Hierarchical Petri net modelling of reconfigurable manufacturing systems with improved net rewriting systems

This paper presents an improved net rewriting system (INRS)-based method for constructing a class of modular and reconfigurable Petri net (PN) models intended for supervisory control of reconfigurable manufacturing systems (RMS). First of all, the INRS is introduced that can implement dynamical adjustments to the structure of a PN model and maintain its important behavioural properties. Subsequently, the formalisms of graph and set are incorporated to provide a formal representation of a RMS configuration. According to the hierarchy of RMS configuration, hierarchical design of PN models with an INRS approach is proposed. Using the proposed method, a modular PN model can be obtained. Such a PN model is not only reconfigurable but also valid, i.e. live, bounded (or safe), and reversible. A reconfigurable manufacturing cell serves as an example to illustrate the main principles and procedures of PN model design, applying the presented method.