Sebastião Cícero Pinheiro Gomes

Tracking System for Underwater Inspection Using Computer Vision

Nowadays, the ocean plays a fundamental role in the global economy, mainly due to oil extraction industry. It makes this environment be populated with human-made structures that needs to be inspected and maintained. In this context, this paper details a system for on-line detecting an underwater cable-like target using computer vision algorithms. It makes able an underwater vehicle to tracking this target. Together with an automatic control, this system could be used to assist a human operator during inspection tasks. This work is concluded with a series of tests and analyses aiming to the system validation.

SLAM in Underwater Environment Using SIFT and Topologic Maps

The use of autonomous underwater vehicles (AUVs) for visual inspection tasks is a promising robotic field. The images captured by the robots can also aid in their localization/navigation. In this context, this paper proposes an approach to localization and mapping problem of underwater vehicle. Supposing the use of inspection cameras, this proposal is composed of two stages: i) the use of computer vision through the algorithm SIFT to extract the features in underwater image sequences and ii) the development of topological maps to localization and navigation. The integration of such systems will allow simultaneous localization and mapping of the environment. A set of tests with real robots was accomplished, regarding online and performance issues. The results reveals an accuracy and robust approach to several underwater conditions, as illumination and noise, leading to a promissory and original SLAM technique.

Adaptive Neuro-Fuzzy Friction Compensation Mechanism to Robotic Actuators

This paper presents a non-linear friction compensation mechanism using a combination of neural network (NN) with fuzzy system (neuro-fuzzy compensator), applied to harmonic-drive robotic actuators. The friction compensation torque is constituted by NN output, which is trained off-line. Since the friction changes significantly over time, temperature and equipment operational conditions, the NN loses its performance. To recover this performance, a fuzzy algorithm is proposed to deal with the variation friction parameters. The output of the fuzzy algorithm is a gain that multiplied by the NN output will adjust the friction compensation torque. Experimental results have shown the efficiency of the proposed mechanism.

Um novo algoritmo para a modelagem dinâmica de manipuladores flexíveis

Active control law development of flexible structures is still an open problem. It has been the object of many researches, mainly starting from the eighties. In spite of many works dedicated to the dynamic modeling of such structures, the obtaining of a realistic dynamic model is of fundamental importance for the control law development. In the present work it is introduced a new algorithm to determinate in a quite simple way, the dynamic differential equations of a one flexible link manipulator. It is still developed analytic transfer functions for this specific problem, which are important for the validation of the lumped mass approach model proposed in the form of an algorithm.

Cable Dynamic Modeling and Applications in Three-Dimensional Space

Dynamic modeling of cables in three-dimensional space is a problem with great difficulty and complexity. This article discusses a new dynamic modeling formalism, including applications in the underwater environment. It is assumed that the cable is formed by rigid links connected by elastic fictitious joints, allowing elevation, azimuth and torsion movements. Algorithms have been developed to automatically generate the dynamic model for any number of links selected for the discrete approximation of the flexible structure. Three practical situations are tested: cable out of the water with free terminal load; underwater considering dynamics with or without ocean current; with terminal load fixed to the seabed. Constraint forces obtained through proportional and derivative control were applied to the terminal load to fix it to the seabed. The algorithms were determined from the Euler-Lagrange formalism, and in all situations the simulations showed physically consistent results.

AUTOMATIC GENERATION OF CABLE’S DYNAMIC MODELS

Dynamic modeling of cables is a research theme of great importance and practical application nowadays in the underwater oil industry. However, due to non-linearity behavior present on cable dynamics, as well as the need to work with many degrees of freedom, to develop dynamic models for these systems becomes a hard task. To develop dynamic models of cables, in this article is proposed a discrete formalism, which supposes the cable consisting of rigid links connected by fictitious elastic joints. The cables were considered with one of its endings articulated to a floating structure (ship or platform), while on the other ending were considered two cases: one free terminal loading; ending fixed to the ground. The cables are submersed and the hydrodynamic drag was considered from a simple model, proportional to the square of the relative velocity between the structure and the fluid. Using the Euler-Lagrange formalism, the dynamic models for cables considering two, three and four links were developed. From these models algorithms have been developed to automatically generate dynamic models for any number of links to represent in a discrete form the cable’s continuous flexibility. Simulations were performed, which showed the results agreeing qualitatively with the physical expected. A software has been developed to display animation from the spatial configuration of the cable. This animation, based on data from numerical simulation, allowed us show that the developed dynamic models give a great sense of physical reality.

Active Control of Flexible Structures Submitted to Incompressible Flows

This work presents a survey on the control law development to actively attenuate the vibrations of a flexible structure submitted to fluid flow. Firstly, a robust controller with LQG/LTR approach was developed. Numerical tests were carried out being robustness characteristics to flow induced vibration and to noise rejection verified, for the case of equal nominal and real plants. The same robustness was not verified, when parametric variations were introduced. Therefore, another controller, based on regulator and filter pole placement approach, was developed where the direct loop obeys stability and performance robustness criterions, allowing to obtain good numerical results, even in the presence of significant parametric variations.Copyright