Performance modelling of autonomous vehicle storage and retrieval systems with generally distributed service times

This paper proposes extensions of system conceptualisation models for autonomous vehicle storage and retrieval systems (AVS/RSs) to deal with non-exponential lift service times when the number of lifts and vehicles are both design variables. These extensions are based on an adaptation of a computational algorithm for estimating the probability distribution of queue lengths in capacitated, non-Poisson queuing systems. Simulation-based validation studies suggest that the proposed model extensions yield estimation errors comparable to those observed in earlier studies restricted to cases where the number of vehicle and lifts is treated as a single design variable. [Received: 20 February 2010; Revised: 8 June 2010; Accepted: 9 June 2010]