CPNs (Colored Petri Net) are used to model the dynamics of a railway system: places represent tracks and stations, tokens are trains. Using digraph tools, deadlock situations are characterized and a strategy is established to define off-line a set of constraints that prevent deadlocks. It is shown that these constraints limit the weighted sum of coloured tokens in subsets of places. In particular, GMECs (Generalized Mutual Exclusion Constraint) are extended to CPN and it is shown that the above constraints, as well as the collision avoidance constraints, can be written as coloured GMEC. To solve this problem, the theory of monitor places for place/transition nets is extended to the case of CPN and it is shown that these constraints can be enforced by a coloured monitor place that minimally restricts the behaviour of the closed-loop system. Both types of constraints, namely collision prevention constraints and deadlock prevention constraints are considered. Starting from the analysis of deadlock on the basis of digraph tools, a deadlock prevention strategy was defined and expressed by a set of linear inequality constraints.
Monitor design for colored Petri nets: An application to deadlock prevention in railway networks
Überwachung von farbigen Petri-Netzen: Eine Anwendung zur Vermeidung von Deadlocks in Bahnnetzen
2006
17 Seiten, 8 Bilder, 31 Quellen
Conference paper
English
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