Patent Publication Number: US-7594360-B2

Title: Lateral release mechanism for movable roof panels

Description:
This application claims priority under 35 USC § 119(e) based on U.S. Provisional Application Ser. No. 60/659,848, filed Mar. 9, 2005, the entire disclosure of which is hereby incorporated by reference as if set forth fully herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains, in general, to the field of retractable covers or roofs for large structures, such as athletic stadiums. More specifically, the invention relates to an improved transport mechanism for such a structure that is more compact, reliable, stable, mechanically simple and inexpensive to construct than comparable mechanisms heretofore known. 
     2. Description of the Related Technology 
     It is common these days for athletic stadiums to be constructed with retractable roofs, because this type of construction offers spectators the pleasure of being outdoors on pleasant days, while providing shelter when necessary against extreme temperatures and inclement weather conditions. In addition, retractable roof construction permits the use of natural grass in a stadium, which is important to many athletes. 
     A number of factors must be taken into account in the design of a stadium that has a retractable roof. For instance, the forces created by the exertion of natural forces such as wind, rain snow and even earthquakes on such a large structure can be significant and unpredictable, and the roof, the underlying stadium structure and the transport mechanism that is used to guide and move the roof between its retracted and operational positions must be engineered to withstand the worst possible confluence of such forces. In addition, for reasons that are both aesthetic and practical, it is desirable to make the structural elements of the roof and the transport mechanism to be as unobtrusive and as space-efficient as possible. It is desirable to make the roof structure and the transport mechanism to be as simple and maintenance-free as possible, and to be constructed so as to be able to open and close as quickly as possible. 
     Many cities in the United States and elsewhere are now using or building convertible stadiums that have retractable roof panels. The designs of the various stadiums that have been built and proposed are quite different, but there are a number of deficiencies that seem to be common to many of the designs that have been implemented thus far. For example, the transport mechanisms in most of the stadiums tend to be quite large, being as much as twenty to thirty feet in height. The transport mechanisms further tend to include a relatively small number of very large, heavily loaded wheels and bearings, and a small number of very large motors or actuators to drive the roof between the retracted and operational positions. The small number of large wheels exert very large concentrated loads onto the support structure, which requires the support structure to be heavily reinforced, adding to the cost and complexity of the stadium as a whole. The roof and transport mechanisms in existing designs further tend to be relatively heavy and inflexible, and often experience alignment problems during movement. While many of these problems have been eliminated through the efforts of Uni-Systems, LLC, as is described in U.S. Pat. Nos. 6,082,054; 6,367,206; and 6,415,556, all to Silberman et al., the disclosures of which are hereby incorporated as if set forth fully herein, additional improvements are possible and are sought after by Uni-Systems, Inc. and others. 
     When large retractable roofs are built onto stadiums, shipyards or other large buildings, it is difficult to establish two perfectly parallel raceways or tracks on which the roof will rest and travel. The difficulty is trying to get the two tracks perfectly parallel. There are a number of reasons why they may vary in width, including (1) variation from the construction itself; (2) variation from expansion and contraction of the building foundations and walls; (3) variation from external wind forces and/or ice and snow that might develop on one side or the other of the wall; (4) variation from the retractable roof itself which is the result of expansion and contraction from thermal variations; (5) variation from dead-load camber from within the spanning truss and/or (6) variations from racking. It is very difficult to keep a square or rectangular roof perfectly square as it travels down a pair of tracks; this tends to create variable dimensions. The inventors have determined that all of these variations can be accommodated by a properly designed and constructed lateral or horizontal release mechanism. 
     U.S. Pat. No. 6,415,556 to Silberman et al. discloses a system having a four bar linkage as orientation structure for maintaining the transport mechanism in a predetermined orientation while permitting a limited amount of movement of the roof member in a direction that is nonparallel to the direction of transport. The four-bar linkage does a good job of providing this orientation function if there is sufficient vertical height within the retractable roof to accommodate the four-bar linkage. Key to any orientation mechanism is its ratio of horizontal drag as compared to the vertical gravity component. 
     For example, if a roof weighs 1,000 tons then the reaction if the sidewall desires to move will be restrained by the coefficient of friction of whatever lateral release mechanism has been utilized. In the case of the four-bar linkage, as long as the linkage bars are exactly straight, up and down vertical, aligned with gravity, the resulting side force from the 1,000 ton roof would be zero. However, as soon as either the roof expands, or the wall line contracts, an angle develops between the four-bar linkage struts. While the struts remain parallel they become tilted when compared to a straight line aligned with gravity. This tilt results in a horizontal thrust or reaction. That reaction becomes more severe as the displacement continues to grow. At some point the angle of the parallel bar linkage becomes too great and the horizontal thrust on the wall and/or roof becomes unacceptably high. The only way to correct this with a four-bar linkage is to extend the length of the parallel bars, which in some cases is objectionable for architectural reasons and the simple geometry of the installation. Accordingly, on many roofs there just isn&#39;t sufficient room to use the parallel bar or four-bar linkage orientation system. 
     A need exists for an improved design for a retractable roof and transport mechanism that is compact, lightweight and mechanically simple, and that is capable of maintaining its stability and alignment during normal use and in extreme conditions more capably than comparable mechanisms heretofore known. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to provide an improved design for a retractable roof and transport mechanism that is compact, lightweight and mechanically simple, and that is capable of maintaining its stability and alignment during normal use and in extreme conditions more capably than comparable mechanisms heretofore known. 
     In order to achieve the above and other objects of the invention, a system for supporting a large overhead structural member for stable movement with respect to an underlying structure according to a first aspect of the invention includes a transport mechanism that is constructed and arranged to permit the large overhead structural member to move in a predetermined path with respect to the underlying structure; and a lateral release system for maintaining the transport mechanism in a predetermined orientation while simultaneously permitting a limited amount of movement of the large overhead structural member in a direction that is nonparallel to the predetermined path, the lateral release system comprising a linear slide bearing. 
     A large edifice having a retractable roof includes, according to a second aspect of the invention, an area to be covered; a stationary roof structure over the area; a large, heavy roof movable roof panel mounted for movement with respect to said stationary roof structure; a transport mechanism that is constructed and arranged to permit the movable roof panel to move in a predetermined path with respect to the underlying structure; and a lateral release system for maintaining the transport mechanism in a predetermined orientation while simultaneously permitting a limited amount of movement of the movable roof panel in a direction that is nonparallel to the predetermined path, the lateral release system comprising a linear slide bearing. 
     According to a third aspect of the invention, a convertible stadium having a retractable roof includes a playing field; a spectator area; a stationary roof structure; a large, heavy roof movable roof panel mounted for movement with respect to the stationary roof structure; a transport mechanism that is constructed and arranged to permit the movable roof panel to move in a predetermined path with respect to the underlying structure; and a lateral release system for maintaining the transport mechanism in a predetermined orientation while simultaneously permitting a limited amount of movement of the movable roof panel in a direction that is nonparallel to the predetermined path, the lateral release system comprising a linear slide bearing. 
     These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of the convertible stadium constructed according to a preferred embodiment of the invention; 
         FIG. 2  is a fragmentary cross-sectional view taken along lines  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a fragmentary cross-sectional view of the portion of the convertible stadium depicted in  FIG. 1 ; and 
         FIG. 4  is a fragmentary cross-sectional view of the portion of the convertible stadium depicted in  FIG. 1 , with certain elements omitted for clarity. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to  FIG. 1 , a convertible stadium  10  that is constructed according to a preferred embodiment of the invention includes a playing field  12  which in the preferred embodiment is an American football field, and a seating area  14  for spectators. Convertible stadium  10  is preferably what is generally considered to be a large stadium, i.e. a stadium that can accommodate over 40,000 spectators and that is suitable for professional sporting events such as National Football League games. The term “large edifice” is defined herein as an edifice that is over 15,000 square feet. 
     Convertible stadium  10  further preferably includes stationary roof structure  16 , a first movable roof panel  18  and a second movable roof panel  20 . The first and second movable roof panels  18 ,  20  are large, relatively heavy structures in engineering terms, having a length and a width of at least 100 feet in each dimension and a weight of at least 100 tons. Preferably, both the first and second movable roof panels  18 ,  20  are constructed as a lenticular truss as taught in U.S. Pat. No. 4,789,360 to Silberman et al., the disclosure of which is incorporated by reference as if set forth fully herein. 
     Referring now to  FIG. 2 , it will be seen that the second movable roof panel  20  includes an internal lenticular roof truss  22  and an external fabric cover  24 . Second movable roof panel  20  is supported at a first end  25  by a first transport mechanism  26  that is mounted for movement along a first predetermined path defined by a trolley rail  28  that is securely mounted to an underlying structural support  30 . Second movable roof panel  20  is further supported at a second, opposite end  27  by a second transport mechanism  32  that is mounted for movement along a second predetermined path that is designed to be parallel to the first predetermined path and that is defined by a trolley rail  34  that is securely mounted to an underlying structural support  36 . The first end  25  of the second movable roof panel  20  is preferably securely mounted to the first transport mechanism  26 , while the second end  27  of the second movable roof panel  20  is provided with a lateral release system  29  that maintains the transport mechanism in a predetermined orientation while simultaneously permitting a limited amount of movement of the movable roof panel and a direction that is nonparallel to the second predetermined path. Lateral release system  29  is preferably embodied as a linear slide bearing, as will be described in greater detail below. 
     Looking now to  FIG. 3 , it will be seen that second transport mechanism  32  includes a roof carrier unit  38  that preferably includes a plurality of rail follower wheels  40  and is adapted to ride upon the trolley rail  34 . Lateral release system  29  is structurally interposed between the rail follower wheels  40  and the movable roof panel  20 , as is clearly shown in  FIG. 3 . It includes a linear bearing assembly  42  that is adapted to permit limited movement of the second end  27  of the second movable roof panel  20  in a direction that is nonparallel to the transport direction of the movable roof panel  20 . In the preferred embodiment, lateral release system  29  and linear bearing assembly  42  permits limited movement of the second end  27  in a direction  44  that is substantially perpendicular to the transport direction of the movable roof panel  20 . In other words, the longitudinal axis of the linear bearing assembly  42  is preferably substantially perpendicular to the predetermined path of travel of the movable roof panel  20 . As  FIG. 3  clearly shows, the transport mechanism  32  includes a single trolley rail  34  on the underlying structure with no additional rail and a plurality of rail follower wheels  40  on the large overhead structural member that are adapted to ride on the single trolley rail  34 . 
     Referring briefly to  FIG. 4 , it will be seen that linear bearing assembly  42  includes a cylindrical guide shaft  46 , which is oriented in a substantially horizontal position for movement within a cylindrical guide shaft collar  48 . Cylindrical guide shaft  46  is preferably a 1026 hot finished seamless steel tube that is turned and polished and then finished with an electroless nickel plating. First and second flexible boots  50 ,  52  are provided that extend over portions of the guide shaft  46  that protrude upwardly from each end of the guide shaft collar  48 . The purpose of the first and second flexible boots  50 ,  52  is to protect the guide shaft  46  and the rest of the linear bearing assembly  42  against contamination from the environment. Bearing sleeves  54 ,  55  are interposed between the guide shaft collar  48  and the guide shaft  46  at each end of the guide shaft collar  48  for providing a bearing surface to permit sliding movement of the guide shaft  46  with respect to the guide shaft collar  48 . Bearing sleeves  54 ,  55  are preferably fabricated from a fiberglass epoxy composite with a polytetrafluoroethylene (PTFE) fabric inner liner, and are commercially available under the trade name DURALON from Rexnord Corporation. 
     An outer mounting bracket  56  is provided to securely mount a first distal end  57  of the cylindrical guide shaft  46  to the lenticular roof truss  22 . An inner mounting bracket  58  securely mounts a second distal end of the cylindrical guide shaft  46  to the lenticular roof truss  22 . A mounting flange  60  that is securely welded to the guide shaft collar  48  is securely fastened to the roof carrier unit  38 , as is best shown in  FIG. 3 . In order to prevent lightning from damaging the linear bearing assembly  42 , a lightning shunt  62  is provided to redirect electricity from the lenticular roof truss  22  to the mounting flange  60 . A walkway  64  having a guard rail  66  is provided adjacent to the linear bearing assembly  42  in order to permit maintenance personnel to gain access to the linear bearing assembly  42  and to the transport mechanism  32 . 
     Preferably, the linear bearing assembly  42  is constructed so as to be operative at a frictional ratio of 20% or less of the weight being applied thereto by the lenticular roof truss  22  during operation. More preferably, linear bearing assembly  42  operates at a frictional ratio of 15% or less, and most preferably at a frictional ratio of 10% or less. Linear bearing assembly  42  is preferably constructed so as to be operative at weight loads within a range of about 40 kips to about 260 kips. 
     This lateral release mechanism is an improvement over the four-bar linkage and all other systems that have been used to date. This system is unique because it reduces the ratio of horizontal friction to vertical gravity, thus transmitting a very small side-load to the wheels and bearings for the main load supporting wheels on the main rails. It also reduces the amount of space that is required for the lateral release mechanism. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.