1,720,962 research outputs found
On the motion/stiffness decoupling property of articulated soft robots with application to model-free torque iterative learning control
Full text linkThis paper tackles the problem of controlling articulated soft robots (ASRs), i.e., robots with either fixed or variable elasticity lumped at the joints. Classic control schemes rely on high-authority feedback actions, which have the drawback of altering the desired robot softness. The problem of accurate control of ASRs, without altering their inherent stiffness, is particularly challenging because of their complex and hard-to-model nonlinear dynamics. Leveraging a learned anticipatory action, Iterative Learning Control (ILC) strategies do not suffer from these issues. Recently, ILC was adopted to perform position control of ASRs. However, the limitation of position-based ILC in controlling variable stiffness robots is that whenever the robot stiffness profile is changed, a different input action has to be learned. Our first contribution is to identify a wide class of ASRs, whose motion and stiffness adjusting dynamics can be proved to be decoupled. This class is described by two properties that we define: strong elastic coupling - relative to motors and links of the system, and their connections - and homogeneity - relative to the characteristics of the motors. Furthermore, we design a torque-based ILC scheme that, starting from a rough estimation of the system parameters, refines the torque needed for the joint positions tracking. The resulting control scheme requires minimum knowledge of the system. Experiments on variable stiffness robots prove that the method effectively generalizes the iterative procedure w.r.t. the desired stiffness profile and allows good tracking performance. Finally, potential restrictions of the method, e.g., caused by friction phenomena, are discussed
Stiffness Bounds for Resilient and Stable Physical Interaction of Articulated Soft Robots
Full text linkIt is widely recognized that impedance modulation is a
key aspect in applications in which robots significantly interact with
the environment or humans. Either active impedance controllers
or actuators with passive variable impedance can be exploited to
modulate the impedance. However, methods capable of determining the right (constant or time-varying) impedance profile in order
to guarantee task performance as well as resilience and stability are
required. In this letter, we discuss how task-related aspects, such
as uncertainties, contact surface shapes, and interaction forces, set
bounds on the admissible Cartesian stiffness. We recall that, an
upper bound on the stiffness is required to prevent high forces
exchanged during the interaction to guarantee adaptability and
safety. Despite this, however, there is also a lower bound to be
considered in order to preserve stability during the interaction. To
this purpose, we study the interaction of a robot, with controllable
Cartesian impedance, with a curved surface. Thus, we provide an
analytic lower bound for the Cartesian stiffness that guarantees
stability of such interaction task, and we prove that this bound
directly depends on task parameters, namely contact force and
surface curvature. Theoretical results are experimentally validated
on robots powered by variable stiffness actuators and compliance
controlled industrial robots
Robotics Laboratory within the Italian School-Work Transition Program in High Schools: A Case Study
No full textThis paper presents a robotics laboratory originated by the collaboration between the university and high school within the Italian school-work transition program. The educational objective of the proposed lab is twofold: 1) ease the transfer of robotic researchers' expertise into useful means for the students' learning; 2) teaching by practice the multidisciplinarity of robotics. We exploited the RoboCup Junior Race as a useful scenario to cover topics from 3D printing for fast prototyping to low-level and high-level controller design. An ad-hoc end-of-term student survey confirms the effectiveness of the approach. Finally, the paper includes some considerations on how general problems in the robotic and scientific community, such as gender issues and COVID-19 restrictions, can impact the educational robotics activities
An Open-Source ROS-Gazebo Toolbox for Simulating Robots With Compliant Actuators
Full text linkTo enable the design of planning and control strategies in simulated environments before their direct application to the real robot, exploiting the Sim2Real practice, powerful and realistic dynamic simulation tools have been proposed, e.g., the ROS-Gazebo framework. However, the majority of such simulators do not account for some of the properties of recently developed advanced systems, e.g., dynamic elastic behaviors shown by all those robots that purposely incorporate compliant elements into their actuators, the so-called Articulated Soft Robots ASRs. This paper presents an open-source ROS-Gazebo toolbox for simulating ASRs equipped with the aforementioned types of compliant actuators. To achieve this result, the toolbox consists of two ROS-Gazebo modules: a plugin that implements the custom compliant characteristics of a given actuator and simulates the internal motor dynamics, and a Robotic Operation System (ROS) manager node used to organize and simplify the overall toolbox usage. The toolbox can implement different compliant joint structures to perform realistic and representative simulations of ASRs, also when they interact with the environment. The simulated ASRs can be also used to retrieve information about the physical behavior of the real system from its simulation, and to develop control policies that can be transferred back to the real world, leveraging the Sim2Real practice. To assess the versatility of the proposed plugin, we report simulations of different compliant actuators. Then, to show the reliability of the simulated results, we present experiments executed on two ASRs and compare the performance of the real hardware with the simulations. Finally, to validate the toolbox effectiveness for Sim2Real control design, we learn a control policy in simulation, then feed it to the real system in feed-forward comparing the results
DESIGN AND METHODS FOR COMPLIANT CONTROL OF ARTICULATED SOFT ROBOTS
No full textNowadays, we are observing the growth of a new generation of robots, able to safely collaborate and cohabit with people, interacting with them and with unstructured environments. These robots are characterized by having lightweight structures and by presenting a gentle way of interacting with the external world.
To face the challenges posed by the human/environment-robot interaction, novel control methods and robotic structure designs have been presented in the past years.
The key idea was the introduction of force/impedance modulation. From one side, actively through impedance controllers, adopted e.g., in collaborative robots of modern industries, and from the other side by inserting passive compliant elements in the robot’s structure, leading to soft robotics.
Both these two approaches allow us to set the robot to be "soft" or to be "stiff" w.r.t. the environment. However, a good planning strategy is needed since different tasks may require different impedance behaviors to be achieved. Besides this, the complexity of compliant robots, derived mainly by the presence of non-linear elastic mechanisms, increases the difficulty in modeling the system. This makes the use of classical modelbased control methods less robust. Moreover, the elastic behavior of the system may be altered if a high-gain feedback is used to compensate for the lack of a good model, and the energy stored within the elastic elements, as well as possible interactions with the environment, may lead to oscillatory behaviors. For these reasons, new control strategies that account for the presence of the elastic dynamics should also be developed.
Motivated by this, in this thesis, I present advanced control concepts that allow achieving the desired link trajectory for soft robots, while simultaneously enabling the impedance selection, thus preserving their elastic behavior. Furthermore, I propose methods for planning the trajectory and also the impedance behavior needed to achieve specific task requirements of these robots. Finally, I present a novel design for the elastic mechanism that allows improving the range of applicability and overcoming the limitations of the current implementation. These novel approaches are validated, in this thesis, through numerical simulations and experimental tests on impedance-controlled robots and robotic platforms with either variable and fixed stiffness actuators
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
Torque-based decoupled control technique for variable stiffness actuators: theoretical and experimental analysis
No full textNowadays, to work safe with Human, robotics machines are forced inside cages, limiting the possible applications.
Soft robotics wants to achieve safe human-robot interaction and cooperation even in unstructured environments. This is done by making deformable robots with soft materials or with fixed or variable compliant mechanical parts.
The compliant behaviors of several Variable Stiffness Actuators (VSAs) are hard to model and introduce non-linear terms into the system dynamic equations. For this reason, it is necessary to develop specific identification and control techniques.
Moreover, most of the present techniques, to compensate for this lack, act with predominant feedback (FB) control components. This latter could compromise the dynamic behavior of the system.
To preserve these dynamic proprieties feedforward (FF) actions would be better. In this context, one strategy, named Iterative Learning Control (ILC) was proposed. Furthermore, this method does not require knowledge of the model.
This work proposes an ILC-based torque control strategy designed to decouple the control of the stiffness from the control of link position. The intent is to achieve simultaneous trajectory and stiffness tracking.
The dynamic model of a generic VSA, and specific agonistic-antagonistic VSA, system are analyzed. The problem is to find a control action independent from the deflection model of the stiffness mechanism. The proposed solution consists in control equilibrium torque and preset angle of the actuator. This strategy was implemented in the firmware of the device.
Moreover, a parametric identification through Least Square (LS) is presented.
Finally, several experiments were performed on systems with different degrees of freedom (DoF) to test the effectiveness of the method. All these experiments were realized using qbMove Advanced variable stiffness actuators
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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