The mixture of conflicting transitions and concurrent transitions in Petri nets can lead to the loss of conflict information, which is an unfortunate phenomenon in discrete event systems, usually called confusions. They appear in the processes of resource allocation and may cause incomplete decision‐making on conflicts. Hence, a confusion detection method and a control strategy are required. This paper proposes a class of confusion control event reconfigurable (CCR) nets to control confusions with the evolution of markings. Their properties such as safety and liveness with the mapping from original Petri nets to CCR nets are investigated. Two confusion control algorithms are proposed to generate a set of control code sequences, which can completely control the occurrences of confusions. Then, a confusion detection algorithm with polynomial time complexity is developed. Finally, an example of confusion analysis in automated manufacturing systems is presented.

As a significant structural object, siphons are extensively employed to implement a large number of deadlock prevention and liveness-enforcing methods for flexible manufacturing systems modeled by Petri nets. By linear combinations, a set of elementary siphons is chosen from all strict minimal ones to be controlled and thus the structural complexity of a supervisor is greatly reduced. The concept of elementary siphons is originally proposed for ordinary Petri nets. When applied to generalized Petri nets, their selection and controllability require an additional study. In this work, the concept of augmented siphons is proposed to extend the application of the elementary ones to a class of generalized Petri nets, GLS 3 PR. Based on graph theory, a siphon extraction algorithm is developed to obtain all strict minimal siphons, from which augmented elementary ones are computed. In addition, the controllability conditions of dependent siphons are developed. Through fully investigating the net structure, especially weight information, the set of augmented elementary siphons is more compact and well suits for generalized Petri net models under consideration. Some examples are used to illustrate the proposed method.

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Petri nets are robust mathematical tools for the modelling, handling, and control of deadlock problems in automated manufacturing systems (AMSs). Several methods have been proposed to prevent deadlocks in AMSs. However, it is important to convert the controlled system represented by Petri nets into the program of a programmable logic controller (PLC) for the implementation of automation tasks. This study proposes a methodology based on Petri nets for deadlock prevention, and generates PLC codes for an AMS. In the suggested methodology, a Petri net model of an uncontrolled system is built, and the controlled Petri net model is developed using a deadlock-prevention method. The controlled Petri net model is then transformed into an automation-controlled Petri net model, which is further converted into a controlled token-passing logic model. The controlled tokenpassing logic model is utilised to generate the ladder diagrams for the AMS under consideration. The proposed methodology was tested using a real-world AMS at King Saud University labs. It provides an effective method for PLC implementation from a controlled system model represented by Petri nets.

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