon rotation of the latch  1 . This is achieved when the spherical protrusions  25 , 26  fall into holes  29  and  30 . This will occur when the latch is rotated exactly by ¼ turn. 
     In order to demonstrate an application for the latch according to the invention. FIG. 11 shows a prior art electronic air filter of the charged media type  41  which has a pair of rectangular hollow frames  42  and  43 . The filter is held closed with “U”-shaped, external latches  44  and  45 . In use, the filter  41  is inserted through slots in air handling units and the external latches  44  make it difficult to insert and retrieve the filter  41  because the latches  44  catch on the sides of the slots. Using a latch  12  or  12   a  of the design as shown in FIGS. 13 through 14 installed in the hollow frame  42  of the filter eliminates this problem since the head  2  of the latch is even with the filter&#39;s frame  42  and does not protrude outside the frame  42 . 
     CONCLUSION 
     The foregoing has constituted a description of specific embodiments showing how the invention may be applied and put into use. These embodiments are only exemplary. The invention in its broadest, and more specific aspects, is further described and defined in the claims which now follow. 
     These claims, and the language used therein, are to be understood in terms of the variants of the invention which have been described. They are not to be restricted to such variants, but are to be read as covering the full scope of the invention as is implicit within the invention and the disclosure that has been provided herein.