1,721,016 research outputs found
A miniaturized tendon-driven continuum robot for direct laser deposition
No full textDirect laser deposition, a form of additive manufacturing, shows potential in numerous high-value applications such as aeroengine blade repair. However, conventional setups are bulky and unsuitable for in-situ repair, requiring costly engine disassembly. This letter presents a miniaturized high-repeatability tendon-driven robot that showed good potential for delivering additive manufacturing equipment for in-situ processes like direct laser deposition. The integrated actuation and ruggedized control unit make the robot portable and compatible with various aeroengines. The actuation design prevents excessive fiber optic bending and damage. While continuum robots have the advantage of flexible and redundant structures, they often lack accuracy and repeatability. The optimized kinematics and actuation of the robot presented permitted to achieve in controlled laboratory conditions an excellent repeatability with a standard deviation of 0.02 mm on a linear path and below 0.1 mm on a path that simulates the reconstruction of a blade. The robot showed excellent linearity on each segment of the path with a coefficient of determination to the 3D best-fit line of 0.999, while maintaining the commanded end effector velocity magnitude with a standard deviation of 0.05 mm/s along the whole path
A kinematic coupling mechanism with binary electromagnetic actuators for high-precision positioning
Full text linkRather than working in a continuous range of motion, binary actuators can only maintain two positions. This lack of flexibility is compensated by high accuracy, repeatability, and reliability. These features make binary-actuated mechanisms appealing for space exploration systems, repetitive pick & place tasks, and biomedical applications. This paper introduces a novel class of binary-actuated mechanisms driven by electromagnets. As these systems rely on the extreme positions of their binary actuators for positioning, the proposed design aims to increase repeatability with a kinematic coupling. By inverting the polarity of its electromagnets, the configuration of the mechanism can be changed from a discrete state to another one. Thus, when the actuation is known, the pose of the system can be accurately computed without any external feedback. A sensorless design simplifies both the control and the architecture of the proposed design, as well as reducing manufacturing and maintenance costs. The conceptual design of the proposed class of mechanisms is described through two examples with three and four configurations, and alternative designs with higher mobility are discussed. Then, a kinematic synthesis procedure is discussed. Finally, the advantages of asymmetric and irregular designs are outlined. Overall, the proposed mechanisms are suited to a wide range of applications that require a rapid, accurate and interchangeable positioning of sensors and tools
A Novel Underactuated Continuum Robot With Shape Memory Alloy Clutches
Full text linkThe many degrees of freedom of continuum robots (CRs) enable unique applications in the search and rescue, medical and aerospace industries. However, the many motors required result in unwieldy external actuation packs and additional weight. Underactuation can achieve any pose with four motors by locking sections through clutching of cables. Existing underactuated (UA) solutions are characterized by lengthy joint locking times, add significant weight and are not scalable. In this article, a novel design and motion strategy is introduced, with shape memory alloy wires to control clutches that lock cables for section locking. In addition to using conventional smooth cables, beaded cables are proposed for improved clutching strength. The workspace of the design is analyzed, and design tools are proposed to optimize bead pitch. Finally, the operation of the proposed UA CR is demonstrated on a prototype that achieves a mean repeatability of 1.41mm, equivalent to 0.43% of the backbone length. Section locking is achieved in 1 s and section unlocking is achieved in 5 s
An Efficient Follow-the-Leader Strategy for Continuum Robot Navigation and Coiling
No full textEfficient path planning for hyper-redundant continuum and snake-like robots is a challenging task due to limited sensing capabilities, high computational loads, multiple possible solutions, and non-linear models. This letter presents a new approach to snake robot navigation and coiling, with an algorithm that enables online step-by-step position adjustment with a follow-the-leader strategy, significantly improving the performance of the robot when compared to previous methods. The proposed algorithm is demonstrated on a 16-degree-of-freedom snake-like robot for inspection and maintenance tasks in nuclear facilities
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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