Fault-tolerant control of a servohydraulic positioning system with crossport leakage

This brief details the design of a fault-tolerant control (FTC) scheme for a servohydraulic positioning system with a faulty actuator piston seal that introduces internal (crossport) leakage between the actuator chambers. It is shown that the leakage fault changes the plant type from 1 to 0, decreases the open-loop gain, and increases the effective damping. A fixed-gain linear time-invariant control law is synthesized via quantitative feedback theory (QFT) to guarantee satisfaction of a priori-defined reference tracking and stability requirements, despite the occurrence of the leakage fault. Experiments verify the ability of the designed fault-tolerant controller to compensate for the degrading effects of this fault. Experiments also demonstrate the superior tracking performance of the FTC scheme as compared to a control loop in which the effects of the leakage fault are not considered in the controller design.