Automated storage and retrieval systems—often simply called AS/RS—are computer-controlled systems for storing and retrieving products in warehouses or manufacturing facilities without manual labor.

Large systems, known as unit-load AS/RS, typically store and retrieve pallet loads. Smaller systems, often called mini-load AS/RS, handle products in totes, trays or cartons.

Regardless of size, most AS/RS have the same basic configuration: 

• Two rows of metal rack face each other with a narrow aisle in between.
• Down the center of the aisle is a raised metal rail.
• A tall mast travels through the aisle along the rail.
• When the mast reaches a designated storage location, a carriage travels up or down the mast to the level of the location.
• A load-handling mechanism mounted on the carriage then reaches into the storage location to putaway or retrieve a load.

The mast, carriage and load-handling device are collectively known as an S/R machine or SRM. They are sometimes also called a crane.

Most AS/RS use one S/R machine per aisle. Some sophisticated high-throughput systems assign multiple machines to one aisle. Some low-throughput systems assign one machine to multiple aisles. In these systems, the S/R machine makes a turn at the end of its aisle or is moved from aisle to aisle by a transfer car.

S/R machines may have single or double masts. 
With a single-mast machine, the carriage is attached to the front of the mast. With a double-mast machine, the carriage rides between two masts, providing added stability in particularly tall AS/RS or in systems that handle heavy loads.

Unit-load AS/RS are designed to store large loads of roughly 1,000 pounds or more. These loads are typically stored on pallets or in pallet-sized containers. Some specialized systems handle oversized loads such as furniture and long rolls of carpet.

A unit-load AS/RS can rise beyond 100 feet tall, but a typical system is less than 40 feet.

A standard AS/RS stores loads in steel pallet rack designed specifically for automated systems. This rack, like drive-in rack, stores loads on rails that run perpendicular to the aisles. (Standard pallet rack stores loads on cross beams that run parallel to the aisles.) AS/RS rack can be configured single-deep, double-deep or as deep-lane rack with several pallets stored one behind the other.

The load-handling mechanism for a unit-load AS/RS is usually a telescoping device called a shuttle that reaches out into the storage location, slides under the pallet, and then pulls the pallet back onto the carriage.

Less common turret-style S/R machines use a rotating fork instead of a shuttle. Turret machines are slower than typical S/R machines, but they can interface with standard pallet rack instead of needing special AS/RS rack.

• dense storage in a finished goods warehouse,
• buffer storage for work-in-process in a factory,
• a dynamic pick face for a case-picking operation, or
• parts sequencing for an assembly line.

Small-scale automated storage and retrieval systems that handle lighter loads (typically less than 1,000 pounds) in containers such as trays, totes or cartons are known by a number of different names.

Some suppliers use the term "mini-load AS/RS" to describe systems that handle loads between 100 and 1,000 pounds and the term "micro-load AS/RS" to describe those that handle loads of less than 100 pounds. Others simply call all of them mini-load systems. "Case-handling machine," and "tote stacker" are other terms used to describe light-duty AS/RS.

This article will refer to all less-than-unit-load systems as mini-load AS/RS.

In additional to having many names, mini-load AS/RS also take numerous forms. Most are configured along the same principles as unit-load systems, but instead of using shuttles to pick up and retrieve loads, they use one of a variety of load-handling devices. Examples include extractors that grasp and pull handles on metal trays, vacuums that attach to corrugated cases and robotic arms that grip plastic totes.

A typical mini-load AS/RS stands between 10 and 40 feet tall.

Mini-load AS/RS have numerous applications, some of which fall outside the manufacturing and distribution industries. Government agencies use them to store documents, and universities use them to store library books. Most, however, are used in factories and warehouses for small parts storage or order fulfillment.

Automated storage and retrieval systems minimize the space and labor needed to store and retrieve materials. These systems are particularly popular in Europe and Japan where labor is expensive and space is limited, says Dave Bartley of HK Systems, chair of theAS/RS product section of Material Handling Industry of America.

An AS/RS can also increase the productivity of a storage facility. Unlike manual labor, says Bartley, an automated system can run "day in and day out." These systems are also a good option, he says, in freezers and other harsh environments that can be hazardous to people.

Because they are directed by computers, AS/RS can also provide extremely accurate inventory control.