Enrica Zereik

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.

Agility for underwater floating manipulation: Task & subsystem priority based control strategy

The need for actual autonomy in underwater robotic systems is rapidly increasing. Many challenging issues derive from such a trend, one in all the requirement of coordinately controlling the motion of an underwater floating I-AUV endowing a robotic arm, to accomplish complex manipulation tasks. This work is aimed to present a strategy based on the prioritization of tasks of equality and inequality type, once combined with Dynamic Programming techniques, for coordinately controlling the motion of such I-AUV. A general algorithmic framework is developed and simulative results supporting its resulting effectiveness are presented.

A real-time mosaicking algorithm using binary features for ROVs

This article presents a real-time mosaicking algorithm based on a SLAM framework. The mosaic of the seafloor can be useful in real time for a ROV operator that is piloting the ROV. Two important aspects arise in this kind of work: data association and computational time. In order to solve the first one, a combination of SURF features and template correlation methods is used. To minimize the computational time, a very recent approach in the domain of feature description is used: BRIEF binary features. Finally, to be able to update the whole mosaicking in a fast and easy way, local mosaics are used instead of a global one. The algorithm was tested using data collected in a typical experiment and the results show the improvement with respect to previous versions of a similar algorithm.

Space robotics supporting exploration missions: vision, force control and coordination strategy for crew assistants

Many research activities are being carried out about space exploration missions, in order to strongly improve man’s working conditions in planetary environments. Along this line, this work presents some results obtained within the development of an effective robotic crew assistant. This robot can execute a number of operations, both in a completely autonomous manner (i.e. without requiring human supervision) and in a strict cooperation with the astronauts; thus supporting and helping them in executing operations otherwise very difficult or unfeasible to be accomplished. The developed and then adopted functional and algorithmic control architecture for the considered robot assistant, also including vision and force feedback, is described with some details in the present paper.

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.

A collision avoidance algorithm based on the virtual target approach for cooperative unmanned surface vehicles

This paper presents a collision avoidance algorithm based on the virtual target path-following guidance technique, developed for Unmanned Surface Vehicle (USV) multiagent frameworks. The proposed collision avoidance procedure is integrated with the distributed guidance module already developed for cooperative and coordinated navigation of USVs, in particular with Cooperative Path Following and Wingman-based coordination scheme. A basic integration of the collision avoidance system with the COLREGS “Rules of the Road” is proposed too. Results of the overall collision free cooperative system are then presented.

Swarm-based path-following for cooperative unmanned surface vehicles

This article proposes a swarm-based path-following guidance system for an autonomous marine multi-vehicle system. In particular, a team of unmanned surface vehicles is required to converge to and navigate along a desired reference path, while at the same time aggregating and maintaining a range-based formation configuration. First, a separate description is given for a swarm methodology, initially developed for small ground mobile robots and exploited to aggregate the robot team, and a virtual target–based path-following guidance system developed for unmanned surface vehicles, exploited to drive not the single vehicles but the robot formation as a whole. Then, the integration of the two proposed methodologies is reported and proven, in order to guarantee the feasibility and stability of the overall guidance framework. Simulative results are proposed to validate the effectiveness of the proposed methodology and to evaluate the system performances.

Jacobian Task Priority-Based Approach for Path Following of Unmanned Surface Vehicles

Abstract As marine robotics becomes more and more effective and useful for many real applications, control techniques too must be gradually enhanced in order to answer to the arising need of full autonomy for such vehicles. Hence more advanced control algorithms are currently under-development in the marine robotics community in order to accomplish many tasks with more robustness and reliability. In particular, the present work addresses the path following problem, applying the control paradigm of prioritized tasks, usually exploited for robotic manipulators. Such a technique, besides allowing to keep separate the different tasks, thus getting an “emergent behavior” for the vehicle, also provides the ability to easily add further control tasks without changing the architecture. In the present paper the case of two simple tasks allowing the completion of a path following mission, as well as the vehicle velocity regulation, is dealt with and some simulative results are described.