1,720,963 research outputs found
TRACKING OF A BASE REACTION PROFILE FOR A SPACE MANIPULATOR
No full textA manipulator that is performing a manoeuvre generates reaction forces and
torques that dynamically load the supporting base. A special interest in the control of the base
reactions arises for robots mounted on a moving base, due to the interaction between the
motion of the manipulator and the motion of the base itself, which in many cases needs to be
controlled at the same time. In this paper the problem of tracking an arbitrary base reaction
profile is considered. The present work gives a contribution to the subject of the kinematic
control of spacecraft mounted manipulators and their dynamical effects in terms of reaction
forces and torques, and can be used for the development of centralized control systems aimed
at controlling multiple robots mounted on the same spacecraft, where a non-operating
manipulator can cooperate to compensate the disturbances generated by a second operating
robot, together with the reaction control system actuators. The solution to the problem is
given in the form of a kinematic law for the joint variables of the manipulator, and the joint
acceleration trajectories related to the desired base reaction profile are obtained.
Furthermore, the influence of the degree of redundancy of the robot is analyzed, with respect
both to the kinematic and the dynamic tasks. The availability of the redundancy can be
exploited in order to prescribe a desired trajectory to the end-effector, and specifically the
problem of realizing a defined base reaction profile and in the meantime achieve the best
approximation of an end-effector trajectory is considered. The proposed solutions are
developed in terms of pseudoinverse formulations, and the reaction control problems are set
in local optimization form, leading to the definition of constrained least squares problems.
The implementation of the proposed kinematic schemes in a robot simulator allowed to test
the capabilities of the proposed concepts
CONTACT FORCES OPTIMIZATION OF A BIO-INSPIRED CLIMBING ROBOT
No full textControl torques applied at the climbing robot
joints can be optimized in order to minimize the
required strength of the synthetic dry adhesives
that are used to keep the robot attached to an
inclined surface. Optimal torques are computed
by using MiniMax and Least Squares optimization
approaches. This paper focuses on a preliminary
investigation intended to identify the
convenient control torques that the joint actuators
of a Legged Climbing Robot (LCR) should
exert, in order to improve its stability and take
full advantage of the adhesive contact properties.
The results obtained are compared to a natural
reference condition in which all the joints
are unloaded, by placing the robot in an overconstrained
static configuration. An experimental
setup is designed in order to test the control
concepts and validate the simulation campaign.
Results show that the use of optimal
torques could be highly desirable as the maximum
pulling force exerted at the contact tips is drastically
reduced, enhancing the stability margin of
the climbing robot configuratio
Reaction Torque Control of Redundant Space Robotic Systems for Orbital Maintenance and Simulated Microgravity Tests
No full textThis paper presents the theoretical formulation and the experimental validation of a novel solution for the inverse kinematics of redundant space robotic systems aimed at locally minimizing the torque transferred to the spacecraft due to the robotic arm movement. The differential kinematics is formulated at the acceleration level and an additional constraint is imposed in order to locally minimize the torque transferred to the spacecraft center of mass. This problem can be expressed as a constrained linear least squares problem and a closed-form solution is obtained. An extension of this method is presented in order to take into account the physical limits of the manipulator, by limiting the joint accelerations under acceptable values. In this case the problem can be expressed as a constrained linear least squares problem with both equality and inequality constraints. The proposed solution has been experimentally tested using a 3D free-flying robot previously tested in an ESA Parabolic Flight Campaign. In this test campaign the 3D robot has been converted in a 2D robot taking advantage of its modular structure, and it has been suspended by means of air-bearings on a granite plane. In this way it is possible to perform simulated microgravity tests without time constraints. The base of the robot is fixed on ground by means of a custom design dynamometer, which measures the torque transferred to ground to be minimized. The experimental results validated the proposed solutions and confirmed their good performance
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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