Modeling Sequence Dependent Changeovers. A Comparison of Different Approaches

ARMANDO GUARNASCHELLI,; OMAR CHIOTTI,; ENRIQUE SALOMONE

Costa Verde, RJ

Congreso; 4th Mercosur Congress on Process Systems Engineering; 2005

EMPROMER

Sequence dependent changeovers arise in a wide range of scheduling problems. These changeovers affect the time needed to schedule the tasks involved, but very often they also affect the cost of operation. When a changeover requires material transitions, out-of-spec products or just waste materials are generated and the associated costs are not necessarily correlated with the changeover time. This characteristic is very common in semi continuous multiproduct manufacturing and is a critical aspect in many Process Industries such as the production of lube oils, polymers, paints, etc. The importance of the subject is clearly recognized by plant’s managers who often schedule the operation of the plants through heuristics, searching for schedules that minimize transition (changeover) costs. In this work we address a Mixed Integer Linear Programming (MILP) disjunctive modeling strategy capable of representing the single machine scheduling problem with sequence dependent setup times (SDST), its limitations are discussed and its correct application is defined. Some modifications to the modeling strategyare introduced in order to give it the feature of considering the objective of minimizing sequence dependent setup costs also. Computational results for a real problem are presented using the disjunctive formulation and another classic formulation for the problem. Conclusions are given.