Scheduling integrated flexible job - shop problem with preventive maintenance to minimize makespan and system unavailability

Integrating flexible job-shop scheduling problem (FJSP) with preventive maintenance (PM) is pondered in this paper. Minimizing the makespan for scheduling part and minimizing the system unavailability for maintenance part are simultaneously under consideration. For doing it, the assignment of n jobs on m machines in production side and executing the PM actions at appropriate time intervals in maintenance part are carried out at the same time. Also, for carrying out the maintenance side, reliability model is employed. Moreover, number of maintenance actions and maintenance intervals are not fixed in advanced. In order to ensure of obtained results, two multi-objective evolutionary algorithms (NSGA-II and NRGA) are compared. Besides, these genetic algorithms were hybridized with both well-known composite dispatching rule (CDR) and active scheduling and then compared as a two new evolutionary algorithms named CDRNSGA-II and CDRNRGA. Furthermore, the algorithms are compared with more than 4800 test instances.