An experimental investigation of FMS scheduling rules under uncertainty

This article reports the results of an experimental investigation of scheduling decision rules for a dedicated FMS with variable performance times and machine break-downs. An existing FMS was modeled using the actual performance times obtained from the system’s transaction log. The performance of six heuristic scheduling rules were tested under differing uncertainty conditions. The simulation model included three types of uncertainty, namely: minor breakdowns, which averaged two hours and occurred once every two shifts; major breakdowns, which averaged ten hours and occurred once every ten shifts; and operation time deviations, which ranged from 0% to 20% of standard time. The runtime for the simulation approximated the work to be done over a ten-week period of time, or 7590 parts. Six different part loading rules were used to determine whether they could produce different performance results. The smallest proportion of jobs launched and the next empty pallet rule worked appreciably better than the rest of the rules in obtaining the highest FMS utilization.