1,721,089 research outputs found
Feedback linearization and simultaneous stiffness-position control of robots with antagonistic actuated joints.
No full textIn this paper, the dynamic model of a robot with antagonistic actuated joints is presented, and the problem of full linearization via static state feedback is analyzed. The use of transmission elements with nonlinear relation between the displacement and the actuated force allows to control both the position and the stiffness of each joint. The main advantage of this actuation modality is that the achieved stiffness becomes same mechanical characteristic of the system and it is not the result of an immediate control action as in the classical impedance control scheme. Different examples of implementation of this kind of devices are known in literature, even if limited to one single joint and the application of antagonistic actuated kinematic chains in the field of robotic hand design is under investigation. After a brief review of the dependence of the properties of antagonistic actuation on the transmission elements characteristics, a scheme for simultaneous stiffness-position control of the linearized system is presented. Finally, simulation results of a two-link antagonistic actuated arm are reported and discussed
On the Control of Redundant Robots with Variable Stiffness Actuation
No full textIn this paper, the control of a redundant robotic manipulator with variable stiffness actuation is addressed. The problem of controlling simultaneously the end-effector position and stiffness exploiting the robot redundancy for the optimization of the robot configuration is considered, and the relation between the manipulator redundancy and the selection of both the joint and end-effector stiffness is discussed. The controller is configured as a cascade system that allows the decoupling of the actuators dynamics from the arm dynamics and the consequent reduction of the order of the manipulator dynamic model. Only the actuator and joint positions are needed by the controller, introducing in this way a significant simplification with respect to previously proposed state feedback techniques. The effectiveness of the proposed approach is verified by simulations of a 3-DOF planar manipulator
Modelling and control of robotic joints based on sliding pairs
No full textIn this paper, the investigation on the friction phenomena acting at joint level in the robotic hand developed within the DEXMART project is reported. This side effect is given by the adoption of joints based on sliding pairs to reduce the complexity of the mechanism and to ease the assembly procedure. The joint friction has been modelled by means of a specialised version of the LuGre friction model in which the friction coefficients vary with the normal force. The estimated friction has been used in the joint position control loop as a feed-forward term for reducing the position error, as shown by experimental results. The developed friction model has been also used in the experiment to reconstruct the effects of the contact force applied to the joint by the external environment by means of a suitable observer. © 2013 IEEE
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
Development of the UB hand IV: Overview of design solutions and enabling technologies
No full textThe replication of the human hand's functionality and appearance is one of the main reasons for the development of robot hands. Despite 40 years of research in the field [1], the reproduction of human capabilities, in terms of dexterous manipulation, still seems unachievable by the state-of-the-art technologies. From a design perspective, even defining the optimal functionalities of a robotic end-effector is quite a challenging task since possible applications of these devices span industrial robotics, humanoid robotics, rehabilitation medicines, and prosthetics, to name a few. Therefore, it is reasonable to think that the design solutions, which are well suited to a single domain, might not be readily taken as general guidelines. For example, industrial manipulators are often equipped with basic grippers, which are conceived so as to increase the throughput and the reliability, and are assumed to operate in structured environments. In this case, the enhanced manipulation skills and the subsequent cost increases must be carefully motivated by the application requirements
Progetto e realizzazione di un attuatore a rigidezza variabile per applicazioni robotiche
No full textLo sviluppo di robot sicuri ed affidabili per l'interazione fisica uomo-macchina sta cambiando il modo in cui i robot stessi sono progettati, introducendo nuove problematiche tecnologiche. Esempi rilevanti sono l'adozione di ricoprimenti soffici e trasmissioni cedevoli (compliant) o la definizione di leggi di controllo del moto che garantiscono elevata cedevolezza in caso di possibili urti preservando, allo stesso tempo, elevate prestazioni e precisione durante l’esecuzione di compiti. In questo contesto, un interesse crescente è stato dedicato allo studio di giunti a rigidezza variabile. Questa memoria propone un giunto di tale tipologia basato sull'uso di meccanismi compliant, con l'obiettivo di migliorare la compattezza e la flessibilità delle soluzioni meccaniche esistenti. Si introduce una procedura sistematica per la sintesi di un quadrilatero articolato compliant che permette l'implementazione di un profilo di rigidezza desiderato. Infine, si mostra un prototipo del giunto complessivo
Progetto e realizzazione di un attuatore a rigidezza variabile per applicazioni robotiche
No full textLo sviluppo di robot sicuri ed affidabili per l'interazione fisica uomo-macchina sta cambiando il modo in cui i robot stessi sono progettati, introducendo nuove problematiche tecnologiche. Esempi rilevanti sono l'adozione di ricoprimenti soffici e trasmissioni cedevoli (compliant) o la definizione di leggi di controllo del moto che garantiscono elevata cedevolezza in caso di possibili urti preservando, allo stesso tempo, elevate prestazioni e precisione durante l’esecuzione di compiti. In questo contesto, un interesse crescente è stato dedicato allo studio di giunti a rigidezza variabile. Questa memoria propone un giunto di tale tipologia basato sull'uso di meccanismi compliant, con l'obiettivo di migliorare la compattezza e la flessibilità delle soluzioni meccaniche esistenti. Si introduce una procedura sistematica per la sintesi di un quadrilatero articolato compliant che permette l'implementazione di un profilo di rigidezza desiderato. Infine, si mostra un prototipo del giunto complessivo
Design and control of variable stiffness actuation systems
No full textThe paper describes a variable stiffness actuated joint based on two counter-acting actuators that operate on two elastic elements purposely designed in order to exhibit a non-linear elastic characteristic
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
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