In this paper, an adaptive nonsingular terminal sliding mode control (ANTSMC) is investigated for attitude tracking of spacecraft with actuator faults. Firstly, a nonsingular fast terminal sliding mode surface is designed to avoid singularity. A finite-time attitude control is developed using nonsingular terminal sliding mode technique, which can make the attitude and angular velocity tracking errors converge to zero in finite time in the presence of uncertainties and external disturbances. Secondly, the total uncertainty is deduced to be bounded. Adaptive laws are incorporated to develop the ANTSMC, removing the restriction on the upper bound of lumped uncertainty. Finite-time convergence of the closed-loop system with ANTSMC is proved using the Lyapunov stability theory. Finally, simulation results are presented to demonstrate the performance of the proposed controllers.

Electrohydraulic loading system is a torque servo system with high-accuracy and high-frequency response. In this paper, an adaptive extended state observer-based flatness nonlinear output control is proposed to improve the torque tracking performance of electrohydraulic loading system. This method combines a flatness concept, expected state, adaptive extended state observer and system output to develop a stable control system. Expected input feedforward based on the flatness property is designed to provide model compensation for bandwidth enhancement. An adaptive extended state observer is proposed to estimate the unmeasured states and the unmodeled dynamics. Based on estimated states and disturbances, state feedback control is developed to ensure the stability of closed-loop system, and to improve torque tracking accuracy and system robustness. The stability of the closed-loop system is proved by the Lyapunov stability theory. Extensive experiments were carried out to verify the performance of high-accuracy tracking of the proposed control strategy.

The paper investigates a modified adaptive super-twisting sliding mode control (ASTSMC) for robotic manipulators with input saturation. To avoid singular perturbation while increasing the convergence rate, a modified sliding mode surface (SMS) is developed in this method. Using the proposed SMS, an ASTSMC is developed for robot manipulators, which not only achieves strong robustness but also ensures finite-time convergence. The boundary of lumped uncertainties cannot be easily obtained. A modified adaptive law is developed such that the boundaries of time-varying disturbance and its derivative are not required. Considering input saturation in practical cases, an ASTSMC with saturation compensation is proposed to reduce the effect of input saturation on tracking performances of robot manipulators. The finite-time convergence of the proposed scheme is analyzed. Through comparative simulations against two other sliding mode control schemes, the proposed method has been validated to possess strong adaptability, effectively adjusting control gains; simultaneously, it demonstrates robustness against disturbances and uncertainties.