An analytical approach for a performance calculation of shuttle-based storage and retrieval systems

This paper deals with a method for performance calculation of shuttle-based storage and retrieval systems (SBS/RS) with tier captive shuttles. A continuous time open queueing system with limited capacity approach is applied. The cycle times of shuttles and lifts can be used directly with their time distributions. These cycle times are determined by a discrete spatial value approach. The main novelty of this approach is the use of a time continuous queueing model to take the interactions between lifts and shuttles combined with a spatial discrete approach for the processes of lifts and shuttles into account. A comparison between the analytical approach and a discrete events simulation is presented to validate the developed model. The data used in this comparison to validate this approach was given by an European material handling provider. Finally, it will be outlined how the model can be used for designing SBS/RS, to meet given requirements.