Abstract:
A latch assembly for releasably fastening two elements is disclosed. The latch assembly comprises a housing; a plunger for sliding in the housing; at least one arm, pivotally secured to the plunger, for retractably extending through an opening in the housing; and a spring for urging the plunger out of the housing.

Description:
TECHNICAL FIELD  
       [0001]     This disclosure generally relates to latch assemblies for releasably connecting two elements, and, more particularly, to latch assemblies for use with luminaires.  
       BACKGROUND  
       [0002]     The “INESA Lighting Handbook” published by the Illuminating Engineering Society of North America, is incorporated by reference here in its entirety. As discussed in chapter seven of that handbook, a “luminaire” is a device for producing, controlling, and distributing light. It is typically a complete lighting unit consisting of one or more lamps, sockets for positioning and protecting the lamps and for connecting the lamps to a supply of electric power, optical devices for distributing the light, structural components for protecting the luminaire, and mechanical components for supporting or attaching the luminaire. Luminaires are also sometimes referred to as “light fixtures.” 
         [0003]     Typically, luminaires can be classified by their application, such as indoor use or outdoor use. However, it is not uncommon for a particular luminaire to be used in both applications. As well, it is common for luminaires used outdoors and/or indoors to be mounted within a protective housing. For example, whereas a luminaire used indoors may require a housing to prevent physical contact with the luminaire and subsequent damage, a luminaire used outdoors may require a protective housing to prevent both damage from physical contact and damage from the weather and related elements. The protective housings may include removable access panels to facilitate maintenance, such as lamp replacement.  
         [0004]     Various latches for use on the noted access panels are known. Existing latches are typically complex structures including numerous parts. The complex construction and multiple parts increase manufacturing costs and often require skilled assembly of the latch when installing the latch onto the protective housing or access panel of the luminaire. Complex construction and multiple parts also lend themselves to the failure of various components, and subsequent failure of the latch. Failed latches can cause access panels to open inadvertently, thereby exposing the luminaire within the protective housing to increased damage risks. Thus, damaged latches are preferably replaced or fixed to maintain the protective integrity of the housing, thereby increasing maintenance costs.  
         [0005]     Conventional latches are often difficult to operate. For example, many require an individual to use both hands, and/or require one or more tools, to open and close the latch. The latches requiring the use of tools and/or both hands of the individual often create safety concerns. For example, housed luminaires are frequently mounted in elevated locations such as tall lighting poles, the tops of walls, or suspended from ceilings. Thus, stepladders, hydraulic lifts, and similar devices may be used to reach the luminaire. Accordingly, ease of operation of the latch and the ability of the individual to maintain his or her balance when using lifts, ladders, or similar devices is paramount. As well, existing latches typically require precise alignment during closure and provide no audible feedback to indicate the latch has been properly engaged, thereby further complicating operation of the latch.  
         [0006]     One existing means for coupling or locking two parts together is disclosed in U.S. Pat. No. 3,669,441 to Bergman. One part is provided with a conical stud which can be inserted against a stop in a conical recess in another part. One, or preferably two or more, spring actuated latching members are pivotally attached to the stud about shafts at right angles to the axial direction of the stud and are free to enter an enlarged section of the recess. The latching members act like barbs of a hook or harpoon, thereby preventing the stud from returning. An operating device, rotatable or axially displaceable within the stud, and actuated from one or both ends thereof, is used to effectuate the return of the latching members.  
         [0007]     However, the spring actuated latching members disclosed in U.S. Pat. No. 3,669,441 would not be preferable to use in various lighting applications for at least the reason that the latching members, being attached to the exterior housing (the conical stud), would apparently be exposed to the environment.  
       SUMMARY  
       [0008]     These and other drawbacks of such conventional technologies are addressed here by providing a latch assembly for releasably fastening two elements. For example, the elements may be a luminaire housing and an access panel for the luminaire housing. One embodiment of a latch comprises a housing; a plunger for sliding in the housing; at least one arm, pivotally secured to the plunger, for retractably extending through an opening in the housing; and a spring for urging the plunger out of the housing.  
         [0009]     One embodiment may further comprise a second spring for urging the arm out of the opening. The latch may be configured such that one of the housing and plunger includes a guide slot, and the other of the housing and the slot includes a pin for extending into the slot and guiding the plunger in the housing. The exterior of the housing may include a flange and threads for engaging a fastener on one side of the flange.  
         [0010]     In one embodiment of the fastener, the arm includes a reduced width at a free end thereof for engaging a coupling surface of a first element. The first element may be a luminaire housing, for example. The latch may be configured such that one of the housing and plunger include a guide slot, and the other of the housing and the slot includes a pin for extending into the slot and guiding the plunger in the housing. The exterior of the housing may include a flange and threads for engaging a fastener on one side of the flange.  
         [0011]     In another embodiment, the exterior of the housing may include a flange and threads for engaging a fastener on one side of the flange.  
         [0012]     In yet another embodiment, the latch may be configured such that one of the housing and plunger includes a guide slot, and the other of the housing and the slot includes a pin for extending into the slot and guiding the plunger in the housing.  
         [0013]     Another embodiment of the technology is a latch including a housing; means for sliding in the housing; means, pivotally secured to the plunger, for retractably extending through an opening in the housing; and means for urging the plunger out of the housing. The latch further comprises second means for urging the arm out of the opening. The latch may further be configured such that one of the housing and means for sliding in the housing includes a means for guiding, and the other of the housing and the slot include means for extending into the means for guiding.  
         [0014]     In another embodiment of the latch, the means for retractably extending through an opening includes a means, with a reduced width at a free end thereof, for engaging a coupling surface of a first element. The embodiment may be further configured such that one of the housing and the means for sliding in the housing include means for guiding, and the other of the housing and the slot include means for extending in the means for guiding. An exterior of the housing may include a flange and means for engaging a fastener on one side of the flange.  
         [0015]     Another embodiment of the latch may be configured such that one of the housing and means for sliding in the housing includes a means for guiding, and the other of the housing and the slot includes means for extending into the means for guiding.  
         [0016]     In yet another embodiment, an exterior of the housing of the latch includes a flange, and means for engaging a fastener on one side of the flange. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Various aspects of the invention will now be described with reference to the following figures (“FIGS.”) in which the same reference numerals are used to designate corresponding parts throughout each of the several views.  
         [0018]      FIG. 1  is a perspective view of a latch assembly in accordance with the present disclosure.  
         [0019]      FIG. 2  is a cross-sectional view of the latch assembly in  FIG. 1 .  
         [0020]      FIG. 3  is a cross-sectional view of the latch assembly in  FIG. 1 .  
         [0021]      FIG. 4  is a cross-sectional view of an alternate embodiment of a latch assembly in accordance with the present disclosure.  
         [0022]      FIG. 5  is a cross-sectional view of the latch assembly of  FIG. 1  during closure operations.  
         [0023]      FIG. 6  is a cross-sectional view of the latch assembly of  FIG. 1  during closure operations, in the closed position.  
         [0024]      FIG. 7  is a cross-sectional view of the latch assembly of  FIG. 1  during closure operations.  
         [0025]      FIG. 8  is a cross-sectional view of the latch assembly of  FIG. 1  during closure operations.  
         [0026]      FIG. 9  is a cross-sectional view of the latch assembly of  FIG. 1  during opening operations. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Referring now to  FIGS. 1-3 , a latch assembly  100  in accordance with the present disclosure is shown. The latch assembly  100  includes a hollow housing  110  and a plunger  160  slidably received therein. Plunger  160  includes a proximal end  164  which is capable of transmitting an external force to plunger  160 . Proximal end  164  may, for example, comprise a head formed integrally with plunger  160 , or may comprise a separate head attachable to plunger  160  via, for example, a threaded connection. In one embodiment, proximal end  164  may include a cap (not shown), constructed of a durable material such as thin sheet metal, for covering the head. Accordingly, the separate head and/or the cap may be painted separately (e.g. via powder coating) from the remainder of latch assembly  100  to provide a more finished and aesthetically pleasing appearance without subjecting the entire latch assembly  100  to masking or to the high temperature of a powder-coat paint system.  
         [0028]     A pin  119  (preferably a set screw) extends outwardly from the plunger  160  into a longitudinal guide slot  118  formed in the hollow housing  110 . Interaction between the longitudinal guide slot  118  and the pin  119  limits the fore and aft travel of the plunger  160  within the hollow housing  110 . Furthermore, the pin guides the plunger  160  in the hollow housing  110 .  
         [0029]     As best shown in the cross-section of  FIG. 2 , both ends of pin  119  extend outwardly from plunger  160  into corresponding guide slot  118 , formed in each side of the hollow housing  110 . For example, during the assembly of latch  100 , plunger  160  may be inserted into hollow housing  110 . Then, pin  119  may be pushed through a hole in plunger  160  until both ends of pin  119  extend outwardly from plunger  160  and into the associated guide slot  118 , thereby securing plunger  160  within hollow housing  110 .  
         [0030]     Other embodiments, such as the embodiment depicted in  FIG. 9 , may include only a single guide slot  118 , with only a single end of pin  119  extending outwardly from plunger  160 . Additionally, although the pin  119  and guide slot  118  have been described as being located on the plunger and housing, respectively, it should be understood that the latch could be configured such that a pin extends inwardly from the hollow housing and into a slot within the plunger.  
         [0031]     A spring  140  is positioned within the hollow housing  110  between the distal end  112  of the hollow housing  110  and the distal end  162  of the plunger  160 . In the extended position shown in  FIG. 1 , the spring  140  urges the plunger  160  outwardly from the hollow housing  110 , the outward motion of the plunger  160  being limited by the pin  119  abutting the back end of the longitudinal guide slot  118 . As shown in  FIG. 2 , opposing ends of the spring  140  are seated within recesses  115  and  166  formed in the distal ends  112  and  162  of the hollow housing  110  and plunger  160 , respectively.  
         [0032]     As best shown in  FIGS. 2 and 3 , the latch assembly  100  includes a pair of arms  120  pivotally secured to the plunger  160  on opposite ends of a pivot pin  138 . A pair of openings  116  are provided on the hollow housing  110  such that an end portion of each arm  120  retractably extends through and beyond the outer diameter of the hollow housing  110  when the spring  140  is in the extended position. In this example, no substantial inward pressure is being exerted on the plunger  160  by spring  140 . However, in other embodiments the spring may be configured to exert some force on plunger  160 , even in the extended position.  
         [0033]     Outward force is exerted on each arm  120  by a pair of flat coil springs  130 , one flat coil spring  130  being provided for each arm  120 , as shown in  FIG. 3 . Each flat coil spring  130  has a first end  132  secured to the pivot pin  138 , such as in a recess, and a second end  134  secured to the respective arm  120 , such as in a recess.  
         [0034]     As discussed in Marks&#39; Standard Handbook for Mechanical Engineers, eighth edition, which is also incorporated by reference herein its entirety, a mechanism is that part of a machine which contains two or more pieces so arranged that the motion of one compels the motion of the others according to a definite law depending upon the nature of the combination. Cams are one such mechanism. A cam is usually a plate or cylinder which communicates motion to a follower by means of its edge or a groove cut in its surface.  
         [0035]     As noted, in the extended position, each flat coil spring  130  urges the respective arm  120  outwardly, through the respective opening  116 . However, as force is exerted on the proximal end  164  of the plunger  160 , the plunger  160  slides into the hollow housing  110 , causing a camming surface  122  of each arm  120  to engage the leading edge  116   a  of the respective opening  116 , which acts as the cam. Additional inward motion of the plunger  160  relative to the hollow housing  110  causes each arm  120 , which acts as a cam follower, to be rotated inwardly as the camming surface  122  interacts with the leading edge  116   a  of the opening  116 . The continued inward motion of the plunger  160  overcomes the outward force exerted by each flat coil spring  130  on the respective arm  120 . Eventually, each arm is fully retracted within the outer diameter of the hollow housing  110  ( FIG. 7 ).  
         [0036]     One potential advantage of the described latch is the protection afforded to the arms  120 , pivot pin  138 , and the flat coil spring  130 , all of which are attached to the plunger  160  and located within the hollow housing  110 . Thus, with the exception of the portion of the arms  120  which extend outwardly from the housing when spring  140  is in the extended position, the moving parts of the device are hidden and protected from weather and other potential damage.  
         [0037]     In the embodiment shown, the proximal end of hollow housing  110  includes a flange  114  extending outwardly therefrom and a threaded barrel  111 . The threaded barrel  111  is configured to receive a fastener such as threaded nut  150 . Threaded nut  150  screws onto threaded barrel  111  to secure the latch assembly  100  to an element  102  ( FIG. 5 ), which may be an access panel for a luminaire housing.  
         [0038]     Specifically, to secure the latch assembly  100  to the access panel  102 , a portion of the access panel  102  is secured between the threaded nut  150  and one side of the outwardly extending flange  114 . Preferably, a self-locking, threaded nut  150  is used to prevent the latch assembly  100  from loosening due to repeated use. As well, the distal end  112  of the hollow housing  110  includes a beveled edge  113  about its circumference. The beveled edge  113  helps insure proper closure of the latch assembly  100 , although the distal end  112  of hollow housing  110  and the mating receptacle  106  ( FIG. 5 ) may be somewhat misaligned. Similarly, the distal end  162  of the plunger  160  also includes a beveled edge  163  to help ensure proper motion of the plunger  160  relative to hollow housing  110 .  
         [0039]     Another embodiment of latch assembly  100 , shown in  FIG. 4 , includes a pair of sheet springs  142  to exert outward force on the pair of arms  120 . Each sheet spring  142  includes a mounted end  144  disposed in a recess in the plunger  160  and a free end  146  in contact with the respective arm  120 . As shown, the sheet spring  142  is in the extended position (in this case, not substantially deflected), thereby holding the arm  120  in an outward position from the hollow housing  120 . As inward force is exerted on the arm  120 , the arm  120  exerts force on the free end  146  of the sheet spring  142 , causing the sheet spring  142  to deflect in the direction opposite of the applied force. After the applied force is removed, the sheet spring  142  returns to the extended position, thereby exerting outward force on the arm  120  with the free end  146 . As such, the arm  120  extends outwardly through the adjacent opening  116 .  
         [0040]     Referring now to  FIGS. 5 and 6 , the latch assembly  100  is used to secure an access panel  102  to a fixture housing  104 . As previously described, the latch assembly  100  is secured to the access panel  102  by securing a portion thereof between the outwardly extending flange  114  of the hollow housing  110  and the threaded nut  150 . As shown, the latch assembly  100  is secured to a recessed portion of the access panel so that the proximal end  164  of the plunger  160  is flush with the access panel  102  when the spring  140  is in the extended position.  
         [0041]      FIGS. 5 and 6  depict the operation of securing the access panel  102  to fixture housing  104  by means of an individual exerting force on the access panel  102  rather than the plunger  160 . As the latch assembly  100  passes through the mating receptacle  106  formed in the fixture housing  104 , the camming surface  122  of each arm  120  will eventually come into contact with a portion of the circumference of the mating receptacle  106 . As such, the mating receptacle  106  causes both arms  120  to rotate inwardly until contact between the arms and the mating receptacle  106  ceases, meaning the arms  120  have passed fully through the mating receptacle  106 . Note, the mating receptacle  106  can be formed directly in the wall of the fixture housing  104  (as shown) or can be formed on a separate member that is then mounted to the fixture housing  104 .  
         [0042]     Once this contact is ceased, the constant outward force exerted by each flat coil spring  130  on the respective arm  120  causes the arm  120  to rotate outwardly until a portion of each arm  120  extends beyond the outer diameter of hollow housing  110 . Once the arms  120  have rotated outwardly, the individual may cease exerting force on the access panel  102 . The access panel  102  is now secured to the fixture housing, trapping the inner surface of the fixture housing  104  between abutment surfaces  124  of the arms  120  and the hollow housing, as shown in  FIG. 6 . The abutment surfaces  124  may comprise a reduced width at a free end of the arm. Depending on the orientation of the fixture, gravity may cause the abutment surfaces  124  of the arms  120  to rest against the inner coupling surface of the fixture housing  104 . Closure of the access panel  102  can be obtained utilizing a single arm  120 , but at least two are preferred.  
         [0043]     Referring now to  FIGS. 7 and 8 , closure of the access panel  102  is shown, wherein the individual exerts force on the proximal end  164  of the plunger  160 . Exerting force on the plunger  160  causes the plunger  160  to move inwardly relative to hollow housing  110  as the spring  140  is compressed. Eventually, as previously discussed, the camming surface  122  of each arm  120  will come into contact with the leading edge  116   a  of the respective opening  116 . As such, continued inward motion of the plunger  160  relative to hollow housing  110  causes the arms  120  to rotate inwardly until they are located within the outer diameter of the hollow housing  110 .  
         [0044]     Eventually, inward motion of the plunger  160  relative to the hollow housing  110  will cease, due either to the spring  140  being fully compressed or the pin  119  abutting the forward edge of the longitudinal guide slot  118 . At this time, further force exerted on the plunger  160  causes the access panel  102  to move toward the fixture housing  104  and the latch assembly  100  is inserted into the mating receptacle  106 . As best seen in  FIG. 8 , both arms  120  are retracted prior to passing through the mating receptacle  106 .  
         [0045]     When the access panel  102  is closed by exerting force on the plunger  160  rather than the access panel  102 , the arms  120  are not automatically returned to their fully extended positions. Rather, the force exerted on the plunger  160  is removed such that the spring  140  returns to its extended position. The spring  140  urges the plunger  160  downwardly with respect to hollow housing  110  such that the leading edge  116   a  of each opening  116  no longer exerts inward force on the respective arm  120 . For example, with the latch assembly  100  positioned as shown in  FIG. 9 , the individual exerts upward force on the access panel  102  while securing upward force on the plunger  160 . Once the spring  140  returns to the extended position and the arms  120  are outwardly extended, the individual then ceases to exert upward force on the access panel  102  and the abutment surfaces  124  of each arm  120  rest on the inner surface of the fixture housing  104 , as shown in  FIG. 6 .  
         [0046]     As shown in  FIG. 9 , to open the access panel, the individual exerts force on the plunger  160 , causing inward motion of the plunger relative to the hollow housing  110 . Subsequently, the arms  220  rotate inwardly within the outer diameter of the hollow housing  110 , as previously discussed. Adequate clearance between arms  220  and fixture housing  104  should be provided such that the arms may freely rotate inwardly to the retracted position without impedance by fixture housing  104 . It should be emphasized that the clearance provided in  FIG. 9  for the arms to freely rotate inwardly is substantially more than required. Next, while maintaining adequate pressure on the plunger  160  to keep the arms  120  retracted, the individual exerts downward force on the access panel  102  such that the latch assembly  100  is removed from the mating receptacle  106 . Once the arms  120  have cleared the mating receptacle  106 , exertion of force on the plunger  160  is no longer required.  
         [0047]     It should be emphasized that the embodiments described above, and particularly any “preferred” embodiments, are merely examples of various implementations that have been set forth here to provide a clear understanding of various aspects of the invention. One of ordinary skill will be able to alter many of these embodiments without substantially departing from scope of protection defined solely by the proper construction of the following claims.