Narcís Palomeras

Girona 500 AUV: From Survey to Intervention

This paper outlines the specifications and basic design approach taken on the development of the Girona 500, an autonomous underwater vehicle whose most remarkable characteristic is its capacity to reconfigure for different tasks. The capabilities of this new vehicle range from different forms of seafloor survey to inspection and intervention tasks.

I-AUV docking and intervention in a subsea panel

While commercially available autonomous underwater vehicles (AUVs) are routinely used in survey missions, a new set of applications exist which clearly demand intervention capabilities: the maintenance of permanent underwater structures as well as the recovery of benthic stations or black-boxes are a few of them. These tasks are addressed nowadays using manned submersibles or work-class remotely operated vehicles (ROVs), equipped with teleoperated arms under human supervision. In the context of the TRITON Spanish funded project, a subsea panel docking and an intervention procedure are proposed. The light-weight intervention AUV (I-AUV) Girona 500 is used to autonomously dock into a subsea panel using a funnel-based docking method for passive accommodation. Once docked, an autonomous fixed-based manipulation system, which uses feedback from a digital camera, is used to turn a valve and plug/unplug a connector. The paper presents the techniques used for the autonomous docking and manipulation as well as how the adapted subsea panel has been designed to facilitate such operations.

Mission control system for dam inspection with an AUV

This paper presents a complete control architecture that has been designed to fulfill predefined missions with an autonomous underwater vehicle (AUV). The control architecture has three levels of control: mission level, task level and vehicle level. The novelty of the work resides in the mission level, which is built with a Petri network that defines the sequence of tasks that are executed depending on the unpredictable situations that may occur. The task control system is composed of a set of active behaviours and a coordinator that selects the most appropriate vehicle action at each moment. The paper focuses on the design of the mission controller and its interaction with the task controller. Simulations, inspired on an industrial underwater inspection of a dam grate, show the effectiveness of the control architecture

A distributed architecture for enabling autonomous underwater Intervention Missions

This work introduces the main aspects related with a new architecture defined for an ongoing research project named RAUVI (i.e. Reconfigurable AUV for Intervention Missions). Two initially independent architectures for the underwater vehicle and the robotic arm have been combined into a new schema that allows for reactive and deliberative behaviours on both subsystems. Reactive actions are performed through a low-level control layer in communication with the robot hardware via an abstraction interface. On the other hand, the intervention mission is supervised at a high-level by a Mission Control System (MCS), implemented using the Petri net formalism. Both, the arm and vehicle perception and control modules communicate with the MCS by means of actions and events. They also share a centralized database where some sensor data is stored. The proposed architecture allows for the supervised execution of intervention missions requiring a tight coordination between the vehicle and the manipulator.

Using petri nets to specify and execute missions for autonomous underwater vehicles

This paper presents the design and implementation of a mission control system (MCS) for an autonomous underwater vehicle (AUV) based on Petri nets. In the proposed approach the Petri nets are used to specify as well as to execute the desired autonomous vehicle mission. The mission is easily described using an imperative programming language called mission control language (MCL) that formally describes the mission execution thread. A mission control language compiler (MCL-C) able to automatically translate the MCL into a Petri net is described and a real-time Petri net player that allows to execute the resulting Petri net onboard an AUV are also presented.

Toward persistent autonomous intervention in a subsea panel

Intervention autonomous underwater vehicles (I-AUVs) have the potential to open new avenues for the maintenance and monitoring of offshore subsea facilities in a cost-effective way. However, this requires challenging intervention operations to be carried out persistently, thus minimizing human supervision and ensuring a reliable vehicle behaviour under unexpected perturbances and failures. This paper describes a system to perform autonomous intervention—in particular valve-turning—using the concept of persistent autonomy. To achieve this goal, we build a framework that integrates different disciplines, involving mechatronics, localization, control, machine learning and planning techniques, bearing in mind robustness in the implementation of all of them. We present experiments in a water tank, conducted with Girona 500 I-AUV in the context of a multiple intervention mission. Results show how the vehicle sets several valve panel configurations throughout the experiment while handling different errors, either spontaneous or induced. Finally, we report the insights gained from our experience and we discuss the main aspects that must be matured and refined in order to promote the future development of intervention autonomous vehicles that can operate, persistently, in subsea facilities.

Real-time mosaicing with two-dimensional forward-looking sonar

Forward-looking sonar can be used for underwater mapping when water visibility is poor. The generation of an acoustic mosaic of the environment is of high interest when underwater vehicles are used for surveys or search tasks. Moreover, if the mosaic is generated in real-time it can be used to provide instantaneous location feedback (e.g. to a ROV pilot or to an AUV), to ensure complete coverage of an area or facilitate the immediate location of targets. In this paper, we present an approach for achieving such a real-time mosaicing capability. Our system considers a simplified imaging model and estimates 2D sonar motions from the pairwise registration of sonar frames. The registration is performed by using a Fourier-based technique, avoiding the extraction of features and ensuring a fast implementation. The mosaicing problem is formulated using a pose graph, with the vertices being the sonar image positions and the edges being constraints from the vehicle odometry and the registration of consecutive and non-consecutive frames. The graph is incrementally optimized using the g2o framework and the optimized poses are then used to build the mosaic online. We apply the method on data gathered on real conditions and show that the resulting sonar mosaic closely matches both the offline generated mosaic as well as ground truth measurements while operating under real-time constraints.

Autonomous I-AUV Docking for Fixed-base Manipulation

Abstract While commercially available autonomous underwater vehicles (AUVs) are routinely used in survey missions, a new set of applications exist demanding intervention capabilities. This is the case, for instance, of the maintenance of permanent underwater observatories or submerged oil wells. These tasks, currently undertaken by remotely operated vehicles (ROVs), can be automated using intervention AUVs (I-AUVs) reducing their complexity and costs. The TRITON spanish funded project proposes the use of light I-AUV for autonomous intervention tasks, such as valve turning or connector pluging/unpluging, in adapted sub-sea infrastructures. To this aim, this paper presents the design and implementation of an I-AUV-friendly sub-sea docking panel, as well as the vision-based autonomous docking procedure for the Girona 500 lightweight I-AUV. The panel implements a funnel-based docking method for passive accommodation. It also includes a T valve and a custom designed hot stab connector. Once docked, the I-AUV and the panel become rigid and basic fixed-base manipulation strategies can be used for manipulation.

Towards a Mission Control Language for AUVs

This paper presents the design and implementation of a Mission Control System (MCS) for an AUV. The mission is easily described using an imperative-like pseudo-code called Mission Control Language (MCL) that allows sequential/parallel, conditional and iterative task execution. MCL can be automatically translated into a Petri net, to formally describe the mission thread of execution. Then the MCS executes the Petri net in real-time over a generic layer that communicates with a particular control architecture using predefined actions and events. Concepts are illustrated with a simple mission.

Coverage path planning with realtime replanning for inspection of 3D underwater structures

We present a novel method for planning 3D coverage paths for inspection of complex structures on the ocean floor (such as seamounts or coral reefs) using an autonomous underwater vehicle (AUV). Our method initially uses an a priori map to plan a nominal coverage path that allows the AUV to pass its sensors over all points on the target structure. We then go beyond previous approaches in the literature by considering the vehicles position uncertainty rather than relying on the unrealistic assumption of an idealized path execution. To this aim, we present a replanning algorithm based on stochastic trajectory optimization that reshapes the nominal path to cope with the actual target structure perceived in situ. The replanning algorithm runs onboard the AUV in realtime during the inspection mission, adapting the path according to the measurements provided by the vehicles range sensing sonars. We demonstrate the efficacy of our method in experiments at sea using the GIRONA 500 AUV where we cover a concrete block of a breakwater structure in a harbor and an underwater boulder rising from 40 m up to 27 m depth. Moreover, we apply state-of-the-art surface reconstruction techniques to the data acquired by the AUV and obtain 3D models of the inspected structures that show the benefits of our planning method for 3D mapping.