Ettore A. de Barros

Development of the Pirajuba AUV

Abstract This work introduces the Pirajuba vehicle, an autonomous underwater vehicle that has been developed at the University of Sao Paulo. The paper describes its main systems, emphasizing hardware and software control architectures. The embedded system is low cost and based on off-the-shelf components, and on free and largely known software tools, like C language, and GNU compiler. Results of preliminary tests in a swimming pool are also presented, demonstrating the real-time operation of the AUV.

Study of autonomous underwater vehicle wave disturbance rejection in the diving plane

Autonomous underwater vehicles operating near the sea surface are subject to wave disturbances in their motion, which can affect severely the data acquisition during the vehicle motion. Bathymetric maps, for example, may suffer a big loss in quality due to such kind of disturbances that can impose oscillations in the vehicle depth and attitude. This article describes a controller structure for compensating the wave disturbances in the vertical plane for a torpedo-like autonomous underwater vehicle, based on a modified version of the linear quadratic Gaussian with loop transfer recovery control combined with a wave filter. The proposed methodology uses additional to the classic linear quadratic Gaussian with loop transfer recovery design the measurement of non-controlled states, such as the pitch rate and heave velocity, in the control action. The wave disturbances were filtered away by a shaping filter fitted to the sea spectrum, and the sensor signals were integrated by an extended Kalman filter. The proposed control methodology was tested against the classical linear quadratic Gaussian with loop transfer recovery controller in a 6-degree-of-freedom non-linear autonomous underwater vehicle simulator, producing a better performance in most demanding conditions such high wave crests. The tests also revealed the impact of the hydroplane geometry on the controller performance, which should not be underestimated by the autopilot designer.

Longitudinal Control of Pirajuba Autonomous Underwater Vehicle, Using Techniques of Robust Control LQG/LTR

Abstract This work presents a study on a robust controller design for the motion on the vertical plane of an AUV at low depths. The LQG/LTR control strategy is proposed for rejecting disturbances originated from sea waves on the depth, attitude and axial velocity of an AUV. The vehicle is an adapted version of the Pirajuba AUV, developed at the Unmanned Vehicles Laboratory, in the University of Sao Paulo. The plant modeling was based on previous studies on manoeuvrability predictions for the AUV, and a simplified model for wave disturbances. Modeling errors for manoeuvring coefficients were considered in the controller design. The validation is based on simulation studies using a set of non-linear equations of motion.

AUV parameter identification

Abstract An extended Kalman filter is used to tackle the problem of parameter identification of an autonomous underwater vehicle (AUV). Since a large number of parameters must be identified, two alternative sub-approaches are investigated. A classical approach seems to have a better performance in cases where a specific parameter will be identified. However, a modified approach guarantees a better identification when dealing with multiple parameters. A sway/yaw mathematical model for an AUV is obtained considering motions in the horizontal plane. Circular and zig-zag maneuvers are tested to assess the identification approaches employed. Results are presented and analysed.

ROV Navigation with Mechanically Scanned Sonar and Inertial Sensors

Abstract The task of navigating a Remotely Operated underwater Vehicles (ROV) during inspection of man-made structures is performed mostly by visual references and occasionally a magnetic compass. Yet, some environments present a combination of low visibility and ferromagnetic anomalies that negates this approach. This paper, motivated by the development of a ROV designed to work on such environment, proposes a navigation method based on data from a mechanically scanned imaging sonar, a Doppler Velocity Log and a gyroscope, combined with prior information about the environment. To perform the data fusion, is used a particle filter that is a nonparametric implementation of the Bayes filter which estimate the states based on the sequential Monte Carlo method. The estimation of the position in this work was restricted to the horizontal plane because the development of the ROV is in the initial stage and so a floating platform was used in its place (since ROVs are usually statically stable on pitch and roll, this is a good approximation). The tests were conducted in a rectangular tank of know size, and the results shows that the propose navigation system can estimates planar position of the vehicle with great precision

Analysis of Identification Methods Applied to Free Model Tests of the Pirajuba AUV

Abstract System identification based methods represent a compromise between accuracy and cost in the estimation of a marine manoeuvring dynamics. However, the use of this kind of approach requires the adoption of a methodology capable of identify satisfactorily the vehicle dynamics, filter away the perturbations that occur during the experiments, and validate the identified model. This paper presents the results of a proposed identification methodology applied to the free model tests of the AUV Pirajuba. In this methodology, deterministic and stochastic identification models are applied to the AUV yaw rate signal of zigzag manoeuvres of several amplitudes, so that the influence of nonlinear effects could be assessed. The estimated models are validated against experimental results from zig-zag manoeuvres and a number of turning manoeuvres. The identified models provide an envelope which includes the vehicles behavior. Such result can be applied to robust identification and control design.

AUV Control in the Diving Plane Subject to Waves

Abstract Underwater vehicles operating near of the sea surface are subject to wave disturbances in their motion, severely affecting the quality of bathymetric maps obtained. This paper describes a controller structure for compensating the wave disturbances in the vertical plane for a torpedo-like Autonomous Underwater Vehicle (AUV), based on a modified version of the LQG/LTR controller methodology with a wave filter. The proposed methodology uses additionally to the classic LQG/LTR design the measurement of non-controlled states, such as the pitch rate and heave velocity, in the control action. The wave disturbances were filtered away by a shaping filter fitted to the sea spectrum, and the sensors signals were integrated by a extended Kalman filter. The proposed control methodology was tested against the classical LQG/LTR controller in a six degrees of freedom non-linear AUV simulator, producing a better performance in most demanding conditions, like high wave crests.

Critical Real-Time Software for an AUV Navigation System

Abstract This work describes the navigation software for the AUV Pirajuba. It is considered a critical real-time system and, therefore it should be developed according to a critical real-time methodology. The methodology proposed was based into five guidelines: development process; norms; operating system tools, application tools, and mathematical tools. The GESAM control architecture is presented for achieving generality, extensibility, safety, reliability, deliberation and reactivity. Inside GESAM, an Extended Kalman Filter was implemented for integrating information from Inertial Measurement Unit, GPS and Compass sensors. Performance tests showed that the system could fulfill requirements using 38.3% of processing consumption.

Modelagem matemática de um giroscópio sintonizado dinamicamente

This work describes the principle of operation and the motion dynamics of a dynamically tuned gyroscope, DTG. The complete set of equations of motion are derived, and a simplified representation for the transfer functions are obtained, emphasizing the concepts related to important parameters, and phenomena that affect the DTG performance.

Arquitetura de controle de uma UV baseada em engenharia de sistemas

Este trabalho apresenta uma arquitetura de controle descentralizada para um AUV desenvolvida com conceitos da engenharia de sistemas para assegurar desenvolvimento paralelo, continuidade do trabalho e sinergia positiva entre os alunos. O primeiro conceito e a modularidade para definir escopos de responsabilidade precisos e pequenos, permitindo que os problemas possam ser identificados e resolvidos durante o desenvolvimento. O segundo e o plano tecnologico, que visa assegurar a disponibilidade dos componentes ao longo do projeto e reduz a diversidade tecnologica, facilitando os aspectos logisticos. O terceiro aspecto e a definicao de interfaces, permitindo o trabalho independente dentro de cada perimetro, respeitando as interfaces, que devem ser o mais simples e precisas possivel. O quarto aspecto e a classificacao funcional para identificar funcionalidades que precisam ser simples e de alta qualidade para proteger a planta enquanto a grande maioria das funcionalidades pode ser desenvolvida com qualidade normal. Essa arquitetura tem os objetivos de ter baixo custo, de ser extensivel e versatil. Baixo custo significa componentes baratos de prateleira, ferramentas gratuitas e amplamente conhecidas de desenvolvimento de software, como linguagem C e compilador GNU, que requerem pouco tempo de treinamento para um estudante de engenharia, o que significa pouco esforco para adicionar novas funcionalidades. Um sistema de controle para veiculos submarinos autonomos (AUV) foi feito e resultados experimentais preliminares sao mostrados.