Queueing network model for a class of material-handling systems

A queueing network-based approximation model was developed to evaluate the performance of a fixed-route material-handling system supporting a multiple-workcentre manufacturing facility. The closest transporter allocation scheme was used to assign empty transporters to jobs needing to be moved between various workcentres. This control methodology creates two interesting difficulties that require solving for an accurate approximation model. A model of the distributions of the location of an assigned transporter as a function of the number of available transporters is developed. In addition, it is shown that owing to the strong dependent service time aspect of this situation, the standard queueing network decomposition approach of treating the material-handling systems as a GI/G/c queue can be highly inaccurate. Thus, it is necessary to develop a dependent service-time model for approximating the queueing delay encountered while waiting for an empty transporter assignment.