Patent Publication Number: US-11028639-B2

Title: Low friction high speed roll door at high wind loads

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a United States Non-Provisional Patent Application which claims the benefit of and priority to U.S. Provisional Patent Application No. 62/348,654 filed Jun. 10, 2016. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to high-speed roll up fabric barriers. 
     BACKGROUND 
     High speed roll doors are often used in industry environments that have high traffic, differences in atmospheric temperature and pressure, and high exterior wind conditions. For example, warehouses may employ high speed roll doors to allow forklifts to travel through air-conditioned sections of a building quickly while limiting wind, pressure, temperature, or noise disturbances. 
     High speed roll doors commonly include a flexible curtain made of a fabric or polymer material. The flexible curtain is often opaque but can include windows made of another transparent flexible material. Because of the flexible properties, the flexible curtain needs constraints at its perimeters. For example, a top roller defines the maximal height of the opening and provides source of motion to open and close the roll door; a bottom bar defines the actual height of the opening and provides a gravitational pull for keeping the flexible curtain taught; and two side columns constrains the side edges of the flexible curtain so that the curtain does not give in to wind loads or loads due to pressure differences. 
     When the flexible curtain is under high wind load or high pressure, the constraint of the side columns causes a reactive force perpendicular to the side columns. The reactive force can result in a high frictional force that prevents the normal operation of the roll door, such as to reduce the operation speed or even prevent the movement. This issue can occur both when the flexible curtain is completely deployed (i.e., the door is at closed position) or when the flexible curtain is partially deployed (i.e., the door is partially open). 
     SUMMARY 
     This disclosure relates to high-speed roll up fabric barriers that have reliable and efficient mechanisms to reduce movement friction and to secure the barriers at the closed position when loaded with normal forces in high winds. 
     In a first general aspect, a roll door is movable between an open position and a closed position. The roll door includes a flexible curtain having a pair of opposed side edges. Each side edge is configured to be inserted within a track member. At least one rigid cross-bar is secured to the flexible curtain. The cross-bar extends between the pair of opposed side edges of the flexible curtain. The cross-bar has opposed ends. There is at least one roller secured to each end of the cross-bar. The roller is positioned to move within the track member as the roll door is moved between the open and closed positions. 
     In some embodiments, the at least one cross bar further includes a first rigid bar pivotally connected to a second bar along an axis extending between the opposed side edges of the flexible curtain. The first rigid bar connects to a first section of the flexible curtain and the second rigid bar connects to a second section of the rigid bar. 
     In some other embodiments, the at least one rigid bar connects a first section of the flexible curtain to a second section of the flexible curtain. 
     In yet some other embodiments, the at least one cross bar further includes a wheel secured to each respective end of the cross-bar, the wheel movable within the track member. 
     In some embodiments, the roll door further includes a bottom bar secured to a bottommost portion of the flexible curtain. The bottom bar has a flexible tab extending from an end thereof and is configured to removably engage the track member. 
     In some other embodiments, the flexible tab further includes a stopper member secured thereto. 
     In yet some other embodiments, the roll door further includes a number of spherical members secured to each of the opposed side edges for engaging the track member. 
     In a second general aspect, a roll door movable between an open position and a closed position at an opening of a building structure includes a flexible curtain for shielding wind from entering the building structure. The flexible curtain has a pair of side edges. The flexible curtain is deployable from the open position to the closed position and retractable from the closed position to the open position. The flexible curtain further includes multiple spaced apart gliding spheres that are coupled to the flexible curtain at both side edges. The gliding spheres are disposed within the pair of side columns to support the flexible curtain and allow the curtain to travel at high wind loads under low frictional forces. The roll door also includes a pair of side columns providing guides and supports to the flexible curtain during deployment and retraction. A pair of lateral restrictors is also included. Each restrictor has a base member extending toward the flexible curtain for defining an inner allowable play in an entry direction of the roll door and an angled support member covering an end of the base member and forming a reception angle for receiving the plurality of spaced apart spheres when the flexible curtain is under front wind loads. 
     In some embodiments, the spaced apart gliding spheres are made from ultra-high-molecular-weight polyethylene. 
     In some other embodiments, each of the spaced apart gliding spheres is affixed onto the flexible curtain by means of assembly or by molding. 
     In some embodiments, each of the pair of side columns profiles a rectangular cross section bent from a set of metal sheets. The set of metal sheets forms an inner track for receiving the flexible curtain and the plurality of spaced apart gliding spheres at the side edges of the flexible curtain. Two bent metal sheets may further be included to form the column profile. Each metal sheet may have an end side, a front side, an entrance side, and a track side. The end sides of the two bent metal sheets are affixed to each other for forming the rectangular cross section. 
     In some other embodiments, a pair of brush liners is affixed at the inner track of each of the pair of side columns. Each of the pair of brush liners is angled toward and to contact the flexible curtain. 
     In a third general aspect, a roll door movable between an open position and a closed position at an opening of a building structure includes a flexible curtain shielding wind from entering the building structure. The flexible curtain includes a lower edge and a pair of parallel side columns each guiding and supporting the flexible curtain with a track during the flexible curtain&#39;s deployment and retraction. The pair of side columns has a distance less than a minimum width of the flexible curtain and its lower edge. The lower edge extends at each end a flexible tab into the tracks of the side columns. A drive assembly may be included and operable to deploy the flexible curtain from the open position to the closed position and to retract the flexible curtain from the closed position to the open position. A pair of lock plates each positioned at the floor and inside each of the pair of side columns near the track such that when the flexible curtain is lowered to the closed position, the flexible tab on each end of the lower edge slides into the corresponding lock plate, wherein the pair of lock plates constraining lateral movements of the flexible tabs such that the lower edge stays in place when the roll door is loaded with high wind pressures. 
     In some embodiments, each of the flexible tabs includes a flexible plate that bends elastically and allows the lower edge to be broken off from the tracks of the pair of side columns. The flexible tab further includes a pair of stoppers sandwiching the flexible plate to achieve a thickness variation to engage the lock plates, wherein the pair of stoppers are prevented from exiting the pair of side columns at the lock plates when the roll door is at the closed position. The pair of stoppers is made from ultra-high-molecular-weight polyethylene. 
     In some other embodiments, the door further includes an opening at an upper portion of each of the pair of side columns, wherein the opening allows the flexible tabs to reenter the tracks of the pair of side columns when the roll door is at the open position. 
     In some embodiments, the lower edge further includes an accelerometer for detecting the breaking off of the flexible tab and wirelessly sending the detection to a control unit. 
     In yet some other embodiments, the flexible tabs are made from ultra-high-molecular-weight polyethylene. 
     In a fourth general aspect, a roll door movable between an open position and a closed includes a pair of side channels for guiding a flexible curtain movable between the open and closed positions via a plurality of retention members. Each of the side channels has a back wall, an angular end wall, and a pair of sidewalls. Each of the plurality of retention members further includes a rectangular portion and a non-rectangular portion. The non-rectangular portion is operable to engage the angular end wall at an angle to prevent the retention members from passing through a space between a first of the pair of sidewalls and the angular end wall extending from a second of the pair of side walls, when the flexible curtain is under sufficient loads to pull the plurality of retention members from a neutral position at which the plurality of retention members is not in contact with the angular end wall of the side channels to a contact position at which the non-rectangular portion is pressed against the angular end wall. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of a first embodiment of a high speed roll door. 
         FIG. 2A  is a perspective side view of an end of a wind strut for the roll door of  FIG. 1 . 
         FIG. 2B  is a local front view of the end of the wind strut of  FIG. 2A . 
         FIG. 3A  is a perspective view of a lock plate installed in one of the side columns of the high speed roll door of  FIG. 1 . 
         FIG. 3B  is a perspective view of the lock plate holding the flexible curtain of the high speed roll door of  FIG. 3A . 
         FIG. 4A  is a top view of a flexible tab for engaging the lock plate of  FIG. 3A . 
         FIG. 4B  is a perspective view of the flexible tab shown in  FIG. 4A . 
         FIG. 4C  is a side view of the flexible tab shown in  FIGS. 4A-4B . 
         FIG. 5A  is a perspective view of a second embodiment of a high speed roll door, showing local features inside one of the two side columns. 
         FIG. 5B  is a top view of the local features shown in  FIG. 5A . 
         FIG. 6  is a front view of another embodiment of a high speed roll door. 
         FIG. 7  is a section view of the track in  FIG. 6  taken along the line  7 - 7 . 
     
    
    
     Like elements are referenced with like numerals. 
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a high speed roll door  100  (hereinafter “roll door  100 ”). The roll door  100  is movable between an open position, to allow access or passage through a passageway  105  of a building structure, such as, for example, a loading dock or an area divider of a warehouse, and a closed position, to prevent access or passage through the passageway  105 . As illustrated in  FIG. 1 , the passageway  105  is defined by a pair of jambs  108  and  110 , a floor  112  and a header  114 . In the embodiment illustrated in  FIG. 1 , the roll door  100  includes a flexible curtain  145  that winds onto and unwinds from a drum and is bound at each end by respective tracks  137  that are disposed within side columns  135 . The flexible curtain  145  has a pair of side edges  147 . 
     In operation, a drive assembly  125  moves the flexible curtain  145  between the open and closed positions. According to some embodiments, a second drive assembly  127  is used to operate concurrently with or as a backup to the drive assembly  125 . In the embodiment illustrated in  FIG. 1 , the drive assembly  125  and the second drive assembly  127  are connected to a control terminal  120 , which sends signals to control movement of the roll door  100 . 
     Referring specifically to  FIG. 1 , the roll door  100  includes a bottom bar  130  coupled to the bottommost portion of the flexible curtain  145 . As explained in greater detail below, the bottom bar  130  includes two ends  160  having flexible tab members  330  extending therefrom and into engagement with the tracks  137 . The bottom bar  130 , in some embodiments, includes a sensor  140  for monitoring the position or other condition of the bottom bar  130 . For example, the sensor  140  may be used to detect an impact to the bottom bar  130  and in particular, whether the bottom bar  130  has detached from one or both of the tracks  137 . 
     In operation, the bottom bar  130  extends laterally into the tracks  137  without significantly restricting and/or otherwise resisting the vertical movement of the flexible curtain  145 . As discussed in greater detail below, when the roll door  100  is in the closed position, the ends  160 , and in particular the flexible tabs  330  of the bottom bar  130 , extend into and otherwise engage with the respective lock plates  170  disposed within the side columns  135 . This engagement secures the flexible curtain  145  in the closed position and resists wind and other forces acting on the flexible curtain  145  potentially causing the bottom bar  130  from detaching from the tracks  137 . 
     According to some embodiments, the flexible curtain  145  may include one or more cross-bars (or wind struts)  150 , which support the flexible curtain  145  at spaced apart vertical intervals. As illustrated in  FIG. 1 , the cross-bars  150  extend laterally across the width of the flexible curtain  145  in a generally parallel and horizontal fashion, however, it should be understood that the cross-bars  150  may be otherwise oriented (e.g., in a non-parallel relationship and non-horizontal relationship). In the embodiment illustrated in  FIG. 1 , a single cross-bar  150  is illustrated; but more or fewer cross-bars may be utilized depending on the height of the curtain and the amount of reinforcement that is desired. In operation, the cross-bars  150  provide structural support for the flexible curtain  145  under wind loading conditions thereby acting to transfer the wind-loads acting on the door to the side columns  135 , and thus, to the door jambs  108  and  110 . As described in greater detail below, each of the cross-bars  150  includes an end  152  extending at least partially into the track  137 . 
     Referring to the embodiment illustrated in  FIGS. 2A and 2B , the cross-bar  150  is formed having a first longitudinal bar  230  with a slot  231  to receive and otherwise engage a portion of the flexible curtain  145  to secure the curtain to the cross-bar  150 . The cross-bar  150  further includes a second longitudinal bar  232  pivotally connected to the first longitudinal bar  230  via a hinge  225 . Similar to the first longitudinal bar  230 , the second longitudinal bar  232  includes a slot  233  to receive and otherwise engage a portion of the flexible curtain  145  to secure the flexible curtain  145  to the cross-bar  150 . The hinge  225  has an axis of rotation  226  parallel to the first and the second longitudinal bars  230  and  232  to facilitate rolling and unrolling of the flexible curtain  145  onto the drum when the flexible curtain  145  is moved between the open and closed positions. 
     According to some embodiments, a pair of wheels  210  and  212  is rotatably affixed to each end of the cross-bar  150 , and in one embodiment, to the second longitudinal bar  232 . In operation, the wheels  210  and  212  engage and are otherwise movable within the track  137  such that under high wind loads, the translational movement of the plurality of cross bars  150  will not encounter significant frictional increase while the flexible curtain  145  moves between the open and closed positions. Furthermore, the wheels  210  and  212  are sized so as to be secured and maintained within the track  137  even when high wind forces act against the flexible curtain  145 . 
     The wheels  210  and  212  are supported on shafts  220  and  224  having bearings  228 . The bearing  228  may be a rolling-element bearing, a journal bearing, or other types of bearings, such as a magnetic bearing. In some embodiments, the wheels  210  and  212  are coaxially aligned for providing balanced support while moving inside the track  137 . In operation, the track  137  provides a vertical pathway to support wheels  210  and  212  for vertical movement while at the same time restraining the horizontal movement, deflection and possible separation of the cross-bars  150  from the track  137 . 
     The second longitudinal bar  232  includes a back piece  221 , which provides a first half support for the flexible curtain  145  and a receiving opening  235  aligned with a common axis  227 . The wheels  210  and  212  are mounted concentric to the common axis  227 . The second longitudinal bar  232  further includes a front piece  223  that is coupled to the back piece  221 . The front piece  223  provides a second half support for the flexible curtain  145 . The extended distance between the front piece  223  and the back piece  221  provides an increased stability to the shaft  220  to avoid substantial bending or rotation deformation under loads. As a result of the extended distance, the second longitudinal bar  232  has a greater thickness than the first longitudinal bar  230 . The increased thickness further provides the cross-bar  150  an improved bending resistance for the width of the flexible curtain  145 . The wheels  210  and  212  are positioned beyond the side edges  147  relative to the flexible curtain  145 . Thus, when the flexible curtain  145  is rolled up, the wheels  210  and  212  do not interfere with the rolling operation. 
     Referring specifically to  FIGS. 1, 3A and 3B , the lock plate  170  is illustrated positioned at the floor  112  and inside the side column  135  near or otherwise adjacent the inner track  137  such that the flexible curtain  145 , and in particular, the bottom bar  130 , engages the lock plates  170  for resisting lateral movement when the roll door  100  is in the closed position ( FIG. 3B ). As illustrated, the lock plate  170  is disposed within the side column  135  and not inside or otherwise blocking the passageway formed by the door jambs  108  and  110  and the side columns  135 . Thus, as vehicles, such as, for example, fork lifts, travel through the passageway  105 , the lock plates do not obstruct the passageway  105  and potentially damage a vehicle or otherwise themselves damaged. In the embodiment illustrated in  FIG. 3A , for example, the lock plate  170  includes a base section  326  and an upright section  310 , both being sized to fit within the side column  135  so as to not block or otherwise obstruct the passageway  105  defined by the door jambs  108  and  110 . According to some embodiments, the lock plate  170  may be made from a piece of sheet metal, such as steel. 
     In use, the lock plate  170  may be fastened to the side columns  135  by fasteners  322 . Furthermore, in the embodiment illustrated in  FIG. 3A , for example, the base section  326  includes openings  324  to enable the lock plate  170  to be fastened directly to the floor  112 . Additional mounting openings can be provided to secure the lock plate  170  in place. In  FIG. 3A , the upright section  310  is formed having a top edge  314  with guide chamfers  312  for guiding the bottom bar  130  into a receiving slot  320  when the flexible curtain  145  is lowered and positioned in the closed position. As discussed more fully below, when the roll door  100  is in the closed position  112 , the bottom bar  130  contacts the ground and the flexible tab  330  extending from each end of the bottom bar  130  is positioned inside the receiving slot  320 . 
     Referring now to  FIGS. 4A through 4C , the flexible tab  330  is illustrated extending from the bottom bar  130 . In the embodiment illustrated in  FIG. 4A , the flexible tab  330  is sandwiched between a first portion and a second portion of the bottom bar  130  and is secured via a plurality of fasteners  420 . However, it should be understood that the flexible tab  330  may otherwise be secured to the bottom bar  130 . For example, the flexible tab  330  may be secured to a front or rear surface of the bottom bar  130  by any method of attachment (screws, glue, tape, etc.). Furthermore, while only one flexible tab  330  is illustrated extending from the end of the bottom bar  130 , it should be understood that more than one flexible tab  330  may be utilized. 
     According to some embodiments, the flexible tab  330  may be made from any material that allows for substantial elastic bending. For example, according to one embodiment, the flexible tab  330  is formed of rubber or any other type of elastic polymer to enable deflection or bending thereof. Regardless of the material, the stiffness of the flexible tab  330  should be less than the stiffness of the bottom bar  130  so that the flexible tab  330  bends in lieu of the bottom bar  330  bending. Thus, for example, if a forklift impacts the roll door  100 , the flexible tab  330  is able to deflect or otherwise bend to allow the bottom bar  130  to break away from the tracks  137  without damaging the tracks  137  or the bottom bar  130 . When the bottom bar  130  breaks away, the flexible curtain  145  may fold along the cross bar  150  closest to the bottom bar  130 , where the flexible curtain  145  is laterally restrained (e.g., by the wheels  210  and  220 ). In some other embodiments, the flexible curtain  145  may fold along a line where there is other lateral constraint closest to the bottom bar  130  (such as, for example, constraints by spheres  530  as discussed in  FIGS. 5A and 5B ). 
     According to some embodiments, a flexible tab  330  can include a stopper member  410 , which, as explained in greater detail below, is sized to engage with the lock plate  170  to prevent the flexible tab  330  from separating from the track  137 . With reference to  FIGS. 3A and 3B , the stopper member  410  is positioned on the end of the flexible tab  330  opposite the bottom bar  130 . As such, when the roll door  100  is in the closed position, as best illustrated in  FIG. 3B , the stopper member  410  is disposed on the opposite side of the lock plate  170  from the flexible curtain  145 . As such, when a wind force acting in the direction of arrow  101  acts on the roll door  100 , the size of the stopper member  410  prevents the flexible tab  330  from traveling through the slot  320  (and thus separating from the track  137 ) due to the increased thickness of the stopper member  410  engaging the upright section  310  of the lock plate  170 . As such, when the roll door  410  is in the closed position, the pair of lock plates  170 , in conjunction with the flexible members  330 , prevents the bottom bar  130  from separating from the tracks  137  due to high wind forces. 
     In some embodiments, the stopper members  410  sandwich and are otherwise disposed on both sides of the flexible tab  310  and are secured via a plurality of fasteners  412 . In other embodiments, a stopper member  410  is secured to a single side of the flexible tab  310 . In the alternative, the stopper members  410  can be formed integral with the flexible tab  310  and can be any shape or size. According to embodiments disclosed herein, the size of the stopper members  410  should be large enough to not travel through the slot  320  on the lock plate  170 , but sized small enough to travel through and otherwise exit the tracks  137  so that, as explained above, the bottom bar  130  can break-away from the tracks  137  and thus, the side columns  135  in the event of contact by a vehicle. 
     According to some embodiments, the stopper members  410  may be made from ultra-high-molecular-weight polyethylene or other strong and light materials to engage the lock plate  170 . In some embodiments, the flexible tab  330  may be made from ultra-high-molecular-weight polyethylene in one piece, for example, to mold the flexible tab  415 , the stoppers  410  as one and removes the need to assemble. The stoppers  410  are removable such that in the event a stopper becomes damaged, they can be replaced without replacing the flexible tab  330 . 
     Referring now to  FIGS. 1, 5A and 5B , the flexible curtain  145  includes two side edges  505  extending inside the tracks  137 . The flexible curtain  145  includes a plurality of spaced apart locking or spherical members  530  coupled to the flexible curtain  145  along the side edges  505  and are disposed within the tracks  137  to guide the flexible curtain  145  between the open and closed positions. According to some embodiments, the spaced apart locking members  530  are spherical in shape and are affixed onto the flexible curtain  145  by sandwiching the curtain between two half portions of the spheres  530 . In other embodiments, however, the gliding spheres  530  may be integrally formed with the flexible curtain  145  or positioned on a single side of the flexible curtain  145  and further, can be any size or shape, so long as they can fit within and remain inside the track sections  137  when a force (wind or otherwise) is applied to the flexible curtain  145 . 
     In operation, the spaced apart gliding spheres  530  support the flexible curtain  145  within the tracks  137  for movement of the flexible curtain  145  between the open and closed positions while also prevent separation of the flexible curtain  145  from the tracks  137  under high wind load conditions. Preferably, the spheres  530  are formed of a material having a low frictional coefficient so as to minimize frictional engagement between the spheres  530  and the tracks  137 . In some embodiments, the gliding spheres  530  are made from ultra-high-molecular-weight polyethylene or other lightweight and durable material. 
     Referring specifically to  FIGS. 5A and 5B , each side column  135  contains a rectangular cross sectional area and is formed having a front wall  550 , a rear wall  552  and a pair of sidewalls  554  and  556 . In some embodiments, the side columns  135  includes a pair of lateral restrictors  503  extending from the sidewalls  554  and  556  in order to, as explained in greater detail below, secure and maintain the gliding spheres  530  inside the track section  137  as the flexible panel  145  is positioned between the open and closed positions. 
     According to some embodiments, each of the pair of side columns  135  is formed having a rectangular cross section bent from a set of metal sheets  501 . For example, the side column  135  includes a first section  501   a  bent at three locations to form a bracket having an end side  541   a , and a second section  501   b , bent at four locations to form a bracket having an end side  541   b . In the embodiment illustrated in  FIGS. 5A and 5B , the end sides  541   a  and  541   b  are bolted, welded, or otherwise affixed to each other to form the rectangular cross section. It should be understood that although the side column  135  is formed of two separate pieces  501   a  and  501   b , the column may be otherwise formed. For example, the side column  135  may include more than two pieces  501  or a singular and uniform piece  501  bent or otherwise formed into a tubular rectangular shape with a track opening. Further, in other embodiments, the side column  135  may be formed with different cross sectional profiles, such as circular, triangular, elliptical or others. 
     According to the embodiment illustrated in  FIGS. 5A and 5B , the front wall  550  includes a pair of inwardly turned opposed guide walls  558  and  560  forming a gap  552  to receive and guide the flexible curtain  145  therein. In addition, the opposed guide walls  558  and  560  support anchoring slots  510  for brush liners  512 , which as further discussed below, are configured for sealing action. 
     Each lateral restrictor  503  includes extends from the sidewalls  554  and  556  a sufficient distance forming a gap  540  therebetween ( FIG. 5B ). In the embodiment illustrated in  FIGS. 5A and 5B , each lateral restrictor  503  optionally includes an angled support member  535  covering an end of the restrictor  503  so as to protect the flexible curtain  145  from repetitive wear and potentially damaging contact between the end of the restrictor  503  and the flexible curtain  145 . In addition, the angled support members  535  allow the spherical members  530  to more easily slideingly travel within the track  137 . According to embodiments disclosed herein, the angled support members  535  are formed of a plastic material so as to avoid damage to the flexible curtain  145  and reducing the frictional forces between the spherical members  530  and the restrictors  503  to facilitate the movement of the flexible curtain  145  between the open and closed positions. 
     Referring specifically to  FIG. 5B , each angled support member  535  forms a reception angle  542  for receiving the plurality of spaced apart spheres  530  when the flexible curtain  145  is under front wind loads such that the spheres  530  are pulled toward and in contact with the support members  535 . In the current example, the reception angle  542  is an arc function forming a curved cross section. In other embodiments, the reception angle  542  may have a constant numerical value. The reception angle  542  may have a significant impact on the ability for the spheres  530  to reduce friction when they are in contact with the support member  535 . For example, an optimum contact area size may be achieved by specific profile selected for the reception angle  542  and the materials used in the spheres  530  and the support member  535 . 
     Referring to  FIGS. 5A and 5B , the brush liners  512  are affixed at slots  510  and are angled toward and to contact the flexible curtain  145 . In operation, the brush liners  512  seal the spaced apart spheres  530  from dirt or other contaminants that could enter the inner track  137 . The brush liners  512  may also provide a barrier for noise and serve as a guide for the flexible curtain  145  to move between the open and the closed positions. 
       FIGS. 6-7  illustrate another embodiment of a high speed roll door  600 . The high speed roll door  600  includes a door frame  602  and a flexible door or curtain  604  that is movable along the door frame  602  between an open position and a closed position. While in the open position, the door  604  is at least partially rolled onto a drum  606 . Likewise, when the door  604  is in the closed position, the door  604  covers the door opening to prevent access therethrough. The door  604  is formed of any flexible material, such as for example, a rubber, plastic or fabric material and is defined by a pair of side edges  608   a ,  608   b , a bottom edge  608   c  and a top edge  608   d . In the embodiment illustrated in  FIG. 6 , the top edge  608   d  is secured to the drum  606 , a bottom bar  610  is secured to the bottom edge  608   c , and a plurality of spaced apart retention members  612  are secured on or generally adjacent to the side edges  608   a  and  608   b , as illustrated in  FIG. 9  and as explained in greater detail below. 
     In the embodiment illustrated in  FIGS. 6-7 , the door fame  602  includes a right side channel  614 , a left side channel  616 , and an overhead transverse member  618  that extends between the upper ends of the right and left side channels  614  and  616 . In the embodiment illustrated in  FIG. 6 , the transverse member  618  houses and/or otherwise supports the drum  620  and a motor  622  for positioning the door  604  between the open and closed positions. 
     In the embodiment illustrated in  FIG. 6 , the door  604  generally rectangular in shape and is slightly wider than a distance between the right and left side channels  614  and  616  so that the main body  608 , and in particular, the side edges  608   a  and  608   b , extends at least partially inside the right and left side channels  614  and  616 . 
       FIG. 7  is a cross sectional view of the side channel  616  taken along the line  7 - 7  of  FIG. 6 . It should be understood that the side channel  614  is formed having the same configuration; thus, for simplicity, discussion will be limited to the side channel  616 . As illustrated, the channel  616  includes two parallel and spaced apart side walls  624  and  626  that are oriented generally parallel to the door  604 . The side wall  624  is supported by the back wall  628 , which together forms a first right angle piece  652 . The side wall  626  further includes a back wall  654  and an angular end wall  630 , the angular end wall  630  extending to prevent and/or otherwise resist the retention members  612  from exiting the side channels  616  due to lateral forces acting on the door  604  (i.e., wind, unwanted contact on the door, etc.). In particular, end wall  630  angularly extends from the end of the wall  626  to reduce the gap in which the curtain extends through to prevent or otherwise resist movement of the retention members  612  from exiting the side channel  616 . According to some embodiments, the components of the side channel  616 , such as the right angle piece  652  and angle piece  654 , are formed from materials of a high rigidity to withstand designed wind and other loads without being plastically deformed and otherwise damaged. 
     According to embodiments disclosed herein, the retention members  612  are formed having a first member  630  and a second member  632  that attach together and are otherwise secured to respective opposite sides of the door  604 . In  FIG. 7 , the member  630  contains a generally rectangular cross section and the second member  632  includes a sloped or angular portion  633  having a surface that is sloped at an angle to correspond to the slope of the angular end wall  630 . Thus, as explained in greater detail below, during movement of the door  604  between the open and closed positions, the angular portion  633  slideably abuts against the angular end wall  630 . 
     According to some embodiments, each of the members  630 ,  632  are secured together via at least one fastener, such as, for example, a threaded screw, that extends through the door  604  and engages threads in a corresponding threaded interior opening in the member  630  and/or  632 . In other embodiments, each member  630  and  632  can be secured directly to each side of the door  604  via an adhesive or otherwise. According to embodiments disclosed herein, a plurality of retention members  612  are coupled in an aligned, spaced-apart relationship along the right and left side edges  608   a  and  608   b  of the main body door  604  to guide and retain the door  604  within the door frame  602 , as schematically illustrated in  FIG. 6 . The retention members  612  may be made of any type of rigid material such as a rubber, plastic, or a metal material. In use, if the door  604  receives an impact in the direction of arrow  634  ( FIG. 7 ), for example, the retention members  612  engage the right and left side channels  614  and  616  to retain the door  604  within the door frame  602 . 
     In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as “left” and right”, “front” and “rear”, “above” and “below” and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms. 
     In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear. 
     In addition, the foregoing describes some embodiments of the disclosure, and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive. 
     Furthermore, the disclosure is not to be limited to the illustrated implementations, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the disclosure. Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.