Representing the material handling system in tractable queuing network models of flexible manufacturing systems: A workload data aggregation approach

This paper deals with the use of queueing network (QN) models for quantitatively evaluating the impact of the material handling system (MHS) on the steady-state performance of a flexible manufacturing system (FMS) at the strategic and tactical decision levels. A direct exploitation of the workload data provided by industrial experts often results in QN models that cannot be analyzed efficiently because of the prohibitive number of customer classes. In this paper, we propose a systematic data aggregation approach for deriving the aggregated characteristics of the service offered by a device of the MHS at steady state. This generic aggregation scheme explicitly captures empty trips on the device, MHS devices that have different motions depending on whether they travel empty or loaded, and enables further, consistent use of the various central server QN models appearing in the literature. The quality of the estimates provided by this automated data aggregation approach is tested on several examples, and their integration into a QN model for performance evaluation is illustrated on an FMS presented in the literature.