An analytical approach of multiple-aisle shuttle-based storage and retrieval systems

This paper deals with a method for performance calculation of shuttle-based storage and retrieval system (SBS/RS) with tier-captive aisle-changing shuttles and different storage strategies. The shuttles are assigned to a certain number of aisles in this system. The invented approach takes place in the design process of SBS/RS. A continuous time open-queueing system with a limited capacity approach is applied. A discrete spatial value approach determines the inter-arrival times and service times. A probability-based model mentions the aisle changing. This approach is validated by comparison to a Monte-Carlo simulation. A European material handling provider gave the data used in this comparison to validate this approach. Finally, an example of the usage in the design process of SBS/RS of the invented analytical approach is depicted. The result is an increase in throughput with an increasing number of aisles per shuttle. Likewise, the storage strategy greatly influences the throughput between random storage and retrieval and same aisle storage and retrieval.