Cross-aisles
To reduce travel between storage and receiving/shipping, it is generally preferable to orient aisles so that they run parallel with the direction of material flow. However, it is sometimes advantageous to support movement between storage locations, such as if a forklift, operating under dual-cycle, travels directly from putting away one pallet to retrieving another as in Figure 6.12.
There is also a cost to having a cross-aisle in that more floorspace is required for the same number of pallet locations, and so additional travel is introduced. If receiving and shipping are located on opposite sides of the cross-aisle, then every location is made slightly less convenient because each pallet must be carried across that the aisle once.
Figure 6.12: A cross-aisle allows more direct and therefore shorter travel between storage locations.
And if receiving and shipping are on the same side of the cross-aisle, the near locations are unaffected, but the far locations are made even less convenient, because each pallet stored there must cross the aisle twice: once to store and again to retrieve the pallet.
Angled aisles
Most warehouses have parallel aisles aligned with the receiving and shipping docks,perhaps with orthogonal cross-aisles; but this need not always be the case. Kevin Gue of Auburn University and Russ Meller of the University of Arkansas [26] have
argued that travel times can be reduced by up to 20% by reorienting some aisles and including some angled cross-aisles, as in Figure 6.13, which they call a fishbone layout. The overall warehouse must be slightly larger to compensate for the space lost to the additional aisles; but this is more than made up for by the efficiency of more direct travel to or from a centralized point of receiving and shipping.
It is possible to take advantage of this more direct travel if most pallet movement is to or from the central dispatch point. But if a forklift finishes putting away a pallet and then must retrieve another, the orientation of the aisles of the fishbone arrangement may not help at all, and indeed may be an impediment. Nevertheless, this possible inefficiency seems to be more than made up for by the direct travel to and from the central dispatch point.
Figure 6.13: Angled aisles, suggested by Gue and Meller, allow more direct travel between storage and a central location of receiving/shipping (at the bottom).
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