Analysis of dynamic dispatching rules for a flexible manufacturing system

This paper presents a simulation model of a flexible manufacturing system (FMS) which subjects to minimization three performance criteria simultaneously such as mean flow time, mean tardiness, and mean earliness. The dispatching rule will be changed at a frequency that is varied by the number of outputs produced by the system. Therefore, the dynamic nature is event-triggered rather than changing the rule at a regular time interval, which is passive. Three indexes are calculated to represent the three criteria under monitoring and the indexes are ranked in descending order: the greater the index, the worse is the situation of the criterion in the system. Thus, an appropriate rule will be selected for the next operation in order to tackle that criterion with the largest index. This mechanism is so called pre-emptive method. Furthermore, the indexes can be biased so that particular criterion can have a greater weighting as set by the decision-maker. Results show that a solution (range of frequency) can always be determined to change the dispatching rule so that the system is better than just using fixed FMS scheduling rule.