Fault tolerant adaptive control under actuator saturation for robot manipulators

In practice, actuators inherently have natural limitations that are often overlooked by theoretical control strategies, such as bounded output and discrepancies between calculated and actual responses. Consequently, reliable control techniques must be employed to ensure safe and dependable operation. We propose an adaptive control law for global regulation in the case of partial loss of effectiveness due to input faults. The proposed control strategy maintains the system at the desired configuration while accounting for the physical limitations of the actuators. Additionally, it is suitable for dealing with unknown parameters in the vector of gravitational forces, making it robust to these uncertainties. The approach treats the inputs as time-varying signals, allowing for an infinite number of faults. The methodology has the advantage of operating in continuous time. Thus, it is theoretically capable of counteracting any fault event of arbitrary magnitude, as long as the actuators are able to continue overcoming gravitational effects while maintaining inertial and gravitational counteracting responses. The closed-loop system is analyzed using Lyapunov's stability theory for non-autonomous systems, concluding global asymptotic convergence of all signals. The effectiveness of the control strategy is illustrated through simulations that exhibit resilience to degradation in actuator performance.