Analytical models to evaluate system performance measures for vehicle based material-handling systems under various dispatching policies

摘要

Queueing network-based approximation models were developed to evaluatethe performance of fixed-route material-handling systems supporting a multipleworkcenter manufacturing facility. In this research, we develop analytical models forfixed-route material-handling systems from two different perspectives: theworkcenters?? point of view and the transporters?? point of view. The state-dependentnature of the transportation time is considered here for more accurate analyticalapproximation models for material-handling systems. Also, an analytical methodologyis developed for analytical descriptions of the impact of several different vehicledispatchingpolicies for material-handling systems. Two different types of vehicledispatchingpolicies are considered. Those are workcenter-initiated vehicledispatching rules and vehicle-initiated vehicle dispatching rules. For the workcenterinitiatedvehicle dispatching rule, the Closest Transporter Allocation Rule (CTAR)was used to assign empty transporters to jobs needing to be moved between variousworkcenters. On the other hand, four different vehicle-initiated vehicle dispatchingrules, Shortest Distance Dispatching Rule (SDR), Time Limit/Shortest DistanceDispatching Rule (TL/SDR), First-Come First-Serve Dispatching Rule (FCFSR),Longest Distance Dispatching Rule (LDR), are used to select job requests fromworkcenters when a transporter is available. From the models with a queue space limitof one at each workcenter and one transporter, two different types of extensions areconsidered. First, the queue space limit at each workcenter is increased from one totwo while the number of transporters remains at one. Second, the number oftransporters in the system is also increased from one to two while maintaining thequeue space limit of one at each workcenter. Finally, using a simulation approach, wemodified the Nearest Neighbor (NN) heuristic dispatching procedure for multi-loadtransporters proposed by Tanchoco and Co (1994) and tested for a fixed-routematerial-handling system. The effects of our modified NN and the original NNtransporter dispatching procedures on the system performance measures, such as WIPor Cycle Time were investigated and we demonstrated that the modified NN heuristicdispatching procedure performs better than the original NN procedure in terms ofthese system performance measures.