Alessandro Sperindé

Floating Underwater Manipulation: Developed Control Methodology and Experimental Validation within the TRIDENT Project

This paper presents the control framework that has been proposed and successfully employed within the TRIDENT EU FP7 project, the aim of which is to develop a multipurpose Intervention Autonomous Underwater Vehicle I-AUV exhibiting smart manipulation capabilities, for interventions within unstructured underwater environments. In particular, the work focuses on the exploitation of the highly redundant system for achieving a dexterous object grasping, while also satisfying a set of conditions of scalar inequality type to be achieved ultimately. These represent safety and/or operational-enabling conditions for the overall system itself, such as, for instance, respecting joint limits and keeping the object grossly centered in the camera system. Thus the design of a control architecture exhibiting such a property first required an extension of the classical task priority framework, to be performed in such a way as to also account, in a uniform manner, for inequality conditions to be achieved ultimately. Then, following a description on how such an extension has been made, both simulations and experimental trials are successively presented to show how the developed TRIDENT I-AUV system is able to properly exploit all the redundant degrees of freedom for achieving all the established objectives.

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.

On autonomous cooperative Underwater Floating Manipulation Systems

In this paper we present a novel co-operative control policy purely for the transportation of large objects in underwater environments using two free floating vehicles, each one endowed with a 7 D.O.F redundant manipulator. Due to the presence of harsh conditions in underwater scenarios, it is extremely important to realize algorithms that depend on a minimal amount of explicit information exchanged by the agent, or without any exchange of information at all. To achieve this goal the control policy proposed in the paper only requires the exchange of six numbers at each time instant, while however exhibiting extremely good performances, inspite of the restraints on the information exchange.

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

A Task & Subsystem Priority Based Control Strategy for Underwater Floating Manipulators

Abstract The need for actual autonomy in underwater vehicle is rapidly increasing. Many challenging issues derive from such a trend, one in all the need of controlling the motion of an I-AUV to accomplish complex tasks. To this aim, this work presents a control coordination strategy based on Task Priorities and Dynamic Programming techniques for an I-AUV endowed with a redundant manipulator. The resulting algorithmic structure is able to manage prioritized tasks of both equality and inequality type, while also establishing motion priorities among the composing mechanical subsystems. Simulative results are presented with respect to the floating manipulator which is currently under development within the EU-FP7 funded TRIDENT project.

Analysis of the accuracy of a LBL-based underwater localization procedure

The use of Long Baseline (LBL) systems for localizing underwater vehicles is quite consolidated, as they guarantee a good nominal accuracy, not dependent on the operative depth and almost constant at any point inside the area delimited by the transponders. However the real achievable accuracy can be affected by different factors, mainly related with the knowledge of some environmental parameters (like the speed of sound), the quality of the employed instrumentations, and the level of calibration of the system, after its deployment in water. The paper specifically addresses the accuracy of a LBL-based localization procedure and presents the results of an error budget analysis. For each considered error source, a closed form of the induced localization error is derived and discussed with the intent of enabling the characterization of the real obtainable accuracy within a typical application. The overall study is finally supported and validated by a detailed set of simulative results.

Experimental validation of an acoustic-based localization technique for AUVs in the absence of information on the speed of sound profile

The paper deals with the problem of underwater localization for Autonomous Underwater Vehicles (AUVs) by using a set of acoustic transponders located in known fixed positions. More specifically, the work proposes an effective technique for enabling an AUV to on-line estimate its 3D position, by only employing the measurements of the Time-of-Flights (ToFs) of the signals exchanged with the transponders, without any a-priori information on the Speed of Sound (SoS) of the considered water area. The value of SoS is indeed considered as an additional unknown parameter within the estimation procedure. For any set of received ToFs, a cost function (dependent on the AUV coordinates and the SoS value) is defined and minimized via a standard gradient-descent technique. The optimization process exhibits very good properties in terms of speed of convergence, thanks to the simple structure of the considered cost function. The algorithm has been first tested in a simulated environment and then experimentally validated on an eFOLAGA AUV interrogating four Hydroid transponders.

On cooperation between autonomous underwater floating manipulation systems

This paper describes an unifying control framework which has been proposed and successfully employed within the recently concluded TRIDENT EU FP7 project. It further describes the extension of this proposed framework to dual arm free floating control case (single underwater vehicle with two 7 d.o.f redundant manipulators), and even the more challenging cooperative control of two I-AUVs for the transportation of large objects which is part of the currently ongoing Italian national project MARIS. The paper presents simulation results as well as actual experimental trials showing the effectiveness of this proposed control framework.

A new software architecture for developing and testing algorithms for space exploration missions

In recent years, planet exploration has received an increasing interest due to the possibility of exploiting planet resources and assuring a human–robotic colonized presence on suitable planetary surfaces. These goals can be reached through the development of smart robots, which are able to work on their own and without requiring a constant human supervision but, at the same time, assuring a great level of safety and reliability. To this aim, the development of effective architectures, concerning both software and hardware issues, could represent a great improvement toward this ambitious objective. This paper presents a novel modular architecture called Test Bench for Robotics and Autonomy (TBRA), the main objective of which is to create a test bench for rover autonomy missions where different implementations of a particular subsystem can be easily tested, while keeping the rest of the system unchanged. Thus, it allows the developers to be able to compare the results of tests and understand which version works better. Such architecture has been built on top of the Workframe, a generic middleware for real-time robotics. This two-layered approach allows the final user to deal only with the TBRA interface, which is designed to be extremely simple to use and takes care of most real-time programming problems, while allowing flexibility in the development, maintenance and future extension of the TBRA itself.

A Task Priority and Dynamic Programming Based Approach to Agile Underwater Floating Manipulation

Abstract The present paper deals with a specific part of the activities performed within the currently on going EU-FP7 funded project TRIDENT ( http://www.irs.uji.es/trident ), whose objectives include the development of a multipurpose Intervention Autonomous Underwater Vehicle (I-AUV) exhibiting smart manipulation capabilities within unstructured underwater environments. The considered activities are those developed within WP 5 of the project, aiming to design the functional and algorithmic real-time control architecture (and the relative real-time control software) in charge of coordinating both vehicle and arm motions in a concurrent way; this is done to improve the overall performances via the system agility obtained by reducing at most the need for separate sequential motions, while also guaranteeing the fulfilment of all the enabling and safety system conditions.