1,720,991 research outputs found
Control of Nonlinear Mechatronic Systems
Full text linkThis dissertation is divided into four self-contained chapters. In Chapter 1, an adaptive nonlinear tracking controller for kinematically redundant robot manipulators is presented. Past research efforts have focused on the end-effector tracking control of redundant robots because of their increased dexterity over their non-redundant counterparts. This work utilizes an adaptive full-state feedback quaternion based controller developed in [1] and focuses on the design of a general sub-task controller. This sub-task controller does not affect the position and orientation tracking control objectives, but instead projects a preference on the configuration of the manipulator based on sub-task objectives such as the following: singularity avoidance, joint limit avoidance, bounding the impact forces, and bounding the potential energy. In Chapter 2, two controllers are developed for nonlinear haptic and teleoperator systems for coordination of the master and slave systems. The first controller is proven to yield a semi-global asymptotic result in the presence of parametric uncertainty in the master and the slave dynamic models provided the user and the environmental input forces are measurable. The second controller yields a global asymptotic result despite unmeasurable user and environmental input forces provided the dynamic models of the master and slave systems are known. These controllers rely on a transformation and a flexible target system to allow the master system\u27s impedance to be easily adjusted so that it matches a desired target system. This work also offers a structure to encode a velocity field assist mechanism to provide the user help in controlling the slave system in completing a pre-defined contour following task. For each controller, Lyapunov-based techniques are used to prove that both controllers provide passive coordination of the haptic/teleoperator system when the velocity field assist mechanism is disabled. When the velocity field assist mechanism is enabled, the analysis proves the coordination of the haptic/teleoperator system. Simulation results are presented for both controllers. In Chapter 3, two controllers are developed for flat multi-input/multi-output nonlinear systems. First, a robust adaptive controller is proposed and proven to yield semi-global asymptotic tracking in the presence of additive disturbances and parametric uncertainty. In addition to guaranteeing an asymptotic output tracking result, it is also proven that the parameter estimate vector is driven to a constant vector. In the second part of the chapter, a learning controller is designed and proven to yield a semi-global asymptotic tracking result in the presence of additive disturbances where the desired trajectory is periodic. A continuous nonlinear integral feedback component is utilized in the design of both controllers and Lyapunov-based techniques are used to guarantee that the tracking error is asymptotically driven to zero. Numerical simulation results are presented for both controllers. In Chapter 4, a new dynamic model for continuum robot manipulators is derived. The dynamic model is developed based on the geometric model of extensible continuum robot manipulators with no torsional effects. The development presented in this chapter is an extension of the dynamic model proposed in [2] (by Mochiyama and Suzuki) to include a class of extensible continuum robot manipulators. First, the kinetic energy of a slice of the continuum robot is evaluated. Next, the total kinetic energy of the manipulator is obtained by utilizing a limit operation (i.e., sum of the kinetic energy of all the slices). Then, the gravitational potential energy of the manipulator is derived. Next, the elastic potential energy of the manipulator is derived for both bending and extension. Finally, the dynamic model of a planar 3-section extensible continuum robot manipulator is derived by utilizing the Lagrange representation. Numerical simulation results are presented for a planar 3-section extensible continuum robot manipulator
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
A Passivity-based Decomposing Method for Operational Space Control of Kinematical Redundant Tele-operation Systems
No full textIn the passivity-based decomposing method, a bilateral tele-operation system is virtually decomposed into 2 sub-systems (shape/locked) to ensure coordination between the master and slave robots and to provide a general referenced motion of the closed-loop bilateral tele-operation along with the passivity of the master and slave robots. So far, the passivitybased decomposing methods in the literature have been studied only for the joint-space control of tele-operation systems with kinematical similar master and slave robots. In this study, a passivity-based decomposing method is proposed for operational space control of bilateral teleoperation systems with kinematic redundancy in the slave robot. The main objectives of the proposed method are to ensure operational space coordination between the robots' end-effector trajectories and to achieve a referenced general movement of the closed-loop tele-operation system. In addition, the kinematic redundancy of the slave robot, which usually complicates the control problem, is turned into an advantage, and secondary tasks are designed for the slave robot. Moreover, experiments are carried out to validate the achievement of the proposed method using a kinematical redundant tele-operation setup.</p
A Passivity-based Decomposing Method for Operational Space Control of Kinematical Redundant Tele-operation Systems
No full textIn the passivity-based decomposing method, a bilateral tele-operation system is virtually decomposed into 2 sub-systems (shape/locked) to ensure coordination between the master and slave robots and to provide a general referenced motion of the closed-loop bilateral tele-operation along with the passivity of the master and slave robots. So far, the passivitybased decomposing methods in the literature have been studied only for the joint-space control of tele-operation systems with kinematical similar master and slave robots. In this study, a passivity-based decomposing method is proposed for operational space control of bilateral teleoperation systems with kinematic redundancy in the slave robot. The main objectives of the proposed method are to ensure operational space coordination between the robots' end-effector trajectories and to achieve a referenced general movement of the closed-loop tele-operation system. In addition, the kinematic redundancy of the slave robot, which usually complicates the control problem, is turned into an advantage, and secondary tasks are designed for the slave robot. Moreover, experiments are carried out to validate the achievement of the proposed method using a kinematical redundant tele-operation setup.</p
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
An adaptive method approach in designing a linear filter based output feedback controller for robot manipulators
No full textThis study addresses the tracking problem for robot arms with parametric uncertainties in the model, position measurements available, and no velocity measurements. A filtering technique based on position information is used to compensate for the unmeasured velocity information. A linear filter-based controller is designed to eliminate the controller's dependence on velocity measurements by utilizing adaptive neural networks for model uncertainties. The stability of the closed-loop system is guaranteed by the Lyapunov method. To demonstrate the performance of the proposed controller, numerical simulation results are generated using a two-degree-of-freedom robot arm model and compared comparatively with adaptive fuzzy logic method
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