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FIELD OF THE INVENTION 
     The invention relates to a driving and storing mechanism for flexible curtain material that covers openings in a structure which provide protection for the opening from high wind velocity pressure (i.e., hurricanes and tornadoes) and impacts from windborne debris. Instead of a flexible curtain any type of covering including a garage door or other structure made of slats may be used employing the principles of the instant invention. The mechanism of the invention includes a system where a substantially constant tension is maintained on the curtain material as it is unwrapped from its storage roller to close an opening in a structure and as it is wrapped in returning it to the fully stored condition. 
     BACKGROUND OF THE INVENTION 
     It is desired to keep approximately the same amount of tension on the curtain as it is lowered from the completely stored position into the completely dispensed position. Further, it is desired to keep approximately the same amount of tension on the curtain between the storage roller and the driving roller. Constant tension on the curtain between the storage and driving rollers results in the curtain&#39;s smooth storage in a small area. Further, and importantly, constant tension between the storage and driving rollers enables use of a smaller and lower powered electric motor. Employing a variable reference point for the spring of the instant invention enables the maintenance of approximately constant tension in the flexible curtain as it traverses between the open and closed positions and between the closed and open positions. By closed it is meant that the curtain covers the opening in the building and by open it is meant that the curtain does not cover the opening in the building. In the closed position the curtain is fully deployed or dispensed from the storage roller and in its open position the curtain is fully stored or wound on the storage roller. Without a variable reference, the driving motor must use more energy as the curtain progresses from the open position toward a closed position. During rewind of the curtain from the closed position to the open position, constant tension between the driving roller enables smooth winding of the flexible curtain of the storage roller. 
     U.S. Pat. No. 958,605 to Doring discloses a fixed sleeve “c” and a nut “l” having lugs or projections “k.” Nut “l” moves leftwardly and rightwardly as it is driven by threaded shaft “g.” A curtain is affixed to a roller “a” and the roller is affixed to a toothed gear/hub “b.” Gear/hub “b” is rotatable with respect to the fixed sleeve “c.” Gear “b” drives gears “d” and “e” which drive gear “f” in the same direction as gear “b.” Gear “f” is affixed to shaft “g” which is threaded. Rotation of the roller “a” causes the threaded shaft “g” to rotate through nut “l” causing nut “l” to move leftwardly storing energy in the spring as the curtain is pulled downwardly. The spring is fixed at one end, however, and a variable reference is not employed. Energy stored in the spring is released when the curtain is released from a restraint and it is this energy which returns the curtain to its stored position. 
     U.S. Pat. No. 2,842,198 to Prieto discloses a split ring torsion regulator which limits expansion and, hence, tension in a spring. The split ring is adjustable but a variable reference is not employed. 
     U.S. Pat. No. 667,302 to Edwards discloses an apparatus by which the tension of the spring in a roller may be changed or adjusted without the removal of the roller from its brackets or mountings. More specifically, a spring is connected to a roller and to a rotatable part or a spring is connected to a barrel and a rotatable spindle. The rotatable part or the rotatable spindle are adjustable as desired. However, the adjustment is permanent and does not provide a variable reference point for the spring in either instance. 
     U.S. Pat. No. 1,828,623 to G. M. Sacerdote discloses a pulley driven shaft and a spring connected to its shaft and to a roller. When the screen is unwound from the roller the belts will be wound around the pulleys and vice versa. As the screen and belts are thus wound, the diameter of the roller and pulleys vary and the tension upon the screen is such to keep the curtain taut, varying between two limits which are not far apart. 
     U.S. Pat. No. 3,955,611 to Coles et al. discloses an awning construction particularly adapted for mounting on a mobile home. The awning includes an awning shade having one end fixed to an outside wall of the mobile home, and the other end of the awning shade is attached to an awning roller, which roller is pivotedly connected to the same outside wall. The awning roller includes an elongated torque rod which is nonrotatably connected to a pair of support arms. The support arms are pivotedly connected to the outside wall. A tube is rotatably mounted on the torque rod and is secured to the other end of the awning shade. A torsion spring connects the torque rod with the tube to rotate the tube relative to the torque rod and holds the tube up against the wall of the mobile home in its normal condition. A lock  126  releasably locks the tube relative to the torque rod to allow the tube to stay selectively in an extended position away from the side wall. See, FIG.  6 . 
     U.S. Pat. No. 4,013,113 to Frei discloses a shutter which includes a curtain formed of elongated bars hinged to one another at longitudinal edges and guided at their ends in laterally spaced guide grooves extending along opposite sides of an opening to be controlled by the shutter. A rotatable member is mounted in an upper receiving zone, such as a lintel above the opening, and the rolling bar curtain is trained about this member for direction reversal during raising and lowering. The laterally spaced guide grooves extend along the peripheral portion of this rotary member and are then branched to form branch guide grooves extending downwardly from the rotatable element into a recess formed in the lintel or the like. Guide elements, such as pins or rollers on the ends of each bar, cooperated with the branch guide means to conjointly guide the bars to form at least one vertical pile of bars superposed in horizontal orientation in the recess, responsive to raising of the curtain. The rotatable element may be circular or may be polygonal and if polygonal, has sides each conforming to the width of a bar of the curtain. This invention is demonstrative of the complexities of guiding and managing a curtain that is somewhat flexible and made from rigid sections. 
     U.S. Pat. No. 4,478,268 to Palmer discloses a door for closing a vehicular traffic passageway. The door is a curtain fabricated from a hard flexible material. The curtain runs in opposing channels, is mounted on a counterbalanced windup drum and under impact changes weight and moves out of the channels and is wound up to open the vehicular passageway. 
     U.S. Pat. No. 4,601,320 to Taylor discloses a pressure differential compensating door which includes a curtain for closing a doorway having a first upper end, a second lower end and side edges and a counterbalanced curtain winding mechanism having the first end of the curtain attached thereto for raising and lowering the curtain. 
     None of the related art, however, solves the problem of maintaining approximately constant tension between the storage roller and the drive roller throughout the travel of the curtain from a fully stored position to a fully deployed position and back. Further, none of the related art solves the problem of maintaining approximately constant tension between the drive roller and the storage roller so as to enable use of a relatively low power motor. Present designs require the use of a large motor so as to overcome the resistance of a spring connected at one end to a storage roller and at the other end to a fixed structure (ground). Present designs require a large motor because the resistance of the spring increases linearly as the curtain extends toward its fully deployed position. 
     SUMMARY OF THE INVENTION 
     The instant invention is an apparatus for maintaining approximately constant tension of a curtain between a drive roller and a storage roller. The constant tension is achieved by pre-tensioning the curtain between the drive roller and the storage roller and then maintaining approximately the same amount of tension by rotating the reference to which one end of a spring is attached. The rotating reference is a shaft which is affixed to and rotates with a shaft gear. The other end of the spring is affixed to a cylindrical tube member, i.e., the storage roller, upon which the flexible curtain is stored. A motor driven gear drives a gear affixed to the drive roller. The gear affixed to the drive roller in turn drives idler gears which in turn drive the shaft gear. 
     It is an object of the present invention to provide an apparatus for maintaining approximately constant tension on a flexible curtain between a storage roller and a drive roller. Cogs or toothed projections on the driving roller engage apertures in the flexible curtain enabling the curtain to be driven between open and closed positions. 
     It is an object of the present invention to provide an apparatus for storing and driving a flexible curtain which requires a low power motor. A low power motor may be used when the tension between the driving roller and the storage roller is approximately constant between initial (curtain fully stored) and final (curtain fully dispensed) conditions. 
     It is an object of the present invention to provide a method for opening and closing a flexible curtain under approximately constant tension between a storage roller and a driving roller. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevational view of the driving and storing mechanism of the present invention illustrating the curtain material covering an opening (shown in phantom) in a building structure; 
     FIG. 1A is a vertical cross-section of the mechanism shown in FIG.  1  and specifically illustrated as being along the lines  1 A— 1 A of FIG. 2; 
     FIG. 2 is a fragmentary cross-sectional view taken generally along the lines  2 — 2  of FIG. 1A; 
     FIG. 3 is a rear view of the driving and storing mechanism illustrated in FIG. 1; 
     FIG. 4 is a view similar to FIG. 1 but omits the openings in the building structure as seen in phantom in FIG. 1; 
     FIG. 4A is a diagrammatic view taken generally along the lines  4 A— 4 A of FIG. 4 illustrating the arrangement; 
     FIG. 4B is a view taken generally in the same direction as FIG. 4A but showing only the tube member (storage roller) which is used to store the flexible curtain material and the curtain engagement member (drive roller) which is used to engage and drive the curtain material in its up and down movements; 
     FIG. 4C is an enlarged portion of FIG. 4A; 
     FIG. 4D is an enlarged partial cross-sectional view taken generally along the lines  4 D— 4 D of FIG.  4 A and showing the cylindrical tube member (storage roller) upon which the flexible curtain material is wrapped in stored condition; 
     FIG. 4E illustrates an inverted belt drive  97  operating between a pulley affixed to the drive shaft and a pulley affixed to a shaft within the storage roller; 
     FIG. 4F is an enlarged portion of FIG. 4B illustrating the interengagement of cogs/pins of the drive roller with apertures in the flexible curtain; 
     FIG. 5 is an isometric view of a variation in the means for driving the storing mechanism illustrated in the previous figures; 
     FIG. 6 is an elevational view of the electric motor and its connections and as illustrated in FIG. 5; and 
     FIG. 7 is a fragmentary isometric view from another angle illustrating the parts also shown in FIG.  5  and FIG.  6 . 
    
    
     A better understanding of the drawings will be had when reference is made to the Description of the Invention and the claims which follow hereinbelow. 
     DESCRIPTION OF THE INVENTION 
     Referring to FIG. 4D, a cylindrical tube member  40  (sometimes referred to as a storage roller  40 ) has an outer cylindrical surface  41  for the reception of a length of curtain material  22  in a rolled up configuration. The storage roller  40  is mounted in the frame structure of a window opening. See, FIG. 1A as well. This frame structure includes 2×6 inch wooden members  29  and as shown in FIG. 1A, siding  31  covering the exterior of the building and plasterboard or other internal wall structure  32 . Vertical bearing members  35  and  36  are provided in the building structure  28  and serve to position and mount the storage roller  40  and other structures to be described hereinafter. One end of the storage roller  40  at  42  is mounted for rotation in the bearing structure  35  and the other end is mounted for rotation in the bearing member  36 . This is accomplished by a first shaft  44  best seen in the enlarged view of FIG. 4D which has first  45  and second  46  end portions with the first end portion  45  extending coaxially into the tube member  40  and with the second end portion  46  of the first shaft  44  extending exteriorly of the tube member. This second end portion  46  is seen as extending into the vertical bearing member  36  in FIG.  1 A. 
     Still referring to FIG. 4D, a first gear  50  is connected to the second end portion  46  of the first shaft  44  for rotation in unison therewith. A torsion spring  52  as seen in FIG. 4D surrounds the first end portion  45  of the first shaft  44 . First end  53  of spring  52  is connected to the first end portion  45  of the first shaft  44 . Second end portion  54  of spring  52  is connected to sleeve  51  which is affixed to storage roller  40  by pins  56  secured to the storage roller  40  and sleeve  51 . With this construction, it will be apparent to those skilled in the art that a cylindrical tube or storage member  40  and the shaft  44  may be rotationally positioned in a plurality of positions with respect to each other which are dependent on the spring constant and the desired tension between the storage members and the driving roller  70 . This will be referred to hereinafter as pre-tensioning the storage roller  40  relative to the driving roller. 
     Referring to FIGS. 4,  4 A and  4 C, a first idler gear  58  is mounted for rotation about a first idler shaft  59  and it is in meshing engagement with the first gear  50 . The first idler shaft  59  is mounted in the vertical bearing member  36 . A second idler gear  62  is mounted for mounted for rotation about a second idler shaft  63  and gear  62  is in meshing engagement with the first idler gear  58 . The idler shafts are mounted in vertical bearing member  36 . A curtain drive gear  66  is mounted for rotation about a second shaft  67  and it is in meshing engagement with the second idler gear  62 . The second shaft  67  is likewise mounted and supported by vertical bearing member  36 . See, FIG.  1 A. 
     A curtain engagement member,  70 , sometimes referred to herein as a roller drive  70 , is also mounted on the second shaft  67  for rotation therewith and in unison with the curtain drive gear  66 . The curtain engagement member  70  is provided with pins  72  at each of its two end portions which are rotatively or circumferentially spaced from each other and are adapted to fit into openings  74  in the flexible curtain material so that when the drive roller  70  is driven rotatively, it drives the curtain material either up or down depending upon the direction of rotation. 
     Referring to FIGS. 1,  3 , and  4 , drive motor  76  is mounted in the mechanism and has a drive shaft  77  which in turn is rotatively connected to a drive gear  78  which meshes with the curtain drive gear  66 . Rotation of the drive motor in one direction therefore causes the curtain material to be unrolled from the tube member to cover an opening  25  as illustrated in FIG.  1  and in the opposite direction causes the curtain material  22  to fold up onto storage roller  40  to uncover the opening. 
     Guides  79  on opposite sides of the structure (see FIG. 1) are adapted to receive the outer edges of the flexible curtain material to keep it in position as it moves from its lowermost to its uppermost position. A latch  81  (FIG. 2) is adapted to secure the curtain in its lowermost position. 
     FIGS. 5,  6  and  7  are simply different showings of how the drive and storing mechanism can be motorized to be driven between its uppermost and lowermost positions. In these figures where the structure is essentially the same as in FIGS. 1-4, reference numerals 100 units higher have been designated to illustrate the parts. Drive roller  170  is driven by drive gear  166  which, in turn, is driven by the worm gear drive  86 . Drive gear  166  drives idler gear  162  which drives idler gear  158 . Idler gear  158  drives gear  150  which drives the shaft (not seen). 
     The mechanism of FIGS. 5-7 primarily is an alternative to the drive motor  76  shown in the previous drawing and its drive shaft  77  as well as gear  78 . In this showing there has been illustrated a worm gear drive indicated generally by the reference numeral  86  and this worm gear drive includes a worm gear housing  88  and a worm gear reduction housing  90 . See, FIG.  5 . The associated gears (not shown) within these housings are driven from motor  93 . The motor is reversible which enables the mechanism to drive the curtain in either an up direction or a down direction. The drive mechanism in FIGS. 5-7 illustrates variations in drive mechanisms which can be used to couple the drive roller  170  to the storage roller  140 . 
     FIG. 4E illustrates an inverted belt drive  97  operating between pulley  95  affixed to shaft  67  and pulley  96  affixed to shaft  44 . Referring to FIG. 4C, rotation of the drive shaft  78  in a clockwise direction results in rotation of shaft  44  in a counterclockwise direction. Similarly, rotation of the drive shaft  67  in a counterclockwise direction results in rotation of shaft  44  in a clockwise direction. Inverted belt drive maintains this relationship because it is inverted. A motor may still be used to operate a gear affixed to shaft  67  but use of the belt would eliminate the need for the idler gears and the gear  50 . The belt would have to be reasonably tight so as to prevent slippage during pre-tensioning. As with the gearing arrangement set forth in FIG. 4A, it is necessary that the curtain apertures  74  engage at least two of the cogs  72  to insure tensioning of the curtain and positive driving of the curtain. FIG. 4F is an enlarged portion of FIG. 4B illustrating the interengagement of cogs/pins  72  of the drive roller with apertures  74  in the flexible curtain. FIG. 4A illustrates the storage roller  40  placed rightwardly or rearwardly from the drive roller  70 . This insures that the curtain  22  will sufficiently wrap around roller  70  and constantly engage at least two cogs/pins  72 . 
     Referring now particuarly to the detailed drawing of FIG. 4D, it will be appreciated by those skilled in the art that pre-tensioning of the mechanism is accomplished by rotating the cylindrical tube member  40  relative to the shaft  44 . The curtain  22  is affixed to the storage roller  40  by mushroom headed pins  56 . The storage roller is rotated clockwise as viewed in FIGS. 4A or  4 C. Roller  40  rotates clockwise and creates tension in spring  52  as shaft  44  does not turn since the gear train  78 ,  66 ,  62 ,  58  and  50  are locked up through resistance of the gears, the driver roller  70  and the inertia of the drive motor. Sleeve  51  rotates with roller  40  as the curtain is pulled by hand downwardly such that the openings  74  of the curtain material  22  fit over the pins  72  in the drive roller  70 . The relative movement between the storage roller  40  and the shaft  44  creates tension in the torsion spring  52  to a predetermined level and the tension is then maintained by placing the openings  74  over the pins  72 . 
     Referring to FIG. 4B, the curtain  22  extends from the back side of storage roller  40  and engages cogs/pins  72  so as to secure the curtain  22  over the cogs/pins  72 . Cogs/pins  72  are on both sides of the drive roller  70 . Apertures  74  are formed in the curtain  72  where the curtain is folded over onto itself. See, FIG.  4 D. Reference numeral  23  represents the folded portion and stitching  24  secures the folded portion to the main portion of the curtain. 
     The curtain  22  is positioned by the rotation of the drive roller  70 . Usually, the curtain  22  is a three ply curtain having a reinforced polyester sheet laminated between two polymeric plys. As such, the curtain is usually of lightweight construction. 
     Referring to FIG. 4C, as the curtain drive gear  66  is rotated counterclockwise to bring curtain  22  downwardly, idler gear  62  is rotated clockwise, idler gear  58  is rotated counterclockwise and the first gear  50  connected to shaft  44  is rotated clockwise. As indicated in FIG. 4C, all of the gears are the same size such that one rotation of curtain drive gear  66  results in one rotation of first gear  50  in the opposite direction. Any size gears may be used and the relative positioning of the gears may change. It is necessary, however, to maintain the ratio of the drive gear  66  to the first gear  50  in approximately a 1:1 ratio so as to ensure approximately uniform tensioning between the drive roller  70  and the storage roller  40 . The size of the motor drive gear may change without affecting the 1:1 ratio. 
     From the initial condition of the curtain material  22  being fully stored on the storage roller  40 , and hence the diameter of the stored curtain being larger than the diameter of the drive roller  70 , one counterclockwise rotation of drive gear  66  results in one clockwise rotation of first gear  50  and shaft  44  but roller  40  rotates in the clockwise direction (referring to FIG. 4C) less than one rotation thus changing slightly the pretension in the curtain between the storage roller  40  and the drive roller  70 . Those skilled in the art will readily recognize that the diameter of the storage roller  40 , the diameter of the stored curtain material, the spring constant of spring  52 , the size of the gears  50  and  66 , the size of drive roller  70  and its cogs/pins  72 , and the weight of the curtain material  22  will all influence the slight change in pre-tension. 
     As the shaft  44  and cylindrical tube member  40  are rotated to either bring the curtain material down to cover the opening  25  or to move it in the reverse direction in storing the curtain material on the storage roller  40 , this predetermined tension maintains the curtain material taut between the cogs/pins  72  on the drive roller  70  and the storage roller  40 . As a result, the flexible curtain material is maintained in a neat and orderly wrapped up condition without folds or wrinkles. The tension that is provided between the storage roller  40  and shaft  44  remains essentially constant in unwinding and winding up the curtain material. As discussed earlier, the diameter of the curtain material  22  on the storage roller slightly influences the tension between the storage roller  40  and the drive roller  70 . 
     Although this invention has been specifically described for use in connection with a flexible material, those skilled in the art will readily recognize that the principles can be applied to other covering such as garage doors or slatted door coverings. 
     Those skilled in the art will recognize that the invention has been set forth by way of example only and that changes may be made to the invention without departing from the spirit and the scope of the appended claims.

Summary:
The instant invention is an apparatus for maintaining approximately constant tension of a curtain between a drive roller and a storage roller. The constant tension is achieved by pre-tensioning the curtain between the drive roller and the storage roller and then maintaining approximately the same amount of tension by rotating the reference to which one end of a spring is attached. The rotating reference is a shaft which is affixed to and rotates with a shaft gear. The other end of the spring is affixed to a cylindrical tube member, i.e., the storage roller, upon which the flexible curtain is stored. A motor driven gear drives a gear affixed to the drive roller. The gear affixed to the drive roller in turn drives idler gears which in turn drive the shaft gear. A method of using the apparatus is also disclosed.