Could there be a warehouse where you could travel anywhere in a straight line?

In 2009, Gue and Meller introduced the Fishbone Layout, a warehouse layout with two diagonal cross aisles and the aisles in the lower zones are perpendicular to the aisles in the upper zones (read more about them here in this blog). It is a layout focus for unit-load warehouses, where the picker will start at the pick and deposit point (P&D) and go to pick up only one item at the time and come back. Since there is a better layout than a traditional design for unit-load warehouses, will there be one order picking warehouses, where pickers have to pick multiple items in one tour?

The question is not settled, very difficult to prove there is not one, but nobody has publicly advertise there is one. Here, we show some insights of our approach with the goal to start a conversation; by no means we provide a definitive answer.

The theoretical ideal warehouse layout, will there be a warehouse were you could travel anywhere in a straight line? how would it be?


Approach

We built an simulation model inspired in the behavior of ant colonies. Ants depart the anthill searching for food following random paths until they find one source, then they come back in what the can recall is the best way back. Along the way, ants release pheromones to let other ants what path they took. Through time, paths of ants start building up through the concentration of pheromones along their way.

Taking this system as an analogy, our anthill is the P&D, the ants the pickers in our simulation model, where the warehouse is represented by an empty rectangle where each point has equal probability to be visited. Our goal to identify that the most visited paths by the pickers that will be ideal candidates for aisles in the warehouses.

source: wikimedia

Results

We define a simulation scenario by the number of items in a tour for a picker. For example for the case of two items, each picker visited 2 random locations following the optimal path — the routing algorithm for this is a standard TSP of no special interest for this post. We simulated 1,000,000 of these tours and recorded the paths that each picker took in the form of a heat map. The following is the result:

From up to 5 items in a tour there is some kind of triangular tour, that becomes a donout shape for 10 and 15 items. At 35 items, we see more like rectangular contours that fade towards the center of the warehouse. We have no conclusive evidence from this experiment to find the new layout for order picking warehouses, but we gained two insights:

  • It looks like there can be candidates different than traditional designs for up to 5 items per tour.
  • For warehouse with large pick list, it looks like the ant colony simulation points out towards traditional layouts.