Abstract:
A latching spring for a push-back cart storage system includes a pair of spaced apart support rails, at least two cross members and a cart frame having a wheel assembly supported on the support rails and at least one latching spring. The latching spring is mounted on the cross members and engages with the cart frame. The spring latch prevents premature rearward rolling of unloaded carts in multiple cart push-back systems wherein the wheels of rearward rolling loaded carts roll on the unloaded carts.

Description:
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. 
     With the present push back cart systems, the first pallet is placed on the first rolling cart by a forklift. The forklift then pushes the pallet along with the first cart so that the second cart can receive a pallet. Ideally, the second cart will be fully exposed so that it can receive a pallet. However, because the first cart&#39;s rollers roll along rails in the second cart, a frictional force is created by the rollers which tends to move the second cart along with the first cart. As a result of this movement, the second cart is not fully exposed and cannot receive a pallet. In cart systems having more than two carts, the same unwanted movement occurs in the other carts as they are subsequently loaded. 
     Although various push-back cart storage systems have been used in the past, there is a need for an improved system which prevents this unwanted movement of the cart immediately underneath the cart that is currently being loaded and pushed back. 
     SUMMARY OF THE INVENTION 
     To these ends, the present push-back cart storage system includes a pair of spaced apart support rails. An outer or first cart has wheels which roll on the support rails. The outer cart has side members and a middle or second cart has front wheels which roll on 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 side members of the middle cart, and with rear wheels of the inner cart rolling directly on the support rails. 
     A latching mechanism in a push-back cart storage system has a latch preferably mounted to cross members which are mounted to the support rails of the push back cart storage system. 
     In the preferred embodiment, the latching mechanism comprises a pair of spaced apart spring members mounted to cross members. Each spring member advantageously includes of a pair of spring plates mounted between the cross members. The carts are held in place by the engaged first spring plates until the loaded first cart reaches its rearmost position relative to the second cart. Once the first cart reaches that position, the front cross member on the second cart releases the first pair of spaced apart spring plates. The release is caused by the force of the forklift, which, in moving the second pallet into the pallet bay for ultimate placement onto the second cart, continues to push the first pallet rearwardly even after the first cart is in its rearmost position relative to the second cart. This rearward movement of the first pallet causes the front cross member of the second cart to push against the first pair of spring plates causing them to deflect downward and release the second cart so that it can move in the rearward direction. As the forklift continues to push the first pallet rearwardly, the front cross member of the second cart then pushes against the second pair of spring plates, causing them to deflect downward and release the second cart so that it can continue to move rearwardly until it reaches the rearmost position relative to the third cart. 
     Of course, in addition to this spring latch, various other mechanical equivalents, such as detent mechanisms, bump ramps, magnetic holding elements, may be used with the scope of the invention, to hold the carts in position while loading. 
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
     FIG. 1 is a perspective view of a 6-deep push back cart storage system with the spring latch; 
     FIG. 2 is a partial perspective view of the spring latch shown in FIG. 1; 
     FIG. 3A is a plan view of a push back cart storage system with the spring latch; 
     FIG. 3B is a section view taken along line  3 A— 3 A of FIG. 3; 
     FIG. 4A is a plan view of a push back cart storage system with the top cart pushed back against the spring latch; and 
     FIG. 4B is a section view taken along line  4 A— 4 A of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With the present push back cart system  10 , as described in U.S. Pat. No. 5,598,934, the disclosure of which is incorporated by reference, typically a first pallet is placed on a first cart by a forklift. Then a second pallet is moved into the pallet bay for placement onto a second cart, and it pushes the first pallet back. Ideally, this should cause the first cart to move back and thereby fully expose the second cart, for reception of the second pallet. However, because the first cart rolls inside of the second cart, a frictional force is created by the wheels of the first cart which tends to move the second cart backwards with the first cart. Heavy pallet loads, imperfect bearings and fast pallet movements may increase the extent of unwanted cart movement. As a result of the premature movement, the second cart is not properly positioned to receive the second pallet, i.e., the second cart tends to be shifted rearwardly from the front of the storage rack. In cart systems having more than two carts, the same disadvantageous premature rolling movement can arise due to friction between, e.g., the third cart and the wheels of the second cart, etc. 
     To overcome this disadvantage, a latching mechanism is provided, as shown in FIGS. 1-4A, where at least two spaced apart cross members  62  are attached to the spaced apart support rails  12  and at least one spring member  64  is attached to the cross members. The cross members  62  may be of various designs, e.g., I-beam, C-beam, etc. Preferably, the latching mechanism comprises three spaced apart cross members  62  attached to the support rails  12  and two spring members  64  attached to the cross members  62 . 
     Referring to FIG. 1, the top of the cross members  62  are attached to the bottom flange  14  of the support rails  12 . The cross members  62  are spaced apart such that the spring members  64  will fit between the cross members. The spring member  64  preferably consists of a pair of plates bent into approximately an N-shape with the first plate  64   a  attached to the front and middle cross members  62  and the second plate  64   b  attached to the middle and rear cross members  62 , as shown in FIG.  2 . The spring plates  64   a  and  64   b  are thin enough to allow for the spring plate to deflect downward, yet sufficiently thick enough so that they will return to their original shape after being deflected downward. The spring member  64 , thus has two vertical projections  63 , which extend above the top of the bottom flange  14  of support rails  12 . The vertical projections  63  extend a sufficient height, such that the vertical projection  63  will engage with front cross member  24   b  of inner cart  50 , as shown in FIGS. 3 and 3 a.    
     Preferably two spaced apart spring members  64  are attached to the cross members  62  to provide additional resistive force to the carts. Each spring plate,  64   a  and  64   b  have horizontal extensions  65  on each end with holes  67  in each extension. Each cross member  62  also has holes  67  such that when the spring plates  64   a  and  64   b  of the spring member  64  are placed between the cross members  62 , the holes  67  in the horizontal extensions  65  of the spring plates  64   a  and  64   b  align with the holes  67  in the cross members  62 . A bolt  66  can then be placed through the hole and secured in place with a nut  69 . In the middle cross member  62 , the rear horizontal extension  65  of spring plate  64   a  and the front horizontal extension  65  of spring plate  64   b  overlap each other with the holes  67  in each horizontal extension  65  and the holes  67  in cross member  62  being in alignment so that bolt  66  can be inserted into the holes and secured in place by a nut  69 . Preferably a nut and bolt is used to attach the spring members  64  to the cross members  62 , however, any other attachment means can be used. 
     In a three cart arrangement, as shown in FIG. 3, with the empty carts nested, a first load-bearing pallet is placed upon the inner most cart  50  by a forklift. Then, a second load-bearing pallet is lifted by the forklift to above the level of the intermediate cart  40 , such that, as the second pallet is moved into the pallet bay, it pushes against the first pallet previously loaded onto the inner most cart  50 . The engagement of the first pallet by the second pallet causes the wheels  34 , which are connected to the inner most cart  50  to roll rearwardly. During the time that the front wheels  34  of cart  50  are traversing the lower flanges  46  of side members  26   a  of cart  40  in the rearward direction, the engaged spring member  64  prevents friction between the wheels  34  and the side members  26   a  from causing the cart  40  to move rearwardly. 
     Thus when the wheels  34  of the cart  50  arrive at the rear end of side members  26   a  of cart  40 , cart  40  has yet to appreciably move, and thereby is properly positioned to receive the second pallet. At that point, the force of the forklift, which in inserting the second pallet into the bay for placement onto cart  40 , continues to push the first pallet rearwardly even after the wheels  34  hit the end of side members  26   a  of cart  40 . This causes the first spring plate  64   a  to deflect downward as the cross-member  24   a  of cart  40  is forced against it by the forklift as shown in FIGS. 4A and 4B. As the force of the forklift continues to push the first pallet, the spring plate  64   a  is deflected downward such that cross member  24   a  is released and cart  40  is free to roll backward until it reaches the second spring plate  64   b , at which point the cart  40  is again prevented from rearward movement. As the forklift continues to push the first pallet, the second spring plate  64   b , will deflect downward releasing cross member  24   a  of cart  40 . The forklift can then place the second load bearing pallet onto cart  40 . 
     Once cart  40  is past the second spring plate  64   b , the forklift can lift a third load bearing pallet to above cart  20 , which has been prevented from rearward movement by the first spring plate  64   a  engaging with cross member  24  of cart  20 . As the third pallet is lifted into position above cart  20 , it pushes against the second pallet previously loaded onto cart  40 , causing cart  40  to roll rearwardly. During the time the wheels  34  of cart  40  are traversing the lower flanges  46  of side member  26  in the rearward direction, the first spring plate  64   a  prevents friction between the wheels  34  and the side members  26  of cart  20  from causing cart  20  to move rearwardly. Thus, when the wheels  34  of cart  40  reach arrive at the end of side member  26  of cart  20 , cart  20  has yet to appreciably move, and thereby is properly positioned to receive the third pallet. As the forklift continues to push against the second pallet, the first spring plate  64   a  again deflects downward, disengaging from cross member  24 , allowing cart  20  to roll rearward until it reaches the second spring plate  64   b . As the forklift continues to push the second pallet, the second spring  64   b  deflects downward, disengaging cross member  24  and once again allowing cart  20  to roll rearwardly. 
     In addition to the foregoing spring latch embodiment, there are various other mechanical equivalents that could readily be used within the scope of the invention. Such equivalents which include detent mechanisms; bump ramps; magnets; etc., hold the second cart from rolling back due to wheel friction yet release when the larger force of forklift loading is exerted. 
     Various numbers of the above-described latching mechanisms can be used to prevent premature rolling in push-back cart storage systems, depending on the number of carts used. 
     Thus, while the preferred embodiments have been shown and described, many changes and modifications may be made thereunto without the departing from the spirit and scope of the invention. The invention, therefore, should not be limited, except by the following claims, and their equivalents.