Displacement Sensor Fault Tolerance for Hydraulic Servo Axis

In this paper, a fault management system for a hydraulic servo axis is described. This system is capable of sustaining faults in the piston displacement sensor of the position-controlled hydraulic servo axis. By means of a parity equation based fault detection stage, faults in the displacement sensor as well as other sensors and components of the servo axis can be detected and subsequently be diagnosed by means of a fuzzy-logic based reasoning system. Upon the diagnosis of a piston displacement sensor fault, the system switches to a “model-sensor” which provides an estimate for the piston position. To ensure the utmost model fidelity of the model sensor, the model parameters are constantly updated by means of parameter estimation during the fault-free operation of the servo axis. Experiments at a hydraulic servo axis conclude this paper and show the high quality of the reconstructed piston displacement sensor signal.