Heterarchical control for flexible manufacturing systems using Petri nets

This thesis presents a methodology for development of a heterarchical control system in flexible manufacturing systems (FMS) environment. A new Petri net based model for the heterarchical architecture has been developed. The basic concept of the modeling scheme is to represent distributed and locally autonomous nature of individual controller entities and their communication with others. The model can be applied for development of control software. A real-time scheduling methodology for the heterarchical system has also been developed and it is used as a software entity in the overall architecture. The partition of generic and specific modules in control software development is emphasized. The control system performs its control tasks in two stages: (1) generation of generic control code and distribution of them to each controller entity prior to system execution; (2) generation of specific control code according to job arrival and its process plan. The model and the control software has been evaluated at an extended version of CIM Lab of the Pennsylvania State University by a simulation program.