Equipment 101: Automated storage and retrieval systems (AS/RS)
This mini-load staging buffer uses computer-controlled shuttles equipped with a load transfer device. The shuttles can deliver loads to a person who will pick items. When the pick is complete, the load is automatically returned to its storage location.
Automated storage and retrieval systems, known as AS/RS, have been around since the 1960s. Put simply, they are computer-controlled systems that put away, store and retrieve product in warehouses, distribution centers and manufacturing facilities.
“The first systems were built to handle large loads,” explains Ralph Mills, executive director of sales Daifuku America . “From there, pallet loads developed into mini-loads, and most recently AS/RS is being used for replenishment and to sequence items.”
Over the years, AS/RS have evolved into smarter, sophisticated materials handling solutions that can handle smaller loads and strategically deliver product to the right place at the right time without manual labor.
Large systems, known as unit-load AS/RS, typically store and retrieve pallet loads. Smaller systems, mini-load AS/RS, handle product 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 put away or retrieve a load.
The mast, carriage and load-handling device collectively are known as a storage and retrieval machine (for short an S/R machine or SRM) or a crane.
Most AS/RS use one SRM per aisle, but sophisticated high-throughput systems might assign multiple machines to one aisle. Some low-throughput systems assign one machine to multiple aisles. In these systems, the SRM makes a turn at the end of its aisle or is moved from aisle to aisle by transfer cart.
SRMs 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 tall AS/RS or in systems that handle heavy loads.
Unit-load AS/RS are designed to store large loads of 1,000 pounds or more, which are typically stored on pallets. Some specialized systems handle oversized loads like furniture and long rolls of carpet.
While a unit-load AS/RS can reach 100 feet, a typical system is less than 40 feet high. A standard AS/RS stores loads on rails 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 and 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 into the storage location, slides under the pallet, then pulls it onto the carriage.
Less common turret-style SRMs that use a rotating fork are slower but can interface with standard pallet rack instead of special AS/RS rack.
A unit-load AS/RS can provide:
• dense storage in a warehouse,
• buffer storage for work-in-process,
• a dynamic pick face for a case-picking operation, or
• parts sequencing for an assembly line.