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TECHNICAL FIELD 
     This invention relates generally to sliding doors, and in particular to an assembly that utilizes two sliding glass doors and a stationary screen. 
     BACKGROUND OF THE INVENTION 
     A sliding glass door in combination with a sliding screen door are commonly used to provide access to and from houses and other buildings. They provide greater sunlight and view than a standard swinging door, without the dangers that might be associated with a glass door that swings open. Furthermore, objects may be placed close to the sliding door without need to leave a path for the door to swing open. In the standard arrangement, there are two glass components and a single screen component all contained within a doorframe. Each of the glass components comprises a rectangular frame, typically made of wood, steel, aluminum, or vinyl, which surrounds a glass pane. The screen component comprises a rectangular frame across which a mesh screen is stretched. One of the glass components is stationary and forms a seal at one end of the doorframe, while the other can slide back and forth within the doorframe. The screen also slides back and forth within the doorframe. 
     This standard arrangement has a fully closed position to prevent access through the doorframe and to prevent natural ventilation across the doorframe. In this fully closed position the sliding glass component is slid to the opposite end of the doorframe from the stationary component. The frames of the glass components form a seal to prevent drafts, water, or insects from crossing the doorframe. When it is desired to have natural ventilation, while still maintaining a barrier to insects, birds, and the like, the sliding glass component is slid within the door frame towards the same end as the stationary component. The screen component is adjusted so that it is slid to the opposite end from the stationary glass component. In this arrangement, ventilation across the screen is allowed, while the screen provides a barrier to insects, small animals, and the like. In order to go in or out of the doorway, the screen must be slid back and forth. 
     The sliding glass component and the screen are retained in the doorframe by standard trackways. One of the common problems with this standard arrangement is that the screen becomes untracked easily. When this happens it is difficult to move the screen and it is necessary to fix the screen so that it is back in proper engagement with the track. However, getting the screen back into proper engagement with the track can be difficult and frustrating. As a result of its weight and rigidity, the sliding glass component is generally very reliable and rarely becomes untracked. 
     Another difficulty with standard sliding doorway designs is that the mechanism for locking the doors closed tends to be easily defeated. For this reason, it is common to wedge a broomstick, or other elongated rigid item, between the rear of the sliding glass door and the door frame to prevent the door from being opened. For this reason it would be beneficial to provide a secondary locking mechanism integrated with the door that would reinforce the standard locking mechanism. 
     In certain instances it would be desirable to change the side of the doorway that is being used for entrance and exit. For this reason it would be advantageous to have a sliding glass door system that is capable of quick conversion between left-hand and right-hand orientation. 
     The difficulties encountered in the prior art and discussed above are substantially eliminated by the present invention. 
     SUMMARY OF INVENTION 
     Accordingly, it is an object of the present invention to provide a sliding glass door entryway in which the screen remains stationary and the glass components are both slidable. 
     It is another object of the present invention that is more reliable than past sliding glass door entryways. 
     By the present invention it is proposed to overcome the difficulties encountered heretofore. To that end, a sliding door assembly is proposed for connection within a standard sliding door doorway or the type having a lower frame member, an upper frame member, and first and second vertical frame members at opposite ends of the upper and lower doorway frame members. The doorway is located between an inside area and outside area. The sliding door assembly has first and second glass doors slidably received by the upper and lower frame members of the doorway, the second glass door being located to the outside of the first glass door. A screen panel is operably received by the upper and lower frame members of the doorway and is located to the outside of the first and second glass doors. The assembly includes means for locking the screen panel in place against the first vertical frame member of the doorway such that when the glass doors are slid against the second vertical frame member the screen panel in combination with the glass doors form a barrier to prevent insects and the like from crossing the doorway but still allow ventilation between the inside area and the outside area across the screen panel. When the screen panel is locked in place against the first vertical frame member, and one of the glass doors is against first vertical frame member and the other glass door is against the second vertical frame member, the glass doors form a barrier that substantially prevents ventilation across the doorway. When the screen panel is locked in place against the first vertical frame member of the doorway and both glass doors are slid toward the first vertical frame member of the doorway, an opening is formed between the doors and the second vertical frame member to allow egress across the doorway between the inside and outside areas. Preferably, the screen panel is adapted to be used in both a right-hand and a left-hand orientation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of the present invention showing the glass doors fastened together and slid partially open; 
     FIG. 2 is a front elevation view of a preferred embodiment of the present invention with the screen panel in a left-hand orientation and the glass doors in a fully closed position; 
     FIG. 3 is a front elevation view of a preferred embodiment of the present invention with the screen panel in a left-hand orientation showing the outside door slid partially open and the inside door slid partially open; 
     FIG. 4 is a front elevation view of a preferred embodiment of the present invention with the screen panel in a left-hand orientation showing both the outside door and the inside door slid against the right frame member of the doorway to allow ventilation and prevent egress across the doorway; 
     FIG. 5 is a front elevation view of the preferred embodiment of FIG. 1; 
     FIG. 6 is a front elevation view of a preferred embodiment of the present invention with the screen panel in a left-hand orientation showing the inside door fastened to the outside door with both doors slid to the left side of the doorway to allow egress across the doorway; 
     FIG. 7 is a is a front elevation view of a preferred embodiment of the present invention with the screen panel in a right-hand orientation showing the outside door coupled to the inside door with the doors slid to the left side of the doorway to allow ventilation; 
     FIG. 8 is a front elevation view of a preferred embodiment of the present invention with the screen panel in a right-hand orientation showing the outside door coupled to the inside door, and both doors slid to the right side of the doorway to allow egress across the doorway; 
     FIG. 9 a  is a detail drawing showing a preferred embodiment for the latching mechanism used to retain the screen panel in connection with the door frame, with the latching mechanism in a released position; 
     FIG. 9 b  is a detail drawing showing a preferred embodiment for the latching mechanism used to retain the screen panel in connection with the door frame, with the latching mechanism in a locked position; 
     FIG. 10 a  is a detail drawing showing a preferred embodiment of the coupling mechanism used to couple the sliding glass doors together with the coupling member in a coupling position; and 
     FIG. 10 b  is a detail drawing showing a preferred embodiment of the coupling mechanism used to couple the sliding glass doors together with the coupling member in a retracted position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Shown generally in the figures is a preferred embodiment of a sliding glass door assembly  10  according to the present invention. The door assembly  10  is contained within a standard sliding door doorway formed by a door frame  12 . The door frame  12  is a rectangle formed by a top frame member  14 , a bottom frame member  16 , and first and second vertical frame members  18  and  20 . The door frame  12  is generally placed between an inside area  22  and an outside area  24 . The sliding glass door assembly  10  has a first sliding glass door  26 , a second sliding glass door  28 , and a screen panel  30 . 
     For the purpose of this description, “left” and “right” will refer to the door frame  12  as viewed from the inside area  22  looking towards the outside area  24 . Those of ordinary skill in the art will realize that the glass door assembly  10  could be constructed opposite hand from what is shown in the drawings. The screen panel  30  is formed by a rectangular frame  32  and a screen mesh  34  stretched across the rectangular frame  32 . The screen mesh  34  should be sufficiently open to allow ventilation between the inside area  22  and the outside area  24 , and should be sufficiently fine to prevent insects and small animals from crossing the doorway. The rectangular frame  32  of the screen panel  30  is formed by a right screen frame member  36 , a left screen frame member  38 , a bottom screen frame member  40 , and a top screen frame member  42 . The bottom screen frame member  40  is in engagement with the bottom frame member  16  of the door frame  12 . The top screen frame member  42  is in engagement with the top frame member  14  of the door frame  12 . The screen panel  30  may be used in a left-hand orientation as shown in FIGS. 1-6, with the left screen frame member  38  in engagement with the left vertical frame member  18  of the door frame  12 . The screen panel  30  may also be used in a right-hand orientation as shown in FIGS. 7 and 8, with the right screen frame member  36  in engagement with the right vertical frame member  20  of the door frame  12 . 
     The inside sliding glass door  26  is formed by a rectangular frame having a left frame member  44 , a right frame member  46 , a top frame member  48 , and a bottom frame member  50 . A pane of glass is held in sealed engagement with the frame members  44 ,  46 ,  48 , and  50 . The bottom frame member  50  of the inside sliding glass door  26  is adapted to slidably engage a track  52  on the bottom frame member  16  of the door frame  12 . Similarly, the top frame member  48  of the inside sliding glass door  26  is adapted to slidably engage track  54  on the top frame member  14  of the door frame  12 . Those of ordinary skill in the art will know of other manners to slidably engage the inside glass door  26  with the door frame  12 . 
     The outside sliding glass door  28  is similar to the inside sliding glass door  26 . The outside sliding glass door  28  has a left frame member  56 , a right frame member  58 , a top frame member  60 , and a bottom frame member  62 . A glass pane is in sealed engagement with the rectangular frame members  56 ,  58 ,  60 , and  62 . The bottom frame member  62  of the outside sliding glass door  28  is adapted for slidable engagement with track  64  in the bottom frame member  16  of the door frame  12 . The top frame member  60  of the outside sliding glass door  28  is adapted for slidable engagement with track  66  in the top frame member  14  of the door frame  12 . 
     In the preferred embodiment, each of the sliding glass doors  26  and  28  have a door handle  70  formed in both the left frame member  44 ,  56  and the right frame member  46 ,  58 . Each of the door handles  70  has associated with it a locking member  72  to lock the sliding glass doors  26 ,  28  in engagement with the vertical frame members  18 ,  20  of the door frame  12 . As seen FIG. 1, left vertical frame member  18  of the door frame  12  has a lock receiver  74  formed in it to engage the locking member  72 . A similar lock receiver is also formed in the right vertical frame member  20  of the door frame  12 , but is not shown. Those of ordinary skill in the art will be aware of numerous satisfactory designs for door handles and locks to lock the glass doors  26  and  28  in engagement with the vertical frame members  18  and  20 . 
     The inside sliding glass door  26  is provided with two coupling mechanisms  76  to latch the inside sliding glass door  26  to the outside sliding glass door  28 . The coupling mechanisms  76  are provided in the left frame member  44  and right frame member  46  of the inside sliding glass door  26 . Detailed views of the coupling mechanism  76  are shown in FIGS. 10 a  and  10   b . The coupling mechanism  76  comprises a coupling member  78  contained within a passageway  80  within the frame member  44  or  46 . The coupling member  78  has a finger ring  82  connected to a coupling rod  84 . The coupling member  78  can be adjusted within the passageway  80  such that the coupling rod  84  is either entirely contained within the passageway  80 , or such that the coupling rod  84  extends beyond the outside edge of frame member  44  or  46  of the inside sliding glass door  26  (FIG. 10 a ). The left and right frame members  56 ,  58  of the outside sliding glass door  28  are provided with a receiver bore  86 . The receiver bore  86  is of a slightly greater diameter than the diameter of the coupling rod  84  such that the coupling rod  84  may be captured by the receiver bore  86  when the passageway  80  of the coupling mechanism  76  is aligned with the receiver bore  86  and the coupling member  78  is adjusted such that the coupling rod  84  extends beyond the outside edge of the frame members  44  and  46  of the inside sliding glass door  26 . 
     The screen panel  30  is preferably provided with means for locking the panel  30  in place against either the left vertical frame member  18  or the right vertical frame member  20  of the door frame  12 . Those of ordinary skill in the art will be aware of several mechanisms for accomplishing this objective. In the preferred embodiment shown, the rectangular frame  32  of the screen panel  30  is provided with spring loaded pins  88 . The spring loaded pins  88  are generally biased so that they extend beyond the edge of the rectangular frame  32 . When the screen panel  30  is locked in place in the door frame  12 , the spring loaded pins  88  are received within screen locking holes  90  formed in the door frame  12 . When it is desired to remove the screen panel  30  from the door frame  12 , the spring loaded pins  88  are pulled such that they are retracted within the rectangular frame  32  of the screen panel  30 . In the preferred embodiment, a center frame member with a weather strip  94  is also provided to provide additional support for the screen panel  30 . With the spring loaded pins  88  retracted into the rectangular frame  32 , the screen panel  30  may be removed from the door frame  12  for cleaning or adjustment to the opposite end of the door frame  12 . The retracted position is shown in FIG. 9 b , and the standard biased position is shown in FIG. 9 a.    
     FIGS. 1-6 show a preferred embodiment of the present invention with the screen panel  30  in a left-hand orientation, and use of the door assembly  10  with the screen panel  30  in this orientation will be described in detail. FIGS. 7 and 8 show the screen panel  30  in a right-hand orientation. Use of the assembly  10  in this orientation will not be discussed in detail, but should be apparent from the discussion relating to use of the sliding glass door assembly  10  with the screen panel  30  in the left-hand orientation. 
     During times when the inside area  22  is being heated or mechanically cooled, or other times when it is desired to prevent ventilation across the door frame  12 , the sliding glass door assembly  10  can be adjusted such that the sliding glass doors  26  and  28  substantially seal the door frame  12 . FIG. 2 shows the sliding glass doors  26  and  28  adjusted to completely seal the door frame  12 . To lock the sliding glass doors  26  and  28  in the sealed position of FIG. 2, the locking member  72  in the right frame member  46  of the inside sliding glass door  26  is adjusted to engage the lock receiver (not shown) in the right vertical frame member  20  of the door frame  12 . The inside sliding glass door  26  is thus prevented from sliding within the door frame  12  by the locking member  72  in engagement the lock receiver. The outside sliding glass door  28  is adjusted so that the left frame member  56  of the outside sliding glass door  28  is in sealed engagement with the left vertical frame member  18  of the door frame  12 . In this position, the receiver bore  86  in the right frame member  58  of the outside sliding glass door  28  is aligned with the passageway  80  in the left frame member  44  of the inside sliding glass door  26 . The coupling mechanism  76  in the left frame member  44  of the inside sliding glass door  26  may then be adjusted to latch the outside sliding glass door  28  in a fixed relation with the inside sliding glass door  26 . This is accomplished by inserting the finger into finger slot  82  and moving the coupling member  78  within the passageway  80  such that coupling rod  84  is extended into the receiver bore  86  of the right frame member  58  of the outside sliding glass door  28 . The outside sliding glass door  28  is thusly prevented from sliding within the door frame  12  by the coupling rod  84  received within receiver bore  86 . This coupling mechanism  76  further provides a redundant means of locking the inside sliding glass door  26  in addition to the locking member  72  in engagement with the lock receiver  74 . 
     If it is desired to permit ingress or egress across the door frame  12 , the inside sliding glass door  26  must be unlocked by adjusting locking member  72  within the right frame member  46  of the inside sliding glass door  26  such that it is out of engagement with the lock receiver in the right vertical frame member  20  of the door frame  12 . The coupling mechanism  76  must also be unlatched. This is accomplished by sliding the coupling member  78  within the passageway  80  such that the coupling rod  84  is completely withdrawn into the left frame member  44  of the inside sliding glass door  26 , as shown in FIG. 10 b . The inside glass door  26  may then be slid to the left within the door frame  12  by pulling door handle  70  on the right frame member  46  of the inside sliding glass door  26  away from the right vertical frame member  20  of the door frame  12 . (See FIG.  3 ). This creates an open space  92  through which ingress and egress across the door frame  12  is permitted. It should be appreciated that locking member  72  and lock receiver  74  provide a redundancy with the coupling mechanism  76 , and need not be used if it desired to avoid making two adjustments in order to open the sliding glass door  26 . It should further be appreciated that unlike conventional assemblies wherein the screen panel must be slid back and forth within the door frame  12  in order to permit ingress and egress across the door frame  12 , no adjustment needs to be made to the screen panel  30  of the sliding glass door assembly  10  of the present invention to allow ingress and egress across the door frame  12 . 
     If it is desired to permit ventilation across the door frame  12 , the sliding glass door assembly  10  of the present invention can be conveniently adjusted to accomplish this result. Both sliding glass doors  26 ,  28  are slid so that their right frame members  46 ,  58  are in sealed engagement with the right vertical frame member  20  of the door frame  12 . (See FIG.  4 ). With both sliding glass doors  26 ,  28  slid to this rightmost position, the passageway  80  of the coupling mechanism  76  in the left frame member  44  of the inside sliding glass door  26  is in alignment with the receiver bore  86  in the left frame member  56  of the outside sliding glass door  28 . The coupling member  78  may then be adjusted within the passageway  80  such that the coupling rod  84  extends into the receiver bore  86 , thereby coupling the inside sliding glass door  26  to the outside sliding glass door  28  such that the two doors slide together within the door frame  12  as a unit, as shown in FIG. 10 a . The sliding glass doors  26 ,  28  may be locked in this position by adjusting the locking member  72  in the right frame member  46  of the inside sliding glass door  26  into engagement with the lock receiver in the right vertical frame member  20  of the door frame  12 . To permit ingress and egress across the door frame  12  with the door assembly  10  in the ventilation arrangement, the locking member  72  is adjusted to unlocked position, and the sliding glass doors  26 ,  28  are slid to the left away from the right vertical frame member  20  of the door frame  12  by pulling on door handle  70  on the right frame member  46  of the inside sliding glass door  26 . (See FIG.  5 ). It should be appreciated that unlike conventional sliding glass door assemblies, the sliding glass door assembly  10  of the present invention permits ingress and egress across the door frame  12  without adjustment of the screen panel  30 . 
     The sliding glass door assembly  10  of the present invention may also be adjusted to allow only partial ventilation across the door frame  12  as shown in FIG.  3 . This arrangement is accomplished by uncoupling the inside sliding glass door  26  from the outside sliding glass door  28  so that the sliding glass doors  26 ,  28  slide separately from each other within the door frame  12 . The outside sliding glass door  28  may then be adjusted to an intermediate position such that neither its left frame member  56  nor its right frame member  58  are in contact with the vertical frame members  18  and  20  of the door frame  12 . The inside sliding glass door  26  is then slid all the way to the right into sealed engagement with the right vertical frame member  20  to prevent ingress or egress across the door frame  12 . Ingress and egress across the door frame  12  may then be permitted by sliding the inside sliding glass door  26  to the left as shown in FIG.  3 . Again, it is not necessary to adjust the screen panel  30  in order to achieve this result. 
     When it is desired to have the screen panel  30  on the right side of the door frame  12 , and to allow ingress and egress through the left side of the door frame  12 , the screen panel  30  may be removed from the door frame  12  by releasing spring loaded pins  88 . The screen panel  30  may then be placed in sealed engagement with the right vertical frame member  20  of the door frame  12 , as shown in FIGS. 7 and 8, by aligning the spring loaded pins  88  with the corresponding screen locking holes  90 . The sliding door assembly  10  would then work the same as described above, except that the left and right distinctions would be reversed. Providing the door handle  70 , the locking member  72 , and the coupling mechanism  76  in both the left frame member  44  and the right frame member  46  of the inside sliding glass door  26  allows for this simple reversal of orientation. 
     It is expected that those skilled in the art will understand that the foregoing description relates merely to preferred embodiments, and that changes and modifications can be made thereto without departing from the scope of the invention as defined in the following claims.

Summary:
An assembly for use in a generally rectangular sliding doorway. The assembly includes two sliding glass doors and a stationary screen that are provided in the doorway. The sliding glass doors can be slid within the doorway to allow access across the doorway, to seal the doorway, or to permit ventilation across the doorway through the screen. The assembly also includes a coupling rod provided in a frame of one of the sliding glass doors to be selectively extended into a frame of the other sliding glass door. The sliding glass doors can be locked together to slide as a unit in a fixed relation to each other. The sliding glass doors can also be locked together to lock the sliding glass doors in a closed position to seal the doorway. The same coupling rod serves to lock the sliding glass doors together in the position where they slide together as a unit and in the closed position. The assembly is fully adjustable to be configured with the screen on the right or left side of the doorway. In standard usage, the glass doors will slide to open and close the doorway, but the screen will remain stationary.