APPARATUS FOR STACKING OR DESTACKING CONTAINERS Field of the invention This invention relates to container handling and in particular to the handling of containers in the form of plastic baskets or trays which are used to transport all types of products from manufacturers, producers and suppliers to retailers of these products. Typically such baskets or trays are used many times, being returned by the retailers to the source once the products have been unloaded. Such reusable plastic baskets or trays are referred to as"Returnable Transport Packaging" (RTP) in the industry.

Background of the invention The plastic containers (baskets or trays) of the type with which this invention is concerned are provided with a pair of arms in the form of metal or plastic rods located at both ends of the square or oblong, open-topped container so that each arm, known as a bale arm, extends along an upper edge of the side of the container, each end of the bale arm being located in a respective recess or slot located in the body of the basket. The arrangement is such that the bale arm can be moved between at least two positions. In the first position, the bale arm lies outside the open top of the container. With the two bale arms in this first position, then two or more containers may be stacked in a"nested"configuration with one container lying almost wholly within another lower container. The bale arms are used in this position when the containers are empty and are to be returned to their source. In this way, a stack of containers will take up a minimum amount of space.

When the bale arms are in a position other than that for nested stacking, they extend across the container at a position spaced inwardly from their respective end walls.

Accordingly, when containers are stacked one upon another they are each seated on the bale arms of the next lower container and are in a"denested"configuration. The bale arms are then said to be"inboard"whereas when they are in their"nesting" position they are stated to be"outboard".

Some containers allow only a single inboard position for the bale arm. Others are designed such that there are two or more inboard positions which differ from each other by the height of the bale arm relative to the container. In a first inboard position, the bale arm may be located at the height of the upper edge of the container.

In the second inboard position, the bale arm may be located well below the upper edge of the container. The first inboard position will be used when the container is substantially full of the product to be transported. The second inboard position may be used when the container is substantially less than full.

Containers of the type with which this invention is concerned typically have sides which taper slightly inwardly in the downward direction to enable one to seat within another, lower container, at least when the containers are in their nested configuration. When in this configuration, the containers may be jammed together and be quite difficult to separate, particularly if liquid or other material is lodged between the mating surfaces of adjacent containers.

Whether the containers are empty, partially full of goods or wholly full of goods, they are transported in stacks. A stack of fully loaded containers may comprise about 12 containers. A stack of unloaded nested containers may comprise 25 or more containers. In order to load containers with goods, it is necessary to destack a stack of nesting containers and, similarly, in order to transport loaded or partially loaded containers, it is necessary to stack them. Hitherto, such operations have been performed manually. However, this is time consuming and also, for loaded or partially loaded containers, work which requires considerable strength and dexterity, particularly when handling the uppermost containers in the stack.

As far as is known, there is no equipment currently available which will stack or destack containers of the type with which this invention is concerned. This may be because equipment to carry out these operations has been perceived to operate according to the manual method of stacking or destacking, that is to say, adding or

removing containers to or from the top of the stack. As a result, the equipment would probably have to be rather complex and take up a considerable amount of space, both factors which would perhaps lead to the conclusion that such equipment would not be commercially justifiable.

Statements of invention According to the present invention there is provided apparatus for stacking or destacking containers comprising a stacking or destacking assembly, means for positioning a stack of at least one container within said stacking or destacking assembly, the assembly including means for raising the stack such that the base of the lowermost container of the stack is at a height greater than the height of the container, means for locating a container directly below the raised stack, and means for adding said located container to the bottom of the stack or for removing said located container from below said stack.

Reference has been made above to a stack of containers having at least one container.

It will be appreciated that a single container, although not strictly a stack, is a starting point for a stacking operation.

By removing containers from the bottom of the stack, or by adding containers to the bottom of the stack, it is possibly to utilise equipment which is relatively less complex and expensive than that which would be required for adding or removing containers at the top of the stack. Furthermore the space requirement is relatively less, the stacking or destacking assembly merely having to have a length and width sufficient to accommodate a stack, or a plurality of side-by-side stacks, since the removed or added container is subjected to vertical movement only directly below the stack. There is no need to raise or lower this container alongside the stack between the top of the stack and its base.

The present invention also provides a method of stacking or destacking containers comprising raising a stack of at least one container such that the base of the stack is

at a height greater than the height of a container, locating a container directly below said raised stack, and adding said located container to the bottom of the stack or removing said located container from below said stack.

Brief description of the drawings The accompanying drawings are as follows:- Figure 1 is a diagrammatic perspective view of apparatus in accordance with the present invention; Figure 2 is a diagrammatic front elevation of the apparatus of Figure 1.

Detailed description of invention An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings.

The apparatus includes a housing 1 having a top 3 and solid side walls 5. The front of the housing is provided with upper and lower doors 7 and 9, each comprising a pair of pivotally mounted door panels 11 which, in their closed position, form a front guide. A feed conveyor 13 extends into the housing 1 from the rear thereof through a rear opening in the housing. The housing will accommodate two side-by-side stacks of containers, one stack located adjacent the front of the housing and the other stack located adjacent the rear of the housing.

Within the housing there is a located stack lifting and lower mechanisms. These mechanisms include a permanent guide platform 14 capable of being raised or lowered, an adjustable lift platform 15 capable of being raised or lowered and also of being laterally extended or retracted towards and away from the stack of containers 17. The mechanism further includes stack engaging arms 19, capable of moving towards and away from the stack 17. For each stack within the housing, there are two pairs of members 14,15 and 19, the pairs being located on opposite sides of the stack.

In operation, a wheeled support platform 21, known as a dolly, having loaded thereon two stacks of empty nested containers 23, only the lowermost containers being shown in Figure 1, is wheeled into the housing with feed conveyor 13 in the retracted position. In the next step of the operation permanent guide member 14, together with lift platform 15 is raised until the upper surface of guide member 14 engages the underside of the upper rim or lip of the lowermost container 23. Continued raising of permanent guide 14 causes the entire stack 17 to be raised off the dolly 21. Lower doors 9 open and the dolly is then wheeled out of the front entrance of the housing 1.

The lower doors 9 are then closed again and the conveyor extended forward to the de-nesting position where the destacking operation proper then commences.

Arms 19 are moved towards the stack to engage the sides of the second container from the bottom. The adjustable lift platforms 15 are then moved towards stack 17 and engage the lowermost container in the stack. The permanent guides 14 and adjustable lift platforms 15 are then lowered together carrying with them the lowermost container but leaving the rest of the stack in position supported on arms 19. The positive engagement of adjustable lift platforms 15 with the lowermost containers ensures that these lowermost containers are dragged away from the stack even if the frictional engagement with the stack is very strong. The lowermost container is lowered onto feed conveyor 13 and during this lowering operation, the adjustable lift platforms 15 are retracted. The feed conveyor 13 then transports the lowered container (actually two side-by-side containers derived from the two stacks within the housing) out of the rear of the housing.

The permanent guide members 14, together with adjustable lift platforms 15 are then raised until guide members 14 engage the underside of the upper rims of the container which is now lowermost in the stack. The arms 19 are now retracted and the guide members 14 together with lift platforms 15 lowered by a distance such that arms 19 then lie adjacent the gripping position of the second containers in each stack.

Arms 19 are then moved inwardly to engage these containers, adjustable lift platforms 15 are moved inwardly to engage the lowermost containers and the cycle is

repeated whereby the lowermost container is extracted downwardly from the stack and on to the feed conveyer 13.

This process is repeated until all the containers have been destacked and transported out of the housing by means of feed conveyor 13, after which the conveyor automatically retracts and doors 7 are opened in readiness for the next dolly load.

It will be appreciated that, by adjustment of the precise operations of the members 14,15 and 19, the above described procedure can be applied to a stack of fully or partially loaded containers, the containers in each stack not being in their nested positions but each resting on the bail arms of the next lower container.

It will also be appreciated that a substantially similar apparatus can be used to form a stack of containers by an operation which is substantially the reverse of that described above although it may not be necessary to include the equivalent of the adjustable lift platforms 15 because the frictional forces between adjacent containers do not have to be overcome during a stacking operation.