Patent Publication Number: US-7588045-B2

Title: Collapsible structure with door mechanism

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of collapsible structures. More specifically, the present invention pertains to door mechanisms for simplified and unobstructed passage through the entranceway of a collapsible structure. 
     BACKGROUND OF THE INVENTION 
     Collapsible structures such as vestibules and tents are useful in a wide variety of applications for providing shelter and storage from the elements. Vestibules, for example, are frequently used in outdoor applications for sheltering and storing personal belongings, backpacks, cooking utensils, mobility devices, etc. from elements such as wind or moisture. These structures are generally available as either a stand-alone model for use independent of another structure, or as an adaptive structure configured to attach to an adjacent vehicle or structure. In certain models, the vestibules may have a modularizing feature that permits multiple structures to be attached together. 
     Entry into the collapsible structure is generally accomplished through an entranceway suitably dimensioned to permit access into or out of the interior of the structure. A door, panel, flap, screen, or other door mechanism equipped with a zipper, Velcro®, snap-fitting or other fastening means may be employed to seal the structure from the outside, or to block access to other connected structures (e.g. an adjacent vestibule, tent or vehicle). In some designs, the wall containing the entranceway may include a number of support members that provide additional strength for the collapsible structure. The collapsible structure may include, for example, several vertically oriented poles positioned along the wall containing the entranceway to prevent the wall from sagging or bowing from the weight supported above. In some designs, a raised lip or lower doorway edge is also employed to laterally tension the collapsible structure to reduce swaying or other horizontal motion that can affect the structural integrity of the structure. 
     Access through conventional door mechanisms can often prove difficult, particularly for individuals confined to a wheelchair, stroller, or other mobility device. The zipper, Velcro® or snap-fitting fasteners used by many prior art devices to seal the door mechanism are difficult and, in some cases impossible, to operate for those individuals who lack the manual dexterity to activate the fastener. In those designs employing a zipper, for example, the user must be capable of reaching along the entire perimeter of the entranceway to zip and/or unzip the zipper. This may pose a significant hardship for individuals confined to a mobility device since certain areas along the path of the zipper may be beyond the individual&#39;s reach. Moreover, the support members used to provide vertical and lateral support to the structure may, in certain cases, interfere with the wheels or feet of the mobility device as it enters or exits through the entranceway. As a result, there is a need in the art for a door mechanism that permits simplified and unobstructed passage through the entranceway of a collapsible structure. 
     SUMMARY OF THE INVENTION 
     The present invention pertains to door mechanisms for simplified and unobstructed passage through the entranceway of a collapsible structure. In one exemplary embodiment, a door mechanism adapted to fit within an entranceway of the collapsible structure may be configured to move between an open position and a closed position. The door mechanism may comprise a door formed from a flexible material, and may include one or more reinforcement members that support and provide shape to the door. The door mechanism can be ergonomically designed to permit simplified and unobstructed passage through the entranceway of the collapsible structure, reducing the amount of dexterity required to operate the door. The door mechanism can be utilized in either a stand-alone collapsible structure, or in an adaptive structure for use with a vehicle, tent, or other adjacent structure. 
     In one exemplary embodiment, the door mechanism may include a fan-shaped door constructed from a flexible material adapted to fold upon itself and away from the entranceway. The fan-shaped door may include a number of reinforcement members that provide structural support to the door. An attachment joint operatively coupled to at least one of the reinforcement members may be used to pivotally secure the members to the structure, allowing the fan-shaped door to fan between an open position and a closed position. In some embodiments, a hook, clip, clamp, pole or other suitable fastener may be utilized to secure the door to the structure once closed. 
     In another exemplary embodiment, the door mechanism may comprise one or more swinging or café-style doors configured to move between an open position and a closed position. A closure mechanism operatively coupled to each door may be configured to automatically close the doors during periods of nonuse. The closure mechanism may include, for example, a flexible cable or cord operatively coupled at one end to the door and at the other end to a counterweight. The flexible cable or cord may be threaded through a number of eyelets or pulleys that allow the counterweight to pull the doors shut in the absence of a sufficient force applied thereto. In some embodiments, a fastener can be used to secure the doors together once closed. 
     In another exemplary embodiment, the door mechanism may comprise a sliding door adapted to retract within a double-layered wall of the collapsible structure. The sliding door may be configured to slide along, for example, a guiding member such as a mesh strap that extends laterally across the bottom portion of the entranceway. The sliding door may be releasably secured to the guiding member using, for example, a retaining strap equipped with a snap fitting. In some embodiments, an optional threshold located along the bottom portion of the entranceway may also be utilized to guide the door as it is moved from an open position to a closed position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative collapsible structure in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a perspective view showing another illustrative collapsible structure attached to a tent; 
         FIG. 3  is a perspective view showing another illustrative collapsible structure attached to a vehicle and other structure; 
         FIG. 4  is a perspective view showing another illustrative collapsible structure attached to a number of other structures; 
         FIG. 5  is a fragmentary elevation view of a door mechanism for use with an illustrative collapsible structure; 
         FIG. 6  is an exploded fragmentary elevation view showing an attachment joint in accordance with an exemplary embodiment of the present invention; 
         FIG. 7  is a fragmentary elevation view showing an attachment joint in accordance with another exemplary embodiment of the present invention; 
         FIG. 8  is a fragmentary elevation view showing an attachment joint in accordance with another exemplary embodiment of the present invention; 
         FIG. 9  is a fragmentary elevation view of an exemplary fastener used to secure the door to the collapsible structure; 
         FIG. 10  is another fragmentary elevation view showing the fastener of  FIG. 9  in an engaged position; 
         FIG. 11  is a fragmentary elevation view of a fastener in accordance with another exemplary embodiment of the present invention; 
         FIG. 12  is another fragmentary elevation view showing the fastener of  FIG. 11  in an engaged position; 
         FIG. 13  is a cross-sectional view taken along line  13 - 13  illustrated in  FIG. 12 ; 
         FIG. 14  is a fragmentary elevation view of a fastener in accordance with another exemplary embodiment of the present invention; 
         FIG. 15  is another fragmentary elevation view showing the fastener of  FIG. 14  in an engaged position; 
         FIG. 16  is a fragmentary elevation view showing the door mechanism of  FIG. 5  in a first position; 
         FIG. 17  is another fragmentary elevation view showing the door mechanism of  FIG. 5  in a fully open position; 
         FIG. 18  is a fragmentary elevation view of another exemplary door mechanism for use with a collapsible structure; 
         FIG. 19  is a fragmentary elevation view showing the door mechanism of  FIG. 18  in a closed position from a vantage point within the interior of the collapsible structure; 
         FIG. 20  is another fragmentary elevation view showing the door mechanism of  FIG. 18  in an open position from a vantage point within the interior of the collapsible structure; 
         FIG. 21  is an exploded fragmentary elevation view showing a locking mechanism in accordance with an exemplary embodiment of the present invention; 
         FIG. 22  is a fragmentary elevation view of another exemplary door mechanism for use with a collapsible structure; 
         FIG. 23  is another fragmentary elevation view showing the door mechanism of  FIG. 22  in an open position; 
         FIG. 24  is another fragmentary elevation view showing the door mechanism of  FIG. 22  in a slight open position from a vantage point within the interior of the collapsible structure; and 
         FIG. 25  is an exploded fragmentary elevation view showing the attachment of the door mechanism to the collapsible structure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Although examples of construction, dimensions, and materials are illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized. 
     As indicated above, the present invention is directed generally to an ergonomically designed door mechanism that provides simplified and unobstructed passage through an entranceway of a collapsible structure. While the various embodiments depicted herein are described specifically with respect to door mechanisms for vestibules, it should be understood the present invention is intended for use in a wide variety of structures including, but not limited to, tents, gazebos, screen-porches, domes, ice-houses, sunshades/wind blocks, canopies, cabanas, yurts, or the like. 
     Referring now to  FIG. 1 , a collapsible structure  10  employing a door mechanism  12  in accordance with an exemplary embodiment of the present invention will now be described. Collapsible structure  10 , illustratively a vestibule, includes a roof structure  14  and a number of walls  16 . The roof structure  14  and walls  16  of the collapsible structure  10  are formed from a flexible material that can be easily stretched to assume a particular shape with the aid of a collapsible support frame  18 . For example, the roof structure  14  and walls  16  can be made from Nylon, plastic tarpaulin, or other lightweight material commonly used in the construction of tents or the like. In certain embodiments, the roof structure  14  and walls  16  may be made from silicon impregnated Nylon, which is relatively lightweight and breathable, and which provides excellent resistance to moisture. The materials used in forming the roof structure  14  and walls  16  can be selected for their ability to easily fold and collapse into a protective bag or other storage means. Other factors such as durability, cost, opacity, weight, and ease of manufacturing may also be considered in the selection of materials used to construct the roof structure  14  and walls  16 . 
     The collapsible support frame  18  may include a number of vertical support members  20  and roof support members  22 , which in combination provide support and shape to the roof structure  14  and walls  16 . The roof support members  22  overlie and support the roof structure  14  from above, pitching the roof structure  14  in a slight upward slope. In use, the roof support members  22  provide additional lateral support for the collapsible structure  10 , reducing swaying or shifting caused by wind or other external force. The vertical support members  20  may be attached to the roof support members  22  at a number of joints  26  disposed about the upper corners of the walls  16 . From these joints  26 , the vertical support members  20  extend downwardly to the bottom corners  28  of each wall  16 . The vertical support members  20  can be secured to the collapsible structure  10  using, for example, a holster, pin, grommet, hook, or other suitable fastener. 
     In certain embodiments, the vertical support members  20  and roof support members  22  may each be formed from poles that can be bent or flexed slightly during assembly. The support members  20 ,  22  may comprise a lightweight material such as fiberglass, carbon fiber, polyvinylchloride (PVC), or aluminum. A number of sleeves  24  attached to the roof structure  14  and portions of the walls  16  may be configured to slidably receive the support members  20 ,  22  therein. The sleeves  24  may be sewn onto or otherwise attached to the material forming the roof structure  14  and walls  16 , and function by holding the support members  20 ,  22  in place adjacent to the material. 
     The illustrative collapsible structure  10  depicted in  FIG. 1  is configured for use as a stand-alone shelter for storing personal belongings or supplies, or for use as a common gathering place. The collapsible structure  10  may include an entranceway  32 , which, as is discussed in greater detail below, may be equipped with a door mechanism  12  to facilitate passage through the entranceway  32  without requiring a zipper, Velcro®, snap-fitting, or other similar fastener typically employed to seal such structures. A screen door, window or other opening  34  located adjacent or opposite the wall containing the entranceway  32  may also be employed, if desired, to open the interior space of the structure  10  to the outside, or to permit access to an adjacent structure (not shown). 
       FIGS. 2-4  illustrate variations of the collapsible structure  10  similar to that depicted in  FIG. 1 . In  FIG. 2 , a collapsible structure  36  may include an opening  38  and fly  40  configured to attach to a single person tent  42  or other adjacent structure. The fly  40  may be releasably secured to one of the walls  44  of the collapsible structure  36  using a suitable fastener that can be used to quickly attach/detach the fly  40  from the tent  42  and wall  44 . One or more elastic cords  46  (e.g. bungee cords) configured to stretch and attach to the ground may be used to maintain the fly  40  taut against the tent  42 . 
     An entranceway  48  equipped with a door mechanism  50  may be used to gain access to the interior of the collapsible structure  36  and attached tent  42 . The door mechanism  50  may be configured to permit passage into the interior of the collapsible structure  36  without requiring the user to manually open or close the door mechanism with a zipper, Velcro® or other similar fastening mechanism, thus reducing the amount of dexterity necessary to pass through the entranceway  48 . 
       FIG. 3  illustrates a collapsible structure  52  adapted for use with a vehicle such as a camper, van, car or truck. Collapsible structure  52  may include an opening  54  and fly  56  connecting the interior of the structure  52  to the rear hatch of, for example, an automobile  58 . The fly  56  may be releasably secured to one of the walls  60  of the collapsible structure  52  with a suitable fastener (e.g. snap fittings), and may include one or more elastic cords that maintain the fly  56  taut against the automobile  58 . 
     The collapsible structure  52  may further include a second opening  62  and fly  64  connecting the interior of the structure  52  to an adjacent structure  66  such as a vestibule or tent. Access to the adjacent structure  66  and automobile  58  may be obtained through an entranceway  68  equipped with a door mechanism  70  in accordance with the present invention. As with other embodiments described herein, the door mechanism  70  can be configured to permit passage into the interior of the collapsible structure  52  without requiring the user to manually open or close the door mechanism with a zipper, Velcro® or other similar fastening mechanism. 
     In certain embodiments, multiple structures may be coupled to the collapsible structure to form a modularized system of portable shelters. As depicted in  FIG. 4 , for example, a collapsible structure  72  may be connected to a number of other adjacent structures  74 , 76  (e.g. tents). Each adjacent structure may  74 ,  76 , in turn, be further linked to other structures (not shown), if desired, to increase the amount of interior space within the system. The number and type of connected structure may, of course, vary depending on the user&#39;s needs. As with the other collapsible structure discussed herein, the collapsible structure  72  depicted in  FIG. 4  may include an entranceway  78  equipped with a door mechanism  80  configured to permit simplified and unobstructed passage into or out of the structure  72 . 
     Referring now to  FIG. 5 , an exemplary door mechanism  82  for use with an illustrative collapsible structure  84  may comprise a fan-shaped door  86  configured to fit contiguously within an entranceway  88  formed through one of the walls  90  of the structure  84 . As indicated by dashed lines in  FIG. 5 , the entranceway  88  curves downwardly from left to right, defining an arch-shaped opening  174  ( FIG. 17 ) located contiguously behind the fan-shaped door  86 . A mesh strap  92  or other elongated member configured to lie flush with the ground or an optional floor spans the lower edge of the entranceway  88 , providing lateral support for the wall  90 . Two vertical support members  94 ,  96  provide vertical support for each side of the wall  90 . 
     The fan-shaped door  86  may be formed from a flexible material that can be positioned across the entranceway  88  to provide a seal for the collapsible structure  84 . In certain embodiments, the fan-shaped door  86  can be made from silicon impregnated Nylon, plastic tarpaulin, or other lightweight material, similar to that used in the construction of the roof structure  14  and walls  16  described above with respect to  FIG. 1 . Reinforced textile materials may also be utilized in the construction of the fan-shaped door  86 , if desired. The particular materials used in the construction of the fan-shaped door  86  can be selected for its ability to withstand creasing when folded onto itself, allowing the fan-shaped door  86  to revert to the same shape each time the door  86  is closed. 
     The fan-shaped door  86  may have a shape that correlates generally with the shape of the entranceway  88 , but of greater size to block access through the entranceway  88  when the door  86  is placed in the closed position. A left edge  98  of the fan-shaped door  86  is connected to the left side of the wall  90  at or near vertical support member  94 . The upper, lower, and right edges  100 ,  102 ,  104  of the fan-shaped door  86 , in turn, are unconstrained relative to the wall  90 , allowing the door  86  to fan from left to right across the arch-shaped opening  174  to seal the entranceway  88 . 
     A second layer of material  106  coupled to the wall  90  contiguous and in front of the fan-shaped door  86  acts as a guide, constraining movement of the door  86  in a plane substantially parallel to the plane of the wall  90 . As shown in  FIG. 5 , the second layer of fabric  106  extends from the top left corner of the wall  90  and slopes downwardly and to the right, terminating at the lower right corner of the wall  90 . In use, the second layer of fabric  106  forms a double-layered wall that receives the fan-shaped door  86  therein. The space between the two layers of fabric forms a guide channel for the fan-shaped door  86 , and acts as a seal to prevent elements such as moisture and wind from entering the collapsible structure  84 . 
     The fan-shaped door  86  may further include one or more reinforcement members, which provide structural support for the door  86 . In the embodiment illustrated in  FIG. 5 , for example, the fan-shaped door  86  includes three reinforcement members  108 ,  110 ,  112  that together support the door  86  within the entranceway  88 . In certain embodiments, the reinforcement members  108 , 110 ,  112  may comprise poles, rods, tubes, battens, wires or the like formed from a lightweight material such as fiberglass, carbon fiber, polyvinylchloride (PVC), or aluminum. 
     The first and second reinforcement members  108 ,  110  may each be connected to the fan-shaped door  86  via a number of respective sleeves  114 ,  116 . Each sleeve  114 ,  116  may extend along only a portion of the length of the two reinforcement members  108 ,  110 , allowing the members  108 ,  110  to be easily removed from within the sleeves  114 ,  116  during disassembly. The third reinforcement member  112  may be placed within a third sleeve (not shown) that extends along all or a portion of the right edge  104  of the fan-shaped door  86 . 
     The first and second reinforcement members  108 ,  110  may be pivotally coupled at an attachment joint  118  located along the lower edge of the entranceway  88 . The first and second reinforcement members  108 ,  110  converge at joint  118  to form a V-shaped support structure for the fan-shaped door  86 . This V-shaped structure permits the upper, lower, and right edges  100 ,  102 ,  104  of the fan-shaped door  86  to pivot about the joint  118 , allowing the user to move the door  86  between an open position and a closed position. 
       FIG. 6  is an enlarged fragmentary elevation view showing the connection of the first and second reinforcement members  108 ,  110  to the attachment joint  118 . As shown in  FIG. 6 , the attachment joint  118  may comprise a flexible pocket  120  configured to retain the ends of the first and second reinforcement members  108 ,  110  therein. In certain embodiments, the flexible pocket  120  may be formed from a reinforced textile material that is sewn into the fan-shaped door  86  or, in the alternative, to the wall  90  or mesh strap  92 . In use, the flexible pocket  120  pivotally secures the first and second reinforcement members  108 ,  110  to the structure  84 , allowing the user to actuate the fan-shaped door  86  between an open position and a closed position. 
       FIG. 7  is a fragmentary elevation view of another exemplary attachment joint  124  configured to pivotally secure the first and second reinforcement members  108 ,  110  of  FIG. 5  to the collapsible structure  84 . Attachment joint  124  includes a first locking ring  126  having a first mounting post  128  (indicated by dashed lines) that can be inserted into the bottom end of the first reinforcement member  108 . A second locking ring  130  having a second mounting post  132  (shown in  FIG. 7  in a detached position) can be inserted into the bottom end of the second reinforcement member  110 . The first and second locking rings  126 ,  130  may be coupled to the mesh strap  92  using a mounting bracket  134  or the like. 
       FIG. 8  is a fragmentary elevation view of another exemplary attachment joint  136  configured to pivotally secure the first and second reinforcement members  108 ,  110  of  FIG. 5  to the collapsible structure  84 . Attachment joint  136  includes a first grommet  138  and second grommet  140 , each disposed through a portion of the mesh strap  92 . The first grommet  138  may be configured to receive a reduced diameter portion (not shown) on the bottom end of the first reinforcement member  108 . The second grommet  140  may be similarly configured to receive a reduced diameter portion  142  on the bottom end of the second reinforcement member  110 , which in  FIG. 8  is shown removed from the second grommet  140  for sake of clarity. In use, the first and second grommets  138 ,  140  may be used to pivotally secure the reinforcement members  108 ,  110  to the collapsible structure  84 . 
     Referring now to  FIGS. 9-10 , an exemplary fastener  144  for securing the fan-shaped door  86  to the collapsible structure  84  will now be described. As shown in  FIG. 9 , fastener  144  may comprise a reinforced textile portion  146  attached to or formed integrally with the material forming the lower right portion of the fan-shaped door  86 . An upwardly projecting indentation  148  in the reinforced textile portion  146  allows the third reinforcement member  112  to be inserted into a capture  152  attached to, for example, the wall  90  of the collapsible structure  84 . To secure the fan-shaped door  86  to the collapsible structure  84 , the user pulls the door  86  upwards and to the right a slight distance, causing the reinforcement member  112  to align with the capture  152 . Once aligned, the reinforcement member  112  is then advanced downwardly and inserted into the capture  152 , securing the fan-shaped door  86  to the collapsible structure  84 , as shown in  FIG. 10 . 
     In an alternative embodiment depicted in  FIG. 11 , a fastener  154  suitable for securing the fan-shaped door  86  to the collapsible structure  84  may comprise a hook or clip member  156  configured to releasably secure to the vertical support member  96  supporting the right side of the wall  90 . A curved portion  158  of the hook or clip member  156  may be dimensioned to tightly fit about and grip the vertical support member  96 . 
     To secure the fan-shaped door  86  to the vertical support member  96 , the user pulls the door  86  towards the support member  96  and downwardly a slight distance, causing the curved portion  158  of the hook or clip member  156  to engage the support member  96 , as shown in  FIG. 12 . As can be seen in cross-section in  FIG. 13 , the curved portion  158  of hook or clip member  156  tightly grips the vertical support member  96 , holding the fan-shaped door  86  in sealing engagement with the wall  90 . The hook or clip member  156  can be disengaged from either outside or inside of the collapsible structure  84  by pulling the hook or clip member  156  away from the vertical support member  96  vis-à-vis handles  160 ,  162  located on both faces of the fan-shaped door  86 . 
     In an alternative embodiment depicted in  FIG. 14 , a fastener  164  suitable for securing the fan-shaped door  86  to the collapsible structure  84  may include a hook or clip member  166  configured to releasably secure to the third reinforcement member  112  of the door  86 . The hook or clip member  166  may include a curved portion  168  disposed within the double-layered wall that is adapted to tightly grip the third reinforcement member  112  at or near a reinforced opening  170  formed through the fan-shaped door  86 . To secure the fan-shaped door  86  to the collapsible structure  84 , the user pulls the reinforced opening portion of the door  86  towards the hook or clip member  166  until the curved portion  168  engages the third reinforcement member  112 , as shown in  FIG. 15 . 
       FIGS. 16-17  are fragmentary elevation views showing the operation of the fan-shaped door  86  between a closed position and an open position. To open the fan-shaped door  86  from an initially closed position (see  FIG. 5 ), the user grips the third reinforcement member  112  or one or more optional handles  172  and moves the door  86  from right to left, causing the first and second reinforcement members  108 ,  110  to pivot about joint  118  and fan open, as shown in  FIG. 16 . Continued movement of the fan-shaped door  86  to the left causes the door  86  to fold upon itself, as shown in  FIG. 17 , permitting unobstructed passage through an arch-shaped opening  174 . When placed into a fully open position, the fan-shaped door  86  is configured to rest at a slight angle past vertical, allowing the door  86  to remain in an open position under its own weight with gravity. 
     Closure of the fan-shaped door  86  can be accomplished by pulling the door  86  to the right a slight distance until the reinforcement members  108 ,  110 ,  112  are re-oriented to the right of vertical. Once advanced beyond vertical, the weight of the fan-shaped door  86  causes the door  86  to automatically fan shut to the closed position. The fan-shaped door  86  can then be secured to the collapsible structure  84  with, for example, fasteners  144 ,  154 , or  164 , as described above. 
       FIG. 18  is a fragmentary elevation view of another exemplary door mechanism  176  for use with a collapsible structure  178  employing one or more swinging doors  180 ,  182 . Door mechanism  176  comprises one or more swinging or café-style doors  180 ,  182  ergonomically designed to facilitate unobstructed passage through an entranceway  184  into the interior of the structure  178 . The doors  180 ,  182  are hingedly connected at their respective far edges  186 ,  188  to the wall  190  in a manner that permits the doors  180 ,  182  to swing in either direction when pushed. The edges  186 ,  188  may be oriented at a slight angle away from vertical, causing the doors  180 ,  182  to swing upwardly and away from the ground a slight distance when opened. This vertical offset reduces the likelihood that the doors  180 ,  182  will catch on grass, rocks or other objects located on the ground, and provides momentum for the doors  180 ,  182  as they are closed. 
     The doors  180 ,  182  may extend vertically down towards the base or floor of the structure  178 , obviating the need for a raised lip or lower doorway edge. A mesh strap  192  or other elongated member configured to lie flush with the ground or floor may span the lower portion of the entranceway  184 , providing lateral support for the wall  190 . The inner edge  194 ,  196  of each door  180 ,  182  may include a strip  198  adapted to create a seal between the doors  180 ,  182 . In certain embodiments, the strips  198  may comprise a heavy duty Nylon material such as pack cloth or Cordura®, which has a greater stiffness than the fabric used in the construction of the doors  180 ,  182 . The strips  198  may also comprise a suitable plastic material in some embodiments. One or more strips  200  may also be placed on the top and bottom edges (see  FIG. 19 ) of the entranceway  184  to create a seal between the doors  180 ,  182  and the wall  190 . The strips  198 ,  200  are configured to provide a seal against wind, moisture or other elements without affecting the movement of the doors  180 ,  182  within the entranceway  184 . 
       FIG. 19  is a fragmentary elevation view showing the door mechanism  176  in a closed position from a vantage point within the interior of the collapsible structure  178 . As shown in  FIG. 19 , each door  180 ,  182  may include a number of cross reinforcement members  202 , vertical reinforcement members  204 , and lateral reinforcement members  206  sandwiched between two layers  208 ,  210  of fabric or textile material (e.g. Nylon). A portion of one of the layers (e.g. layer  210 ) can be removed to allow the reinforcement members  202 ,  204 ,  206  to be inserted through several sleeves  212  sewn into one or both of the layers  208 ,  210 . Once inserted into the sleeves  212 , a number of pockets  214  disposed about the corners of each door  180 ,  182  may be used to firmly secure the cross and vertical reinforcement members  202 ,  204  thereto. 
     The door mechanism  176  may further include one or more closure mechanisms  216  configured to automatically close each of the doors  180 ,  182 . Each closure mechanism  216  may include a flexible cable or cord  218  having a first end  220  attached to the top, inner edge of the door  180 ,  182 , and a second end  222  operatively coupled to a counterweight  224  (e.g. a sandbag). The flexible cable or cord  218  may be threaded through a number of eyelets or pulleys  226  that allow the counterweight to pull the doors  180 ,  182  shut in the absence of a sufficient force applied thereto. As can be seen in  FIG. 20 , when the doors  180 ,  182  are forced open, the tension in the flexible cable or cord  218  causes the counterbalance  224  to move upwardly, allowing the doors  180 ,  182  to swing open to permit unobstructed passage through the entranceway  184 . 
     In certain embodiments, the door mechanism  176  may include a fastener  228  that can be used to secure the doors  180 ,  182  together. As shown in greater detail in  FIG. 21 , the fastener  228  may comprise a first latch arm  230  that can be rotated via a handle  232  to engage a first latch  234  into a catch  236  (see  FIG. 20 ) located on the opposite door. A second latch arm  238 , latch  240 , and handle (not shown) positioned on the opposite face of the door may be used to engage a corresponding catch located on the opposite door. The first and second latch arms  230 ,  238  may be rotatably coupled to a plate  242  equipped with a curved slot  244 . In use, the curved slot  244  acts to constrain or limit the travel of the latch arms  230 ,  238 , as indicated by the arrow in  FIG. 21 . 
       FIG. 22  is a fragmentary elevation view of another exemplary door mechanism  246  for use with a collapsible structure  250  employing a sliding door  252 . As with other embodiments described herein, the sliding door  252  may be ergonomically designed to permit simplified and unobstructed passage through an entranceway  254  of the collapsible structure  250 . The sliding door  252  is configured to slide back and forth between an open position and a closed position within a double-layered wall  256  of the structure  250 . The sliding door  252  may extend vertically to the base or floor of the structure  250 , obviating the need for a raised lip or lower doorway edge. 
     The door mechanism  246  may be formed from one or more layers of fabric material (e.g. Nylon) supported by one or more cross reinforcement members  258  and lateral reinforcement members  260 . The reinforcement members  258 ,  260  may be held in place adjacent to the fabric material via a number of pockets  262  disposed about the corners of the sliding door  252 . A vertical reinforcement member  264  located on the leading edge of the sliding door  252  further supports the sliding door  252  in an upright position within the entranceway  254 . A second vertical reinforcement member (not shown) located on the trailing edge of the sliding door  252  may also be employed, if desired, to further support the door  252  in an upright position. A handle  266  located on each face of the sliding door  252  may be used to open or close the door  252  from a position either within or outside of the collapsible structure  250 . In certain embodiments, the door mechanism  252  may be configured to detach from the collapsible structure  250  to facilitate disassembly, or to permit use of the structure  250  without a door. 
       FIG. 23  is another fragmentary elevation view showing the door mechanism  246  of  FIG. 22  in an open position. As shown in  FIG. 23 , the door mechanism  246  retracts within the space between the double-layered wall  256  of the structure  250  to permit unobstructed passage through the entranceway  254 . The door mechanism  246  may be configured to slide along a mesh strap  268  or other guiding member that extends laterally across the bottom portion of the entranceway  254 . An optional threshold  270  located along the bottom portion of the entranceway  254  and in front of the sliding door  252  may also be used to guide the door  252  as it is moved from an open position to a closed position. The mesh strap  268  and/or threshold  270  may be configured to lie flush with the ground to prevent interference with the wheels or feet of a mobility device passing through the entranceway  254 . 
       FIG. 24  is another fragmentary elevation view showing the door mechanism  246  of  FIG. 22  in a slight open position from a vantage point within the interior of the collapsible structure  250 . As indicated by the arrow in  FIG. 24 , the sliding door  252  is configured to slide along the mesh strap  268  in a plane substantially parallel to the wall  254 . A second, larger mesh strap  272  disposed adjacent the smaller mesh strap  268  may be employed to prevent the sliding door  252  from moving in a direction towards the interior of the collapsible structure  250 , and acts as a seal to prevent elements such as moisture and wind from entering the collapsible structure  250 . The larger mesh strap  272 , which is shown broken in  FIG. 24  for sake of clarity, extends along the bottom portion of the entranceway  254 , and is oriented with its thickness in a vertical plane. 
       FIG. 25  is an exploded fragmentary elevation view showing the attachment of the sliding door  252  to the mesh strap  268 . As illustrated in  FIG. 25  with the second mesh strap  272  shown removed for clarity, a retaining strap  274  equipped with a snap fitting  276  or other suitable fastener may be used to releasably secure the sliding door  252  to the mesh strap  268 . In use, the retaining strap  274  provides a guide for the sliding door  252 , which can be subsequently detached to permit removal of the door  252  from the collapsible structure  250 . 
     Having thus described the several embodiments of the present invention, those of skill in the art will readily appreciate that other embodiments may be made and used which fall within the scope of the claims attached hereto. Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention.