Impact of order pick policies on warehouse efficiency
Across all warehouse activities, order picking is one of the most labour intensive and costly. Within this, industry estimates show that travel occupies 55% of the order picking time, while searching consumes up to 15%. The balance, 30%, relates largely to item extraction and other activities.
Aside from automation / technology, there are many techniques available to companies to help improve pick efficiencies. Order analysis and item profiling can help determine the expected frequencies of pick-face visits and this can provide the warehouse manager with powerful insights into minimizing the travel distance when picking an order.
In routing, the path followed by the picker when assembling an order should be designed to minimize the total travel distance. In practice, there is no one best solution to routing order pickers and picking policies are largely solved heuristically and on a case-by-case basis. To help guide the order picker across different configurations, a number of standard routing methods have evolved.
- Most common among these is the so-called S-Shape Here, the picker enters the aisle from one end and leaves from the other and aisles without any item to pick are skipped
- The next simplest route is the Return path where aisles without any item to pick are not visited
- In the case where the warehouse is logically sectioned in two, the Mid-Point policy is often preferred. If the items to pick are in the front-half, they will be accessed from the front-end, and vice versa
- When the number of picks per aisle is low, the Largest Gap strategy is used. In this method, the picker enters the first aisle and traverses this aisle to the back of the warehouse. Each subsequent aisle is entered up to the largest gap and departs from the same side as entered. The gap represents the separation between any two adjacent picks, between the first pick and the front aisle or between the last pick and the back aisle
- For warehouses having multiple cross-aisles, the Combined policy performs well. Every time all items within one aisle are picked, a dynamic programme compares what alternative is shortest; advance to the rear of the aisle or return to the front end; the shortest route is then selected
- Finally, an Optimal policy (usually a hybrid of the S-Shape and Largest Gap methods) produces routes that at times may seem illogical to order pickers yet but provides the shortest path
Clearly, the selection of the order picking method influences the travel distance required. In a recent client study, we compared the existing S-Shape path with pick strategy alternatives, in this case concluding that travel distance could be reduced by 14% merely by re-routing the pick tours.
Although these guiding principles are sound, no two warehouses are identical. As warehouses and technology continue to evolve, data remains plentiful and a useful resource for analysis to improve warehouse operations.