Diagnosis of Actuator Lock-in-place for Flight Control Systems

In this paper, the diagnosis problem of actuator lock-in-place is studied. Based on multiple-model structure, an adaptive unknown input observer (UIO) approach is developed to detect and isolate aircraft actuator faults. Existing multiple-model FDI (fault detection and isolation) approaches assumed that the model for each fault case is known a priori. However, in the cases of lock-in-place, the locked position is unknown and varies in the range of maximum deflections. Thus, there exists an infinite family of models which is impossible to model exhaustively. To solve this problem, we developed an adaptive approach to estimate the unknown parameters on-line. The proposed adaptive algorithms guarantee that both the residual signals and the estimation errors of the unknown parameters converge exponentially when a model matches the system. To the best of our knowledge, this is the first adaptive UIO presented.