Higher Order Sliding Mode observers for actuator faults Diagnosis in robot manipulators

A diagnostic scheme for actuator faults which can occur on a robot manipulator using a model-based Fault Diagnosis (FD) technique is addressed. With the proposed FD scheme it is possible to detect a fault, which can occur on a specific component of the system. To detect actuator faults, higher order sliding mode Unknown Input Observers (UIO) are proposed to make analytical redundancy. The observers input laws are designed according to the so-called Super-Twisting Second Order Sliding Mode Control (SOSMC) approach and they are proved to be capable of guaranteeing the exponential convergence of the fault estimate to the actual fault signal. The proposed approach is verified in simulation and experimentally on a COMAU SMART3-S2 robot manipulator.