Jorge Luis Bustamante

A Speed-Gradient Adaptive Control with State/Disturbance Observer for Autonomous Subaquatic Vehicles

In this paper the design of a nonlinear adaptive control system for fully actuated autonomous underwater vehicles in 6 degrees of freedom is presented. Both the positioning and kinematic tracking-problem are dealt with jointly in the adaptive approach. No knowledge about parameters of the vehicle dynamics and hydrodynamics is required beforehand for the design, except only for the thruster dynamics. The adaptation was carried out through a nonlinear speed-gradient adaptive control law. The dynamics of thrusters is considered in the design employing an inverse-dynamics technique and state/disturbance observation. The proof of the asymptotic convergence of the overall controlled system is shown. Selected numerical simulations depict the features of the proposed approach

Guidance of Underwater Vehicles With Cable Tug Perturbations Under Fixed and Adaptive Control Systems

This paper is concerned with the study of guidance of underwater vehicles subject to cable perturbations due to action of currents and harmonic waves. The general case involves a variable cable length that is usually deployed during vehicle tactics. Control situations are considered, namely, trajectory tracking and position regulation when the reference trajectory for the vehicle is given beforehand. To this end, a control system is designed with adaptive features. A great effort is made in this paper for modeling the cable dynamics in a quasi-stationary state. This model can serve the operator to compensate for the perturbation automatically during teleoperation. Moreover, in the adaptive systems, the perturbation is filtered automatically without having to embed the cable model in the controller design. Effects of the cable perturbation on the control system in adaptive and fixed systems are analyzed comparatively. Proofs of convergence to the tracking error to a residual set are given rigorously in the framework of total stability. The features of the controlled behavior are illustrated by numerical simulations in a case study in six degrees of freedom.

On the Presence of Nonlinear Oscillations in the Teleoperation of Underwater Vehicles under the Influence of Sea Wave and Current

The contribution of this paper is the study of nonlinear oscillations of remotely operated vehicles (ROVs) subject to strong currents and harmonic waves when the vehicle is servocontrolled around a fixed position. A complete model for quasi-stationary dynamics of a ship-cable-ROV system was developed. A high-performance control system was designed, in which the cable force is calculated on the basis of measured end positions. Our analysis reveals that the ROV behavior can transit from period one to chaos without the thrusts enter saturation zones. This feature appears more marked as long as the cable stiffness increases. In view of recent results, one can broadly say that the cable elasticity acts as a suppressor of the complete subspectrum of subharmonics in the vehicle dynamics, and simultaneously, as an effective attenuator of its superharmonics.

Adaptive Control for Guidance of Underwater Vehicles

Underwater vehicles are extensively employed in the offshore industry, subaquatic scientific investigations and rescue operations. They are sophisticated mechanisms with complex nonlinear dynamics and large lumped perturbations. They can remotely be operated or eventually autonomously navigate along specified scheduled trajectories with geometric and kinematic restrictions for obstacle avoidance or time-optimal operations (Fossen, 1994). In a wide spectrum of applications, underwater vehicles are generally described by nonlinear and time-varying dynamics. For instance, dynamics with variable inertia and buoyancy arriving from sampling missions or hydrodynamics related to large changes of operation velocity or current perturbations in which laminar-to/from-turbulent transitions are involved in the hydrodynamics. Due to the inherent nonlinear equations of motions, perturbed environments and complex missions, subaquatic vehicles require the guidance by means of complex controllers that usually involve automatic speed controls, dynamic positioning and tracking, and autopilot systems for automatic steering of depth and altitude. It is experimentally corroborated that adaptive techniques may provide superior trajectory tracking performance compared with the fixed model-based controllers (Smallwood & Whitcomb, 2003; 2004). Many different adaptive and robust adaptive approaches for underwater vehicles have been discussed in the literature in the past 15 years to handle uncertainties related to the dynamics, hydrodynamics and external disturbances, see for instance Fossen & Fjellstad, 1995; Hsu et al., 2000, Antonelli et al., 2004; Wang & Lee, 2003; Do et al., 2004. However, the employment of novel high-performance nonlinear control design methodologies like backstepping (Krstic et al., 1995), passivity-based approaches (Fradkov et al., 1999) or sliding modes (Hsu et al., 2000) do not appear in the literature except as incipient applications, see for instance, Do & Pan, 2003; Li et al., 2004; Jordan & Bustamante, 2006; 2007; Conte & Serrani, 1999. From previous theoretic results and some experimental corroborations, it seems that novel adaptive techniques can give rise to an improvement of the global performance in path tracking, above all when more precise manoeuvrability with a high celerity in motion is necessary in a changeable and uncertain subaquatic environment. O pe n A cc es s D at ab as e w w w .in te ch w eb .o rg

Oscillation control in teleoperated underwater vehicles subject to cable perturbations

In this paper a control scheme in fixed and adaptive modus for path tracking of ROVs under perturbations of waves and uniform flow is presented. Particularly, the case of systematic sampling missions at constant depth or altitude with variable cable length are focused in the investigation. A model of the cable perturbation is developed in order to embed it in the controller design. The controller is based on speed-gradient laws in adaptive or fixed modes alternatively. The proposed scheme allows the estimation of the cable perturbation based on a model of force, shape and position of the extremes. Simulations show the presence of nonlinear oscillations particularly in the regulation about fixed positions, where chaotic behaviors can be observed. The paper compares the control performance obtained with and without the estimation of the cable perturbation in both the fixed and adaptive controls. The results are illustrated by means of a case study in six degrees of freedom for both path tracking and regulation.

A Totally Stable Adaptive Control for Path Tracking of Time-Varying Autonomous Underwater Vehicles

Abstract This paper deals with the problem of adaptive path tracking of autonomous underwater vehicles with time-varying dynamics. The controller design is based on a speed-gradient adaptive law. A high-performance control behavior is aimed, so the full actuator dynamics is considered together with that of the vehicle. To this end, a state/disturbance observer is developed in the state feedback employing inverse dynamics. It is proved that the error paths can converge asymptotically to null when only the nonlinear static characteristic of the thrusters is involved in the design. When the actuator dynamics is considered too, only attractivity of the error paths to a residual set can be stated. The framework for this last proof relies on the concept of total stability. One main characteristic of our approach is that it can cope with a wide variety of bounded time-varying parameters with no limitations at all on their rates or a-priori knowledge.

An adaptive control system for perturbed ROVs in discrete sampling missions with optimal-time characteristics

An approach to direct adaptive control and a fast guide system design for 3D path tracking for full actuated ROVs is presented. This combines a speed-gradient algorithm with and optimal-time path following algorithm. The work is oriented to applications of systematic sampling missions on the sea bottom. Here, the perturbed case is treated, in where several disturbances like flow, cable tugs and stepwise mass-variation are assumed acting on the vehicle. The algorithm for optimal- time path tracking is based on the generation of a virtual time that works as independent variable in any smooth geometric reference path, which is previously specified. So, the rate of the virtual time is maximized according to a state-dependent law that pushes the set of thrusts to the limits of saturation without crossing them. A suitable tactics for discrete sampling is developed and simulated together with the proposed adaptive approach.

ON-LINE IDENTIFICATION OF HYDRODYNAMICS IN UNDERWATER VEHICLES

Abstract In this work an algorithm for on-line estimation of the nonlinear hydrodynamics in underwater vehicles is presented. The algorithm is able to estimate physical parameters from natural operation signals. Identifiability and convergence of the parameter trajectories are analyzed. The application of the algorithm to a spherical vehicle is described with numerical simulations.