224 research outputs found
Optical spectroscopy of X-ray sources in the Taurus molecular cloud: discovery of ten new pre-main sequence stars
No full textAims. We have analyzed optical spectra of 25 X-ray sources identified as potential new members of the Taurus molecular cloud (TMC), in order to confirm their membership in this star-forming region. Methods: Fifty-seven candidate members were previously selected among the X-ray sources in the XEST survey, having a 2MASS counterpart compatible with a pre-main sequence star based on color-magnitude and color-color diagrams. We obtained high-resolution optical spectra for 7 of these candidates with the SARG spectrograph at the TNG telescope, which were used to search for lithium absorption and to measure the Hα line and the radial and rotational velocities. Then, 18 low-resolution optical spectra obtained with the instrument DOLORES for other candidate members were used for spectral classification, for Hα measurements, and to assess membership together with IR color-color and color-magnitude diagrams and additional information from the X-ray data. Results: We found that 3 sources show lithium absorption, with equivalent widths (EWs) of 500 mÅ, broad spectral line profiles, indicating rotational velocities of 20{-}40 km s-1, radial velocities consistent with those for known members, and Hα emission. Two of them are classified as new weak-lined T Tauri stars, while the EW ( -9 Å) of the Hα line and its broad asymmetric profile clearly indicate that the third star (XEST-26-062) is a classical T Tauri star. Fourteen sources observed with DOLORES are M-type stars. Fifteen sources show Hα emission. Six of them have spectra that indicate surface gravity lower than in main sequence stars, and their de-reddened positions in IR color-magnitude diagrams are consistent with their derived spectral type and with pre-main sequence models at the distance of the TMC. The K-type star XEST-11-078 is confirmed as a new member on the basis of the strength of the Hα emission line. Overall, we confirm membership to the TMC for 10 out of 25 X-ray sources observed in the optical. Three sources remain uncertain
Friction Observer and Compensation for Control of Robots with Joint Torque Measurement
No full textIn this paper we introduce a friction observer for robots with joint torque sensing (in particular for the DLR medical robot) in order to increase the positioning accuracy and the performance of torque control. The observer output corresponds to the low-pass filtered friction torque. It is used for friction compensation in conjunction with a MIMO controller designed for flexible joint arms. A passivity analysis is done for this friction compensation, allowing a Lyapunov based convergence analysis in the context of the nonlinear robot dynamics. For the complete controlled system, global asymptotic stability can be shown. Experimental results validate the practical efficiency of the approach. ©2008 IEEE
Planning and Real Time Control of a Minimally Invasive Robotic Surgery System
No full textThis paper introduces the planning and control software of a teleoperating robotic system for minimally invasive surgery. It addresses the problem of how to organize a complex system with 41 degrees of freedom including robot setup planning, force feedback control and nullspace handling with three robotic arms. The planning software is separated into sequentially executed planning and registration procedures. An optimal setup is first planned in virtual reality and then adapted to variations in the operating room. The real time control system is composed of hierarchical layers. The design is flexible and expandable without losing performance. Structure, functionality and implementation of planning and control are described. The robotic system provides the surgeon with an intuitive hand-eye-coordination and force feedback in teleoperation for both hands
Safe Acting and Manipulation in Human Environments: A Key Concept for Robots in our Society
No full textIn this paper we review our work on safe acting and manipulation in human environments. In order for a robot to be able to safely interact with its environment it is primary to be able to react to unforeseen events in real-time on basically all levels of abstraction. Having this goal in mind, our contributions reach from fundamental understanding of human injury due to robot-human collisions as the underlying metric for “safe” behavior, various interaction control schemes that ground on the basic components impedance control and collision behavior, to real-time motion planning and behavior based control as an interface level for task planning. A significant amount of this work has found found its way into international standardization committees, products, and was applied in numerous real-world applications
On the Passivity Based Impedance Control of Flexible Joint Robots
No full textIn this work a novel type of impedance controllers
for flexible joint robots is proposed. As a target impedance a
desired stiffness and damping are considered without inertia
shaping. For this problem two controllers of different complexity
are proposed. Both have a cascaded structure with an inner
torque feedback loop and an outer impedance controller. For
the torque feedback, a physical interpretation as a scaling of the
motor inertia is given, which allows to incorporate the torque
feedback into a passivity based analysis. The outer impedance
control law is then designed differently for the two controllers.
In the first approach the stiffness and damping terms and the
gravity compensation term are designed separately. This outer
control loop uses only the motor position and velocity, but no noncollocated
feedback of the joint torques or link side positions. In
combination with the physical interpretation of torque feedback,
this allows us to give a proof of the asymptotic stability of the
closed-loop system based on the passivity properties of the system.
The second control law is a refinement of this approach, in which
the gravity compensation and the stiffness implementation are
designed in a combined way. Thereby, a desired static stiffness
relationship is obtained exactly. Additionally, some extensions of
the controller to visco-elastic joints and to Cartesian impedance
control are given. Finally, some experiments with the DLR
lightweight robots verify the developed controllers and show the
efficiency of the proposed control approach
Contribution à l’étude de la reprise végétative du Chêne liège (Quercus suber L.) après incendie Cas du massif forestier de Beni Affer II (Canton Djouambia) Wilaya de Jijel
No full text57 p. : ill. ; 30 cm. (+ CD-Rom)Le présent travail a été réalisé dans la subéraie domaniale de Beni Affer II située à Jijel, où elle couvre une superficie de 37 680 m2. Cette étude a été menée après l’incendie de l’été 2017 dans 30 placettes, dans un objectif principal était d’évaluer l’impact des incendies sur la de reprise végétative de la subéraie 22 mois après, montrent une bonne reprise végétative des arbres (94%) dont 82% par la couronne. Donc le chêne liège est l’arbre le plus résistant aux feux par ses propriétés isolantes du liège, celles-ci peuvent fournir une protection assez efficace pour la protection des bourgeons dormant
Modular state-based behavior control for safe human-robot interaction: A lightweight control architecture for a lightweight robot
No full textIn this paper we present a novel control architecture
for realizing human-friendly behaviors and intuitive
state based programming. The design implements strategies
that take advantage of sophisticated soft-robotics features for
providing reactive, robust, and safe robot actions in dynamic
environments. Quick access to the various functionalities of the
robot enables the user to develop flexible hybrid state automata
for programming robot behaviors. The real-time robot control
takes care of all safety critical aspects and provides reactive
reflexes that directly respond to external stimuli
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