Solving scheduling problems in distribution centers using symmetry breaking constraints

This paper deals with the problem of scheduling the internal operations in Distribution Centers (DC). Internal operations of the DC consist essentially in de-consolidating inbound cases, sorting products according to customer requests and consolidating outbound cases. The objective is to minimize the total operation time determining the optimal sequence of the internal operations. The problem is modeled by a Mixed Integer Linear Programming formulation that presents a large number of alternative equivalent solutions. To handle with this issue, we use symmetry breaking constraints and objective function perturbations. Moreover, some lower and upper bounds of the operation times are evaluated by heuristic algorithms in order to add constraints to the formulation. Some test results highlight the effectiveness of the proposed formulation.