18.1: Introduction

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Much of the time that material is in a plant, it is being moved or stored. In this chapter, the dynamics of how an automated storage and retrieval system (AS/RS) organizes and maintains an inventory are examined. An AS/RS system provides the following benefits: space efficient storage of materials, high speed controlled transportation of materials, and real-time inventory control. Thus an AS/RS system helps reduce inventory, labor, floor space, and material control costs.

A typical AS/RS system has several components as is shown in Figure 18-1. A storage / retrieval (S/R) machine places pallets (or another standard carrier) having one or more standard sizes in a high rise rack system. A rack consists of a matrix of storage locations. Racks are separated by aisles. There is one S/R machine per aisle. An S/R machine moves in the horizontal direction on a track located in the floor of an aisle and rises vertically via an imbedded mechanism. Typically, vertical speed is about 1/3 of horizontal speed.

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Items to be stored arrive to a pick point. Retrieved items are transported by a the S/R machine to a drop point.

A computer-based control system is an important part of an AS/RS system. The computer keeps track of the exact location of all items in the racks. The control system directs the movement of the S/R machine by providing timely instructions concerning what items to retrieve or store in the racks. These instructions are in response to external requests for storage and retrieval.

The computer-based control system can be tested using simulation. Alternative rack sizes can be assessed. Various storage and retrieval strategies can be compared. In this way, movement of the S/R machine when it is empty, as well as the capital investment in racks, can be minimized.