Routing-based reactive scheduling policies for machine failures in dynamicjob shops

A scheduling and control system can be viewed as a vital component of moder n manufacturing systems that determines companies' overall performance in t heir respective supply chains. This paper studies reactive scheduling polic ies developed against unexpected machine failures. These reactive policies are based on rerouting the jobs to their alternative machines when their pr imary machine fails. Depending on the subset of the jobs considered for rer outing, the long-term performance of four policies are tested under various conditions. Expecting that these rerouting policies would bring an extra l oad for a material-handling system (MHS), a dynamic job shop environment wa s studied with and without a MHS. It is shown that the proper selection of a good reactive policy is based not only on the system characteristics such as utilization, machine down times and frequency of machine failures, but also on the MHS capacity (in terms of speed and number of MH devices). The extensive experiments show that when the MHS is not a bottleneck and/or the down times are long enough to compensate the cost of extra rerouting, rero uting all affected jobs to their alternative machines proves to be the best policy. However, when the MHS cannot handle the extra load due to reroutin g or the down times are relatively short, then rerouting only the jobs that will arrive to the failed machine during repair performs the best.