Dynamic scheduling strategies for FMS hub networks with flow time consideration.

Abstract

This thesis investigates the effects of dynamic rescheduling strategies of jobs at multiple revisited workstations called hubs on the performance of Flexible Manufacturing Systems (FMS). The objective of rescheduling jobs at workstations is to improve various aspects of the production flow and manufacturing productivity. Compared to fixed queue scheduling rules, dynamic changes in queue scheduling rules for hubs at certain intervention times, are shown in some cases to reduce total job flow time (maximum completion time of all jobs in a fixed total "Makespan") and average flow time (average completion time) simultaneously. The development of dynamic hub scheduling rules including intervention time specification to improve job flow measures establish the basis for an Expert System rules base for dynamic scheduling. The rationale for dynamic queue scheduling rules are developed from analysing the machine idle time structure for a simple single hub system operated under fixed queue scheduling rules. The intervention and rescheduling procedure is applied to increasingly complex and concrete FMS cases use a flexible simulation model including animation of the production facility. Specifically, this thesis provides a methodology for developing and evaluating the rescheduling rules with respect to the trade-off between Makespan and average completion time for a mixed number of jobs in an FMS defined by hub and non-hub workstations.