1,720,957 research outputs found
Robotic FDM for free-form fabrication: evaluating adaptive non-planar slicing with different contour methods
No full textPurpose: This study aims to investigate and compare three nonplanar (NP) slicing algorithms. The algorithms aim to control the layer thickness variation (LTV), which is a common issue in supportless fabrication of free-form parts. The comparison underlines the differences between theoretical and real scenarios, resulting in guidelines for toolpath generation of complex objects. Design/methodology/approach: The algorithm comparison uses a representative complex geometry, i.e. the quarter of torus. It presents an increasing overhang and constant curvature. It is represented using a parametric definition in the first two algorithms and by triangular meshes as the real scenario. The algorithms work on the contouring stage, whereas a B-spline approach is used to build the inner side of layers. Constant layer thickness (LT) is imposed, and an adaptive approach is adopted to avoid over-extrusion. Three algorithms are validated with a robotized fused deposition modeling system. LTs are measured on cross-sectioned samples and compared with the theoretical cases. Findings: The results show that two algorithms can provide an LTV of about 0% on the contour. Nevertheless, the theoretical results on the inner side are divergent from the previous evidence, moving on to higher LTV (approximately 90%). The need for an adaptive approach is demonstrated, resulting in an LTV reduction (approximately 30%). Printed parts present the same trends of theoretical results confirming the algorithms’ capabilities. Originality/value: The work shows, for the first time, a comparison between NP slicing techniques. The LTV problem in hollow and filled components is analyzed through theoretical and experimental evidence. The results are promising for supportless fabrication of free-form parts
Non-planar slicing for filled free-form geometries in robot-based FDM
No full textMulti-axis techniques in Additive Manufacturing (AM) unlock promising features such as supportless fabrication, reduced material consumption, improved surface quality and mechanical properties. Among those techniques, non-planar (NP) slicing promises to be the most suitable approach to fabricate 3D-components with significant curvature such as free-form geometries. Those are characterized by a layer thickness variation (LTV) along the curvature, which should be minimized. Industrial 6-axis robots are mandatory to achieve such performances. NP slicing generalization is challenging. On one side, there is a need to define a suitable contouring method compatible with the different geometrical features present in objects. On the other side, the generalized slicing method must be able to reconstruct the inner side not provided by superficial information provided by triangular mesh. In this work, a new algorithm to generate filled NP layer has been proposed using a contouring method that reduces the LTV. The bidirectional rectilinear infill strategy has been adapted for NP layers providing a more feasible toolpath to Fused Deposition Modeling (FDM) and such Direct processes where curved paths are detrimental. The proposed strategy has been validated by fabricating a tubular geometry with a robotized FDM system. Tubular geometry provides a sub-optimal solution of LTV known analytically for the contour. The infill algorithm has been tested with a complex surface applying the NP torus on a waved shape. Previous studies consider only contour providing an LTV ranging in +0% ÷ -46%. This study considers only the inner side. The analytical LTV resulted in a range of +0% ÷ -60%. The cross sections of the components were analyzed and compared with the analytical results. Although the proposed infill strategy does not maintain completely the contour layer thickness in the infill side, it shows to be able to cover more complex NP layers without saddle points
A Novel Infill Strategy to Approach Non-Planar 3D-printing in 6-Axis Robotized FDM
No full textAdditive Manufacturing (AM) is a class of processes with a remarkable growth and evolution during the last years. Those allow to fabricate components deposing a great variety of raw materials with a layer by layer approach. Conventional material deposition strategy is identified by the slicing process layering the 3D component with planes. Although convention slicing enables common Cartesian 3D-printers, is constraining the fabrication of near-net shape components featuring overhangs and particularly to free-form geometries without the use of dedicated supports. Conventional slicing is also limiting industrial 6-axis robots which are more flexible, providing larger working area and introducing more degrees of freedom than Cartesian 3D-printers. Non-planar slicing unlocks such features changing deposition direction according to multi-directional surface. On the other hand, non-planar slicing generalization is a challenging problem due to its own intrinsic complexity. Hence, the goal to achieve a flexible non-planar slicer software is still not reached. This work considers a quarter of torus as representative of a free-form part which only the external surface is known analytically. The aim of this work is to provide a new method to define a non-planar infill to fabricate filled-solid parts starting from the data on the contour. It is a first and preparatory step of problem generalization. An experimental activity is pursued showing the non-planar infill strategy introduced. The printed results are discussed and evaluated, underlining the capabilities of the proposed solution
Brain–Computer Interface and Hand-Guiding Control in a Human–Robot Collaborative Assembly Task
No full textCollaborative robots (Cobots) are compact machines programmable for a wide variety of tasks and able to ease operators’ working conditions. They can be therefore adopted in small and medium enterprises, characterized by small production batches and a multitude of different and complex tasks. To develop an actual collaborative application, a suitable task design and a suitable interaction strategy between human and cobot are required. The achievement of an effective and efficient communication strategy between human and cobot is one of the milestones of collaborative approaches, which can be based on several communication technologies, possibly in a multimodal way. In this work, we focus on a cooperative assembly task. A brain–computer interface (BCI) is exploited to supply commands to the cobot, to allow the operator the possibility to switch, with the desired timing, between independent and cooperative modality of assistance. The two kinds of control can be activated based on the brain commands gathered when the operator looks at two blinking screens corresponding to different commands, so that the operator does not need to have his hands free to give command messages to the cobot, and the assembly process can be sped up. The feasibility of the proposed approach is validated by developing and testing the interaction in an assembly application. Cycle times for the same assembling task, carried out with and without the cobot support, are compared in terms of average times, variability and learning trends. The usability and effectiveness of the proposed interaction strategy are therefore evaluated, to assess the advantages of the proposed solution in an actual industrial environment
Brain computer interface for human-cobot interaction in industrial applications
No full textIn the recent years, the industry has seen the introduction of the collaborative robots (or 'cobots'), designed to interact with human workers in a shared environment. However, the involvement of the cobots in industrial applications is still strongly influenced by the strategies for non-collaborative robotic cells. The researchers are working frantically to find solutions to improve the interactions between the cobot and the operator, simplifying the communication and the programming work. This paper proposes a task-based algorithm which allows a fluid interaction, via biosignals of a Brain Compute Interface (BCI), as an enabling strategy of the collaborative workstations. The goal is to provide an implementation method of the BCI devices for industrial applications in order to make the cobots easy to use and interact with. The proposed solution is tested on an experimental setup which uses the Steady-State Visual Evoked Potential (SSVEP) response signal to drive machine commands to a collaborative robotic arm
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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