Abstract
An adaptive nonsingular fast terminal sliding mode control scheme with extended state observer (ESO) is proposed for the trajectory tracking of an underwater vehicle-manipulator system (UVMS), where the system is subjected to the lumped disturbances associating with both parameter uncertainties and external disturbances. The inverse kinematics for the system is obtained by the quaternion-based closed-loop inverse kinematic algorithm. The proposed controller consists of the modified nonsingular fast terminal sliding mode surface (NFTSMS) and ESO, and the adaptive control law. The utilized NFTSMS can ensure the fast convergence of the tracking errors, together with avoiding the singularity in the derivation. According to the ESO method, the estimation error of the lumped disturbance vector can realize the fixed-time convergence to the origin, along with replacing the sign function with the saturation function to attenuate the chattering. A continuous fractional PI-type robust term with adaptive laws is introduced to handle the unknown bound of the estimation error. The closed-loop system is proved to be asymptotically stable by the Lyapunov theory. Simulations are performed on a ten degree-of-freedom UVMS under four different strategies. Comparative simulation results show that the proposed controller can achieve better tracking performance and stronger robustness of the disturbance rejection.
Highlights
The ocean environment is a potential treasury of resources, including a variety of living creatures, mineral deposits and sustainable energy [1]
Several contributions of this work can be summarized as follows: (1) We propose the quaternion-based CLIKA with replacement of using the Euler-angle form to simplify the inverse kinematics; (2) we design a nonsingular fast terminal sliding mode surface (NFTSMS) that can avoid the singularity, so that the tracking errors can achieve the fast convergence; (3) We modify the extended state observer (ESO) method to estimate the lumped disturbance term of the system, by introducing the saturation function instead of the sign function to alleviate the chattering and (4) we propose a continuous fractional
Incorporating NFTSMS, ESO and adaptive law into the control law, the obtained efforts are taken as the control inputs that can drive both vehicle and manipulator to approximate the reference values
Summary
The ocean environment is a potential treasury of resources, including a variety of living creatures, mineral deposits and sustainable energy [1]. To solve the trajectory tracking problem of an AUV subjected to lumped disturbances, a non-singular fast fuzzy terminal SMC scheme with a disturbance estimator has been addressed [20] It showed that the estimation error of the lumped disturbances can converge to zero in finite time. Several contributions of this work can be summarized as follows: (1) We propose the quaternion-based CLIKA with replacement of using the Euler-angle form to simplify the inverse kinematics; (2) we design a NFTSMS that can avoid the singularity, so that the tracking errors can achieve the fast convergence; (3) We modify the ESO method to estimate the lumped disturbance term of the system, by introducing the saturation function instead of the sign function to alleviate the chattering and (4) we propose a continuous fractional.
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