An artificial immune algorithm for multiple-route job shop scheduling problem with preventive maintenance constraints

In most of the scheduling problems, it is often assumed that machines are available in the planning horizon. This assumption may not be always valid as in practice machines may become unavailable due to preventive maintenances. In this paper, we tackle multiple‐route job shop scheduling problem under availability constraints subject to makespan minimisation. The availability constraints are assumed non‐fixed, namely, the maintenance tasks have to be performed within their pre‐defined time window. The problem is classified as NP‐hard. Mathematical formulation of the problem is first presented. Then, a heuristic approach based on artificial immune algorithm is proposed for solving the problem. In order to evaluate effectiveness of the proposed approach, 30 problems in small, medium, and large size are designed. The problems are solved using the proposed approach and the solutions are compared with the solutions obtained by Lingo software. The computational results show that the proposed approach can yield good solutions in relatively short amount of time.