Structural and functional approach for dependability in FMS

Within the FMS framework, supervision has been introduced to take into account dependability objectives in FMS control. This paper focuses on two modeling lines used to implement some functions of the FMS supervision: a rather functional line and a rather structural line. The model obtained following the first line is named Functional Graph (FG). The FG model is expressed as a graph, which provides a graphic description of logical conditions of the system function using basic functions of the system elements. It is used in diagnostic and prognostic procedures. The model obtained following the second line is named operational accessibility graph (GAG). It models the operating part of an FMS, taking characteristic areas and accessibility relationships into account. It represents the way operations are induced to cooperate. It is used in a recovery procedure to establish the FMS configuration and the operations´ sequences in order to achieve a given production. From modeling and application point of view, FG and OAG are complementary. They are used to implement the reaction loop of the supervision that starts from a failure´s detection to the proposition of a new FMS organization. In order to improve dependability of FMS during the exploitation, a cooperation of the two models is proposed