1,720,958 research outputs found
Design and control optimization for hybrid-controlled overconstrained cable-driven parallel robots
No full textIn Cable-Driven Parallel Robots (CDPRs), multiple cables forming closed kinematic chains move the end-effector (EE). When the number of cables exceeds the degrees of freedom of the EE, the robot is overconstrained (OCDPR). This architecture helps keep cables taut but introduces actuation control challenges due to constraint redundancy. Hybrid Position-Force Control addresses this by using length-controlled cables to regulate the EE pose and force-controlled cables to manage force distribution. A hybrid control turns out to be a fast and intuitive solution in which, however, the choice of force-controlled cables influences the Wrench-Feasible Workspace. This article introduces the Wrench-Feasible Error-Insensitive Workspace (WFEIW), defined as the set of wrench-feasible poses that can be reached even in the presence of length- and tension-control errors. In particular, the paper shows how this workspace, which is inherently control-dependent, can be optimized. The WFEIW is analyzed for different 8-cable OCDPRs, demonstrating the method's efficacy and generality. Ultimately, the volume of the WFEIW is used as a cost function to optimize a robot geometry, thus showing how the presented method provides a practical synthesis tool for design
Hybrid-Control-Based Workspace Analysis of Overconstrained Cable-Driven Parallel Robots
No full textCable-Driven Parallel Robots (CDPRs) are overconstrained when they have more cables than the degrees of freedom of the endeffector (EE). This paper introduces a technique to analyze the wrench feasible workspace of this class of robots when a hybrid force-position control is used in joint space, namely when as many cables as the EE freedoms control the robot pose, and the remaining ones are used to keep all cables under tension
Initial-Pose Self-calibration for Deployable Overconstrained Cable-Driven Parallel Robots
No full textDeployable Cable-Driven Parallel Robots (CDPRs) are often designed to be lightweight so that they can be easily transported and mounted in the field. They often rely on simplified cable transmission systems with non-constant and uncertain transmission ratios. These uncertainties complicate the kinematic model, making pose estimation and calibration challenging, as motor angles are not easily linked to cable lengths. This paper presents a comparative study of three self-calibration algorithms for deployable CDPRs, analyzing the impact of different sensor configurations on initial-pose estimation accuracy. Simulations evaluate each sensor set using position and orientation errors as metrics. Recommendations are proposed on optimal sensor configurations for deployable CDPRs, accounting for measurement and modeling errors and the practical limitations of simplified transmission systems
A Rapid Initial-Pose Self-calibration Method for Underactuated Cable-Driven Parallel Robots
No full textUnderactuated cable-driven parallel robots (UACDPRs) use fewer cables than the end-effector (EE) degrees of freedom to control their motion. Depending on the sensors installed on the robot, the initial pose of the EE may not be known at startup, and determining it is essential for subsequent operations. This paper presents a rapidly executable self-calibration procedure for estimating the initial pose of a UACDPR. The procedure employs a nonlinear weighted least square optimization, whose tentative solution is also optimized for rapid global convergence. Experiments on a 4-cable UACDPR demonstrates the procedure
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
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