Abstract:
Described are seismic-resistant equipment cabinets and door latches for enabling a hinged door to remain attached to the cabinet during a seismic event of a particular intensity. The door has a latch disposed along one edge of the door. The latch includes a latch-keeper receptacle and a latching bolt disposed in the latch-keeper receptacle. The latching bolt is slideable between a latched and an unlatched position. The frame has a latch keeper assembly attached to an edge thereof. The latch keeper assembly is positioned to enter the latch-keeper receptacle when the door latches to the frame. The latch keeper assembly includes a protruding member having a tapered edge and a latching-bolt aperture to receive the latching bolt when in the latched position. The tapered edge establishes a close fit by the latch keeper assembly within the latch receptacle to limit relative motion therebetween during a seismic event.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to equipment enclosures. More particularly, the present invention relates to door latches for securing doors to such equipment enclosures. 
     BACKGROUND 
     Equipment cabinets are commonly used to store telecommunications and networking equipment found at many sizeable businesses today. Such equipment cabinets are often provided in a tall and narrow configuration, housing equipment stacked vertically to conserve floor space. One such standard cabinet configuration is about 72 inches tall by about 22 inches wide. It is common for these equipment cabinets to include front and rear panel doors to provide a uniform appearance, shield unsightly clutter, protect devices housed therein from environmental hazards, and restrict unauthorized access. 
     During a seismic event, these equipment cabinets are often subject to violent forces. Such forces can cause the cabinet to move in one or more directions. Tall cabinets are particularly susceptible to lateral movements, as they tend to deform the rack, at least temporarily. The deformation is due at least in part to inertia of heavy equipment located in a top portion of the cabinet. 
     Lateral movement of the cabinet&#39;s base, combined with inertia of top-mounted equipment, produces torque along sidewalls of the cabinet. This torque can cause the rectangular cabinet to sway, resulting in deformation to a non-rectangular, parallelogram. For standard equipment racks that are deeper than they are wide, the deformation is often pronounced along the front and rear sides. Unfortunately, these sides are the ones most often fitted with panel doors. 
     The equipment cabinet doors are typically attached to the cabinet frame with two or more hinges located along one of the vertical sides. One or more latches are also provided along the opposite vertical side to secure the door in a closed position. Because the doors are typically rigid and often made of steel, they tend to maintain their original shape as the cabinet deforms to a non-rectangular parallelogram. The resulting difference in shapes creates stresses and strains at the points of attachment. Namely, forces are focused at the hinges and the latches, causing one or more of the hinges and latches to fail during the seismic event and the panel door to open or detach from the cabinet altogether. 
     Such an open or unattached cabinet door, particularly during the seismic event, could lead to injury of nearby personnel and to potential damage to other surrounding equipment. Open or unattached cabinet doors can also pose additional obstacles that may hamper rescue efforts following the seismic event. 
     The need for designing structurally sound equipment cabinets in view of a seismic event of a predetermined magnitude is recognized. One such standard adopted to qualify testing of equipment cabinets is NEBS GR-63-CORE. Unfortunately, designing equipment cabinets to meet the stringent seismic requirements often leads to added complexity and cost. 
     SUMMARY 
     In one aspect, the invention features a seismic-resistant latching system for securing a door to a frame. The latching system includes a latch disposed along one edge of one of the door and the frame. The latch includes a latch-keeper receptacle and a latching bolt disposed in the latch-keeper receptacle. The latching bolt is slideable between a latched and an unlatched position. A latch keeper is attached to an edge of the other of the door and the frame. The latch keeper is positioned to enter the latch-keeper receptacle when the door latches to the frame. The latch keeper includes a protruding member having a tapered edge and a latching-bolt aperture to receive the latching bolt when in the latched position. The tapered edge establishes a close fit by the latch keeper within the latch receptacle to limit relative motion therebetween during a seismic event. 
     In another aspect, the invention features a seismic latch keeper assembly for securing a door to a frame under seismic load. The door has a latch receptacle and a slideable latch bolt in the latch receptacle operable between latched and unlatched positions. The latch keeper assembly comprises a protruding member having a distal end sized to enter the latch receptacle with a first clearance, a proximal end opposite the distal end, and a bolt-receiving aperture disposed between the proximal and distal ends. A shoulder portion attaches to the protruding member. The shoulder portion has an expanding taper for engaging the latch receptacle with a second clearance less than the first clearance when the protruding member enters the latch receptacle. The second clearance operates to limit relative movement of the protruding member within the latch receptacle during a seismic event. A mounting flange can couple the protruding member to the frame. 
     In still another aspect, the invention features an electronic enclosure cabinet comprising a door and a frame. The door has a latch disposed along one edge of the door. The latch includes a latch-keeper receptacle and a latching bolt disposed in the latch-keeper receptacle. The latching bolt is slideable between a latched and an unlatched position. The frame has a latch keeper assembly attached to an edge thereof. The latch keeper assembly is positioned to enter the latch-keeper receptacle when the door latches to the frame. The latch keeper assembly includes a protruding member having a tapered edge and a latching-bolt aperture to receive the latching bolt when in the latched position. The tapered edge establishes a close fit by the latch keeper assembly within the latch receptacle to limit relative motion therebetween during a seismic event. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and further advantages of this invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which like numerals indicate like structural elements and features in the various figures. The drawings are not meant to limit the scope of the invention. For clarity, not every element may be labeled in every figure. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  illustrates an isometric view of one embodiment of an equipment enclosure constructed in accordance with the present invention. 
         FIG. 2  illustrates a schematic view of equipment enclosure deformation during a seismic event. 
         FIG. 3  illustrates a perspective cut-away view of one embodiment of an equipment enclosure chassis including a seismic-resistant latch keeper. 
         FIG. 4  illustrates a perspective cut-away view of one embodiment of an equipment enclosure door including a latching rod adapted to engage the latch keeper of  FIG. 3 . 
         FIG. 5  illustrates a perspective cut-away view of one embodiment of an equipment enclosure chassis including a first leaf hinge component. 
         FIG. 6  illustrates a perspective cut-away view of one embodiment of an equipment enclosure door including a second leaf hinge component adapted to engage the first leaf hinge component of  FIG. 3 . 
         FIG. 7  illustrates a cross-sectional top view of a front portion of the equipment enclosure chassis illustrated in  FIG. 1 . 
         FIG. 8  illustrates a cross-sectional top view of the equipment enclosure door illustrated in  FIG. 1 . 
         FIG. 9A  illustrates a partial elevation view of the equipment enclosure door, approaching the equipment enclosure frame during closure, including the seismic-resistant latch keeper of  FIG. 3 , shown in an unlatched position. 
         FIG. 9B  illustrates a partial elevation view of the equipment enclosure door in a closed and latched position. 
         FIG. 10  illustrates an exploded perspective view of a two-piece embodiment of the seismic-resistant latch keeper of  FIG. 3 . 
         FIG. 11  illustrates a cut-away view of one embodiment of the seismic-resistant latch keeper having a curvilinear tapered edge. 
     
    
    
     DETAILED DESCRIPTION 
     A seismic-resistant door latch constructed in accordance with the invention enables a hinged door to remain attached to its frame and closed during a seismic event. The hinged door includes one or more hinges disposed along one edge and one or more latches disposed along another edge. A reinforced latch keeper on the cabinet engages a latch channel (or aperture) in the hinged door. The reinforced latch keeper includes an expanding taper that presents a narrowed leading edge to a latch channel when the latch keeper enters the latch channel in order to close the panel door. The latch keeper&#39;s narrowed leading edge presents a first clearance to the latch channel; whereas, its wider shoulder presents a second, reduced clearance to the same latch channel. The reduced clearance provided by the expanding taper of the latch keeper to the latch channel inhibits movement therebetween during a seismic event. Such a reduction in movement reduces or eliminates banging of the door&#39;s latch channel against the latch keeper, a condition referred to as “jack hammering,” that can lead to damage and in some instances unintended disengagement of the latch keeper. 
     The reinforced and tapered latch keeper is combined with an offset leaf hinge adapted to retain pivotal engagement between the hinged door and the equipment cabinet during a seismic event. Beneficially, the offset leaf hinge provides the hinge pivot with a supporting structure capable of plastic deformation during a seismic event. Thus, relative movement between the hinged door and the equipment cabinet, as might occur from deformation of the equipment cabinet during the seismic event, is substantially absorbed by deformation of the offset hinge member. Although one or more of the hinges may be deformed, perhaps even losing their ability to pivot the door during such an event, the hinges are more easily replaced and at substantially less expense than either the door or the equipment cabinet. 
       FIG. 1  illustrates an electronic equipment enclosure  100  constructed in accordance with the principles of the present invention. The equipment enclosure  100  is shown as a rectangular configuration including a cabinet  105  for housing electronic equipment therein and a hinged panel door  110  for providing access to the electronic equipment housed therein. In this illustrative equipment enclosure  100 , panel door  110  provides access along a front side  115  of the cabinet  105 . In some embodiments, the panel door  110  provides access to a rear side, or to one of the left and right sides of the cabinet  105 . In yet other embodiments, the cabinet  105  includes multiple doors on the same or different sides of the cabinet  105 , each constructed in accordance with the principles of the present invention. 
     The enclosure  100  is shown in a vertical configuration in which the height H of the cabinet  105  is greater than its width W. For example, the cabinet  105  has a width of about 22-24 inches to accommodate standard 19-inch rack-mountable electronic devices. The height of the equipment enclosure  100  can be depend upon the size and quantity of equipment to be housed therein. Often, the height of the equipment enclosure  100  is expressed in terms of rack units (RUs), with one RU corresponding to about 1.75 inches. The depth D of the cabinet  105  again depends upon the intended application. For standard types of electronic equipment enclosures, the depth is often greater than the width, as shown. 
     The cabinet  105  typically includes a structural frame providing support to the cabinet  105  and to the electronic equipment housed therein. Continuing with the illustrative embodiment, the structural frame includes at least two vertical frame segments  120   a ,  120   b  disposed along opposite corners of the front side  115  of the cabinet  105 . These vertical frame segments  120   a ,  120   b  also provide structural support to the panel door  110 . As illustrated, the panel door  110  is pivotally coupled along one edge of the vertical left frame segment  120   a  using at least two hinges  125   a ,  125   b  (generally  125 ). The hinges  125  are coupled between one edge of the panel door  110  and the left vertical frame segment  120   a , such that the panel door  110  is allowed to pivot between open and closed positions. As shown, the panel door  110  is mounted in a right-to-left configuration, sometimes referred to as a left-hand reverse door configuration. In other embodiments, the panel door  110  can be mounted in other configurations, such as a left-to-right configuration in which the hinges would be coupled to the right vertical frame segment  120   b.    
     The equipment enclosure  100  also includes a latching mechanism adapted to selectively secure the panel door  110  in a closed position. For example, the latching mechanism includes two latching bolts  180   a ,  180   b  (generally  180 ) coupled to the panel door  110  and corresponding latch keepers  135   a ,  135   b  (generally  135 ) coupled to a right frame member of the equipment cabinet  105 . The keepers  135  are aligned with the latching bolts  180  when the panel door  110  is closed. 
       FIG. 2  illustrates a schematic view of deformation experienced by a rectangular equipment cabinet  105  during a seismic event. In a seismic event, the ground (e.g., the floor of a building) is subjected to movement in one or more different directions. This movement includes vertical or up-and-down movement and lateral or side-to-side movement. In a general sense, the lateral motion can occur in any direction along the surface of the ground. Often the motion is oscillating, including a back-and-forth component. Illustrated is an example of an oscillating lateral motion in which the floor  140  moves alternately from left to right as shown by the straight arrows adjacent to the bottom of the equipment cabinet  105 . 
     Often, the equipment cabinet  105  is secured to the floor of an equipment room. In some embodiments, the equipment cabinet  105  is bolted to the floor  140  using a mounting bracket  145 . Thus, the movement of the floor  140  due to the seismic event will be directly transferred to the bottom of the equipment cabinet  105 . Because equipment housed within the cabinet  105  can be of considerable weight, it has an associated inertia that develops torque acting along the vertical structural supports of the equipment cabinet  105 . 
     The resulting torque can cause the equipment cabinet  105  to at least temporarily deform. For example, a rectangular equipment rack can deform to a non-rectangular parallelogram during the seismic event. A seismic force is produced at the bottom of the equipment cabinet  105 , caused by the lateral movement of floor  140 . This force combines with inertia due to equipment housed in the top portion of the equipment cabinet  105  and provides countering forces along the top of the equipment cabinet  105 . These counter-directed forces at opposite ends of the vertical supports result in a torque that can lead to the type of deformation shown. Thus, right angles a 1 , a 2  formed at the interior junction of the vertical side support at the base of the equipment cabinet  105  deform to non-right angles a 1 ′, a 2 ′ during a seismic event. 
     Further, oscillations can develop along the top of the equipment cabinet  105  as the resting inertia is overcome and the top begins to move to one side, while the bottom of the equipment cabinet  105  is moved to an opposite side. Thus, the equipment cabinet  105  may oscillate back and forth during such lateral movements. A rectangular door fitted to the front of the equipment cabinet  105  may not deform and thus remains generally rectangular throughout the seismic event. Deformation of the rack to a non-rectangular parallelogram will produce forces along any points of attachment to the rectangular door. For example, such forces would be experienced along the hinges  125  and latch keepers  135  ( FIG. 1 ). 
       FIG. 3  illustrates a perspective cut-away view of one embodiment of an equipment enclosure chassis including a seismic-resistant latch keeper  150 . The latch keeper  150  is attached through a mounting flange  155  to one of the vertical frame members  120   b  of the equipment cabinet  105  ( FIG. 1 ). For example, the mounting flange  155  can be attached using mechanical fasteners, such as screws  160 , rivets, or chemical fastening means including welding or chemical bonding. The latch keeper  150  includes a blade or fin  165  that protrudes outward and away from the front face of the vertical frame member  120   b . Thus, the fin  165  extends out toward the front of the equipment cabinet  105  to engage the panel door  110  ( FIG. 1 ), when closed. Preferably, the fin  165  is formed from a rigid material, such as a metal. In some embodiments, the fin  165  is formed from 1010 steel having a thickness of about 0.060 inch. Structural strength of the fin  165  serves to bear the forces produced between the equipment cabinet  105  ( FIG. 1 ) and the front panel door  110  ( FIG. 1 ) during a seismic event. 
     The fin  165  includes at least one horizontal portion  170 ′ with an aperture  175   a  sized and positioned to accommodate an end portion of the latch pin  180   a  ( FIG. 1 ). For example, the top latch keeper  135   a  ( FIG. 1 ) includes a bottom horizontal portion  170 ″ including an aperture  175   b  sized and positioned to receive an end portion of the top latch pin  180   a . Conversely, the bottom latch keeper  135   b  ( FIG. 1 ) includes a top horizontal portion  170 ′ including an aperture  175   a  sized and positioned to receive an end portion of the bottom latch pin  180   b . Depending upon the linear displacement or “throw” (the distance that the end portion of the latch pin  180  travels between its latched and unlatched positions), the fin  165  can include both top and bottom horizontal portions  170 ′,  170 ″, each defining a respective aperture  175   a ,  175   b . Thus, the end portion of the latch pin  180   a  can reside simultaneously within both apertures  175   a ,  175   b  when in the latched position. 
     The latch keeper  150  includes a leading end  185  opposite the mounting flange  155  that is sized to fit within a corresponding aperture of the panel door  110  ( FIG. 1 ) when closed. Preferably, the leading end  185  is dimensioned to fit within such a door aperture providing sufficient clearance to avoid interference with the door during opening and closing of the door. Thus, the linear dimensions of the leading end  185  are less than the dimensions of its corresponding door aperture. 
     The latch keeper  150  also includes an increasing taper  195  provided along at least a portion of the fin  165 . The taper  195  expands in a linear dimension along a profile of the fin  165  from the leading end  185  to the mounting flange  155 . In one embodiment, the latch keeper  150  includes a reinforcing plate  200  extending vertically along one side of the fin  165 . The reinforcing plate  200  can be formed from the same material as the fin  165 . In some embodiments, the reinforcing plate  200  is about 0.100 inch thick. The reinforcing plate  200  includes a neck portion  205  extending from the leading end  185  toward the mounting flange  155 . The reinforcing plate  200  also includes a shoulder portion  210  disposed between the neck portion  205  and the mounting flange  155 . For example, the shoulder portion  210  includes a top taper  195   a  and a bottom taper  195   b . The tapers  195   a ,  195   b  can be symmetric as shown and can take any number of different forms including a linear taper, a piecewise linear taper, a curved taper, a curvilinear taper ( FIG. 11 ), or any combination thereof. 
     In some embodiments, the aperture  175   a  is fitted with a bushing insert  215 . Thus, the aperture  175   a  can be oversized, with the bushing insert  215  receiving an end portion of the latch pin  180   a . The bushing insert  215  can be formed of a different material than the fin  165 . For example, the bushing insert  215  can be formed from a polymer (i.e., a polyolefin or polytetrafluoroethylene (PTFE)) for ease of manufacture and for reducing friction during latching and unlatching. 
       FIG. 4  illustrates a perspective cut-away view of one embodiment of the panel door  110  formed with an outer panel  220  and an inner panel  225 . The outer and inner panels  220 ,  225  can be formed from a sturdy material, such as steel, to provide protection and structural integrity. In some embodiments, the panels  220 ,  225  are secured to a frame. For example, the panels  220 ,  225  may be formed around and secured to a vertical frame (not shown). 
     Formed along an interior portion of one edge of the panel door  110  is an aperture providing access to an end portion of the latching rod  230 . As illustrated, the inner panel  225  includes an aperture or latch channel  235  that can be formed by a cut-out in the edge of the inner panel  225 . The latch channel  235  includes a top leading edge  240   a  and a bottom leading edge  240   b  along a portion of the perimeter of the latch channel facing the latch keeper, when the panel door  110  is closed. The top and bottom leading edges  175   a ,  175   b  are spaced apart, such that the leading end  185  ( FIG. 3 ) of latch keeper  150  ( FIG. 3 ) fits therebetween with sufficient clearance to permit unhindered opening and closing of the panel door  110 . 
     Disposed between the inner and outer panels  225 ,  220  along an outer edge of the panel door  110  is the latch channel  235 . A latching rod end portion  230  is accessible through the latch channel  235 . In an unlatched position, the latching rod end portion  230  is substantially recessed between the inner and outer panels  225 ,  220  providing an unobstructed latching channel  235  and providing clearance to the latch keeper  150  during opening and closing of the panel door  110 . After the panel door  110  is closed and the fin portion  165  of the latch keeper  150  resides at least partially within the latch channel  235 , the latching rod end portion  230  is translated into the latch channel  235 , thereby entering the aperture  175   a  of the latch fin  165  and latching the panel door  110  in a closed position. The latching rod end portion  230  is slideable within a guide  250  that maintains axial integrity of the end portion  230  throughout the latching and unlatching process. Interference caused by the latching rod end portion  230  and the latch keeper  150  prevents the panel door  110  from being pulled or otherwise forced open. 
     In some embodiments, the panel door  110  ( FIG. 1 ) is mounted to a cabinet  105  using one or more hinges  125   a ,  125   b  ( FIG. 1 ). One family of hinges commonly used includes leaf hinges, similar to those commonly found residential passageway doors. Each leaf hinge typically has at least two hinge components, one fastened to the panel door  110  and the other fastened to the cabinet  105  ( FIG. 1 ). The two hinge components are joined along a common axis, typically by a pin, allowing them to pivot therebetween. 
     Shown in  FIG. 5  is a perspective cut-away view of one embodiment of a hinge component  255  mounted to the equipment cabinet  105 . More precisely, the hinge component is an offset-frame leaf hinge component  255  in which the pivot point is displaced away from the doorframe. 
     The offset-frame leaf hinge component  255  includes a frame-leaf mounting bracket  260  adapted to abut an adjacent portion of the left vertical frame member  120   a . The frame-leaf mounting bracket  260  can be attached to the vertical frame member  120   a  using mechanical fasteners, such as screws  265 , rivets, or chemical fastening means including welding or chemical bonding. The offset-frame leaf hinge component  255  also includes top and bottom knuckle arms  270   a ,  270   b  (generally  270 ) each including at one end a respective knuckle  275   a ,  275   b  (generally  275 ). The knuckles  275  define apertures therein to accommodate a hinge pin aligned with the hinge&#39;s pivot axis. The knuckle arms  275  are each coupled at another end to a pivot-offset member  280 . The pivot-offset member  280  provides support to the knuckle arms  270 , positioning them in a plane parallel to the left vertical frame member  120   a , but displaced away from the frame member  120   a . In some embodiments, the pivot offset member is formed from a rigid material, such as 1010 steel. The rigid material can have a thickness of about 0.060 inch. 
     The frame-leaf mounting bracket  260 , the pivot offset member  280 , and the knuckle arms  270  can be formed from a single piece of U-channel stock. The knuckles  275  can be formed by rolling an end portion of the knuckle arm  270  over onto itself, creating a cylindrical cavity therein. In some embodiments, the knuckle arms  270  are separated by one or more cutouts  285  that provide clearance for mechanical fasteners of a mating leaf hinge component mounted to the panel door  110 . The cutouts  285  avoid interference with such fasteners when the hinge  125  is in a closed position. 
     In some embodiments, the offset-frame leaf hinge component  255  includes a doorstop bracket  290 . The doorstop bracket  290  includes a doorstop surface  295  positioned to interfere with a corresponding surface of the panel door  110  ( FIG. 1 ) when in an open position. For example, the doorstop surface  295  can be formed from an ‘L’ bracket, as shown, and mounted along one side to the left vertical frame member  120   a . Thus, one side of the ‘L’ bracket defines a doorstop mounting bracket  287  that is placed against the left vertical frame member  120   a . The other side of the ‘L’ bracket extends away from the frame providing the doorstop surface  295 . In some embodiments, the doorstop surface  295  can be formed integrally with the offset-frame leaf hinge component  255 , or as a separate component as shown. In some embodiments that use a separate doorstop surface  295 , the doorstop surface  295  can be attached to the left vertical frame member  120   a  using the same mechanical fasteners  265  used to secure the offset-frame leaf hinge component  255 . 
       FIG. 6  illustrates a perspective cut-away view of an interior edge of the panel door  110 . Detailed is one embodiment of a door leaf hinge component  300  of the leaf hinge assembly adapted to engage the offset-frame leaf hinge component  255  ( FIG. 5 ) and pivotally secure one edge of the panel door  110  to the equipment cabinet  105 . The door leaf hinge component  300  includes a leaf member  305  for mounting the door leaf hinge component  300  to an edge of the panel door  110 . As shown, the leaf member  305  is mounted to a leaf mounting bracket  310  coupled to the interior door panel  225 . 
     The leaf member  305  can be attached to the leaf mounting bracket  310  using any suitable fastening means including mechanical fasteners, such as screws, rivets, or chemical fastening means including welding or chemical bonding. Mechanical fasteners  315  are used for the illustrative embodiment. As some mechanical fasteners  315  may protrude as shown, they preferably align with the cutouts  285  in the offset-frame leaf ( FIG. 5 ), thereby avoiding interference between the door leaf hinge component  300  and the offset-frame leaf hinge component  255  ( FIG. 5 ) when in the closed position. 
     A cutout along the interior edge of the panel door  110  provides access to the door leaf hinge component  300 . The cutout may be formed from portions of one or more of the inner panel  225 , the outer panel  220 , and the first vertical frame member  345   a . The cutout defines top and bottom edges  325   a ,  325   b  that are spaced sufficiently apart to accept the offset-frame leaf hinge component  255  ( FIG. 5 ) when the panel door  110  is mounted to the cabinet  105 . Thus, the hinge  125  ( FIG. 1 ) is hidden from view when the panel door  110  is closed. A cutout in the outer panel  220  extending between the top and bottom edges  325   a ,  325   b  defines an elongated edge  327 . When the panel door  110  is fully open, the elongated edge  327  interferes with door stop surface  295  ( FIG. 5 ) preventing further opening of the panel door. 
     In some embodiments, the door leaf hinge component  300  includes a top and bottom hinge pins  330   a ,  330   b  (generally  330 ) disposed along a pivot axis. The hinge pins  330  are positioned to pivotally engage apertures of the knuckles ( 275 ) of the offset-frame leaf hinge component  255 . The hinge pins  330  can be spring loaded, such that they can be retracted into the door leaf hinge component  300  during installation and removal of the panel door  110  from the cabinet  105 . Each of the hinge pins  330   a ,  330   b  (generally  330 ) can include a respective release pin  335   a ,  335   b  (generally  335 ) extending radially outward from the pivot axis. Each of the hinge pins  330  is slideable within a respective slot formed within the door leaf hinge component  300 . Each slot includes a respective detent  340   a ,  340   b  (generally  340 ) into which the release pin  335  can be positioned, thereby temporarily retaining the hinge pin  330  in a retracted position. After the panel door  110  is aligned with the corresponding edge of the equipment cabinet  105 , the release pin  335  is moved out of the detent  340  allowing the spring-loaded hinge pin  330  to extend into a portion of the knuckle  275  of the mating offset-frame leaf hinge component  255  ( FIG. 5 ). In some embodiments, a commercially available door leaf hinge component  300  can be used. For example, the removable door leaf hinge component  300  can be a part number F6-940 door leaf, commercially available from Southco, Inc. of Concordville, Pa. 
       FIG. 7  illustrates a cross-sectional top view of a front portion of the equipment cabinet  105 . Located on the right-hand side of the front portion of the cabinet  105  is the latch keeper  150 . The latch keeper  150  is shown mounted to a right vertical cabinet frame member  120   b  providing rigid structural support thereto. Visible is a top horizontal surface  170 ′ of the latch keeper  150  defining the aperture  175   a . The aperture  175   a  resides at a distance  1   1  away from the front surface of the cabinet  105  and is positioned to align with an axis of the latching rod end portion  230  ( FIG. 4 ) when the panel door  110  ( FIG. 1 ) is in the closed position. 
     Located on the left-hand side of the front portion of the cabinet  105  is the one portion of the leaf hinge assembly. The offset-frame leaf hinge component  255  is shown mounted to a left vertical cabinet frame member  120   a  providing rigid structural support thereto. Visible is an open end of the knuckle  275   a  revealing the pivot axis. The knuckle  275   a  (and thus the pivot axis) resides at a distance  1   2  away from the front surface of the cabinet  105  and is positioned to align with the top hinge pin  330   a  of the door leaf hinge component  300  ( FIG. 6 ), the panel door  110  ( FIG. 1 ) pivoting between open and closed positions along the pivot axis. 
       FIG. 8  illustrates a cross-sectional top view of the panel door  110 . The panel door  110  includes inner panel  225  and outer panel  220  joined together along each of a first and second vertical frame members  345   a ,  345   b . Located adjacent to the right-hand edge of the inner panel  225  is an end portion of the latching rod  230 . The latch guide  250  is shown mounted to the inner panel  225  providing rigid structural support thereto. The latch guide  250  maintains the end portion of the latching rod  230  along a latching axis positioned to align with the aperture  175   a  of the latch keeper  150  ( FIG. 7 ) when the panel door  110  is in the closed position. As described above in reference to  FIG. 4 , the inner panel  225  includes a latch guide channel  235  positioned and dimensioned to accept at least a leading end  185  of the latch keeper  150  ( FIG. 3 ) when the panel door  110  is in the closed position. 
     Located on the left-hand side of the panel door  110  is the door leaf hinge component  300  of the leaf hinge assembly. The door leaf hinge component  300  can be mounted to a door-leaf mounting bracket  310  provided within the inner panel  225 . The door leaf hinge component  300  includes hinge pins  330  aligned along the hinge-pivot axis, such that the hinges pins  330  reside within the knuckles  275  of the offset frame member  255  ( FIG. 7 ).  FIG. 7  and  FIG. 8  are positioned relative to each other to further illustrate the alignment of the panel door  110  to one surface of the equipment cabinet  105 . 
       FIG. 9A  schematically illustrates engagement of the leading end  185  of the latch keeper  150  into the latch channel  235  of the panel door  110 . The arrow indicates the direction of closing of the panel door  110 . The latching rod end portion  230  is shown in an unlatched position, such that it is retracted below a bottom leading edge  240   b  of the channel aperture  235 . This positioning ensures that the leading edge  185  of the latch keeper  150  will not interfere with the rod  230  when the panel door  110  is closed. The end portion of the latching rod  230  is retained along the latching axis by the latch guide  250 . 
     The opening dimension of the channel  235  defined between the top and bottom leading edges  240   a ,  240   b  is sufficient to accept the leading edge  185  of the latch keeper  150  without interference. This condition can be met by maintaining a first minimum clearance S 1a  between the top of the latch fin  165  and the top leading edge  240   a  and a second minimum clearance S 2a  between the bottom of the latch fin  165  and the bottom leading edge  240   b . The first and second clearances S 1a , S 2a  do not need to be equal. 
     Referring next to  FIG. 9B , the fin  165  is shown positioned within the latch channel  235  corresponding to a closed position of the panel door  110 . When the fin  165  is so positioned, the latching rod end portion  230  is substantially aligned with the aperture  175   b  of the latch keeper  150 . In some embodiments, the tip of the latching rod end portion  230  includes a taper  350  to bring the latching rod end portion  230  into alignment with the aperture as the latching rod end portion  230  is moved from the unlatched to the latched position. Thus, if there is a slight misalignment, the tapered tip  350  will adjust the relative position of the latch keeper  150  and the panel door  110 , bringing them into alignment. 
     A linear distance ‘H’ measured between the latching rod end portion  230  in the latched and unlatched positions is referred to as the “throw.” Depending upon the throw, at least a portion of the latching rod end portion  230  will reside within the aperture  175   a  of the latch keeper  150  forming an interference therebetween. The resulting interference prevents unwanted opening of the panel door  110  as long as the latch keeper  150  continues engaging the latching rod end portion  230 . 
     As shown in more detail, the top and bottom tapers of the shoulder  195   a ,  195   b  result in a reduction in the clearance when the panel door  110  is closed between the respective top and bottom leading edges  240   a ,  240   b . These clearances are illustrated as S 2a  and S 2b . Preferably, the taper causes the following expression to be satisfied:
 
 S   1a   +S   1b   &gt;S   2a   +S   2b   (1)
 
     Beneficially, the reduced clearance between the latch keeper  150  and the panel door  110  minimizes the amount of play available therebetween. In a seismic event, distortion of the rack ( FIG. 2 ) combined with a rigid rectangular door  110  will tend to produce vertical movement along the latching edge of the door  110 . With a larger clearance (i.e., S 1a +S 1b ), the movement results in the unwanted “jack hammering” of the top and bottom leading edges  240   a ,  240   b  against the top and bottom surfaces  170 ′,  170 ″ ( FIG. 3 ) of the latch keeper  150 . Sufficient jack hammering can lead to disengagement of the latching rod end portion  230  from the latch keeper  150  (particularly when a relative small throw is provided) and even to mechanical failure of the latch keeper  150 . In either situation, the latching end of the panel door  110  can become disengaged from the latch keeper, despite it being in the latched position, leading to unwanted opening of the panel door  110 . By reducing the clearance in the latched position (i.e., S 2a +S 2b ), the jack hammering effect is reduced or eliminated. Thus, the panel door  110  remains latched to the equipment cabinet  105  throughout the seismic event. 
     In some embodiments, the clearance between the one or more of the top and bottom tapers  195   a ,  195   b  and the corresponding adjacent leading edge  240   a ,  240   b  is not more than about 0.020 inch. Additionally, one or more of the tapers  195   a ,  195   b  can also aid in bringing the panel door  110  into proper alignment upon closure. 
     Despite the latched portion of the panel door  110  remaining secured to the equipment cabinet  105  during a seismic event, there can be some deformation between the panel door  110  and the equipment cabinet  105 . Beneficially, the design of the offset-frame leaf hinge component  255  is to deform during a seismic event, thereby allowing a closed panel door  110  to move relative to the equipment cabinet  105 , without disengaging from the equipment cabinet  105 . The offset pivot of the hinge component  255  moving with the edge of the panel door  110 , while the frame leaf mounting bracket  260  ( FIG. 5 ) remains attached to the left vertical frame member  120   a  can satisfy this condition. Distortion of the pivot axis relative to the left vertical frame member  120   a  is absorbed by a deformation of one or more of the knuckle support arms  270  and the pivot offset member  280  ( FIG. 3 ). Thus, the offset-frame leaf hinge component  255  is preferably made from a ductile material, that is rigid enough to support the panel door  110  during normal operation, yet capable of plastic deformation under the stresses and strains resulting from a seismic event. The thickness of the offset-frame leaf hinge component  255  contributes to making the hinge deformable during the seismic event in order to absorb seismic energy. For this purpose, a suitable range of thicknesses is approximately 0.090 to 0.125 inches. When formed using the same or similar material, the combined thickness of the fin  165  and reinforcing plate  200  is generally larger than 0.125 inches to promote deformation of the leaf hinge component  255  before the latch keeper  150 . For example, a combined thickness of the fin  165  material and the reinforcing plate  200  can be about 0.160 inch or more. 
       FIG. 10  illustrates an exploded perspective view of a two-piece embodiment of the seismic-resistant latch keeper  150 . The latch keeper  150  includes a latch-keeper housing  360  coupled to a latch-keeper reinforcing member  365 . The latch-keeper housing  360  includes the top and bottom horizontal surfaces  170 ′,  170 ″, a leading end  185 , and a side wall  370 . In some embodiments, the latch-keeper housing  360  can be stamped or cut from a single piece of sheet stock that can be bent into the configuration shown. The side wall can maintain the side profile of the latch keeper  150 , also having a shoulder  210  with top and bottom tapers  195   a ′,  195   b′.    
     The reinforcing member  365  includes a reinforcing plate  200 ′ that also maintains the side profile of the latch keeper  150 , having a shoulder  210 ′ with top and bottom tapers  195   a ″,  195   b ″. A mounting bracket  155  is attached at the shouldered end of the reinforcing plate  200 ′. The mounting bracket resides in a plane orthogonal to the reinforcing plate  200 ′ and can include one or more mounting apertures  385 . 
     The latch-keeper housing  360  is brought into alignment with the reinforcing plate  200 ′, such that the side wall  370  abuts one side of the reinforcing plate  200 ′. Additionally, the top and bottom shoulders  195   a ′,  195   b ′ of the side wall  370  are brought into alignment with the top and bottom shoulders  195   a ″,  195   b ″ of the reinforcing plate  200 ′. In some embodiments, the latch keeper housing  360  includes one or more alignment holes  390  positioned for alignment with similar holes  395  provided in the reinforcement plate  200 ′. One or more pins can be inserted temporarily through the holes  395 ,  390  to hold the latch-keeper housing  360  into alignment with the reinforcing plate  200 ′. The two components  360 ,  365  can be attached together using mechanical fasteners, such as screws, rivets, or chemical fastening means including welding or chemical bonding. 
     While the present invention has been shown and described herein with reference to specific embodiments thereof, it should be understood by those skilled in the art that variations, alterations, changes in form and detail, and equivalents may be made or conceived of without departing from the spirit and scope of the invention. Accordingly, the scope of the present invention should be assessed as that of the appended claims and by equivalents thereto.