Improved Tightened Milp Formulations for Single-stage Batch Scheduling Problems

This work presents a set of improved MILP mathematical formulations for the scheduling of single-stage batch plants with parallel production lines. Minimization of the average weighted earliness and the makespan, i.e. the time needed to complete all processing tasks, are considered as alternative problem goals. For each objective function an enhanced model that incorporates specific tightening constraints is presented. These constraints improve each model’s efficiency by increasing the corresponding objective function lower bound, thus accelerating the branch and bound node pruning process. Several problem instances with different number of batches demonstrate that the proposed approach reduces the computational effort by orders of magnitude. Sequence dependent setup times can also be effectively accommodated. Copyright © 2006 IFAC