Fault-tolerant output-constrained control of unknown Euler-Lagrange systems with prescribed tracking accuracy

This paper explores the output-constrained tracking control problem for unknown Euler–Lagrange systems subject to actuator faults, in the case where the reference trajectory is unknown in advance. The presence of actuator faults may lead to the loss of strong controllability of the system assumed in the existing literature on robust control of multi-input multi-output nonlinear systems. The lack of a priori knowledge on the reference trajectory renders the current constraint-handling techniques to achieve prescribed tracking accuracy infeasible. To conquer the above obstacles, a novel fault compensation scheme is designed in this paper, and a new-type error boundary is introduced to the control design. It is proved that the proposed approach guarantees output tracking with prescribed accuracy and constraint satisfactions simultaneously, even if actuator faults occur. A comparative simulation on a robot manipulator is conducted to further illustrate the established theoretical findings.