An automated storage and retrieval system (AS/RS) is a set of machines that stores goods in tall, dense racks and fetches them on demand, with no person walking among the racks. The wider system usually includes the conveyors that carry goods to and from the racks, and the sorters that send each finished parcel down the right lane.
There are two common kinds. In a unit-load system, a machine called a stacker crane runs up and down a narrow aisle between racks that can be more than 30 metres high. It lifts whole pallets in and out of the rack. In a shuttle system, small vehicles called shuttles run along each level of the rack. They carry plastic bins or cartons to a lift at the end of the aisle. In both kinds, the racks can be taller and the aisles narrower than in a warehouse where people and forklifts work. So the same building, on the same land, holds far more goods.
The warehouse management system decides what must come in or go out. It sends each instruction to the AS/RS's own control software. The control software chooses a free slot for each incoming bin or pallet, and decides which crane or shuttle fetches each outgoing one. It records the slot of every item. Nobody has to search the racks, and stock does not get lost.
Take, for example, a tractor-parts distributor in Chennai that holds 30,000 different spare parts. Many of them are small and sell slowly, such as a type of seal that sells twice a month. At 11 a.m., a dealer in Madurai orders 12 different parts. The WMS sends the 12 order lines to the shuttle system. Within a few minutes, shuttles on different levels bring the 12 bins to the lifts, and a conveyor carries them to a pick station. An employee takes out the parts and scans each one. The bins go back up into the racks. The parts travel on another conveyor to packing. The employee did not walk at all.
At the end of the line, a parcel sorter reads the label on each packed box and pushes it into the lane for its courier or its city. The sorting centres of an express courier network use sorters that handle thousands of parcels an hour. AS/RS machines are also used in automated cold stores, refrigerated warehouses where machines store and fetch the goods, so that people spend less time working in the cold. These cold stores are part of cold-chain logistics.
An AS/RS costs far more than ordinary racks and forklifts, and it is hard to move once it is built. It pays off where land is expensive, where there are many small items, or where the building must be kept cold. It differs from goods-to-person robots, which carry ordinary shelves across a flat floor, and to which a warehouse can add a few robots at a time.