Fault detection and isolation of smart actuators using bond graphs and external models

This paper deals with fault detection and isolation (FDI) of smart actuators combining the benefits of bond graph modelling with external models. An external model is a generic method which can be used to specify and verify the functional specifications of smart equipment. It uses the concept of services provided to the user and the organization of operating modes as a state graph with the logical conditions (depending on available services) required to move from one operating mode to another. One drawback of the external model is that it describes the system in terms of functions without taking into account the dynamics of the equipment. In addition, the availability of the services is not determined by FDI procedures. The integration of the bond graph methodology as a graphical and multi-disciplinary modelling tool quantifies the services by associating one or more bond graph elements to each service. Furthermore, the causal and structural properties of the bond graph methodology can be used to design FDI algorithms (i.e. the generation of fault indicators) to determine the availability of the services. This information is used to determine the transition conditions in the state graph. This technique has been applied to monitor a complex pneumatic servo-positioner.