You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION  
       [0001]     The field of the invention relates to a curtain that forms a seal with the frame of an opening such as a window or door as the curtain is urged across that opening. The curtain is durable so that it is able to withstand substantial external pressure without breakage.  
       BACKGROUND OF THE INVENTION  
       [0002]     The use of sealed curtains is known in the prior art. Generally, a sealed curtain apparatus comprises a curtain and tracks along the frame of an opening such as a door or window. The edges of the curtain are engaged by the tracks. As the curtain is moved towards a position covering the opening, the edges of the curtain travel along the tracks. The benefit of this design is that the sealed curtain prevents matter such as insects and debris from passing through the space between the curtain and the frame. However, because the curtain is sealed, the apparatus becomes less durable because it cannot yield to external forces. With unsealed curtains, an external force applied to the curtain will merely briefly displace the curtain from the door or window frame. With sealed curtains, the engagement of the curtain edges with the tracks on the frame prevents the curtain from becoming displaced. Consequently, an external force applied to the sealed curtain may cause stress on the curtain leading to breakage.  
         [0003]     In this respect, the durable sealing curtain according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus which provides a seal between the edges of a curtain and the frame of an opening such as a door or window that is better able to withstand the application of substantial external forces without suffering failure of the apparatus.  
         [0004]     Furthermore, in the prior art, the more tautly a sealed curtain is pulled across an opening, the more difficult it generally is to slide the curtain along the tracks. In this respect, the durable sealing curtain according to the present invention allows the curtain to be loosened while urged open or shut and then returned to a taut position when the curtain is in place.  
       SUMMARY OF THE INVENTION  
       [0005]     In view of the foregoing disadvantages inherent in the known types of sealed curtains present in the prior art, the present invention provides an improved apparatus wherein the same is able to withstand the application of substantial external forces without suffering failure of the apparatus and provides a more easily slidable curtain that is still taut when the curtain is in place.  
         [0006]     To attain this, the preferred embodiment of the present invention is a sealed curtain which preferably comprises a pair of tracks slidably attached to opposite sides of an opening such as a door or window, a curtain having edges engaged by the tracks, and spring systems attached to each track, whereby the spring systems urge the tracks outwardly to maintain the curtain taut yet allow the tracks to slide inwardly towards the center of the opening so that the curtain does not endure excessive pressure upon application of an external force. At least one track preferably also includes a cam mechanism that is operative to urge the track inwardly to decrease tension on the curtain and thereby allow the curtain to be more easily raised or lowered, after which, the cam mechanism can be disengaged to allow the track to return to its outwardly biased position, thus returning the curtain to a taut condition. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The invention will be better understood when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:  
         [0008]      FIG. 1  is a perspective view of the preferred embodiment of the present invention.  
         [0009]      FIG. 2  is a sectional view of the preferred embodiment taken along line  2 - 2  of  FIG. 1 .  
         [0010]      FIG. 3  is the sectional view of  FIG. 2  with the curtain displaced away from the plane of the opening by an external force in the direction of the arrows.  
         [0011]      FIG. 4  is a sectional view of an alternate embodiment of the present invention comprising tracks on each side of the opening designed for holding two curtains.  
         [0012]      FIG. 5  is a detailed view of an alternate embodiment of the present invention showing a cam mechanism disengaged from the track to keep the curtain taut.  
         [0013]      FIG. 6  is a detailed view of the embodiment of  FIG. 5  showing the cam mechanism engaging the track to release tension from the curtain.  
         [0014]      FIG. 7  is an exploded perspective view of the embodiment of  FIG. 5 .  
         [0015]      FIG. 8  is a perspective view of an alternate track comprising a diagonally-shaped slot.  
         [0016]      FIG. 9  is a perspective view of an alternate embodiment of the present invention comprising a rod attached to each track for engaging the edge of the curtain.  
         [0017]      FIG. 10A  is a sectional view of the embodiment of  FIG. 9  taken along line  10 - 10  of  FIG. 9 .  
         [0018]      FIG. 10B  is a sectional view of an alternate embodiment of the invention of  FIG. 10A  showing each hem of a multi-layered curtain located on the side of the rod opposite the opening.  
         [0019]      FIG. 11  is a perspective view of an alternate embodiment of the present invention designed for horizontal movement of the curtain across a door frame.  
         [0020]      FIG. 12  is a sectional view of the embodiment of  FIG. 11  taken along line  12 - 12  of  FIG. 11 .  
         [0021]      FIG. 13  is a sectional view of an alternate embodiment of the invention of  FIG. 1I  comprising sloped floor tracks above the floor plane. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     The curtain apparatus is indicated generally by the numeral  10 . The curtain apparatus  10  is designed to be attached to the frame of an opening  4  such as a door or window. However, the invention does not require the use of a pre-existing frame and could be practiced whereby the invention is incorporated into a prefabricated frame. The curtain apparatus  10  has a first track  1  and a second track  2 . The first track  1  is slidably attached to a first frame member  5  of the opening  4 . The second track  2  is slidably attached to a second frame member  6  of the opening  4 . The curtain apparatus  10  has a curtain  7 . The lateral edges  11  of the curtain  7  and the lateral edges  12  of the tracks  1 ,  2  are each shaped to allow the curtain edges to be engaged by the lateral edges of the tracks. This engagement is preferably accomplished with U-shaped or V-shaped curtain edges  11  and track edges  12 . Where the curtain edges  11  are V-shaped, the apex of the curtain edges  11  are preferably heat sealed or hemmed. However, what is important is that the curtain edges  11  and track edges  12  are sufficiently engaged to prevent the curtain  7  from detaching from either track  1 ,  2 . The curtain edges  11  are of sufficient rigidity so that they remain engaged by the track edges  12 . The engagement of the curtain edges  11  by the track edges  12  allow the curtain  7  to be slidably engaged by the tracks  1 ,  2  so that the curtain  7  may be positioned at any location along the opening  4 . The U-shaped or V-shaped fold in the curtain edges  11  remains present when the curtain  7  is rolled.  
         [0023]     At any given position, the portion of the curtain  7  not covering the opening  4  is wound around a rotatable shaft  51 . As the curtain  7  is urged to cover the opening  4 , the shaft  51  rotates to unwind the curtain  7 . As the curtain  7  is urged to uncover the opening  4 , the shaft  51  rotates in an opposite direction to wind the curtain  7  around the shaft  51 . Rotation of the shaft  51  is preferably controlled by a driving mechanism  53 , which is preferably motorized. However, the driving mechanism  53  may be manually operated and also may include a counter spring. A bracket  54  is attached to each frame member  5 ,  6  to support the shaft  51 . The curtain  7  has a leading edge  55  that preferably has a weighted member  56  hemmed therein.  
         [0024]     In an alternate embodiment shown in  FIGS. 9 and 10 A, the tracks  1 ,  2  each have a rod  40  attached thereto. In this embodiment, each track  1 ,  2  preferably has an extension  43  at one end and a guide  44  at the opposite end. The lower end of the rod  40  is preferably fixedly attached to the rod extension  43 . The rod guide  44  has an opening therethrough for receiving the upper end of the rod  40 . Each lateral edge of the curtain  7  has a hem  41  forming an elongated channel  42  for slidably receiving a rod  40 . In an alternate embodiment, the curtain may be multi-layered with a single channel along each lateral edge. The use of a multi-layered curtain allows air to become trapped between the layers so that the apparatus  10  may provide greater insulation. As best shown in  FIG. 10B , this multi-layered curtain design may also be practiced whereby each hem  41  is located on the side of a rod  40  opposite the opening  4 . Similarly, this design may also be practiced without hems  41  whereby the multi-layered curtain is comprised of a continuous material surrounding both rods  40 .  
         [0025]     Each track  1 ,  2  preferably has two spring mechanisms  8  that bias the track away from the opening  4 , thereby keeping the curtain  7  taut. The spring mechanisms  8  allow the tracks  1 ,  2  to move inwardly towards the opening  4  in the event an external force is applied to the curtain  7 , thus reducing the possibility of damage to the curtain  7 . The spring mechanisms are preferably placed near the opposite ends of each track  1 ,  2 . Each spring mechanism  8  preferably comprises a first post  13  and a second post  14 , each fixedly attached to a track  1 ,  2 . The first and second posts  13 ,  14  are preferably screws. The first post  13  and second post  14  are preferably positioned in such a manner whereby a line intersecting both posts  13 ,  14  would be substantially parallel to the line dividing the frame members  5 ,  6  and the opening  4 . Approximately equidistant from the first post  13  and the second post  14  is a connecting member  15  that connects the tracks  1 ,  2  to the frame members  5 ,  6 . The connecting member  15  is preferably on the opposite side of the line intersecting the first post  13  and the second post  14  from the opening  4 . A horizontal slot  16  is cut into each track through which the connecting member  15  passes. The slot  16  allows the tracks  1 ,  2  to move relative to the connecting member  15  and thus relative to the frame members  5 ,  6 . Consequently, when an external force is applied to the curtain  7 , the slot  16  allows the tracks  1 ,  2  and curtain edges  11  to move inwardly so that the external force is not as likely to damage the curtain  7  or the seal of the edges  11 . A spring  17  is preferably attached at its first end to the first post  13  and at its second end to the second post  14 , therebetween engaging the connecting member  15  to bias the tracks  1 ,  2  away from the opening  4 . The spring  17  can be a coil or any flexible, resilient member.  
         [0026]     With no external forces applied to the apparatus, the first track  1  abuts the first frame member  5  and the second track  2  abuts the second frame member  6 . As best shown in  FIGS. 2-3 , both tracks  1 ,  2  are on the same side of their respective frames  5 ,  6 , referred to as the track side  30  of the apparatus  10 . The opposite side of the apparatus  10  is the non-track side  31 . As best shown in  FIG. 3 , if an external force is applied originating from the non-track side  31 , then the edges of the track  12  are not only able to slide inwardly towards the opening  4 , but are also able to separate from the frame and move in the direction of the force. This movement allows even less stress to be borne by the curtain  7  and thus less chance that the curtain  7  will fail. Preferably, the tracks  1 ,  2  are on the inside of the building whose door or windows are sought to be covered by the curtain  7  of the present invention, thus lessening the opportunity for the apparatus  10  to be vandalized or disabled by individuals outside of the building. In this design, external forces such as wind would always originate from the non-track side  31 . While the apparatus is still able to withstand forces originating from the track side  30 , the ability of the track edges  12  to separate from the frame members  5 ,  6  allows the apparatus to withstand even greater forces originating from the non-track side  31 . So that the track edges  12  may separate from the frame members  5 ,  6 , the connecting member  15  is preferably a bolt where the head of the bolt prevents the tracks  1 ,  2  from completely detaching from the frame members  5 ,  6 , but is not completely tightened to maintain the tracks  1 ,  2  flush with the frame members  5 ,  6 , thereby allowing the tracks  1 ,  2  to move in the plane perpendicular to the plane of the opening  4 . While such positioning of the connecting member  15  allows the track edges  12  to separate from the frame members  5 ,  6  upon the application of an external force, it is preferable that, in the absence of such a force, the track edges  12  abut the frame members  5 ,  6 . Thus, as best shown in  FIGS. 2-3 , a compression spring  101  and a washer  102  are preferably located between the head of each connecting member  15  and its corresponding tracks  1 ,  2 . The tension of the compression springs  101  are preferably weak enough to permit the track edges  12  to separate from the frame members  5 ,  6  upon the application to the apparatus  10  of an external force, yet strong enough to urge the track edges  12  to return to their original positions abutting the frame members  5 ,  6  upon the termination of such external force.  
         [0027]     In an alternate embodiment shown in  FIG. 4 , the present invention has a track on both the first frame  5  and the second frame  6 , wherein each track has at least two slightly offset substantially U-shaped track edges  12  for receiving the edges of a plurality of curtains  7 . Consequently, this embodiment allows for at least two curtains  7  to be pulled across the same opening  4 . Most preferably, the curtains  7  in this embodiment would be made of different materials, such as where one curtain  7  is made of mesh to allow some visibility and the other curtain  7  is opaque. Since the curtains  7  are on different track edges  12 , this embodiment allows the user to close either curtain  7 , for example the mesh or opaque curtain  7  as he or she desires.  
         [0028]     In the embodiment of the invention shown in  FIGS. 5-7 , the apparatus  10  has a cam plate  20 . While the apparatus  10  could have a cam plate  20  on each track  1 ,  2  of the apparatus  10 , the cam plate  20  is preferably on only one track of the apparatus  10 , the description herein showing the cam plate mounted adjacent track  2 . The cam plate  20  abuts at least one fixed member, in this case connecting member  15  performs the function of the fixed member, and at least one mobile member, in this case fixed post  14  performs the function of the mobile member. The fixed member  15  is attached to the frame member  6  and the mobile member  14  is attached to the track  2 . The cam plate  20  has a diagonal cam surface  23  in abutment with fixed member  15 .  
         [0029]     When the cam plate  20  is activated by being urged along the track  2 , the cam surface  23  engages the fixed member  15 , thereby urging the cam plate  20  towards the opening  4 . Since the cam plate  20  abuts mobile member  14 , the urging of the cam plate  20  towards the opening  4  also causes the mobile member  14  to be urged towards the opening  4 . Since the mobile member  14  is attached to the track  2 , the result of the activation of the cam plate  20  is that the track  2  is urged toward the opening  4 . The urging of the track  2  towards the opening  4  decreases tension on the curtain  7 . Consequently, the curtain  7  is less taut and is easier to slide open or closed when the cam plate  20  has been engaged. While the cam plate  20  may be engaged through the manual manipulation of a lever  26 , this embodiment may also be practiced by using an automated device where, for example, the cam plate  20  is activated while the curtain  7  is being opened or closed. Once the curtain  7  reaches a predetermined setting, a sensor detects this positioning and the cam plate  20  is disengaged and the curtain  7  is pulled taut. The cam plate  20  preferably has a securing notch  50  adjacent to the cam surface  23 . When the cam plate  20  is activated by being urged along the track  2 , cam surface  23  slides along fixed member  15  until fixed member  15  is positioned within the securing notch  50 , best shown in  FIG. 5 , thereby securing the cam plate  20  as shown in  FIG. 6 .  
         [0030]     While the preferred embodiment accomplishes the aforementioned camming action through a track  2  having an abutting cam plate  20 , another embodiment shown in  FIG. 8  achieves a similar action without the use of a cam plate  20 . In this embodiment, the slot  21  is angled upwardly and inwardly towards the opening  4 . While such features may be present, this embodiment does not require a spring assembly  8 . This embodiment requires at least one fixed member  22  located within the slot  21 . The diagonally-shaped slot  21  described above creates the cam surface  23  described in other embodiments of this invention. A lower shelf  26  is formed on the bottom of the track  2  and is preferably substantially perpendicular to the track  2 . Using this construct, the track  2  may be urged upwardly and inwardly towards the opening  4 , causing the curtain  7  to be loosened while it is urged in either direction along the track. When the curtain  7  is lowered, the leading edge  55  will engage shelf  26  and force shelf  26  in a downward direction. Since the shelf  26  is connected to the track  2 , the track  2  is thus urged downwardly and outwardly from the opening  4 , thus tensioning the curtain  7 .  
         [0031]     While the most common embodiment of the invention is where the curtain  7  is urged upwardly and downwardly over an opening  4  such as a door or window,  FIGS. 11-13  show alternate embodiments where the curtain  7  is urged sideways over an opening  4  such as a patio door. In these embodiments, the features are substantially the same, but rotated ninety degrees. For example, the first  1  and second tracks  2  are upper and lower tracks rather than left and right tracks as in the most common embodiment. However, the lower track will be referred to as the floor track  25  and the lower frame member as the floor frame member  24 . The first embodiment of this design, as shown in  FIG. 12 , has a floor track  25  below the plane separating the floor frame member  24  from the opening  4 . The second embodiment of this design, as shown in  FIG. 13 , has a floor track  25  mounted on top of the floor frame  24 . In this embodiment, the floor track  25  has a ramped front end  27  and back end  28 . The upper surface of the floor track  25  is substantially horizontal. The angle of the ramped front end  27  and back end  28  is preferably less than or equal to 45°, more preferably less than or equal to 35°, and even more preferably less than or equal to 25°. This allows the opening  4  to be traversed with reduced risk of serious injury from tripping over the floor track  25  due to the gentle sloping nature of the floor track  25 .  
         [0032]     It is to be understood that the forms of the invention shown and described are preferred embodiments thereof and that various changes and modifications may be made therein without departing from the spirit of the invention or scope as defined in the following claims.

Summary:
A durable sealing curtain assembly preferably comprising a pair of tracks slidably attached to opposite sides of an opening such as a door or window, a curtain having its lateral edges engaged by the tracks, and spring systems attached to each track, whereby the spring systems urge the tracks outwardly to maintain the curtain taut yet allow the tracks to slide inwardly towards the center of the opening so that the curtain does not endure excessive pressure upon application of an external force. At least one track preferably also comprises a cam mechanism that is operative to urge the track inwardly to release tension from the curtain and thereby allow the curtain to be more easily raised or lowered, after which, the cam mechanism can be disengaged to allow the track to return to its outwardly biased position, thus returning the curtain to a taut condition.