Push-back cart storage system

A push-back cart storage system includes an outer cart having wheels rolling on support rails. A middle cart has forward wheels rolling on side members of the outer cart. Rear wheels on the middle cart role on the support rails. An inner cart has front wheels rolling on side members of the middle cart, while rear wheels of the inner cart role on the side rails. The rolling carts are all of equal height.

BACKGROUND OF THE INVENTION 
The field of the invention is push-back storage systems. 
Push-back cart storage systems typically use rolling carts for carrying 
pallets or other cargo, on slightly inclined rails. By providing several 
carts on a set of rails, useable space between aisles in e.g., a 
warehouse, is increased as multiple pallets can be stored and retrieved 
from a single aisle. Consequently, aisle space necessary in conventional 
storage racks for forklift access may be used for additional storage 
racks, providing more efficient use of space. 
Although various push-back cart storage systems have been used in the past, 
there is a need for an improved system which may be readily fabricated 
from standard structural members, is convenient and effective in use, and 
which provides for increased storage efficiency. 
SUMMARY OF THE INVENTION 
To these ends, the present push-back cart storage systems includes a pair 
of spaced apart support rails each having a lower inside flange or roller 
support surface. An outer cart has wheels which roll on the lower inside 
flange of the support rails. The outer cart 20 has side members 26 also 
having a lower inside flange. A middle cart has front wheels which roll on 
the lower inside flanges of the side members of the outer cart. Rear 
wheels on the middle cart roll directly on the support rails. For a four 
deep system, an inner cart may be provided with front wheels rolling on 
lower inside flanges of side members of the middle cart, and with rear 
wheels of the inner cart rolling directly on the support rails. 
Accordingly, it is an object of the invention to provide an improved 
push-back cart storage system. Other and further objects and advantages 
will appear hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the drawings, as shown in FIG. 1, the present push-back cart 
storage system 10 includes a pair of spaced apart support rails 12. The 
support rails 12 may be of various designs, e.g., I-beams, C-sections, 
etc., and as shown in FIG. 1 in a preferred embodiment, include an upper 
leg or flange 18, a lower flange 14 longer than the upper flange 18, and a 
web 16 connecting the upper flange 18 and lower flange 14. Alternatively, 
any supporting surface or floor may be used instead of the rails 12. 
Referring to FIGS. 1, 2, and 6, an outer cart 20 includes a preferably 
rectangular frame 22 having a front cross member 24, side members 26 and a 
rear cross member 28. The rectangular frame 22 may be made of welded 
together standard structural beams or shapes. The side members 26 include 
a lower inner flange 46 similar to flange 14 of the support rails 12. 
Angle plates 32 are preferably attached at the four corners of the frame 22 
of the outer cart 20 to support wheels 34. The wheels 34 may be attached 
to the angle plates 32 via a nut 38 clamping the wheel stud to the angle 
plate 32, as shown in FIG. 1. 
Referring to FIGS. 1, 2, and 8-10, a middle cart 40 also includes a 
preferably rectangular frame 22a having a front cross member 24a, side 
members 26a and a rear cross member 28a, each slightly shorter than the 
corresponding members on the outer cart 20, such that the middle cart 40 
may be fit within or contained by the outer cart 20. 
As shown in FIG. 8, the front end of the middle cart 40 preferably includes 
angle plates 32. However, the back end of the middle cart 40 has extended 
angled ends projecting from the rear cross member 28a. 
Referring to FIGS. 1-4, the front wheels 34 of the middle cart 40, 
supported on the angle plates 32, roll on the lower flange 46 of the side 
members 26 of the outer cart 20. However, the rear wheels 34 on the middle 
cart 40, mounted on the angle ends 44 of the rear cross member 28a, roll 
on the flange 14 of the support rails 12. Referring to FIG. 9, the rear 
wheels on the middle cart 40 are positioned slightly below the front 
wheels, so that the middle cart 40 remains level with its front wheels 
riding on the support rails 12 and its rear wheels riding on the side 
members 26 of the outer cart 20. 
As shown in FIGS. 1 and 5, slots 30 are provided in the side members 26 on 
the outer cart 20 to allow the front wheels of the middle cart 40 to be 
positioned into the lower flange of the side members 26 of the outer cart 
20, during installation. 
As shown in FIG. 4, the wheels 34 of the outer cart 20 and middle cart 40 
preferably are attached at a slight angle, so that the wheels role 
perpendicularly on their supporting surfaces. 
Using the outer cart 20 and middle cart 40, as described above, a 
three-deep push-back cart storage system is provided, as a first pallet 
may be supported on the middle cart 40, a second pallet supported on the 
outer cart 20, and a third pallet supported directly on top of the support 
rails 12, with the middle and outer carts pushed back. 
In a four-deep push-back cart storage system an inner cart 50 as shown in 
FIGS. 1-3 and 11-13, includes a rectangular frame 22b having front cross 
member 24b, side member 26b and rear cross member 28b, dimensioned to 
allow the inner cart to fit within the middle cart. Similar to the middle 
cart 40, the inner cart 50 preferably includes angle plates 32 at its 
front corners, and angle ends or plates on the rear cross member 28b. The 
rear wheels of the inner cart 50 are positioned slightly below the forward 
wheels. As shown in FIGS. 1-4, the front wheels on the inner cart 50 roll 
on the side members 26a of the middle cart 40, while the rear wheels of 
the inner cart 50 roll on the support rails 12. The middle cart 40 also 
includes slots 30 so that the inner cart 50 may be installed into the 
middle cart 40. 
As shown in FIG. 4, the outer, middle and inner carts are all of equal 
height. The small amount of vertical clearance between the carts allows 
flat pallets to be supported only on the top surface of a single cart. 
Referring to FIGS. 1 and 4, the carts roll into each other, in a somewhat 
telescoping arrangement, rather than rolling over or under each other. In 
addition, the front wheels of the middle cart 40 and inner cart 50 roll on 
the middle cart and outer cart 20, respectively rather than on the support 
rails 12. 
Of course, in addition to the three-deep and four-deep embodiments 
described above, a five (or more)-deep embodiment may also be used, by 
providing one or more additional carts, as will be understood by those 
skilled in the art. In addition, the carts need not be rectangular, and 
other arrangements of the cart wheels and supporting flanges or rails may 
be used. 
Thus, although a preferred embodiment has been shown and described, it 
would be apparent to those skilled in the art that many changes and 
modifications may be made thereunto without the departing from the spirit 
and scope of the invention.