Abstract:
A door system for a cold storage locker has increased resistance to damage when by including resilient door panels that flex when hit by a forklift. A high degree of insulation is achieved by the choice and thickness of the resilient foams therein. Also, the resilient door panels are magnetically attracted to a gasket seal on a doorframe to provide an affirmative seal. Active magnetic control may enhance the attraction or repulsion of the door panel. Frost control is realized by warming air from the cold storage locker and passing it through air channels in the door panel proximate to the gasket seal and down an astragal interface between door panels. Door panels of laminate, bagged poured foam formation, and self-skinning foam formation give further reduced cost of manufacture and shipping.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates, in general, to top-supported doors, and more particularly to resilient doors suitable for cold storage rooms.  
         BACKGROUND OF THE INVENTION  
         [0002]    So-called horizontal sliding doors include at least one door panel that is suspended by a carriage that travels along an overhead track. The door panel may be manually or automatically moved from a blocking position to an unblocking position along the overhead track. Wider door openings are often spanned by having two bi-parting door panels. In some instances, the amount of overhead track required to extend beyond the door opening is reduced by having the door panel vertically divided into a number of coupled (e.g., over-lapped, hinged) vertically-separated leaves that take up less horizontal space when moved to the unblocking position.  
           [0003]    Cold storage lockers are often accessed through a door opening closed by a sliding door. The panels for this purpose are typically transparent vinyl sheets, minimally insulated flexible panels or foam filled rigid panels. The transparent vinyl sheets are selected to reduce the likelihood of damage to the door. In particular, such doors are used in institutional (e.g., warehouse) setting wherein palletized cargo is moved in and out of a cold storage locker by forklift. Another advantage to these doors is that forklift operators can see what is on the other side of the door before opening the door. Although providing damage resistance, these types of panels have a very low insulation value and are too flexible to provide an effective air seal between the environments on either side of the opening. Because of the properties of the material, the transparent vinyl sheets may develop a warp that prevents a good seal. Air pressure differentials will cause leakage due to the lack of a compressive seal between the door panels and the doorframe. This will allow a significant amount of warm moist air to enter the cold storage locker and/or refrigerated air to be lost into an unrefrigerated space. Consequently, such door systems are less efficient to operate and can suffer from ice accumulation in the cold storage locker.  
           [0004]    Rigid door panels are often used, especially in the United States, in order to reduce the operating costs of a cold storage locker. The rigid panel provides a consistent surface to seal to the doorframe. The thickness of the rigid door panel is selected to provide a specific amount of insulation. While these rigid door panels provide an effective closure, impact by a forklift can cause damage to the door system that would make them inoperative and limit access to the cold storage locker.  
           [0005]    Attempts have been made to provide a damage resistant door panel for a sliding door system that also provides sufficient insulation. Resilient door panels have been suggested which have sufficient thickness to insulate like a rigid door panel, but yield to a degree when impacted by a forklift. While the panel itself achieves a degree of insulation, the insulation capability of the overall door system suffers from poor sealing between panels and poor sealing between a panel and the doorframe. Specifically, the stiffness of each door panel tends to be less than that of a rigid door panel, and thus presents less of a compressive contact to a doorframe gasket to achieve a seal. To achieve a seal with this type of panel different devices have been tried. Interlocking gaskets can be damaged as the door is pulled away from the casing. In addition they require rigid plates in the door panel for attachment which makes the panel heavier and less resilient. Others have used wall mounted guide tracks to pull the middle of the door back. This adds additional cost, makes installation more difficult and does not address sealing of the entire edge of the door; it only forces a seal at the top, bottom and middle. Because of the application it is difficult to add electrical wiring to the panel because it is flexible and could be torn open and damage or expose wiring. Condensation control on the panel is typically done using resistance wire but that will does not work because of the panel design. Others have tried using external heaters and blowers that are an inefficient means of controlling the condensation.  
           [0006]    Consequently, a significant need exists for an improved door system that is suitable for institutional cold storage lockers by providing significant thermal insulation, efficient condensation control yet being resistant to damage from impacts.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    The invention overcomes the above-noted and other deficiencies of the prior art by providing a resilient door panel for a sliding door system that achieves a good seal to a doorframe by attracting the door panel. The compressive seal is achieved without reliance upon a rigid back surface of the door panel, or upon the weight of the door panel. Therefore, materials and assembly methods may be selected for a desired resilience, insulation and economy of manufacture.  
           [0008]    In one particular aspect of the invention, a resilient door panel is used in a closure system. A seal formed between a doorframe and the door panel is effectively achieved by attracting the door panel to the doorframe either pneumatically or magnetically. Eliminating the need for rigid components in the door panel enables the use of numerous manufacturing approaches, such as bagged foam sheets, bagged poured foam door panels, and even unbagged foam doors that self-skin. Thereby, the manufacturing steps are greatly reduced and thus the cost of each door panel.  
           [0009]    In another aspect of the invention, an approach to keeping the door seals free of ice is provided that is particularly suitable to resilient door panels. In particular, since the resilient door panel readily flexes, it is desirable to eliminate electrical wiring in the door panel that may be damaged during impact. Thus, heating of a door panel periphery by electrical resistive heating is eliminated;  
           [0010]    however, it is desirable to ensure that the seals between the doorframe/door panel, door panel/floor and door panel/door panel does not accumulate frost. Otherwise, the door system drive mechanism or the seal may be damaged in attempting to overcome a frozen seal. The door system may fail to open altogether if sufficiently stuck to stall the drive mechanism. Other problems associated with frost accumulation include achieving a poor seal with the resulting economic inefficiencies and safety and appearance issues related to accumulating ice and moisture.  
           [0011]    In yet a further aspect of the invention, an automated door system includes a door position sensor that senses the door panel being in a closed position with a periphery of a door panel registered to a doorframe. A door positioning system responds to the door position sensor indicating that the door has been impacted by resetting the door panel to an open position, thereby mitigating possible damage to the door system.  
           [0012]    Thus, in another aspect of the invention, a frost control system is incorporated into the closure system to warm the refrigerated air from the cold storage locker, which advantageously tends to contain less water vapor than air from the unrefrigerated side of the door. The warmed air is directed through an air passage to proximity of a periphery of the door panel and its seal to the doorframe. In particular versions of the invention, this air passage includes passing inside of the door panel.  
           [0013]    These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0014]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and, together with the general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention.  
         [0015]    [0015]FIG. 1 is front exploded perspective view of a damage resistant door system for an institutional cold storage locker.  
         [0016]    [0016]FIG. 2 is a diagrammatic view of a frost resistant sealing system of the door system of FIG. 1.  
         [0017]    [0017]FIG. 3 is a top diagrammatic view of an astragal between the two door panels of the door system of FIGS.  1 - 2 .  
         [0018]    [0018]FIG. 4 is a front view of a doorframe-mounted portion of a frost control system of the door system of FIG. 1.  
         [0019]    [0019]FIG. 5 is side cross sectional view along line  5 - 5  of FIG. 1 exposing an air passage of the frost control system passing through both the doorframe-mounted portion and a door panel.  
         [0020]    [0020]FIG. 6 is a cross sectional, detail view taken along line  6 - 6  of the air channel and gasket seal of the door system of FIG. 1.  
         [0021]    [0021]FIG. 7 is an exploded perspective view of a resilient, laminated door pad with a cover removed for the door system of FIG. 1.  
         [0022]    [0022]FIG. 8 is an exploded perspective view of the door panel of FIG. 1 including the resilient laminated door pad of FIG. 7.  
         [0023]    [0023]FIG. 9 is a cross sectional view along line  9 - 9  of a magnet embedded portion of the door panel of FIG. 8.  
         [0024]    [0024]FIG. 10 is a cross sectional view along line  10 - 10  of a bottom edge air passage of a sill of the door panel of FIG. 8.  
         [0025]    [0025]FIG. 11 is an exploded view of the door mounted gasket assembly of the door system of FIG. 1.  
         [0026]    [0026]FIG. 12 is a horizontal cross sectional view along line  12 - 12  of FIG. 1 illustrating a passive gasket system of the door system.  
         [0027]    [0027]FIG. 12A is a horizontal cross sectional view along line  12 - 12  of FIG. 1 illustrating an alternative, active gasket system of the door system.  
         [0028]    [0028]FIG. 12B is a horizontal cross sectional view along line  12 - 12  of FIG. 1 illustrating an alternative, loop gasket system of the door system.  
         [0029]    [0029]FIG. 13 is a diagrammatic view of an alternative frost control system including recycled warmed air for the door system of FIG. 1.  
         [0030]    [0030]FIG. 14 is a diagrammatic view of an alternative air-stiffened door panel for the door system of FIG. 1.  
         [0031]    [0031]FIG. 15 is a horizontal cross sectional view of the door panel of FIG. 14.  
         [0032]    [0032]FIG. 16 is a further alternative air stiffened door panel for the door system of FIG. 1.  
         [0033]    [0033]FIG. 17 is a perspective, partially cutaway view of an alternative bagged, poured foam door panel for the door system of FIG. 1.  
         [0034]    [0034]FIG. 18 is a horizontal cross sectional view of the bagged, poured foam door panel of FIG. 17.  
         [0035]    [0035]FIG. 19 is front diagrammatic view of the door panel of FIG. 17 being filled with poured foam.  
         [0036]    [0036]FIG. 20 is a perspective, partially cutaway view of a further alternative fixture for forming an unbagged, poured foam door panel for the door system of FIG. 1.  
         [0037]    [0037]FIG. 21 is a front cross sectional view along line  21 - 21  of the fixture and foam attachment device of FIG. 19.  
         [0038]    [0038]FIG. 22 is a perspective view of a completed self-skinning door panel formed in the fixture of FIG. 19.  
         [0039]    FIGS.  23 A-F are top view diagrams of a damage resistant door system incorporating an auto-reset feature. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]    Turning to the Drawings wherein like numbers denote like components throughout the several views, in FIGS.  1 - 3 , a closure system, depicted as a bi-parting horizontal sliding door system  10 , advantageously includes fully resilient door panels  12 ,  14  for damage resistance that are affirmatively sealed to a doorframe  16  by an attraction sealing system, depicted as a magnetic sealing system  18 , to effectively separate a warm space  20  from a cold space  22  (e.g., a cold storage locker). As shown particularly in FIG. 1, the door panels  12 ,  14  are supported by and power actuated by an overhead carriage  24 , as is generally understood by those skilled in the art.  
         [0041]    With particular reference to FIG. 2, the sliding door system  10  advantageously includes a frost control system  26  for preventing accumulation of ice on a sealing gasket  28  on the doorframe  16 . Cold air from the cold space  22  passes through and is warmed by an air passage  30  that includes an air channel  32  in a periphery of each door panel  12 ,  14 . In particular, the cold air is drawn through an intake manifold  34 , which is encompassed and warmed by an upstream electric heater  36 , into an air mover, depicted as a blower fan  38  driven by an electric motor  40 . The upstream heater  36  provides dry, warm air to the blower fan  38 , allowing the blower fan  38  to operate in an environment that promotes its reliability. Pressurized air from the blower fan  38  is then directed through an exhaust manifold  42 , which is advantageously encompassed by a downstream electric heater  44  that further warms the air to a temperature sufficient to keep the sealing gasket  28  frost free, although it will be appreciated that one heater may be sufficient in some applications or that the heating is performed in the air mover.  
         [0042]    With particular reference to FIG. 3, an astragal contact  46  between the right door panel  12  and the left door panel  14  is depicted. In the nearly closed position as depicted, a concave, vertical recess  48  of the left door panel  14  receives a vertical rounded end  50  of the right door panel  12 . A vertical The recess  48  and rounded end  50  define a vertical astragal air channel  52  that is in communication with a horizontal air channel  54  of the right door panel  12  and with a horizontal air channel  56  of the left door panel  14 . Thereby, leading edges  58 ,  60  respectively of panels  12 ,  14  contact each other for a good sealing between the warm and cold spaces  20 ,  22  while also directing warned air downward throughout the astragal contact  46  to prevent frost accumulation.  
         [0043]    With particular reference to FIG. 4, the exhaust manifold  42  is shown separating into right and left outlet ports  62 ,  64  for directing warmed air to a respective door panel  12 ,  14  (not shown in FIG. 3). Also depicted is a down-and-in track  66  of the overhead carriage  24  that presents the door panels  12 ,  14  into compressive contact with the outlet ports  62 ,  64  and a horizontal gasket assembly  68  of the sealing gasket  28 , yet avoid frictional wear as the door panels  12 ,  14  are positioned.  
         [0044]    In FIG. 5, the right outlet port  62  is depicted as positioned to communicate with the horizontal air channel  54  in the right door panel  12  via back face air passage  70 . Also depicted in more detail is the overhead carriage  24 .  
         [0045]    In FIG. 6, the horizontal air channel  54  in the door panel  12  is shown proximate to the horizontal gasket assembly  68 . In this illustrative version, the door panel  12  is compressed into the horizontal gasket assembly  68  without having to use magnetic attraction. Thus, the horizontal gasket assembly includes a resilient plug  72  between its over surface and a heated support structure  74 .  
         [0046]    In FIG. 7, the resilient portions of the door panel  14  are shown. In particular, a composite pad  76  is formed from two flexible neoprene sheets  78 ,  80 , selected for a high degree of resilience for impacts, which are glued respectively to each side of a more rigid polyethylene slab  82 , selected for holding the shape of the pad  76  and for receiving a drilled horizontal air channel  54  and routered vertical air channel (both not shown in FIG. 7) about its trailing edge  84 . Permanent magnets  82  are embedded in the back neoprene sheet  78 .  
         [0047]    Alternatively, a composite pad (not shown) may be formed from a rigid material of polyurethane insulation, typically used in rigid door panels, in place of the polyethylene slab  82 . Flexibility is achieved by dividing the urethane insulation into a plurality of mosaic, tile-like pieces. The pieces are held in place between the neoprene sheets  78 ,  80 . The size of the pieces may advantageously be chosen for the desired degree of flexibility. For example, the tile size may be reduced at lower portions more prone to impact. Moreover, for a given thickness, the urethane has a higher insulation value than polyethylene. Thus, if more flexibility is desired, the thickness of the panel may be reduced without sacrificing insulation. Alternatively, the same thickness of the panel may be maintained with a realized increase in economic efficiency.  
         [0048]    It will be appreciated that a number of materials may be used depending upon the degree of insulation, flexibility, thickness, cost, chemical environment, etc. Additional examples include a silicone sheet, a bead board, cross linked polyethylene, etc.  
         [0049]    In FIGS. 6 and 8, the assembled pad  74  is shown with a cover  84  of polyvinyl chloride (PVC) fabric that is glued over the pad  74 . The assembly is attached with adhesive and mechanical fasteners to a structural member  86  across the top of the pad  74 . Attachment members  88  spaced along the top of the structural member  86  are fastened to a roller assembly  90 , which rides on the track  66  of the overhead carriage  24  (shown in FIG. 4).  
         [0050]    In FIG. 9, one permanent magnet  82  is shown embedded in an assembled panel  12 .  
         [0051]    In FIGS. 8 and 10, a bottom sill  92  is shown wherein a bottom structural member  94  is affixed to the bottom of the pad  74 . Perforated supports  96  space the pad  74  above the bottom structural member  94  and defines the bottom portion of the air channel  32  in the door panel  12 .  
         [0052]    In FIGS.  11 - 12 , the magnetic sealing system  18  of the gasket seal  28  is shown in greater detail. A frame casing  98  is mounted to a front face of a wall  100  that defines a door opening  102 . For instance, the casing  98  may comprise metal sheeting encasing a wood beam as is generally known. The wood may be replaced with another core material such as urethane to avoid problems associated with use of wood in a moist environment (e.g., swelling, bacteria growth, rotting). If plastics are used, the covering material may be adhered to the core material to minimize thermal distortion. This can be done by injecting the core material into a preformed cover or wrapping a cover of a preformed core and bonding it to the core. Advantageously, the casing  98  may comprise formed or extruded material (metal, plastic, fiber reinforced composites) as strength, stiffness or temperature conditions dictate.  
         [0053]    An aluminum extruded guide  104  cradles two resistive electrical cables  106 ,  108  and is held in place between a ferrous strip  110  and a front surface  112  of the casing  98  by fasteners  114 . A primary gasket  116  of PVC or other flexible reinforced fabric is bolted through a strip  117  to the front surface  112  and is wrapped over the ferrous strip  110  and a spacer block  118 , over which a secondary gasket  120  is placed and held in place by an angled bracket  122 . The secondary gasket  120  may alternatively be positioned outboard of the primary basket  116  as well as inboard at the door opening as depicted. Fasteners  124  pass through the bracket  122 , secondary gasket  120 , primary gasket  116 , spacer block  118  to attach to an inner surface  126  of the casing  98 . When the door panel  12  draws near its closed, blocking position, the magnets  82  draw the door panel  12  toward the ferrous strip  110   
         [0054]    [0054]FIG. 12A depicts an active magnetic attraction system  128  that provides additional control features over the previously described passive magnetic attraction system  18 . A gasket seal  130  that incorporates the active magnetic attraction system  128  is similar to that described for FIG. 12 with an electromagnet  134  mounted to a ferrous or non-ferrous strip  110 . In the case of a non-ferrous strip, the door pad  12  tends to stay in place under the magnetic attraction between the permanent magnet  82  and the electromagnet  134 . When opening the door panel  12 , the electromagnet  134  may be advantageously polarized to the same magnetic pole as the adjacent face of the permanent magnet  82 , thereby repulsing the door panel  12 . The repulsion assists in overcoming any frost present and tends to hold the panel  12  away during movement to avoid frictional damage. The electromagnet  134  may assist in pulling the door close enough to the ferrous strip  110  that the permanent magnets  82  in the door will thereafter hold the door in place without the help of the electromagnet. When the door opens, the pole on the electromagnet  134  can be reversed to break the seal and make it easier for the door to open.  
         [0055]    It will be appreciated that the door panel  12  may include a ferrous target (not shown) rather than a permanent magnet wherein the electromagnet  134  actively holds the door panel  12  closed and is deactivated when opening the door panel  12 .  
         [0056]    [0056]FIG. 12B depicts a low-wear gasket system  18   a,  similar to the magnetic sealing system  18  of FIG. 12 except that the main gasket is no longer under pressure from a magnet assembly thereby eliminating a source of friction and wear to the door panel  14 . Instead, the magnetic attraction feature has been provided separately as a rearwardly projecting, trailing edge magnetic flap  131  that acts as its own primary seal. A loop  133  of PVC fabric is attached along the full height of the trailing edge of the door panel  14  and is directed inwardly toward the wall  100 . A small permanent magnet  82   a,  affixed to the inside of the loop  133 , is registered to be attracted to a ferrous plate  135  attached to a vertical, outward edge of the frame casing  98 . In addition to eliminating the frictional wear from the secondary gasket  120 , this trailing edge magnetic flap  133  may accommodate a door panel  14  with additional flexibility and curve. Moreover, the permanent magnet  82   a  is advantageously small in that its amount of magnetic field strength need only be great enough to draw a rather light weight flap  133  into contact with the ferrous plate  135  rather than to draw the entire door panel  14  into contact.  
         [0057]    Returning to FIG. 2, the operation of the door system  10  generally begins with the door panels  12 ,  14  closed as depicted, with permanent magnets  82  drawing the door panel  12  into contact with the gasket seal  28 . A door controller  136  energizes resistive electrical cables  106 ,  108  in the gasket seal  28  to assist in frost control. The door controller  136  also energizes the motor  40  to turn the blower fan  38  to draw cold, dry air from the cold space  22  into the air passage  30 . Specifically, in the intake manifold  34 , the cold air is partially warmed by the upstream electrical heater  36  to keep the blower fan  38  and motor  40  in an optimum temperature range. Also, the pressurized air is further warmed by the downstream electric heater  44 . The door controller  136  may closed-loop control the temperature of the warmed air with a temperature sensor  138 , such as depicted in the intake manifold  34 . It will be appreciated that one or more sensor may be used to optimize the temperature in various regions of the air passage  30 . The warmed air is passed through the outlet port  62  into the air channel  32  in the door panel  12 . The warmed air passes through the astragal passage air channel  52  with the panel  14  and around the periphery of the door panel  12  proximate to the gasket seal  28  and thereafter is vented into the warm space  20 . The door controller  136  may condition activation of the frost control system  26  on confirming that the door panel  12  is closed, as sensed by a switch  140 .  
         [0058]    In response to user actuation of an opening device, depicted as a door pull rope switch  142 , the door controller  136  deactivates the frost control system  26  and may activate the electromagnet  134  (if present) (not shown in FIG. 2) to repulse the door panel  12 . The door controller  136  then actuates a door motor  144 , such as a two-speed, three phase electric brake motor, that is coupled to the door panel  12 . It will be appreciated that a single speed motor with a variable frequency drive may be used as another alternative. Once opened, the door controller  136  awaits until user actuation of the door pull rope switch  142  to close the door panel  12 . The door controller  136  may monitor a sensed pneumatic pressure on one or both leading edges  58  to reverse or stop the door motor  144  as a safety feature. The door controller  136  may also monitor stalling of the door motor  144  indicative of system failure or other blockage, such as by monitoring motor current “I” with a current sensor  146 . It will be appreciated that due to the flexible nature of the door panel  12 , monitoring of motor current may be sufficient without a pneumatic sensor on the leading edge.  
         [0059]    In FIG. 13, an alternative door system  148  illustrates additional features that may be incorporated into a pressurized frost control system  150 . Recycling the pressurized air rather than venting the air into the warm space  20  may advantageously reduce the amount of electrical power required to keep the door panel  12  warm. Another advantage or use would be to air stiffen the door panel  12  by inflating air tubes  152  in the door panel  12 .  
         [0060]    Air recycling is shown with a return passage  154  from the door panel  12  to an upstream intake  156  of the blower fan  38 . A check valve  158  may be included in the intake manifold  34  to prevent inadvertent porting of return air into the cold space  22 . In addition, a pressure relief check valve  160  may advantageously be included in the return passage  154  to prevent damage to the door panel  12  such as during an impact.  
         [0061]    In FIGS.  14 - 15 , an air-stiffened door panel  162  is depicted wherein the warmest air is first directed around the periphery for gasket warming purposes and also allowed to pressurize vertical air tubes  164  In FIG. 16, an alternative air-stiffen door panel  166  includes a porous or quilted central portion  168  that is pressurized.  
         [0062]    In FIGS.  17 - 19 , a bagged, poured foam door panel  170  is depicted as an alternative to glued foam laminate construction. A bag cover  172  includes a plurality of vertical dividers constructed of a material similar to the bag  174  that control the flow of uncured foam so that the resulting door panel  170  has the desired shape. Thereby, use of a large fixture may not required. Moreover, large shipping containers may be avoided by shipping an unfilled bag cover  172  with a supply of uncured foam (not shown) that is used on location. Features such as permanent magnets (not shown) may be affixed to the bag cover  172 .  
         [0063]    In FIGS.  20 - 22 , an unbagged, poured foam door panel  176  that may have advantages in reducing cost of manufacturer by eliminating the bag cover. A fixture (not shown) positions hanger structures  178  and other door hardware  180  until injected foam  182  cures onto these elements, the hanger structures  178  may be of various forms that facilitate a large surface area attachment to the foam with horizontal protrusions to resist pull-out, for instance, a “tree root” like structure, perforated plate, or simple bar with cross pieces etc. A self-skinning flexible foam advantageously attaches to the hanger structures  178  and forms a wear resistant surface without the additional manufacturing step of attaching a cover.  
         [0064]    FIGS.  23 A-F depict operation of an auto-reset feature of a damage resistant door system  200  that may advantageously be incorporated into applications that are automatically actuated. In FIG. 23A, the door system  200  is depicted in its normal, closed position with left pad  202  abutting right pad  204 , thereby closing a door opening  206 . The distal lower portions of the left and right pads  202 ,  204  are each inwardly held by left and right restraining devices  208 ,  210  against left and right doorframes  212 ,  214 , respectively, forming a seal against corresponding left and right gaskets  216 ,  218 .  
         [0065]    In the illustrative embodiment, the restraining devices  208 ,  210  are rollers but could be any device protruding upwards on the front side of the panels  202 ,  204 . These restraining devices  208 ,  210  may be attached to the floor or to the door casing. In the latter configuration, the restraining device may require that a bracket go under the door to hold the restraining device. It should be appreciated that the left and right restraining devices  208 ,  210  may have application in manually opened door systems as well as automatically opened door systems, especially when significant air pressure differential exist at times across the door opening or when the door pads  202 ,  204  are sufficiently flexible as to needing an urging at their lower portions to seal against the doorframe  212 ,  214 . In some applications, the normal travel of the door panels  202 ,  204  may maintain the respective restraining device  208 ,  210  in contact, avoiding any damage when the leading edge of the door panels  202 ,  204  encounters the restraining device  208 ,  210  when closing. In other applications, the door panels  202 ,  204  at their most open position are not in contact with the restraining devices  208 ,  210 . Thus, guides (not shown) may inwardly direct the leading edge of the door panels  202 ,  204  to counter any outward deflection of the lower portion of the door panel  202 ,  204 .  
         [0066]    Although the restraining devices  208 ,  210  advantageously assists in sealing the flexible door panels  202 ,  204 , mitigating damage from impacts is enhanced by having the restraining devices  208 ,  210  sufficiently low as to allow an outwardly forced door panels to pop over the restraining device  208 ,  210 .  
         [0067]    Sufficient lateral travel in the overhead carriage (not shown in FIG. 23A) thus allows the door to be reinserted between the restraining devices  208 ,  210  and doorframe  212 ,  214  when cycled fully open and then closed.  
         [0068]    In some applications it is advantageous to retain a normal operation wherein the door remains at all times in contact with the restraining device  208 ,  210 , avoiding impacts to the leading edge, while also providing for the resetting after the door panel  202 ,  204  is forced outward during an impact. Moreover, it is a further advantage for the door to begin to open when a forklift impacts the door panel  202 ,  204  to thereby minimize the amount of deflection required for the vehicle to pass through.  
         [0069]    To that end, a capability for sensing that the door panels  202 ,  204  have achieved a fully closed position with an effective seal is provided by left and right sensors, depicted as left and right magnetic field transducers  220 ,  222  (e.g., Hall effect transducers) that sense the proximity respectively of left and right magnets  216 ,  218  in respective pads  202 ,  204 . Signal lines  224 ,  226  to each transducer  220 ,  222  respectively communicate to a control system (not shown) that respond to the sensed position. It will be appreciated that sensing the magnets  216 ,  218  takes advantage of magnets that also assist in sealing the door panel  202 ,  204  to the doorframe  212 ,  214 . However, other types of sensors may be used, such as mechanical limit switches, optical sensors, etc.  
         [0070]    In FIG. 23B, an impact is illustrated at arrow  228  as coming inside the cold storage space, forcing the door pads  202 ,  204  outward. The selection and placement of sensors  220 ,  222  may advantageously detect impacts from both directions. For instance, an impact from either direction may tend to draw the lower, trailing edge of the door pad  202 ,  204  upward and inward, which may detected by various proximity sensors. Alternatively, the impact from either direction may pull the lower, trailer edge of the door pad  202 ,  204  completely out from the doorframe  212 ,  214  and restraining device  208 ,  210 , which may be detected by a limit switch. As yet a further alternative, multiple sensors on each side may be used to detect impact from either direction.  
         [0071]    In FIG. 23C, the impact has caused each door pad  202 ,  204  to ride over the respective restraining device  208 ,  210 . Also, the door system  200  has responded to the sensed impact by beginning to auto-set by opening the door pads  202 ,  204 .  
         [0072]    In FIG. 23D, the door pads  202 ,  204  have been drawn to a fully open position, wherein the leading edges are beyond the respective restraining devices  208 ,  210 . The pads  202 ,  204  are thereafter maintained in this position for a period of time or until sensed as having swung back toward the doorframe  212 ,  214  under the influence of gravity, as depicted in FIG. 23E.  
         [0073]    In FIG. 23E, the door system  200  has closed the pads  202 ,  204 , completing the auto-reset back to the condition that existed prior to the impact. It will be appreciated that closing may be contingent upon a timer typically sufficient for any impacting vehicle to have left the door opening  206 . Alternatively or in addition, automatic closing during auto-reset may be contingent upon sensing an unimpeded door opening, such as by an unblocked optical beam across the door opening  206 .  
         [0074]    While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications may readily appear to those skilled in the art.  
         [0075]    For example, while air warming of the entire periphery of a door panel may be advantageous, in some applications only one, two or three edges may be warmed. For instance, a upper edge and a trailing edge may rely solely on electrical warming in the doorframe as sufficient, whereas the leading edge and bottom edge are internally warmed by air.  
         [0076]    While a magnetic attraction is depicted and described for advantageously compressively sealing the door panel to the doorframe, it will be appreciated that other approaches may be employed to attract the door panel to the doorframe. For example, pneumatic suction may created about the doorframe that is presented to pull in the periphery of the door panel.  
         [0077]    While air warming of the door panel has been advantageously depicted, it should be appreciated that other warming techniques may be employed that do not rely upon electrical wiring in the door panel. For example, inductive targets may be embedded or affixed to the periphery of a door panel. A radiated electromagnetic signal from the doorframe may then be used to inductively couple power into the inductive targets to cause resistive heating in the door panel.  
         [0078]    Air stiffening of the door panel  12  may also be provided separate from a frost control system. For example, separate air tubes dedicated for use as air stiffening bladders may be pressurized and left pressurized rather than recycling the air for heating.  
         [0079]    Synergy exists between using these aspects of the invention together in a door system for a cold storage locker; however, it will be appreciated that aspects of the present invention may be used separate and apart from the other features.  
         [0080]    For instance, separating environments may be very desirable for soundproofing or preventing airborne particulates from passing through the doorway. Another example is coolers that are maintained above freezing. Consequently, the effective sealing of the door panel by attraction may be employed without the need for a frost control system. As a further example, the configuration of how the door panels is positioned may provide sufficient affirmative urging into sealing contact with the doorframe that an attraction capability is not required, although the elimination of frost at the sealing contact may still be desired.  
         [0081]    It will be appreciated that aspects of the present invention have application to door systems that fold individual panels in an according fashion in order to require less lateral travel when opened. Furthermore, aspects of the present invention have application to door systems that are not supported from an overhead track.  
         [0082]    In the illustrative embodiment of FIGS.  23 A-F, the door system  200  includes both restraining devices  208 ,  210  and door position sensors  220 ,  222  that may be used in an auto-resetting feature. Although a door closed and sealed sensing capability is disclosed in combination with a physical restraining capability, it will be appreciated that door-positioning sensing has applications without the physical restraining capability. For instance, a failure indication may be given to operators when a situation is detected where the door should have achieved full travel yet a seal is not achieved. Furthermore, automatic opening of the door upon impact may advantageously reduce damage to the door system even if restraining devices are not present.