Tracking control of an autonomous tethered underwater vehicle (ATUV) for a successful marine operation is a challenging task due to the complex and nonlinear dynamics of the vehicle characterized by parametric uncertainties. Besides these issues, the vehicle mainly operates in an uncertain and unpredictable environment. To deal with the ATUV control tracking problem, this article proposes a new tracking control approach that will be named saturation-based adaptive computed torque+ (SACT+). The proposed SACT+ is designed using a variable saturation function, a computed torque structure, a saturation-based dynamic feedback, and an adaptive mechanism. Then, several arguments, based on the well-known Lyapunov techniques, are proposed to prove the stability behavior of the final closed-loop dynamics. This ensures the convergence (theoretically) of the vehicle tracking error to the origin, leading to stable and safe operations. However, this tracking error (experimentally) only stays around the origin due to many factors, such as the measurement noise from the vehicle’s sensors, the inherent uncertainties of the vehicle combined with external disturbances from the marine environment, etc. Different tests are conducted in real-time using our underwater vehicle Leonard prototype to validate the proposed SACT+. The obtained experimental results show the effectiveness and robustness of the proposed SACT+ approach in real-life cases. Finally, the performance and energy consumption indices, as well as comparative experimental studies with two well-established controllers (from the literature), confirm the relevance of the proposed approach for controlling small-sized and/or low-cost underwater vehicles.

Many operations performed by work class Remotely Operated Vehicles (ROVs) require the manipulation of heavy loads. An example is the manipulation and grouting of armour stones. A way to increase the working capabilities of the ROV is to introduce cables among the set of actuators. The cable lengths and tensions are controlled by winches placed on the vehicle. Being similar to a cable-driven parallel robot (CDPR), the resultant system inherits some advantages such as the possibility to generate large forces over a large workspace and the possibility to use CDPR techniques to estimate the pose of the ROV. This paper proposes a complete control architecture for the Hybrid Cable-Thruster actuated ROV (HCT-ROV) and analyzes, in computer simulations, the performances of such a system while it performs real world operations, such as heavy lifting and hovering in presence of water current.

This paper deals with the dynamic modeling and identification of an electrically driven underwater robot manipulator. The proposed study includes the dynamic modeling of the actuators of the arm as well as the identification of the parameters of the model. The proposed method deals with the specific case of heterogeneously actuated arms, namely arms with actuators behaving differently for each joint, being considered at the kinematic level. Indeed, we show how to estimate the arms parameters when some of their revolute joints are directly actuated by geared motors, while the others are actuated by linear actuators. A minimum set of identifiable parameters is determined, and adequate excitation trajectories are generated and used in the identification procedure. Realtime experimental validation on the manipulator arms of Ifremer's HROV (Hybrid Remotely Operated Vehicle) Ariane underwater vehicle demonstrates that the proposed method improves the estimation of the dynamic model.

Traditional underwater vehicle-manipulator systems (UVMS) consist mainly of an underwater vehicle on which a manipulator is mounted. In addition to the vehicle thrusters, this paper proposes to use cables to actuate UVMSs. The main goal of this extra source of actuation is to enhance UVMS work capabilities. Similarly to cable-driven parallel robots, the cables are attached to the UVMS and a set of fixed winches permit the control of the cable lengths or tensions. We refer to this new system as a hybrid cable-thruster (HCT)-actuated UVMS. Based on the kinematic and dynamic model of HCTactuated UVMSs, this paper focuses on the determination of the available set of end-effector forces in a suitable mathematical representation. An illustrative simple planar example of HCTactuated UVMS is also presented.

This paper presents the design and experimental implementation of an ℒ1adaptive control on a tethered underwater vehicle. This controller, well known for its fast adaptation and its robustness, is proposed to be applied for the first time in the field of underwater vehicles control. This paper summarizes the implementation and experimental results obtained on a modified version of the AC-ROV underwater vehicle. Various experimental scenarios are presented to illustrate the ability of the ℒ1adaptive law not only to successfully control pitch and depth (even with strong modeling uncertainties), but also to be efficient towards disturbances like waves or buoyancy changes.

Navigation of autonomous underwater vehicles (A.U.V.) in very shallow waters implies acoustic detection. In single beam sonar systems, sound emitted by ultrasonic transducers is diffracted and secondary lobes appear. Considering the sea bottom's backscattering properties, secondary lobes can be used to enhance knowledge of seabed features such as slope, and marked variations. In this paper, we firstly consider characteristics of electro-acoustic transducers and study the resulting acoustic diffraction. Then, we introduce a new method aiming to extract seabed features from the received acoustic echo. Thus, single beam sonar systems can be used for bottom tracking purposes. We present the results of our simulations and experimental validation.

This paper introduces a method aiming to allow underactuated autonomous underwater vehicles navigating in an unknown environment to avoid underwater cliffs. Three electro-acoustic transducers situated in the front part of the vehicle provide bathymetric data. In this article we detail the method adapted to an irregular seabed, i.e., with substantial changes in depth like underwater cliffs. The obtained trajectories respect the dynamic constraints of the vehicle. We also explain how to choose the orientation angle of transducers in order to optimize the quality of seabed following. Our method was validated with the hydrodynamic simulator of the "Taipan" vehicle, which is our laboratory's autonomous underwater vehicle prototype.

We present a theoretical study of the coordination of the geometrical movements of one flotilla of autonomous underwater vehicles. We make the assumption that the flotilla must move by respecting geometrical constraints of forming which we indicate by the term of geometrical constellation. Under this hypothesis, every vehicle has to follow a trajectory so that the whole flotilla forms a desired geometrical figure. We make depend this geometrical constellation of the state vector of each vehicle. All the time, if this constellation is not realized, it is then possible to compute the deformation between the real constellation of the flotilla and a desired constellation. From this deformation, we compute the movement that every vehicle should make to obtain a regulation around zero of the deformation. The control of the flotilla should be compatible with the possibility for every vehicle, to realize obstacle avoidance We use an approach called the "deformable virtual zones", and show that all these constraints can be resolved in a homogeneous way and supply a command vector for each vehicle.