Goods-to-person robots are robots that carry whole shelves, or bins of goods, to a picker who stays in one place. The picker no longer walks the aisles. The software that directs the robots also directs the people, across the whole warehouse.
In a traditional warehouse, the picker goes to the goods. This is called person-to-goods picking. A picker pushes a trolley along the aisles and stops at each shelf on the pick list. Much of the shift is spent walking, not picking, and in a large warehouse a picker can walk many kilometres in a day.
In a goods-to-person warehouse, the storage area is closed to people. The shelves stand close together in a grid, with narrow paths between them. Each robot is a low, flat machine about the size of a coffee table. It drives under a shelf, lifts it a few centimetres and carries it to a pick station at the edge of the grid. The robot knows its position by reading codes fixed to the floor. The central software plans every robot's path, so that no two robots block each other. At the station, a screen and a light show the picker which compartment of the shelf to pick from, and how many items to take. The picker takes the items, scans them, and puts them in a tote, a plastic crate, that belongs to one order. Then the robot carries the shelf away, and the next one arrives.
Imagine a grocery e-commerce warehouse near Kolkata in the week before Durga Puja. The order management system has sent it 18,000 orders for the day. The warehouse management system passes the order lines to the robot software. One pick station holds 12 totes, one for each order in progress. Six of those 12 orders need the same 1-litre pack of ghee. So the software brings the ghee shelf to that station once, and the picker puts one pack into each of the six totes before the shelf leaves. Through the day, the software also parks the shelves of the fastest-selling goods closest to the stations, so their trips are shorter.
The main gain is speed. A picker at a station can pick several times as many items in an hour as a picker who walks, and the work is less tiring. The grid also stores more goods in the same building, because shelves can stand closer together than aisles for people allow. A warehouse can add robots for a sale season and return them afterwards. The costs are high, though, and the building must be laid out for the robots.
Goods-to-person robots are a kind of autonomous mobile robot, but they work only inside a grid planned for them. For even denser storage, warehouses use an automated storage and retrieval system. Taking the item off the shelf is still done by hand. Robotic picking arms are beginning to take over that step, and some stations already present the shelf to an arm instead of a person.