REACTIVE SCHEDULING - IMPROVING THE ROBUSTNESS OF SCHEDULES AND RESTRICTING THE EFFECTS OF SHOP-FLOOR DISTURBANCES BY FUZZY-REASONING

Practical scheduling usually has to reach to many unpredictable events and uncertainties in the production environment. Although often possi ble in theory, it is undesirable to reschedule from scratch in such ca ses. Since the surrounding organization will be prepared for the predi cted schedule, it is important to change only those features of the sc hedule that are necessary. We show how, on one side, fuzzy logic can b e used to support the construction of schedules that are robust with r espect to changes due to certain types of event. On the other side, we show how a reaction can be restricted to a small environment by means of fuzzy constraints and a repair-based problem-solving strategy. We demonstrate the proposed representation and problem-solving method by introducing a scheduling application in a steelmaking plant. We constr uct a preliminary schedule by taking into account only the most likely duration of operations. This schedule is iteratively ''repaired'' unt il some threshold evaluation is found. A repair is found with a local search procedure based on Tabu Search. Finally, we show which events c an lead to reactive scheduling and how this is supported by the repair strategy.