A robust sensor fault tolerant control scheme implemented on a flexible joint

This paper presents a flexible joint system with a sensor fault tolerant control scheme applied to it. Sensor faults affect the system's performance in the closed loop when the faulty sensor readings are used to generate the control input. In this paper, the measured outputs are separated into potentially faulty and non-faulty components, and the latter are injected into a linear observer to reconstruct the faults. The reconstruction is subtracted from the faulty sensors to form a compensated 'virtual sensor' and this signal is then used to generate the control input. A design method for the observer is also presented in which the reconstruction signal is made as insensitive as possible to any uncertainties or nonlinearities present in the system. Several fault conditions were tested; step, ramp and total failure of the sensor. Excellent results have been obtained; the system performance is almost identical to the fault-free scenario.