Evaluation of the throughput of a multiple-picker order picking system with congestion consideration

This study investigates an order picking system involving multiple pickers in a warehouse. Travel distance or travel time has usually been employed to measure order picking efficiency, since most previous studies assumed an order picking system only undertakes single-picker operations. However, multiple pickers frequently work in the same area concurrently in an actual warehouse system and congestion inevitably takes place and the traditional travel distance or travel time might not be a proper measure for the system efficiency. Consequently, this study proposes a throughput model for the determination of the picking operation performance for such multiple-picker environment to consider a trade-off between the picking distance and the blocking-caused delay for the storage assignment. The proposed model is first validated by a simulation experiment and then used to compare the throughput of the warehouse under two popular storage assignment strategies with different demand distributions of stock keep units in the order picking system.