C. Mancel*, P. Lopez
N. Rivière, R. Valette
LAAS-CNRS,
F-31077 Toulouse Cedex 4, France
* : also IXI - GFI Consulting,
Immeuble Zodiaque, 2-3 Passage de l'Europe,
Parc Technologique du Canal,
F-31400 Toulouse - FRANCE
cmancel@laas.fr, lopez@laas.fr,
nriviere@laas.fr,
robert@laas.fr
Presented at
15th IFAC world congress, Barcelona, Spain, 21-26 July 2002,
n. 634.
Petri nets are commonly used to define resource allocation mechanisms for flexible manufacturing systems. They can be enriched by temporal inscriptions in different ways (t-timed, t-time, p-timed and p-time Petri nets) allowing thus the specification of complex contraints involving time and resources. Constraint graphs and activity-on-arc graphs are also commonly used for the analysis of temporal constraints encountered in scheduling issues for manufacturing.
The purpose of the paper is to compare the two approaches and to show that it is possible, from a Petri net model, to derive scenarios, each one being a constraint graph. Note that scenario derivation implies conflict resolution involving a combinatorial exploration. The obtained graphs are simpler in the case of t-timed or p-time Petri nets than in the case of t-time Petri nets. For p-time Petri nets, they can be translated into Linear programs without integer variables. Usefulness of these results in the context of manufacturing system scheduling will be discussed.