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RELATED APPLICATION 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/969,671 Oct. 21, 2004 now abn and claims the benefit of 35 U.S.C. 120. 

   SCOPE OF THE INVENTION 
   This invention relates to a filing cabinet, and in particular, to a filing cabinet with a locking system. 
   BACKGROUND OF THE INVENTION 
   Filing cabinets are known having drawers that open forwardly to provide access to paper files and the like inside. One example of a filing cabinet structure is shown in U.S. Pat. No. 4,480,883 to Edwards issued Nov. 6, 1984 which is directed to an internal anti-tip blocking device that permits only one drawer of a stacked column of drawers to be opened at any one time. 
   Filing cabinets are known to have internal lock structures which are internal of the cabinet and prevents any of the drawers from being opened. For added security, it is also known to provide external locking devices with a metal bar which extends vertically across the height of a column of drawers and is secured at the top and bottom of the cabinet to prevent opening of any drawers. Such external bar has the disadvantage that it must be removed and stored when not in use. 
   SUMMARY OF THE INVENTION 
   To at least partially overcome the disadvantages of previously known devices, the present invention provides an external locking mechanism for a filing cabinet incorporating two hinged blocking plates at each side of the cabinet and a locking bar which is movable without removal from attachment to the cabinet to positions such that the blocking plates can be selectively prevented from being moved to unblocked positions or permitted to be moved to unblocked positions. 
   An object of the present invention is to provide an improved external locking system for a filing cabinet. 
   Another object of the present invention is to provide a filing cabinet with a locking system which is very simple to use, and also relatively easy and inexpensive to manufacture. 
   In one aspect, the present invention provides a filing cabinet having a compartment with at least one drawer slidably mounted in the compartment between retracted and withdrawn positions. Blocking plates are hinged to each opposite side of the compartment rotatable on a vertical axis between: (i) a blocked position in the path of the drawer to prevent the drawer from withdrawal from the retracted position; and (ii) an unblocked position out of the path of the drawer to permit withdrawal to the withdrawn position. A locking bar is mounted to the cabinet movable between: (i) a locked position where at least a portion of the locking bar is in the path of both of the blocking plates and prevents each of the blocking plates from movement from the blocked position to the unblocked position; and (ii) unlocked positions where the locking bar is out of the path of the blocking plates and does not prevent the blocking plates from movement from the blocked position to the unblocked position. 
   In a preferred embodiment, the cabinet has a framework comprising by two opposite sidewalls, a back wall, a top wall, and a bottom wall which define a compartment therein containing sliding drawers and with an opening from the compartment from which the drawers are slidable through the opening. 
   The framework preferably includes a crossbeam which has ends that are secured to the opposite side walls of the framework preferably to extend horizontally between two drawers and with the locking bar mounted to the crossbeam, preferably for sliding or pivotal movement thereto. 
   The crossbeam preferably has a forward facing surface and the locking bar is mounted to the forward facing surface of the crossbeam. A locking bar is mounted to the crossbeam against removal from the crossbeam yet for movement such as sliding or pivoting relative thereto. 
   In one preferred embodiment, the two opposite side walls each have a forward facing surface. A continuous hinge is mounted to the forward facing surface of the side wall with one hinge plate of the continuous hinge forming or carrying blocking plate. 
   In another preferred embodiment, the two opposite side walls each have a forward facing gable surface and a continuous hinge is mounted to the gable panel with one hinge plate mounted flush with the gable surface and the other hinge plate of the piano hinge pivotable relative the fixed hinge plate and forming a blocking plate which extends inwardly in front of the drawers. 
   Preferably, the length of the locking bar is such that it does not extend past the two opposite side walls, regardless of the position of the locking bar. 
   In an alternative embodiment, the filing cabinet comprises two locking bars mounted at opposite sides of the compartment. Each of the two locking bars is movable between: (i) a locked position where at least a portion of the locking bar is in the path of one of the blocking plates and prevents the blocking plate from movement from the blocked position to the unblocked position; and (ii) an unlocked position where the locking bar is out of the path of the blocking plate and does not prevent the blocking plate from movement from the blocked position to the unblocked position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further aspects and advantages will become apparent from the following description taken together with the accompanying drawings in which: 
       FIG. 1  is a front pictorial view of a filing cabinet in accordance with a first embodiment of the present invention showing the drawers closed and locked; 
       FIGS. 2 to 5  are front pictorial views of a filing cabinet in accordance with the first embodiment of the present invention, wherein the drawers and associated slides have been removed; 
       FIGS. 6 ,  8 ,  10  and  12  are partially cut-away top views of  FIGS. 2 to 5 , respectively; 
       FIGS. 7 ,  9 ,  11 , and  13  are partially cut-away front perspective views of  FIGS. 2 to 5 , respectively; 
       FIG. 14  is a front view similar to  FIG. 1  but unlocked and with one drawer open; and 
       FIGS. 15 and 16  are cross-sectional plan views along section lines D-D′ and E-E′ in  FIG. 2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference is made to  FIGS. 1 to 14  which illustrate a first embodiment of a filing cabinet in accordance with the present invention. 
   As seen in  FIGS. 1 to 14 , the cabinet  10  has a framework comprising opposite side walls  12  and  13 , a back wall  52 , a top wall  54  and a bottom wall  56 . The framework defines a compartment therein. As seen in  FIGS. 1 and 14 , three drawers  60  are mounted in the compartment for horizontal sliding between closed, retracted positions shown in  FIG. 1  and open, extended positions.  FIG. 14  shows a middle of the three vertically stacked drawers in an open, extended position. The drawers  60  are slidable on associated slides (not shown) mounted to the interior of the side walls  12  and  13  on each side of each drawer  60 . The framework of the filing cabinet  10  includes a horizontal crossbeam  20 . The crossbeam  20  has both of its ends permanently secured to the opposite side walls  12  and  13 . The crossbeam  20  extends horizontally between the sidewalls  12  and  13  vertically between two of the drawers  60  and presents a forward facing surface  62  best seen in  FIG. 24 . Each of sidewalls  12  and  13  carry a forward facing gable surface  14  and  15  effectively forming a gable or post extending vertically beside each drawer  60  throughout the height of the cabinet. 
     FIGS. 2 to 13  illustrate the filing cabinet  10  of  FIGS. 1 and 14  from which the drawers  60  and associated slides have been removed. 
   As seen in  FIGS. 15 and 16 , two continuous hinges  80  and  81  also known as piano hinges are mounted to the forward facing gable surface  14  and  15  of each side wall  12  and  13 . Each hinge  80  and  81  has two hinge plates namely a base plate  82 ,  83 , a blocking plate  16 ,  17  joined by a hinge pin  84 ,  85  with the base plate  82 ,  83  and blocking plate  16 ,  17  pivotable relative each other about the pin  84 ,  85 . The base plate  82 ,  83  is fixedly secured to the respective gable surface  14  and  15  of the side walls as by screws, nuts, welding or the like with the hinge pin  84  disposed to not extend laterally beyond the respective side wall  12  and  13 . Each blocking plate  16 ,  17  is thus hinged to its relative side wall  12 ,  13  for pivoting about the vertical hinge pin  84 ,  85 . 
   The blocking plates  16 ,  17  are adapted to be rotatable from: (i) a blocked position, as shown in  FIGS. 2 ,  6  and  7 , in which the blocking plates  16 ,  17  lie forward of the drawers  60  in the front plane of the front face of the cabinet  10  to (ii) an unblocked position, as shown in  FIGS. 5 ,  12  and  13 , in which the blocking plates  16 ,  17  are rotated to extend forwardly preferably perpendicular to the front face of the cabinet  10  and thus parallel to side walls  12  and  13 .  FIGS. 15 and 16  show the blocking plates  16 ,  17  in solid lines in an unblocked position and in dashed lines in a blocked position. 
   A locking bar  22  is slidably mounted to the forward facing surface  62  of the crossbeam  20  for sliding in the horizontal direction relative the crossbeam  20 . The locking bar  22  is mounted to the crossbeam  20  against removal from the crossbeam  20 .  FIGS. 2 ,  6  and  7  show a middle locked position in which the locking bar  22  overlaps both of the blocking plates  16 ,  17  and prevents opening of the drawers. As seen in  FIG. 6  which is a top view of  FIG. 2 , the left end  30  of the locking bar  22  is forward of the left blocking plate  16  and prevents its movement from the blocked position shown and the right end  31  of the locking bar  22  is forward of the right blocking plate  17  and prevents its movement from the blocked position. 
   The locking bar  22  is slidable from the position shown in  FIG. 2  to the right to the position shown in  FIGS. 3 ,  8  and  9  such as to be clear of the blocking plate  16  thus allowing the blocking plate  16  to be rotated between the blocked and the unblocked position.  FIGS. 4 ,  10  and  11  show a position which after the locking bar  16  has been rotated to the unblocked position, the locking bar  22  has been slid to the left to a position shown in  FIG. 4  such as to be clear of blocking plate  17  thus allowing the blocking plate  17  to be rotated between the unblocked position and a blocked position.  FIGS. 5 ,  12 ,  13  and  14  show a condition which from the position of  FIG. 4 , the blocking plate  17  is pivoted to the unblocked position and the locking bar  22  is slid back to the middle position. As seen in  FIG. 12  in a top view the hinged blocking plates  16 ,  17  are in a position where they are out of the path of the drawers  60  and therefore, do not prevent the opening of the drawers  60 , as shown in  FIG. 29  with one drawer open. 
   The length of locking bar  22  is such that when it is slid to the right, as shown in  FIG. 3 , the left end  30  of the locking bar  22  is clear of the blocking plate  16  on the left side of the filing cabinet  10 , and the right end  31  of the locking bar  22  does not extend past the edge of side wall  13 . Similarly, when the locking bar  22  is slid to the left, as shown in  FIG. 4 , the right end  31  of the locking bar  22  is clear of the blocking plate  17  on the right side of the filing cabinet  10 , and the left end  30  of the locking bar  22  does not extend past the edge of side wall  12 . Therefore, the locking bar  22  is designed such that it does not extend laterally past vertical planes of the side walls  12  and  13  of the filing cabinet  10 , and does not move into, for example, a wall adjacent the filing cabinet  10  or into the path of the drawers of any other filing cabinets which are adjacent to filing cabinet  10 . 
   In the middle locked position of  FIGS. 2 ,  6  and  7 , the locking bar  22  is adapted to be fixed in the position to prevent movement of the locking bar  22 . In this regard as best seen in  FIGS. 6 and 7 , a lock bracket  36  is secured to a central portion of the crossbeam  20  providing a horizontally extending flange with a vertical opening therethrough which is to align with vertical opening in the lock bar  22  such that a locking device such as a padlock may lock the locking bar  22  to the crossbeam  20  against movement. The locking bar  22  shown in  FIGS. 1 to 13  has a L-shaped in cross-section with one flange vertical and the other flange horizontal. The horizontal flange carries the vertical opening to receive a padlock. 
   As seen, for example, in  FIG. 14 , the locking bar  22  has a vertical extent which is not greater than the vertical extent of the crossbeam  20  such that with the locking bar  22  itself doe not interfere with movement of the drawers  60  on either side of the crossbeam  20  to an open extended position. 
     FIG. 23  is a cross-sectional view along section line A-A of  FIG. 22  showing a preferred configuration by which the locking bar  22  is pivotally mounted to the crossbeam  20  for pivoting about pivot axis  26 . The locking bar  22  is L-shaped is cross-section having vertical leg  40  and horizontal leg  41 . The crossbeam  20  has a vertical portion  61  presenting a forward face  62 . A top flange  63  and a bottom flange  64  extending rearwardly from the vertical portion  61 . At the location of pivot axis  26 , a strengthening plate  66  is secured to the rear of the vertical portion  61 . A screw  65  carrying washers  67  and  68  extends through an aperture the plate  66  and the vertical portion  61  and into a threaded nut  69  welded to a rear of the vertical leg  40  of the locking bar  22 . The screw  65  serves to secure the locking bar  22  to the crossbeam  20  against removal from the crossbeam  20  in normal use. This has the advantage that with the locking bar secured to the crossbeam  20 , the locking bar is always secured to the cabinet and cannot be removed or lost. 
   In all of the embodiments illustrated, the lock bar is preferably secured to the crossbeam  20  against removal from the crossbeam as is advantageous such that the crossbeam is always available and ready for use. The arrangement of the crossbeam of course permits movement of the crossbeam as by pivoting and/or sliding relative to the crossbeam  20  to provide for movement of the locking plates between the blocked and unblocked positions. 
   The figures show a filing cabinet with a crossbeam  20  which is preferred but not necessary. The sliding locking bar  22  of  FIG. 1  could be mounted to one or both of the gable-like crossbeams  95  and  96  forward as part of and adjacent top wall  10  and bottom wall  56 . 
   The continuous hinges forming the blocking plates  16 ,  17  are shown in each embodiment to extend the entire height of the cabinet  10 . This is not necessary but preferred. The hinges need to only extend adjacent a portion of each drawer  60  whose opening is to be blocked. 
   Although this disclosure has described and illustrated preferred embodiments of the invention, it is to be understood that the invention is not restricted to these particular embodiments. Rather, the invention includes all embodiments that are functional or mechanical equivalents of the specific embodiments and features that have been described and illustrated herein. Many modifications and variations will now occur to those skilled in the art. For a definition of the invention, reference is made to the following claims.

Summary:
An external locking mechanism for a filing cabinet incorporating two hinged blocking plates at each side of the cabinet and a locking bar which is movable without removal from attachment to the cabinet to positions such that the blocking plates can be selectively prevented from being moved to unblocked positions or permitted to be moved to unblocked positions.