Patent Publication Number: US-2011062100-A1

Title: Anti-tip bracket for use with mobile shelving

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed generally to a mobile in-track anti-tip system for use with a mobile shelving unit. 
     2. Description of the Related Art 
     Conventional mobile shelving units are shelving units supported by wheels that travel along one or more floor mounted tracks. The mobile shelving units may be arranged in a series and spaced apart along the track(s) so that a user can move the shelving units forward and backward along the track to gain access items stored in the shelving units. In many areas of the United States, laws or regulations require that mobile shelving units withstand at least a predetermined amount of seismic activity before tipping over and possibly injuring a user. Anti-tip systems typically used in conventional mobile shelving units include overhead systems and in-track systems. Overhead systems are coupled to the upper portions of the mobile shelving units. In contrast, in-track systems are configured to couple the shelving units to the track(s) to preventing tipping. 
     A need exists for new anti-tip systems for use with mobile shelving units. For example, an in-track anti-tip system that accommodates misaligned tracks is desirable. Further, an anti-tip system that may be serviced without the need to dissemble the shelving unit is also desirable. Additionally, anti-tip systems that may be configured to comply with the American&#39;s with Disabilities Act (“ADA”) are also desirable. Anti-tip systems that can be used with existing rack configurations are also desirable. The present application provides these and other advantages as will be apparent from the following detailed description and accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  is a perspective view of a pair of shelving units each mounted to a separate mobile in-track anti-tip system supported on a surface by a pair of spaced apart substantially parallel tracks. 
         FIG. 2  is an enlarged fragmentary perspective view of an anti-tip assembly of the mobile in-track anti-tip system coupled to one of the shelving units of  FIG. 1 . 
         FIG. 3  is an enlarged fragmentary view of the mobile in-track anti-tip system coupled to one of the shelving units of  FIG. 1 . 
         FIG. 4  is an exploded fragmentary view of the mobile in-track anti-tip system of  FIG. 3 . 
         FIG. 5  is an enlarged exploded fragmentary view of a left front corner portion of the mobile in-track anti-tip system of  FIG. 3  including a portion of the track adjacent the corner portion. 
         FIG. 6  is an enlarged exploded fragmentary view of the movable support assembly of the left front corner portion of the mobile in-track anti-tip system depicted in  FIG. 5 . 
         FIG. 7  is an enlarged fragmentary perspective view of the left front corner portion of the mobile in-track anti-tip system of  FIG. 3  including a portion of the track adjacent the corner portion taken from the back. 
         FIG. 8  is an enlarged exploded fragmentary view of the anti-tip assembly of the left front corner portion of the mobile in-track anti-tip system depicted in  FIG. 5 . 
         FIG. 9  is an enlarged perspective view of a second anti-tip assembly of the mobile in-track anti-tip system of  FIG. 3 . 
         FIG. 10  is an enlarged perspective view of a braking assembly of the anti-tip assembly of  FIG. 2 . 
         FIG. 11  is an enlarged fragmentary perspective view of the left front corner portion of the mobile in-track anti-tip system of  FIG. 3  taken from the back and illustrating the braking assembly in the brake released position. 
         FIG. 12  is an enlarged fragmentary perspective view of the left front corner portion of the mobile in-track anti-tip system of  FIG. 3  taken from the front and illustrating the braking assembly in the brake released position. 
         FIG. 13  is an enlarged perspective view of a first alternate embodiment of a braking assembly for use with the anti-tip assembly of  FIG. 2 . 
         FIG. 14  is an enlarged fragmentary perspective view of an alternate embodiment of a track for use with an alternate embodiment of a wheel, which may be incorporated in the mobile in-track anti-tip system. 
         FIG. 15  is a partially exploded perspective view of a shelving unit movable along a plurality of spaced apart substantially parallel tracks including at least one anti-tip assembly coupling the shelving unit to one of the tracks. 
         FIG. 16  is an exploded perspective view of a support assembly of the shelving unit of  FIG. 15 . 
         FIG. 17  is an enlarged perspective view of an alternative embodiment of an anti-tip assembly for use with an alternate embodiment of a braking assembly illustrated in a brake released position. 
         FIG. 18  is an enlarged fragmentary perspective view of the braking and anti-tip assemblies of  FIG. 17 . 
         FIG. 19  is an enlarged perspective view of an inner C-shaped bracket of the anti-tip assembly of  FIG. 17 . 
         FIG. 20  is an enlarged fragmentary perspective view of an upright member, a retaining member, and a housing of the braking assembly of  FIG. 17  connected to the first and second inner C-shaped brackets of the anti-tip assembly of  FIG. 17  by a limit bolt having its distal end portion positioned inside the retaining member. 
         FIG. 21  is an enlarged perspective view of the anti-tip and braking assemblies of  FIG. 17  illustrated in a brake engaged position. 
         FIG. 22  is an enlarged perspective view of the limit bolt, a first braking member, a second braking member, and a lock nut of the anti-tip and braking assemblies of  FIG. 17 . 
         FIG. 23  is an enlarged front view of the anti-tip and braking assemblies of  FIG. 17  illustrated in a brake released position. 
         FIG. 24  is an enlarged front view of the anti-tip and braking assemblies of  FIG. 17  illustrated in a brake engaged position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a shelving unit  100  coupled to a mobile in-track anti-tip system  102  supported on a surface  104 , such as a floor, by a first track “T 1 ” spaced apart from and substantially parallel with a second track “T 2 .” 
     Tracks 
     In the embodiment illustrated, the first track “T 1 ” is substantially identical to the second track “T 2 .” Each of the tracks “T 1 ” and “T 2 ” is elongated and defines a separate path of travel (illustrated by a double headed arrows “P 1 ” and “P 2 ,” respectively) for the shelving unit  100  along the surface  104 . The tracks “T 1 ” and “T 2 ” are spaced apart and arranged along the surface  104  such that they are substantially parallel with one another. Unfortunately, real world constraints make it difficult to align the tracks “T 1 ” and “T 2 ” to be perfectly parallel. Thus, a certain amount of misalignment is generally present. The anti-tip system  102  is configured to travel along a less than perfectly aligned pair of tracks “T 1 ” and “T 2 ,” avoid binding that might otherwise be caused by such misalignment, and at the same time prevent the shelving unit  100  from becoming disengaged from the tracks “T 1 ” and “T 2 ” and tipping over. 
     As mentioned above, the first track “T 1 ” is substantially identical to the second track “T 2 .” For ease of illustration, the structures of the first and second tracks “T 1 ” and “T 2 ” will be described with respect to the second track “T 2 .” However, all of the structures described with respect to the second track “T 2 ” are also present in the substantially identical first track “T 1 .” 
     Turning to  FIG. 2 , the second track “T 2 ” has a longitudinally extending central portion  140  and a first pair of flanges  142  and  144  that extend outwardly away from the central portion  140  and along the surface  104  (see  FIG. 1 ). For ease of illustration, the surface  104  has been omitted from  FIG. 2 . Fasteners  146 , such as concrete fasteners, concrete anchors, bolts, screws, and the like, may be used to fasten the first pair of flanges  142  and  144  to the surface  104  (see  FIG. 1 ). 
     The second track “T 2 ” includes a second pair of flanges  152  and  154  spaced upwardly from the first pair of flanges  142  and  144 , respectively, and extending outwardly away from the central portion  140 . The flange  152  has a distal portion  156  and the flange  154  has a distal portion  158 . 
     A first longitudinally extending channel  162  is defined between the flange  142  and the flange  152  and a second longitudinally extending channel  164  is defined between the flange  144  and the flange  154 . The flange  152  overhangs the first channel  162  and the flange  154  overhangs the second channel  164 . The first channel  162  has a bottom portion  166  and the second channel  164  has a bottom portion  168 . 
     The central portion  140  has an upwardly opening channel  170  defined between a pair of spaced apart angled sidewalls  172  and  174  and a bottom portion  176  extending transversely between the sidewalls  172  and  174 . The bottom portion  176  may be curved or trough shaped. At least a portion of each of the sidewalls  172  and  174  may be lined along the inside of the channel  170  by a wear strip  178 . In the embodiment illustrated, each of the sidewalls  172  and  174  has a pair of spaced apart lips  182  and  184  configured to retain the wear strip  178  against the sidewall. 
     The central portion  140  includes a stiffener  190  opposite the channel  170  and adjacent the surface  104  (see  FIG. 1 ). The stiffener  190  is configured to help maintain the shape of the central portion  140  and/or provide guiding for multiple sections of track. 
       FIG. 14  illustrates an alternate embodiment of the second track “T 2 .” Like reference numerals have been used to identify like components in  FIG. 14  and  FIG. 2 . Turning to  FIG. 14 , a track  192  includes a longitudinally extending rail  194  disposed within an upwardly opening channel  195  located in the central portion  140  of the track  192 . In the embodiment illustrated, the rail  194  has a generally circular cross-sectional shape. However, this is not a requirement and embodiments in which the rail has alternate cross-sectional shapes, such as oval, elliptical, square, rectangular, arbitrary, and the like, are within the scope of the present teachings. A first longitudinally extending side channel  196  extends along one side of the rail  194  and a second longitudinally extending side channel  197  extends along the other side of the rail  194 . Further, in the embodiment illustrated, the wear strips  178  (see  FIG. 2 ) and lips  182  and  184  (see  FIG. 2 ) configured to retain the wear strip  178  against the sidewalls  172  and  174  have been omitted. The track  192  may be used with the mobile in-track anti-tip system  102  (see  FIG. 1 ) in place of the first track “T 1 ,” and/or the second track “T 2 .” 
     Shelving Unit 
     The shelving unit  100  depicted in  FIG. 1  and described herein is provided for illustrative purposes. As is appreciated by those of ordinary skill in the art, the shelving unit  100  is not intended to be limiting and through application of ordinary skill to the present teachings, the anti-tip system  102  could be used with other shelving unit configurations. 
     The shelving unit  100  illustrated includes four spaced apart upright supports  200 A- 200 D and at least one shelf  202  extending between the upright supports  200 A- 200 D. Each of the shelves  202  is illustrated as being generally rectangular in shape supported at its corners by the upright supports  200 A- 200 D. As may best be viewed in  FIG. 3 , each of the upright supports  200 A- 200 D has a lower or base portion  204 A- 204 D, respectively, that is coupled to the anti-tip system  102 . Optionally, each of the base portions  204 A- 204 D includes at least one aperture  206 . 
     Optionally, a second shelving unit  220  may be coupled to a second mobile in-track anti-tip system  222  substantially identical to the first mobile in-track anti-tip system  102  and configured to move the second shelving unit  220  along the first and second tracks “T 1 ” and “T 2 .” Further, additional shelving units (not shown) may be arranged in a series along the first and second tracks “T 1 ” and “T 2 ” and configured to move along the first and second tracks “T 1 ” and “T 2 .” 
     Mobile in-Track Anti-Tip System 
     As may best be viewed in  FIGS. 3 and 4 , the anti-tip system  102  includes a support frame  300 , a plurality of movable support assemblies  302 A- 302 D, and a plurality of anti-tip assemblies  304 A- 304 D. The support frame  300  provides attachment points to couple the movable support assemblies  302 A- 302 D, and the anti-tip assemblies  304 A- 304 D to the base portions  204 A- 204 D of the shelving unit  100 . The support assemblies  302 A- 302 D support the shelving unit  100  (see  FIG. 1 ) and allow it to be moved along the tracks “T 1 ” and “T 2 ” (see  FIG. 1 ). The anti-tip assemblies  304 A- 304 D prevent the shelving unit  100  from being tipped over or otherwise disengaged from the tracks “T 1 ” and “T 2 ” (see  FIG. 1 ). Optionally, the anti-tip system  102  includes a braking assembly  306  configured to prevent movement of the shelving unit  100  along the tracks “T 1 ” and “T 2 .” 
     Support Frame 
     The support frame  300  includes a plurality of corner brackets  310 A- 310 D, and a plurality of frame members  312 A- 312 D. The corner brackets  310 A- 310 D couple the frame members  312 A- 312 D to the base portions  204 A- 204 D of the upright supports  200 A- 200 D. The corner brackets  310 A- 310 D are substantially identical to one another. However, as is apparent to those of ordinary skill in the art, the orientation of the brackets  310 A- 310 D varies depending upon to which of the upright supports  200 A- 200 D the brackets are coupled. Each of the corner brackets  310 A- 310 D may be implemented as an upright L-shaped member having a first arm portion  314  coupled to a second arm portion  316  by a bent portion  318 . The first arm portion  314  and the second arm portion  316  may mirror one another across the bent portion  318 . 
     The first arm portion  314  and the second arm portion  316  each include one or more through-holes  319  and at least one aperture  320  (illustrated as a slot). Each of the apertures  320  is configured to receive a fastener (not shown) that may be used to couple the corner brackets  310 A- 310 D to the base portions  204 A- 204 D, respectively, of the upright supports  200 A- 200 D, respectively, of the shelving unit  100  (see  FIG. 1 ). For example, after the apertures  320  of each of the corner brackets  310 A- 310 D are aligned with the apertures  206  formed in the base portions  204 A- 204 D, respectively, fasteners (not shown) may be inserted through the aligned apertures  320  and  206  and used to couple the corner brackets  310 A- 310 D to the upright supports  200 A- 200 D, respectively. 
     Each of the frame members  312 A- 312 D is generally L-shaped having a first arm portion  322  coupled to a second arm portion  324  by a bent portion  326 . Each of the frame members  312 A- 312 D further includes a first end portion  332  opposite a second end portion  334 . A first through-hole  336  is formed in the second arm portion  324  in the first end portion  332  of each of the frame members  312 A- 312 D. A second through-hole  338  is formed in the second arm portion  324  in the second end portion  334  of each of the frame members  312 A- 312 D. 
     One or more through-holes  339  may be formed in the first arm portion  322  at both the first end portions  332  and the second end portions  334  of the frame members  312 A and  312 C. The through-holes  339  formed in the first end portion  332  of the frame member  312 A are configured to be aligned with the through-holes  319  formed in the first arm portion  314  of the corner bracket  310 B. The through-holes  339  formed in the second end portion  334  of the frame member  312 A are configured to be aligned with the through-holes  319  formed in the second arm portion  316  of the corner bracket  310 A. The through-holes  339  formed in the first end portion  332  of the frame member  312 C are configured to be aligned with the through-holes  319  formed in the first arm portion  314  of the corner bracket  310 D. The through-holes  339  formed in the second end portion  334  of the frame member  312 C are configured to be aligned with the through-holes  319  formed in the second arm portion  316  of the corner bracket  310 C. 
     At the first corner bracket  310 A, the second end portion  334  of the first frame member  312 A is coupled to the first end portion  332  of the fourth frame member  312 D. When so coupled, the first through-hole  336  of the first end portion  332  of the fourth frame member  312 D is aligned with the second through-hole  338  of the second end portion  334  of the first frame member  312 A and a fastener  340 A, such as a bolt, screw, and the like, is inserted through the aligned through-holes  336  and  338  to couple the frame members  312 A and  312 D together. 
     At the second corner bracket  310 B, the first end portion  332  of the first frame member  312 A is coupled to the second end portion  334  of the second frame member  312 B. When so coupled, the second through-hole  338  of the second end portion  334  of the second frame member  312 B is aligned with the first through-hole  336  of the first end portion  332  of the first frame member  312 A and a fastener  340 B, such as a bolt, screw, and the like, is inserted through the aligned through-holes  338  and  336  to couple the frame members  312 A and  312 B together. 
     At the third corner bracket  310 C, the first end portion  332  of the second frame member  312 B is coupled to the second end portion  334  of the third frame member  312 C. When so coupled, the first through-hole  336  of the first end portion  332  of the second frame member  312 B is aligned with the second through-hole  338  of the second end portion  334  of the third frame member  312 C and a fastener  340 C, such as a bolt, screw, and the like, is inserted through the aligned through-holes  336  and  338  to couple the frame members  312 B and  312 C together. 
     At the fourth corner bracket  310 D, the first end portion  332  of the third frame member  312 C is coupled to the second end portion  334  of the fourth frame member  312 D. When so coupled, the second through-hole  338  of the second end portion  334  of the fourth frame member  312 D is aligned with the second through-hole  336  of the first end portion  332  of the third frame member  312 C and a fastener  340 D, such as a bolt, screw, and the like, is inserted through the aligned through-holes  338  and  336  to couple the frame members  312 C and  312 D together. 
     Movable Support Assemblies 
     In the embodiment illustrated, the movable support assemblies  302 A- 302 D are coupled to the support frame  300 . Each of the movable support assemblies  302 A- 302 D is configured to support at least a portion of the shelving unit  100  via the support frame  300 . Together the movable support assemblies  302 A- 302 D are movable along the tracks “T 1 ” and “T 2 ” (illustrated in  FIG. 1 ). Referring to  FIG. 1 , when sufficient motive force is applied to the shelving unit  100  (for example, when a user manually pushes the shelving unit  100 ), the shelving unit  100  is movable along the paths of travel (illustrated by the double headed arrows “P 1 ” and “P 2 ,” respectively) defined by the tracks “T 1 ” and “T 2 .” Motive force may be applied to the shelving unit  100  manually by a user and/or mechanically by an assist device (not shown), such as a mechanical or electrically powered assist device (not shown). 
     Returning to  FIGS. 3 and 4 , in the embodiment illustrated, the first support assembly  302 A is coupled to second end portion  334  of the first frame member  312 A, the second support assembly  302 B is coupled to first end portion  332  of the first frame member  312 A, the third support assembly  302 C is coupled to second end portion  334  of the third frame member  312 C, and the fourth support assembly  302 D is coupled to first end portion  332  of the third frame member  312 C. The support assemblies  302 A- 302 D are substantially identical to one another. Therefore, for the sake of brevity, only the second support assembly  302 B will be described in detail. 
       FIG. 5  provides an exploded view of the second support assembly  302 B and the components of the anti-tip system  102  adjacent the second support assembly  302 B.  FIG. 6  provides an enlarged exploded view of the components of the second support assembly  302 B.  FIG. 7  illustrates the support assembly  302 B coupled to first end portion  332  of the first frame member  312 A. For ease of illustration, the second frame member  312 B has been omitted from  FIGS. 5-7 . 
     Referring to  FIG. 7 , the support assembly  302 B includes a wheel  342  configured to be received inside the upwardly opening channel  170  of the second track “T 2 .” The wheel  342  may be rolled along the wear strips  178  lining the sidewalls  172  and  174  when the shelving unit  100  (see  FIG. 1 ) is moved from one location to another. 
       FIG. 14  illustrates an alternate embodiment of the wheel  342  for use with the track  192  having the rail  194 . Like reference numerals have been used to identify like components in  FIG. 14  and  FIG. 7 . Turning to  FIG. 14 , a wheel  343  includes a circumferentially extending groove  344  configured to receive an upper portion of the rail  194 . The wheel  343  may roll along the rail  194  in a manner similar to the manner in which a wheel of train rolls along a rail of a train track. The groove  344  is flanked by a first circumferentially outwardly extending portion  345  and a second circumferentially outwardly extending portion  347 . The first outwardly extending portion  345  extends downwardly into the first longitudinally extending side channel  196 , which extends longitudinally alongside the rail  194 , and the second outwardly extending portion  347  extends downwardly into the second longitudinally extending side channel  197 , which extends longitudinally alongside the rail  194 . The first and second outwardly extending portions  345  and  347  help maintain the rail  194  inside the groove  344  of the wheel  343  thereby helping to maintain the wheel  343  on the track  192  as it rolls along the track  192 . 
     Turning to  FIG. 6 , the support assembly  302 B includes a U-shaped wheel mount member  346 . In the embodiment illustrated in the figures, the wheel mount member  346  has a pair of spaced apart substantially parallel sidewalls  350  and  352  defining a gap  356  therebetween. Each of the sidewalls  350  and  352  has a top portion  360 , a bottom portion  362  opposite the top portion, a first edge portion  364 , and second edge portion  366  opposite the first edge portion. Further, a through-hole  368  extends laterally through each of the sidewalls  350  and  352 . The through-holes  368  formed in the sidewalls  350  and  352  are juxtaposed with one another and aligned across the gap  356 . The sidewalls  350  and  352  are coupled together along their top portions  360  by a transverse portion  370 . A through-hole  374  is formed in the transverse portion  370 . 
     Optionally, the wheel mount member  346  includes a plurality of bores or channels  378  each configured to receive a fastener  380  (see  FIGS. 5 and 7 ), such as a bolt, screw, and the like, used to fasten the wheel mount member  346  to the first arm portion  322  of the first frame member  312 A at its first end portion  332 . Each of the channels  378  has an open end portion  379  along the first edge portion  364  of the sidewalls  350  and  352 . 
     In the embodiment illustrated, the wheel  342  is rotatably coupled to the wheel mount member  346  by an axle  384 . The axle  384  is disposed inside the through-holes  368  formed in the sidewalls  350  and  352  and extends between the spaced apart sidewalls  350  and  352  through the gap  356 . The wheel  342  rotates on the axle  384  within the gap  356 . 
     The wheel mount member  346  is coupled to the first frame member  312 A between the first and second arm portions  322  and  324 . In the embodiment illustrated, the transverse portion  370  of the wheel mount member  346  is adjacent the second arm portion  324  of the first frame member  312 A and the through-hole  374  is aligned with the first through-hole  336  formed in the second arm portion  324  of the first frame member  312 A at its the first end portion  332 . The first edge portions  364  of the sidewalls  350  and  352  are adjacent the first arm portion  322  with the open end portions  379  of the channels  378  aligned with the through-holes  339  formed in the first arm portion  322  of the first frame member  312 A at its first end portion  332 . When so aligned, the fasteners  380  (see  FIGS. 5 and 7 ) may be passed through the through-holes  339  and into the channels  378  and used to fasten the wheel mount member  346  to the first frame member  312 A. 
     Anti-Tip Assemblies 
     The anti-tip assemblies  304 A- 304 D are substantially identical to one another. Therefore, for the sake of brevity, only the second anti-tip assembly  304 B will be described in detail. However, because the second anti-tip assembly  304 B is illustrated as being configured for use with the optional braking assembly  306 ,  FIG. 9  has been included to provide a view of the fourth anti-tip assembly  304 D, which has not been configured for use with the braking assembly  306 . 
       FIG. 2  provides a front view of the assembled second anti-tip assembly  304 B, and  FIG. 8  provides an enlarged exploded view of the components of the second anti-tip assembly  304 B. The anti-tip assembly  304 B illustrated includes a mounting bracket  410 , an inner C-shaped bracket  420 , an outer C-shaped bracket  422 , an inner slip or wear plate  426 , an outer slip or wear plate  428 , a limit bolt  430  (see  FIGS. 2 and 5 ), a biasing mechanism (e.g., a return spring  434 ), an upper slip spacer  436 , a lower slip spacer  438 , an upper spacer  440 , a lower spacer  442 , and a lock nut  446 . Optionally, the anti-tip assembly  304 B may include a bumper assembly  450 . 
       FIGS. 2 and 5  illustrate the second anti-tip assembly  304 B configured for use with the optional braking assembly  306 . In such an embodiment, the limit bolt  430  is configured to extend through the components of both the optional braking assembly  306  and the anti-tip assembly  304 B. In embodiments of the anti-tip assembly not configured for use with the optional braking assembly  306  (e.g., the fourth anti-tip assembly  304 D illustrated in  FIG. 9 ), the limit bolt  430  may be shorter. 
     Referring to  FIG. 2 , the mounting bracket  410  couples the other components of the anti-tip assembly  304 B to the first arm portion  314  of the corner bracket  310 B of the support frame  300  (see  FIG. 3 ). The mounting bracket  410  includes a U-shaped portion  460  flanked by two outwardly extending flanges  464  and  466 . 
     As may best be viewed in  FIG. 8 , the U-shaped portion  460  includes a first sidewall  461 , a second sidewall  462  spaced apart from the first sidewall, and a transverse portion  463  extending between and connecting the first and second sidewalls  461  and  462 . Referring to  FIG. 2 , when the flanges  464  and  466  are adjacent the first arm portion  314  of the corner bracket  310 B, the first and second sidewalls  461  and  462  of the U-shaped portion  460  extend outwardly from the first arm portion  314  of the corner bracket  310 B to space the transverse portion  463  away from the first arm portion  314  of the corner bracket  310 B. An open-ended chamber  470  is defined between the first arm portion  314  of the corner bracket  310 B, the first sidewall  461 , the second sidewall  462 , and the transverse portion  463 . The open-ended chamber  470  has a first opening  472  opposite a second opening  474  (see  FIG. 9 ). Returning to  FIG. 8 , each of the first and second sidewalls  461  and  462  includes a through-hole  468  (see  FIGS. 8 and 9 ). The through-holes  468  of the first and second sidewalls  461  and  462  are juxtaposed and aligned across the open-ended chamber  470 . 
     The flanges  464  and  466  may include one or more through-holes  476  configured to receive the fasteners  380 . Turning to  FIG. 5 , the fasteners  380  may be inserted into the through-holes  476  of the mounting bracket  410 , through the through-holes  319  formed in the first arm portion  314  of the corner bracket  310 B, through the through-holes  339  formed in the first arm portion  322  of the frame member  312 A at its first end portion  332 , and into the channels  378  of the wheel mount member  346 . Thus, the fasteners  380  may be used to fasten the support assembly  302 B to the first arm portion  322  of the frame member  312 A and the anti-tip assembly  304 B to the first arm portion  314  of the corner bracket  310 B. 
     The inner and outer C-shaped brackets  420  and  422  may be substantially identical to one other. Each has a body portion  480  having an upper flange  484  spaced apart from a lower flange  488 . The upper flange  484  has a notched portion  492  defining an off-center projecting portion  490 . The lower flange  488  has a distal portion  493 . The body portion  480  has a through-hole  494  configured to receive the limit bolt  430 . The body portion  480  has a first edge portion  497  and a second edge portion  498  opposite the first edge portion. Optionally, a notch  496  may be formed in the second edge portion  498 . 
     The inner and outer wear plates  426  and  428  may be substantially identical to one other. In the embodiment illustrated, each of the inner and outer wear plates  426  and  428  is substantially planar and has an upper portion  500  and a through-hole  502  configured to receive the limit bolt  430 . 
     The limit bolt  430  (see  FIGS. 2 and 5 ) has a head portion  510 , and a shaft portion  512  extending away from the head portion  510 . The shaft portion  512  having an unthreaded portion  514 , and a threaded portion  516  opposite the head portion. The threaded portion  516  is configured to thread into the lock nut  446 . Optionally, one or more spacers or washers  518  may be disposed between the lock nut  446  and the inner C-shaped bracket  420 . Further, in embodiments that include the braking assembly  306 , one or more optional spacers or washers  520  may be disposed between the head portion  510  and the braking assembly  306 . Alternatively, referring to  FIG. 9 , in embodiments that do not include the braking assembly  306 , the one or more optional washers  520  may be disposed between the head portion  510  and the outer C-shaped bracket  422 . 
     Returning to  FIG. 2 , the biasing mechanism is illustrated as being the return spring  434 . The return spring  434  is illustrated as a coil spring configured to be disposed circumferentially about portions of the unthreaded and threaded portions  514  and  516  of the limit bolt  430  located between the inner and outer wear plates  426  and  428 . 
     Turning to  FIG. 8 , the upper and lower slip spacers  436  and  438  may be substantially identical to one another. Each of the upper and lower slip spacers  436  and  438  is substantially planar and has an outer planar surface  522  opposite an inner planar surface  524 . A projection or peg  528  extends outwardly from the outer planar surface  522 . 
     The upper and lower spacers  440  and  442  may be substantially identical to one other. Each of the upper and lower spacers  440  and  442  is substantially planar and has a through-hole  530 . The through-hole  530  of the upper spacer  440  is configured to receive the outwardly extending peg  528  of the upper slip spacer  436  and the through-hole  530  of the lower spacer  442  is configured to receive the outwardly extending peg  528  of the lower slip spacer  438 . 
     The optional bumper assembly  450  may include a bumper  540  having an interior channel  544  configured to receive one of the fasteners  380 , which is inserted into one of the through-holes  476  formed in the flange  464  of the mounting bracket  410 . One or more spacers  548  (e.g., washers) may be used to determine how far the bumper  540  extends outwardly from the flange  464  of the mounting bracket  410 . 
     The upper spacer  440 , the lower spacer  442 , the upper slip spacer  436 , and the lower slip spacer  438  are disposed inside the open-ended chamber  470  (see  FIG. 2 ) of the mounting bracket  410 . The inner planar surface  524  of the lower slip spacer  438  faces the inner planar surface  524  of the upper slip spacer  436 . Thus, the outwardly extending pegs  528  extend in opposite directions from the outer planer surfaces  522  of the upper and lower slip spacers  436  and  438 . 
     The outwardly extending peg  528  of the upper slip spacer  436  extends upwardly through the through-hole  530  formed in the upper spacer  440  and the through-hole  468  formed in the first sidewall  461  of the U-shaped portion  460  of the mounting bracket  410 . Thus, the peg  528  is maintained inside the open-ended chamber  470  (see  FIG. 2 ) by the through-hole  468  formed in the first sidewall  461  of the U-shaped portion  460  of the mounting bracket  410 . The outwardly extending peg  528  of the lower slip spacer  438  extends downwardly through the through-hole  530  formed in the lower spacer  442  and the through-hole  468  formed in the second sidewall  462  of the U-shaped portion  460  of the mounting bracket  410 . Thus, the peg  528  is maintained inside the open-ended chamber  470  by the through-hole  468  formed in the second sidewall  462  of the U-shaped portion  460  of the mounting bracket  410 . In this manner, as the flanges  484  of the inner and outer C-shaped brackets  420  and  422  move laterally inside the open-ended chamber  470  (see  FIG. 2 ), lateral movement of the upper slip spacer  436 , the lower slip spacer  438 , the upper spacer  440 , and the lower spacer  442  is limited by the pegs  528  received inside the through-holes  530  and  468 . In other words, the upper slip spacer  436 , the lower slip spacer  438 , the upper spacer  440 , and the lower spacer  442  are anchored to the mounting bracket  410  inside the open ended channel  470 . 
     The flanges  484  of the inner and outer C-shaped brackets  420  and  422  extend into opposite ends  472  and  474 , respectively, of the open-ended chamber  470  of the mounting bracket  410  and are positioned between the inner planar surfaces  524  of the upper and lower slip spacers  436  and  438 . The flanges  484  rest upon the inner planar surface  524  of the lower slip spacer  438  and are slidable relative to the upper and lower slip spacers  436  and  438  inside the open-ended chamber  470 . In the embodiment depicted, the off-center projecting portions  490  of the inner and outer C-shaped brackets  420  and  422  are positioned alongside one another between the upper and lower slip spacers  436  and  438 . Specifically, the off-center projecting portion  490  of the inner C-shaped bracket  420  is at least partially received inside the notch  492  of the outer C-shaped bracket  422  and the off-center projecting portion  490  of the outer C-shaped bracket  422  is at least partially received inside the notch  492  of the inner C-shaped bracket  420 . 
     A depth of insertion of the inner C-shaped bracket  420  into the open-ended chamber  470  is limited by contact with the flange  484  of the outer C-shaped bracket  422  and a depth of insertion of the outer C-shaped bracket  422  into the open-ended chamber  470  is limited by contact with the flange  484  of the inner C-shaped bracket  420 . Further, forward and backward directed movement of the inner and outer C-shaped brackets  420  and  422  inside the open-ended chamber  470  is limited by engagement between their adjacent off-center projecting portions  490 . 
     The inner wear plate  426  is adjacent the body portion  480  of the inner C-shaped bracket  420  between the upper and lower flanges  484  and  488 . An upper portion  500  of the inner wear plate  426  may abut the sidewall  462  of the U-shaped portion  460  of the mounting bracket  410  along the first open end  472  (see  FIG. 2 ) of the open ended channel  470  (see  FIG. 2 ). The outer wear plate  428  is adjacent the body portion  480  of the outer C-shaped bracket  422  between the upper and lower flanges  484  and  488 . An upper portion  500  of the outer wear plate  428  may abut the sidewall  462  of the U-shaped portion  460  of the mounting bracket  410  along the second open end  474  (see  FIG. 9 ) of the open ended channel  470  (see  FIG. 9 ). 
     Turning to  FIG. 2 , the inner and outer wear plates  426  and  428  are positioned to engage the flanges  152  and  154 , respectively, of the track “T 2 .” As the shelving unit  100  (see  FIG. 1 ) is moved along the tracks “T 1 ” and “T 2 ,” the anti-tip assemblies  302 A- 302 D may shift laterally relative to the tracks “T 1 ” and “T 2 ,” causing the inner wear plate  426  and/or outer wear plate  428  to engage the distal portions  156  and  158 , respectively, of the flanges  152  and  154 , respectively. Further, when the braking assembly  306  is engaged (see  FIGS. 2 ,  3 , and  7 ), the inner and outer wear plates  426  and  428  engage the distal portions  156  and  158 , respectively, of the flanges  152  and  154 , respectively. 
     The limit bolt  430  extends through the through-hole  494  formed in the outer C-shaped bracket  422 , the through-hole  502  formed in the outer wear plate  428 , the through-hole  502  formed in the inner wear plate  426 , and the through-hole  494  formed in the inner C-shaped bracket  420 . As mentioned above, the return spring  434  is disposed about the limit bolt  430  between the inner and outer wear plates  426  and  428 . The return spring  434  is compressed between the inner and outer wear plates  426  and  428  and applies an outwardly directed force to each of them, biasing them outwardly. The inner and outer wear plates  426  and  428  bear against the inner and outer C-shaped brackets  420  and  422 , respectively, biasing them outwardly. The lock nut  446  is configured not to pass through either the through-hole  494  formed in the inner C-shaped bracket  420 , or the through-hole  502  formed in the inner wear plate  426 . Thus, the outward movement of the inner C-shaped bracket  420  is limited by the lock nut  446  threaded onto the threaded portion  516  of the limit bolt  430 . The head portion  510  of the limit bolt  430  is configured not to pass through either the through-hole  494  formed in the outer C-shaped bracket  422 , or the through-hole  502  formed in the outer wear plate  428 . Thus, the outward movement of the outer C-shaped bracket  422  is limited by the head portion  510  of the limit bolt  430 . 
     As is apparent to those of ordinary skill in the art, the braking assembly  306  may be disposed between the outer C-shaped bracket  422  and the head portion  510  of the limit bolt  430 . In such embodiments, the outward movement of the outer C-shaped bracket  422  bears against the braking assembly  306 , pressing it outwardly. The outward movement of the braking assembly  306  is limited by the head portion  510  of the limit bolt  430 . In other words, the outward movement of the outer C-shaped bracket  422  is limited by the head portion  510  of the limit bolt  430  even when the braking assembly  306  disposed therebetween. 
     Thus, the distance between the head portion  510  of the limit bolt  430  and the lock nut  446  may determine, at least in part, the spacing between the inner and outer C-shaped brackets  420  and  422 . However, a minimum spacing between the inner and outer C-shaped brackets  420  and  422  may be determined at least in part by the depths of insertion of the inner or outer C-shaped brackets  420  and  422  into the open ended channel  470 . As explained above, the depths of insertion of the inner or outer C-shaped brackets  420  and  422  into the open ended channel  470  may be determined by the depths at which the flanges  484  of the inner and outer C-shaped brackets  420  and  422  engage each other inside the open ended channel  470 . 
     The spacing between the inner and outer C-shaped brackets  420  and  422  is adequate to position the flange  488  of the inner C-shaped bracket  420  under the flange  154  of the track “T 2 ” and inside the second channel  164  and at the same time, position the flange  488  of the outer C-shaped bracket  422  under the flange  152  of the track “T 2 ” and inside the first channel  162 . So long as the flange  488  of the inner C-shaped bracket  420  remains in the inside the second channel  164  and the flange  488  of the outer C-shaped bracket  422  remains in the inside the first channel  162 , the flanges  154  and  152  prevent the flanges  488  of the inner and outer C-shaped brackets  420  and  422  from being disengaged from the track “T 2 .” The spacing between the inner and outer C-shaped brackets  420  and  422  may be adjusted by tightening or loosening the lock nut  446 . 
     As the shelving unit  100  (see  FIG. 1 ) is pushed along the tracks “T 1 ” and “T 2 ,” the inner and outer wear plates  426  and  428  may engage the flanges  154  and  152 , respectively. This engagement causes the flanges  484  to slide between the upper and lower slip spacers  436  and  438  changing the positions of the inner and outer C-shaped brackets  420  and  422  relative to the mounting bracket  410  and in some instances, changing the spacing between the inner and outer C-shaped brackets  420  and  422 . In this manner, the shelving unit  100  (see  FIG. 1 ) may be pushed long tracks that are not perfectly parallel to one another. The compressed return spring  434  helps maintain the spacing between the inner and outer C-shaped brackets  420  and  422  by biasing the inner and outer C-shaped brackets  420  and  422  outwardly after they have been forced inwardly. 
     As explained above, the inner and outer C-shaped brackets  420  and  422  are allowed to float (or change position relative to the mounting bracket  410 ) to accommodate misalignment of the tracks “T 1 ” and “T 2 .” In other words, by allowing the inner and outer C-shaped brackets  420  and  422  to float laterally relative to the track, misalignment is tolerated. Further, the inner and outer C-shaped brackets  420  and  422  are held in position by the limit bolt  430  and the return spring  434 . The limit bolt  430  and the return spring  434  maintain a predetermined spacing between the inner and outer C-shaped brackets  420  and  422  while allowing them to float between the upper and lower slip spacers  436  and  438 . The predetermined spacing may be adjusted during installation by tightening or loosening the lock nut  446 . 
     As is apparent to those of ordinary skill in the art, because the anti-tip assemblies  304 A- 304 D are coupled to the support frame  300  separately from the movable support assemblies  302 A- 302 D, the support frame  300  and the support assemblies  302 A- 302 D used alone. Thus, the tracks “T 1 ” and “T 2 ,” the support frame  300 , and the support assemblies  302 A- 302 D may be installed without the anti-tip assemblies  304 A- 304 D. Optionally, the anti-tip assemblies  304 A- 304 D may then be installed at a later time. 
     The mobile in-track anti-tip system  102  may be serviced without the need to dissemble the shelving unit  100 . Further, while the anti-tip system  102  has been illustrated as including the anti-tip assemblies  304 A- 304 D, one at each corner of the support frame  300 , fewer anti-tip assemblies may be coupled to the support frame. For example, only the anti-tip assemblies  304 A and  304 B may be used. Alternatively, only the anti-tip assemblies  304 C and  304 D may be used. By way of another non-limiting example, only the anti-tip assemblies  304 B and  304 C may be used. By way of yet another non-limiting example, only the anti-tip assemblies  304 A and  304 D may be used. 
     Turning to  FIG. 1 , the compact nature of the anti-tip system  102  may be configured to require little extra spacing between adjacent shelving units  100  and  220 . Further, the anti-tip system  102  may be configured so that it does not require extra track. Additionally, the anti-tip system  102  may be configured to comply with American&#39;s with Disabilities Act (“ADA”) standards. For example, the tracks “T 1 ” and “T 2 ” may be constructed to have a height measured from the surface  104  that is less than a legal prescribed amount (e.g., less than about ⅝ inches). 
     Braking Assembly 
     In a first embodiment depicted in  FIGS. 1-5 ,  7 ,  10 - 12 , the optional braking assembly  306  includes a foot actuated pedal  600  and a braking member  610 . Turning to  FIG. 10 , the foot actuated pedal  600  includes a lever portion  620  having a distal end portion  622  coupled to a foot receiving portion  624  and a proximal end portion  626  pivotally coupled to the second anti-tip assembly  304 B. The proximal end portion  626  includes a through-hole  628  configured to receive the limit bolt  430  (see  FIG. 5 ) which passes through the through-hole  628  and couples the proximal end portion  626  to the second anti-tip assembly  304 B (see  FIG. 5 ). The lever portion  620  pivots about the unthreaded portion  514  (see  FIG. 5 ) of the limit bolt  430  (see  FIG. 5 ) which functions as a pivot pin. Optionally, the foot receiving portion  624  may include treads  630  or other anti-slip structures to prevent the users foot from slipping off the foot receiving portion  624 . 
     The lever portion  620  pivots about the limit bolt  430  (see  FIG. 5 ) between a brake engaged position (see  FIGS. 2 ,  3 , and  7 ) and a brake released position (see  FIGS. 11 and 12 ). Alternatively, the lever portion  620  may rotate the limit bolt  430  (see  FIG. 5 ) as the lever portion  620  pivots between the brake engaged position and the brake released position. Turning to  FIG. 7 , when the lever portion  620  is in the brake engaged position, the braking assembly  306  presses against the outer C-shaped bracket  422  pressing the outer wear plate  428  into the distal portion  156  of the flange  152  of the track “T 2 .” At the same time, the braking assembly  306  pulls longitudinally on the limit bolt  430 , drawing the inner C-shaped bracket  420  toward the flange  154  of the track “T 2 ” and pressing the inner wear plate  426  into the distal portion  158  of the flange  154 . As the outer wear plate  428  is biased toward the flange  152  and the inner wear plate  426  is biased against the flange  154 , the return spring  434  (see  FIG. 2 ) is compressed between the inner and outer wear plates  426  and  428 . In other words, the inner and outer C-shaped brackets  420  and  422  (and the inner and outer wear plates  426  and  428 ) clamp or pinch the track “T 2 .” Frictional engagement between the inner and outer wear plates  426  and  428  and the flanges  154  and  152 , respectively, limit the movement of the support assembly  302 B along the track “T 2 ,” thereby braking the shelving unit  100  (see  FIG. 1 ). 
     Optionally, when the lever portion  620  is in the brake engaged position, the distal portion  493  of the flange  488  of the outer C-shaped bracket  422  may be biased against the inside of the channel  162  of the track “T 2 .” For example, the distal portion  493  of the flange  488  of the outer C-shaped bracket  422  may be biased against the bottom portion  166  of the channel  162  of the track “T 2 .” Similarly, as may best be viewed in  FIG. 2 , when the lever portion  620  is in the brake engaged position, the distal portion  493  of the flange  488  of the inner C-shaped bracket  420  may be biased against the inside of the channel  164  of the track “T 2 .” For example, the distal portion  493  of the flange  488  of the inner C-shaped bracket  420  may be biased against the bottom portion  168  of the channel  164  of the track “T 2 .” Frictional engagement between the distal portions  493  of the flanges  488  of the inner and outer C-shaped brackets  420  and  422  and the inside of the channels  164  and  162 , respectively, limit the movement of the support assembly  302 B (see  FIG. 7 ) along the track “T 2 ,” thereby braking the shelving unit  100  (see  FIG. 1 ). 
     Turning to  FIGS. 11 and 12 , when the lever portion  620  is in the brake released position, the braking assembly  306  does not exert force on either the outer C-shaped bracket  422  or the inner C-shaped bracket  420 . Thus, the braking assembly does not cause the frictional engagement between the inner and outer wear plates  426  and  428  and the flanges  154  and  152 , respectively. Further, the braking assembly does not cause the frictional engagement between the distal portions  493  of the flanges  488  of the inner and outer C-shaped brackets  420  and  422  and the inside of the channels  164  and  162 , respectively. In other words, the movement of the support assembly  302 B (see  FIG. 11 ) along the track “T 2 ” is not limited by the braking assembly  306  when the lever portion  620  is in the brake released position. 
     Depending upon the implementation details, the braking assembly  306  may be foot actuated. For example, the lever portion  620  may be manually pivoted about the limit bolt  430  from the brake released position to the brake engaged position when a user applies a downwardly directed force with his/her foot to the foot receiving portion  624  coupled to the distal end portion  622  (see  FIG. 10 ) of the lever portion  620 . The lever portion  620  may be manually pivoted about the limit bolt  430  from the brake engaged position to the brake released position when a user applies an upwardly directed force (e.g., with his/her foot) to the foot receiving portion  624  coupled to the distal end portion  622  (see  FIG. 10 ) of the lever portion  620 . 
     The braking member  610  is configured to rotate with the lever portion  620  about the limit bolt  430 . This may be achieved by non-rotatably coupling the braking member  610  to the lever portion  620 . By way of a non-limiting example, the braking member  610  may be welded or otherwise affixed or adhered permanently or removably to the lever portion  620 . 
     Returning to  FIG. 10 , the braking member  610  includes a through-hole  640  configured to receive and retain a portion of the unthreaded portion  514  (see  FIG. 2 ) of the limit bolt  430  (see  FIG. 2 ). The through-hole  640  may be formed along an outside edge  643  of the braking member  610 . The through-hole  640  may include a lip portion  648  configured to retain the unthreaded portion  514  (see  FIG. 2 ) of the limit bolt  430  (see  FIG. 2 ) inside the through-hole  640 . 
     The braking member  610  has a generally c-shaped portion  642  with a body portion  644  and a pair of spaced part outwardly extending flanges  646  and  648 . Each of the flanges  646  and  648  extends toward the proximal end portion  626  of the lever portion  620 . Depending upon the implementation details, the flanges  646  and  648  may be affixed to the proximal end portion  626  of the lever portion  620 . In the embodiment depicted, the through-hole  640  is formed in the body portion  644  and the flanges  646  and  648  are substantially parallel to the limit bolt  430 . 
     The body portion  644  includes a projection or dimple  650  that extends inwardly toward the second anti-tip assembly  304 B (see  FIG. 2 ). Turning to  FIG. 11 , the dimple  650  is configured to be received inside the notch  496  of the outer C-shaped bracket  422  when the lever portion  620  is in the brake released position. Turning to  FIG. 7 , the dimple  650  is further configured to press upon the body portion  480  of the outer C-shaped bracket  422  when the lever portion  620  is in the brake engaged position. In other words, when the lever portion  620  is pivoted about the limit bolt  430 , the dimple  650  travels between the notch  496  (the brake released position) and a location on the body portion  480  of the outer C-shaped bracket  422  (the brake engaged position). 
     Returning to  FIGS. 2 and 10 , the braking member  610  includes two stops  660  and  662 . The first stop  660  extends inwardly from the body portion  644  toward the second anti-tip assembly  304 B. The stop  660  may be implemented as a flange extending parallel to the limit bolt  430  and toward the inner C-shaped bracket  420 . The stop  660  is substantially parallel to the un-notched first edge  497  of the body portion  480  of the outer C-shaped bracket  422  when the lever portion  620  is in the brake engaged position (see  FIGS. 2 ,  3 , and  7 ). 
     The stop  660  is configured to limit the pivoting of the lever portion  620  about the limit bolt  430  by contacting the un-notched first edge  497  of the body portion  480  of the outer C-shaped bracket  422 . For example, turning to  FIG. 12 , when the lever portion  620  is pivoted toward the brake released position, the stop  660  will abut a first (lower) position  670  of the un-notched first edge  497  of the body portion  480  of the outer C-shaped bracket  422  to limit the rotation of the lever portion  620  about the limit bolt  430 . Similarly, turning to  FIG. 2 , when the lever portion  620  is pivoted toward the brake engaged position, the stop  660  will abut a second (upper) position  672  of the un-notched first edge  497  of the body portion  480  of the outer C-shaped bracket  422  to limit the rotation of the lever portion  620  about the limit bolt  430 . 
     The second stop  662  extends upwardly from the flange  646  and inwardly toward the second anti-tip assembly  304 B. The stop  662  may be implemented as a flange that is substantially orthogonal to the flange  646 . Referring to  FIG. 2 , the stop  662  may be substantially parallel to the first arm portion  314  of the corner bracket  310 B when the lever portion  620  is in the brake engaged position. The stop  662  is configured to limit the pivoting of the lever portion  620  about the limit bolt  430  by contacting the first arm portion  314  of the corner bracket  310 B whenever the lever portion  620  is pivoted from the brake released position to the brake engaged position. Specifically, when the lever portion  620  is pivoted toward the brake engaged position, the stop  662  will abut the first arm portion  314  of the corner bracket  310 B and limit the rotation of the lever portion  620  about the limit bolt  430 . However, the stop  662  does not limit the rotation of the lever portion  620  when it is pivoted toward the brake released position. 
     The braking assembly  306  includes few moving parts and may be readily incorporated into the mobile in-track anti-tip system  102  (see  FIGS. 1-3 ). Further, an amount of braking force required to pivot the lever portion  620  from the brake released position to the brake engaged position may be adjusted by tightening or loosing the lock nut  446  on the limit bolt  430 . 
     In a first alternate embodiment, illustrated in  FIG. 13 , the stop  662  (see  FIG. 10 ) is omitted from a braking member  710  of a braking assembly  706 . Further, in the embodiment illustrated, the optional treads  630  (see  FIG. 10 ) have also been omitted. 
     Alternate Embodiment 
       FIGS. 17-24  illustrate a braking assembly  720  for use with an anti-tip assembly  722  which may be used with the movable support assembly  302 B (see  FIGS. 23 and 24 ) and the support frame  300  (see  FIGS. 1 and 3 ). As is apparent to those of ordinary skill in the art, the anti-tip assembly  722  may be used in place of any of the anti-tip assemblies  304 A- 304 D (see  FIG. 4 ). As is also apparent to those of ordinary skill in the art, the anti-tip assembly  722  may be used without the braking assembly  720 . For ease of illustration, like reference numerals have been used in the figures to identify like components. Only the components of the anti-tip assembly  722  that differ substantially from the components of the anti-tip assembly  304 B (see  FIG. 5 ) will be described in detail. 
     In  FIG. 17 , the braking assembly  720  is illustrated in the brake released position. Turning to  FIG. 17 , the braking assembly  720  is coupled to the anti-tip assembly  722  by a generally L-shaped limit bolt  730 . The limit bolt  730  includes a first leg portion  732  connected to a second leg portion  736  by a bent portion  738 . The first leg portion  732  and the second leg portion  736  each extend away from the bent portion  738  in different directions. The first leg portion  732  may be substantially orthogonal to the second leg portion  736 . However, this is not a requirement. The first leg portion  732  functions in a manner similar to the manner in which the shaft portion  512  of the limit bolt  430  functions (see  FIG. 5 ). Thus, to use the anti-tip assembly  722  without the braking assembly  720 , the limit bolt  430  may be substituted for the limit bolt  730 . 
     For illustrative purposes, the upright support  200 B (illustrated in  FIG. 17 ) and the second frame member  312 B (illustrated in  FIG. 17 ) have been omitted from  FIGS. 18 ,  21 ,  23 , and  24 . Turning to  FIG. 18 , the anti-tip assembly  722  includes the mounting bracket  410 , the biasing mechanism (e.g., the return spring  434 ), and the lock nut  446 . Optionally, the anti-tip assembly  722  may include the bumper assembly  450 , the upper slip spacer  436 , the lower slip spacer  438  (see  FIG. 8 ), the upper spacer  440  (see  FIG. 8 ), the lower spacer  442 . In the embodiment illustrated, the anti-tip assembly  722  includes the upper slip spacer  436 , the lower spacer  442 , and the bumper assembly  450 . 
     The anti-tip assembly  722  includes an inner C-shaped bracket  740  substantially similar to the inner C-shaped bracket  420  (see  FIG. 8 ) of the second anti-tip assembly  304 B and an outer C-shaped bracket  742  substantially similar to the outer C-shaped bracket  422  (see  FIG. 8 ) of the second anti-tip assembly  304 B. The inner and outer C-shaped brackets  740  and  742  may be substantially identical to one another. In the embodiment illustrated, the inner and outer C-shaped brackets  740  and  742  are identical to one another. The inner C-shaped bracket  740  is rotated 180 degrees relative to the outer C-shaped bracket  742  and juxtaposed across the track “T 2 ” from the outer C-shaped bracket  742 . For this reason, only the inner C-shaped bracket  740  will be described in detail. 
       FIG. 19  illustrates the inner C-shaped bracket  740 . The inner C-shaped bracket  740  has a body portion  748  which includes the upper flange  484  spaced apart from the lower flange  488 . The body portion  748  includes the through-hole  494 , which in this embodiment is configured to receive the first leg portion  732  of the limit bolt  730 . However, the body portion  748  omits the notch  496  (see  FIG. 8 ) formed in the second edge portion  498  of the body portion  480  of the inner C-shaped bracket  420  (see  FIG. 8 ). The body portion  748  has a dimple  750  formed therein that extends in a direction opposite the direction in which the upper and lower flanges  484  and  488  extend. Referring to  FIG. 18 , when the anti-tip assembly  722  is assembled, the dimple  750  projects outwardly from the body portion  748  away from the upwardly opening channel  170  of the track “T 2 .” Returning to  FIG. 19 , in the embodiment illustrated, the dimple  750  is located between the through-hole  494  and the lower flange  488 . The dimple  750  is located approximately midway between the first edge portion  497  and the second edge portion  498  of the body portion  748 . 
     Returning to  FIG. 18 , the flanges  484  of the inner and outer C-shaped brackets  740  and  742  extend into opposite ends  472  and  474 , respectively, of the open-ended chamber  470  of the mounting bracket  410  and are positioned the upper slip spacer  436  and the lower spacer  442 . The flanges  484  rest upon lower spacer  442  and are slidable relative to the upper slip spacer  436  and the lower spacer  442  inside the open-ended chamber  470 . 
     The anti-tip assembly  722  includes inner and outer wear plates  756  and  758 . However, unlike the inner and outer wear plates  426  and  428  (illustrated in  FIG. 8 ) of the second anti-tip assembly  304 B (see  FIG. 8 ), the inner and outer wear plates  756  and  758  do not include the through-hole  502  (see  FIG. 8 ). Instead, the inner and outer wear plates  756  and  758  extend along only a portion of the body portion  748  located between the through-hole  494  (see  FIG. 19 ) and the lower flange  488  of the inner and outer C-shaped brackets  740  and  742 , respectively. Further, the inner and outer wear plates  756  and  758  extend from the first edge portion  497  (see  FIG. 19 ) to the second edge portion  498  (see  FIG. 19 ) of the body portions  748  of the inner and outer C-shaped brackets  740  and  742 , respectively. In the embodiment illustrated, each of the inner and outer wear plates  756  and  758  is substantially planar. The inner and outer wear plates  756  and  758  may be affixed to the inner and outer C-shaped brackets  740  and  742 , respectively, using any method known in the art. 
     The inner wear plate  756  is positioned between the body portion  748  of the inner C-shaped bracket  740  and the flange  154  of the track “T 2 .” When the braking assembly  720  is in the brake engaged position (illustrated in  FIGS. 21 and 24 ), the inner wear plate  756  engages the flange  154  of the track “T 2 .” When the braking assembly  720  is in the brake released position (illustrated in  FIGS. 17 ,  18 ,  20 , and  23 ), the inner wear plate  756  is spaced apart from the flange  154  but may engage therewith if the tracks “T 1 ” and “T 2 ” are misaligned. Similarly, the outer wear plate  758  is positioned between the body portion  748  of the outer C-shaped bracket  742  and the flange  152  of the track “T 2 .” When the braking assembly  720  is in the brake engaged position, the outer wear plate  758  engages the flange  152  of the track “T 2 .” When the braking assembly  720  is in the brake released position, the outer wear plate  758  is spaced apart from the flange  152  but may engage therewith if the tracks “T 1 ” and “T 2 ” are misaligned. 
     The first leg portion  732  of the limit bolt  730  includes a distal threaded portion  762  opposite the bent portion  738  and an unthreaded portion  764  located between the bent portion  738  of the limit bolt  730  and the distal threaded portion  762 . The return spring  434  is located between the inner and outer C-shaped brackets  740  and  742  and disposed circumferentially about a portion of the unthreaded portion  764  and optionally, about a portion of the threaded portion  762 . 
     The distal threaded portion  762  is configured to thread into the lock nut  446 . The threaded portion  762  has a first relieved portion  766 A opposite a second relieved portion  766 B. Each of the relieved portions  766 A and  766 B extend longitudinally from the end of the first leg portion  732  toward the bent portion  738 . Thus, the threaded portion  762  has a cross-sectional shape other than circular. Each of the relieved portions  766 A and  766 B has a generally planar outer surface  768 . However, this is not a requirement. 
     Returning to  FIG. 17 , optionally, the second leg portion  736  includes a downwardly bent distal portion  769  opposite the bent portion  738 . 
     The braking assembly  720  includes an upright actuator assembly  770  mounted by an upright mounting bracket  772  to the upright support  200 B of the shelving unit  100  (see  FIG. 1 ). The upright actuator assembly  770  includes an upright member  774  having a distal end portion  776  coupled to a foot receiving portion  778  and a proximal end portion  780  coupled to a retaining member  782 . Optionally, the foot receiving portion  778  may include treads (not shown) or other anti-slip structures to prevent the users foot from slipping off the foot receiving portion  778 . By way of a non-limiting example, the proximal end portion  780  may be coupled to the retaining member  782  by a fastener  783 , such as a bolt, screw, and the like. 
     Returning to  FIG. 18 , the retaining member  782  includes a channel  784  configured to receive and trap the bent distal portion  769  of the second leg portion  736  of the limit bolt  730  therein. The channel  784  is at least partially defined between an upper wall  785  (see  FIG. 24 ) and a lower wall  787  (see  FIG. 24 ). The bent distal portion  769  passes at least part way through the channel  784  and is free to move therein relative to the retaining member  782  as the braking assembly  720  transitions between the brake released position and the brake engaged position. 
     For illustrative purposes, the upright support  200 B, the first frame member  312 A, the second frame member  312 B, the upright mounting bracket  772 , the corner bracket  310 B, and the support assembly  302 B have been omitted from  FIG. 20 . Turning to  FIG. 20 , the upright member  774  is slidably received inside a housing  786 . The upright member  774  and the retaining member  782  move together as a unit when the upright member  774  slides relative to the housing  786 . The housing  786  has an interior chamber  788  which, in the embodiment illustrated, is open along a portion  789  adjacent the upright mounting bracket  772  (see  FIG. 17 ). However, this is not a requirement. In the embodiment illustrated, the open portion  789  of the interior chamber  788  is closed by the upright mounting bracket  772  (see  FIG. 17 ). 
     An intermediate portion  790  of the upright member  774  located between the distal end portion  776  (see  FIG. 17 ) and the proximal end portion  780  (see  FIG. 17 ) extends through the interior chamber  788  of the housing  786 . A transverse member or pin  792  extends laterally through the upright member  774 . Opposite end portions of the transverse pin  792  extend outwardly beyond the upright member  774  and provide stops for a biasing member, illustrated as a coil spring  794 . The coil spring  794  extends between a bottom surface  796  of the interior chamber  788  and the end portions of the transverse pin  792 . Thus, the coil spring  794  may be compressed between the bottom surface  796  of the interior chamber  788  and the end portions of the transverse pin  792 . When so compressed, the coil spring  794  exerts an upwardly directed biasing force on the end portions of the transverse pin  792  which is translated to the upright member  774  biasing the upright member upwardly. 
     Turning to  FIG. 17 , optionally, a cushioning member  798  is pivotably coupled to the housing  786  with its bottom surface  901  facing toward at least a portion of an upper exterior surface  799  of the housing  786  adjacent the interior chamber  788  (see  FIG. 20 ). A through-hole  903  is formed in the upper exterior surface  799  to provide access into the interior chamber  788 . The cushioning member  798  has a through-hole  905  formed therein and aligned with the through-hole  903 . The upright member  774  passes through the through-hole  905  and the through-hole  903  and into the interior chamber  788 . 
     A biasing member, illustrated as a coil spring  906 , extends between the bottom surface  901  of the cushioning member  798  and the upper exterior surface  799  of the interior chamber  788 . Thus, when the cushioning member  798  is pivoted toward the upper exterior surface  799  of the interior chamber  788 , the coil spring  794  is compressed between the bottom surface  901  of the cushioning member  798  and the upper exterior surface  799  of the interior chamber  788 . When so compressed, the coil spring  794  exerts an upwardly directed biasing force on the bottom surface  901  of the cushioning member  798  which pivots the cushioning member  798  away from the upper exterior surface  799  of the interior chamber  788 . The cushioning member  798  in turn biases the foot receiving portion  778  (see  FIGS. 17 and 21 ) upwardly. 
     Referring to  FIGS. 22-24 , the braking assembly  720  includes an inner braking member  910  and an outer braking member  912 . The inner and outer braking members  910  and  912  may each be substantially planar. By way of a non-limiting example, the inner and outer braking members  910  and  912  may be constructed from sheet metal. Both the inner and outer braking members  910  and  912  are non-rotatably connected to the first leg portion  732  of the limit bolt  730  and configured to rotate therewith as a unit. 
     The inner braking member  910  includes a through-hole  916  (see  FIG. 22 ) configured to non-rotatably receive the first and second relieved portions  766 A and  766 B of the distal threaded portion  762  of the first leg portion  732  of the limit bolt  730 . The inner braking member  910  is positioned between the inner C-shaped bracket  740  and the lock nut  446 . The interior shape of the through-hole  916  may correspond to the outer shape of the portion of the threaded portion  762  received therein. For example, the through-hole  916  may include a first flat portion  918 A adjacent the planar outer surface  768  of the first relieved portion  766 A and a second flat portion  918 B adjacent the planar outer surface  768  (see  FIG. 18 ) of the second relieved portion  766 B (see  FIG. 18 ). Thus, the through-hole  916  provides a keyway configured to receive the first and second relieved portions  766 A and  766 B of the threaded portion  762 , which define a key that is non-rotatable within the keyway. Engagement between the key and keyway cause the inner braking member  910  and the first leg portion  732  of the limit bolt  730  to rotate together as a unit. 
     The outer braking member  912  includes a through-hole  920  configured to receive the unthreaded portion  764  of the first leg portion  732  of the limit bolt  730 . The outer braking member  912  is positioned on the unthreaded portion  764  between the outer C-shaped bracket  742  and the bent portion  738  of the limit bolt  730 . The shape of the through-hole  920  may correspond to the outer shape of the portion of the unthreaded portion  764  received therein. For example, both the through-hole  920  and the unthreaded portion  764  may have generally circular cross-sectional shapes. The outer braking member  912  is non-rotatably fastened to the unthreaded portion  764 . By way of a non-limiting example, the outer braking member  912  may be welded to the unthreaded portion  764 . Thus, the outer braking member  912  and the first leg portion  732  of the limit bolt  730  are rotatable together as a unit. 
     Turning now to  FIGS. 23 and 24 , optionally, the one or more washers  518  may be disposed between the inner braking member  910  and the inner C-shaped bracket  740 . Further, one or more optional washers (not shown) may be disposed between the outer braking member  912  and the outer C-shaped bracket  742 . 
     As mentioned above, the return spring  434  is compressed between the inner and outer C-shaped brackets  740  and  742  and applies an outwardly directed force to each of them, biasing them outwardly. The lock nut  446  is configured not to pass through the through-hole  916  (see  FIG. 22 ) formed in the inner braking member  910 , which is configured not to pass through the through-hole  494  (see  FIG. 19 ) formed in the inner C-shaped bracket  740 . Thus, the outward movement of the inner C-shaped bracket  740  is limited by the lock nut  446  threaded onto the distal threaded portion  762 . The outer braking member  912  is configured not to pass through the through-hole  494  (see  FIG. 19 ) formed in the outer C-shaped bracket  742 . Thus, the outward movement of the outer C-shaped bracket  742  is limited by the outer braking member  912 . 
     The inner and outer C-shaped brackets  740  and  742  are allowed to float (or change position relative to the mounting bracket  410 ) to accommodate misalignment of the tracks “T 1 ” and “T 2 .” The limit bolt  730  and the return spring  434  maintain a predetermined spacing between the inner and outer C-shaped brackets  740  and  742  while allowing them to float within the channel  470  (see  FIG. 18 ). The predetermined spacing may be adjusted during installation by tightening or loosening the lock nut  446 . 
     Both the inner and outer braking members  910  and  912  include a first cutout  930  formed in their forward facing edge portions  934 . The first cutout  930  of the inner braking member  910  is configured to receive the dimple  750  formed in the inner C-shaped bracket  740 , when the braking assembly  720  is in the brake released position (see  FIG. 23 ). The first cutout  930  of the outer braking member  912  is configured to receive the dimple  750  formed in the outer C-shaped bracket  742 , when the braking assembly  720  is in the brake released position. 
     Both the inner and outer braking members  910  and  912  include an inwardly facing portion  938  adjacent the first cutout  930 . The inwardly facing portion  938  of the inner braking member  910  is configured to abut the dimple  750  formed in the inner C-shaped bracket  740  and apply an inwardly directed force thereto when the braking assembly  720  is in the brake engaged position (see  FIG. 24 ). The inwardly facing portion  938  of the outer braking member  912  is configured to abut the dimple  750  formed in the outer C-shaped bracket  742  and apply an inwardly directed force thereto when the braking assembly  720  is in the brake engaged position. In other words, as the inner and outer braking members  910  and  912  are rotated, they travel relative to the dimples  750  to selectively position the dimples  750  inside the first cutouts  930  (the brake released position) and to selectively position the inwardly facing portions  938  adjacent the dimples  750  (the brake engaged position). 
     Returning to  FIG. 22 , optionally, both the inner and outer braking members  910  and  912  include a second cutout  940  formed in their rearward facing edge portions  944 . The second cutouts  940  of the inner and outer braking members  910  and  912  allow the inner and outer braking members  910  and  912  to be rotated with the limit bolt  730  without interference from other components. In other words, the second cutouts  940  are configured to avoid interference between the inner and outer braking members  910  and  912  and the other components. 
       FIGS. 21 and 24  illustrate the braking assembly  720  in the brake engaged position. A user actuates the braking assembly  720  (i.e., transitions the braking assembly  720  from the brake released position to the brake engaged position) by pressing downwardly (e.g., with his/her foot or hand) on the foot receiving portion  778  coupled to the distal end portion  776  of the upright member  774  thereby compressing the coil spring  794  (see  FIG. 20 ) inside the interior chamber  788  (see  FIG. 20 ) and moving the retaining member  782  coupled to the proximal end portion  780  of the upright member  774  downwardly. 
     When the retaining member  782  moves downwardly, the bent distal portion  769  of the second leg portion  736  of the limit bolt  730  is pressed downwardly by the retaining member  782 , which rotates the first leg portion  732  of the limit bolt  730  relative to the inner and outer C-shaped brackets  740  and  742 . By way of a non-limiting example, the upper wall  785  of the channel  784  may press downwardly on the bent distal portion  769  of the second leg portion  736  of the limit bolt  730 , which is free to move within the channel  784  to allow the L-shaped limit bolt  730  to rotate within the through-holes  494  (see  FIG. 19 ) of the inner and outer C-shaped brackets  740  and  742 . 
     As the braking assembly  720  transitions from the brake released position to the brake engaged position, the rotation of the first leg portion  732  of the limit bolt  730  rotates the inner and outer braking members  910  and  912  to position the inwardly facing portion  938  of the inner braking member  910  adjacent the dimple  750  of the inner C-shaped bracket  740  and the inwardly facing portion  938  of the outer braking member  912  adjacent the dimple  750  of the outer C-shaped bracket  742  thereby exerting an inwardly directed force on the inner and outer C-shaped brackets  740  and  742 . This presses the outer wear plate  758  into the distal portion  156  of the flange  152  of the track “T 2 ” and the inner wear plate  756  into the distal portion  158  of the flange  154  of the track “T 2 .” As the outer wear plate  758  is biased toward the flange  152  and the inner wear plate  756  is biased against the flange  154 , the return spring  434  (see  FIG. 24 ) is compressed between inner and outer C-shaped brackets  740  and  742 . In other words, the inner and outer C-shaped brackets  740  and  742  (and the inner and outer wear plates  756  and  758 ) clamp or pinch the track “T 2 .” Frictional engagement between the inner and outer wear plates  756  and  758  and the flanges  154  and  152 , respectively, limit the movement of the support assembly  302 B along the track “T 2 ,” thereby braking the shelving unit  100  (see  FIG. 1 ). 
     Optionally, the distal portion  493  of the flange  488  of the outer C-shaped bracket  742  may be biased against the inside of the channel  162  of the track “T 2 .” For example, the distal portion  493  of the flange  488  of the outer C-shaped bracket  742  may be biased against the bottom portion  166  of the channel  162  of the track “T 2 .” Similarly, the distal portion  493  of the flange  488  of the inner C-shaped bracket  740  may be biased against the inside of the channel  164  of the track “T 2 .” For example, the distal portion  493  of the flange  488  of the inner C-shaped bracket  740  may be biased against the bottom portion  168  of the channel  164  of the track “T 2 .” Frictional engagement between the distal portions  493  of the flanges  488  of the inner and outer C-shaped brackets  740  and  742  and the inside of the channels  164  and  162 , respectively, limit the movement of the support assembly  302 B along the track “T 2 ,” thereby braking the shelving unit  100  (see  FIG. 1 ). 
       FIGS. 17 and 23  illustrate the braking assembly  720  in the brake released position. To release the braking assembly  720  (i.e., transition the braking assembly  720  from the brake engaged position to the brake released position), the user pulls upwardly (e.g., with his/her foot or hand) on the foot receiving portion  778  coupled to the distal end portion  776  of the upright member  774  thereby uncompressing the coil spring  794  (see  FIG. 20 ) inside the interior chamber  788  (see  FIG. 20 ) and moving the retaining member  782  coupled to the proximal end portion  780  of the upright member  774  upwardly. The upward movement of the foot receiving portion  778  may be assisted by the biasing force exerted on the upright member  774  by the coil spring  794 . 
     When the retaining member  782  moves upwardly, the bent distal portion  769  of the second leg portion  736  of the limit bolt  730  is pulled upwardly by the retaining member  782 , which rotates the first leg portion  732  of the limit bolt  730  relative to the inner and outer C-shaped brackets  740  and  742 . By way of a non-limiting example, the lower wall  787  of the channel  784  may push upwardly on the bent distal portion  769  of the second leg portion  736  of the limit bolt  730 , which is free to move within the channel  784  to allow the L-shaped limit bolt  730  to rotate within the through-holes  494  (see  FIG. 19 ) of the inner and outer C-shaped brackets  740  and  742 . 
     Rotation of the first leg portion  732  of the limit bolt  730  rotates the inner and outer braking members  910  and  912  to position the dimples  750  inside the first cutouts  730  thereby eliminating the inwardly directed force exerted by the inwardly facing portions  938  on the inner and outer C-shaped brackets  740  and  742  when the braking assembly  720  was in the brake engaged position. The return spring  434  pushes the outer C-shaped bracket  742  and the outer wear plate  758  away from the distal portion  156  of the flange  152  of the track “T 2 ” and the inner C-shaped bracket  740  and the inner wear plate  756  away from the distal portion  158  of the flange  154  of the track “T 2 .” Thus, the track “T 2 ” is released by the inner and outer C-shaped brackets  740  and  742  (and the inner and outer wear plates  756  and  758 ). In this configuration, the braking assembly  720  does not exert an inwardly directed force on either the outer C-shaped bracket  742  or the inner C-shaped bracket  740 . Thus, the braking assembly does not cause the frictional engagement between the inner and outer wear plates  756  and  758  and the flanges  154  and  152 , respectively. Further, the braking assembly  720  does not cause the frictional engagement between the distal portions  493  of the flanges  488  of the inner and outer C-shaped brackets  740  and  742  and the inside of the channels  164  and  162 , respectively. In other words, the movement of the support assembly  302 B (see  FIG. 23 ) along the track “T 2 ” is not limited by the braking assembly  720  when it is in the brake released position. 
     Alternate Embodiment 
       FIGS. 15 and 16  illustrate a mobile shelving unit  800  having a plurality of spaced apart upright supports  810 A,  810 B, and  810 C. The upright supports  810 A and  810 B may be coupled together by laterally extending members  814  and  816  and the upright supports  810 B and  810 C may be coupled together laterally by laterally extending members  818  and  820 . One or more cantilever shelf supports  830  may be coupled to each of the upright supports  810 A,  810 B, and  810 C and arranged to support storage units (e.g., a storage bin  834 , a wire basket  836 , and the like) and shelves (e.g., a planar shelf  840 , a wire shelf  842 , and the like). The storage units and/or shelves may be coupled to the cantilever shelf supports  830  in any manner known in the art. 
     The upright supports  810 A,  810 B, and  810 C are supported by movable support assemblies  850 A,  850 B, and  850 C, respectively, disposed on tracks “T 3 ,” “T 4 ,” and “T 5 ,” respectively. Each of the tracks “T 3 ,” “T 4 ,” and “T 5 ” may be implemented as the track “T 2 ” illustrated in  FIG. 2 , the track  192  illustrated in  FIG. 14 , and the like. The tracks “T 3 ,” “T 4 ,” and “T 5 ” are spaced apart and substantially parallel to one another. However, as explained above, a certain amount of misalignment is generally present. The tracks “T 3 ,” “T 4 ,” and “T 5 ” define a travel path for the mobile shelving unit  800 . 
     The support assemblies  850 A,  850 B, and  850 C are substantially identical to one another. Therefore, only the support assembly  850 A will be described in detail. As may best be viewed in  FIG. 16 , the support assembly  850 A includes an outer cover  860  having an open lower portion  862  closed at one end by a first downwardly extending end flange  863 , and closed at the other end by a second downwardly extending end flange  864 . 
     The support assembly  850 A includes an elongated support member  866  substantially aligned longitudinally with the track “T 3 .” The support member  866  is configured to nest inside the open lower portion  862  of the outer cover  860  between the first and second end flanges  863  and  864 . Optionally, the support member  866  may be coupled to the outer cover  860 . The support member  866  may have a generally U-shaped cross-sectional shape defined by a first downwardly extending sidewall  872 , a second downwardly extending sidewall  874  spaced part from the first sidewall, and a transverse upper wall  876  connecting the first and second sidewalls together. 
     A downward opening channel  878  is defined between the spaced part first and second sidewalls  872  and  874 . The channel  878  has an open first end portion  879  opposite an open second end portion  880 . The open first end portion  879  is adjacent the first end flange  863  when the support member  866  is inside the open lower portion  862  of the outer cover  860 . Thus, the first end flange  863  may close the open first end portion  879  of the channel  878 . Similarly, the open second end portion  880  is adjacent the second end flange  864  when the support member  866  is inside the open lower portion  862  of the outer cover  860 . Thus, the second end flange  864  may close the open second end portion  880  of the channel  878 . 
     A plurality of axles  882  extend between the first and second sidewalls  872  and  874  within the downward opening channel  878 . Each of the axles  882  may be substantially identical to the axle  384  (see  FIGS. 5 and 6 ). Wheels  884  are rotatably mounted to the axles  882  and configured to rotate within the open channel  878  and roll along the track “T 3 .” Each of the wheels  884  may be substantially identical to the embodiment of the wheel  342  illustrated in  FIG. 6 , the embodiment of the wheel  342  illustrated in  FIG. 14 , and the like. 
     In the embodiment illustrated in  FIG. 16 , a first anti-tip assembly  890  is coupled to the first end flange  863  adjacent the open first end portion  879  of the open channel  878  by one or more brackets  894 . The first anti-tip assembly  890  may be substantially identical to the anti-tip assembly  304 B (see  FIG. 5 ). Optionally, the braking assembly  306  may be coupled to the first anti-tip assembly  890 . An optional cover  896  may be coupled over the first anti-tip assembly  890  by a cover mounting bracket  898 . 
     Optionally, a second anti-tip assembly (not shown) may be coupled to the second end flange  864  adjacent the open second end portion  880  of the open channel  878  by one or more brackets (not shown) substantially identical to the brackets  894 . The second anti-tip assembly may be substantially identical to the anti-tip assembly  304 B (see  FIG. 5 ). Optionally, a second braking assembly  306  may be coupled to the second anti-tip assembly (not shown). An optional cover (not shown) substantially identical to the optional cover  896  may be coupled over the second anti-tip assembly by a cover mounting bracket (not shown) substantially identical to the cover mounting bracket  898 . 
     In the embodiment illustrated, one or more brackets  900  are coupled to the second end flange  864  adjacent the open second end portion  880  of the open channel  878 . Further, an optional cover  902  is coupled to the brackets  900  by a cover mounting bracket  904 . The cover  902  may be substantially identical to the cover  896  and the cover mounting bracket  904  may be substantially identical to the cover mounting bracket  898 . 
     Returning to  FIG. 15 , the support assembly  850 A, the first anti-tip assembly  890 , and the optional second anti-tip assembly (not shown) are configured to allow the mobile shelving unit  800  to travel along the less than perfectly aligned tracks “T 3 ,” “T 4 ,” and “T 5 ,” avoid binding that might otherwise be caused by such misalignment, and at the same time prevent the mobile shelving unit  800  from becoming disengaged from the track “T 3 ” and tipping over. 
     While the support assemblies  850 A,  850 B, and  850 C have been described as being substantially identical to one another, they may differ from one another with respect to whether they include the first anti-tip assembly  890 , the second anti-tip assembly, and neither the first anti-tip assembly nor the second anti-tip assembly. For example, as illustrated in  FIG. 15 , the support assembly  850 A may include only the first anti-tip assembly  890  and the support assemblies  850 B and  850 C may include neither the first anti-tip assembly  890  nor the second anti-tip assembly (not shown). 
     The foregoing described embodiments depict different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality. 
     While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. Furthermore, it is to be understood that the invention is solely defined by the appended claims. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). 
     Accordingly, the invention is not limited except as by the appended claims.