Niccolò Monni

Preliminary design and fast prototyping of an Autonomous Underwater Vehicle propulsion system

The Mechatronics and Dynamic Modelling Laboratory of the Department of Industrial Engineering, University of Florence, as a partner of THESAURUS (Italian acronym for ‘TecnicHe per l’Esplorazione Sottomarina Archeologica mediante l’Utilizzo di Robot aUtonomi in Sciami’) project, has developed an innovative low-cost, multirole autonomous underwater vehicle, called Tifone. This article deals with the adopted methodologies for the autonomous underwater vehicle design: in particular, the main focus of this study is related to its propulsion system. According to the expected performances and requirements of THESAURUS project, the vehicle has to maintain good autonomy and efficiency (typical features of an autonomous underwater vehicle), with high manoeuvrability and hovering capabilities, which are more common of remotely operated vehicles. Moreover, cooperative underwater exploration and surveillance involve the use of a swarm of vehicles. In particular, the optimization of costs versus benefits is achieved through the design of a fleet of three multirole vehicles. Each autonomous underwater vehicle has five controlled degrees of freedom, thanks to four thrusters and two propellers: in this article, the preliminary design criteria concerning the vehicle and the design and testing of its actuation system are described.

Typhoon at CommsNet13: Experimental experience on AUV navigation and localization

The CommsNet 2013 experiment took place in September 2013 in the La Spezia Gulf, North Tyrrhenian Sea. Organized and scientifically led by the NATO S&T Org. Ctr. for Maritime Research and Experimentation (CMRE, formerly NURC), with the participation of several research institutions, the experiment included among its objectives the evaluation of on-board acoustic Ultra-Short Base Line (USBL) systems for navigation and localization of Autonomous Underwater Vehicles (AUVs). The ISME groups of the Universities of Florence and Pisa jointly participated to the experiment with one Typhoon class vehicle. This is a 300 m depth rated AUV with acoustic communication capabilities originally developed by the two groups for archaeological search. The CommsNet 2013 Typhoon, equipped with an acoustic modem/USBL head, navigated within the fixed nodes acoustic network deployed by CMRE. This allows the comparison between inertial navigation, acoustic self-localization and ground truth represented by GPS signals (when the vehicle was at the surface). The preliminary results of the experiment show that the acoustic USBL self-localization is effective, and it has the potential to improve the overall vehicle navigation capabilities.

An Attitude Estimation Algorithm for Mobile Robots Under Unknown Magnetic Disturbances

Attitude estimation is a crucial aspect for navigation and motion control of autonomous vehicles. This concept is particularly true in the case of unavailability of localization sensors when navigation and control rely on dead reckoning strategies; in this case, indeed, the orientation estimate is also used along with speed measurements to update the position estimate. Among the different approaches proposed in the literature, the de facto state of the art in this field is represented by nonlinear complementary filters: they fuse the measurements of angular rate obtained through gyroscopes, and a measurement of gravity and Earths magnetic field vectors respectively obtained through accelerometers and magnetometers. This paper is focused on an attitude estimation strategy for autonomous underwater vehicles (AUV). The proposed novelty includes the identification of some critical issues that arise when AUV attitude estimation algorithms are applied in practice. They are mainly due to the use of low-accuracy low-cost microelectromechanical systems (MEMS) sensors and on different sources of magnetic disturbances. Some strategies to overcome the identified issues are proposed, including the integration of a single-axis fiber optic gyroscope (FOG) that ensures a considerable performance improvement with a moderate cost increase. The proposed strategies for detection of issues and sensor fusion have been experimentally tested and validated in a real application scenario estimating the attitude of an AUV performing a lawn mower path. The expected performance improvement is confirmed; the obtained results are described and analyzed in this paper.

Thesaurus: AUV teams for archaeological search. Field results on acoustic communication and localization with the Typhoon

The Thesaurus project, funded by the Tuscany Region, had among its goals the development of technologies and methodologies for archaeological search with Autonomous Underwater Vehicles working as a team in exploration missions. This has led to the design and realization of a new AUV class, the Typhoon, on the basis of the archaeological requirements, and of an appropriate acoustic simultaneous communication and localization scheme. The paper describes the project background, the technical characteristics of the Typhoon AUVs, and the field results in acoustic localization as obtained in the CommsNet13 cruise, led by the NATO CMRE (Centre for Maritime Research and Experimentation), to which the Thesaurus project teams of the University of Pisa and Florence took part. In particular, the fields result reports the performance of acoustic localization through on-board USBL communicating with fixed modems placed in initially unknown locations.

Fusing acoustic ranges and inertial measurements in AUV navigation: The Typhoon AUV at CommsNet13 sea trial

The paper presents some experimental results of autonomous underwater navigation, based on the fusion of acoustic and inertial measurements. The work is in the framework of the Thesaurus project, funded by the Tuscany Region, aiming at developing techniques for systematic exploration of marine areas of archaeological interest through a team of Autonomous Underwater Vehicles (AUVs). The test was carried out with one Typhoon vehicle, a 300m depth rated AUV with acoustic communication capabilities, during the CommsNet13 experiment, organized and scientifically coordinated by the NATO S&T Org. Ctr. for Maritime Research and Experimentation (CMRE, formerly NURC), with the participation of several research institutions. The fusion algorithm is formally casted into an optimal stochastic filtering problem, where the rough estimation of the vehicle position, velocity and attitude, are refined by using the depth measurement, the relative measurements available on the acoustic channel and the vehicle surge speed.

Toward underwater acoustic-based simultaneous localization and mapping. Experimental results with the Typhoon AUV at CommsNet13 sea trial

An algorithmic framework and experimental results on acoustic self-localization and mapping for an AUV equipped with an USBL modem are reported. The methodology proposed is quite general and applicable to a wide range of AUV and of navigation needs; however, the results presented refer to the Typhoon AUV and to the experimental configuration as available in the CommsNet13 cruise, led by the NATO S&T Ctr. for Maritime Research and Experimentation. The obtained results show that, even with a low cost, inertial motion units, and in presence of hostile acoustic channel conditions, the approach is able to keep the navigation error bounded and within 3-4 times GPS accuracy.

A low cost Autonomous Underwater Vehicle for patrolling and monitoring

The involvement of autonomous underwater vehicles for patrolling, monitoring or maintenance activities of submersed structures in the coastal strip, harbors or in proximity of off-shore plants (e.g. in oil& gas and military fields), can represent a high benefit for the economy of the related areas. For instance, continuous or more frequent monitoring can be possible, with a reduction of the necessary costs: The use of remotely operated vehicles with the linked implication of support ships and specialized pilots, or the involvement of professional divers, could be avoided or significantly reduced. The paper describes the FeelHippo autonomous underwater vehicles, the vehicle designed and built by the MDM Lab of the University of Florence; it is a low cost autonomous underwater vehicles suitable for these purposes. In particular, an onboard acoustic localization system, based on a low cost approach, has been implemented and preliminary experimental results are here reported.

Underwater Vehicles attitude estimation in presence of magnetic disturbances

An accurate orientation estimation is a primary requirement in autonomous navigation tasks of mobile robots, especially when such operation is involved in the solution of the position estimation problem (e.g. dead reckoning navigation systems). This is the case of Autonomous Underwater Vehicles (AUVs), subject of this paper; for this class of robots, a complete attitude estimation system based on the adaptation of a Nonlinear Complementary Filter (NCF) is proposed. The presented filter fuses the measurements of an Inertial Measurement Unit (IMU) comprising magnetometers. The integration of a single-axis Fibre Optic Gyroscope (FOG) is evaluated to overcome issues due to magnetic disturbances. In addition, a calibration procedure for magnetometers to be exploited within the attitude estimation filter is proposed. The whole system has been experimentally validated and tested on the University of Florence Typhoon AUV; the results prove that the proposed approach allows to obtain a reliable orientation estimate even in the presence of external unpredictable disturbances.

Towards a Robust System Helping Underwater Archaeologists Through the Acquisition of Geo-referenced Optical and Acoustic Data

In the framework of the ARROWS project September 2012 - August 2015, a venture funded by the European Commission, several modular Autonomous Underwater Vehicles AUV have been developed to the main purposes of mapping, diagnosing, cleaning, and securing underwater and coastal archaeological sites. These AUVs consist of modular mobile robots, designed and manufactured according to specific suggestions formulated by a pool of archaeologists featuring long-standing experience in the field of Underwater Cultural Heritage preservation. The vehicles are typically equipped with acoustic modems to communicate during the dive and with different payload devices to sense the environment. The selected sensors represent appealing choices to the oceanographic engineer since they provide complementary information about the surrounding environment. The maini¾?topics discussed in this paper concern i performing a systematic mapping of the marine seafloors, ii processing the output maps to detect and classify potential archaeological targets and finally iii developing dissemination systems with the purpose of creating virtual scenes as a photorealistic and informative representation of the surveyed underwater sites.

Marine Robots in Environmental Surveys: Current Developments at ISME—Localisation and Navigation

Despite the growing interest that marine engineering has received during the past few decades, autonomous underwater navigation can be still considered a daunting task. Unfavourable environmental conditions and limitations on the typologies of available sensors increase the difficulties autonomous vehicles encounter during the execution of planned missions. As of today, one of the main challenges researchers face is the precise localisation of underwater vehicles, where the limitation of the error drift over time becomes extremely important for long navigation missions. In recent years, the authors, within ISME—Interuniversity Center of Integrated Systems for the Marine Environment, extensively worked on autonomous underwater navigation, with special focus on positioning techniques. Working in parallel, research was conducted on the topics of both the improvement of state-of-the-art navigation techniques and on the employment of local sensor networks to periodically reset position errors. This contribution reports the most significative results obtained by the authors during these years.