Effect of a propeller duct on AUV maneuverability

A number of autonomous underwater vehicles, AUV, are equipped with commercial ducted propellers, most of them produced originally for the remote operated vehicle, ROV, industry. However, AUVs and ROVs are supposed to work quite differently since the ROV operates in almost the bollard pull condition, while the AUV works at larger cruising speeds. Moreover, they can have an influence in the maneuverability of AUV due to the lift the duct generates in the most distant place of the vehicle's center of mass. In this work, it is proposed the modeling of the hydrodynamic forces and moment on a duct propeller according to a numerical (CFD) simulation, and analytical and semi-empirical, ASE, approaches. Predicted values are compared to experimental results produced in a towing tank. Results confirm the advantages of the symbiosis between CFD and ASE methods for modeling the influence of the propeller duct in the AUV maneuverability. (C) 2012 Elsevier Ltd. All rights reserved.

Experimental model identification of open-frame underwater vehicles

Most of the works published on hydrodynamic parameter identification of open-frame underwater vehicles focus their attention almost exclusively on good coherence between simulated and measured responses, giving less importance to the determination of “actual values” for hydrodynamic parameters. To gain insight into hydrodynamic parameter experimental identification of open-frame underwater vehicles, an experimental identification procedure is proposed here to determine parameters of uncoupled and coupled models. The identification procedure includes: (i) a prior estimation of actual values of the forces/torques applied to the vehicle, (ii) identification of drag parameters from constant velocity tests and (iii) identification of inertia and coupling parameters from oscillatory tests; at this stage, the estimated values of drag parameter obtained in item (ii) are used. The procedure proposed here was used to identify the hydrodynamic parameters of LAURS—an unmanned underwater vehicle developed at the University of São Paulo. The thruster–thruster and thruster–hull interactions and the advance velocity of the vehicle are shown to have a strong impact on the efficiency of thrusters appended to open-frame underwater vehicles, especially for high advance velocities. Results of tests with excitation in 1-DOF and 3-DOF are reported and discussed, showing the feasibility of the developed procedure.

Numerical analysis of control surface effects on AUV

Computational fluid dynamics, CFD, is becoming an essential tool in the prediction of the hydrodynamic efforts and flow characteristics of underwater vehicles for manoeuvring studies. However, when applied to the manoeuvrability of autonomous underwater vehicles, AUVs, most studies have focused on the de- termination of static coefficients without considering the effects of the vehicle control surface deflection. This paper analyses the hydrodynamic efforts generated on an AUV considering the combined effects of the control surface deflection and the angle of attack using CFD software based on the Reynolds-averaged Navier–Stokes formulations. The CFD simulations are also independently conducted for the AUV bare hull and control surface to better identify their individual and interference efforts and to validate the simulations by comparing the experimental results obtained in a towing tank. Several simulations of the bare hull case were conducted to select the k –ω SST turbulent model with the viscosity approach that best predicts its hydrodynamic efforts. Mesh sensitivity analyses were conducted for all simulations. For the flow around the control surfaces, the CFD results were analysed according to two different methodologies, standard and nonlinear. The nonlinear regression methodology provides better results than the standard methodology does for predicting the stall at the control surface. The flow simulations have shown that the occurrence of the control surface stall depends on a linear relationship between the angle of attack and the control surface deflection. This type of information can be used in designing the vehicle’s autopilot system.

Designing a Computer Vision System for Underwater Robotic Interventions

This thesis deals with the challenging problem of designing systems able to perceive objects in underwater environments. In the last few decades research activities in robotics have advanced the state of art regarding intervention capabilities of autonomous systems. State of art in fields such as localization and navigation, real time perception and cognition, safe action and manipulation capabilities, applied to ground environments (both indoor and outdoor) has now reached such a readiness level that it allows high level autonomous operations. On the opposite side, the underwater environment remains a very difficult one for autonomous robots. Water influences the mechanical and electrical design of systems, interferes with sensors by limiting their capabilities, heavily impacts on data transmissions, and generally requires systems with low power consumption in order to enable reasonable mission duration. Interest in underwater applications is driven by needs of exploring and intervening in environments in which human capabilities are very limited. Nowadays, most underwater field operations are carried out by manned or remotely operated vehicles, deployed for explorations and limited intervention missions. Manned vehicles, directly on-board controlled, expose human operators to risks related to the stay in field of the mission, within a hostile environment. Remotely Operated Vehicles (ROV) currently represent the most advanced technology for underwater intervention services available on the market. These vehicles can be remotely operated for long time but they need support from an oceanographic vessel with multiple teams of highly specialized pilots. Vehicles equipped with multiple state-of-art sensors and capable to autonomously plan missions have been deployed in the last ten years and exploited as observers for underwater fauna, seabed, ship wrecks, and so on. On the other hand, underwater operations like object recovery and equipment maintenance are still challenging tasks to be conducted without human supervision since they require object perception and localization with much higher accuracy and robustness, to a degree seldom available in Autonomous Underwater Vehicles (AUV). This thesis reports the study, from design to deployment and evaluation, of a general purpose and configurable platform dedicated to stereo-vision perception in underwater environments. Several aspects related to the peculiar environment characteristics have been taken into account during all stages of system design and evaluation: depth of operation and light conditions, together with water turbidity and external weather, heavily impact on perception capabilities. The vision platform proposed in this work is a modular system comprising off-the-shelf components for both the imaging sensors and the computational unit, linked by a high performance ethernet network bus. The adopted design philosophy aims at achieving high flexibility in terms of feasible perception applications, that should not be as limited as in case of a special-purpose and dedicated hardware. Flexibility is required by the variability of underwater environments, with water conditions ranging from clear to turbid, light backscattering varying with daylight and depth, strong color distortion, and other environmental factors. Furthermore, the proposed modular design ensures an easier maintenance and update of the system over time. Performance of the proposed system, in terms of perception capabilities, has been evaluated in several underwater contexts taking advantage of the opportunity offered by the MARIS national project. Design issues like energy power consumption, heat dissipation and network capabilities have been evaluated in different scenarios. Finally, real-world experiments, conducted in multiple and variable underwater contexts, including open sea waters, have led to the collection of several datasets that have been publicly released to the scientific community. The vision system has been integrated in a state of the art AUV equipped with a robotic arm and gripper, and has been exploited in the robot control loop to successfully perform underwater grasping operations.

Underwater acoustic networks: the FP7 UAN project

The EU-funded project UAN - Underwater Acoustic Network aims at conceiving, developing and testing at sea an innovative and operational concept for integrating in a unique communication system submerged, surface and aerial sensors with the objective of protecting off-shore and coastline critical infrastructures. A crucial aspect of the project consisted in the use of autonomous underwater vehicles (AUVs) as mobile nodes in the underwater acoustic communication network. In particular, AUVs have the role of adapting the network geometry to the variation of the acoustic channel. This paper reports on the project concept and vision as well as on the progress of its various development phases. The recent at-sea successes that have been demonstrated within the UAN framework are detailed and results of the final UAN project demonstration, UAN11, held in the May of 2011, are reported. The UAN network was in operation for five continuous days with up to five nodes, of which three of them were mobile nodes. © IFAC.

A ROS-based software architecture for a versatile collaborative dual-armed autonomous mobile robot for the manufacturing industry

The industrial context is changing rapidly due to advancements in technology fueled by the Internet and Information Technology. The fourth industrial revolution counts integration, flexibility, and optimization as its fundamental pillars, and, in this context, Human-Robot Collaboration has become a crucial factor for manufacturing sustainability in Europe. Collaborative robots are appealing to many companies due to their low installation and running costs and high degree of flexibility, making them ideal for reshoring production facilities with a short return on investment. The ROSSINI European project aims to implement a true Human-Robot Collaboration by designing, developing, and demonstrating a modular and scalable platform for integrating human-centred robotic technologies in industrial production environments. The project focuses on safety concerns related to introducing a cobot in a shared working area and aims to lay the groundwork for a new working paradigm at the industrial level. The need for a software architecture suitable to the robotic platform employed in one of three use cases selected to deploy and test the new technology was the main trigger of this Thesis. The chosen application consists of the automatic loading and unloading of raw-material reels to an automatic packaging machine through an Autonomous Mobile Robot composed of an Autonomous Guided Vehicle, two collaborative manipulators, and an eye-on-hand vision system for performing tasks in a partially unstructured environment. The results obtained during the ROSSINI use case development were later used in the SENECA project, which addresses the need for robot-driven automatic cleaning of pharmaceutical bins in a very specific industrial context. The inherent versatility of mobile collaborative robots is evident from their deployment in the two projects with few hardware and software adjustments. The positive impact of Human-Robot Collaboration on diverse production lines is a motivation for future investments in research on this increasingly popular field by the industry.

Motion Control of an Advanced Electric Implement for Agricultural Autonomous Vehicles

Nowadays, the development of intelligent and autonomous vehicles used to perform agricultural activities is essential to improve quantity and quality of agricultural productions. Moreover, with automation techniques it is possible to reduce the usage of agrochemicals and minimize the pollution. The University of Bologna is developing an innovative system for orchard management called ORTO (Orchard Rapid Transportation System). This system involves an autonomous electric vehicle capable to perform agricultural activities inside an orchard structure. The vehicle is equipped with an implement capable to perform different tasks. The purpose of this thesis project is to control the vehicle and the implement to perform an inter-row grass mowing. This kind of task requires a synchronized motion between the traction motors and the implement motors. A motion control system has been developed to generate trajectories and manage their synchronization. Two main trajectories type have been used: a five order polynomial trajectory and a trapezoidal trajectory. These two kinds of trajectories have been chosen in order to perform a uniform grass mowing, paying a particular attention to the constrains of the system. To synchronize the motions, the electronic cams approach has been adopted. A master profile has been generated and all the trajectories have been linked to the master motion. Moreover, a safety system has been developed. The aim of this system is firstly to improve the safety during the motion, furthermore it allows to manage obstacle detection and avoidance. Using some particular techniques obstacles can be detected and recovery action can be performed to overcome the problem. Once the measured force reaches the predefined force threshold, then the vehicle stops immediately its motion. The whole project has been developed by employing Matlab and Simulink. Eventually, the software has been translated into C code and executed on the TI Lauchpad XL board.

Supervisão, comando e controlo para sistemas robóticos

Mestrado em Engenharia Electrotécnica e de Computadores. Área de Especialização em Sistemas Autónomos

Sistema de localização de um veículo autónomo terrestre

Mestrado em Engenharia Electrotécnica e de Computadores.

Sistema de controlo de um veículo autónomo terrestre

A crescente necessidade imposta pela gama de aplicações existentes, torna o estudo dos veículos autónomos terrestres um objecto de grande interesse na investigação. A utilização de robots móveis autónomos originou quer um incremento de eficiência e eficácia em inúmeras aplicações como permite a intervenção humana em contextos de elevado risco ou inacessibilidade. Aplicações de monitorização e segurança constituem um foco de utilização deste tipo de sistemas quer pela automatização de procedimentos quer pelos ganhos de eficiência (desde a eficiência de soluções multi-veículo à recolha e detecção de informação). Neste contexto, esta dissertação endereça o problema de concepção, o desenvolvimento e a implementação de um veículo autónomo terrestre, com ênfase na perspectiva de controlo. Este projecto surge pois no âmbito do desenvolvimento de um novo veículo terrestre no Laboratório de Sistemas Autónomos (LSA) do Instituto Superior de Engenharia do Porto (ISEP). É efectuado um levantamento de requisitos do sistema tendo por base a caracterização de aplicações de monitorização, transporte e vigilância em cenários exteriores pouco estruturados. Um estado da arte em veículos autónomos terrestres é apresentado bem como conceitos e tecnologias relevantes para o controlo deste tipo de sistemas. O problema de controlo de locomoção é abordado tendo em particular atenção o controlo de motores DC brushless. Apresenta-se o projecto do sistema de controlo do veículo, desde o controlo de tracção e direcção, ao sistema computacional de bordo responsável pelo controlo e supervisão da missão. A solução adoptada para a implementação mecânica da estrutura do veículo consiste numa plataforma de veículo todo terreno (motociclo 4X4) disponível comercialmente. O projecto e implementação do sistema de controlo de direcção para o mesmo é apresentado quer sob o ponto de vista da solução electromecânica, quer pelo subsistema de hardware de controlo embebido e respectivo software. Tendo em vista o controlo de tracção são apresentadas duas soluções. Uma passando pelo estudo e desenvolvimento de um sistema de raiz capaz de controlar motores BLDC de elevada potência, a segunda passando pela utilização de uma solução através de um controlador externo. A gestão energética do sistema é abordada através do projecto e implementação de um sistema de controlo e distribuição de energia específico. A implementação do veículo foi alcançada nas suas vertentes mecânica, de hardware e software, envolvendo a integração dos subsistemas projectados especialmente bem como a implementação do sistema computacional de bordo. São apresentados resultados de validação do controlo de locomoção básico quer em simulação quer descritos os testes e validações efectuados no veículo real. No presente trabalho, são também tiradas algumas conclusões sobre o desenvolvimento do sistema e sua implementação bem como perspectivada a sua evolução futura no contexto de missões coordenadas de múltiplos veículos robóticos.

Controlo difuso de um AGV

Neste trabalho pretende-se introduzir os conceitos associados à lógica difusa no controlo de sistemas, neste caso na área da robótica autónoma, onde é feito um enquadramento da utilização de controladores difusos na mesma. Foi desenvolvido de raiz um AGV (Autonomous Guided Vehicle) de modo a se implementar o controlador difuso, e testar o desempenho do mesmo. Uma vez que se pretende de futuro realizar melhorias e/ou evoluções optou-se por um sistema modular em que cada módulo é responsável por uma determinada tarefa. Neste trabalho existem três módulos que são responsáveis pelo controlo de velocidade, pela aquisição dos dados dos sensores e, por último, pelo controlador difuso do sistema. Após a implementação do controlador difuso, procedeu-se a testes para validar o sistema onde foram recolhidos e registados os dados provenientes dos sensores durante o funcionamento normal do robô. Este dados permitiram uma melhor análise do desempenho do robô. Verifica-se que a lógica difusa permite obter uma maior suavidade na transição de decisões, e que com o aumento do número de regras é possível tornar o sistema ainda mais suave. Deste modo, verifica-se que a lógica difusa é uma ferramenta útil e funcional para o controlo de aplicações. Como desvantagem surge a quantidade de dados associados à implementação, tais como, os universos de discurso, as funções de pertença e as regras. Ao se aumentar o número de regras de controlo do sistema existe também um aumento das funções de pertença consideradas para cada variável linguística; este facto leva a um aumento da memória necessária e da complexidade na implementação pela quantidade de dados que têm de ser tratados. A maior dificuldade no projecto de um controlador difuso encontra-se na definição das variáveis linguísticas através dos seus universos de discurso e das suas funções de pertença, pois a definição destes pode não ser a mais adequada ao contexto de controlo e torna-se necessário efectuar testes e, consequentemente, modificações à definição das funções de pertença para melhorar o desempenho do sistema. Todos os aspectos referidos são endereçados no desenvolvimento do AGV e os respectivos resultados são apresentados e analisados.

Radar Based Collision detection developments on USV ROAZ II

This work presents the integration of obstacle detection and analysis capabilities in a coherent and advanced C&C framework allowing mixed-mode control in unmanned surface systems. The collision avoidance work has been successfully integrated in an operational autonomous surface vehicle and demonstrated in real operational conditions. We present the collision avoidance system, the ROAZ autonomous surface vehicle and the results obtained at sea tests. Limitations of current COTS radar systems are also discussed and further research directions are proposed towards the development and integration of advanced collision avoidance systems taking in account the different requirements in unmanned surface vehicles.

A New ROV Design: Issues on Low Drag and Mechanical Symmetry

This paper reports the design of a new remotely operated underwater vehicle (ROV), which has been developed at the Underwater Systems and Technology Laboratory (USTL) - University of Porto. This design is contextualized on the KOS project (Kits for underwater operations). The main issues addressed here concern directional drag minimization, symmetry, optimized thruster positioning, stability and layout of ROV components. This design is aimed at optimizing ROV performance for a set of different operational scenarios. This is achieved through modular configurations which are optimized for each different scenario.

Thermographic and visible spectrum camera calibration for marine robotic target detection

Oceans - San Diego, 2013

Multi-robot cooperative stereo for outdoor scenarios

13th International Conference on Autonomous Robot Systems (Robotica), 2013