An AS/RS has 4 major components:

• storage racks
• storage & retrieval machine (SRM)
• shuttle
• planning & control system

A horizontal material handling equipment is also required as the interface between AS/RS & other systems.

Rack Structure: An AS/RS rack structure is composed of a set of columns (bays) & a set of rows (tiers). As a common practice, the bays & tiers are aligned by height & width. The intersection of bays & tiers are referred to as cells.

A typical AS/RS structure module consists of single-deep stored unit loads in 2 parallel long narrow racks, with an aisle between them. As the storage racks interface with the storage & retrieval machine, very tight tolerances are required. Hence, the guide rails installed in the aisle must always allow for free movement in & out. One type of configuration with the Pick-up/Delivery (P/D) station located at one end on the lowest level of each rack is commonly referred to as end-of-aisle order picking.

For end-of-aisle order picking, there are 2 popular varieties. One type is configured to store loads in single-deep racks. This is very advantageous if the throughput requirement is moderate & share similar attributes. The other type has multiple P/D stations located at both end points, as well as mid points. This greatly helps to separate the inbound & outbound loads, improve throughput & boost efficiency of the horizontal material handling system.

Storage & Retrieval Machine (SRM) or AGV: The SRM is capable of moving in both horizontal & vertical directions. It moves along floor-mounted rails parallel to the storage racks for horizontal trips & along a mast for the vertical part of the trip. The SRM picks up a load from the P/D station (or storage cell), delivers the load to an empty cell (or P/D station), sets the load down & returns empty to the P/D station (or loaded cell). Such a trip is referred to as a Single Command (SC). It accomplishes either a store or retrieval between successive visits to the P/D station.

In a double command (DC) trip, the SRM picks up a load at the P/D stand, travels loaded to an empty location, sets down the load in the empty location, travels empty to a loaded cell in the rack, picks up the load, travels loaded to the P/D station & sets down the load on the P/D station.

The Shuttle (Stacker Crane or Rack Master): The SRM moves in X & Y directions, while the shuttle moves in Z direction. Pick-up & delivery in storage cells & P/D stands are accomplished via a specially-designed shuttle mounted on the SRM. When the SRM is positioned accurately both in horizontal & vertical directions with the cell or P/D stand, the shuttle starts a move in the direction perpendicular to the movement plane of the SRM.

Planning & Control System containers arrive on a random basis. As soon as a P/D station becomes empty, a container is delivered to it, after which the SRM moves the load to an empty location in the rack. Pick-up & delivery on both P/D stations & storage cells are automated & controlled by computer. Request for retrieval of items also follows a random nature.

When this incoming & outgoing randomness are combined with material storage policies, an additional stochastic factor, the location of items in the rack, is introduced. The location assignment & planning, tracking & control of the total system are accomplished through a distributed system. These systems are often customized to suit & fit into the customer´s daily operation.