DETAILED DESCRIPTION OF THE INVENTION

[0015] The cart of the subject invention has a spring-loaded self-leveling platform. The platform rests upon springs which encircle posts on a base. A load of materials stacked on the platform compress the springs and the platform moves toward the base. As materials are removed from the stack, the springs expand pushing the materials up toward the user.

[0016] The subject invention is shown generally 10 in FIG. 1. The cart has a spring-loaded platform that continually presents materials to a worker at a convenient, desirable height. The cart comprises a base 12 having posts 14. The posts 14 are loaded with springs 16 which bolster a platform 18. As the platform is stacked with items, the springs compress so the top of the stack remains at the desired height. As materials are removed from the stack, the springs expand pushing the platform away from the base and pushing the newly uncovered items in the stack toward the worker presenting them to the worker at the desired height.

[0017] The base 12 is preferably square or rectangular but can be any suitable and convenient shape useful for the intended purpose of the cart. In the exemplified embodiment, a base frame defines the base. The base however can be solid or the base frame can be reinforced with cross-braces or with solid or mesh decking.

[0018] In the exemplified embodiment, the cart is designed for use in presenting acoustical ceiling tiles to workers installing nine foot ceilings. The workers are perched atop three foot stilts. Acoustical ceilings tiles are packaged in bundles of eight with each tile weighing six pounds. The bundles therefore weight 48 pounds. The cart is constructed to support about 10 of these bundles. Thus, the base frame of the exemplified embodiment is constructed of 1.50 inch×3 inch steel square stock giving the cart adequate strength to support nearly 500 pounds. Suitable materials for constructing the cart of the subject invention for alternative purposes are dictated by the carts intended use. Carts used to support materials that are lighter in weight can be constructed of other metals, such as aluminum, or rigid plastics, such as polyvinyl chloride.

[0019] The size of the subject cart likewise varies with the intended use. The cart of the exemplified embodiment measures approximately two feet wide by about five feet long. This allows adequate space to place a single stack of bundles of acoustical ceiling tiles on the platform 18. The cart however could be made longer to support two or three stacks of tiles. Additionally, wider carts may be desired to support other types of materials.

[0020] The intended use of the cart will also dictate how the base is supported. The cart can be stationary or attached to other mechanisms. In some cases it is advantageous if the cart is moveable. In a particularly preferred embodiment, the cart of the subject invention rolls upon casters 20. The presence or absence of casters on the cart, as well as the size and type of the casters, employed on the cart depends upon the intended use of the cart. Traditionally, transportation of heavier weights requires the use of larger casters. For example the cart of the exemplified embodiment has eight inch swivel casters at each corner of the base.

[0021] Upright posts 14 are attached to the base 12. The posts 14 can be fixedly attached to the base 12 by conventional means including, but not limited to, gluing, welding or bolting. Preferably, the posts are removably attached to the base. Removable attachment allows the cart to be broken down into at least two pieces for convenient moving and storage. A particularly preferred embodiment of the cart of the subject invention is shown in FIGS. 1-5. In this embodiment, the four posts 14 are removably attached to the base 12 as the posts rest on pins 24. The base frame 12 has plates 22 welded to each corner. The pins 24 are welded to these plates 22. The pins 24 have an outer diameter slightly smaller than the inner diameter of the posts 14. The posts 14 are positioned by slipping them over the pins 24. The described means for attaching the posts to the cart is desirable in that it offers some play in the supports which allows the platform to move freely. Another preferred embodiment of the subject cart is shown in FIGS. 6-9. In this embodiment, the posts are removably attached to the base by inserting the posts into pockets 34 in the base frame. This means for attaching the posts to the base also provides some play in the posts which prevents binding of the platform as it slides along the posts. This embodiment is shown most clearly in FIG. 8 where the posts 14 rest in pockets 34.

[0022] The length of the posts is determined by the desired height at which the material is to be presented to the worker. For example, the posts for a cart used to supply acoustical ceiling tiles to a worker on stilts installing a nine foot ceiling are about 68 inches in length. The casters 20 and base 12 add approximately 12 inches to the height of the cart. The platform 18 sits approximately six inches below the top of the posts. Therefore, the platform 18 presents the materials to the worker at approximately 74 inches.

[0023] The diameter of the posts 14 is determined by the size of the spring 16 required to support the weight of the materials on the platform. The cart shown in FIG. 1 has four posts 4. Additional posts provide added stability to the cart. For example, another set of posts can be added along one or more sides of the exemplified cart to stabilize the cart. Addition of these posts would likewise enhance the lifting power of the cart if new springs are added to the new posts.

[0024] The posts of the cart of the subject invention can be hollow tubes or solid bars. It has been found that utilizing square posts on the subject cart is particularly advantageous. The springs encircling the post of the subject cart must be in relatively close proximity to the posts to avoid non-linear compression of the springs. Non-linear compression reduces the efficiency of the spring. Because the spring must be in close proximity to the post, each point where the spring touches the post is a point of friction. A rounded post contacts the spring about its periphery. A squared post contacts the spring at only the four corners reducing friction as the spring moves along the post. Other shaped posts would likewise be useful in the cart of the subject invention, for example, triangular posts, pentagonal posts or octagonal posts. In the exemplified embodiment, the posts measure 1.75 inches square and 2.47 inches on the diagonal. The inner diameter of the (compression) spring is 2.53 inches which is just larger than the post's diagonal. This post and spring combination provides adequate strength and stability to support a platform loaded with about 500 pounds of acoustical ceiling tiles and level the platform of the cart with the removal of each six pound piece of tile.

[0025] Springs 16 surround the posts 14. One skilled in the art would be able to identify the appropriate spring and its desired tension when constructing the cart of the subject invention. The spring must compress a distance approximately equal to the height of a single item within a stack and have adequate strength to support the full weight of the stack. The length of the springs 16 also determines the height of the platform 18. The cast of the subject invention with a 68 inch spring is useful for installing nine foot ceilings. The cart can be adapted for use in installing higher ceilings with post extensions fitted with lengths of spring.

[0026] The platform 18 rests upon the springs 16. In a preferred embodiment, a platform frame 26 surrounds the posts 14 (FIG. 1). In this embodiment, plates 40 (FIG. 2) are welded into the corners and underneath of the frame 26. Apertures in these plates are of a size to accept the posts but exclude the spring. Thus, the platform 18 is supported upon the springs 16. In another preferred embodiment, the springs have a flange 36 welded to the top of the spring (FIG. 7). The flange 36 prevents the spring from entering the sleeve 32 when the platform 18 is loaded. The frame 26 supports a floor 28. The platform floor 28 of the embodiment shown in FIG. 1 is solid however the floor can be mesh or have bars to reduce its weight.

[0027] Sleeves 32 on the platform 18 receive and guide the posts 14. These sleeves can be simple tubes having an inner diameter slightly greater than that of the posts. In a preferred embodiment shown in FIG. 1, the sleeves 32 are supported by plates 30 which are welded to the corners of the platform frame 26. In another preferred embodiment shown in FIG. 6, the sleeves 32 are merely welded into the corners of the platform frame 26.

[0028] The sleeves 32 preferably have bearings 38. One or more bearing reduces the friction of the post moving through the sleeve. Further, these bearings guide the post within the sleeve leveling the platform and preventing binding. In a preferred embodiment, these bearings are roller bearings.

[0029] In use, bundles of acoustical tiles are loaded upon the platform 18 of a cart, the platform being at a desired height. As each bundle of tiles is loaded on the platform, the springs 16 compress and the platform 18 moves toward the base 12 a distance approximately equal to the height of a bundle of tiles. When loaded, the cart can be moved, if on casters, to its desired location. As the individual tiles are removed and installed on the ceiling, the load upon the platform becomes less releasing tension on the springs. The springs relax and push the platform away from the base a distance approximately equal to the height of each tile. Thus, the cart presents each piece of work material to the installer at about the desired height.

[0030] A stable platform or work station can be attached to the cart of the subject invention. Likewise, a motorized or manual push scaffold can be attached to a cart for larger operations where the cart has been constructed to accept full pallets of tiles so a worker need never handle a single bundle of tiles. Further, as noted previously, the cart can be used for other purposes such as masonry work or restocking warehouse shelves.

[0031] It is understood that the foregoing examples are merely illustrative of the present invention. Certain modifications of the compositions and/or methods employed may be made and still achieve the objectives of the inventions. Such modification are contemplated as within the scope of the claimed section.