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Hyo-sung Ahn - One of the best experts on this subject based on the ideXlab platform.

  • Distributed formation control of the special Euclidean group SE(2) via Global orientation control
    IET Control Theory & Applications, 2020
    Co-Authors: Jae-gyeong Lee, Minh Hoang Trinh, Hyo-sung Ahn, Byung-hun Lee
    Abstract:

    The authors propose fully distributed strategies for multi-agent formation control of the two-dimensional special Euclidean group. To control the rotated local Reference Frames, they firstly estimate the orientation angle of each agent with regard to a Global Reference Frame. By using only local measurements, the orientation angle is estimated in a distributed way. The estimated orientation is, then, exploited to control each agent's orientation. Each agent's orientation converges to the prescribed desired orientation. Finally, a distributed formation control strategy based on displacement measurement is proposed to achieve the desired formation shape of the two-dimensional special Euclidean group. Under the proposed strategy, the authors ensure that the formation shape including position and orientation exponentially converges to the desired formation shape. Moreover, the formation shape is invariant to a translation and a rotation compared with the desired formation shape.

  • Shape and orientation control of moving formation in multi-agent systems without Global Reference Frame
    Automatica, 2018
    Co-Authors: Sung-mo Kang, Hyo-sung Ahn
    Abstract:

    In this paper, distance-based formation control laws for the multi-agent systems are proposed when the Reference velocity is unknown to the followers. Especially, not only the shape but the orientation of formation is also controlled. Each agent measures only the relative positions of neighbors with respect to their own local coordinate system. The local coordinate systems in each agent are not aligned and unknown to the other agents; thus the control laws are completely decentralized. Using the measured local information, the unknown Reference velocity is estimated by applying an adaptive method. The shape and orientation of formation are controlled based on the estimated Reference velocity. The stability and convergence of the system are analyzed mathematically and verified through numerical simulation.

  • CCTA - Bearing-Based Formation Control and Network Localization via Global Orientation Estimation
    2018 IEEE Conference on Control Technology and Applications (CCTA), 2018
    Co-Authors: Minh Hoang Trinh, Byung-hun Lee, Hyo-sung Ahn
    Abstract:

    Consider a system of single-integrator agents in the d-dimensional space whose goal is to achieve a target formation shape specified by some desired bearing vectors. Suppose that the agents do not share a common Global Reference Frame but can sense the relative orientations and bearing information with regard to some neighbor agents. We propose solutions to two problems: Global orientation estimation and bearing-only measurement based formation control. Combining the solutions to the two problems, we solve the distributed bearing-based formation control problem. The combined strategy guarantees the desired formation shape is almost Globally achieved up to a translation, a rotation and a scaling. Furthermore, we apply the proposed strategy to bearing-based network localization as a dual problem.

  • Leader-follower type distance-based formation control of a group of autonomous agents
    International Journal of Control Automation and Systems, 2017
    Co-Authors: Hyo-sung Ahn
    Abstract:

    We study distance-based formation control of a group of mobile agents consisting of several leaders and the remaining followers. The leaders sense their own positions with respect to a Global Reference Frame whereas the followers sense only relative positions of their neighbors with respect to their own local Reference Frames. The relative position sensing topology is given as a directed acyclic graph. The objective of the agents is to reach their desired positions in the Global Reference Frame. By applying a distance-based control law to the followers, we allow the agents to reach their desired positions if the sensing graph satisfies some graph rigidity conditions. Further we study the case that the desired positions are time-varying.

  • Distance-Based Cycle-Free Persistent Formation: Global Convergence and Experimental Test With a Group of Quadcopters
    IEEE Transactions on Industrial Electronics, 2017
    Co-Authors: Sung-mo Kang, Myoung-chul Park, Hyo-sung Ahn
    Abstract:

    In this paper, distributed formation control for multi-agent systems is considered. The proposed control laws are designed to Globally obtain and keep the desired formation in a two-dimensional space. It is assumed that the local Frames of the agents are not aligned with each other and each agent does not know the orientation of others’ coordinate Frames. Further, the agent measures only relative positions of neighbors with respect to the local Reference Frame. Therefore, the control of the system is completely decentralized and the Global convergence is achieved without the Global Reference Frame. The stability and convergence of the system are analyzed mathematically and the experiment using quadcopters is performed to verify the results of the theoretical analysis. In addition, the ambiguity problem and time-varying velocity case are also handled and discussed.

Carlos Sagues - One of the best experts on this subject based on the ideXlab platform.

  • distributed formation control of non holonomic robots without a Global Reference Frame
    International Conference on Robotics and Automation, 2016
    Co-Authors: Eduardo Montijano, Mac Schwager, Eric Cristofalo, Carlos Sagues
    Abstract:

    In this paper we consider the problem of controlling a team of non-holonomic robots to reach a desired formation. The formation is described in terms of the desired relative positions and orientations the robots need to keep with respect to each other, and it is assumed that the robots do not have a common shared Reference Frame. In other words, the robots can use only on-board sensing to achieve the formation. We first consider a holonomic Framework, using a well known distance-based approach to reach a formation for the positions. We then include a control law for the orientations. We further discuss the problem of mirror configurations that appear when different desired relative orientations can satisfy the same distance-based constraints through different formations. Exploiting the concept of chirality, we present a relabeling strategy to reassign the robots' roles to reach the desired pattern when a mirror configuration occurs. The distance-based holonomic control is then transformed to cope with the non-holonomic constraints using a piecewise-smooth function. Simulation results, as well as hardware experiments with five m3pi robots demonstrate the applicability of our approach.

  • ICRA - Distributed formation control of non-holonomic robots without a Global Reference Frame
    2016 IEEE International Conference on Robotics and Automation (ICRA), 2016
    Co-Authors: Eduardo Montijano, Mac Schwager, Eric Cristofalo, Carlos Sagues
    Abstract:

    In this paper we consider the problem of controlling a team of non-holonomic robots to reach a desired formation. The formation is described in terms of the desired relative positions and orientations the robots need to keep with respect to each other, and it is assumed that the robots do not have a common shared Reference Frame. In other words, the robots can use only on-board sensing to achieve the formation. We first consider a holonomic Framework, using a well known distance-based approach to reach a formation for the positions. We then include a control law for the orientations. We further discuss the problem of mirror configurations that appear when different desired relative orientations can satisfy the same distance-based constraints through different formations. Exploiting the concept of chirality, we present a relabeling strategy to reassign the robots' roles to reach the desired pattern when a mirror configuration occurs. The distance-based holonomic control is then transformed to cope with the non-holonomic constraints using a piecewise-smooth function. Simulation results, as well as hardware experiments with five m3pi robots demonstrate the applicability of our approach.

  • distributed formation control without a Global Reference Frame
    Advances in Computing and Communications, 2014
    Co-Authors: Eduardo Montijano, Dingjiang Zhou, Mac Schwager, Carlos Sagues
    Abstract:

    This paper presents a decentralized controller to drive a team of agents to reach a desired formation in the absence of a Global Reference Frame. Each agent is able to measure its relative position and orientation with respect to its neighbors. The different orientations imply that the relative positions between pairs of agents are sensed differently for each agent. In order to reach the desired configuration, the agents use two simultaneous consensus controllers, one to control their relative orientations, and another for their relative positions. The convergence to the desired configuration is shown by comparing the system with time-varying orientations with the equivalent approach with fixed rotations, showing that their difference vanishes as time goes to infinity. While the analysis in the paper is performed in a 2-dimensional space with orientations belonging to SO(2), our approach can be extended to handle 3 dimensions and orientations in SO(3). Simulation results, as well as hardware experiments with two quadrotor UAVs, corroborate the theoretical findings of the paper.

  • ACC - Distributed formation control without a Global Reference Frame
    2014 American Control Conference, 2014
    Co-Authors: Eduardo Montijano, Dingjiang Zhou, Mac Schwager, Carlos Sagues
    Abstract:

    This paper presents a decentralized controller to drive a team of agents to reach a desired formation in the absence of a Global Reference Frame. Each agent is able to measure its relative position and orientation with respect to its neighbors. The different orientations imply that the relative positions between pairs of agents are sensed differently for each agent. In order to reach the desired configuration, the agents use two simultaneous consensus controllers, one to control their relative orientations, and another for their relative positions. The convergence to the desired configuration is shown by comparing the system with time-varying orientations with the equivalent approach with fixed rotations, showing that their difference vanishes as time goes to infinity. While the analysis in the paper is performed in a 2-dimensional space with orientations belonging to SO(2), our approach can be extended to handle 3 dimensions and orientations in SO(3). Simulation results, as well as hardware experiments with two quadrotor UAVs, corroborate the theoretical findings of the paper.

Jean-bernard Hayet - One of the best experts on this subject based on the ideXlab platform.

  • a visual landmark Framework for indoor mobile robot navigation
    International Conference on Robotics and Automation, 2002
    Co-Authors: Jean-bernard Hayet, Frédéric Lerasle, Michel Devy
    Abstract:

    Presents vision functions needed on a mobile robot to deal with landmark-based navigation in buildings. Landmarks are planar, quadrangular surfaces, which must be distinguished from the background, typically a poster on a wall or a door-plate. In a first step, these landmarks are detected and their positions with respect to a Global Reference Frame are learned; this learning step is supervised so that only the best landmarks are memorized, with an invariant representation based on a set of interest points. Then, when the robot looks for visible landmarks, the recognition procedure takes advantage of the partial Hausdorff distance to compare the landmark model and the detected quadrangles. The paper presents the landmark detection and recognition procedures, and discusses their performances.

  • ICRA - A visual landmark Framework for indoor mobile robot navigation
    Proceedings 2002 IEEE International Conference on Robotics and Automation (Cat. No.02CH37292), 1
    Co-Authors: Jean-bernard Hayet, Frédéric Lerasle, M. Devy
    Abstract:

    Presents vision functions needed on a mobile robot to deal with landmark-based navigation in buildings. Landmarks are planar, quadrangular surfaces, which must be distinguished from the background, typically a poster on a wall or a door-plate. In a first step, these landmarks are detected and their positions with respect to a Global Reference Frame are learned; this learning step is supervised so that only the best landmarks are memorized, with an invariant representation based on a set of interest points. Then, when the robot looks for visible landmarks, the recognition procedure takes advantage of the partial Hausdorff distance to compare the landmark model and the detected quadrangles. The paper presents the landmark detection and recognition procedures, and discusses their performances.

Michael Heflin - One of the best experts on this subject based on the ideXlab platform.

  • Comparison of a GPS-defined Global Reference Frame with ITRF2000
    Gps Solutions, 2002
    Co-Authors: Michael Heflin, Donald Argus, David C. Jefferson, F. Webb, James F. Zumberge
    Abstract:

    The Global Positioning System is a constellation of 24–28 satellites, which can be used to define a Global terrestrial Reference Frame. Daily offsets between a GPS defined Frame and ITRF2000 have been estimated using more than a decade of GPS observations from 1990–2001. A linear fit to the full span of data shows agreement between the two Frames at the level of –1 ppb and –0.1 ppb/year for scale, 5 mm and 0 mm/year for the X component of center of mass, –2 mm and –3 mm/year for the Y component, and 4 mm and 6 mm/year for the Z component. GPS is a viable tool for defining the Global Reference Frame either alone, or in combination with other geodetic techniques.

  • The International GPS Network for Charting the Evolving Global Reference Frame
    1995
    Co-Authors: J. F. Zumberge, Michael Heflin, U. J. Lindqwister, R. E. Neilan, Michael M. Watkins
    Abstract:

    The Telecommunications and Engineering Division of Caltech's Jet Propulsion Laboratory is funded by the National Aeronautics and Space Administration to play a variety of roles in applying the Global Positioning System (GPS) to geodesy and geodynamics. Among these are the operation of dozens of Globally-distributed, permanently-operating Earth fixed GPS stations. This, and other applications are described.

  • Global Reference Frame: Intercomparison of results (SLR, VLBI and GPS)
    1994
    Co-Authors: Michael M. Watkins, Michael Heflin
    Abstract:

    The terrestrial Reference Frame (TRF) is realized by a set of positions and velocities derived from a combination of the three space geodetic techniques, SLR, VLBI and GPS. The standard International TRF is constructed by the International Earth Rotation Service in such a way that it is stable with time and the addition of new data. An adopted model for overall plate motion, NUVEL-1 NNR, defines the conceptual Reference Frame in which all the plates are moving. In addition to the measurements made between Reference points within the space geodetic instruments, it is essential to have accurate, documented eccentricity measurements from the instrument Reference points to ground monuments. Proper local surveys between the set of ground monuments at a site are also critical for the use of the space geodetic results. Eccentricities and local surveys are, in fact, the most common and vexing sources of error in the use of the TRF for such activities as collocation and intercomparison.

Tom Drummond - One of the best experts on this subject based on the ideXlab platform.

  • vision based augmented reality visual guidance with keyFrames
    Computer Graphics International, 2006
    Co-Authors: Timothy S. Y. Gan, Tom Drummond
    Abstract:

    A vision-based augmented reality visual guidance system is presented. It utilises naturally occurring point features and does not require a Global Reference Frame. KeyFrames extracted from a training sequ- ence are used to provide multiple local Reference Frames. These keyFrames are selected by minimising the uncertainties in structure recovery to find an optimal tradeoff between narrow and wide baselines.

  • Computer Graphics International - Vision-based augmented reality visual guidance with keyFrames
    Advances in Computer Graphics, 2006
    Co-Authors: Timothy S. Y. Gan, Tom Drummond
    Abstract:

    A vision-based augmented reality visual guidance system is presented. It utilises naturally occurring point features and does not require a Global Reference Frame. KeyFrames extracted from a training sequ- ence are used to provide multiple local Reference Frames. These keyFrames are selected by minimising the uncertainties in structure recovery to find an optimal tradeoff between narrow and wide baselines.