Papers by Flavius Martins
6º CONGRESSO BRASILEIRO DE ENGENHARIA DE FABRICAÇÃO 6 th BRAZILIAN CONFERENCE ON MANUFACTURING ENGINEERING 11 a 15 de abril de 2011 – Caxias do Sul – RS - MODELAGEM, SIMULAÇÃO E VALIDAÇÃO EXPERIMENTAL DE PROCESSOS DE PEEN FORMING EM PLACAS DE LIGAS DE ALUMÍNIO
Application of Optical Techniques to Materials Characterization and Modeling
Comprehensive Materials Processing, 2014
ABSTRACT This chapter focuses on the combined use of experimental techniques based on photometric... more ABSTRACT This chapter focuses on the combined use of experimental techniques based on photometric measurements and on statistical methods to characterize the visual appearance of metallic test probes. After briefly revising the theory concerning the measurement of colorimetric properties, a design of experiments is proposed and the derived experimental data are analyzed according to suitable statistical methods in order to generate a robust metric that can reliably characterize the color of a test probe independently of the texture exhibited by its surface.
Identification of the state-space dynamics of oil flames through computer vision and modal techniques
Expert Systems with Applications, 2015
ABSTRACT In industrial oil furnaces, unstable flames can lead to potentially dangerous conditions... more ABSTRACT In industrial oil furnaces, unstable flames can lead to potentially dangerous conditions. For this reason, elaborate control systems are used to monitor the various parameters of the process that could become the source of such problems. A current trend in research is the one that seeks to apply artificial intelligence techniques to efficiently identify a priory anomalous behavior of the flames, so as to help improving the time response of the automatic control. In system dynamics theory, it is common sense that an accurate modeling of the process under study directly affects the performance of the controlling apparatus. Unfortunately, due to the complexity of the process, physical models of flame propagation are still not as much faithful as they should to be used for control purposes. On the other hand, could the complex dynamics of flame propagation be described in terms of an identified assumed model, one would come up with a tool for the improvement of the control strategy. In this work, a new approach based on Operational Modal Analysis (OMA) tools is used to identify four degree-of-freedom second order state-space models of oil flame dynamics in a prototype furnace. Grabbed images of a CCD camera, after being processed through a computer vision method, provide sets of characteristic vectors which, then, serve as input data to an identification OMA algorithm based on the Ibrahim Time Domain Method. Models of unstable and stable flames are built and validated through spectral analysis of the reconstructed time-domain characteristic vectors. The truthfulness of the validation scheme was then confirmed by a quantitative modal assurance criterion modified to suit the current application. On the grounds of the results obtained, it is possible to assert that the proposed approach for the description of flame dynamics can likely predict the occurrence of unstable conditions, thus becoming another tool that might be used in an automated control system.
Sistema de leitura automática de códigos de licença
This paper presents some solutions proposed by IPT to solve the problems of automatic reading lic... more This paper presents some solutions proposed by IPT to solve the problems of automatic reading license plates of moving vehicles. In particular, the following points are stressed: optical flow interpretation, background estimation, intelligent selection of interest images, plate localization, license code segmentation and character recognition.
Ferramenta de apoio à formulação simbólica de modelos cinéticos microbianos não-estruturados
Com o intuito de aprimorar e facilitar as atividades de modelagem, desenvolveu-se umsoftware de a... more Com o intuito de aprimorar e facilitar as atividades de modelagem, desenvolveu-se umsoftware de apoio à formulação de modelos cinéticos não-estruturados, o qual gera,automaticamente, estruturas matemáticas simbólicas. Estas são montadas a partir de seleçõesque o usuário realiza utilizando as informações que detém sobre os principais fenômenos queafetam a cinética dos processos fermentativos. Para, tanto, são combinadas variadas fontes deconhecimento, representadas através de cláusulas Prolog, e que abrangem os seguintesaspectos do processo: tipos de sistema de cultivo, reações estequiométricas, fenômenos delimitação, inibição, morte celular, manutenção microbiana, decomposição de substratos eformação de produtos. O resultado final são conjuntos de equações diferenciais simbólicas,com parâmetros conhecidos e/ou a estimar, as quais podem ser exportadas e utilizadas emprogramas de determinação e ajuste de parâmetros cinéticos e de simulação, otimização eprojeto de reatores bioquímicos.
Converting CT scan images into impeditivity measurements to form an anatomical atlas for Electrical Impedance Tomography
Electrical Impedance Tomography is a non invasive medical imaging technique used to infer living ... more Electrical Impedance Tomography is a non invasive medical imaging technique used to infer living tissue impeditivity from surface electrical measurements. Mathematically this is a ill-posed non-linear inverse problem. An anatomical atlas based on the resistivity of the tissue can be used as a regularization metgod for solving the inverse problem. CT scan images and in vivo measurements of tissue impeditivity of swine thorax performed by our group and form published data were used. The CT scan images must be segmented so that impeditivity information of each tissue can be used to obtain impeditivity images. In this work we document how CT images were mapped, segmented and converted into gray scale impeditivity images. These impeditivity images are then used to obtain a probabilistic model of clinically probable images called anatomical atlas.
This paper proposes to use decision trees for finding defects on mounted printed circuit boards, ... more This paper proposes to use decision trees for finding defects on mounted printed circuit boards, using an inductive algorithm and previously classified examples. During a training stage the algorithm learns how to differentiate classes, evaluating dependencies between example’s characteristics (cause) and its respectives classes (effect). The result is a classifier that can be used to evaluate new examples whose classes are unknown. Experiments were carried using a set of mounted printed circuit board images, composed of subsets previously classified as “without defect” and “with defect”. On average, the generated classifiers had 86,7% of success rate.
Neste trabalho propõe-se a utilização de aprendizado de máquina para identificar defeitos em plac... more Neste trabalho propõe-se a utilização de aprendizado de máquina para identificar defeitos em placas de circuito impresso montadas, utilizando-se, para tanto, um algoritmo indutivo e um conjunto de exemplos previamente classificados. Durante a etapa de treinamento, o algoritmo aprende como fazer distinção entre classes, avaliando as dependências entre as características (causas) dos exemplos e suas respectivas classes (efeitos). O resultado é um classificador, que pode ser utilizado para avaliar novos exemplos cujas classes são desconhecidas. Foram realizados experimentos utilizando-se um conjunto de imagens-exemplo de placas de circuito impresso montadas, composto de subconjuntos previamente classificados como “sem defeito” e “com defeito”. De cada imagem extraiu-se um conjunto de características calculadas por um programa de processamento de imagens, as quais foram então submetidas a diferentes algoritmos indutivos. Em média, os classificadores gerados atingiram uma taxa de acerto ...
Quantitative evaluation of parameters used in wear testing simulators of total hip arthroplasty components
Wear
Biomechanical simulators are extensively used in wear tests of total hip arthroplasty components.... more Biomechanical simulators are extensively used in wear tests of total hip arthroplasty components. Those tests should be in accordance with ISO 14242-1, which specifies three or four abscissæ ordinates of angular displacements and six loads to be attained by the simulators. Nevertheless, the standard does not provide directions on the interpolation method; consequently, wear rates from similar specimens tested in distinct simulators present considerable dispersion which, in turn, prevents the establishment of quality patterns for those components. In this work, continuous gait curves are generated from ISO 14242-1 specified points through Piecewise Cubic Hermite Interpolation Polynomials. A subset of 100 points that best fit ISO specified tolerances, extracted from the continuous curves, is provided for using in wear simulators as a means of decreasing discrepancies in results from different machines. Moreover, a cross-correlation comparison between interpolated and actual gait curve...
Aiming at contributing to the development of a robust computer vision traffic surveillance system... more Aiming at contributing to the development of a robust computer vision traffic surveillance system, in this work a method for vehicle identification and tracking that applies the Scale Invariant Feature Transform (SIFT) and a Kalman filter is proposed. The SIFT algorithm extracts keypoints of the moving object on a sequence of images and the Kalman Filter provides a priori estimates of vehicle position and velocity which are used to improve the said algorithm. This strategy allows reducing the amount of pixels to be tested for matches within the whole image scenario by dynamically redefining the ROI (Region of Interest). Using algorithms from OpenCV Library to compose the required computer vision tracking method, a prototype system was constructed and submitted to off-line experiments based on a series of grabbed traffic image sequences. From the results, it is possible to assert that the joint use of SIFT and Kalman filtering techniques is able to improve the overall algorithm perfo...
Planejamento de trajetória de jateamento para obtenção de cobertura uniforme em processos de peen forming
Dentre as diversas variáveis do processo de conformação de placas por peen forming, destaca-se a ... more Dentre as diversas variáveis do processo de conformação de placas por peen forming, destaca-se a cobertura (razão entre área atingida por impactos e área total). Para se controlar adequadamente esse processo, é necessário operar com uma cobertura uniforme, o que comumente se faz mediante a sobreposição de trajetórias retilíneas do jato sobre a placa. Neste artigo exploram-se as técnicas de medição da freqüência de ocorrência de impactos e a posterior estimação da cobertura a partir da equação de Avrami. Em seguida, calculam-se os valores ótimos da velocidade de avanço do bocal e do passo entre trajetórias sucessivas do jato, de modo a se minimizar a variação espacial da cobertura.
Purpose: this paper aims to present a simple method to synthesize an empirically-based model that... more Purpose: this paper aims to present a simple method to synthesize an empirically-based model that permit to estimate the maximum displacement of a plate when a shotpeening process values are known.Design/methodology/approach: This approach regards the difficulty to develop a mathematical model to describe the relationship between the shot peening process variables (shot diameter, impact velocity, static preload and coverage) and the curvature of the piece. Such a model was generated through the application of statistical inference methods – multivariable regression and neural networks – to a set of experimental data concerning the application of peen forming processes to a group of 215 aluminium 7050 alloy rectangular plates.Findings: Although the estimated displacements from both models comply reasonably well with the experimental data, the obtained results exposed the superiority of the regressive model concerning accuracy.Research limitations/implications: Shot peen forming, a di...
Analysis of the residual stress induced by peen forming in aluminum alloy specimens
Peen forming is a cold work process based on the application of a regulated blast of small round ... more Peen forming is a cold work process based on the application of a regulated blast of small round steel shots on the surface of a metallic plate or panel. The local plastic deformations caused by the impacts give rise to a thin compressive residual stress layer that stretches the worked surface. Therefore, in order to give a piece a pre-defined shape, it is necessary to properly control the peen forming process variables, for which a reference model for the measurements is required. Aiming at developing a computer-aided tool for planning peen forming processes for the aeronautical industry, a series of experiments have been carried out, encompassing the variation of four relevant variables – shot diameter, impact velocity, coverage (% of the surface area affected by the shots) and pre-loading, and the use of 88 test rectangular plates of aluminum 7050 and 7075 alloys. For each conformed specimen, the residual stress distribution at midspan was measured using the blind-hole drill meth...
Vapor flow rate (VFR) is one of the main variables affecting the nebulization quality of oil flam... more Vapor flow rate (VFR) is one of the main variables affecting the nebulization quality of oil flames in petroleum refinery furnaces. Too low values of VFR are directly correlated to a significant increase of the solid particulate material rate; as a consequence, the overall efficiency of the process decreases. As it has been observed, changes in VFR give rise to modifications of the flame visual patterns. Using characteristic vectors based on geometric properties of the gray level histogram of instantaneous flame images related to combustion processes with known a priori VFR values, feature vectors were calculated for all the images of a properly organized training set; then, a classification algorithm created a fuzzy measurement vector whose components represented membership degrees to the 'high nebulization quality' fuzzy set. Aiming at developing a real-time diagnostic system to describe the nebulization quality of the process when VFR is unknown, the fuzzy classification ...
LEITURA AUTOMÁTICA DE INSTRUMENTOS ANALÓGICOS DE MEDIÇÃO
ABSTRACT A computer vision system for automatic reading of analogical measurement devices is prop... more ABSTRACT A computer vision system for automatic reading of analogical measurement devices is proposed. Such a system can be especially useful to the automation of calibration processes or other tests that require repetitive readings. The approach is based on the comparison between the slopes of the pointer and the display scale marks. Several automatic reading tests were carried out and the uncertainties obtained were equivalent to the human ones. The process success rate was around 99%. 1 Introdução Neste trabalho apresenta-se um sistema de visão computacional para leitura de mostradores de instrumentos analógicos, desenvolvido com o propósito de se automatizar processos que requerem o registro em série das medidas de instrumentos que não disponham de quaisquer interfaces de comunicação digital. Tais processos permeiam parte significativa dos trabalhos realizados por muitos dos laboratórios do IPT (Instituto de Pesquisas Tecnológicas do Estado de São Paulo), mas a mesma necessidade é identificada junto aos demais operadores da Rede Brasileira de Metrologia. Embora apresente grande potencial de utilização no país, essa aplicação não tem sido muito abordada na literatura. Sablatnig e Kropatsch (1994) implementaram um sistema dedicado à leitura automática de hidrômetros analógicos, cujo escopo pretendiam estender a outros instrumentos com características similares. Posteriormente, Alegria e Serra (2000) desenvolveram algoritmos de visão computacional para a leitura de voltímetros com mostradores analógicos e digitais, mas sem interface de comunicação digital.
Um ambiente de simulação de algoritmos anticolisão para apoio ao desenvolvimento de aplicações de RFID
Revista Brasileira de Computação Aplicada, 2012
ABSTRACT Dentre os aspectos técnicos a serem considerados no projeto de um sistema baseado em RFI... more ABSTRACT Dentre os aspectos técnicos a serem considerados no projeto de um sistema baseado em RFID (Radio Frequency Identification) um dos mais importantes é a análise do processo de colisão de informações, ou seja, a sucessão de eventos que ocorrem quando etiquetas RFID adentram a zona de abrangência de um dispositivo leitor e transmitem suas informações simultaneamente, dificultando sua correta identificação. Para evitar os efeitos danosos que seriam causados por tais eventos é necessário integrar aos dispositivos transmissores e receptores um algoritmo – denominado ‘anti-colisão’ – responsável pelo isolamento da comunicação entre cada etiqueta e o leitor. Neste trabalho propõe-se o desenvolvimento de um ambiente de simulação de algoritmos anti-colisão para sistemas RFID que permite sua análise comparativa em situações variadas, facilitando a avaliação de desempenho desses algoritmos e sua subseqüente seleção, de modo a atender às características da aplicação pretendida. Também são apresentados alguns experimentos realizados com os algoritmos anti-colisão implantados no ambiente de simulação e analisados à luz das métricas de desempenho adotadas.
Identification of a scaled-model riser dynamics through a combined computer vision and adaptive Kalman filter approach
Mechanical Systems and Signal Processing, 2014
ABSTRACT Aiming at overcoming the difficulties derived from the traditional camera calibration me... more ABSTRACT Aiming at overcoming the difficulties derived from the traditional camera calibration methods to record the underwater environment of a towing tank where experiments of scaled-model risers are carried on, a computer vision method, combining traditional image processing algorithms and a self-calibration technique was implemented. This method was used to identify the coordinates of control-points viewed on a scaled-model riser submitted to a periodic force applied to its fairlead attachment point. To study the observed motion, the riser was represented as a pseudo-rigid body model (PRBM) and the hypotheses of compliant mechanisms theory were assumed in order to cope with its elastic behavior. The derived Lagrangian equations of motion were linearized and expressed as a state-space model in which the state variables include the generalized coordinates and the unknown generalized forces. The state-vector thus assembled is estimated through a Kalman Filter. The estimation procedure allows the determination of both the generalized forces and the tension along the cable, with statistically proven convergence.
On the Euler and Lagrange's points of view in rigid body mechanics
International Journal of Mechanical Engineering Education, 2011
... Flavius Portella Ribas Martins (corresponding author), Flávio Celso Trigo and Agenor de Toled... more ... Flavius Portella Ribas Martins (corresponding author), Flávio Celso Trigo and Agenor de Toledo Fleury Mechanical Engineering Department (corresponding author ... body points that pass through P [ω] angular velocity matrix Ω→ angular velocity vector s trajectory arc length V ...
Singularities in the expression of the kinetic energy of a system of particles subject to holonomous constraints
International Journal of Mechanical Engineering Education, 2012
ABSTRACT In the textbooks on classical mechanics normally adopted for courses on mechanical engin... more ABSTRACT In the textbooks on classical mechanics normally adopted for courses on mechanical engineering there is no mention of the paradoxical fact that a material system subject to holonomous constraints can exhibit singular configurations for which the cross-products of their generalized velocities, not all identically nil, give rise to a zero value for the kinetic energy. Given the importance of this subject for the analysis of dynamic systems and as a contribution to education on mechanics, we analyse in this article a material system composed of discrete masses subject to holonomous constraints and exhibiting the mentioned behaviour. After deriving an analytical expression for the kinetic energy of the system, numerical simulations permit the identification of some singular material configurations for which the initial statement holds.
A new approach based on computer vision and non-linear Kalman filtering to monitor the nebulization quality of oil flames
Expert Systems with Applications, 2013
ABSTRACT The nebulization quality of oil flames, an important characteristic exhibited by combust... more ABSTRACT The nebulization quality of oil flames, an important characteristic exhibited by combustion processes of petroleum refinery furnaces, is mostly affected by variations on the values of the vapor flow rate (VFR). Expressive visual changes in the flame patterns and decay of the combustion efficiency are observed when the process is tuned by diminishing the VFR. Such behavior is supported by experimental evidence showing that too low values of VFR and solid particulate material rate increase are strongly correlated. Given the economical importance of keeping this parameter under control, a laboratorial vertical furnace was devised with the purpose of carrying out experiments to prototype a computer vision system capable of estimating VFR values through the examination of test characteristic vectors based on geometric properties of the grey level histogram of instantaneous flame images. Firstly, a training set composed of feature vectors from all the images collected during experiments with a priori known VFR values are properly organized and an algorithm is applied to this data in order to generate a fuzzy measurement vector whose components represent membership degrees to the ‘high nebulization quality’ fuzzy set. Fuzzy classification vectors from images with unknown a priori VFR values are, then, assumed to be state-vectors in a random-walk model, and a non-linear Tikhonov regularized Kalman filter is applied to estimate the state and the corresponding nebulization quality. The successful validation of the output data, even based on small training data sets, indicates that the proposed approach could be applied to synthesize a real-time algorithm for evaluating the nebulization quality of combustion processes in petroleum refinery furnaces that use oil flames as the heating source.
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Papers by Flavius Martins