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RELATED APPLICATIONS 
     The current application claims priority to the U.S. Provisional Application Ser. No. 61/892,201 filed Oct. 17, 2013. 
    
    
     BACKGROUND 
     Technological advancements in storm shelter design have made them more affordable, and hence more available, to the homeowner. The market for storm shelters has grown significantly; underground storm shelters and safe rooms are much more prevalent in new home construction in recent years. Modern underground storm shelters are also readily adaptable to being installed inside the garage area of an existing house, without interfering with parking a car over the space occupied by the shelter. Typically, the prior attempted solutions provide an open top enclosure constructed of sheet metal, and a lid assembly constructed of plate steel. It has been determined by the inventors of this technology that the sheet metal construction can be improved upon, and that a two piece sliding lid can be improved by making the entire lid surface flush to the surrounding surface when the storm shelter is closed. It is to these improvements that the embodiments of the present invention are directed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Details of various embodiments of the present invention are described in connection with the accompanying drawings that bear similar reference numerals. 
         FIG. 1  depicts a top view of a sliding entry door assembly for an enclosure. 
         FIG. 2  depicts a cross sectional view along the line  1 - 1  in  FIG. 1 . 
         FIG. 3  depicts an enlarged cross sectional view of a portion of the assembly of  FIG. 2  in an underground storm shelter. 
         FIG. 4  depicts a cross sectional view similar to  FIG. 2  but with the sliding lid partially opened. 
         FIG. 5  depicts modular forms for constructing an underground open-top concrete enclosure that is sized to support the sliding entry door assembly of  FIG. 1 . 
         FIG. 6  depicts a top view of the concrete forms in  FIG. 5  joined together for pouring the underground open-top concrete enclosure. 
         FIG. 7  depicts a built-in ratcheting mechanism to assist opening the sliding lid. 
     
    
    
     DESCRIPTION 
       FIG. 1  depicts a top view of a sliding entry door assembly  100  that is constructed in accordance with illustrative embodiments of the present invention. For purposes of this description the sliding entry door assembly  100  is incorporated into an underground storm shelter, and as such is commonly referred to as a sliding lid assembly  100 . More particularly, in the described embodiments the sliding lid  100  is sized to close the open top of a rectangular underground concrete structure, although the contemplated embodiments are not so limited. That is, in alternative equivalent embodiments the technology disclosed herein can be employed in other types of shelters both underground and above ground, and likewise can be employed in other types of non-shelter structures such as shipping containers and the like, without any need to enumerate all the possible applications for the skilled artisan to readily ascertain the nature and scope of the contemplated technology described herein. 
     The sliding lid assembly  100  has a structural framework made by joining opposing side members  102 ,  104  to opposing end members  106 ,  108 . The members  102 - 108  are preferably metal structural framing members such as L-shaped beams welded together to define an opening. A stationary lid  110  is rigidly affixed to the framework to partially fill the opening. A sliding lid  112  is selectively moveable between the closed position depicted in  FIG. 1  and an opened position. In the closed position the sliding lid  112  and the stationary lid  11  together fill the opening formed by the framework, thereby securely closing the shelter for its intended purpose. 
     A transparent window  114  can be provided in the stationary lid  11  so that occupants of the shelter can observe conditions outside the shelter. Alternative embodiments contemplate the window  114  in the sliding lid  112 . To endure the potentially harsh conditions of storm debris hitting the window  114 , and to adequately protect the occupants of the shelter, the window  114  is preferably constructed of a polycarbonate having a high impact strength such as ballistic grade Lexan®. In alternative embodiments not depicted more than one window can be constructed in either or both of the lids  110 ,  112 . 
     The sliding lid  112  supports a hinged access panel  116  that can be locked in the closed position, such as by a key actuated lock  118 . A finger hole  119 , or alternatively a knob, gives the user a grasp of the access panel  116  for opening it. 
       FIG. 2  depicts a cross sectional view taken along the section line  1 - 1  in  FIG. 1 , depicting the sliding lid  112  in the closed position. Importantly, the embodiments of this technology generally provide a sliding lid  112  that, in the closed position, forms an entirely flush surface with the surrounding floor surface. That is, in the closed position of the sliding lid  112  as depicted in  FIG. 2 , a top surface  120  of the end member  106  is flush to the top surface of the sliding lid  112 . For the purposes of this description and meaning of the claims, the term “flush” means substantially coplanar, meaning two flush surfaces form substantially coplanar surfaces. The top surface of the sliding lid  112  is also flush with the top surface of the stationary lid  110  in the closed postition, and likewise flush with a top surface  122  of the other end member  108 . 
     The sliding lid assembly  100  thereby operates such that in the closed position it is entirely flush-mounted to the surrounding floor surface, such as flush to the surrounding concrete floor surface.  FIG. 3  is an enlarged detail view of a portion of the sliding lid assembly  100  in the manner in which it can be receivingly engaged in the open top of an underground concrete enclosure  124 , consisting of opposing poured concrete end walls (one of the concrete end walls depicted), opposing poured concrete side walls, and all extending from a poured concrete bottom. 
     To retrofit a storm shelter into an existing floor  126 , an oversize trench is dug through the existing floor  126 , concrete forms are placed inside the trench, and then concrete is poured against the forms to form the open-top enclosure  124 . The existing floor  126  is drilled in multiple places to receive reinforcement rods  127  (such as rebar) before pouring the enclosure  124 , to tie the newly poured concrete enclosure  124  to the existing floor  126 . In these illustrative embodiments the concrete form provides a notch  128  around the perimeter of the top opening of the enclosure  124  to receive the end member  106  so that its top surface  120  is flush to both the enclosure  124  and the existing floor  126 . 
     Returning to  FIG. 2 , a track  130  is supported by the side member  102 . In these depicted embodiments the track  130  is sloped downwardly from the left-side to the right-side of the side member  102 , although the contemplated embodiments are not necessarily so limited as discussed below. A roller  132  attached to the sliding lid  112  is rollingly supported upon the track  130 . The track  130  is positioned to raise one end of the sliding lid  112  to be flush-mounted when the sliding lid  112  is closed, as depicted. A selectively rotatable cam  134  also attached to the sliding lid  112  is likewise supported upon the track  130  and, in turn, supports the other end of the sliding lid  112  to be flush-mounted when the sliding lid  112  is closed. 
     A lever  136  is externally accessible by opening the unlocked access panel  116 . The lever  136  is depicted in the latched position in  FIG. 2 . In the latched position, a latch member (not depicted) that is fixed in rotation with the lever  136  lockingly engages a catch member (not depicted) such as may be supported by the end member  106 . That locking engagement prevents any sliding movement of the sliding lid  112 . 
     A linkage  138  ( FIG. 4 ) transfers the user&#39;s selected rotation of the lever  136  to a rotation of the cam  134 .  FIG. 4  depicts the lever  136  having been selectively rotated by the user in a clockwise direction to likewise rotate the cam  134  clockwise so that the cam  134  no longer contactingly engages the track  130 . This is referred to as the “lowered” position of the sliding lid  112 . In the lowered position, the contacting disengagement of the cam  134  from the track  130  causes that end of the sliding lid  112  to lower. The sliding lid  112  supports another roller  140  that rollingly engages the track  130  in the lowered position. 
     The clockwise rotation of the lever  136  also disengages the latch member from the catch member so that the sliding lid  112  has freedom of movement to roll upon the rail  130 , such as to the partially opened position depicted in  FIG. 4 , to open the shelter so that the user can enter or exit the shelter.  FIG. 4  depicts only one side of the sliding lid  112  in the manner that it is rollingly supported upon the track  130  on the side member  102 , and it will be understood that the sliding lid  112  is likewise rollingly supported by a track (not depicted) on the opposing side member  104 . Note that in the lowered position the sliding lid  112  is capable of rolling under the stationary lid  110 . Advantageously, debris laying on either of the panels  110 ,  112  does not prevent the movement of the sliding lid  112  between the closed and opened positions. 
       FIG. 4  best depicts the sliding lid  112  has a tab  142  affixed thereto at one end so that, in the closed position of the sliding lid  112  depicted in  FIG. 2 , the tab  142  is receivingly engaged within an opening  144  defined in the end member  106 . Similarly, the sliding lid  112  has another tab  146  affixed thereto at the other end so that, in the closed position of the sliding lid  112  depicted in  FIG. 2 , the tab  146  abuttingly engages the bottom side of the stationary lid  110 . Engagement of the tabs  142 ,  146  in the closed position of the sliding lid  112  prevents any lifting force from raising the sliding lid  112  upwardly off the track  130 . 
       FIG. 5  depicts a modular concrete form system for constructing the open-top concrete enclosure to which the sliding lid assembly  100  is attached. An end panel assembly  148  is constructed by joining two panels  150 ,  152  together edge-to-edge. Flanges  154 ,  156  at the mating edges of the panels  150 ,  152  provide protuberant surfaces that are well adapted for connecting together with a clamping mechanism  158 , such as a c-clamp or a vise-grip and the like. A flange  160  extends substantially orthogonal to the panel  152 , and another flange  162  extends substantially orthogonal to the flange  160 . Although not depicted, the panel  152  likewise has two orthogonal flanges extending inwardly and downwardly, respectively. Fastening members  164  can be affixed to yet another flange  166  to matingly align with openings in a flange on the side panel assembly  168 . The side panel assembly  168  and the bottom panel assembly  170  are constructed in like manner.  FIG. 6  is a top view depiction of two opposing end panel assemblies  148  and two opposing side panel assemblies  168  attached to the bottom panel assembly  170 . Note that the top-side orthogonal flanges such as  160 ,  162  abuttingly engage each other to position the panel assemblies  148 ,  168  squarely to the bottom panel assembly  170 . Preferably, the corner flanges are diagonally shaped to provide the mitered corners depicted in  FIG. 6 . The completely assembled forms advantageously permit constructing all four sides and the bottom of the enclosure  124  in a monolithic pour. 
     As mentioned above, the depicted embodiments are merely illustrative and in no way limiting of the contemplated embodiments. For example, in the depicted embodiments the track  130  is sloped relative to the floor surface about ten degrees from left to right, but in alternative equivalent embodiments more or less slope may be provided so long as the sliding lid  112  is operably capable of sliding under the stationary lid in the opened position of the sliding lid  112 . 
     In yet other equivalent alternative embodiments the track can be substantially level relative to the floor surface. In that case each end of the sliding lid  112  can be raised and lowered by two cams linked to the lever for either individual or simultaneous selected rotation. In the latched position of the lever (as depicted in  FIG. 2 ), two cams on each side of the sliding lid  112  can cooperatively and simultaneously lift respective ends of the sliding lid  112  to be flush-mounted. As described above, in the latched position the latching member also engages the catch member to prevent movement of the sliding lid  112 . In the unlatched position of the lever (as depicted in  FIG. 4 ) the two cams on each side of the sliding lid  112  cooperatively and simultaneously lower the sliding lid  112  so that both rollers on each side of the sliding lid  112  rollingly engage the respective track. 
     In either event of one or two cams on each side of the sliding lid  112 , in other alternative embodiments of this technology the linkage can be eliminated by providing a lever connected directly to each cam. In that case one lever can be rotated to raise the sliding lid  112  to the closed position and another lever can be rotated to lock the sliding lid  112  in the closed position. 
       FIG. 7  depicts alternative embodiments that include an assist mechanism for opening the sliding lid  112 . The built in feature can be advantageous in the event debris has fallen on the sliding lid  112 , resisting the opening. In these illustrative embodiments a gear rack  180  is attached to the bottom side of the stationary lid  110 . A ratcheting latch is pivotally connected to the bottom side of the sliding lid  112 , having a handle  182  at one end and a pawl  184  at the other end. The pawl is preferably spring biased to maintain a contacting engagement with the gear rack  180 , and the handle is preferably biased to the horizontal position depicted in  FIG. 7 . A user grasping the handle  182  and pivoting it clockwise forces the pawl  184  against the gear rack  180 , resulting in a force that moves the sliding panel  112  in a direction toward the left, or toward the opened position, as depicted in  FIG. 7 . 
     The various features and alternative details of construction of the apparatuses described herein for the practice of the present invention will readily occur to the skilled artisan in view of the foregoing discussion, and it is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Summary:
An apparatus and associated method for a sliding entry door assembly. The sliding door assembly has a frame, and a fixed lid attached to the frame. A rail is attached to the frame. A lid is selectively slidable upon the rail relative to the fixed lid to an opened position. A cam is selectively operable to raise the slidable lid to be flush with the fixed lid in a closed position.