A New Continuous-time MILP Model for the Short- Term Scheduling of Multi Stage Batch Plants

This paper presents a new multiple time grid continuous time MILP model for the short-term scheduling of multistage, multiproduct plants. It can handle both release and due dates and different objective functions efficiently, such as the minimization of total cost, total earliness or makespan. This formulation is compared to other existing mixed-integer linear programming approaches and to a constraint programming model. The results show that the proposed formulation is much more efficient than its uniform time grid counterpart and is comparable to a continuous-time formulation that uses global precedence sequencing variables. Discrete-time formulations are preferred for larger scheduling problems where a reasonable number of time points are enough to consider the exact problem data. The results also show that the constraint programming model is the best approach for makespan minimization. * To whom correspondence should be addressed. Tel.: +351-217162712. Fax: +351-217167016. E-mail: [email protected]