Most scheduling literature assumes that machines are available at all times. In this paper, we study the flexible Job-shop scheduling problem where the machine maintenance has to be performed within certain intervals and hence the machine becomes unavailable during the maintenance periods. We propose an assignment technique based successively on the use of different priority rules and a local search procedure. An adequate criteria is developed to evaluate the quality of the assignment. The sequencing problem is solved by a hybrid genetic algorithm which takes into account the constraint of availability periods.
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