Scheduling of multi-product batch plants using reachability analysis of timed automata models

Standard scheduling approaches in process industries are often based on algebraic problem formulations solved as MI(N)LP optimization problems to derive production schedules. To handle such problems techniques based on timed automata have emerged recently. This contribution reports on a successful application of a new modeling scheme to formulate scheduling problems in process industries as timed automata (TA) models and describes the solution technique to obtain schedules using symbolic reachability analysis. First, the jobs, resources and additional constraints are modeled as sets of synchronized timed automata. Then, the individual automata are composed by parallel composition to form a global automaton which has an initial location where no jobs have been started and at least one target location where all jobs have been finished. A cost optimal symbolic reachability analysis is performed on the composed automaton to derive schedules. The main advantage of this approach over other MILP techniques is the intuitive graphical and modular modeling and the ability to compute better solutions within reasonable computation time. This is illustrated by a case study.