Simulation model of a single-server order picking workstation using aggregate process times

In this paper we propose a simulation modeling approach based on aggregate process times for the performance analysis of order picking workstations in automated warehouses with first-in-first-out processing of orders. The aggregate process time distribution is calculated from tote arrival and departure times. We refer to the aggregate process time as the effective process time. We distinguish between the effective process time distribution for the first tote of an order and that of the remaining totes of an order. These two distributions are used in an aggregate model to predict tote and order flow times. Results from a test case show that the aggregate model accurately predicts the mean and variability of tote and order flow times. The effect of the order size distribution on the flow time prediction accuracy is also investigated.