Mechanised storage systems are well known in the prior art and are particularly used in warehousing and invoicing control. The mechanical or retrieving device used to address a particular storage location and retrieve a pallet or tray therefrom is generally complex in its mechanical structure and the control thereof. Examples of such prior art systems are described in Australian Patent Specifications 490,439 (81,733/75) in the name of Leif Anderson and 461,488 (44,551/72) in the name of Conco Inc. The Anderson specification describes a complex "transportation device" which transfers a unit load to and from a storage compartment. The transportation device has means to grasp the unit load, tilt the unit load, lift the unit load and move it laterally. A combination of movements is required to move an edge of the unit load onto a roller conveyor before the unit load can be transferred into a storage compartment. Unloading a unit load from a storage compartment entails a reversed sequence of operation. The lateral transfer of the unit load is performed by dogs attached to a chain drive. A pair of dogs are provided at either end of the transportation device to effect transfer in ether lateral direction. The transfer of a unit load requires the operation of at least 3 separate mechanical systems to elevate, tilt and move laterally the unit load.
In the Conco specification a warehousing and invoicing system is disclosed. A stacker crane enables two pallets to be placed side by side. One pallet carries the goods required to fulfill a particular inventory request. The other pallet carries items from which a choice is to be made. Pallets are advanced onto a stacker crane from their selected storage bin by an extensible fork structure while transfers between each of the pallets are made by a pneumatic or vacuum head.
Each of the above systems involve complex mechanical arrangements and complex sequencing of actions to perform an operation.
Another storage system of which the applicants are aware is the use of a carousel to position storage bins at a particular location. At this location the items stored in a storage bin may be removed or otherwise modified in some manner. A typical carousel comprises a number of storage bins carried on a chain about a pair of sprockets. In order to position a particular storage bin the entire collection of storage bins must be moved until the desired bin is positioned at the desired location. Such a system has several disadvantages. In particular, the full weight carried by the chains must be moved requiring large motive power, strengthened components in the chain and sprockets able to withstand these loads and in particular the stresses occasioned when the storage bins circulate over a sprocket. These problems tend to limit the size and capacity of such a system as well as affecting its cost and reliability.