Decomposition of first-order Hybrid Petri Nets for hierarchical control of manufacturing systems

Although Hybrid Petri Net (HPN) is a popular formalism in modeling hybrid production systems, the HPN models of large scale systems are substantially complicated to analyze and control due to large dimensions of such systems. To overcome this problem, a typical approach is to decompose the net into subnets and control the plant through hierarchical or decentralized structures. Although this concept has been widely discussed in the literature for discrete PNs, there is a lack of research for HPNs. In this paper, a new method for decomposition of first-order HPNs (FOHPN) and the hierarchical control of the subnets through a coordinator is proposed. The advantage of using the proposed approach is validated by an existing example. A Job-shop case study is analyzed using decomposed FOHPN model and the optimization results are compared with the results of the original system. The proposed hierarchical control structure of FOHPN model yields reduction in cost of communication links, improvement in the reliability of the system, local maintenance, and partially system redesign.