Underactuated Underwater Vehicles Research Articles

Hybrid-tracked finite-time path following control of underactuated underwater vehicles with 6-DOF

This paper introduces a novel hybrid-tracked finite-time path following control approach for controlling the surge speed and attitude angles of underactuated underwater vehicles with six degrees of freedom (6-DOF). This method integrates 6-DOF line-of-sight (LOS) guidance with nonzero roll dynamics. In kinematics layer, the Rodrigues rotation matrix ensures a unique solution and a slight desired roll angle in LOS guidance calculations. A second-order finite-time differentiator bridges the kinematics and dynamics layers, processing LOS guidance commands and ensuring differential errors converge to zero in finite time. In dynamics layer, a hybrid thrust calculation strategy achieves finite-time convergence of attitude angles in the inertial frame and surge speed in body-fixed frame. Extensive numerical simulations comparing various initial conditions and control strategies demonstrate the superior performance and efficiency of the proposed hybrid-tracked finite-time controller (HTFTTC). The HTFTTC significantly outperforms existing hybrid-tracked backstepping and direct finite-time controllers, reducing the root mean square error of attitude angles or speed by at least 67.2% in steady-state.

Distributed Neurodynamics-Based Backstepping Optimal Control for Robust Constrained Consensus of Underactuated Underwater Vehicles Fleet.

Robust constrained formation tracking control of underactuated underwater vehicles (UUVs) fleet in 3-D space is a challenging but practical problem. To address this problem, this article develops a novel consensus-based optimal coordination protocol and a robust controller, which adopts a hierarchical architecture. On the top layer, the spherical coordinate transform is introduced to tackle the nonholonomic constraint, and then a distributed optimal motion coordination strategy is developed. As a result, the optimal formation tracking of UUVs fleet can be achieved, and the constraints are fulfilled. To realize the generated optimal commands better and, meanwhile, deal with the underactuation, at the lower-level control loop a neurodynamics-based robust backstepping controller is designed, and in particular, the issue of "explosion of terms" appearing in conventional backstepping-based controllers is avoided and control activities are improved. The stability of the overall UUVs formation system is established to ensure that all the states of the UUVs are uniformly ultimately bounded in the presence of unknown disturbances. Finally, extensive simulation comparisons are made to illustrate the superiority and effectiveness of the derived optimal formation tracking protocol.

The Hand Position Concept for Control of Underactuated Underwater Vehicles

The Hand Position Concept for Control of Underactuated Underwater Vehicles

Virtual-Target based Path-Following in the 3D Underwater Environment

This work focuses on the design of a 3D path-following strategy for under-actuated underwater vehicles. The modeling of the problem relies on the Serret-Frenet apparatus, leading to the definition of the position error dynamics, with respect to a generic smooth curve in the operational 3D space. On the basis of such a model, a virtual-target based non-linear guidance law, derived by the exploitation of Lyapunov methodology, is designed. The theoretical proof and simulation results prove the functionality and reliability of the proposed approach.

Adaptive fixed-time containment control of uncertain underactuated underwater vehicles under dynamic event-driven mechanism

This paper presents a dynamic event-driven fixed-time design strategy for the three-dimensional containment control of underactuated underwater vehicles under a directed topology. Our main contribution is the development of a novel error transformation approach based on adaptive multi-leader estimation to address the fixed-time containment (FTC) control problem in the presence of underactuation input and unknown leaders’ velocity. An adaptive FTC control law using stabilizing auxiliary variables and nonlinear filters is constructed based on event-driven conditions. The dynamic thresholds, which depend on containment errors, are presented to efficiently reduce communication resources required for implementing the FTC controller. According to Lyapunov theory, it is shown that the trajectories of the followers converge to the convex hull spanned by multiple leader signals within a fixed time while ensuring the avoidance of the Zeno phenomenon. Finally, the effectiveness of the suggested control approach is verified through simulation results.

Stable nullspace adaptive parameter identification of 6 degree-of-freedom plant and actuator models for underactuated vehicles: Theory and experimental evaluation

Model-based approaches to navigation, control, and fault detection that utilize precise nonlinear models of vehicle plant dynamics will enable more accurate control and navigation, assured autonomy, and more complex missions for such vehicles. This paper reports novel theoretical and experimental results addressing the problem of parameter estimation of plant and actuator models for underactuated underwater vehicles operating in 6 degrees-of-freedom (DOF) whose dynamics are modeled by finite-dimensional Newton-Euler equations. This paper reports the first theoretical approach and experimental validation to identify simultaneously plant-model parameters (parameters such as mass, added mass, hydrodynamic drag, and buoyancy) and control-actuator parameters (control-surface models and thruster models) in 6-DOF. Most previously reported studies on parameter identification assume that the control-actuator parameters are known a priori. Moreover, this paper reports the first proof of convergence of the parameter estimates to the true set of parameters for this class of vehicles under a persistence of excitation condition. The reported adaptive identification (AID) algorithm does not require instrumentation of 6-DOF vehicle acceleration, which is required by conventional approaches to parameter estimation such as least squares. Additionally, the reported AID algorithm is applicable under any arbitrary open-loop or closed-loop control law. We report simulation and experimental results for identifying the plant-model and control-actuator parameters for an L3 OceanServer Iver3 autonomous underwater vehicle. We believe this general approach to AID could be extended to apply to other classes of machines and other classes of marine, land, aerial, and space vehicles.

Robust trajectory tracking control scheme using transformed velocities for asymmetric underactuated marine vehicles

The paper addresses the issue of trajectory tracking control for underactuated underwater vehicles whose model is described by quasi-velocities resulting from the decomposition of the inertia matrix. The control algorithm takes into account unmodeled dynamics and external disturbances. It is shown that such mathematical models can be diagonalized and described by inertial quasi-velocities (IQV). The control scheme consists of a kinematic velocity controller and a dynamic adaptive integral sliding mode control algorithm. The paper extends the concept based on velocity transformation and backstepping methods to systems with a symmetric inertia matrix. A proof of the stability of a closed system in IQV space was carried out. The proposed approach was verified on two 3 DOF models of underwater vehicles with constraints due to the application of thruster force limitations.

Trajectory Tracking Nonlinear Controller for Underactuated Underwater Vehicles Based on Velocity Transformation

This paper proposes an algorithm that performs the task of tracking the desired trajectory for underactuated marine vehicles (primarily underwater) that move horizontally. The control scheme, which takes into account model inaccuracies and external disturbances, was designed using the quantities obtained after the transformation of the dynamic equations of motion resulting from the decomposition of the inertia matrix. This, in turn, led to the equation of dynamics with a diagonal inertia matrix. A specific feature of the offered controller is its dual role. It not only allows tracking the desired trajectory, but at the same time, makes it possible to estimate the impact of dynamic couplings when the vehicle is in motion. Such an approach to the tracking task is important at the initial design stage when the choice of the control algorithm has not yet been decided and experimental tests have not been performed. This is feasible because the new variables after the velocity transformation include not only vehicle parameters, but also actual velocities and forces. Therefore, it is also possible to track the original variables. The theoretical results were followed up with simulation tests conducted on a model with three degrees of freedom for two underwater vehicles.

A Novel 3D Path Following Scheme for a Class of Underactuated Underwater Vehicles with Unconventional Actuation

A 3D path following algorithm involving a novel motion control methodology is investigated for use on a new class of autonomous underwater vehicle (AUV). Unlike standard path following AUV control algorithms for underactuated vehicles, where roll perturbations are avoided, this unconventional algorithm utilizes active roll control to achieve a desired heading. The desired heading is calculated using traditional look-ahead techniques, and is achieved by performing a roll rotation to align the body-fixed yaw plane with the desired heading, and then a yaw rotation is performed to achieve that desired heading. It is demonstrated that this new path following algorithm achieves good tracking results, but experiences complications for increased forward velocities. It is also demonstrated that the complications at higher velocities can be overcome with adaptive adjustment of the look-ahead algorithm parameters.

A Quasi-Velocity-Based Tracking Controller for a Class of Underactuated Marine Vehicles

This paper investigates the trajectory tracking control problem for underactuated underwater vehicles, for which a model is expressed in terms of quasi-velocities arising from the inertia matrix decomposition. The control approach takes into account non-modeled dynamics and external disturbances and is suitable for symmetric vehicles. It is shown that such systems can be diagonalized using inertial quasi-velocities (IQVs). The strategy consists of the velocity controller and two adaptive integral sliding mode control algorithms. The proposed approach, introducing velocity transformation and using backstepping methods and integral sliding mode control, allows trajectory tracking for vehicles in described models with symmetric inertia matrix. Proof of the stability of the closed system was carried out using IQV. The proposed scheme has been verified on two 3 DOF models of underwater vehicles with thruster limitations. A brief discussion of the results is also given.

Numerical Study on Hydrodynamic Coefficient Estimation of an Underactuated Underwater Vehicle

Hydrodynamic coefficient estimation is crucial to the shape design, dynamic modeling, and control of underwater vehicles. In this paper, we conduct a numerical study on the hydrodynamic coefficient estimation of an underactuated underwater vehicle (actuated only in the surge, heave, and yaw degrees of freedom) by adopting the computational fluid dynamics (CFD) approach. Firstly, the mechanical structure of an underactuated underwater vehicle is briefly introduced, and the dynamic model of the underwater vehicle with hydrodynamic effects is established. Then, steady and unsteady Reynolds Averaged Navier–Stokes (RANS) simulations are carried out to numerically simulate the towing test, rotating arm test, and Planar Motion Mechanism (PMM) test of the underwater vehicle numerically. To simulate unsteady motions of the underactuated underwater vehicle, a sliding mesh model is adopted to simulate flows in the computational fluid domain that contain multiple moving zones and capture the unsteady interactions between the underwater vehicle and the flow field. Finally, the estimated hydrodynamic coefficients of the underwater vehicle are validated in a physical experiment platform, and the results show that the numerical estimates are in good agreement with the experimental data.

Application of a Trajectory Tracking Algorithm for Underactuated Underwater Vehicles Using Quasi-Velocities

In this work, an application of the trajectory tracking algorithm proposed in the literature for underactuated marine vehicles is presented. The main difference relies on that here the dynamics of the vehicle are expressed in terms of some quasi-velocities (QV). This fact has a double meaning. First of all, it is shown that using the QV, it is possible to control a vehicle in the absence of one variable because the works related to marine vehicles have only concerned fully actuated systems. In addition, a controller using QV provides information that gives some insight into vehicle dynamics and that is not available in classical equations of motion. The simulations done on two 3-DOF models of different underwater vehicles and using two desired trajectories show performance of the considered control strategy. A discussion of the presented control scheme and selected control approaches from recent years was also conducted, and the benefits of the proposed approach were pointed out.

Distributed event-triggered adaptive output-feedback formation tracking of uncertain underactuated underwater vehicles in three-dimensional space

We present an adaptive-observer-based event-triggered design for distributed three-dimensional output-feedback formation tracking of multiple uncertain underactuated underwater vehicles (UUVs) under a directed network. It is assumed that all nonlinear functions of the vehicle dynamics are unknown and the velocity information of vehicles is immeasurable for feedback. Compared with existing distributed tracking results for UUVs, the primary contribution of this study is the development of a state-transformation-based adaptive observer using a time-varying scaling signal to achieve the output-feedback three-dimensional formation tracking in the presence of unknown nonlinearities and the underactuation constraint. Based on the state transformation, local adaptive observers using neural network approximators and their adaptive laws are designed to estimate local unmeasured velocities of UUV followers. By designing distributed nonlinear error functions and auxiliary stabilizing signals, local output-feedback tracking laws with triggering conditions are recursively constructed to ensure preselected formation performance while solving the underactuation problem of the UUV dynamics. It is shown that the formation tracking errors remain within pre-designable time-varying bounds and finally converge to a neighborhood of the origin. Simulation results are presented to show the effectiveness of the suggested output-feedback formation tracking strategy.

Adaptive neural network control for visual docking of an autonomous underwater vehicle using command filtered backstepping

AbstractThis article proposes an unscented Kalman filter‐based visual docking controller for underactuated underwater vehicles using a position‐based visual servoing (PBVS) approach. The relative pose of an underwater vehicle with respect to a moving docking station is estimated by an unscented Kalman filter with the visual measurements of multiple point features installed on the station. Based on the estimated pose, the Euler angles commands are designed via an integral cross‐tracking docking method to drive the underwater vehicle to move along the desired docking path. Then, an adaptive neural network (NN) controller is designed to track the desired yaw and pitch angles using command filtered backstepping, in which a single‐hidden‐layer (SHL) neural network is employed to compensate for dynamic uncertainties and external disturbances. A barrier Lyapunov function is defined to improve the stability of tracking errors under attitude constraints to ensure the features are in the field of view, and hyperbolic tangent functions are utilized to deal with input saturation. Simulation studies and pool experiments are provided to demonstrate the performances of the proposed visual docking controller.

Simulation-based usability testing of some tracking controllers for underactuated underwater vehicles using simplified criteria

This paper proposes a method for the preliminary verification of known control algorithms designed for tracking the desired trajectory of underactuated underwater vehicles. It is based on simplified criteria for the selection of suitable controllers. Moreover, a certain method for the selection of controller parameters is indicated, which can be effective in the initial analysis of the suitability of selected control schemes. In order to demonstrate the possible application of the described approach, several control strategies known from the literature were selected and numerical tests for them were performed for two 3 DOF models of underwater vehicles with different dynamics. The method given here can be useful for simulation studies at the stage of controller selection without its experimental validation.

Fault diagnosis and reconfigurable control for underwater vehicles

This paper proposes a control framework that can be automatically reconfigured based on the inputs malfunctions in kinetics, with specific application to trajectory tracking control from fully-actuated to underactuated underwater vehicles. The controller design procedure is divided into kinematic and kinetic stages through the backstepping technique. A diagnostic component is introduced to generate fault signals that are robust to model uncertainties and unknown time-varying disturbances by analyzing the boundedness of tracking errors. The diagnostic signals are then utilized by the kinematic controller to replan the referenced velocities. It is proven that the position tracking error can converge to a neighborhood about zero, which can be made arbitrarily small. Simulation and experimental results verify the efficiency of the proposed strategy.

Neural network for 3D trajectory tracking control of a CMG-actuated underwater vehicle with input saturation

This paper considers the trajectory tracking problem of an underactuated underwater vehicle actuated by control moment gyros (CMGs) in three-dimensional (3D) space, with the constraints from input saturation, partial parameter uncertainty and unknown external disturbance. First, utilizing a physical translation of the motion equations, the overall system can be decomposed to an input decoupling system. Then a modified virtual velocity guidance law is derived to transform the tracking error signals into the controllable velocity signals. Subsequently, the Gaussian error function is employed to update the common saturation model. To avoid complex derivations of the virtual control signals, first-order sliding mode differentiator is explored in the dynamic control layer. Then, the adaptive neural network (NN) control method is introduced into the backstepping procedure to account for nonlinear uncertainties and bounded disturbances. Among this, the constrained steering law is used to steer the CMG system to avoid its inherent singularity and fulfill the global tracking control. It is proved that the proposed controller can guarantee all closed-loop signals converge to a small neighborhood of the origin. Finally, two case studies are presented to illustrate the tracking performance of the proposed design.

Nonlinear-Observer-Based Design Approach for Adaptive Event-Driven Tracking of Uncertain Underactuated Underwater Vehicles

A nonlinear-observer-based design methodology is proposed for an adaptive event-driven output-feedback tracking problem with guaranteed performance of uncertain underactuated underwater vehicles (UUVs) in six-degrees-of-freedom (6-DOF). A nonlinear observer using adaptive neural networks is presented to estimate the velocity information in the presence of unknown nonlinearities in the dynamics of 6-DOF UUVs where a state transformation approach using a time-varying scaling factor is introduced. Then, an output-feedback tracker using a nonlinear error function and estimated states is recursively designed to overcome the underactuated problem of the system dynamics and to guarantee preselected control performance in three-dimensional space. It is shown that the tracking error of the nonlinear-observer-based output-feedback control system exponentially converges a small neighbourhood around the zero. Efficiency of the resulting output-feedback strategy is verified through a simulation.

Adaptive prescribed performance tracking control for underactuated autonomous underwater vehicles with input quantization

This paper investigates the adaptive prescribed performance trajectory tracking control problem for underactuated underwater vehicles subjected to unmodeled hydrodynamics, ocean disturbances and input quantization. The controller is synchronized through the command filter-based backstepping design and minimum learning parameter algorithm, thus the adverse effect of “explosion of complexity” and computational complexity inherent in neural network is avoided. To endow tracking errors with prescribed performance guarantees, a mapping function is applied such that the constrained control problem could be transformed to the unconstrained one. By resorting to the hysteresis quantizer, the frequency of data transmission is considerably reduced and the quantization errors are effectively reduced under the proposed control scheme. Through Lyapunov stability analysis, it is verified that the proposed method is capable of ensuring asymptotic stability for tracking errors. Numerical simulation results reveal the advantage and effectiveness of this work.

Adaptive Event-Triggered Control Strategy for Ensuring Predefined Three-Dimensional Tracking Performance of Uncertain Nonlinear Underactuated Underwater Vehicles

This paper presents an adaptive event-triggered control strategy for guaranteeing predefined tracking performance of uncertain nonlinear underactuated underwater vehicles (UUVs) in the three-dimensional space. Compared with the related results in the literature, the main contribution of this paper is to develop a nonlinear error transformation approach for ensuring predefined three-dimensional tracking performance under the underactuated property of 6-DOF UUVs and limited network resources. A nonlinear tracking error function is designed using a linear velocity rotation matrix and a time-varying performance function. An adaptive event-triggered control scheme using the nonlinear tracking error function and neural networks is constructed to ensure the practical stability of the closed-loop system with predefined three-dimensional tracking performance. In the proposed control scheme, auxiliary stabilizing signals are designed to resolve the underactuated problem of UUVs. Simulation results are presented to illustrate the effectiveness of the theoretical methodology.