Push back storage rack system

The push back storage rack system comprises a framework defining a storage bay for multiple pallets including a plurality of generally vertical uprights and a plurality of generally horizontal shelf beams. A pair of laterally spaced, generally parallel rails is supported by the framework and extends into the storage bay. Each of the rails defines inner and outer wheel tracks and is inclined in a direction towards the rear of the storage bay. A generally rectangular first cart has a pair of front wheels and a pair of rear wheels. The front and rear wheels roll along the inner wheel tracks. The generally rectangular second cart is positioned behind the first cart and has a pair of front wheels and a pair of rear wheels. The front wheels roll along the outer wheel tracks and the rear wheels roll along the inner wheel tracks. A generally rectangular third cart is positioned behind the second cart and has a pair of front wheels and a pair of rear wheels. The front and rear wheels roll long the outer wheel tracks. The third cart supports a second pair of laterally spaced, generally parallel rails, each of which defines an outwardly facing wheel track. The rear of the second pair of rails is supported by a pair of wheels that roll along the inner wheel tracks. A fourth generally rectangular cart is positioned behind the third cart and has a pair of front wheels and a pair of rear wheels. The front wheels roll along the second pair of rails and the rear wheels roll along the outer wheel tracks. The second pair of rails is oriented such that downward forces placed on the front wheels of the fourth cart inhibit development of a horizontal force component tending to move the fourth cart rearwardly into the storage bay.

FIELD OF THE INVENTION 
The present invention relates to storage racks for pallets and the like and 
in particular to a push back storage rack system to allow multiple pallets 
to be stored behind one another. 
BACKGROUND OF THE INVENTION 
Push back storage rack systems employing rolling carts for carrying pallets 
or skids are well known in the art and many variations have been 
considered. For example, U.S. Pat. No. 5,415,300 to Krummel et al. 
discloses a push back cart storage system including an outer cart having 
wheels rolling on a pair of laterally spaced, parallel, inclined support 
rails. A middle cart has forward wheels rolling on side members of the 
outer cart. The rear wheels on the middle cart roll on the support rails. 
An inner cart has front wheels rolling on the side members of the middle 
cart. The rear wheels of the inner cart roll on the support rails. 
U.S. Pat. No. 5,184,738 to Allen discloses a storage rack system having a 
plurality of storage bays adapted to store pallets three, four and five 
pallets deep. A pair of laterally spaced, parallel, inclined outer tracks 
extend the full depth of the storage bay while a pair of inclined inner 
tracks extend partially into the storage bay. A plurality of carts roll 
along the tracks and support pallets. 
Although the above references disclose push back storage rack systems, 
problems exist. In particular, the design of these push back storage rack 
systems allows carts to be double loaded with pallets which may result in 
overloading and damage to the wheels of the carts. Furthermore, the design 
of the carts requires the depth of the storage rack systems to exceed 
significantly the actual depth required to store the pallets resulting in 
wasted space. 
Accordingly, there exists a need for an improved push back storage rack 
system. It is therefore an object of the present invention to provide a 
novel push back storage rack system. 
SUMMARY OF THE INVENTION 
According to one aspect of the present invention there is provided a push 
back storage rack system comprising: 
a framework defining a storage bay for multiple pallets including a 
plurality of generally vertical uprights and a plurality of generally 
horizontal shelf beams; 
a first pair of laterally spaced, generally parallel rails supported by 
said framework and extending into said storage bay, each of said rails 
defining inner and outer wheel tracks and being inclined in a direction 
towards the rear of said storage bay; 
a generally rectangular first cart having a pair of front wheels and a pair 
of rear wheels, said front and rear wheels rolling along said inner wheel 
tracks; 
a generally rectangular second cart behind said first cart and having a 
pair of front wheels and a pair of rear wheels, said front wheels rolling 
along said inner wheel tracks and said rear wheels rolling along said 
outer wheel tracks; 
a generally rectangular third cart behind said second cart and having a 
pair of front wheels and a pair of rear wheels, said front and rear wheels 
rolling along said outer wheel tracks, said third cart supporting a second 
pair of laterally spaced, generally parallel rails, each rail of said 
second pair defining an outwardly facing wheel track, the rear of said 
second pair of rails being supported by a pair of wheels rolling along 
said inner wheel tracks; and 
a fourth generally rectangular cart behind said third cart and having a 
pair of front wheels and a pair of rear wheels, said front wheels rolling 
along the outwardly facing wheel tracks of said second pair of rails and 
said rear wheels rolling along said outer wheel tracks, wherein said 
second pair of rails is oriented such that downward forces placed on the 
front wheels of said fourth cart inhibit development of a horizontal force 
component tending to move said fourth cart rearwardly into said storage 
bay. 
Preferably, the third cart has a generally U-shaped rail assembly mounted 
thereon. The rail assembly includes a pair of side members defining the 
second pair of rails which are bridged by a rear member. The rear member 
supports the pair of wheels rolling along the inner wheel tracks. Stops 
are provided on the second pair of rails adjacent the rear ends thereof to 
inhibit removal of the front wheels of the fourth cart from the second 
pair of rails. 
Preferably, the push back storage rack system further includes a retaining 
mechanism to inhibit at least one of the carts from inadvertently being 
pushed rearwardly into the storage bay. In a preferred embodiment, the 
retaining mechanism is in the form of a resilient strip on the framework 
positioned to contact the third cart. The strip flexes easily in a forward 
direction to permit the third cart to roll towards the front of the 
storage rack. It is more difficult to flex the strip in a rearward 
direction thereby to retain the third cart adjacent the front of the 
storage bay when the fourth cart is pushed back into the storage bay. 
Preferably, the third cart carries a downwardly extending tab which 
interacts with the strip. 
Preferably, each of the carts includes a pair of side members bridged at 
opposed ends by front and rear members. The side members are laterally 
spaced apart a distance corresponding to the distance between stringers of 
conventional pallets. It is also preferred that the side members carry 
upwardly extending tabs to inhibit sliding of pallets placed on the carts 
in a forward direction. 
According to another aspect of the present invention there is provided a 
push back storage rack system comprising: 
a framework defining a storage bay for multiple pallets including a 
plurality of generally vertical uprights and a plurality of generally 
horizontal shelf beams; 
a first pair of laterally spaced, generally parallel rails supported by 
said framework and extending into said storage bay, each of said rails 
defining inner and outer wheel tracks and being inclined in a direction 
towards the rear of said storage bay; 
a generally rectangular first cart having a pair of front wheels and a pair 
of rear wheels, said front and rear wheels rolling along said inner wheel 
tracks; 
a generally rectangular second cart behind said first cart having a pair of 
front wheels and a pair of rear wheels, said front wheels rolling along 
said inner wheel tracks and said rear wheels rolling along said outer 
wheel tracks; 
a generally rectangular third cart behind said second cart and having a 
pair of front wheels and a pair of rear wheels, said front and rear wheels 
rolling along said outer wheel tracks, said third cart supporting a second 
pair of laterally spaced, generally parallel rails, each rail of said 
second pair defining an outwardly facing wheel track, the rear of said 
second pair of rails being supported by a pair of wheels rolling along 
said inner wheel tracks; and 
a fourth generally rectangular cart behind said third cart and having a 
pair of front wheels and a pair of rear wheels, said front wheels rolling 
along said second pair of rails and said rear wheels rolling along said 
outer wheel tracks, the wheels of said first, second, third and fourth 
carts being positioned on said carts so that said carts present generally 
horizontal support surfaces for pallets. 
In still yet another aspect of the present invention there is provided a 
push back storage rack system comprising: 
a framework defining a storage bay for multiple pallets including a 
plurality of generally vertical uprights and a plurality of generally 
horizontal shelf beams; 
a pair of laterally spaced generally parallel rails supported by said 
framework and extending into said storage bay, each of said rails defining 
inner and outer wheel tracks and being inclined in a direction towards the 
rear of said storage bay; 
a plurality of generally rectangular, interlocked carts, each of said carts 
having pairs of front and rear wheels rolling along said wheel tracks; and 
a retaining mechanism adjacent the front of said storage bay to inhibit at 
least one cart from inadvertently being pushed rearwardly into said 
storage bay when an upper most cart is pushed into said storage bay. 
The present invention provides advantages in that the design of the carts 
inhibits the carts from being double-loaded by pallets as well as inhibits 
unintentional carry back of the carts as the carts are individually loaded 
with pallets and pushed back along the wheel tracks into the storage bay. 
In addition, the present invention provides advantages in that the carts 
present generally level pallet supporting surfaces and are interlocked to 
avoid rear cart "hang-ups". Furthermore, the design of the carts inhibits 
wheels on adjacent carts from contacting one another.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 1 to 3, a push back storage rack system is shown and 
is generally indicated to by reference numeral 10. The push back storage 
rack system 10 includes a framework 12 having a plurality of generally 
vertical uprights 14 and a plurality of generally horizontal shelf beams 
16. Horizontal and angled supporting crossbars 18 extend between pairs of 
uprights 14. The framework 12 defines a storage bay 20 for multiple 
pallets. 
A pair of laterally spaced, generally parallel rails 30 extend the depth of 
the storage bay 20. The rails 30 are secured to the shelf beams 16 and are 
inclined in a direction towards the rear of the storage bay. A plurality 
of interlocked, pallet supporting carts generally indicated to by 
reference numeral 31 are positioned in the storage bay 20 and are moveable 
along the rails 30. In the present embodiment, the storage bay 20 
accommodates four interlocked carts each positioned one behind the other 
and provides storage for up to five pallets. The inclination of the rails 
30 causes the carts 31 to move to the front of the storage bay 20. When 
the carts are unloaded, the carts 31 assume a stacked relation with the 
upper most cart being the only cart whose upper surface is exposed. Each 
cart is however, moveable inwardly into the storage base to expose the 
upper surface of the cart below it. 
FIG. 9 shows one of the rails 30 and as can be seen, it is in the form of 
an I-beam having upper and lower flanges 30a and 30b respectively joined 
by a central web 30c. The I-beam defines an inner wheel track 32 and an 
outer wheel track 34. Notches 36 are formed in the upper flange 30a near 
the front of the storage bay 20 to expose the inner and outer wheel tracks 
32 and 34 respectively to facilitate placement and removal of carts from 
the rail. The upper flange 30a shelters the wheel tracks 32 and 34 to 
inhibit debris from falling on the running surfaces of the wheel tracks 
and inhibit the carts from being removed from the wheel tracks if the 
carts are accidentally lifted. 
A tempered steel strip 40 (see FIG. 10) is mounted on and extends upwardly 
from the shelf beam 16 near the front of the storage bay 20. The strip 40 
is positioned to contact the third cart as that cart moves towards the 
front of the storage bay 20. The strip 40 flexes easily in a forward 
direction to allow the third cart to roll along the rails 30 to the front 
of the storage bay. The strip 40 however requires a significant force to 
flex in the opposite direction thereby to inhibit accidental carry back of 
the third cart into the storage bay 20 when the fourth cart is loaded with 
a pallet and pushed back into the storage bay. 
Referring now to FIGS. 4a and 4b, the first cart is better illustrated and 
is generally indicated to by reference numeral 50. First cart 50 includes 
a generally rectangular open frame 52 constituted by a pair of side 
members 54 bridged at their opposed ends by front and rear members 56 and 
58 respectively. The side, front and rear members are in the form of 
structural angles including pairs of plates arranged at right angles. 
Sharp tabs 60 are punched in the upper plate of each side member 54 and 
project upwardly. The tabs 60 inhibit pallets from moving forward once 
placed on the cart 50. Front and rear pairs of wheels 62 and 64 
respectively are rotatably mounted on the upright plates of the side 
members 54 and roll along the inner wheel tracks 32 of the rails 30. The 
front wheels 62 are positioned below the rear wheels 64 to offset the 
inclination of the rails 30 so that the frame 52 of the cart 50 remains in 
a generally horizontal disposition. Laterally spaced tabs 66 extend 
upwardly from the rear member 58 and engage the second cart thereby to 
interlock the first and second carts. 
FIGS. 5a and 5b better illustrate the second cart 70 which is positioned 
behind the first cart 50. The second cart 70 also includes a generally 
rectangular open frame 72 constituted by a pair of side members 74 bridged 
at their opposed ends by front and rear members 76 and 78 respectively. 
The side, front and rear members are in the form of structural angles 
including pairs of plates arranged at right angles. Sharp tabs 80 are 
punched in the upper plate of each side member 74 and project upwardly. 
The tabs 80 inhibit pallets from moving forward once placed on the cart 
70. Legs 82 in the form of structural angles are secured to the rear 
member 78 and extend below the frame 72. Outwardly facing rear wheels 84 
are rotatably mounted on the legs 82 below the frame 72 and roll along the 
inner wheel tracks 32 of the rails 30. Legs 86 in the form of structural 
angles are also secured to the ends of the front member 76 and extend 
below the frame 72. Inwardly facing front wheels 88 are rotatably mounted 
on the legs 86 below the frame 72 and roll along the outer wheel tracks 34 
of the rails 30. The front wheels 88 are positioned below the rear wheels 
84 to offset the inclination of the rails 30 so that the frame 72 of cart 
70 remains in a generally horizontal disposition. Laterally spaced tabs 89 
extend upwardly from the rear member 78 and engage the third cart thereby 
to interlock the second and third carts. 
Referring now to FIGS. 6a and 6b, the third cart 90 is better illustrated. 
As can be seen, the third cart 90 includes a generally rectangular open 
frame 92 constituted by a pair of side members 94 bridged at their opposed 
ends by front and rear members 96 and 98 respectively. The side, front and 
rear members are in the form of structural angles including pairs of 
plates arranged at right angles. Sharp tabs 100 are punched in the upper 
plate of the each member 94 and project upwardly. The tabs 100 inhibit 
pallets from moving forward once placed on the cart. Legs 102 in the form 
of structural angles depend from the upright plates of the side members 94 
near the rear member 98 and extend below the frame 92. A hole 106a is 
provided through each leg 106 intermediate its length. Inwardly facing 
rear wheels 104 are rotatably mounted on the legs 102 and roll along the 
outer wheel tracks 34 of the rails 30. Legs 106 in the form of structural 
angles also depend from the upright plates of the side members 94 near the 
front member 96 and extend below the frame 92. A hole 106a is provided 
through each leg 106 intermediate its length. Inwardly facing front wheels 
108 are rotatably mounted on the legs 106 and roll along the outer wheel 
tracks 34 of the rails. The front wheels 108 are positioned below the rear 
wheels 104 to offset the inclination of the rails 30 so that the frame 92 
of the cart 90 remains in a generally horizontal disposition. A pair of 
laterally spaced tabs 109 extend upwardly from the rear member 98 and a 
centrally located tab 110 extends downwardly from the rear member 98. The 
tab 110 and strip 40 act to form a retaining mechanism for the third cart 
when it is positioned adjacent the front of the storage bay 20. The tabs 
109 engage the fourth cart thereby to interlock the third and fourth 
carts. 
FIGS. 7a and 7b best illustrate a rail assembly 120 mounted on the third 
cart 90. As can be seen, the rail assembly 120 includes a generally 
U-shaped frame 122 constituted by a pair of side channel members 124 
defining outwardly facing wheel tracks 126 bridged at their rear ends by a 
rear member 128. Each side member 124 is supported on the third cart 90 by 
way of a foot 130 near its distal end. Each foot 130 has a hole 130a 
provided through it which aligns with one of the holes 106a. Fasteners 
(not shown) in the form of nuts and bolts pass through the holes 130a and 
106a to secure the rail assembly 120 to the third cart 90. Spaced legs 132 
depend from the rear member 128 and rotatably support outwardly facing 
wheels 134. The wheels 134 roll along the inner wheel tracks 32 of the 
rails 30. A hole 136 is also provided through each side member 124 near 
its rear end. A bolt (not shown) extends through each hole 136 and is 
sufficiently long to inhibit wheels from rolling out of the wheel tracks 
126. 
Referring now to FIGS. 8a and 8b, the fourth cart 140 is better 
illustrated. As can be seen, the fourth cart includes a generally 
rectangular open frame 142 constituted by a pair of side members 144 
bridged by front and rear members 146 and 148 respectively at their 
opposed ends. The side and rear members are in the form of structural 
angles including pairs of plates arranged at right angles. Sharp tabs 149 
are punched in the upper surface of each side member 144 and project 
upwardly to inhibit pallets from moving forward once placed on the cart. 
The front member 146 is tubular and extends beyond both of the side 
members 144. A central longitudinal, tubular cross-member 150 spans the 
front and rear members 146 and 148. A second cross-member 152 spans the 
side members 144 near to but spaced from the rear member 148. One of the 
plates 162 of the cross-member 152 extends upwardly and functions as a 
push plate. Legs 154 in the form of structural angles depend from the 
opposed ends of the rear member 148. Inwardly facing rear wheels 156 are 
rotatably mounted on the legs 154 and roll along the outer wheel tracks 32 
of rails 30. Legs 158 in the form of structural angles also depend from 
the ends of the front member 146. Inwardly facing front wheels 160 are 
rotatably mounted on the legs 158 and roll along the wheel tracks 126 
defined by side members 124 of the rail assembly 120. As mentioned above, 
the bolts extending through the holes 136 inhibit the wheels 160 from 
being removed from the wheel tracks 126. The length of the legs 158 
relative to the legs 154 is such that the position of the front wheels 160 
relative to the rear wheels 156 maintain the frame 142 in a generally 
horizontal disposition. 
When no pallets are placed on the carts, the inclination of the rails 30 
causes the carts to remain at the front of the storage bay 20 in a stacked 
relation. The carts overlap so that the upper surface of the fourth cart 
140 is the only cart on which a pallet can be placed. When a pallet is to 
be loaded into the storage bay 20, the pallet is placed on the frame 142 
of the cart 140 so that the back of the pallet contacts the push plate 
162. The inclination of the channel members 124 defining the wheel tracks 
126 is such to inhibit the development of a horizontal force component 
tending to move the fourth cart 140 rearwardly into the storage bay 20 
along the wheel tracks 126 when the fourth cart is loaded with a pallet. 
When the next pallet is to be loaded into the storage bay 20, the pallet is 
pushed against the pallet on the fourth cart 140 causing the fourth cart 
to roll along the wheel tracks 126 and 34 into the storage bay 20 and 
expose the third cart 110. The retaining mechanism constituted by the tab 
110 and the strip 40 inhibits the third cart 110 from being carried back 
into the storage bay 20 by the fourth cart 140. When the third cart is 
exposed, the pallet is placed on the frame of the third cart. Loading of 
pallets onto the remaining carts is achieved in the same manner. 
Once pallets have been loaded onto the four carts, an additional pallet can 
be loaded onto the framework 12 at the front of the storage bay 20 by 
pushing the first cart 50 into the storage bay and placing the additional 
pallet on the rails 30 so that the pallet also rests on the front shelf 
beam 16 of the framework. The front shelf beam of the framework 12 is 
elevated to compensate for the inclination of the rails so that the 
additional pallet remains in a generally horizontal disposition. 
As pallets are removed from the storage bay, the carts roll towards the 
front of the storage bay due to the inclination of the rails 30 so that a 
pallet is always positioned at the front of the storage bay 20 and is 
accessible. The tabs on the rear member of each cart contact the interior 
side surfaces of the front member of the cart behind it to interlock the 
carts. Thus, several loaded carts must roll together towards the front of 
the storage bay 20. If a "hang-up" should occur, the hung up cart can only 
be hung up a distance equal to one pallet position. 
The wheels on the various carts are arranged so that wheel load forces are 
transferred to the rails 30 such that no two sets of wheels act on one 
local area of the rails thereby to minimize torsional effects on the 
rails. This allows the amount of steel required for the flanges of the 
I-beams to be reduced. The width of each cart is selected so that the side 
members of each cart are positioned to align generally with the stringers 
of conventional pallets. The depth of the carts is such that once the 
fourth cart is loaded with a pallet which contacts the push plate 162, the 
pallet extends slightly beyond the front of the cart. Thus, the pallet on 
the fourth cart serves as a push plate for the next pallet to be loaded on 
the third cart. All pallets loaded on subsequent carts extend slightly 
beyond the front of the respective carts. Since the pallets extend beyond 
the front of the carts, the carts cannot be double loaded and support more 
than one pallet. 
Although the carts are described as having open generally rectangular 
frames, the tops of the carts can be covered with a sheet of steel or 
other suitable material in cases where additional support is desired 
and/or when pallets are structurally weak. 
Although a preferred embodiment of the present invention has been 
described, it should be apparent to those of skill in the art that 
variations and modifications may be made to the present invention without 
departing from the spirit and scope thereof as defined by the appended 
claims.