Electro-Mechanical Actuators (EMA) are gaining prominent roles in the next generation fly-by-wire aircraft and spacecraft. With these roles often being safety-critical (control surface or landing gear actuation, for instance), the key to faster adoption of EMA in aerospace applications is development of accurate and reliable prognostic health management (PHM) systems that not only detect and identify faults, but also predict how the identified they affect the remaining useful life (RUL) of both the faulty component and the actuator as a whole. Such information can be invaluable to pilots, controllers, and maintenance personnel in assessing how to complete or re-plan the desired mission with a sufficient safety margin. A team consisting of members of NASA Ames Diagnostic & Prognostic Group has developed a prototype PHM system for EMA that provides coverage for a number of faults modes typical to this type of actuators. The diagnostic portion of the system is implemented using a hybrid approach which utilizes both qualitative (bond graph, model-based) and quantitative (data-driven) reasoners to achieve low false positive and false negative detection rates and a high accuracy of diagnostic output. Once a fault has been diagnosed, the prognostic component, which is implemented using Gaussian Process Regression (GPR) principles, estimates the RUL of the component that is faulted.
Experiments were conducted both in laboratory and flight conditions to validate the PHM
system using an innovative Flyable Electromechanical Actuator (FLEA) test stand. The test stand allows experimental actuators to be subjected to environmental and operating conditions similar to what actuators on the host aircraft are experiencing, while providing researchers with the capability to safely inject and monitor propagation of various fault modes. Prognostic run-to-failure experiments were done in laboratory conditions on ballscrew jam and motor winding short faults. Flight experiments (albeit not run-to-failure)were conducted in collaboration with the US Army on UH-60 Blackhawk helicopters. The paper describes these experiments in detail and presents the results obtained from the PHM system with regard to the estimation of the RUL of the actuator.