Abstract
A nonlinear robust control method for the trajectory tracking of the underwater vehicle and manipulator system that operates in the presence of external current disturbances is proposed using double closed-loop integral sliding mode control. The designed controller uses a double closed-loop control structure to track the desired trajectory in the joint space of the underwater vehicle and manipulator system, and its inner and outer loop systems use integral sliding surface to enhance the robustness of the whole system. Then, the continuous switching mode based on hyperbolic tangent function is used instead of the traditional discontinuous switching mode to reduce the chattering of the control input of the underwater vehicle and manipulator system. In addition, the control method proposed in this article does not need to estimate the uncertainties of the underwater vehicle and manipulator system control system through online identification, but also can ensure the robustness of the underwater vehicle and manipulator system motion control in underwater environment. Therefore, it is easier to be implemented on the embedded platform of the underwater vehicle and manipulator system and applied to the actual marine operation tasks. At last, the stability of the control system is proved by the Lyapunov theory, and its effectiveness and feasibility are verified by the simulation experiments in MATLAB software.
Highlights
The underwater vehicle and manipulator system (UVMS) is a relatively efficient and advanced underwater working tool, which can be applied to underwater tasks such as offshore oil and gas exploration and deep-sea scientific investigation.[1,2] When the UVMS performs highprecision underwater operations, precise control of the position and orientation of the end-effector is important, and the position and orientation of the end-effector are in turn dependent on the orientation and position of the underwater robot and the joint position of the underwater manipulator
The sliding mode controller as another classic robust control method was proposed to solve the problem of robust control of nonlinear systems, which has been widely used in the control of various types of robots.[5,6,7]
A great many researchers have concentrated on the tracking control for UVMS and other underwater vehicles and proposed various advanced control methods and techniques such as adaptive control,[9,10,11,12,13] intelligent control,[14,15,16] and backstepping control,[17,18,19] and more and more promising control strategies can be applied to resolve the problems of motion control of UVMS and underwater vehicles
Summary
The underwater vehicle and manipulator system (UVMS) is a relatively efficient and advanced underwater working tool, which can be applied to underwater tasks such as offshore oil and gas exploration and deep-sea scientific investigation.[1,2] When the UVMS performs highprecision underwater operations, precise control of the position and orientation of the end-effector is important, and the position and orientation of the end-effector are in turn dependent on the orientation and position of the underwater robot and the joint position of the underwater manipulator. The controller can be designed based on an inaccurate mathematical model and rely on the robustness of the controller itself to resist ocean current disturbances Compared with those methods that need online estimation of unknown uncertainties of the UVMS, the computational complexity has been greatly reduced, and it is more convenient to run on the UVMS embedded platform. 1⁄4 1⁄2u; v; w; p; r; q_ 2; q_ 3T denotes the vector of time derivative of the joint space variables of the simplified UVMS model; MðqÞq,Cðq; zÞq, Dðq; zÞq, and Gqðq; I RBÞ represent inertial, the vector of Coriolis and centripetal terms, hydrodynamic damping term, and the vector of buoyancy as well as gravity influence of the simplified UVMS model; tdq denotes the vector of the external disturbances and other unknown dynamics of the simplified UVMS model; tq shows the vector of its control input; and J kq stands for the simplified Jacobian matrix J kq! k ð3Þ where k 1⁄4 1⁄2x; y; z; ; ; q2; q3T is the vector of the joint space variables of the simplified UVMS model; ! 1⁄4 1⁄2u; v; w; p; r; q_ 2; q_ 3T denotes the vector of time derivative of the joint space variables of the simplified UVMS model; MðqÞq,Cðq; zÞq, Dðq; zÞq, and Gqðq; I RBÞ represent inertial, the vector of Coriolis and centripetal terms, hydrodynamic damping term, and the vector of buoyancy as well as gravity influence of the simplified UVMS model; tdq denotes the vector of the external disturbances and other unknown dynamics of the simplified UVMS model; tq shows the vector of its control input; and J kq stands for the simplified Jacobian matrix
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