Marco Bibuli

Basic navigation, guidance and control of an Unmanned Surface Vehicle

This paper discusses the navigation, guidance and control (NGC) system of an Unmanned Surface Vehicle (USV) through extended at sea trials carried out with the prototype autonomous catamaran Charlie. In particular, experiments demonstrate the effectiveness, both for precision and power consumption, of extended Kalman filter and simple PID guidance and control laws to perform basic control tasks such as auto-heading, auto-speed and straight line following with a USV equipped only with GPS and compass.

Fast in-field identification of unmanned marine vehicles

To design high-level control structures efficiently, reasonable mathematical model parameters of the vessel have to be known. Because sensors and equipment mounted onboard marine vessels can change during a mission, it is important to have an identification procedure that will be easily implementable and time preserving and result in model parameters accurate enough to perform controller design. This paper introduces one such method, which is based on self-oscillations (IS-O). The described methodology can be used to identify single-degree-of-freedom nonlinear model parameters of underwater and surface marine vessels. Extensive experiments have been carried out on the VideoRay remotely operated vehicle and Charlie unmanned surface vehicle to prove that the method gives consistent results. A comparison with the least-squares identification and thorough validation tests have been performed, proving the quality of the obtained parameters. The proposed method can also be used to make conclusions on the model that describes the dynamics of the vessel. The paper also includes results of autopilot design in which the controllers are tuned according to the proposed method based on self-oscillations, proving the applicability of the proposed method.

Integral Line-of-Sight Guidance and Control of Underactuated Marine Vehicles: Theory, Simulations, and Experiments

This paper presents an extensive analysis of the integral line-of-sight (ILOS) guidance method for path-following tasks of underactuated marine vehicles, operating on and below the sea surface. It is shown that due to the embedded integral action, the guidance law makes the vessels follow straight lines by compensating for the drift effect of environmental disturbances, such as currents, wind, and waves. The ILOS guidance is first applied to a 2-D model of surface vessels that includes the underactauted sway dynamics of the vehicle as well as disturbances in the form of constant irrotational ocean currents and constant dynamic, attitude dependent, and forces. The actuated dynamics are not considered at this point. A Lyapunov closed-loop analysis yields explicit bounds on the guidance law gains to guarantee uniform global asymptotic stability (UGAS) and uniform local exponential stability (ULES). The complete kinematic and dynamic closed-loop system of the 3-D ILOS guidance law is analyzed in the following and hence extending the analysis to underactuated autonomous underwater vehicles (AUVs) for the 3-D straight-line path-following applications in the presence of constant irrotational ocean currents. The actuated surge, pitch, and yaw dynamics are included in the analysis where the closed-loop system forms a cascade, and the properties of UGAS and ULES are shown. The 3-D ILOS control system is a generalization of the 2-D ILOS guidance. Finally, results from simulations and experiments are presented to validate and illustrate the theoretical results, where the 2-D ILOS guidance is applied to the cooperative autonomous robotics towing system vehicle and light AUV.

Guidance of Unmanned Surface Vehicles: Experiments in Vehicle Following

Virtual target-based path-following techniques are extended to execute the task of vehicle following in the case of unmanned surface vehicles (USVs). Indeed, vehicle following is reduced to the problem of tracking a virtual target moving at a desired range from a master vessel, while separating the spatial and temporal constraints, giving priority to the former one. The proposed approach is validated experimentally in a harbor area with the help of the prototype USVs ALANIS and Charlie, developed by Consiglio Nazionale delle Ricerche-Istituto di Studi sui Sistemi Intelligenti per lAutomazione (CNR-ISSIA).

Line following guidance control: Application to the Charlie unmanned surface vehicle

A line following guidance solution for underactuated marine systems is presented. The approach differs from other ones known in the literature in the definition of the error variables to be stabilized to zero. The proposed guidance technique has been applied to the Charlie USV (Unmanned Surface Vehicle), developed by CNR-ISSIA Autonomous robotic systems and control group, and experimental results are presented.

PATH-FOLLOWING ALGORITHMS AND EXPERIMENTS FOR AN AUTONOMOUS SURFACE VEHICLE

Abstract This paper addresses the problem of path-following in two-dimensional space, for underactuated surface autonomous robots, defining a set of guidance laws either at kinematic and dynamic level. The proposed nonlinear Lyapunov- based control law yields convergence of the path following error coordinates to zero. Furthermore, the introduction of a dynamic for the target to be followed on the path, removes singularity behaviors present in other guidance algorithms proposed in the literature. Dynamic of the vehicle is then taken into account, applying the Backstepping technique. Some heuristic approaches are then proposed to face the problem of speed of advance adaptation based on path curvature measure and steering action prediction. Finally a set of experimental results of all the proposed guidance laws are presented.

Marine vehicles' line following controller tuning through self-oscillation experiments

This paper demonstrates the use of self-oscillation identification experiments for tuning line following controllers for marine vehicles. Two approaches are described: first, when the controller output is yaw rate and second when controller output is reference heading. In the first case, low level controller is yaw rate while in the second it is heading controller. The identification by use of self-oscillations (IS-O) has been applied to identify the steering equation (for the case of the first controller) and it was used to identify the heading closed loop (for the case of the second controller). The second controller has been tested on different inner loop structures in order to prove the functionality of the method. The IS-O method has been chosen because of its simplicity and applicability in the field (effects of external disturbances are minimized). The methodology was applied to autonomous catamaran Charlie. The results are presented in the paper and demonstrate that the proposed method for identification as well as the developed algorithms give satisfactory performance. All algorithms and results presented here are a result of a joint work of researchers at the Consiglio Nazionale delle Ricerche, Genova and the University of Zagreb.

Underwater Intervention Robotics: An Outline of the Italian National Project MARIS

The Italian national project MARIS (Marine Robotics for InterventionS) pursues the strategic objective of studying, developing and integrating technologies and methodologies enabling the development of autonomous underwater robotic systems employable for intervention activities, which are becoming progressively more typical for the underwater offshore industry, for search-and-rescue operations, and for underwater scientific missions. Within such an ambitious objective, the project consortium also intends to demonstrate the achievable operational capabilities at a proof-of-concept level, by integrating the results with prototype experimental

Performance Indices for Evaluation and Comparison of Unmanned Marine Vehicles' Guidance Systems

Abstract Guidance and control system development for Unmanned Marine Vehicles is a well known and consolidated issue, but a general guideline for quantitatively measuring the performance of robotic systems and comparing them is still lacking in the literature. The importance of establishing standards to follow has become more and more stronger, in particular whenever heterogeneous platforms are employed in a common framework. This work focuses on the definition and exploitation of performance indices for marine robotics applications, paying special attention to path-following tasks. Theoretical formalisations for the considered indices, as well as experimental results proving their effectiveness, are reported.

ILOS Guidance - Experiments and Tuning

Abstract A recently proposed Integral Line-of-Sight (ILOS) guidance law is applied to an underactuated Unmanned Semi-Submersible Vehicle (USSV) for path following of straight lines. Derived from the popular Line-of-Sight guidance, the ILOS methods adds integral action to increase robustness with respect to environmental disturbances such as sea currents, wind and waves that unavoidably affect maritime operations. Integral action makes the vehicle sideslip and hence compensate for the disturbances acting in the underactuated sway direction. Furthermore, the integrator of the ILOS implemented in this paper has embodied, analytically derived, anti-windup properties. It is shown that even if an accurate model of the vessel dynamics is not available, a simple kinematic model and a few test runs give enough information to correctly choose the guidance law parameters. Data from sea trials are presented to verify the ILOS theory and give an experimentally based understanding of the behavior of the USSV when different look-ahead distances and integral gains are used.