HK1244473B - Overhead guide track systems for automated material handling - Google Patents

Description

Overhead rail systems for automated material handling

Background of the Invention

Field of the Invention

The present invention generally relates to an automated multi-functional material handling system that can be used to selectively acquire and unload containers, supplies, cargo, vehicles, armaments, storage silos, etc. within storage facilities, automated docking facilities, warehouses, marine vessels, etc., and wherein the system includes a cost-effective and precise elevated cross-“I” beam elevated guideway support system along which transfer units or carriers can be operated to move materials or items to position such materials and items, or to transfer such materials and items between ground and storage or port facilities and between different modes of transportation.

Brief description of the prior art

Elevated rail systems are known in the art for supporting motorized and non-motorized carriers or transport units for moving or transporting physical objects or groups of objects within warehouses, storage structures, vehicle parking or storage facilities, ship storage facilities, marine or port transportation and transport facilities. Such systems may include elevated open box girders, such as those described in U.S. Patents 7,753,637, 7,850,412, 7,909,558, and 8,408,863 to Benedict et al., the entire contents of which are incorporated herein by reference.

Such overhead transport systems include load carriers or container carriers, collectively referred to as transport units (TUs), suspended from carriages supported within open box girders. The TUs are suspended via open channels or slots extending through the lower plane of the hollow box girders. As previously described in U.S. patents, one of the most efficient and economical ways to transport cargo by land and water is through the use of standardized freight/shipping containers. Containers are manufactured to standard sizes, typically ranging from twenty to forty feet in length. Containers are specifically designed so that they can be loaded into cargo holds and onto the decks of ocean-going vessels, stored in land-based warehouses, and/or moved from ships or warehouses, using shipboard or shore-based cranes that place the containers directly onto land transport vehicles (such as railroad cars and trucks). Conventional container ships, warehouses, and the like include one or more cargo holds or storage spaces, which in some configurations are divided into multiple vertically layered cells by vertical beams, which serve as guides for the corners of the stacked containers within the cells. A typical cell can hold up to six to ten or more stacked containers. In other configurations, the storage space may be more open, allowing containers to be stacked on top of each other without vertical guide beams.

The same type of vertical storage cellular structures with or without vertical guidance can be used in other environments, such as in cities for high-density automated parking facilities for vehicles, dock areas for high-density storage of ships, and for general storage of any type of items and materials in warehouses, as well as other storage systems where standardized containers may not be suitable.

Summary of the Invention

The present invention relates to an automated material storage and retrieval handling system for handling and storing standardized and other types of cargo containers, support bins, pallets, vehicle containers, and the like, such as for vehicles including automobiles, trucks and buses, ships and freighters, and other products, within vertically oriented cells of ships, warehouses, and other storage facilities, wherein the system comprises an overhead grid rail structure securely mounted above the storage cells and loading and unloading areas and defining intersecting, generally vertically oriented rails or tracks on which container transfer units (TUs) are guided. Each transfer unit is mounted with a plurality of carriages supported by the tracks so that the transfer unit is suspended from the overhead rails and is movable in an X-Y pattern to position the transfer unit for placing or retrieving containers or other articles or merchandise from the cells.

The transport unit is typically powered by a motor that powers a drive gear or wheel system that selectively engages the grid track system. The drive motor has an anti-backdrive feature so that when power is not supplied to it, the motor acts as a lock that prevents the transport unit from moving.

The system of the present invention is designed to provide spacing above the upper level of each vertical storage cell that is large enough for a transfer unit to maneuver while hanging a lifting line, balance beam, etc., so that containers or other objects can be manipulated throughout the grid system and can be moved from one cellular area to another below the overhead rail system and above the storage units.

The system of the present invention also reduces the amount of effort and labor required to acquire storage containers, carriers, supplies, components, etc., and allows multiple containers to be moved within the area above the cellular structure below the deck or on top of the structure, thereby allowing containers or other objects to be interchangeably operated from space to space.

A basic object of the present invention is to provide an automated material handling, retrieval and storage system for warehouses, berthing and ship storage buildings, container ships and the like which allows such structures to operate at optimum capacity for a given area or "footprint" so that a maximum number of items, containers or equipment can be stored and/or retrieved from such storage facilities.

It is also an object of the present invention to provide a material handling, retrieval and storage system for standardized and other international and local cargo containers that enables the retrieval of a specific container from any level of a multi-story vertical cellular structure and its movement throughout the structure in an X-Y motion so that multiple transport units can be operated simultaneously within a given system.

It is another object of the present invention to provide an overhead grid track system for supporting motorized and non-motorized load transfer units, wherein the load transfer units have a load lifting system, such as a balance beam-like structure, a crane, a winch, and other lifting equipment suspended from a crane or cable equipment, and wherein the tracks of the system are formed from "I" steel beams joined to each other by welding and sometimes bolting to form generally vertical cross tracks on which the transfer units are movably supported.

It is another object of the present invention to provide a structural grid track guideway structure that can be economically constructed from "I" steel beams by varying the "I" beam X and Y flange configurations and by providing load transfer units that can pass through the open intersections formed at each region where the X and Y "I" beams intersect one another.

Another object of the present invention is to reduce the expenses associated with the construction and maintenance of an elevated grid track system by utilizing more economical, lighter weight and readily available "I" steel beams to form an X-Y grid on which conveyor vehicles can move, and wherein the "I" beams provide greater strength when compared to the more common hollow box beams and therefore have less deflection and fewer fatigue problems.

An additional object of the present invention is to facilitate the combination of a lattice track system with part of the actual support structure so as to eliminate the entire hollow box girder lattice track system, which greatly reduces the supported weight and thus reduces the cost of the system.

It is also an object of the present invention to facilitate maintenance of the carriages supporting the transport units from an overhead grid system by allowing immediate access to the carriages and their components, such as motors, bearings, rollers, spherical ball supports, and allowing open inspection of the components of the grid track system, thereby preventing damage and possible failure of the grid track structure due to long-term metal fatigue.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood with reference to the accompanying drawings, in which:

FIG1 is a top view of a prior art elevated grid track system shown mounted above a plurality of vertically stacked storage cells that are open toward an island of a center row of storage cells, and wherein one or more conveyor units are mounted to travel along the intersecting hollow open box beams, and wherein the conveyor units raise and lower carriers holding items to be placed into and/or removed from the storage cells;

FIG2 is a top view of another prior art elevated hollow box girder grid track system similar to FIG1 , the system being shown mounted above a plurality of vertically oriented storage cells, wherein the storage cells are vertically open to receive containers, pallets, and other enclosures for storing goods and products, and wherein one or more conveyor units are mounted to travel along the intersecting hollow open box girders, and wherein the conveyor units raise and lower carriers holding items to be placed into and/or removed from the storage cells;

FIG3 is an enlarged view of the prior art transport unit shown in FIG1 , the transport unit being suspended from a suspension pin extending through a central open slot of four carriages mounted within a hollow box beam from an overhead grid rail system;

FIG4 is a cross-sectional view taken through two intersecting open box girders of the elevated grid track system shown in FIG3 , and illustrating a prior art support carriage installed within one of the intersecting hollow box girders, and illustrating open rails in the other intersecting open box girder of the grid track system;

5 is a top cross-sectional view showing the prior art carriage of FIG. 4 installed within an open box beam of a prior art grid track system;

FIG6 is a partial view of one of the "I" beams forming the cross-elevated grid rail system of the present invention and which, for the reasons disclosed herein, may replace the open box beam of the prior art;

FIG7 is an end view taken along line 7-7 of FIG6;

FIG8 is a schematic diagram of a pedestal connector for connecting the ends of two X-oriented "I" beams and two Y-oriented "I" beams in a perpendicular relationship to each other, thereby creating an open intersection in an overall elevated grid track system utilizing multiple connected X and Y "I" beams in accordance with the teachings of the present invention;

FIG9 is a cross-sectional view showing the base connector of FIG8 welded between adjacent Y and X “I” beams of the grid track structure of the present invention, and showing a carriage for supporting a load transfer unit from the “I” beam track structure at the intersection of the “I” beams;

10 is a cross-sectional view taken along line 10-10 of FIG. 9 , showing bidirectional rollers and spherical rollers for supporting the carriage of FIG. 9 on the upper surface of the lower flange of the “I” beam forming the elevated grid rail structure of the present invention;

FIG11 is a schematic diagram similar to FIG10 , but showing only the portion supporting the carriage;

FIG12 is a side view of the carriage of FIG11 taken along line 12-12 of FIG11; and

FIG. 13 is a cross-sectional view taken along line 13 - 13 of FIG. 11 .

DETAILED DESCRIPTION

With particular reference to FIG. 1 of the accompanying drawings, the system of the present invention will be described in conjunction with or utilizing a prior art storage warehouse or building 20. It should be noted that the system can be used in other environments, such as mini-warehouses, distribution warehouses, garages, ships, etc. The building is divided into a plurality of rows 23 of vertically layered cells 24. The cells are defined by vertically and horizontally extending steel beams. In this embodiment, the cells are open in the horizontal direction (e.g., at 28) to receive items or containers "C" carried by pallets "P", which are transported by lifting equipment 29, wherein the lifting equipment 29 is connected to a load transfer carrier or unit 30 by cables 32, which is linearly movable in the X and Y directions along an elevated grid track system 22 formed by hollow open box beams taught in the prior art. The grid includes open box beams 25 extending in the X direction and intersecting open box beams 26 extending in the Y direction.

Referring to FIG3 , a transport unit 30 is suspended from similar, adjacent pairs of beams 25 and 26 by spindles 27 extending through open slots 31 in the lower surfaces of the box beams 25 and 26. The spindles are mounted to carriages 35 (see FIG4 and FIG5 ) that are movable within the box beams. Typically, four carriages are attached to each transport unit to support the transport unit on two adjacent X beams 25 and two adjacent Y beams 26, with the X beams 25 and Y beams 26 oriented so that they intersect in a generally perpendicular relationship at an open intersection 37. Each transport unit (see FIG1 and FIG3 ) includes a crane 38 for controlling cables 32, which are used to raise and lower shelves or objects 29 aligned with the cells 24, thereby transferring the items or objects to and from the transport unit and cells.

Referring to FIG2 , the grid track system of the present invention may also utilize an elevated storage system 21 having a plurality of vertically open storage cells 35, wherein multiple containers (C1-C7) may be stacked one upon another in a closely spaced, side-by-side relationship, thereby maximizing the storage capacity of a building or ship. As with the system of FIG1 , the containers are transported along the elevated grid track system 22′ by load transfer carriers or cells 40, which are formed by intersecting X- and Y-oriented hollow open box beams 25′ and 26′, similar to those described with reference to the embodiment of FIG1 . In this embodiment, the cells 40 may be sized to allow conventional and standard freight or international shipping containers (C1-C7) to be transported to and from each cell by conventional means known in the art. In some examples, the cells are sized to accommodate other sizes of items to be stored or temporarily stored, such as for supporting trays when supporting vehicles or ships, such as in high-density automated parking garages. A grid rail system 22' for supporting movable transport units 40 is provided above the cells and spaced a distance above the tallest cell in each vertical array of cells, thereby allowing the transport unit 40 and any supported objects to be moved from cell to cell. Each transport unit includes a crane 41 for raising and lowering container engagement structures, such as a conventional equalizing beam 42, that supports one of the containers "C1-C7" when lowering or raising the container from the cell 35.

Similar to the structure shown in FIG3 , the transport units 40 are suspended from similar and adjacent pairs of beams 25′ and 26′ by spindles 27 that pass through open slots 31 in the lower surfaces of the beams 25′ and 26′. The spindles are mounted to carriages 35 that are movable within the beams (see FIG4 and FIG5 ). The transport units 40 include drive gears or wheels driven by onboard motors to move the units along the beams 25′ and 26′.

With particular reference to Figures 4 and 5 , a portion of a conventional hollow box grid track system is shown. The grid track system comprises intersecting X and Y open box beams forming guide rails 25 and 26, or 25' and 26', respectively. At least one movable transport unit 30 or 40 is mounted for movement along the track system in an X-Y motion pattern. The transport unit is supported by a carriage 35 supported on the upper surface of the lower horizontal flange 45 of the box beam by directional rollers 46 and spherical rollers 47.

As previously stated, multiple transfer units may be operated within the grid track system of the present invention in accordance with the teachings of the present invention, thereby enabling simultaneous relocation of containers within a development area defined above higher level cells within a building or other structure.

The system of the present invention may be fully automated and interfaced with an inventory control system to direct each transport unit to a given container location and a given cell within the storage area by multiplexing command signals from the inventory control system through the power cable trough network.

With such a system, it is possible to automatically position a designated container and to appropriately move containers above the designated container and thereafter reposition a designated container that has once been taken up by the transfer unit and its lifting mechanism.

As previously noted, there are problems with the overhead grid rail system used to support transport vehicles (such as 30 and 40) relative to the storage cells and loading and unloading areas. First, the open box beams are expensive to form and difficult to inspect to ensure that they are free of fatigue or cracks that could cause failures in system operation. Often, cracks and defects occur within the box structure and are therefore not readily apparent to technicians, mechanics, or inspectors. Furthermore, to maintain the support carriages 35 within the box beams, the carriages must be removed, significantly increasing maintenance costs.

With particular reference to Figures 6 to 13, the details of the elevated grid track system of the present invention will be described in detail. Unlike the prior art elevated grid track structures shown in Figures 1 to 5, which utilize open hollow box beams to form the grid track system, with the present invention, the grid track system is formed by "I"-shaped steel beams 50 and 51 that are welded and/or bolted to each other in a cross X-Y pattern. Referring to Figure 10, the "I" beam 50 is shown as extending in the X direction, while the "I" beam 51 extends in the Y direction, but the directions can be reversed. Each "I" beam includes an upper flange 52 and a lower flange 53 that extend outward at a proper angle to a center vertical web 54. Each carriage 55 for supporting the transport unit of the present invention is designed to be supported on the upper surface of the lower flange 53 of each "I" beam 50 and 51, respectively, located at opposite ends of the center vertical web 54 of each "I" beam 50 and 51.

Utilizing "I" beams to form the elevated grid track structure "G" (see FIG. 10 ) improves machinist access to the carriages 55 associated with each transport unit, thereby making maintenance and repair of the carriages much easier, more efficient, and less costly than is achievable utilizing the hollow box beam structures of the disclosed prior art. Furthermore, the utilization of "I" beams reduces the costs associated with the construction and maintenance of the elevated grid track system upon which the transport units will move as part of the support structure by utilizing more economical, lighter weight, and more readily available "I" steel beams to form the X-Y grid. When compared to the more conventional hollow box beams used in the aforementioned prior art, the "I" beams provide greater strength, resulting in less deflection and less fatigue. By opening the beam structure for easily accessible inspection, any indication of cracks or fatigue, or fatigue of the "I" beams, can be quickly identified so that appropriate action or repair can be taken before the "I" beams fully fatigue, thereby resulting in a safer and more reliable track system for supporting transport units or carriers, such as 30 and 40, used on the grid track structure of the present invention.

To allow the carriage to pass through each intersection 59 between the "I" beams of the present invention, where the beams "I" are assembled in the X-Y plane and are generally at appropriate angles relative to each other, the structure of the "I" beams must be modified. Therefore, with particular reference to Figures 6 and 7, each end of the web 54 and lower flange 53 of each "I" beam 50 and 51 is formed with a lower cutout or opening portion 60, wherein the lower horizontal flange 53 includes a leading edge 53' that does not reach the leading edge 52' of the upper horizontal flange 52, wherein the leading edge 52' is shown as not reaching the upper extension 61 of the web. The opening 60 in the center web 54 of each "I" beam is removed to provide clearance for the carriage 55 to pass through. Furthermore, when the beams are welded in assembled relation in an X-Y pattern, openings 60 are provided in both the X and Y directions, allowing the carriage to move linearly along the "I" beams 50 and 51 at all of their intersections.

In order to securely connect the intersecting "I" beams 50 and beams 51 in the desired X-Y grid pattern to each other, the web 54 of each "I" beam must be welded or otherwise secured to at least the web 54 of the mating or intersecting "I" beam. In the present invention, at each intersection 59 of the X-Y "I" beams, and as shown in FIG9 , portions of the upper horizontal flange 52 and lower horizontal flange 53 are inset inwardly into the projected end 61 of the central vertical web 54 of each "I" beam. Furthermore, as shown in FIG6 , the front face 62 of each projected end 61 of each central vertical web includes a concave free end portion 63 for positioning the "I" beam against the support surface of a support base 70 (see FIG8 and FIG9 ) to which the vertical web of each X- and Y-oriented "I" beam will be welded, as indicated by the dark weld lines 65 in FIG9 .

Continuing with reference to FIG9 , at each intersection 59 of the X-Y "I" beams, two pairs of opening areas must be provided for the passage of a carriage 55 supporting a more conventional conveyor unit as described above and in the prior art. The carriage openings are created by aligning the openings or cutout portions 60 of each "I" beam on opposite sides of a central support base 70. Base 70, shown in FIG8 , comprises a central vertically oriented body 71, which is generally enlarged and squared at a lower end 72 and integrally forms the central vertically oriented body 71 with an upper end 73 of smaller cross-sectional dimensions, and wherein outwardly curved or convex surfaces 74 form transition areas with each of the four sides 75 of the base. The curvature of the transition areas is provided to provide complementary support surfaces for the curved free ends 63 of the extensions 61 of the central vertical web 54 of each of the four "I" beams connected at each intersection 59 of the grid track system.

Each base also includes an upper steel plate 76 sized to cooperatively support the spaced area 77 formed between the leading edge 52' of each upper flange 52 of the "I" beam, as shown in FIG9 . In this regard, the upper steel plate is generally the same thickness as the upper flange 52 of the "I" beam, and the plate 76 may be welded to the edge 52' of the flange 52, as indicated by W1. Each flange also includes a lower transfer steel plate 78 integrally formed or welded to the bottom of the lower portion 72 of the body 71 and generally square in shape, having four sides S1, S2, S3, and S4. The transfer plate is sized to fit within the open area 60 defined between the opposing ends 53' of the lower flange 53 of each beam 50 and 51, thereby creating four spaced open passageways 95 and 95' between the ends 53' of the lower flanges of the X and Y beams and the four sides of the transfer plate for passage through the carriage support frame 80, as will be described below. Furthermore, the lower steel plate 76 of each base may be welded or integrally formed with the body of the base. In Figure 9, both the upper plate portion 76 and the lower transfer plate 78 are shown as being integrally formed with the body of the base.

Referring to Figures 11-13, a support carriage 55 for transporting one of the conveyor units 34 and 40, or other similar conveyor units, is shown in greater detail. Figure 11 is a top plan view of the carriage showing four spaced upper corner plates 82 (shown in solid lines) mounted and secured to four pegs 83, which connect the upper plate portion to a generally solid base 84 having a central opening 90 therein for passing a T-shaped pin 87 that connects the carriage 55 to the conveyor unit. The frame of each carriage, formed by the plates, pegs, and base, is preferably formed of steel to provide maximum support. The upper portion of the carriage frame also defines open passageways 91 and 92 (see Figure 11) that allow the carriage to pass through relative to the base 70. As described above, typically four carriages are used to support or suspend each conveyor unit (such as 30 and 40) from a pair of spaced "I" beams 50 and 51.

Mounted to the top of each plate 82 are a plurality of sockets 85 containing spherical ball rollers 86 for supporting the carriage 55 between the upper surface of the lower flange 54 of each "I" beam 50 and 51 and the transfer plate 78 of the base 70. In the figure, nine spherical ball rollers are mounted on each plate 82, but this number can vary. Spherical ball rollers are heavy-duty industrial rollers capable of supporting significant weight, so the carriage can support several tons of weight during use of the storage system. Also mounted to the lower surface of the plate 82 are two sets of spaced-apart, oriented extension rollers 88. Referring to FIG. 13 , the oriented rollers 88 have oriented extension axes so that the rollers support the carriage in the X direction, and the oriented rollers 88′ support the carriage in the Y direction as the carriage moves along the lower flange 53 of the "I" beam of the grid track system. Again, the number of rollers can be varied and maintained within the teachings of the present invention. As shown in Figures 9 and 10, when the carriage moves in the Y direction as in Figure 10, the rollers 88 used to support the carriage in the X direction of the "I" beam 50 pass through the open space 95 formed between the transfer plate 78 and the spaced "I" beams. When the carriage moves in the X direction at the intersection 59, the rollers 88 supporting the carriage along the flange 53 of the "I" beam 51 will pass through the opening 95'. The spherical ball rollers 86 and the guide rollers 88 are shown in phantom in Figure 11.

From above, the grid track system of the present invention allows for modification to more conventional "I" steel beams without loss of strength and assembly in a universal horizontal cross pattern of X-Y oriented rails or tracks by welding the upper flange 52 and web 54 to the body 71 and upper plate portion 76 of the base as shown in Figure 9. Figure 9 also illustrates how one of the carriages used to support the transport unit to the grid track system of the present invention can be through the centrally reinforced base 70.

The above description of the preferred embodiments of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiments described. It is intended that the scope of the invention be defined by all embodiments encompassed within the following claims and their equivalents.

Claims (13)

1. An overhead rail system for an automated material handling and storage facility, wherein at least one conveying unit is suspended from a carriage traveling along the rail system to move objects to and remove objects from vertically oriented storage cells, the rail system comprising a plurality of first and second "I" beams, the plurality of first and second "I" beams being assembled in an X-Y manner such that the first and second "I" beams intersect each other in a vertical relationship, and wherein each first and second "I" beam includes an upper horizontal flange and a lower horizontal flange connected by a central vertical web, each first and second "I" beam having opposing ends, the opposing ends of the plurality of first "I" beams being connected to the ends of a plurality of second "I" beams at a plurality of intersections of the first and second "I" beams, thereby providing clearance space between the opposing ends of the first and second "I" beams, the size of which allows the carriage to pass through it as the conveying unit moves along the rail system. 2. The overhead guide rail system for automated material handling and storage facilities according to claim 1, wherein the carriage is supported on the upper surface of the lower flange of each of a plurality of first and second "I" beams. 3. The overhead guide rail system for automated material handling and storage facilities according to claim 2, comprising a support base provided at each intersection of the ends of a plurality of first and second "I" beams, and means for connecting the ends of the plurality of first and second "I" beams to the support base. 4. The overhead guide rail system for automated material handling and storage facilities according to claim 3, wherein an extension of the central web of each of the plurality of first and second "I" beams extends outward in the longitudinal direction of the beam beyond the upper and lower flanges. 5. The overhead guide system for automated material handling and storage facilities according to claim 4, wherein the extension includes a shaped surface for cooperatively sitting on a complementary surface of an adjacent base. 6. The overhead guide system for automated material handling and storage facilities according to claim 5, wherein the end edge of the lower flange is further away from the formed surface of the web extension than the end edge of the upper flange of the plurality of first and second "I" beams. 7. The overhead guide rail system for automated material handling and storage facilities according to claim 6, wherein each base includes a vertical body and an upper plate portion for mounting between the end edges of the opposing upper flanges of the first and second "I" beams. 8. The overhead guide rail system for automated material handling and storage facilities according to claim 6, wherein each base includes a vertical body and a lower conveyor plate portion connected to the lower part of the body and extending toward the edge of the adjacent lower flange of the first and second "I" beams, and is sized such that it is spaced apart to form a gap for partial carriage passage. 9. An overhead rail system for an automated material handling and storage facility, wherein at least one conveying unit is suspended from a carriage traveling along the rail system to move objects to and remove objects from vertically oriented storage cells, the rail system comprising a plurality of first and second support beams assembled in an X-Y manner such that the first and second support beams intersect each other in a vertical relationship, and wherein each first and second support beam includes a horizontal flange connected to a central vertical web, each first and second support beam having opposing ends, the opposing ends of the plurality of first support beams connecting to the ends of a plurality of second support beams at a plurality of intersections of the first and second support beams, thereby providing clearance space between the opposing ends of the first and second support beams, the size of which allows the carriage to pass through as the conveying unit moves along the rail system. 10. The overhead guide rail system for automated material handling and storage facilities according to claim 9, comprising a support base provided at each intersection of the ends of a plurality of first and second support beams, and means for connecting the ends of the plurality of first and second support beams to the support base. 11. The overhead guide system for automated material handling and storage facilities according to claim 10, wherein an extension of the central web of each of the plurality of first and second support beams extends outward beyond the horizontal flange in the longitudinal direction of the beam. 12. The overhead guide system for automated material handling and storage facilities according to claim 11, wherein the extension includes a shaped surface for cooperatively sitting on a complementary surface of an adjacent base. 13. The overhead guide rail system for automated material handling and storage facilities according to claim 10, wherein each base includes a vertical body and a lower conveyor plate portion connected to the lower part of the body and extending toward the edge of the horizontal flange of the first and second support beams, and is sized such that it is spaced apart therefrom to form a gap for partial carriage passage.