An activity-based predicate/transition net model of operational control planning for a flexible manufacturing system

Abstract

An effective flexible manufacturing system (FMS) relies on a hierarchy of decisions, including the control of the FMS operation. The FMS operation usually is dynamically constrained by the limited resources such as pallets, machines, tools, carts, etc. Most analytical models make many assumptions and oversimplify the complicated decision problems. This study proposes the predicate/transition (Pr/Tr) net, a high level petri net, as a model for operational control planning. Firstly, the activities (modes) and their resources usage in FMS were analysed and aggregated into activity sets. Then, the flow of parts among activities was traced to obtain the "mode transition diagram", and then the Pr/Tr net model was introduced. We incrementally defined the predicates and transitions into this model. Finally, a comprehensive FMS Pr/Tr net model was derived. By implementing it into a rule-based simulation model, it is well suited for FMS operational control planning because of its inclusiveness and high flexibility.