JIT-scheduling in unrelated parallel-machine environment with aging effect and multi-maintenance activities

In this paper, at first we present a new integer linear programming (ILP) model for the parallel-machine scheduling problem with aging effects and multi-maintenance activities simultaneously. A machine returns to its initial condition after each maintenance and the aging effects start a new one. The objective is to find jointly the optimal maintenance frequencies, the optimal positions of the maintenance activities and the optimal job sequences on the machines, such that the total early/tardy and maintenance cost be minimised. Since, this case problem is NP-hard so we provide a Genetic algorithm (GA)for it and the effectiveness of these approaches is evaluated by solving a large number of problem instances.