1,720,981 research outputs found
Adaptive steering control for an azimuth thrusters-based autonomous vessel
No full textThe proposed paper presents the design and development of the combined guidance and control strategies for the autonomous navigation of unmanned vessels characterised by azimuth-based thrust architecture. Autonomous marine vehicles (AMVs) are consolidated technological tools commonly employed for different tasks such as exploration, sampling and intervention. With the final aim of autonomous shipping, the AMVs capabilities have to be migrated and adapted towards the reliable and safe control of commercial-like unmanned vessels. These last are spreading thanks to a number of technological research projects. The employment of unconventional hull shapes combined with propulsive layout based on azimuth thrusters requires robust guidance techniques to provide precise and reliable motion control during navigation. The paper introduces a dual-loop guidance and control scheme able to provide advanced navigation capabilities. An inner control loop, devoted to the actuation of the azimuth thrusters, allows the tracking of reference course angle (namely the autopilot). Such a control loop is characterised by a modified PD regulation scheme, where a novel adaptive derivative component is inserted in order to improve the convergence curve towards the required course reference. The outer guidance loop, based on Lyapunov and virtual-target approach, allows the vessel to track generic desired paths, thus enhancing the autonomous navigation capabilities. The paper will provide a deep design and analysis approach for the developed techniques, as well as simulation results of the combined guidance and control scheme, proving the reliability of the proposed approach in different operative conditions
Design of an obstacle detection system for marine autonomous vehicles
No full textThe need for the transfer of robotic technology from the research laboratories to civilian applications is now a major issue for the robotic community. In the field of marine robotics is particularly important to endow the robot with a safe and highly reliable Navigation Guidance and Control (NGC) system which enables the Unmanned Surface Vehicle (USV) to safely navigate even in presence of human activities such as commercial and recreational traffic, swimmers, rowers, etc. A key aspect to achieve a safe autonomous navigation is the ability of the robot to recognize well in advance the presence of an unexpected, potentially moving, obstacle. This function represents the base brick for the development of a collision avoidance systems smart enough to reactively detect unexpected obstacles and perform the necessary avoidance maneuvers to safely prevent collisions. The present paper describes the design of an a innovative obstacle detection sensor, combining both passive and active optical devices and based on a new concept of optronic system. It is specifically conceived for collision avoidance tasks in marine environments, designed to be easily mounted on small-medium sized USVs. Its innovation consists in the interaction between the different integrated sensors, that are in fact totally decoupled. The paper presents the functional architecture of the object detection sensor together with the preliminary mechanical design. Moreover some experimental data collected by the sensor are reported, and some simulations, highlighting the ability of the system to detect and correctly avoid both still obstacles and mobile traversing obstacles, are shown
e-URoPe: a reconfgurable AUV/ROV for man-robot underwater cooperation
No full textThis work describes the new Unmanned Marine Vehicle e-URoPe developed by CNR-ISSIA. This Remotely Operated Vehicle is realized using the most innovative technical capabilities in order to achieve a fexible structure, adequate to withstand external impacts. The peculiar characteristics of the vehicle, on which is based the design concept, are: easiness of construction, facility of re-confguration and fexibility. Furthermore the vehicle could be completely modifed without big eforts in terms of money and time. The vehicle can be equipped with diferent types of sensors in order to make it fexible and adaptable to various applications such as sampling of water or objects, underwater manipulation, cooperation with underwater operators or with other underwater vehicles, mapping of underwater ground and detection of vegetation lying on the seabed
Advance Speed-Hull-Pump-Jet Interactions in Small ASV
Full text linkThis paper is related to the technological development of an innovative small-size Autonomous Surface Vehicle designed to meet the requirement of accessing, monitoring and protecting the shallow waters peculiar of the Wetlands.The first prototype of a fully electric, modular, portable, lightweight, and highly-controllable Autonomous Surface Vehicle (ASV) for extremely shallow water and remote areas, namely SWAMP, was developed by CNR-INM and DITEN-Unige. This catamaran is equipped with four azimuth Pump-Jet Modular (PJM) actuators designed for small-size (1 to 1.5 m long) ASV. The main advantage of Pump-Jet thrusters is that they are flush with the hull, thus minimizing the risks of damages due to possible grounding. This system is used to increase the manoeuvrability in narrow spaces and to increase the spacial resolution by allowing the access also in extremely shallow waters with smaller risk of loosing manoeuvrability. The knowledge of the hydrodynamic characteristics of the thruster and of the vessel allows to partly or fully identifying the vessel for a better controllability. With this aim a series of tests have been conducted in the DITEN towing tank. In particular advance resistance on the SWAMP hull in deep and shallow water, bollard pull and self-propelling tests with the Pump-Jet Module working have been carried out. The results of the tests with the effects of advance speed on the PJM performance is reported in this paper together with the description of the modelling of the thruster itself
Towards Posidonia Meadows Detection, Mapping and Automatic recognition using Unmanned Marine Vehicles
No full textThis paper reports the development of a new methodology for automatic detection and mapping of underwater vegetation by means of highly autonomous marine robotic platforms. In particular, the work describes the exploitation of a Remotely Operated Vehicle (ROV), equipped with a multi-parametric sensors package, for the exploration and characterization of sea-bottoms interested by the presence of the Posidonia oceanica seagrass, which represents a valuable indicator of the environmental health. The proposed methodology relies on the systematic exploration of the sea-bottom by means of the ROV acquiring acoustic data and video imagery of the seabed, in order to reconstruct a 2.5D model of the environment (i.e. an elevation map of the sea-bottom). The data collection is achieved by the employment of a single beam echosounder for seabed range measurements and a down-looking underwater camera. Furthermore, an acoustic data procedural analysis is developed to automatically detect the Posidonia presence, so that in future works it will be possible to operate also in low-visibility conditions. Data acquisition was carried out over different seafloor types in coastal area near Biograd Na Moru (Croatia) and the results are reported in the paper
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Practical Experience towards Robust Underwater Navigation
No full textAutonomous underwater operations require robust and accurate navigation capabilities, a basic requirement for both precise position and velocity estimation, as well as motion compensation and geo-referencing of exteroceptive sensor data. A great number of theoretical approaches to sensor fusion and filtering can be found in literature, but they have to be matched with practical issues such as multi-rate sampling, measurement glitching, environmental conditions. For these reasons, the preparation, tuning and exploitation of navigation systems require different development steps to achieve reliability and robustness. This paper reports the practical experience of the exploitation of a multi-module extended Kalman filter based navigation system employed on the e-URoPe AUV/ROV. The paper shows the results of motion estimation including linear velocity and position (both horizontal and vertical), as well as angular position and rate. The proposed navigation system relies on the measurement fusion gathered by a variety of sensors: USBL, DVL, FOG, AHRS, depth-meter, GPS (when surfaced). The paper provides experimental proof and ground-truth of the proposed framework
U-swath: An innovative usv design towards the extended ship
No full textMaritime sector is facing a fast increasing in combining innovative aspects with marine operations especially for what regards cooperative operations and environmental monitoring and protection. In this scenario CNR-INM developed a large size innovative Unmanned Marine Vehicle (UMV) named U-SWATH (Unmanned Small-waterplane-area twin hull). The vehicle was studied for extending the unmanned marine operations both cooperating with a mother ship or with other unmanned vehicle like UAV (Unmanned Aerial Vehicle) and UUV (Unmanned Underwater Vehicle) also by providing launch, recovery and reload systems for these vehicles. Char-acterised by a modular structure, U-SWATH is expressly addressed to multi-purpose applications that include sampling and monitoring of environmental parameters in coastal, protected and dangerous waters,seabed mapping and monitoring, chemical-biological on-board analysis, first emergency monitoring for oil-spill, patrolling and civil protection, testing of new technologies and tools. The use of high-tech like U-SWATH is nowadays considered a need for both ordinary and uncommon operations at sea. The envision for U-SWATH is to enhance precision in data collection and increase their spatial resolution with a reduction of the costs of the surveys. For this reason a SWATH non-conventional design was chosen to ensure excellent seakeeping and good efficiency thus increasing the time and precision of the surveys. To increase the flexibility of U-SWATH each of the two submersible hulls is composed of modular and interchangeable elements that can be outfitted with different payloads, equipment, propulsive or manoeuvring elements. An innovative navigation and guidance control was studied in combination with a propulsion layout based on new azimuthal thrusters to increase the survey ability and the cooperation abilities
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