The development of an object-oriented Petri net cell control model

This paper presents an object-oriented Petri net cell control (OPNCC) model for scheduling and controlling the operations of a flexible manufacturing cell. The development of the OPNCC model includes three phases:

1. Static analysis.
2. Dynamic analysis.
3. Integration.

The dynamic analysis, the most important phase in developing the OPNCC model, will first construct the object-oriented Petri net (OPN) for each physical object and connect all the related “encapsulated” OPNs to be a complete OPN model to represent the dynamic behaviour or control logic of shop floor operations. Then, the control logic of the complete OPN model must be analysed through an object behaviour analysis, an inter-object message passing analysis and a conflict analysis. The OPNCC model not only possesses the characteristics of object-oriented method (e.g. inheritance, encapsulation and a higher degree of flexibility and reusability) and Petri nets (e.g. graphical representation and mathematical analysis capabilities), but also incorporates scheduling/dispatching knowledge in the control logic specified by the OPN model. The practical significance of the OPNCC model is that practitioners may apply it to develop both a real-time cell controller and an off-line shop floor scheduling simulator.