Costs for Rescheduling Actions: A Critical Issue for Reducing the Gap between Scheduling Theory and Practice

Rescheduling programmed tasks, when an unexpected event occurs, may affect the smooth operation of the plant if the initial schedule is not taken into account. This work addresses the penalty incurred by rescheduling actions and the optimization procedure to preserve schedule stability. To adjust the rescheduling process to the needs of the decision-maker, rescheduling costs are included to the initial objective function. Namely, unit reallocation and sequencing alterations are the sources of rescheduling costs. A mixed-integer linear programming (MILP) model for the simultaneous rescheduling of multiple operations that permits local reordering, unit reallocation, and accommodation of new orders, is considered. The need to consider rescheduling penalties in the optimization procedure is highlighted through several case studies. As a result, the production plant stability and efficiency are preserved, whereas the generation of pseudo-optimal schedules is avoided. In addition, the tradeoff between the original objective function optimization and the smooth operation of the plant is thoroughly examined.