Abstract:
A latch assembly for securing a cover to a container comprises a base for mounting to the container cover adjacent to an edge thereof, a cover member secured to the base and a slider slidable between the base and cover member between a latched position wherein a portion of the slider interfits with the container and an unlatched position wherein the slider portion is disengaged from the container. A headed spring member interposed between the slider and the base interfits with holes or recesses in the slider to signal when the slider has reached its latched and unlatched positions and to releasably retain the slider at those positions.

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of Ser. No. 09/997,789, filed Nov. 30, 2001, now U.S. Pat. No. 6,508,495. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to covered containers. It relates more particularly to a latch assembly for releasably retaining a cover to a container. The latch assembly is especially advantageous for use on surgical instrument sterilization trays. 
     BACKGROUND OF THE INVENTION 
     A sterilization tray usually comprises a base container with an open top for holding surgical instruments or other articles. The open top of the base container may be closed by a cover which engages over the top of the container. Preferably, the cover and/or the base container are perforated so that steam can circulate through the closed container. To prevent the cover from becoming disengaged from the base container during handling, means are usually provided for releasably securing the cover to that container. 
     Conventionally, the securing means often consist of at least one latch which is usually mounted to one of the base container and cover and which is movable between a locked position wherein the latch engages over the other of the base container and cover, and an unlocked position wherein the latch is released from the other of the base container and cover. One such prior latch in widespread use consists of a rolled metal bracket hinged to the edge of the cover and a rolled metal hook pivotally connected to the bracket at a location thereon spaced from the bracket hinge. To lock the cover, the hook is swung down so that the hook engages a hole or projection in the base container and then the bracket is swung down to a stable over center position against the cover so that tension is applied to the hook whereupon the hook remains tightly engaged to the base container. 
     While that prior cover securement operates satisfactorily in many respects, it is disadvantaged in that if the closed container should be dropped onto a hard surface, the bracket may move away from it&#39;s over-center position due to inertia. Resultantly, the hook member may become disengaged from the base container thereby allowing the cover to separate from the base container so that the contents of the container can spill onto the floor. 
     As an improvement to that over center-type latch arrangement, we developed a safety clasp assembly disclosed in U.S. Pat. No. 5,706,968. It comprises a rocker, an axle pivotally connecting the rocker to the container cover and a slider positioned between the axle and the cover. The slider is slidable along the cover in a direction perpendicular to the axle between a locked position wherein the slider interfits with the base container and an unlocked position wherein the slider is disengaged from that container. When the slider is in its locked position, portions of the rocker and slider interfit preventing movement of the latter. In order to move the slider to its unlocked position, the rocker has to be rocked about its axle against a spring bias to disengage the rocker from the slider allowing the latter to move to be moved to its unlocked position. 
     While that safety clasp assembly has definite advantages over the then prior art, it also has a few drawbacks. More particularly, the container cover has to be modified to form eyes in the container cover to anchor the axle ends of each clasp assembly. Also, some people find it difficult to move simultaneously both the rocker and the slider as necessary to release the clasp using only one hand. Resultantly, some people have been reluctant to use sterilization trays incorporating such clasp assemblies. 
     Accordingly, it would be desirable to be able to provide securing means for reliably releasably securing a cover to a sterilization tray or other base container, which is easy to operate using only one hand, yet does not require modification of the cover or container. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved latch assembly for releasably securing a cover to a sterilization tray or other such base container. 
     Another object of the invention is to provide a latch assembly of this type which can be moved between its latched and unlatched positions quite easily only using one hand. 
     Another object of the invention is to provide such a latch assembly which is relatively easy and inexpensive to make and to assemble. 
     A further object of the invention is to provide a latch assembly of this general type which can be installed on a conventional cover without requiring any appreciable modification of the cover or container. 
     A further object of the invention is to provide a latch assembly which signals when it is in its latched and unlatched conditions. 
     Other objects will, in part, be obvious and will, in part, appear hereinafter. 
     The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the following detailed description, and the scope of the invention will be indicated in the claims. 
     Briefly, the present latch assembly for securing a cover to a container comprises a base for mounting to the container cover adjacent to an edge thereof, a cover member secured to the base and a slider slidable along a passage between the base and cover member between a latched position wherein a portion of the slider interfits with the container and an unlatched position wherein the slider portion is disengaged from the container. A headed spring member interposed between the slider and the base resiliently interfits with holes in the slider to signal when the slider has reached its latched and unlatched positions and to releasably retain the slider at those positions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in connection with the accompanying drawing, in which: 
     FIG. 1 is a perspective view with parts broken away of an instrument sterilization tray having latch assemblies incorporating the invention; 
     FIG. 2 is an exploded perspective view on a larger scale showing in greater detail the components of each latch assembly in the FIG. 1 tray; 
     FIGS. 3A and 3B are sectional views on a larger scale taken along line  3 A— 3 A of FIG. 1, showing the latch assembly in its latched and unlatched conditions, respectively; 
     FIG. 4 is a view similar to FIG. 2 of the components of a second latch embodiment, and 
     FIG. 5 is a sectional view showing the components of the FIG. 4 latch embodiment in their assembled condition. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Refer now to FIG. 1 of the drawings which shows a generally rectangular surgical instrument sterilization tray  10 . Tray  10  is composed of a relatively deep base container  12  having a pair of opposite sidewalls  12   a,    12   a  and a pair of opposite endwalls  12   b,    12   b.  The top of the base container  12  is normally open but may be closed by a cover  14  having a pair of opposite sidewalls  14   a,    14   a,  and a pair of opposite endwalls  14   b,    14   b.  When cover  14  is seated on container  12 , the cover walls  14   a,    14   b,  overlap or interfit with the corresponding container walls  12   a,    12   b.  Preferably, container  12  and cover  14  are made of a strong impact-resistant plastic material able to withstand sterilization temperatures. Preferably also, the cover and/or the base container is formed with a multiplicity of holes  16  through which steam may circulate when instruments in tray  10  are being sterilized. 
     In order to releasably lock cover  14  to container  12 , the tray  10  is provided with a pair of mirror-image latch assemblies shown generally at  20  situated at opposite ends of the tray. Latch assemblies  20  lock cover  14  to base container  12  during the sterilization process and during handling. However, the assemblies  20  can be released easily by operating room personnel, using only one hand, when it is necessary to remove cover  14  in order to use the sterilized instruments in container  12 . 
     Each latch assembly  20  is secured by fasteners  22  to cover  14  near an endwall  14   b  thereof and is adapted to releasably interfit with the underlying endwall  12   b  of base container  12  when the assembly is in its locked position shown in FIGS. 1 and 3A and to be spaced and disengaged from that container endwall when the assembly is in its unlocked position shown in FIG.  3 B. 
     As best seen in FIG. 2, each assembly  20  comprises four main parts which are stacked one on top of the other. More particularly, the assembly includes a base shown generally at  28  which may be an essentially flat, generally rectangular, metal plate formed with a relatively long center segment  28   a  which may be raised relative to a pair of opposite end segments  28   b.  Fastener holes  32  are present at the four comers of base  28  in segments  28   b  and a relatively large, generally rectangular window or hole  34  is present in the raised segment  28   a  for reasons that will become apparent. 
     The second component of assembly  20  is a spring member shown generally at  36 . Member  36  is essentially a thin flat plate preferably of a metal such as spring steel. The spring member  36  has more or less the same dimensions as the raised segment  28   a  of base  28 . Member  36  is also notched to form a pair of generally rectangular, full-width end sections  36   a,    36   a,  which bracket a narrower laterally extending section or tab  36   b.  When spring member  36  is centered on the raised segment  28   a  of base  28 , tab  36   b  is cantilevered out over the window or hole  34  in raised segment  28   a.  As shown in FIG. 2, for reasons that will become apparent, a raised head or protuberance  38  is formed adjacent to the free edge of tab  36   b.  That head may be a blind fastener inserted through tab  36   b  or the head may be created by deforming tab  36   b  to form a mesa or rib or by adhering, welding or brazing the head to the tab. In any event, head or protuberance  38  should be on the side of the spring member  36  facing away from base  28 . 
     Still referring to FIG. 2, the third element of latch assembly  20  is a slider shown generally at  42 . The illustrated slider is a stamped metal part having a generally rectangular top wall  42   a  whose length is comparable to that of the base segment  28   a  and whose width is appreciably greater than that segment. The slider also includes an integral hook  42   b  which extends down from a long edge of top wall  42   a.  The hook has one or more legs  42   c  extending back parallel to top wall  42   a  from a location spaced appreciably below that wall. Also, slider  42  is formed with a lip  42   d  at the opposite long edge of top wall  42   a.  The lip may extend up as shown in solid lines in the drawings or down as shown in phantom in FIG.  3 A. As we shall see, lip  42   d  provides a finger grip for operating the latch assembly. 
     Positioned more or less midway along the length of top wall  42   a  of slider  42  is a is pair of holes or dimples  44   a  and  44   b  opening to the underside of the slider. These holes or dimples are spaced apart laterally on wall  42   a  so that when the slider  42  is centered on the spring member  36 , the imaginary line extending between holes or dimples  44   a  and  44   b  is aligned with the head  38  on spring member  36 . 
     The final component of latch assembly  20  is a cover member shown generally at  46  in FIG.  2 . Cover member  46  is a stamped metal part having a raised central segment  46   a  bracketed by two end segments  46   b.  The width of raised segment  46   a  is comparable to that of the raised segment  28   a  of base  28 . However, its length is slightly greater than that of base segment  28   a.  As with base  28 , fastener holes  48  are provided at the four corners of cover member  46  in the end segments  46   b  thereof. 
     When the latch assembly parts shown in FIG. 2 are properly assembled as seen in FIGS. 3A and 3B, they are stacked one above the other such that the holes  48  in the cover member  46  line up with the corresponding holes  32  in the base  28  and such that the spring member tab  36   b  overlies the window  34  in the base member. During such assembly, the spring member  36  is preferably spot-welded or otherwise secured to base segment  28   a  by spot welds  58  (FIG. 4) to fix the relative positions of those parts. Likewise, after cover member  46  is properly aligned with base  28 , those two members may be permanently secured together by spot-welds  49  (FIG. 1) at end segments  46   b  and  28   b.  In that completed assembly, the holes  48  in the cover member  46  and the holes  32  in the base  28  are in alignment to receive the fasteners  22  that secure the latch assembly to cover  14  as shown in FIG.  1 . 
     Also when the parts are assembled, the spring tab  36   b  is deflected downward by the engagement of the head  38  against the underside of the slider so that the head is biased upward. The window or hole  34  in base  28  provides clearance for the deflected tab  36   b;  see FIG.  5 . 
     When the latch assembly  20  is in its latched condition shown in FIGS. 1 and 3A, slider  42  is positioned inwardly on the tray cover  14  so that the slider hook  42   b  is close enough to the corresponding endwall  12   b  of container  12  that the hook leg(s)  42   c  project through slot(s)  50  formed in that wall. This interfitting engagement of the slider with the container endwall prevents cover  14  from becoming separated from container  12 . 
     As noted previously, the head  38  on the spring tab  36   b  is biased upwardly against the underside of slider  42 . Therefore, when the slider reaches its latched position shown in FIG. 3A, the head  38  snaps into the hole or dimple  44   a  in the underside of the slider top wall  42   a  thereby providing an audible and tactile signal that the slider is in its latched position. Also, the resilient engagement of the head  38  in hole or dimple  44   a  releasably retains the slider in its latched position. Overtravel of the slider in the latching directing is prevented by the engagement of slider hook  42   b  against the adjacent side edge of the base which edge thus functions as a stop. 
     To unlock latch assembly  20  in order to remove cover  14  from base container  12 , the operator, using a thumb or finger, exerts an outward force on slider lip  42   d  that is sufficiently strong to overcome the bias of spring tab  36   b  and dislodge head  38  from hole or dimple  44   a.  The outward motion of the slider retracts the hook leg(s)  42   c  from slot(s)  50  in the base endwall  12   b  as shown in FIG.  3 B. When the slider reaches its unlatched position, the head  38  on spring member  36  will snap into the other hole or dimple  44   b  in the underside of the slider top wall  42   a  thereby providing an unlatch signal and releasably retaining the slider in its unlatched position. Overtravel of the slider beyond that position is prevented by the engagement of lip  42   d  against the adjacent side edge of cover member  46  (or base  28 ) which edge thus functions as a stop. 
     When all of the components of latch  10  are made of metal as described above, there may be a tendency for the head  38  to wear a track in the underside of slider portion  42   a  between holes or depressions  44   a  and  44   b  after prolonged use of the latch. FIGS. 4 and 5 depicted a latch assembly  51  which avoids that potential problem. 
     Latch assembly  51  comprises a flat metal base  52  formed with a central window or depression  54  and corner fastening means  56  which in this case are fastener holes  56   a  at the forward comers of the base and hooks  56   b  at the rear corner thereof which help to secure the latch assembly to the associated tray cover as will be described later. 
     Centered on base  52  and secured thereto by spot welds  58  is a flat spring member  62  having a cantilevered tab  62   a  overlying the window or depression  54  in the base  52 . Tab  62   a  is deformed to form a raised rib  64  adjacent to the free end of the tab. 
     Latch assembly  51  also includes a slider  72  which is similar to slider  42  except that it has a large rectangular opening  74  in its top wall  72   a  in lieu of holes or depressions  44   a,    44   b.  Seated in opening  74  is an insert  76  which is shaped like a capitol letter I in that it is formed with a pair of aligned notches  78   a  and  78   b  between its ends leaving a narrow strip portion  78   c  between the notches, all of which define with the edge of the slider opening  54  a pair of holes or recesses in the underside of the slider as a whole. Preferably insert  78  is of a relatively rigid plastic material having a low coefficient of friction, such as ultra high molecular weight polyethylene or polytetrafluorethylene. 
     The final component of latch assembly  51  is a cover member  82  which is similar to cover member  46  shown in FIG. 2 except that it has corner fastening means  84  in the form of holes  84   a  at its front comers and hooks  84   b  at its rear comers. As with assembly  10 , when cover member  82  is superimposed on, and secured by spot-welds  49  (FIG. 1) to, the base  52  with slider  72  in between, the fastening means  84  are in register with the similar means  56  on base  52 . The latch assembly  51  is secured to the top of tray cover  14  by engaging hooks  56   b,    84   b  in slots present in a raised rib R extending around the top of cover  14  as shown in phantom in FIG.  1 . 
     Latch assembly  51  operates in the same way as assembly  10 . That is, when the slider is in its locked position, the rib  64  on spring tab  62   a  engages in the insert notch  78   a  and when the slider is in its unlocked position, the rib  64  seats in notch  78   b.  When the slider is moving between those two positions as shown in FIG. 5, the rib  64  makes line contact with, and slides along the underside of, the strip portion  78   c  between notches  78   a  and  78   b,  of the plastic insert  78 , the base window  54  providing clearance for the deflected spring member tab  62   a  as shown in that figure. Due to the relatively large area line contact of rib  64  with the low friction insert  78 , there is minimal wear of the insert due to the repetitive sliding motion of the slider  72 . 
     Of course it is also possible to make slider  72  in its entirety (as well as, perhaps, the other latch components) of a strong low friction plastic material such as polyphenyl sulphone, in which case the insert  78  would be integrated right into the slider; i.e., the notches  78   a,    78   b  would be formed as holes or depressions in the plastic slider  72 . 
     The latch assemblies described herein are composed of a minimum number of parts which are easy and inexpensive to make in quantity. Therefore, the assembly should not appreciably increase the overall cost of the sterilization tray on which it is installed. Furthermore, such installation does not require any alteration in the basic design of the tray to accommodate the assembly. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained. Also, certain changes may be made in the above construction without departing from the scope of the invention. For example, the holes  34 ,  44   a  and  44   b  could be depressions instead of through holes and still fulfill their stated purposes. Also, the hook  42   b  of each assembly could just as well engage under a projection or ledge on the corresponding container endwall  12   b.  Therefore, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention described herein.