ROLL-DOCKING - TRANSIT STORAGE FOR SUPER-FAST SELLERS

Mercadona is a family-owned supermarket company based on Spanish capital, whose objective is to fully satisfy all its clients’ food, household cleaning and personal care needs. To do so, it has 1.137 local supermarkets, with an average of 1.300 square metres of sales area, which accounts for 12.1% of the surface area of food stores in Spain. All Mercadona supermarkets have a wide product range of over 9.200 items, and are within easy reach of more than 3.7 million households that annually place their trust in the company.  

In addition to the 3.7 million households that shop every day at its upermarkets, Mercadona works with more than 2.000 suppliers, of which 109 are integrated suppliers, who are equally involved in the total satisfaction philosophy that characterises the company.  

The good results of 2007 are the outcome of the daily effort applied by the whole workforce, with all members of staff doing what they know best: meeting the needs of our “Bosses”. This is demonstrated by Mercadona’s turnover, which in the past twelve months reached 13.986 million euros (15% more than in 2006), and the net profi ts of 336 million euros.
 

REQUIREMENTS & PREREQUISITES

• Delivery of the articles on euro pallets or half pallets in truckloads of a single product type.
• Maximum weight per pallet: 1000 kg.
• Commissioning units that correspond to the delivery units.
• Minimizing of the required Mercadona personnel.
• Buffering of at least 1.5 truckloads per article.First in - first out.
• Handling of up to 800 pallets daily.
   

ROLL-DOCKING SOLUTION

The solution created is not a warehouse in the typical sense but rather a transshipment site with dynamic buffer storage. Truck drivers unload their trucks, with the help of electric or hand-driven pallet trucks, directly onto the accumulating conveyor. The pallet input for this conveyor is implemented at floor level.

A 70 m long accumulating roller conveyor is available for each article. This allows 52 euro pallets or 104 half pallets per article to be placed on the conveyor. For articles with low weight, the capacity can be doubled if stacks of two pallets each are placed on the conveyor.

Commissioning takes place at the end of the accumulating conveyor. Mercadona employees commission the pallets with the help of forklifts, confirm removal with radio scanners, and place the commissioned pallets together at the assigned outgoing goods gate.

STORAGE WITHOUT PRESSURE

The core element of the roll-docking warehouse consists of the accumulating function of the roller conveyors. For this, TGW implemented a mechanical all-roller switch with AND-AND linking of the individual accumulating zones. Toothed chain wheels drive all rollers of an accumulating zone. These toothed chain wheels create a form-fitting connection between the rollers and are driven by a precision roller chain. The drive elements can be swiveled and are connected to one system per accumulating zone by a switch roller and strip. When the pallet passes over the accumulating zone, it triggers a switch roller that separates the accumulating zone from the drive. In this way, the conveyed material is stored “without pressure”. With the AND-AND linking, this decoupling option is only activated once the next accumulating zone in the direction of conveyance is already occupied, i.e. disconnected from the drive. This means that it is also possible to place half pallets on the conveyor not only as pairs but also individually without affecting the accumulating function.

Due to this purely mechanical solution for the accumulating function, no sensor modules are required for the logistical functions. Light barriers are used only to switch off the drives when no pallets are positioned on the driven conveyors.
 

TGW TECHNOLOGY EMPLOYED

The 69 parallel accumulating roller conveyors are each 70 m long, providing a buffer for 52 pallets each, or 1.5 truckloads per article. The conveyors were realized with a roller separation of 175 mm. Each conveyor requires three drives for the 70 m length. Because the conveyors run parallel to each other, up to six adjacent conveyors can be driven by a single drive. Therefore, 39 drives suffice to operate the entire system.