CONTINUOUS-FLOW MODELS FOR BATCH MANUFACTURING - A BASIS FOR A HIERARCHICAL APPROACH

In this paper we propose approximate dynamic models, based on continuo us material flows, in order to overcome the difficulties usually faced by classical machine scheduling methods, such as computational comple xity, limited ability to model all the features of real manufacturing environments and to cope with unpredictable events. The continuous flo w approach, which has been often proposed for repetitive manufacturing environments, is exploited here for a batch manufacturing environment ; a multi-stage case is used to illustrate the methodology. Both discr ete and continuous time dynamic models are considered. Some computatio nal complexity results are given for the resulting optimization proble ms. Based on these models, a two-level hierarchical approach is propos ed: the task of the upper hierarchical level is to solve the continuou s flow scheduling problem, yielding a reference production trajectory; the task of the lower level is detail scheduling, aimed at meeting th e production targets set by the upper level. Constraints may be added to the continuous flow model in order to cope with unfeasibilities det ected by the lower level, resulting in a two-way hierarchical scheme.