A real-time methodology for minimizing mean flowtime in FMSs with machine breakdowns: threshold-based selective rerouting

This paper presents the threshold-based selective rerouting (TSR) heuristic to minimize mean flowtime of parts in a flexible manufacturing system (FMS) with machine failures. Most of the available methodologies considering machine failures are either off-line methods or propose different versions of rerouting all the jobs to alternate machines. The objective of this methodology is to develop an efficient real-time rerouting strategy, which can be easily applicable in case of machine failures and is able to adapt to the dynamic features of an FMS. Parts in the queue of a failed machine are selectively rerouted to alternate machines when the benefit in terms of waiting time obtained from rerouting exceeds a specific pre-determined threshold value. The threshold concept and the performance of TSR in minimizing mean flowtime are tested with extensive simulation experiments. It has been shown that TSR provides significant improvements in system performance measures compared to other real-time rerouting methods and that the threshold value is dependent on system parameters. The relationship between the threshold value and system parameters has also been determined.