Abstract
The loss of conflicting information in a Petri net (PN), usually called confusions, leads to incomplete and faulty system behavior. Confusions, as an unfortunate phenomenon in discrete event systems modeled with Petri nets, are caused by the frequent interlacement of conflicting and concurrent transitions. In this paper, confusions are defined and investigated in bounded generalized PNs. A reasonable control strategy for conflicts and confusions in a PN is formulated by proposing elementary conflict resolution sequences (ECRSs) and a class of local synchronized Petri nets (LSPNs). Two control algorithms are reported to control the appeared confusions by generating a series of external events. Finally, an example of confusion analysis and control in an automated manufacturing system is presented.
Highlights
Fault detection and avoidance through external control are important problems in discrete event systems [1,2,3,4,5]
Conflicts in a Petri nets (PNs) are tied to the competition for limited resources between two or more events, which usually is considered as the information interfaces between the DESs and the human decisions, for example, a switch controlled by humans or a static conflict resolution policy designed by humans [6, 7]
This paper proposes a confusion control strategy in generalized PNs, which is based on external event control in synchronized PNs and based on the proposed elementary conflict resolution sequences (ECRSs)
Summary
Fault detection and avoidance through external control are important problems in discrete event systems [1,2,3,4,5]. Confusion avoidance in a safe marked ordinary net can be considered as a problem to forbid the firing of transitions according to a control specification. The confusion control policies presented in [18] cannot be appropriately enforced since conflict resolution in a generalized PN is related to transition enabling degrees that is not appearing in safe marked ordinary PNs. This study extends the work on confusions in [17, 18] by introducing the concept of information content of conflicts. A class of synchronized PNs with the control information that is called allowable enabling degrees is introduced, in which external events are featured with desired enabling degrees of transitions and can perform a variety of dependency relations of their execution times.
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