Fault Isolation of an Electro-mechanical Linear Actuator

We apply model-based fault-isolation to an electromechanical linear actuator, and demonstrate its use on an unmanned underwater vehicle mass-shifter. Models incorporating the physics of the motor and of the load, and the effect of the servo-controller, are derived for nominal operations, overload faults, and coupling loss faults. A simple parameter identification method based on close-form solutions during startup and at steady-state is used, and is shown to produce good agreement with measurements. Fault-isolation is done by representing the system as a time-dependent mixture of its models, and selecting the model with the smallest error residual. We tested this in three situations – an actual overload fault, an actual coupling fault, and a false-alarm – and found that the correct model was successfully isolated in each case.