Conceptual modeling of an object-oriented scheduling architecture based on the shifting bottleneck procedure

Abstract

The importance of finite-capacity schedulers is increasing, with respect to the widespread MRP packages, due to their ability to model the shop floor more accurately. However, this very advantage may turn into a disadvantage, since it is quite difficult to devise a high-quality general purpose scheduler able to cope with the technological peculiarities of different production environments. Furthermore, a detailed schedule is prone to disruptions due to the uncertainty affecting the shop floor. Hence, we need both a modular approach to devise and assemble local schedulers, and a way to link predictive and real time scheduling. To cope with both requirements, we propose a scheduling architecture inspired by the well-known Shifting Bottleneck method. The knowledge needed to cope with technological peculiarities is pushed down the decision hierarchy, to the level of local schedulers. A material coordinator negotiates a reference trajectory with the local schedulers, by deriving local due dates which can be used as targets to drive real time dispatching. The modularity of the architecture is illustrated through an object-oriented conceptual model based on the Unified Modeling Language.