1,721,005 research outputs found
Drawing up an industrial CT system purchase specification: a Brazilian case study
No full textComputed tomography integration to the quality control loop of Brazilian industries has been continuously growing. Being capable of imaging internal structures of an object, hidden features formerly evaluated only after physically sectioning it became visible through computed tomography. Despite being an engineering technology to be considered in non-destructive
analysis and dimensional metrology, the task of selecting an appropriate CT measurement system is not trivial. This paper outlines a general methodology for defining the quotation bases of an industrial CT system suitable for in-line quality control of light metal parts, and thus assisting the buyoff activity
Experimental assessment of computed tomography dimensional performance using modular test pieces made of polyoxymethylene and aluminum
No full textComputed tomography for dimensional metrology has been part of the quality control loop for more than a decade. Because of the complex measurement-error cause system and the lack of appropriate guidance, usually no consistent uncertainty reporting has been made. Modular test pieces made of polyoxymethylene and aluminum have been devised, manufactured and used to investigate some influence factors intrinsic to CT-based data and their effects on evaluating features of size. The experimental planning and the most significant experimental findings, including the use of artefact reduction algorithms, are presented and discussed in this paper
Experimental investigation of the influencing factors on the structural resolution for dimensional measurements with CT systems
No full textThis paper presents an experimental investigation on the factors influencing the metrological structural resolution (MSR) of CT systems. The investigation consists of structured experiments involving several CT data acquisition and processing parameters. The method used to assess the metrological structural resolution is based on the amplitude transfer function (ATF). Because of the intrinsic relation between structural resolution and noise, the extracted surface RMS deviation was also evaluated. The results show how dependent the MSR is on the influencing factors and provides useful functional relations between data acquisition and processing parameters, the MSR and the surface deviations. They also help demonstrating the applicability of the ATF-based method to characterize the metrological structural resolution of CT systems
Voxel dataset noise reduction algorithm based on CMM reference measurements for geometrical tolerance analysis of prismatic test pieces
No full textComputed tomography for dimensional metrology has been introduced in the quality control loop for about a decade. To make the tolerance verification consistent, GD&T evaluation programs have been developed, which make use of CT point clouds generated through segmentation. This important step in a CT measurement sequence is investigated under the perspectives of tolerance analysis and measurement uncertainty. Based on empirical master part reference measurements, voxel dataset noise can be rationally filtered out by applying point-based reduction algorithms. Their significance on dimensional and geometrical characteristics’ measurements is experimentally tested and discussed in this work
CT Measurement Realization Process: The Need for Advanced Correction Methods
No full textComputed tomography use as a dimensional metrology technique has increased steadily, despite the fact that the uncertainty has been rarely determined and expressed in measurements of production parts. This perception may be attributed in part to a limited way of employing the uncertainty concept. From this perspective, the conceptual integration of the product (and measurement) realization process with the uncertainty approach is first emphazised in this paper. The reasoning behind it is to employ different methods for uncertainty evaluation in a rational sense, where the accuracy required to the uncertainty evaluation process drives the method selection. For critical measurement cases, which can be identified in the proposed concept, the need for advanced correction methods, using master part reference measurements for point-based compensation, is presented, tested and justified for GD&T characteristics
Investigação e redução dos efeitos térmicos em medições geométricas por tomografia computadorizada de raios x
Get PDFDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2013.A ocorrência de deriva térmica em sistemas de tomografia computadorizada industrial (TC) tem sido reportada como uma significativa fonte de erros em avaliações geométricas. Durante o processo de varredura, aquecimento dentro da cabine e variações das condições ambientais podem afetar a posição do ponto focal e distorcer o sistema manipulador, levando a deslocamentos relativos das projeções radiográficas e distorções na imagem reconstruída. Estratégias para minimizar fontes de incertezas da medição relacionadas a gradientes térmicos podem ser classificadas em: A) redução das variações de temperatura; B) redução dos efeitos de variações de temperatura; C) quantificação e compensação dos efeitos de variações de temperatura. O presente trabalho apresenta uma avaliação experimental da efetividade das estratégias A e C. Uma comparação de duas gerações do mesmo modelo de sistema tomográfico foi realizada, tendo o equipamento mais recente sistemas aprimorados de exaustão da cabine e arrefecimento do tubo de raios-X. A efetividade do aprimoramento do equipamento foi verificada através da avaliação do desvio de circularidade de uma esfera de precisão. Os resultados mostraram uma melhoria relevante na estabilidade das projeções, levando a uma redução estatisticamente significante dos valores de desvio de circularidade no equipamento mais recente. Além disso, um método de correção baseado na manipulação das projeções foi desenvolvido e testado. O método consiste em repetir a aquisição da primeira projeção ao final do processo de varredura e calcular o vetor deslocamento entre as projeções. As projeções remanescentes são corrigidas proporcionalmente a esse deslocamento total. A efetividade dessa correção também foi avaliada através do desvio de circularidade medido em uma esfera de precisão. Os valores de circularidade medidos após a implementação da correção foram significativamente menores, validando a utilidade da estratégia C.<br
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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