1,720,988 research outputs found
Shared control of an aerial cooperative transportation system with a cable-suspended payload
Full text linkThis paper presents a novel bilateral shared framework for a cooperative aerial transportation and manipulation system composed by a team of micro aerial vehicles with a cable-suspended payload. The human operator is in charge of steering the payload and he/she can also change online the desired shape of the formation of robots. At the same time, an obstacle avoidance algorithm is in charge of avoiding collisions with the static environment. The signals from the user and from the obstacle avoidance are blended together in the trajectory generation module, by means of a tracking controller and a filter called dynamic input boundary (DIB). The DIB filters out the directions of motions that would bring the system too close to singularities, according to a suitable metric. The loop with the user is finally closed with a force feedback that is informative of the mismatch between the operator’s commands and the trajectory of the payload. This feedback intuitively increases the user’s awareness of obstacles or configurations of the system that are close to singularities. The proposed framework is validated by means of realistic hardware-in-the-loop simulations with a person operating the system via a force-feedback haptic interface
Cooperative transportation of a payload using quadrotors: a reconfigurable cable-driven parallel robot
No full textThis paper addresses the problem of cooperative aerial transportation of an object using a team of quadrotors. The approach presented to solve this problem accounts for the full dynamics of the system and it is inspired by the literature on reconfigurable cable-driven parallel robots (RCDPR). Using the modelling convention of RCDPR it is derived a direct relation between the motion of the quadrotors and the motion of the payload. This relation makes explicit the available internal motion of the system, which can be used to automatically achieve additional tasks. The proposed method does not require to specify a priory the forces in the cables and uses a tension distribution algorithm to optimally distribute them among the robots. The presented framework is also suitable for online teleoperation. Physical simulations with a human-in-the-loop validate the proposed approach
Robust adaptive sliding mode control of a redundant cable driven parallel robot
No full textIn this paper we consider the application problem of a redundant cable-driven parallel robot, tracking a reference trajectory in presence of uncertainties and disturbances. A Super Twisting controller is implemented using a recently proposed gains adaptation law [1], thus not requiring the knowledge of the upper bound of the lumped uncertainties. The controller is extended by a feedforward dynamic inversion control that reduces the effort of the sliding mode controller. Compared to a recently developed Adaptive Terminal Sliding Mode Controller for cable-driven parallel robots [2], the proposed controller manages to achieve lower tracking errors and less chattering in the actuation forces even in presence of perturbations. The system is implemented and tested in simulation using a model of a large redundant cable-driven robot and assuming noisy measurements. Simulations show the effectiveness of the proposed method
Bilateral teleoperation of multiple UAVs with decentralized bearing-only formation control
No full textWe present a decentralized system for the bilateral teleoperation of groups of UAVs which only relies on relative bearing measurements, i.e., without the need of distance information or global localization. The properties of a 3D bearing-formation are analyzed, and a minimal set of bearings needed for its definition is provided. We also design a novel decentralized formation control almost globally convergent and able to maintain bounded and non-vanishing inter-distances among the agents despite the absence of direct distance measurements. Furthermore, we develop a multi-master/multi-slave teleoperation setup in order to control the overall behavior of the group and to convey to the human operator suitable force cues, while ensuring stability in presence of delays and packet losses over the master-slave communication channel. The theoretical framework is validated by means of extensive human/hardware in-the-loop simulations using two force-feedback devices and a group of quadrotors. © 2011 IEEE
Semi-Autonomous trajectory generation for mobile robots with integral haptic shared control
Full text linkA new framework for semi-Autonomous path planning for mobile robots that extends the classical paradigm of bilateral shared control is presented. The path is represented as a B-spline and the human operator can modify its shape by controlling the motion of a finite number of control points. An autonomous algorithm corrects in real time the human directives in order to facilitate path tracking for the mobile robot and ensures i) collision avoidance, ii) path regularity, and iii) attraction to nearby points of interest. A haptic feedback algorithm processes both human's and autonomous control terms, and their integrals, to provide an information of the mismatch between the path specified by the operator and the one corrected by the autonomous algorithm. The framework is validated with extensive experiments using a quadrotor UAV and a human in the loop with two haptic interfaces
Interactive planning of persistent trajectories for human-assisted navigation of mobile robots
No full textThis work extends the framework of bilateral shared control of mobile robots with the aim of increasing the robot autonomy and decreasing the operator commitment. We consider persistent autonomous behaviors where a cyclic motion must be executed by the robot. The human operator is in charge of modifying online some geometric properties of the desired path. This is then autonomously processed by the robot in order to produce an actual path guaranteeing: i) tracking feasibility, ii) collision avoidance with obstacles, iii) closeness to the desired path set by the human operator, and iv) proximity to some points of interest. A force feedback is implemented to inform the human operator of the global deformation of the path rather than using the classical mismatch between desired and executed motion commands. Physically-based simulations, with human/hardware-in-the-loop and a quadrotor UAV as robotic platform, demonstrate the feasibility of the method. © 2012 IEEE
Adaptive-Attentive Geolocalization From Few Queries: A Hybrid Approach
Full text linkWe tackle the task of cross-domain visual geo-localization, where the goal is to geo-localize a given query image against a database of geo-tagged images, in the case where the query and the database belong to different visual domains. In particular, at training time, we consider having access to only few unlabeled queries from the target domain. To adapt our deep neural network to the database distribution, we rely on a 2-fold domain adaptation technique, based on a hybrid generative-discriminative approach. To further enhance the architecture, and to ensure robustness across domains, we employ a novel attention layer that can easily be plugged into existing architectures. Through a large number of experiments, we show that this adaptive-attentive approach makes the model robust to large domain shifts, such as unseen cities or weather conditions. Finally, we propose a new large-scale dataset for cross-domain visual geo-localization, called SVOX
Modeling and analysis of cable vibrations for a cable-driven parallel robot
No full textIn this paper we study if approximated linear models are accurate enough to predict the vibrations of a cable of a Cable-Driven Parallel Robot (CDPR) for different pretension levels. In two experiments we investigated the damping of a thick steel cable from the Cablerobot simulator [1] and measured the motion of the cable when a sinusoidal force is applied at one end of the cable. Using this setup and power spectral density analysis we measured the natural frequencies of the cable and compared these results to the frequencies predicted by two linear models: i) the linearization of partial differential equations of motion for a distributed cable, and ii) the discretization of the cable using a finite elements model. This comparison provides remarkable insights into the limits of approximated linear models as well as important properties of vibrating cables used in CDPR
Mechanical design and control of the new 7-DOF CyberMotion Simulator
No full textThis paper describes the mechanical and control design of the new 7-DOF CyberMotion Simulator, a redundant industrial manipulator arm consisting of a standard 6-DOF anthropomorphic manipulator plus an actuated cabin attached to the end-effector. Contrarily to Stewart platforms, an industrial manipulator offers several advantages when used as motion simulator: larger motion envelope, higher dexterity, and possibility to realize any end-effector posture within the workspace. In addition to this, the new actuated cabin acts as an additional joint and provides the needed kinematic redundancy to cope with the robot actuator and joint range constraints, which in general can significantly deteriorate the desired motion cues the robot is reproducing. In particular, we will show that, by suitably exploiting the redundancy better results can be obtained in reproducing sustained acceleration cues, a relevant problem when implementing vehicle simulators. © 2011 IEEE
Application of a differentiator-based adaptive super-twisting controller for a redundant cable-driven parallel robot
Full text linkIn this paper we present preliminary, experimental results of an Adaptive Super-Twisting Sliding-Mode Controller with time-varying gains for redundant Cable-Driven Parallel Robots. The sliding-mode controller is paired with a feed-forward action based on dynamics inversion. An exact sliding-mode differentiator is implemented to retrieve the velocity of the end-effector using only encoder measurements with the properties of finite-time convergence, robustness against perturbations and noise filtering. The platform used to validate the controller is a robot with eight cables and six degrees of freedom powered by 940 W compact servo drives. The proposed experiment demonstrates the performance of the controller, finite-time convergence and robustness in tracking a trajectory while subject to external disturbances up to approximately 400% the mass of the end-effector
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