Cube storage

Bins are stacked directly on top of one another in a tall steel grid, with no aisles between them. Robots run on rails on top of the grid, lift a bin from a stack and carry it to a port at the edge, where a person picks from it. Because there are no aisles, almost the whole volume is storage; this is called cube storage, or grid storage.

A robot can only lift the bin at the top of a stack, so to reach one lower down it first moves the bins above it aside. The system therefore keeps the bins used most often near the top and works out the rest in software.

Because the grid is built as a block, it suits rooms of regular shape, and it can often be made larger by adding columns, rows or ports, and more robots.

When it pays off

It pays off for a large range of small items in bins, a high number of order lines and costly space, as in city-centre e-commerce, grocery and pharmacy. It pays off less for bulky goods, goods that do not fit a bin, and operations too small to carry the fixed cost of the grid, the controller and the ports. Where some items sell far faster than others, the system's ability to rearrange the stacks by itself is an advantage.

What the warehouse system does with it

The grid has its own controller, which decides which robot lifts which bin. The warehouse system sends it orders or tasks, such as bring the bin with article X to port 2, and receives confirmations when a bin is at the port and when it has been returned. Stock in bins is usually recorded in the WMS by article and bin, so the grid and the WMS have to agree on which articles are in which bin.

Who makes it

AutoStore, Ocado

In alphabetical order. Not a ranking or a recommendation.