One of the limitations of our early work on the aisle design problem was the assumption that all travel begins and ends at a centrally-located pickup and deposit (P&D) point. This is a reasonable assumption for some warehouses, but for many others it is not. In a new paper, my colleagues Russ Meller, Goran Ivanovic, and I address the question, “how should picking and cross aisles in a unit-load warehouse be arranged when there are many pickup and deposit points?” The paper will appear in Transportation Research E: Logistics and Transportation Review.
Unlike our most recent work, we do not allow picking aisles to take on any angle at all. We require that they remain parallel, in the traditional style, but we allow a cross aisle to take on any angle to connect them. We considered two main cross aisle structures: the “modified flying-V” and a new design called the inverted flying-V, which at first seemed non-sensical but then appealing.
The Inverted-V was surprisingly competitive, but in the end was dominated by the modified Flying-V in every case. One issue we had to tackle with these designs is the optimal path from a specific P&D point to each picking location. Below is a graphic illustrating how complicated these paths can be for a modified Flying-V.
The main result from our paper is that
- The flying-V structure works quite well even in the presence of multiple P&D points. The optimal modified Flying-V has expected travel distance approximately 3-6% less than a traditional design.
If you are familiar with our prior work, you might notice that the expected benefit is lower than for a Flying-V with a single P&D point. This is indeed the case: the more distributed the flows are required to be in a warehouse, the less potential benefit of non-traditional aisles. To test this, we solved an optimal design for a warehouse having a single P&D point, then 3 P&D points, then 5 and so on, up to 31 P&D points spanning the entire bottom of the warehouse.
With a single P&D point, we obtain the expected “about 10% advantage” found in our first paper, but as the number of P&D points increases, the advantage of new aisle design decreases. This led to the second main result from the paper:
- The doors most often used should be those near the center, thus concentrating the material flows and improving the benefit of a Flying-V aisle. When there are fewer P&D points than doors, the P&D points should be located as close as possible to the center of the warehouse.
If you would like to download the paper, please visit my Publications page. I welcome your comments.