ON THE RECEDING HORIZON HIERARCHICAL OPTIMAL-CONTROL OF MANUFACTURINGSYSTEMS

This paper concerns the development of a hierarchical framework for th e integrated planning and scheduling of a class of manufacturing syste ms. In this framework, dynamic optimization plays an important role in order to define control strategies that, by taking into account the d ynamic nature of these systems, minimize customized cost functionals s ubject to state and control constraints. The proposed architecture is composed of a set of hierarchical levels where a two-way information h ow, assuming the form of a state feedback control, is obtained through a receding horizon control scheme. The averaging effect of the recedi ng horizon control scheme enables this deterministic approach to handl e random and unexpected events at all levels of the hierarchy. At a gi ven level, production targets to the subsystems immediately below are defined by solving appropriate optimal control problems. Efficient ite rative algorithms based on optimality conditions are used to yield con trol strategies in the form of production rates for the various subsys tems. At the lower level: this control strategy is further refined in such a way that all sequences of operations are fully specified. The m inimum cost sensitivity information provided in the optimal control fo rmulation supports a mechanism, based on the notion of a critical mach ine, which plays an important role in the exploitation of the availabl e flexibility. Finally, an important point to note is that our approac h is particularly suited to further integration of the production syst em into a larger supply chain management framework, which is well supp orted by recent developments in hybrid systems theory.