Abstract:
A push-back storage rack comprises a frame defining at least one storage bay having a depth sufficient to accommodate a plurality of separate storage units; and a track-mounted carriage assembly mounted in the bay. The carriage assembly comprises at least two articulated carts connected together end-to-end for pivotal movement about a transverse horizontal axis. The carts ride on a track that has an upper track section, a lower track section, and an arcuate front section that joins the upper and lower track sections. The track guides the carts for movement between the front and the rear of the bay on the upper track section and directs the carts downwardly and then rearwardly on the lower track section in an inverted position as the carts move forwardly at the front end of the upper track section. The carts are thus stored underneath the upper track section and are brought upwardly to the upper track section as the carts are filled and moved rearwardly in the upper track section.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]    This is a continuation application of applicant&#39;s co-pending U.S. patent application Ser. No. 09/367,408, filed Mar. 14, 2000, which is a continuation-in-part application of co-pending U.S. patent application Ser. No. 08/388,634, filed on Feb. 14, 1995, both entitled PUSH-BACK STORAGE RACK, the disclosure of both applications being incorporated herein by reference. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention relates to push-back storage racks used in warehousing and more particularly to a push-back storage rack wherein moveable pallet carts are connected end-to-end and wrap around and fit under an upper storage rack.  
           [0004]    Warehouse storage racks typically comprise a frame structure divided into rows and columns that define storage bays for depositing storage units (e.g., pallets) of products to be stored. In order to conserve space in a storage facility, storage bays are sometimes more than one pallet deep, and moveable carriages, called “push-back racks”, are used to permit pallets to be moved to rearward storage locations from a single loading station at the front of the rack system. Most push-back racks employ overlying or nesting platforms that fit one on top of the other at the front storage compartment in the bay. As each platform is loaded and pushed rearwardly, the next platform is made available for the next pallet. Generally, the tracks on which the pallets are mounted are inclined forwardly so that gravity causes the pallets to slide or roll to the front of the storage bay. The track mechanisms and carts required for this type of push-back rack can be complex and expensive, and the system requires a different cart construction for each storage location in the bay. Moreover, the maximum storage unit depth of each bay is limited with stacking carts, and the stacking carts introduce height limitations into the bay.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In accordance with the present invention, a push-back storage rack that provides a convenient and effective push-back rack system, comprises a frame defining at least one storage bay having a depth sufficient to accommodate a plurality of separate storage units; a track-mounted carriage assembly is mounted in the bay. The carriage assembly comprises at least two carts, each sized to hold separate pallets or other storage units. The carts are connected together end-to-end for pivotal movement about a transverse horizontal axis. The track on which the carts ride has an upper track section which guides the carts for movement between the front and the rear of the bay. The track also includes a forward section and a lower track section which direct the carts downwardly and then rearwardly in the bay in an inverted position as the carts move forwardly at the front end of the upper track section. The carts are thus stored underneath the upper track section and are brought upwardly to the upper track section for use as the rearmost carts on the upper track section are filled and moved rearwardly on the upper track section.  
           [0006]    The preferred track of the present invention comprises opposed C-shaped track members at opposite sides of the storage bay, with the forward portion of the track section comprising an arcuate section that connects the upper and lower track sections. Other track constructions are possible.  
           [0007]    The storage carts are wheeled carts that ride in the track, with each wheeled cart preferably comprising a plurality of separate wheeled cart sections connected together for pivotal movement about a horizontal transverse axis. Desirably, the individual cart sections also are articulated at an intermediate longitudinal point to provide even further bending ability for the cart sections.  
           [0008]    The cart sections form a flat, stable platform for supporting pallets on the upper track section but bend easily around the arcuate forward track section for storage in an inverted position in an out-of-the-way location underneath the upper track section.  
           [0009]    The individual carts are connected together by a connecting mechanism that includes the axle for the wheels. The wheels are mounted on axles that fit through aligned sleeves that are connected to adjacent cart sections, thus permitting rotation of the wheels as well as pivotal movement of the carts with respect to each other.  
           [0010]    The present invention provides a compact and cost effective push-back rack system with interchangeable components, no stacking cart height limitations, and virtually unlimited bay depth.  
           [0011]    These and other features, objects, and benefits of the invention will be recognized by one having ordinary skill in the art, from the specification, the claims, and the drawing figures. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0012]    [0012]FIG. 1 is a side elevational view of a push-back rack system in accordance with the present invention.  
         [0013]    [0013]FIG. 2 is a fragmentary perspective view showing a forward comer of the track and cart system of the present invention.  
         [0014]    [0014]FIG. 3 is a front elevational view of the present invention, showing a pallet storage unit positioned on one of the carts of the present invention.  
         [0015]    [0015]FIG. 4 is a front elevational view similar to FIG. 3, wherein a final pallet rests on the rails of the track system.  
         [0016]    [0016]FIG. 5 is a perspective view showing the wheeled carts of the present invention.  
         [0017]    [0017]FIG. 6 is a plan view of one cart section of the present invention.  
         [0018]    [0018]FIG. 7 is an exploded perspective view showing the manner in which two carts or two cart sections are connected together.  
         [0019]    [0019]FIG. 8 is a fragmentary sectional view taken along lines  8 - 8  of FIG. 2, showing the manner in which two carts or cart sections are connected together.  
         [0020]    [0020]FIG. 9 is a fragmentary plan view showing the cart connection mechanism of FIG. 7 in an assembled condition.  
         [0021]    [0021]FIG. 10 is a fragmentary side elevational view of an intermediate portion of a cart section, showing the articulated side rails of the cart section.  
         [0022]    [0022]FIG. 11 is a fragmentary front sectional view showing a transverse alignment wheel on the cart riding in the track.  
         [0023]    [0023]FIG. 12 is a fragmentary front sectional view showing an alternative embodiment of a transverse alignment wheel for maintaining proper transverse position of the carts.  
         [0024]    [0024]FIG. 13 is a perspective view of an alternative embodiment of the cart system of the present invention.  
         [0025]    [0025]FIG. 14 is a plan view of the cart system of FIG. 13.  
         [0026]    [0026]FIG. 15 is a side elevational view of a portion of the cart system of FIG. 13, showing the wheels of the cart system riding in a section of track.  
         [0027]    [0027]FIG. 16 is a sectional view taken along line  16 - 16  of FIG. 15.  
         [0028]    FIGS.  17 A- 17 D are schematic drawings showing the manner in which the present invention is used for loading multiple pallets in a storage bay.  
         [0029]    [0029]FIG. 18 is an alternative embodiment showing the use of a separate pallet loading station at the front of the push-back rack system of the present invention.  
         [0030]    [0030]FIG. 19 is the view of FIG. 16 in mirror image and showing an alternative wheel, arrangement.  
         [0031]    [0031]FIG. 20 as a top plan view of a modular rack track middle section.  
         [0032]    [0032]FIG. 21 is an end elevational view along section line XXI-XXI of FIG. 20.  
         [0033]    [0033]FIG. 22 it is a side elevational view along section line XXII-XXII of FIG. 20.  
         [0034]    [0034]FIG. 23 is the view of FIG. 20, showing a strengthened modular rack track end section.  
         [0035]    [0035]FIG. 24 is an end elevational view along section line XXIV-XXIV of FIG. 23.  
         [0036]    [0036]FIG. 25 it is a side elevational view along section line XXV-XXV of FIG. 23.  
         [0037]    [0037]FIG. 26 is the view of FIG. 13, showing an alternative positioning of the cart section links.  
         [0038]    [0038]FIG. 27 is the view of FIG. 15, showing the alternative positioning of the cart section links of FIG. 26.  
         [0039]    [0039]FIG. 28 is a front elevational view of a front guard.  
         [0040]    [0040]FIG. 29 is a top plan view thereof.  
         [0041]    [0041]FIG. 30 is a right end elevational view thereof.  
         [0042]    [0042]FIG. 31 is a fragmentary, side elevational view of a storage rack, showing installation of a modular front curve section into a storage bay.  
         [0043]    [0043]FIG. 32 is the view of FIG. 30, showing the modular front curve section in final position.  
         [0044]    [0044]FIG. 33 is a fragmentary, side elevational view of a storage rack, showing installation of a modular middle section into a storage bay.  
         [0045]    [0045]FIG. 34 is the view of FIG. 33, showing the modular middle section in final position.  
         [0046]    [0046]FIG. 35 is the view of FIG. 33, showing installation of a modular end section into the storage bay.  
         [0047]    [0047]FIG. 36 is the view of FIG. 35, showing the modular end section in final position.  
         [0048]    [0048]FIG. 37 is the view of FIG. 36, showing connection of the modular sections.  
         [0049]    [0049]FIG. 38 is the view of FIG. 36, showing installation of the bottom stop assembly.  
         [0050]    [0050]FIG. 39 is a side elevational view of a back top stop bracket.  
         [0051]    [0051]FIG. 40 is a front elevational view thereof.  
         [0052]    [0052]FIG. 41 is a top plan view of a bottom stop assembly.  
         [0053]    [0053]FIG. 42 is a side elevational view thereof.  
         [0054]    [0054]FIG. 43 is an end elevational view thereof.  
         [0055]    [0055]FIG. 44 is the fragmentary side elevational view detail XLIV of FIG. 38, showing the bottom stop assembly installed. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0056]    Referring now to the drawings, an exemplary warehousing storage rack system  10 , shown in FIG. 1, comprises a frame  12  consisting of spaced vertical columns  14  and horizontal beams  16  that define a series of vertically and horizontally spaced storage bays  18 . A single storage bay  18  is shown in FIG. 1, with the storage bay comprising a front section  18 A, a middle section  18 B, and a rear section  18 C. Each storage bay section is positioned one behind the other and is sized to accommodate a standard size of storage unit. The storage unit is commonly a pallet  19 , which is loaded in the storage bay by a forklift truck  20 , supports products or goods  22 , and is generally known by one having ordinary skill in the art. A typical pallet is about forty inches (1016 mm) wide, about forty-eight inches (1219 mm) long, and about five inches (127 mm) tall.  
         [0057]    A track  24  extends from a front to a rear of the frame  12 , with the track having an upper section  26 , a lower section  28 , and a curved or arcuate front section  30  that connects the upper and lower sections of the track. A carriage mechanism consists of a plurality of wheeled carts  32  that are mounted end-to-end on the track  24 , with each cart being subdivided into separate wheeled cart sections  34 .  
         [0058]    Referring to FIGS. 2 and 3, track  24  comprises separate track sections positioned at opposing sides of storage bay  18 , with the tracks being supported on the columns  14  and separated from the columns by an about three inch (76 mm) square beam  16 . Each track  24  comprises an inwardly facing C-shaped channel member  40  that has opposing, upper and lower flanges  36  desirably spaced about 3-⅛ inches (79 mm) apart by a web portion. Carts  32  are provided with wheels  38  at the four corners thereof, with the wheels extending outwardly from the sides of the carts and riding in the channels  40  of the track  24 .  
         [0059]    The manner in which the carts  32  are constructed are shown in FIGS.  5 - 12 . In the illustrated embodiment, each cart  32  comprises four cart sections  34 , with each cart section comprising a rectangular frame that may be formed of about 2×2×⅛ inch (51×51×3 mm) angle iron, or the like, and that has opposing side rails  42 , a rear member  44 , and a front member  45 . Side rails  42  may preferably be articulated, as shown in FIG. 10. A front side rail section  46  is pivotally connected to a rear side rail section  48  by means of a rivet or pivot pin  50 . Pivot pin  50  extends outwardly from the side of the cart and has a wheel  58  rotatably mounted thereon. The wheel  58  may be a conventional, steel roller skate wheel as is commonly known. The wheel  58  engages the curved arcuate portion  30  of the track  24  and provides a low friction interface between the cart section  34  and the track. More preferably, the pivot pin  50  is provided at its end with a ball caster  56  (FIG. 19) to run along the web portion of the channel  40  and guide the cart section  34 , as will be understood by one having ordinary skill in the art.  
         [0060]    A top edge  49  (FIG. 10) of section  46  is recessed so that a forward edge of the side wall constitutes a flange  52  that overlaps the adjoining edge of side rail section  48 . By constructing the side rails  42  in this manner, they articulate downward, as shown in phantom in FIG. 10, to allow the cart sections to “bend” when they roll around the arcuate front section  30  of the track  24 . When the cart sections  34  are positioned in a horizontal position on the upper track  26 , however, upper edge  49  on section  46  engages upper edge  51  on section  48  to prevent side rail  46  from pivoting upwardly with respect to side rail  48 , beyond the horizontal position shown in FIG. 10. This also prevents the cart  32  from sagging under load when a storage unit, or pallet  19 , is mounted on the cart.  
         [0061]    The articulating side rails  42  are an important feature of the present invention because of the dimensions of the structure. In the preferred practice of the present invention, the distance between the upper and lower track sections  26  and  28 , respectively, is minimized and desirably is about 11.5 inches (292 mm). The individual cart sections  34  are each about 11.25 inches (286 mm) long. Thus, it is necessary to articulate each of the individual cart sections  34  to facilitate the movement of the cart sections around the curved front portion  30  of the track  24 , while minimizing the distance between the upper and lower track sections.  
         [0062]    The manner in which the carts  32  and individual cart sections  34  are connected together is shown in FIGS.  6 - 9 . Cart sections  34  and carts  32  are all connected in the same manner. An axle shaft  60 , having a head  61  and a narrow outer end  64  of reduced diameter, fits through a plurality of tubular axle fittings  68  that are mounted on one of the carts  32  and a tubular axle fitting  68  mounted on another of the carts. Axle fittings  66  are spaced apart sufficiently that tubular fitting  68  fit between them. Axle shaft  60  fits through interior openings  70  in the axle fittings  66 , when the fittings  66  and  68  are placed into alignment with each other. A spring C-clip or E-clip  72  fits in groove  74  in the axle shaft and holds the shaft in the axle fittings. Wheels  38  fit on narrower shaft  64  and are held in place by a nut or pin or the like  73  on the outer end of shaft  64 . A grease fitting  76 , such as a zerk nipple, mounted on the end of axle shaft  60  may be provided to supply grease through an interior opening  78  to grease outlets  80  and lubricate the axle shaft. The respective axle fittings are welded to the carriages.  
         [0063]    The axle fixtures forming the hinge of the present invention desirably have a one inch (25 mm) outside diameter, a {fraction (9/16)} inch (14 mm) inside diameter, and are ½ inch (13 mm) long. The axle is a greasable axle ½ inch (13 mm) in diameter and 3-½ inches (89 mm) in length. The wheels preferably are 1-½ inches (38 mm) wide and 3 inches (76 mm) in diameter and may be formed of phenolic resin or may be a metal wheel with bearings (sometimes referred to as a skate wheel).  
         [0064]    Transverse movement of the carts from a side-to-side direction may be restricted by special transverse alignment wheels of the type shown in FIGS.  11  or  12 . As shown in FIG. 11, wheel  82  is conical and tapered slightly inward as it extends outward, so it fits easily into track  24 . The wheel desirably has a diameter of about 3 to 2¾ inches (about 76 to 70 mm) and a taper of about 7-9E. The wheel also has a flange  84  extending radially greater than the distance between the upper and lower surfaces of the track  24  (preferably the flange diameter is about 3½ inches [89 mm]), providing an inward limit that the wheel may extend into the track. This restricts lateral movement of the cart  32 . Desirably, the axle  86  of the wheel is threaded and is received in a threaded opening  90  in the cart. The lateral position of the alignment wheel thus may be adjusted.  
         [0065]    Another embodiment of an alignment device is shown in FIG. 12. An angle fixture  92  is mounted to the side of the cart section with a horizontal wheel  93  mounted on a vertical axle  94  on flange  92 . The wheel  93  engages the outer wall or web  96  of channel  40  and constrains lateral movement of the cart section  34 .  
         [0066]    Another embodiment of the cart of the present invention is shown in FIG. 13. Cart  100  comprises a plurality of longitudinally spaced C-shaped cross beams  102 , which are mounted to plates  104  at each end thereof. Plates  104  have wheels  106  mounted thereon. Links  108  interconnect the adjacent wheels on each cross beam. Links  108  permit relative pivotal movement of the respective cross beams. The same type of lateral alignment mechanism described above and shown in FIGS. 11 and 12 can be employed with this embodiment of the invention.  
         [0067]    A modified embodiment of the present invention is shown in FIG. 18. In FIG. 18, the push-back rack structure  110 , shown in the right hand portion of the figure, is substantially the same as the rack structure described above, with the exception that an additional storage compartment is provided in each bay, each bay being four storage units deep. To accommodate four storage units, it is necessary that the carriage or cart train be three carts long. After the three carts are moved to the rear, a final pallet can be placed on the rails themselves, as shown in FIG. 4.  
         [0068]    An additional feature of the embodiment of FIG. 18 is that an additional rack section  112  is positioned at the front of the rack and is provided with a series of rollers  114 . This makes it possible to load a pallet  116  on section  112  and thereafter push the pallet onto the roll back rack. With the extra section  112  at the front of the rack, this rack can store pallets in a single bay to a depth of five pallets. Also as shown in the FIG. 18 embodiment, storage bays can be positioned one above the other to any desired height.  
         [0069]    While storage mechanisms employing two and three cart units are shown in the present invention, an advantage of the present system is that almost any number of carts can be employed in the rack system.  
         [0070]    The operation of the present invention is shown in FIG. 17A-D for an exemplary system using a bay that is three units deep. In FIG. 17A, a pallet  19 A is placed on cart  32 A. A stop plate  120  (shown in FIGS. 2, 3 and  4 ) prevents the loaded pallet from rolling under the influence of gravity out through the open end of the bay after the forklift truck has been removed. Stop plate is a right angle plate spaced about one inch above the carriage assembly. The stop plate is about three inches high and has a three inch long flange attached to column A and a 4-½ to 7 inch long stop flange that extends over the track and into the path of the pallet.  
         [0071]    As shown in FIG. 17B, when pallet  19 B is pressed against pallet  19 A, pallet  19 A rolls along with cart  32 A to section  18 B of the storage rack bay. Similarly, as shown in FIG. 17C, when pallet  19 C is pushed against pallet  19 B, all of the pallets slide inwardly one station further, so that (as shown in FIG. 17D) pallet  19 A and cart  32 A are in section  18 C of the bay. Similarly, pallet  19 C and cart  32 B are in section  1   8 B of the bay. Finally, pallet  19 C sits on the rail  24  in section  1   8 A of the bay. Stop  120  prevents any of the pallets from sliding outwardly unless lifted over the stop. The reverse operation is accomplished in removing the pallets from the rack, with gravity causing the cart to roll forwardly as each pallet at the front of the rack is removed. Desirably, the track is inclined at an inclination of one inch (25.4 mm) per four feet (1219 mm) of rack length.  
         [0072]    In the present invention, a simple C-channel track can be used to support and guide the carts. This track can be formed in uniform sections of 8 feet in length or so, with each section being cut to size and bolted together as desired. Thus, only straight sections of uniform track and the curved front portion of the track need to be prefabricated.  
         [0073]    In another embodiment of the invention, the push back storage rack system may be configured as a modular system having a front curve section  202 , an end section  204 , and as many middle sections  206  as are required or desired. This embodiment not only includes the modular configuration, it also incorporates a relocation of the cart interconnecting links  108  to an inboard position on the wheel axle  109  (FIGS. 19, 26, and  27 ).  
         [0074]    The modular middle section  206  is assembled with opposing, mirror image track assemblies  210  that have upper and lower track sections  26  and  28 , respectively, spaced apart, about the width of the carts  32 , and facing one another. A set of cart sections  34  are positioned in and extend along the length of the upper track section  26 . The upper and lower track sections  26  and  28 , respectively, are preassembled with generally vertical structural brackets  212  that hold the upper and lower track sections generally parallel with one another. The vertical structural brackets  212  may also have an inwardly extending flange member  214  that is slidably connected, preferably with the rearward vertical structural bracket, to fasten the modular rack section to a structural cross beam  16  of the rack system frame  12 , as will be understood by one having ordinary skill in the art. Most preferably, the upper and lower track sections  26  and  28 , respectively, are a generally G-shaped modification (FIG. 19) of the C-channel  40 , discussed further above, with an upward turned flange  220  on the lower leg  222 . The flange  220  is useful to maintain the wheels  106  in the channel and minimize any potential for the wheels to drift out of the track channel.  
         [0075]    The modular front curve section  202  is substantially similar to the modular middle section  206 , with mirror image track assemblies  210  having upper and lower track sections  26  and  28 , respectively, a set of cart sections  34  positioned in and extending along the upper track section, the upper and lower track sections been assembled with a generally vertical structural brackets  212 , and the upper and lower track sections being G-shaped. The modular front curve section  202  is, however, distinguished from the modular middle section  206  by a curve portion  230  that extends from the upper track section  26  to the lower track section  28 , connecting the upper and lower track sections for transfer of the cart sections  34  between them. The curve portion  230  also has a forward mounting plate to connect with the first horizontal load beam  16  or vertical column  14  of the rack frame  12 .  
         [0076]    As to the modular end section  204 , it is also substantially similar to the modular middle section  206 , with the same track assemblies  210  and the generally G-shaped track sections. The modular end section  204  is different from the modular middle section  206 , however, because of the use of a single cart  240  that is positioned in and extends along the upper track section, rather than a set of cart sections  34  as is used for each of the modular front curve section  230  and the modular middle section  206 . The single cart  240  of the modular end section generally conforms to the storage unit, pallet  19 , in width and length. The single cart  240  of the modular end section  204  is advantageous in positioning the push back storage rack system in an empty condition. That is, in addition to the stops and guards, the single cart  240  will not traverse around the curve portion  230  of the modular front curve section  202 , and will remain in position in the upper track section  26  of the modular front curve section, standing ready to receive a pallet for storage.  
         [0077]    In use, the modular push back storage rack system is installed into a storage rack frame  12  with the modular front curve section  202  being installed first (FIGS. 31 and 32). The modular section  202  is positioned in a front or first portion  18 A of a storage bay  18  and the second load beam  16  of the rack frame  12  is positioned between the back ends of the upper and lower track sections  26  and  28 , respectively. The modular front curve section  202  is slid reward so the front of the section and the mounting plate  232  clears the rack frame  12  and is positioned for secure attachment to the first or front load beam  16  at the front of the rack frame  12 . With the modular front curve section  202  so positioned, left hand  242 , center  244 , and right hand  246  stops and a front guard  248  (FIGS.  28 - 30 ) are mounted at the front load beam  16  for holding a pallet  19 , for example, in a ready positioned for retrieval or push back by another pallet that is added to the storage bay  18 .  
         [0078]    The modular middle section  206  is similarly positioned in a second portion  18 B of the rack frame  12 , behind of the modular front curve section  202 , by positioning the next, or third load beam  16  between the back ends of the upper and lower track sections  26  and  28 , respectively, and positioning the front of the modular middle section in coupling engagement with the back of the modular front curve section (FIGS. 33 and 34). The modular front curve and middle sections  202  and  206 , respectively, are interconnected with eight ¼-20 screws. As many of the modular middle sections  206  as are desired are sequentially connected, as just described, up to the last portion of the storage bay  18 . A modular end section  204  is then installed in the last portion of the storage bay  18 , in substantially the same manner that each of the modular middle sections  206  is installed (FIGS.  35 - 36 ). Again, the only significant, distinguishing feature of the modular end section  204  as compared to the modular middle section  206  is the use of a single cart  240  that extends along the length of the section  204  as opposed to a set of cart sections  34  that extend along the length of the section.  
         [0079]    With each of the modular curve, middle, and end sections  202 ,  206 , and  204 , respectively, installed in the rack frame  12 , adjoining carts  32  or  240  are interconnected by use of an access hole  250  (FIG. 37) that is positioned about mid-way along the upper track section  26  of the modular front curve section  204 . The last wheel  106  of a cart  32  is aligned with the access hole  250  so a link  108  (FIGS. 19 and 37) that extends forward from the next cart  32  or  240  may engage the axle  109  of that last wheel  106  and be secured with a nut  252 , preferably a cap nut or lock nut, by access to the wheel axle through the access hole  250  and to the nut  252  under the cart  32  (see FIG. 19).  
         [0080]    In addition to the stops and guards described above, a bottom stop (FIGS. 38 and 41- 44 ) may also be installed on the lower track section  28  at a location one pallet position in or forward from the rear of the unit. The bottom stop will, therefore, be positioned near the back end of the last modular middle section  206 , before the modular end section  204 . Also, a back, top stop bracket (FIGS.  38 - 40 ) may be installed at the back of the upper track section  26  of the modular end section  204  to keep the carts  32  and  240  from being pushed out the back of the upper track section  26 .  
         [0081]    Optionally, a center track  260  (FIGS.  23 - 25 ) may be installed between the upper track sections  26  of the modular front curve, modular middle, and modular end sections  202 ,  206 , and  204 , respectively, for rack storage systems that are required to carry extra heavy loads. In the optional, extra heavy load installation, each cart  32  and the singular cart  240  of the modular end section  204  will also be provided with center support wheels  106  to engage and run on the center track  260 .  
         [0082]    It should be understood that the foregoing is merely exemplary of the preferred practice of the present invention and that various changes and modifications may be made in the arrangements and details of construction of the embodiments disclosed herein without departing from the spirit and scope of the present invention, as defined in the appended claims.