Variance-based approximations of transaction waiting times in autonomous vehicle storage and retrieval systems

Approximation strategies for transaction waiting times are proposed for use in Autonomous Vehicle Storage and Retrieval Systems (AVS/RSs) with non-Poisson arrival rates and non-exponential service times. The proposed modelling tools dynamically adjust approximations based on the variance of the transaction inter-arrival times observed in a system. Simulation-based validation studies indicate that this strategy can reduce the magnitude of errors in estimated transaction waiting times by approximately 80% relative to static approximations. The design conceptualisation applications of the proposed technique are demonstrated over a series of realistically sized demonstration problems. [Received 8 April 2008; Revised 20 July 2008; Accepted 2 August 2008]