Design and experimental validation of a nonlinear controller for underactuated surface vessels
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ORIGINAL PAPER
Design and experimental validation of a nonlinear controller for underactuated surface vessels Wei Xie · Joel Reis · David Cabecinhas · Carlos Silvestre
Received: 15 May 2020 / Accepted: 26 October 2020 © Springer Nature B.V. 2020
Abstract This paper addresses the problem of trajectory tracking control of an underactuated surface vessel moving in a two-dimensional space in the presence of unknown disturbances. In a preliminary stage, a couple of nonlinear observers is derived to obtain an estimate of the perturbations, which are assumed to originate from unmodeled time-varying dynamics and/or exogenous disturbances. Secondly, we resort to the Lyapunov-based backstepping technique to design two stabilizing control laws, governing the thrust force and torque actuations, that are proved to render the overall control system error globally uniformly bounded. Each control law yields an actuator signal which is implicitly bounded with respect to the position error, and the resulting estimation and tracking errors can be made arbitrarily small by tweaking the control parameters. A set of realistic simulations results is presented to validate our strategy. Experimental trials using an autonomous surface vehicle are also showcased to further demonstrate the efficacy and robustness of the proposed controller.
W. Xie · J. Reis · C. Silvestre (B) Faculty of Science and Technology, University of Macau, Taipa, Macau, China e-mail: [email protected] D. Cabecinhas Institute for Systems and Robotics, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal
Keywords Underactuated autonomous vehicles · Robust nonlinear control · Time-varying disturbance observers
1 Introduction The spread of automation steadily pushes forward increasingly more complex robotic operations, which lean on control systems that must be capable of guaranteeing an accurate motion in order to allow for competent decisions, as well as systematic planning. Especially in aquatic environments, which are technically challenging for human-based intervention, autonomous apparatuses play a distinctly useful role. Among a vast literature on this subject, see, for example, the works in [1–5], and references therein. One of the most recurrent needs in marine surveying consists in having a surface or underwater vessel, duly equipped with a set of sensors, describing a predetermined path to, for instance, follow a coastline, inspect off-shore oil-field rigs, or cover a certain surface area within the scope of a bathymetry operation. If, in addition to spatial tracking, there is a required temporal parameterization, then the problem becomes a classic scenario of trajectory tracking, which is still actively researched in the community. Alas, in most robotic systems the number of actuators is lower than the degrees of freedom, which limits the vehicles’ rotational and translational motions. As shown in [6], feasible state trajectories can, however,
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be derived that take into account the nonholonomic constraints
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