Modern Thinking: Mastering storage
By Letitia Pohl, Guest Columnist -- Modern Materials Handling, 9/1/2008
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Graduate student, University of Arkansas Education: Working on a Ph.D. in industrial engineering. Bachelor's degree in mechanical engineering. College on an Air Force ROTC scholarship, then spent eight years in the Air Force. Experience: Aircraft-related R&D and earned a master's in systems engineering before leaving to raise a family. |
I am a graduate student at the University of Arkansas,
researching new aisle layout designs
for unit-load warehouses. Working under Russ Meller, professor of logistics and entrepreneurship, we are investigating non-traditional aisle layouts that reduce the amount of travel required to store and retrieve unit-loads.
A couple of years ago, Meller and Kevin Gue from Auburn University posed the question: “Given parallel picking aisles and travel to a single storage location, what is the optimal shape for an inserted cross aisle?” Answering this question led to the “flying-V” cross aisle, which consists of a curved V-shaped cross aisle, whose apex is at a single pickup-and-deposit point on one side of storage.
An alternative design resulted when they relaxed the constraint that the picking aisles must be parallel. The resulting design, which they call “fishbone aisles,” incorporates a V-shaped cross aisle, however the picking aisles below the V are horizontal, while the picking aisles above the V are vertical. Mathematical models showed that travel distances in the new designs, as compared to traditional designs, were reduced by as much as 20%.
I'm now expanding on that research. The first paper I wrote with Meller and Gue considered dual-command operations, or interleaving, where you perform a storage operation, then a retrieval operation, and then return to shipping and receiving. Using fishbone aisles, we showed you can still see a significant reduction in travel, even with dual-command cycles.
We contend that when you minimize travel distances, you may either reduce required labor, thereby reducing costs, or increase throughput, thereby improving customer service. The modeling we've done so far assumes a random storage policy where each of the locations in the warehouse is equally likely to be visited. Since it's common practice to store fast movers near shipping and receiving, we're looking at different storage concepts now. We'll examine how these and other aisle designs perform with a turnover-based storage policy.
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