Supervisor Simplification for AMS Based on Petri Nets and Inequality Analysis

In the framework of automated manufacturing systems (AMS), Petri nets are widely used to model, analyze, and control them. Resolving deadlocks is of paramount significance because their emergence may likely zero a systems throughput, if not necessarily. Supervisory control technique is the most widely adopted method to resolve them. A control policy can be converted into satisfying a set of inequalities, each of which corresponds to a siphon in a Petri net structure. The number of siphons can be exponential in the worst case, so does the number of inequalities. Taking into account the independent and dependent inequalities, this paper proposes a method to remove all the dependent inequalities, while preserving only the independent ones. This method can significantly reduce the size of a supervisory controller. Examples are presented to illustrate the effectiveness and efficiency of this method. Note to Practitioners-Owing to its importance in practice, deadlock arouses interest. Various resolution methods have been proposed by researchers and practitioners. The recent advance is to associate various sensors and actuators to certain predetermined working nodes for the sake of management and coordination of limited resources among concurrent operations. This uses a supervisory controller to a plant model. Nevertheless, existing approaches suffer from structural complexity due to their failure to reduce the sophisticated supervisor structures, which impedes their implementation in practice. Without a simplified control network, the communication cost among heterogeneous nodes increases while the responsive time decreases. Through the analysis on the dependency relationship among different inequalities, this paper presents a reduction technique to significantly simplify the supervisor structures. Without any extra investment, our approach betters a controlled system's performance.