Models and Algorithms for Failure Diagnosis and Recovery in FMSs

Abstract

Within a flexible manufacturing system (FMS) framework, supervision has been introduced to take into account dependability objectives in FMS control. This article focuses on two modeling lines used to implement some functions of FMS monitoring and supervision: a functional line and a structural line. The model obtained by the first line is called a functional graph (FG). The FG provides a graphic description of logical conditions to assume services delivered by the plant from functions of its components. It is used in diagnostic and prognostic procedures. The structural line is called operational accessibility graph (OAG), which models the operations 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 to achieve a required production. From a modeling and application point of view, FG and OAG are complementary. They are used to implement a reaction loop of supervision that starts from a failure's detection to the proposal of a new FMS organization. To improve the dependability of an FMS during exploitation, a cooperation of the two models is proposed.