HIERARCHICAL CONTROL APPROACH USING REFINEMENT FOR RESOURCE ALLOCATiON PROBLEM

Abstract

A manufacturing system is aptly modelled in the Discrete Event Dynamic System framework wherein occurrence of different activities triggers changes in the system. One major problem that is frequently encountered in manufacturing system is the resource allocation problem, i.e., at times, a machine (resource) may have to be shared, at the same time, between many activities more than its capacity. This raises conflict between activities and prevents the system being modelled as an event graph unless a carefully considered logical schedule of activities is imposed on the resource. The work aims at a hierarchical control niethod in the Petri net framework using Dioid algebra to successfully incorporate the schedule on the manufacturing system. While the manufacturing system (with resource allocation problem) is tried to be modelled as a timed event graph by incorporating the schedule (Automata) in the lower level, the refinement thus obtained is used to design a timed event graph controller to achieve the just in time criterion while preserving system transfer relation at the higher level. The work derives the necessary and sufficient conditions required for eliminating Automata in the lower level and modifying the controller designed at higher level so as to include the schedule, thereby solving the resource allocation problem.