Ant colony optimization algorithm to minimize makespan and number of tardy jobs in flexible flowshop systems

This paper studies the problem of scheduling a set of jobs in a hybrid flowshop. Since this problem is known to be NP-hard, a meta-heuristic procedure based on Ant Colony Optimization (ACO) is proposed. The paper considers the multi-objective problem of minimizing both the makespan and the number of tardy jobs. An experimental study is carried out using wellknown instances from the literature. Because this is the first time in literature that these two objectives are considered simultaneously for the hybrid flowshop problem, the proposed procedure is compared with mono-objective heuristics for each optimization criterion. Experimental results show the efficiency and effectiveness of the proposed ACO algorithm.