Order picking in warehouses can be significantly faster thanks to a so-called milk round system, where the picker constantly makes fixed rounds through the warehouse. This is especially true for warehouses where orders arrive in quick succession, PhD student Jelmer van der Gaast of Rotterdam School of Management researched.
Van der Gaast developed models that designers can use to monitor and improve the performance of order picking systems. The PhD student first investigated how picking systems in warehouses split into zones can be optimised. In each zone, pickers collect goods, which they then take to a central picking point, presenting warehouse designers with several challenges. For example, how big should each zone be? Which goods do you store in which zone? And in what quantities?
Unpredictable order flows in warehouses for online orders
Especially in e-commerce warehouses, there are unpredictable peaks in order flow. In his research, Van der Gaast therefore developed an analytical model that can predict how a specific layout will perform even when there are fluctuating order flows. He verified his results using datasets from an existing warehouse. This showed that his model predicts the efficiency of a picking system very accurately. According to the researcher, this makes it a useful tool for testing new systems.
Milk round system
The 'milk round system' or 'milk run' is a relatively new approach to order picking. The picker constantly makes rounds through the warehouse, taking goods along the way and unloading them at the collection point at the end of each round. As soon as a new customer order arrives, it is immediately passed on to the picker on the shop floor. The next time he passes the storage location during his round, he takes the item.
This milk round system has the advantage that order pickers need less time to pick an order. Switching from a traditional system to the 'milk run' does require additional investments. Van der Gaast's calculations show that order picking with the milk run system is an attractive and significantly faster method when orders arrive in quick succession, especially if the products are stored efficiently.
Read the full thesis 'Stochastic models for order picking systems' here.
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