1,720,985 research outputs found
The minimum-time crashing problem for the Dubins' car
No full textThis paper determines the time-optimal trajectories bringing a car-like robot, whose driving velocity is constrained to be strictly positive (Dubins car), in collision with the obstacles in its workspace. Both the robot and the obstacles are assumed to have polygonal shape. Based on these trajectories, a distance function is defined and computed that takes into account the nonholonomic constraints and captures the non-symmetric nature of the system
Visual servoing with exploitation of redundancy: An experimental study
No full textWithin the standard IBVS framework for control of generic robotic systems, a suitable exploitation of redundancy w.r.t. the given visual task can significantly improve the overall task execution. Indeed, redundancy can be used to avoid occlusions, joint limits, or to realize tasks that would be ill-conditioned if addressed altogether. In this respect, we propose an experimental evaluation of the performance of two redundancy resolution schemes, namely Task Priority and Task Sequencing, when adopted to realize IBVS tasks on a mobile robot equipped with a pan-tilt camera onboard. ©2008 IEEE
Passivity-Based Decentralized Connectivity Maintenance in the Bilateral Teleoperation of Multiple UAVs
No full textIn this paper, we present a decentralized passivity- based control strategy for the bilateral teleoperation of a group of Unmanned Aerial Vehicles (UAVs). The human operator at the master side can command the group motion and receive suitable force cues informative about the remote environment. By properly controlling the energy exchanged within the slave side (the UAV group), we guarantee that the connectivity of the group is preserved and we prevent inter-agent and obstacle collisions. At the same time, we allow the behavior of the UAVs to be as flexible as possible with arbitrary split and join maneuvers. The results of the paper are validated by means of human/hardware- in-the-loop (HHIL) simulations
Shortest Paths to Obstacles for a Polygonal Dubins Car
No full textIn this paper, we characterize the time-optimal trajectories leading a Dubins car in collision with the obstacles in its workspace. Due to the constant velocity constraint characterizing the Dubins car model, these trajectories form a sufficient set of shortest paths between any robot configuration and the obstacles in the environment. Based on these paths, we define and give the algorithm for computing a distance function that takes into account the nonholonomic constraints and captures the nonsymmetric nature of the system. The developments presented here assume that the obstacles and the robot are polygons although the methodology can be applied to different shapes
Kinematic modeling and redundancy resolution for nonholonomic mobile manipulators
No full textWe consider robotic systems made of a nonholonomic mobile platform carrying a manipulator (nonholonomic mobile manipulator, NMM). By combining the manipulator differential kinematics with the admissible differential motion of the platform, a simple and general kinematic model for NMMs is derived. Assuming that the robotic system is kinematically redundant for a given task, we present the extension of redundancy resolution schemes originally developed for standard manipulators, in particular the Projected Gradient (PG) and the Reduced Gradient (RG) optimization-based methods. The case of a configuration-dependent task specification is also discussed. The proposed modeling approach is illustrated with reference to representative NMMs, and the performance of the PG and RG methods for redundancy resolution is compared on a series of numerical case studies. ©2006 IEEE
The motion control problem for the cybercarpet
No full textExploration of virtual worlds with unconstrained locomotion possibilities for the user is the main objective of the European research project CyberWalk. This should be achieved through the use of an actuated platform (the CyberCarpet) that compensates for the walker's locomotion in such a way to keep her/him close to the platform center. This paper presents the control problem for the platform motion, including objectives and constraints, overall control architecture, and kinematic modeling. Since the platform has only two actuating devices (linear and angular), the control problem is similar to that of output regulation for nonholonomic wheeled mobile robots in the presence of an unpredictable disturbance due to walker's locomotion. Based on the kinematic model, a velocity control design achieving input-output decoupling and linearization is proposed and its performance is verified by simulations. ©2006 IEEE
Feature depth observation for image-based visual servoing: Theory and experiments
No full textIn the classical image-based visual servoing framework, error signals are directly computed from image feature parameters, allowing, in principle, control schemes to be obtained that need neither a complete three-dimensional (3D) model of the scene nor a perfect camera calibration. However, when the computation of control signals involves the interaction matrix, the current value of some 3D parameters is requiredfor each considered feature, and typically a rough approximation of this value is used. With reference to the case of a point feature, for which the relevant 3D parameter is the depth Z, we propose a visual servoing approach where Z is observed and made available for servoing. This is achieved by interpreting depth as an unmeasurable state with known dynamics, and by building a non-linear observer that asymptotically recovers the actual value of Z for the selected feature. A byproduct of our analysis is the rigorous characterization of camera motions that actually allow such observation. Moreover, in the case of a partially uncalibrated camera, it is possible to exploit complementary camera motions in order to preliminarily estimate the focal length without knowing Z. Simulations and experimental results are presented for a mobile robot with an on-board camera in order to illustrate the benefits of integrating the depth observation within classical visual servoing schemes. © SAGE Publications 2008 Los Angeles
Feedback/feeeforward schemes for motion control of the CyberCarpet
Get PDFThe CyberCarpet is an actuated platform that allows unconstrained locomotion possibilities to a walking user for VR exploration. The platform has two actuating devices (linear and angular) and the motion control problem is dual to that of nonholonomic wheeled mobile robots. The main control objective is to keep the walker close to the platform center. Simple but global kinematic control schemes are presented, addressing in particular the handling of singularity issues. The feedback stabilizing part, which is based only on the user's pose information, is complemented by a feedforward term derived from a walker's velocity observer. Numerical and graphical simulation results are presented
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