Alessio Turetta

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.

A three-layered architecture for real time path planning and obstacle avoidance for surveillance USVs operating in harbour fields

The use of unmanned vehicles in the field of underwater and marine applications is increasing significantly in recent years. Autonomous vehicles (like AUVs and gliders) or teleoperated ones (like ROVs) are currently employed for executing a number of different underwater tasks, like inspecting submerged pipes, executing maintenance interventions on underwater gas- or oil-platforms, collecting environmental or oceanographic data, performing surveys on sites of archeological interest. In parallel with the development of underwater vehicles, unmanned surface vehicles (USVs), are they also witnessing an increasing interest from the robotic community, especially with the goal of performing surveillance applications, like patrolling and maintaining safeguarded against intruders harbours or other “crucial” sites. The potential benefits offered by automated vessels equipped with sensors such as cameras or sonars are quite evident, since they could be used to quickly identify the level of menace of unknown radar track without exposing any human operators to possible threats. However USVs, unlike in the underwater case, have to face the problem of avoiding other vessels which in most cases are manned ones. This is a crucial point especially in that kind of application, where the automated vessel has to move quickly towards a possible menace while at the same time avoiding all the other boats normally operating in the harbour area. Unfortunately, at the current state of art, a reliable methodology to avoid the other vessels and the availability of effective and accurate obstacle detection sensors is still missing. This paper focus its attention on the case of USV used for security applications within a harbour, devising a solution that can be real-time implemented for the obstacle avoidance problem under critical situations where the vehicle as to reach its target as fast as possible while guaranteeing the safety of the other vessels. The presented solution is based on a three layered hierarchical architecture: the first layer computes a global path taking into account static obstacles known a priori, the second layer modifies this path in a locally optimal way (under certain assumptions) exploiting kinematic data of the moving obstacles, while the last layer reactively avoids obstacles for which such data is not available. The paper will be therefore organized as follows: in the first section an introduction and state of art are presented, in the successive section the work will discuss the first layer and the methods for the static obstacles avoidance, while in the third the paper will focus on the moving obstacles and the proposed avoidance algorithm, while also presenting many different detailed simulation results regarding the performances achievable by the overall architecture. Finally a concluding section will also indicate some still open problems and future work directions to be developed.

I-AUV Mechatronics Integration for the TRIDENT FP7 Project

Autonomous underwater vehicles (AUVs) are routinely used to survey areas of interest in seas and oceans all over the world. However, those operations requiring intervention capabilities are still reserved to manned submersibles or remotely operated vehicles (ROVs). In the recent years, few research projects have demonstrated the viability of a new type of submersible, the intervention AUV (I-AUV), which can perform underwater missions involving manipulations in a completely autonomous way. The EU FP7 TRIDENT project is one of the most recent examples of such technological concept. This paper describes the different mechatronic components that constitute the I-AUV developed for the TRIDENT project, their hardware and software integration, and the performance of the vehicle during the project trials.

Coordination and control of multiarm, non-holonomic mobile manipulators

The paper deals with the problem of suitably coordinating the manoeuvring of a non-holonomic vehicle and the motion of a supported manipulation system (composed by one or two arms) when the overall system is commanded to execute a given grasping or manipulation task. The objective being clearly that of suitably exploiting the extra dofs offered by the vehicle for better accomplishing the assigned task in a cooperative way.

TRIDENT: A Framework for Autonomous Underwater Intervention Missions with Dexterous Manipulation Capabilities

TRIDENT is a STREP project recently approved by the European Commission whose proposal was submitted to the ICT call 4 of the 7th Framework Program. The project proposes a new methodology for multipurpose underwater intervention tasks. To that end, a cooperative team formed with an Autonomous Surface Craft and an Intervention Autonomous Underwater Vehicle will be used. The proposed methodology splits the mission in two stages mainly devoted to survey and intervention tasks, respectively. The project brings together research skills specific to the marine environments in navigation and mapping for underwater robotics, multi-sensory perception, intelligent control architectures, vehicle-manipulator systems and dexterous manipulation. TRIDENT is a three years project and its start is planned by first months of 2010.

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.

TRIDENT: Recent Improvements about Autonomous Underwater Intervention Missions

Abstract The need for intervention in underwater environments is significantly increasing in the last years. Possible applications include maintenance intervention in permanent observatories and offshore scenarios, and search & recovery for collecting objects of interest for different application domains like biology, fishery, or marine rescue just to name a few. Nowadays, these kind of tasks are usually solved with “work class” ROVs (i.e. Remote Operated Vehicles) that are launched from support vessels, and remotely operated by expert pilots through an umbilical communications cable and complex control interfaces. These solutions present several drawbacks. Firstly, ROVs are normally large and heavy vehicles that need significant logistics for its transportation and handling. Secondly, the complex user interfaces and control methods require skilled pilots for their use. These two facts significantly increase the cost of the applications. Moreover, the need of an umbilical cable introduces additional problems of control, or range limitation. The fatigue and high stress that users of remotely operated systems normally suffer supposes another serious drawback. All the pointed questions justify the need of more autonomous, cheap and easyto-use solutions for underwater intervention missions, and this is the aim of the current FP7-TRIDENT project. So, in this paper an overview concerning the main research ongoing under this project will be presented and discussed.

Cooperating Auv teams: Adaptive area coverage with space-varying communication constraints

This contribution addresses the problem of area coverage by a team of Autonomous Underwater Vehicle. The case addressed is the one in which the area map is not known in advance but adaptively estimated on-line by the vehicles themselves as they move along the area. The approach proposed is distributed, i.e., the vehicles in the team exchange information among themselves and autonomously take individual decisions on where to move next on the basis of the available information. Communication constraints among the vehicles, in terms of communication range and bandwidth, are explicitly taken into account by the algorithm, and can be dependent by the spatial position in the covered area. The paper proposes a series of algorithms for adaptive sampling with communication constraints in which the communication constraints are expressed in terms of connectivity of the graph of the vehicles. Depending on the structure of the graph (ordered serial graph, ordered tree graph, etc.) the algorithms take the structure of a distributed dynamic programming approach or of minimum spanning tree graph searching.

A Computationally Distributed Self-Organizing Algorithm for the Control of Manipulators in the Operational Space

The present work deals with manipulator arms characterized by the presence of an internal, totally distributed, embedded control system. More specifically, every single joint is assumed to be equipped with a simple local processing unit devoted to properly drive its motion, thus allowing to consider each pair constituted by a single joint and the associated link as a defective “1-dof-only”, separately controlled, atomic manipulator. In this perspective, the paper proposes an effective, computationally distributed, control technique that, based on a repeated data exchange among the processing units, establishes a global self-organizing behaviour among the joints which allows to control the motion of the end-effector of the overall arm in the operational space, by solely exploiting the control capabilities of every local processing unit, while not requiring any centralized global knowledge about the overall arm geometry and kinematics.

Embedded FPGA-based control of a multifingered robotic hand

This paper describes the most significant design issues related with the development of an embedded FPGA-based control system for a human-like robotic hand. Specific features of the mechanical design of the system are discussed firstly, then a general approach to the problem of controlling the motion of the robotic device is provided. Finally a candidate distributed control architecture is presented.