How to Optimization Pallet Storage and Picking

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World-Class Warehousing and Material Handling

A unit-load ASRS usually handles loads in excess of 1,000 pounds and is used for raw materials, work-in-process, and finished goods. A typical ASRS operation involves the storage/retrieval machine picking up a load at the front of the system, transporting the load to an empty location, depositing the load at the empty location, and returning empty to the input-output (I/O) point. Such an operation is called a single-command (SC) operation. Single commands accomplish either a storage or a retrieval between successive visits to the I/O point. A more efficient operation is a dual-command (DC) operation. A dual command involves the storage/retrieval machine picking up a load at the I/O point, traveling loaded to an empty location (typically the closest empty location to the I/O point), depositing the load, traveling empty to the location of the desired retrieval, picking up the load, travel ing loaded to the I/O point, and depositing the load. The key idea is that in a dual-command operation, two operations, a storage and a retrieval, are accomplished between successive visits to the I/O point. A unique feature of storage/retrieval machine travel is that vertical and horizontal travel occurs simultaneously. Consequently, the time to travel to any destination in the rack is the maximum of the horizontal and vertical travel times required to reach the destination from the origin. Horizontal travel speeds are on the order of 600 feet per minute (vertical, 150 feet per minute). The typical unit-load ASRS configuration, if there is such a thing, would include unit loads stored one deep (i.e., single deep) in long, narrow aisles, each of which contains a single storage/retrieval machine. The one I/O point would be located at the lowest level of storage and at one end of this system. More often than not, however, one of the parameters defining the system is atypical. The possible variations include the depth of storage, the number of storage and retrieval machines assigned to an aisle, and the number and location of I/O points. These variations are described in more detail later. When the variety of loads stored in the system is relatively low, through put requirements are moderate to high, and the number of loads to be stored

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