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  • 1.
    Anisi, David A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Active Observers for Mobile Robotic SystemsManuscript (Other academic)
    Abstract [en]

    An important class of non-uniformly observable systems come from applications in mobile robotics. In this paper, the problem of active observer design for such systems is considered. The set of feasible configurations and the set of output flow equivalent states is defined. It is shown that the inter-relation between these two sets serves as the basis for design of active observers. The proposed observer design method is illustrated by considering a unicycle robot model, equipped with a set of range-measuring sensors.

  • 2.
    Anisi, David A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Ögren, Petter
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Communication constrained multi-UGV surveillance2008In: IFAC World Congress, Seoul, Korea, 2008Conference paper (Refereed)
    Abstract [en]

    This paper addresses the problem of connectivity constrained surveillance of a given polyhedral area with obstacles using a group of Unmanned Ground Vehicles (UGVs). The considered communication restrictions may involve both line-of-sight constraints and limited sensor range constraints. In this paper, the focus is on dynamic information graphs, G, which are required to be kept recurrently connected. The main motivation for introducing this weaker notion of connectivity is security and surveillance applications where the sentry vehicles may have to split temporary in order to complete the given mission efficiently but are required to establish contact recurrently in order to exchange information or to make sure that all units are intact and well-functioning. From a theoretical standpoint, recurrent connectivity is shown to be sufficient for exponential convergence of consensus filters for the collected sensor data.

  • 3. Anisi, David A.
    et al.
    Ögren, Petter
    Swedish Defence Research Agency (FOI), Sweden.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cooperative Minimum Time Surveillance With Multiple Ground Vehicles2010In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 55, no 12, p. 2679-2691Article in journal (Refereed)
    Abstract [en]

    In this paper, we formulate and solve two different minimum time problems related to unmanned ground vehicle (UGV) surveillance. The first problem is the following. Given a set of surveillance UGVs and a polyhedral area, find waypoint-paths for all UGVs such that every point of the area is visible from a point on a path and such that the time for executing the search in parallel is minimized. Here, the sensors' field of view are assumed to have a limited coverage range and be occluded by the obstacles. The second problem extends the first by additionally requiring the induced information graph to be connected at the time instants when the UGVs perform the surveillance mission, i.e., when they gather and transmit sensor data. In the context of the second problem, we also introduce and utilize the notion of recurrent connectivity, which is a significantly more flexible connectivity constraint than, e.g., the 1-hop connectivity constraints and use it to discuss consensus filter convergence for the group of UGVs.

  • 4. Anisi, David A.
    et al.
    Ögren, Petter
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Lindskog, Therese
    Cooperative Surveillance Missions with Multiple Unmanned Ground Vehicles (UGVs)2008In: 47TH IEEE CONFERENCE ON DECISION AND CONTROL, 2008 (CDC 2008), 2008, p. 2444-2449Conference paper (Refereed)
    Abstract [en]

    This paper proposes an optimization based approach to multi-UGV surveillance. In particular, we formulate both the minimum time- and connectivity constrained surveillance problems, show NP-hardness of them and propose decomposition techniques that allow us to solve them efficiently in an algorithmic manner. The minimum time formulation is the following. Given a set of surveillance UGVs and a polyhedral area, find waypoint-paths for all UGVs such that every point of the area is visible from a point on a path and such that the time for executing the search in parallel is minimized. Here, the sensor's field of view are assumed to be occluded by the obstacles and limited by a maximal sensor range. The connectivity constrained formulation extends the first by additionally requiring that the information graph induced by the sensors is connected at the time instants when the UGVs stop to perform the surveillance task. The second formulation is relevant to situation when mutual visibility is needed either to transmit the sensor data being gathered, or to protect the team from hostile persons trying to approach the stationary UGVs.

  • 5.
    Blom Västberg, Oskar
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Dong, H.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Optimal pedestrian evacuation using Model Predictive Control2013In: 2013 European Control Conference, ECC 2013, IEEE , 2013, p. 1224-1229Conference paper (Refereed)
    Abstract [en]

    During an emergency in a building complex, an effective evacuation is essential to avoid crowd disasters. This article presents a route guiding that minimize the evacuation time during the evacuating of pedestrians from a building.

  • 6.
    Cedervall, Simon
    et al.
    KTH, Superseded Departments, Mathematics.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Active nonlinear observers for mobile systems2004In: 2004 43RD IEEE CONFERENCE ON DECISION AND CONTROL (CDC), VOLS 1-5, 2004, p. 3898-3902Conference paper (Refereed)
    Abstract [en]

    For nonlinear systems in general, the observability does not only depend on the initial conditions, but also on the control. This presents an interesting issue: how to design an observer together with the exciting control. In this paper a subproblem in the so called SLAM problem-the relocalization problem is studied, namely, observing the state of a mobile system based on distance sensor readings. An observer is proposed for a car-like robotic system.

  • 7. Cedervall, Simon
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nonlinear observers for unicycle robots with range sensors2007In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 52, no 7, p. 1325-1329Article in journal (Refereed)
    Abstract [en]

    For nonlinear mobile systems equipped with exteroceptive sensors, the observability does not only depend on the initial conditions, but also on the control and the environment. This presents an interesting issue: how to design an observer together with the exciting control. In this note, the problem of designing an observer based on range sensor readings is studied. A design method based on periodic excitations is proposed for unicycle robotic systems.

  • 8. Cheng, D.
    et al.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Semi-global non-regular linearization of nonlinear systems2004In: 2004 5th Asian Control Conference, 2004, p. 520-526Conference paper (Refereed)
    Abstract [en]

    In this paper the problem of global or semi-global non-regular static state feedback linearization of affine nonlinear systems is considered. Based on a normal form and a non-regular linearization technique developed recently by authors, this paper first provides a detailed algorithm for the linearization procedure. Then it also presents an easily verifiable condition to estimate the linearizable region, which solves the semi-global linearization problem. An example is included to describe the method and verify the efficiency of the estimation.

  • 9. Cheng, D.
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Set stability and controllability for switched non-homogeneous linear systems2007In: 2006 Chinese Control Conference Proceedings, CCC 2006, IEEE , 2007, p. 2171-2176Conference paper (Refereed)
    Abstract [en]

    In this paper we consider some control problems of switched non-homogeneous linear systems. First, the set stability of switched non-homogeneous linear systems is considered. It is proved that as the linear parts have a common quadratic Lyapunov function the set stability is assured. The problem of searching smallest attracting set is then considered. Then we assume the switching law is controllable and investigate the controllability condition within the attracting region. Finally, we consider the aggregation and the control of aggregation of flocking behavior. Particularly, the results obtained are implemented to analyzing and manipulating of a group of mobile robots.

  • 10. Cheng, D.
    et al.
    Wang, J.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Stabilization of switched linear systems via LaSalle's invariance principle2008Conference paper (Refereed)
    Abstract [en]

    This paper considers the stability of switched linear systems. Assume a common weak quadratic Lyapunov function exists and the switches satisfy certain ergodic property, we investigate two extensions of LaSalle's invariance principle. Unlike most existing results, the systems we investigated may have switching modes, which are not asymptotically stable. An application to the consensus of multi-agent systems is presented.

  • 11. Cheng, Daizhan
    et al.
    Wang, Jinhuan
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    An extension of LaSalle's invariance principle and its application to multi-agent consensus2008In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 53, no 7, p. 1765-1770Article in journal (Refereed)
    Abstract [en]

    In the paper, an extension of LaSalle's Invariance Principle to a class of switched linear systems is studied. One of the motivations is the consensus problem in multi-agent systems. Unlike most existing results in which each switching mode in the system needs to be asymptotically stable, this paper allows that the switching modes are only Lyapunov stable. Under certain ergodicity assumptions, an extension of LaSalle's Invariance Principle for global asymptotic stability is obtained. Then it is used to solve the consensus reaching problem of certain multi-agent systems in which each agent is modeled by a double integrator, and the associated interaction graph is switching and is assumed to be only jointly connected.

  • 12. Deng, Juan
    et al.
    Wang, Lin
    Liu, Zhixin
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Pose Synchronization of Multiple Rigid Bodies Under Average Dwell Time Condition2018In: Journal of Systems Science and Complexity, ISSN 1009-6124, E-ISSN 1559-7067, Vol. 31, no 1, p. 215-233Article in journal (Refereed)
    Abstract [en]

    This paper considers the pose synchronization problem of a group of moving rigid bodies under switching topologies where the dwell time of each topology may has no nonzero lower bound. The authors introduce an average dwell time condition to characterize the length of time intervals in which the graphs are connected. By designing distributed control laws of angular velocity and linear velocity, the closed-loop dynamics of multiple rigid bodies with switching topologies can be converted into a hybrid dynamical system. The authors employ the Lyapunov stability theorem, and show that the pose synchronization can be reached under the average dwell time condition. Moreover, the authors investigate the pose synchronization problem of the leader-following model under a similar average dwell time condition. Simulation examples are given to illustrate the results.

  • 13. Dong, Y.
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Leader-following formation control problem of unicycles2016In: Proceedings of the 35th Chinese Control Conference 2016, IEEE Computer Society, 2016, p. 8154-8159, article id 7554654Conference paper (Refereed)
    Abstract [en]

    This paper proposes a distributed strategy to solve the leader-following formation problem for multiple under-actuated unicycles. Our distributed control law, dependent on the relative information of its nearest neighbor and itself, can not only enable a network of autonomous mobile agents to circulate around a target of interest, but also achieve any physically feasible formation.

  • 14. Dong, Yi
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Distributed control of periodic formations for multiple under-actuated autonomous vehicles2017In: IET Control Theory & Applications, ISSN 1751-8644, E-ISSN 1751-8652, Vol. 11, no 1, p. 66-72Article in journal (Refereed)
    Abstract [en]

    One of the unique global behaviours of a group of under-actuated autonomous vehicles is known as cyclic pursue, which requires a group of vehicles to uniformly distribute on circles and at the same time, to orbit around a centre point, while circumnavigation further requires those vehicles to circumnavigate a predefined target of interest. Such behaviours can also be called periodic formations. This paper further studies the periodic formations for multi-agent systems composed of a group of under-actuated autonomous vehicles and a target of interest by proposing a distributed strategy to maintain any required distance between two vehicles and desired angle difference between vehicle's heading and the line of sight that takes directly towards its pursuing vehicle. The authors' distributed control law, dependent only on the information of its pursuing vehicle and itself, can not only enable a network of autonomous vehicles to circulate around a target of interest, but also achieve any physically feasible periodic formations, which include forming regular polygons as a special case.

  • 15.
    Dong, Yi
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Generalized formation control for unicycles2015In: Chinese Control Conference, CCC, IEEE Computer Society, 2015, Vol. 2015, p. 7535-7540, article id 7260834Conference paper (Refereed)
    Abstract [en]

    This paper studies formation control of a group of unicycles, and proposes a distributed control law, depending only on the relative position and bearing angle of one nearby vehicle, to realize the circular formation and render more achievable general formations by designing the parameters in the control law. For circular formation, not only we can strictly prove that only two sets of equilibria are asymptotically stable, but also by choosing appropriate control parameters, determine the distances of two vehicles and the radius of the circle that all the unicycles converge to.

  • 16. Dong, Yi
    et al.
    Xu, Shengyuan
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Coordinated control with multiple dynamic leaders for uncertain Lagrangian systems via self-tuning adaptive distributed observer2017In: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239, Vol. 27, no 16, p. 2708-2721Article in journal (Refereed)
    Abstract [en]

    This paper studies coordinated control of multiple Lagrangian systems with parametric uncertainties subject to external disturbances by proposing a fully distributed continuous control law based on the improved self-tuning adaptive observer inspired by non-identifier-based high-gain adaptive control technique. Under this distributed continuous control law, a group of Lagrangian systems are driven to the convex hull spanned by multiple heterogenous dynamic leaders, which can be any combination of step signals of arbitrary unknown magnitudes, ramp signals of arbitrary unknown slopes, and sinusoidal signals of arbitrary unknown amplitudes, initial phases, and any unknown frequencies. It is also worth to mention that this control law we propose, depending neither on any information of leader systems for uninformed followers, nor on external disturbances, even independent of neighbors' velocity, can achieve asymptotic tracking of multiple leaders without any additional condition instead of ensuring the ultimate boundedness of the containment error as in the literature.

  • 17. Fontan, Angela
    et al.
    Shi, Guodong
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Altafini, Claudio
    Interval Consensus: a novel class of constrained consensus problems for multiagent networks2017In: 2017 IEEE 56TH ANNUAL CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    In the consensus problem considered in this paper, each agent can impose a lower and an upper bound on the achievable consensus values. We show that if such state constraints are implemented by saturating the value transmitted to the neighboring nodes, the resulting constrained consensus problem must converge to the intersection of the intervals imposed by the individual agents.

  • 18.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Dimarogonas, Dimos V.
    Egerstedt, Magnus
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    On the Number of Leaders Needed to Ensure Network Connectivity in Arbitrary Dimensions2009In: MED: 2009 17TH MEDITERRANEAN CONFERENCE ON CONTROL & AUTOMATION, VOLS 1-3, NEW YORK: IEEE , 2009, p. 98-103Conference paper (Refereed)
    Abstract [en]

    We examine the leader-to-follower ratio needed to maintain connectivity in a leader-follower multi-agent network with proximity based communication topology. The paper extends the one-dimensional results of [2] to the two dimensional case. In the scenario we consider, only the leaders are aware of the global mission, which is to converge to a known destination point. Thus, the objective of the leaders is to drag the team to the desired goal. In the paper we obtain bounds on the number of leaders needed to complete the task. The results are first established for an initially complete communication graph and then extended to the incomplete case. Computer simulations support the derived theory.

  • 19.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Dimarogonas, Dimos V.
    Laboratory for Information and Decision Systems, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
    Egerstedt, Magnus
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Sufficient conditions for connectivity maintenance and rendezvous in leader-follower networks2010In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 46, no 1, p. 133-139Article in journal (Refereed)
    Abstract [en]

    In this paper we derive a set of constraints that are sufficient to guarantee maintained connectivity in a leader-follower multi-agent network with proximity based communication topology. In the scenario we consider, only the leaders are aware of the global mission, which is to converge to a known destination point. Thus, the followers need to stay in contact with the group of leaders in order to reach the goal. In the paper we show that we can maintain the initial network structure, and thereby connectivity, by setting up bounds on the ratio of leaders-to-followers and on the magnitude of the goal attraction force experienced by the leaders. The results are first established for an initially complete communication graph and then extended to an incomplete graph. The results are illustrated by computer simulations.

  • 20.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Estimation of neighbor velocity in a leader-follower networkManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    In applications where mobile robots are set to follow other moving objects, it is often assumed that not only the relative position, but also the velocity of the object in question is available to the tracking robots. In this paper, we consider a leader-follower system where the followers are equipped only with vision and range sensors. Thus, the followers can detect the positions of their neighbors, but they are unable both to measure the velocity of other agents directly and to obtain estimates of the unknown velocities through communication with other agents. In order to implement the desired leader-follower controls, the followers must use available sensor data to compute individual estimates of their respective leaders' velocities. One option would be to use the Extended Kalman Filter to obtain the estimates, but in this paper we take another approach and propose two separate state observers that can be used by the followers to obtain estimates of the missing velocities and that are also shown to stabilize the tracking controls used by the robots. To evaluate the observers, the tracking performance is compared in simulations for a system that uses observer estimates of the leader's velocity in the control equations and a system that computes the velocity estimates using the standard Extended Kalman Filter algorithm.

  • 21.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Formation control for mobile robots with limited sensor information2005In: 2005 IEEE International Conference on Robotics and Automation (ICRA), Vols 1-4, 2005, p. 1791-1796Conference paper (Refereed)
    Abstract [en]

    In this paper mobile multi-agent systems with limited sensor information are studied. Some control algorithms are proposed that do not require global information, and are easy to implement. First two basic controls for a single mobile agent tracking another moving object are derived. Then it is shown how these basic controls can be combined in order to achieve more complex formations.

  • 22.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Navigation coordination for multi-agent systems with limited sensor information2005In: 2005 International Conference on Control and Automation (ICCA), Vols 1 and 2, 2005, p. 77-82Conference paper (Refereed)
    Abstract [en]

    In this paper mobile multi-agent systems with limited sensor information are studied. Some control algorithms are proposed that do not require global information, and are easy to implement. First two basic controls for serial and parallel formations are derived. Then it is demonstrated how these basic controls can be combined in order to achieve more complex formations. Combined with an obstacle avoidance controller, the emerging system can perform quite complex navigation tasks.

  • 23. Gustavi, Tove
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Observer-Based Leader-Following Formation Control Using Onboard Sensor Information2008In: IEEE Transactions on robotics, ISSN 1552-3098, E-ISSN 1941-0468, ISSN 1552-3098, Vol. 24, no 6, p. 1457-1462Article in journal (Refereed)
    Abstract [en]

    In this paper, leader-following formation control for mobile multiagent systems with limited sensor information is studied. The control algorithms developed require information available from onboard sensors only, and in particular, the measurement of the leader (neighbor) speed is not needed. Instead, an observer Is designed for the estimation of this speed, With the proposed control algorithms as building blocks, many complex formations can be obtained.

  • 24.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Robust formation adaptation for mobile robots2006In: 2006 IEEE/RSJ International Conference on Intelligent Robots and Systems, Vols 1-12, NEW YORK: IEEE , 2006, p. 2521-2526Conference paper (Refereed)
    Abstract [en]

    In this paper, formation adaptation and stability for mobile multi-agent systems is studied. The objective is to suggest a set of robust control functions that can be combined to build complex formations of mobile robots. A properly designed formation should be able to follow a single leader in a clustered environment and to, if necessary, adapt to the surroundings by changing its shape. The two control algorithms proposed here are adapted for systems with limited communication capacity and low performance sensors. The algorithms only require information that can be directly achieved from on-board sensors and, in particular, they only need very coarse estimation of the velocity of the neighbors in the formation. An arbitrary change of the shape of a formation may require switching between control algorithms. In the paper, it is shown that switching between the two proposed control algorithms is stable under some reasonable assumptions. The results are verified by simulations, which also show that switching can be performed safely even with a high noise level and no prior filtering of sensor input.

  • 25.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Robust tracking control and obstacle avoidance for non-holonomic mobile agentsManuscript (preprint) (Other academic)
    Abstract [en]

    Mobile robotics is a subfield of robotics that has received much attention in the last decades and the problem of tracking a moving object has been considered in many different settings. In this paper we consider a unicycle robot with non-holonomic motion constraints that tracks a target, using only local information. The presence of non-holonomic constraints is a complicating factor that is often deliberately overlooked in theoretical work. Still, for the results to be directly implementable, the non-holonomic constraints must be taken into account. In the paper, two types of decentralized tracking control algorithms, which do not require global information about the system, are proposed. Robustness to measurement noise is demonstrated in simulations and, in addition, a reactive obstacle avoidance control that can easily be integrated with the tracking functions is suggested.

  • 26.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Karasalo, Maja
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Adaptive formation control for non-holonomic multi-agent systemsManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    The current paper treats the problem of formation keeping for a non-holonomic multi-agent system. In the paper it is shown that tracking controls developed for single-agent systems can be used as base functions for multi-agent formations. To get an idea of the performance that can be expected for such formations,  robustness to noise and error propagation are studied in simulations for a line formation with simple internal structure. In addition, it is shown that switching between different tracking angles and tracking controls can safely be performed. The results on switching stability imply that it is possible to change the structure of a formation on-line. Together, the results obtained in the paper open up for a variety of applications where a team of robots cooperate to perform tasks faster and with higher precision than would be possible for a single agent. To illustrate the potential of the results, two case studies are included in the paper. They are both independent of the rest of the paper and are added as an Appendix.

  • 27.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Karasalo, Maja
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Multi-robot formation control and terrain servoing with limited sensor information2005In: IFAC Proc. Vol. (IFAC-PapersOnline), 2005, p. 577-582Conference paper (Refereed)
    Abstract [en]

    in this paper mobile multi-agent systems with limited sensor information are studied. Two control algorithms are proposed that do not require global information, and are easy to implement. The control problems are motivated by robotic applications such as cleaning, grass mowing and land mines detection, where a common control problem is the complete coverage path planning, for which it is known that parallel formation is optimal. The proposed control algorithms provide terrain servoing for the leading robot and parallel formation keeping for the followers, both of which are only based on measurements from range sensors.

  • 28.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Karasalo, Maja
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Robust formation adaptation using on-board sensor information2005In: Proceedings of the 24th Chinese Control Conference, Vols 1 and 2 / [ed] Cheng, DH; Xu, BG, 2005, p. 1782-1788Conference paper (Refereed)
    Abstract [en]

    In this paper formation adaptation for mobile multi-agent systems with limited sensor information is studied. Based on a switching control algorithm the separations and bearing angles of the formation can be changed arbitrarily. The control algorithms require only information available from on-board sensors, and in particular, only need very coarse estimation of the reference speed.

  • 29.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Karasalo, Maja
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Martin, C.
    Recursive identification of a hybrid system2015In: 2009 European Control Conference, ECC 2009, 2015, p. 4907-4912Conference paper (Refereed)
    Abstract [en]

    In this paper we consider the problem of retrieving information from a set of noisy and distorted measurements. More precisely we consider a scenario where a set of trajectories x1(t),...,xn(t) are observed using a single measuring device so that the output y(ti) of the device at each sampling point is an observation of precisely one of x1(t),...,xn(t). The process can be modeled as a discrete switched system. We develop a recursive Classification, Correction and Identification Algorithm (CCIA), that recovers xj(ti) and the switching parameter δj(ti) together with the ratio zj of measurements from each state xj(ti).

  • 30.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Karasalo, Maja
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Martin, Clyde
    A classification algorithm for mixed time-varying data setsManuscript (preprint) (Other (popular science, discussion, etc.))
  • 31.
    Gustavi, Tove
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Xiaoming, Hu
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Observer based leader-following formation control using on-board sensor information2007In: Proceedings of the 26th Chinese Control Conference, Vol 6 / [ed] Cheng, DZ; Wu, M, 2007, p. 752-755Conference paper (Refereed)
    Abstract [en]

    In this paper leader-following formation control for mobile multi-agent systems with limited sensor information is studied. The control algorithms developed require only information available from on-board sensors, and in particular, the measurement of the leader (neighbor) speed is not needed.

  • 32. He, He
    et al.
    Yang, Bo
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Exploring community structure in networks by consensus dynamics2016In: Physica A: Statistical Mechanics and its Applications, ISSN 0378-4371, E-ISSN 1873-2119, Vol. 450, p. 342-353Article in journal (Refereed)
    Abstract [en]

    This paper investigates the relationship between community structure and consensus dynamics in complex networks. We analyze the dynamical process towards consensus and show that those sets of densely interconnected nodes corresponding to well-defined communities appear in different time scales. In order to reveal such topological scales, two algorithms built around the idea of visualizing the evolution of different measured quantities are proposed. Then we test our algorithms on a few benchmark graphs whose community structures are already known. Numeric simulations are given to demonstrate the effectiveness and reliability of our methods.

  • 33. Hu, J.
    et al.
    Hong, Y.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Distributed shift target estimation using multiple cooperative agents2009In: Proceedings of 2009 7th Asian Control Conference, ASCC 2009, 2009, p. 117-122Conference paper (Refereed)
    Abstract [en]

    In this paper we discuss the estimation of a moving target by cooperative agents equipped with sensors. To locate a moving target, a distributed algorithm is given for the networked agents based on a time-based shift. A nonlinear filter with fusing collected sensor information is proposed to estimate the trajectory of the target with unknown dynamics. The convergence of the estimation in the sensor network is analyzed and proved via a theoretic approach.

  • 34. Hu, J.
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Nonlinear shift estimation and optimal sensor deployment for target tracking2010In: 2010 8th IEEE International Conference on Control and Automation, ICCA 2010, IEEE , 2010, p. 773-778Conference paper (Refereed)
    Abstract [en]

    In this paper, the mathematical model for target tracking using nonlinear scalar range sensors is formulated first. Sensors are classified into active sensors and submissive sensors according to the relative distances with the target. Then two different estimation algorithms accompanying with an optimal sensor deployment strategy are proposed for both active and submissive sensors to estimate the trajectory of the target. Finally, some numerical examples are given to validate the proposed tracking algorithm.

  • 35. Hu, J.
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Zhang, Y.
    Adaptive bipartite tracking control for coopetition networks2015In: 2015 34th Chinese Control Conference (CCC), IEEE Computer Society, 2015, p. 7067-7072, article id 7260757Conference paper (Refereed)
    Abstract [en]

    Cooperation and competition are two typical interactional relationships in natural and engineering networked systems. Some interesting collective behaviors can emerge through local interactions within the networked systems. This paper considers a bipartite consensus for a group of agents interacting both cooperatively and competitively. Meanwhile, the intrinsic nonlinear dynamics of all the agents are unknown for the neighboring agents. Thus, the interaction network, which we call a coopetition network, is firstly represented by a signed graph. Then, some adaptive estimate laws are proposed for the unknown dynamics. Finally, an adaptive tracking control is designed for each agent to reach a bipartite consensus on the state of the leader. Some sufficient conditions are derived for bipartite consensus of multi-agent systems with the help of a structural balance theory. Simulation results are provided to demonstrate the bipartite consensus formation.

  • 36. Hu, J.
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Zhang, Y.
    Bipartite consensus strategies for coopetition networks2014In: 2014 33rd Chinese Control Conference (CCC), IEEE Computer Society, 2014, p. 1505-1510Conference paper (Refereed)
    Abstract [en]

    Cooperation and competition are two typical interactional relationships in natural and engineering networked systems. Some interesting collective behaviors can emerge through local interactions within the networked systems. This paper focuses on the coexistence of competition and cooperation (i.e., coopetition) at the network level and, simultaneously, the collective dynamics on such coopetition networks. The coopetition network is represented by a directed signed graph. The interaction relationship between the agents on the coopetition network is described by a multi-agent system. We investigate two bipartite consensus strategies for the agents such that all the agents converge to a final state characterized by identical modulus but opposite sign. Under a weak connectivity assumption that the signed network has a spanning tree, some sufficient conditions are derived for bipartite consensus of multi-agent systems with the help of a structural balance theory. Finally, simulation results are provided to demonstrate the bipartite consensus formation.

  • 37. Hu, J. -P
    et al.
    Liu, Z. -X
    Wang, J. -H
    Wang, L.
    Hu, Xiao-Ming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Estimation, intervention and interaction of multi-agent systems2013In: Zidonghua Xuebao/Acta Automatica Sinica, ISSN 0254-4156, Vol. 39, no 11, p. 1796-1804Article in journal (Refereed)
    Abstract [en]

    In this paper we provide a brief survey on recent research on multi-agent systems. We focus on results in three areas of the research, namely, estimation and filtering, intervention by external means, and interactive control.

  • 38. Hu, Jiangping
    et al.
    Hu, Xiaoming
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Nonlinear filtering in target tracking using cooperative mobile sensors2010In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 46, no 12, p. 2041-2046Article in journal (Refereed)
    Abstract [en]

    Collaborative signal processing and sensor deployment have been among the most important research tasks in target tracking using networked sensors In this paper the mathematical model is formulated for single target tracking using mobile nonlinear scalar range sensors Then a sensor deployment strategy is proposed for the mobile sensors and a nonlinear convergent filter is built to estimate the trajectory of the target.

  • 39.
    Hu, Jiangping
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Optimal Target Trajectory Estimation and Filtering Using Networked Sensors2008In: PROCEEDINGS OF THE 27TH CHINESE CONTROL CONFERENCE, VOL 7 / [ed] Cheng, D., HAIDIAN QU DISTRICT: BEIJING UNIV AERONAUTICS & ASTRONAUTICS PRESS , 2008, p. 540-545Conference paper (Refereed)
    Abstract [en]

    Target tracking using distributed sensor network is in general a challenging problem because it always needs to deal with real-time processing of noisy information. In this paper the problem of using nonlinear sensors such as distance and direction sensors for estimating a moving target is studied. The problem is formulated as a prudent design of nonlinear filters fora linear system subject to noisy nonlinear measurements and partially unknown input, which is generated by an exogenous system. In the worst case where the input is completely unknown, the exogenous dynamics is reduced to the random walk model. It can be shown that the nonlinear filter will have optimal convergence if the number of the sensors are large enough and the convergence rate will be highly improved if the sensors are deployed appropriately. This actually raises an interesting issue on active sensing: how to optimally move the sensors if they are considered as mobile multi-agent systems? Finally, a simulation example is given to illustrate and validate the construction of our filter.

  • 40.
    Hu, Jiangping
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimal target trajectory estimation and filtering using networked sensors2008In: Journal of Systems Science and Complexity, ISSN 1009-6124, E-ISSN 1559-7067, Vol. 21, no 3, p. 325-336Article in journal (Refereed)
    Abstract [en]

    Target tracking using distributed sensor network is in general a challenging problem because it always needs to deal with real-time processing of noisy information. In this paper the problem of using nonlinear sensors such as distance and direction sensors for estimating a moving target is studied. The problem is formulated as a prudent design of nonlinear filters for a linear system subject to noisy nonlinear measurements and partially unknown input, which is generated by an exogenous system. In the worst case where the input is completely unknown, the exogenous dynamics is reduced to the random walk model. It can be shown that the nonlinear filter will have optimal convergence if the number of the sensors are large enough and the convergence rate will be highly improved if the sensors are deployed appropriately. This actually raises an interesting issue on active sensing: how to optimally move the sensors if they are considered as mobile multi-agent systems? Finally, a simulation example is given to illustrate and validate the construction of our filter.

  • 41.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Control of collective behavior for multi-robotic systems2006In: Proceedings of 2006 International Conference on Artificial Intelligence: 50 Years' Achievements, Future Directions And Social Impacts, 2006, p. PL23-PL23Conference paper (Refereed)
  • 42.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Control of mobile platforms using a virtual vehicle approach2001In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 46, no 11, p. 1777-1782Article in journal (Refereed)
    Abstract [en]

    Two model independent solutions to the problem of controlling wheel-based mobile platforms are proposed. These two algorithms are based on a so called virtual vehicle approach, where the motion of the reference point on the desired trajectory is governed by a differential equation containing error feedback. This, combined with the fact that the proven stable control algorithms are basically proportional regulators with arbitrary positive gains, make the solutions robust with respect to errors and disturbances, as demonstrated by the experimental results.

  • 43.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Discussion on: "A reduced-order controller design for nonlinear systems with uncertainties and disturbances"2004In: European Journal of Control, ISSN 0947-3580, E-ISSN 1435-5671, Vol. 10, no 3, p. 226-227Article in journal (Refereed)
  • 44.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Drift-free attitude estimation for accelerated rigid bodies2004In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 40, no 4, p. 653-659Article in journal (Refereed)
    Abstract [en]

    In this paper we study the attitude estimation problem for an accelerated rigid body using gyros and accelerometers. The application in mind is that of a walking robot and particular attention is paid to the large and abrupt changes in accelerations that can be expected in such an environment. We propose a state estimation algorithm that fuses data from rate gyros and accelerometers to give long-term drift free attitude estimates. The algorithm does not use any local parameterization of the rigid body kinematics and can thus be used for a rigid body performing any kind of rotations. The algorithm is a combination of two non-standard, but in a sense linear, Kalman filters between which a trigger based switching takes place. The kinematics representation used makes it possible to construct a linear algorithm that can be shown to give convergent estimates for this nonlinear problem. The state estimator is evaluated in simulations demonstrating how the estimates are long-term stable even in the presence of gyro drift.

  • 45.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Formation constrained multi-agent control2001In: IEEE transactions on robotics and automation, ISSN 1042-296X, Vol. 17, no 6, p. 947-951Article in journal (Refereed)
    Abstract [en]

    We propose a model independent coordination strategy for multi-agent formation control. The main theorem states that under a bounded tracking error assumption our method stabilizes the formation error. We illustrate the usefulness of the method by applying it to rigid body constrained motions.

  • 46.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Hybrid control approach to action coordination for mobile robots2002In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 38, no 1, p. 125-130Article in journal (Refereed)
    Abstract [en]

    In this paper, the problem concerning how to coordinate the contributions from concurrent controllers, when controlling mobile robots, is investigated. It is shown how a behavior based control system for autonomous robots can be modeled as a hybrid automaton, where each node corresponds to a distinct robot behavior, This type of construction gives rise to chattering executions, but it is shown how regularized automata can be used to solve this problem. As an illustration. the obstacle-negotiation problem is solved by using a combination of a robust path-following behavior and a reactive obstacle-avoidance behavior that move the robot around a given obstacle at a predefined safety distance.

  • 47.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Input-output behavior for stable linear systems2001In: Journal of the Franklin Institute, ISSN 0016-0032, E-ISSN 1879-2693, Vol. 338, no 4, p. 497-507Article in journal (Refereed)
    Abstract [en]

    In this paper, a controllable, observable, asymptotically stable, finite-dimensional linear system is considered. The input-output problem considered is whether the input in a fairly general class of Hilbert spaces will produce the output in the same class. The problem in this generality appears to be very difficult and in this paper a large class of Hilbert spaces is determined for which the result is true and a series of counter examples are given to the more obvious conjectures.

  • 48.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Nonlinear state estimation for rigid-body motion with low-pass sensors2000In: Systems & control letters (Print), ISSN 0167-6911, E-ISSN 1872-7956, Vol. 40, no 3, p. 183-190Article in journal (Refereed)
    Abstract [en]

    In this paper, we consider the state estimation problem for the nonlinear kinematic equations of a rigid body observed under low-pass sensors. The problem is motivated from a walking robot application where inclinometers and gyros are the sensors used. We show that a non-local high gain observer exists for the nonlinear rigid-body kinematic equations and that it under a small angle assumption is possible to use one inclinometer only to estimate two angles.

  • 49.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Non-regular feedback linearization of nonlinear systems via a normal form algorithm2004In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 40, no 3, p. 439-447Article in journal (Refereed)
    Abstract [en]

    In this paper, the problem of non-regular static state feedback linearization of affine nonlinear systems is considered. First of all, a new canonical form for non-regular feedback linear systems is proposed. Using this form, a recursive algorithm is presented, which yields a condition for single input linearization. Then the left semi-tensor product of matrices is introduced and several new properties are developed. Using the recursive framework and new matrix product, a formula is presented for normal form algorithm. Based on it, a set of conditions for single-input (approximate) linearizability is presented.

  • 50.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Observers for systems with implicit output2000In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 45, no 1, p. 168-173Article in journal (Refereed)
    Abstract [en]

    In this correspondence, we prove the convergence of Luenberger-type observers for systems with implicitly defined outputs.

1234 1 - 50 of 160
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