Pere Ridao

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.

A new FPGA/DSP-based parallel architecture for real-time image processing

In this article, we present a new reconfigurable parallel architecture oriented to video-rate computer vision applications. This architecture is structured with a two-dimensional (2D) array of FPGA/DSP-based reprogrammable processors Pij. These processors are interconnected by means of a systolic 2D array of FPGA-based video-addressing units which allow video-rate links between any two processors in the net to overcome the associated restrictions in classic crossbar systems such as those which occur with butterfly connections. This architecture has been designed to deal with parallel/pipeline procedures, performing operations which handle various simultaneous input images, and cover a wide range of real-time computer vision applications from pre-processing operations to low-level interpretation. This proposed open architecture allows the host to deal with final high-level interpretation tasks. The exchange of information between the linked processors Pij of the 2D net lies in the transfer of complete images, pixel by pixel, at video-rate. Therefore, any kind of processor satisfying such a requirement can be integrated. Furthermore, the whole architecture has been designed host-independent.

On the identification of non-linear models of unmanned underwater vehicles

Abstract This documentation presents a comparison between two identification methods for the off-line identification of non-linear models of unmanned underwater vehicles (UUVs), one based on the minimization of the acceleration prediction error (direct method) and another one based on the minimization of the velocity one step prediction error (integral method). The direct method has already been used in UUVs identification (IFAC Conference CAMs’ 2001, Control Application in Marine Systems, Glasgow, Scotland, UK, 2001). Our new proposal, the integral method, can be applied to a quite general class of non-linear multivariable models and is characterized by an excellent numerical performance. Both methods are compared through their application to the identification of the dynamic model of URIS UUV. Results suggest that better models can be obtained using the proposed method (integral method).

SLAM using an Imaging Sonar for Partially Structured Underwater Environments

In this paper we describe a system for underwater navigation with AUVs in partially structured environments, such as dams, ports or marine platforms. An imaging sonar is used to obtain information about the location of planar structures present in such environments. This information is incorporated into a feature-based SLAM algorithm in a two step process: (I) the full 360deg sonar scan is undistorted (to compensate for vehicle motion), thresholded and segmented to determine which measurements correspond to planar environment features and which should be ignored; and (2) SLAM proceeds once the data association is obtained: both the vehicle motion and the measurements whose correct association has been previously determined are incorporated in the SLAM algorithm. This two step delayed SLAM process allows to robustly determine the feature and vehicle locations in the presence of large amounts of spurious or unrelated measurements that might correspond to boats, rocks, etc. Preliminary experiments show the viability of the proposed approach

Visual inspection of hydroelectric dams using an autonomous underwater vehicle

This paper presents an automated solution to the visual inspection problem of hydroelectric dams. A small autonomous underwater vehicle, controllable in four degrees of freedom (surge, sway, heave, and yaw), is used for autonomously exploring the wall of a dam. The robot is easily programmed using a mission control language. Missions are executed by an intelligent control architecture that guides the robot to follow a predefined path surveying the wall. During the mission, the robot gathers onboard navigation data synchronized with optical imagery, sonar, and absolute navigation data, obtained from a moored buoy equipped with an ultra-short baseline system. After the mission, the images of the wall are used to build a photomosaic of the inspected area. First, image features are matched over the image sequence. Then, navigation data and interimage correspondences are optimized together using bundle adjustment techniques. Thus, a georeferenced globally aligned set of images is obtained. Finally, a blending algorithm is used to obtain smooth seam transitions among the different images that constitute the mosaic, compensating for light artifacts and improving the visual perception of the scene.

Vision-based localization of an underwater robot in a structured environment

This paper presents a vision-based localization approach for an underwater robot in a structured environment. The system is based on a coded pattern placed on the bottom of a water tank and an onboard down looking camera. Main features are, absolute and map-based localization, landmark detection and tracking, and real-time computation (12.5 Hz). The proposed system provides three-dimensional position and orientation of the vehicle along with its velocity. Accuracy of the drift-free estimates is very high, allowing them to be used as feedback measures of a velocity-based low-level controller. The paper details the localization algorithm, by showing some graphical results, and the accuracy of the system.

Recent trends in control architectures for autonomous underwater vehicles

This article describes therecenttrends in controlarchitectures for autonomous vehicles. The study has been carried out on 22 architectures, most of which relate to the field of underwater robotics. The main aim of this article is to show the relationships between these various architectures and to show how developments in architectures for autonomous land vehicles have been extended for use in autonomous underwater vehicles. A summary of important features of the 22 architectures is presented and a new hybrid architecture is proposed for the underwater vehicle GARBI.

Designing a Fuzzy-like PD controller for an underwater robot

Abstract The design of a steering and depth control in terms of course-changing and course-keeping tracking mission and motion of an underwater vehicle is described in this paper. Fuzzy-like proportional derivative (PD) controller is used where the Fuzzy-like part of the controller is optimised based on its structure and parameter design aspects, whereas the scaling factors of the PD part is optimised based on the minimum number of experiments in a real environment. The experiments were planned using Taguchi design of experiments method. The experimental trials and their results are presented and analysed extensively.

Neptune: a hil simulator for multiple UUVs

This paper overviews the field of graphical simulators used for AUV development, presents the taxonomy of these applications and proposes a classification. It also presents Neptune, a multivehicle, real-time, graphical simulator based on OpenGL that allows hardware in the loop simulations.

Grasping for the Seabed: Developing a New Underwater Robot Arm for Shallow-Water Intervention

A new underwater robot arm was developed through intensive cooperation between different academic institutions and an industrial company. The manipulator, which was initially designed to be teleoperated, was adapted for our autonomy needs. Its dimensions and weight were reduced, and its kinematic model was developed so that autonomous control can be performed with it. We compare several commercially available underwater manipulators and describe the development of the new one, from its initial configuration to its mechanical adaptation, modeling, control, and final assembly on an autonomous underwater vehicle (AUV). The feasibility and reliability of this arm is demonstrated in water tank conditions, where various innovative autonomous object-recovery operations are successfully performed, both in stand-alone operation and integrated in an AUV prototype.