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CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT OF FEDERALLY FUNDED RESEARCH/DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The invention relates to canopy structures, and in particular to damage-resistant canopies sheltering, for example, drive-up ordering stations of fast food restaurants. 
     It is well known to shelter from the weather particular areas, such as the drive-up ordering stations of fast food restaurants, with overhanging portions of a roof or a free-standing canopy structure. These structures are rigid and fixed in height. Consequently, they provide a prescribed maximum clearance for pedestrian or vehicular travel thereunder. The amount of clearance for roof overhangs usually depends on the height of the building to which it is attached. The height of the canopy may be selected to balance the competing interests of maximum clearance and adequate protection from the elements. That is, the canopy must not be too much higher than the subjects being sheltered, otherwise it may provide insufficient shelter because the weather elements (wind, rain, sleet, snow, etc.) may easily pass around the canopy. The size of the canopy structure is also selected with an eye to material and assembly costs. At the drive-up ordering station of a fast food restaurant, for example, a canopy with 100 inches of clearance may be selected to provide adequate shelter and still allow automobiles and many sizes of trucks to pass underneath. 
     It is possible for the canopy top to be struck by vehicles that are taller, or are carrying loads that are higher, than the maximum clearance. This can cause the canopy and the vehicle (or load) to be damaged. To overcome this problem, canopy structures have been designed with components that move or break-away when struck. For example, U.S. Pat. No. 5,390,710, incorporated herein by reference, discloses a canopy assembly having an upright post and a canopy top that can be pivoted about the post (and out of the way) by an overheight vehicle. The canopy top has an impact bar at a leading edge that when struck activates an alarm and travels a small distance. If the vehicle does not stop, the impact bar travels a further distance to release a latch and allow the canopy top to be swung by the vehicle out of the path of movement. While this device provides a damage-resistant canopy, it must be returned manually to the centered position after the vehicle has passed out of the way. Until the canopy top is repositioned, it will not shelter the desired area and it may be swung about the post by external forces, such as high wind, thus subjecting it (and nearby structures) to damage. 
     Accordingly, there exists a need for an improved canopy structure. 
     SUMMARY OF THE INVENTION 
     The present invention provides a self-centering pivotal canopy assembly overcoming the problems of the prior art. In particular, the canopy assembly includes a support column, at an upper end, a roof structure having a frame supporting one or more sheltering members. A coupler is attached to the column and the roof to allow the roof to be pivoted about the column in response to a moment force about the column. A centering element is mounted to the support column to engage the coupler and bias the roof to a center position such that the roof returns to the center position in the absence of the moment force. 
     In one form, the coupler includes a pair of identical helical slots. In the centered position, the top ends of the slots rest on the pivot post. The coupler can rotate through approximately 180 degrees until the pivot post contacts a bottom end of the helical slots. When the coupler is rotated, the pivot post engages the slots so that the coupler translates upward. Gravity biases the coupler to return to the centered position. Preferably, the pivot post assembly includes a cylindrical rod fixed to the support column and supporting a plurality of cylindrical glides that ride within the helical slots. 
     In another form, a plastic spacer sleeve is disposed in the cavity between the coupler. The support column, coupler and spacer sleeve have a pair of openings aligned to receive the pivot post. The spacer sleeve has a top end with at least one wing extending outwardly to engage the top end of the support column. 
     The roof can also include a rectangular, perforated bottom panel that is supported by a the lip of a skirt extending around the perimeter of the roof frame. A front section of the skirt can be pivoted away from the frame to allow the bottom panel to be slid out from the roof assembly for accessing lighting mounted underneath the sloping panels of the roof assembly. 
     In a preferred form, the present invention provides a canopy assembly for sheltering a drive-up ordering station of a fast food restaurant that can pivot out of the path of a vehicle impacting a leading end of a pivotal portion of the assembly. The canopy assembly includes a support column mounting a roof assembly at a coupler. The support column has an upper end defining a cavity in which is disposed a plastic spacer sleeve through which a pivot post assembly extends across the cavity. The pivot post assembly includes a cylindrical rod fixed to the support column and supporting a plurality of cylindrical glides which ride within a pair of helical slots in the tubular coupler, which is mounted to the frame of the roof assembly. When the coupler is rotated, the pivot post engages the slots so that the coupler translates upward so that the coupler is biased by gravity to a centered position in which the top ends of the slots engage the pivot post. The coupler can rotate through approximately 180 degrees in which the pivot post engages a bottom end of the helical slots. 
     Thus, the invention provides a canopy assembly having a roof assembly that can pivot when impacted by a vehicle that is taller than the maximum clearance height of the canopy assembly. After the vehicle is passed clear of the canopy, the pivotal roof assembly automatically returns to its initial centered position, without manual intervention being necessary. 
     These and other advantages of the invention will be apparent from the detailed description and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a self-centering pivotal canopy assembly of the present invention; 
     FIG. 2 is a front view of the canopy assembly; 
     FIG. 3 is a right side view of the canopy assembly; 
     FIG. 4 is a top view of the canopy assembly; 
     FIG. 5 is an exploded assembly view of the canopy assembly; 
     FIG. 6 is a top view looking down on a pivot assembly and support column from line  6 — 6  of FIG. 2; 
     FIG. 7 is a cut out view taken along arc  7 — 7  of FIG. 1, showing a glide bar in a pair of helical slots; 
     FIG. 8A shows the canopy assembly with the roof assembly centered; 
     FIG. 8B shows the canopy assembly with the roof assembly pivoted 90 degrees; 
     FIG. 8C shows the canopy assembly with the roof assembly pivoted 180 degrees; and 
     FIG. 9 is a rear view of a pivotal front skirt section, showing a perforated bottom panel in cross-section. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although other applications are envisioned, the canopy assembly of the present invention is designed to shelter the drive-up, ordering station at a fast food restaurant. Referring to FIGS. 1-5, the canopy assembly  10  includes as primary components a support column  12  to which is mounted a roof assembly  14  at a pivot assembly  16 . The canopy assembly  10  stands approximately 125 inches tall, with approximately 98 inches of clearance beneath the roof assembly  14 , which is enough to allow automobiles and other passenger vehicles as well as many standard height commercial vehicles to pass thereunder. The canopy assembly  10  thus provides restaurant customers shelter from inclement weather, such as rain, sleet and snow, when ordering. As will be explained, the canopy assembly  10  is designed so that the roof assembly  14  will swing out of the way when impacted by an extra tall vehicle, thereby avoiding substantial damage to the vehicle and the canopy assembly  10 . 
     The support column  12  is a square tubular member with a flanged top end  18  and a flanged bottom end  20  for anchoring the canopy assembly  10  to the ground by suitable bolts or anchors. When used to shelter the ordering station of a restaurant, a two-way communication device  22  with a speaker and microphone is mounted to the support column  12  at a suitable height from the ground to facilitate communication between a customer and the restaurant personnel. 
     The roof assembly  14  includes a rigid rectangular frame  24  with leading end  26  and trailing end  28  members joined together by a front  30  member and two shorter rear members  32  and  34 . A center brace  36  is connected to the middle of the front member  30  and the inner ends of the rear members  32  and  34 . The center brace  36  extends beyond the rear members  32  and  34  and a mounting plate  38  is attached at the intersection of the center brace  36  and the rear members  32  and  34 . The mounting plate  38  includes four through bores (not shown) in which bolts are disposed for fastening the roof assembly  14  to the pivot assembly  16 , described in detail below. The members of the frame  24  are preferably a stock, heavy-gauge, square tubular steel joined together by suitable weldment. Gussets (not shown) are used at the connection of the center brace  36  to the front member  30  and the rear members  32  and  34 . 
     The frame  24  supports a canopy  42  having any suitable configuration, but preferably having sloped front  44  and rear  46  sides joined together at a top ridgeline peak  48  and to the front  30  and rear  32 ,  34  members, respectively. The sides  44 ,  46  are preferably formed of aluminum stiles  50  with panels  52  fastened therebetween. Two triangular end panels  54  cap the leading  26  and trailing  28  ends. A skirt  56  extends around, and slightly below, the front  30 , rear  32 ,  34  and end  26 ,  28  members of the frame  24  to support a bottom panel  50 , (see FIG. 9) which is preferably perforated metal sheet. Referring to FIG. 9, the skirt  56  has an L-shaped cross-section and defines a lip or ledge  60  for supporting the perimeter of the bottom panel  58 . A front section  62  of the skirt  56  can pivot away from he frame  24  to allow the bottom panel  58  to be slid out for accessing suitable lamps (not shown) mounted within the roof assembly  14  beneath the canopy  42 . 
     Referring to FIGS. 5,  6  and  7 , the pivot assembly  16  includes a cylindrical coupler or pivot tube  64  having a top end flange  66  an a pair of opposing helical slots  68  and  70 . The top end flange  66  includes four bores  40  for bolts (not shown) used to secure the pivot tube  64  to the mounting plate  38  of the roof assembly  14 . The helical slots  68  and  70  are preferably cut through the pivot tube  64  using a laser cutting machine at opposite portions of the pivot tube  64  (a shown in FIGS.  5  and  7 ). The slots  68  and  70  allow the roof assembly  14  to pivot through approximately 180 degrees in the counter-clockwise direction. Preferably, the pivot tube  64  is disposed within a spacer sleeve  72  having a square cross-section and made of a self-lubricating material, such as polyethylene. The spacer sleeve  72  fits within the hollow, square cavity  71  defined by the upper end of the support column  12  and is molded to include a pair of wings  74  that rest on the top end flange  18  of the support column. The sleeve  72 , pivot tube  64  and support column  12  are coupled together by a stationary post assembly  76 , which with the helical slots  68  and  70  make up the centering element of the canopy. The post assembly  76 , wings  74  and the square walls of the sleeve  72  prevent the sleeve  72  from rotating or moving within the support column  12  and allow the pivot tube  64  to rotate and translate within the sleeve  72 . 
     Referring to FIGS. 5,  6  and  7 , the post assembly  76  includes a cylindrical rod  78  with a smooth outer diameter and a threaded inner diameter at its ends. About the rod  78  fit three cylindrical glides  80  made of a suitable self-lubricating material. The rod  78  is sized to fit through openings or bores  82  in the support column  12  and bores  73  in the pacer sleeve  72  SO that the two outer glides ride within the helical slots  68  and  70  of the pivot tube  64 . A pair of bushings fit  84  within the bores  82  in the support column  1  and allow the rod  78  to rotate as needed. The rod  78  is secured to the support column  12  by threaded fasteners  86 . The bushings  84  and washers  88  disposed about the rod  78  prevent the threaded fasteners  86  from inhibiting rotation of the rod  78  when the fasteners  86  are tightened. 
     In use, the canopy assembly  10  is ordinarily in the position shown by FIG.  8 A. In this position, the roof assembly  14  is centered, that is oriented so that the front member  30  faces front, i.e., the side with the communication device  22 , so as to provide a ceiling for the ordering area and thereby shelter persons from rain, snow, etc. when ordering. The bottom of the roof assembly  14  rests at a clearance height (h) above the ground. In this position, the pivot tube  64  rests on the post assembly  76  at top ends  90  of the helical  68  and  70  slots, as shown in FIG.  7 . As such, the roof assembly can pivot in only one direction, namely, counterclockwise. This direction is chosen because typically vehicles will be approaching the canopy assembly  10  from the leading end  26  because vehicle operators in the United States are seated on the left-hand side of the vehicles. In the event that the vehicle is too tall to fit under the roof assembly  14 , the vehicle will contact the leading end  26  and create a moment, or rotational force, on the roof assembly  14  and, in turn, the pivot tube  64 . Since the post assembly  76  is fixed in position, it will contact the slots  68  and  70  and force the pivot tube  64  to travel upward as it rotates. 
     When the roof assembly  14  has pivoted 90 degrees, as shown in FIG. 8B, it will be raised upward (D/2), which is roughly one-half the total travel distance (D) allowed. In this position, the post assembly  76  is approximately in the meddle of helical slots  68  and  70 . The pivot tube  64  and roof assembly  14  will continue to rotate while the counter-clockwise rotational force is applied, i.e., while in contact with the vehicle, until the post assembly  76  contacts bottom ends  92  of the slots  68  and  70 . In this position, as shown in FIG. 8C, the pivot tube  64  and roof assembly  14  will have rotated through 180 degrees and traveled upward the total travel distance (D), roughly 6-8 inches. By rotating 180 degrees, the roof assembly  14  is capable of swinging completely clear of the vehicle to prevent or reduce damage to the vehicle and the canopy assembly  10 . 
     Once the vehicle has passed by the canopy assembly  10  so that a rotational force is no longer acting on the roof assembly  14 , the weight of the roof assembly  14  will apply a downward force on the pivot tube  64 . The pivot tube  64  will then be rotated clockwise and travel downward until the top ends  90  of the slots  68  and  70  contact and rest on the post assembly  76 . Thus, the roof assembly  14  returns automatically to the initial, centered position. 
     A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations to the preferred embodiment will be apparent to those skilled in the art, which will be within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiment, rather the following claims should be referenced.

Summary:
A canopy assembly for sheltering a drive-up ordering station of a fast food restaurant can pivot out of the way when impacted by a vehicle and return automatically to a centered position. A centering feature mounted to a column supporting a roof structure engages a pivotal coupler to bias the roof to a center position. This feature includes a pivot post assembly extending across the cavity and through a pair of helical slots in the coupler. When a leading end of the roof assembly is struck by a vehicle, the coupler is rotated and the pivot post engages the slots so that the coupler translates upward. The coupler is biased by gravity to a centered position in which the top ends of the slots rest on the pivot post.