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  • 1.
    Altafini, Claudio
    et al.
    SISSA-ISAS International School for Advanced Studies.
    Speranzon, Alberto
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Johansson, Karl Henrik
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Hybrid control of a truck and trailer vehicle2002In: Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349, Vol. 2289, p. 21-34Article in journal (Other academic)
    Abstract [en]

    A hybrid control scheme is proposed for the stabilization of backward driving along simple paths for a miniature vehicle composed of a truck and a two-axle trailer. When reversing, the truck and trailer can be modelled as an unstable nonlinear system with state and input saturations. Due to these constraints the system is impossible to globally stabilize with standard smooth control techniques, since some initial states necessarily lead to that the so called jack-knife locks between the truck and the trailer. The proposed hybrid control method, which combines backward and forward motions, provide a global attractor to the desired reference trajectory. The scheme has been implemented and successfully evaluated on a radio-controlled vehicle. Results from experimental trials are reported.

  • 2.
    Altafini, Claudio
    et al.
    KTH, Superseded Departments, Mathematics.
    Speranzon, Alberto
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Wahlberg, Bo
    KTH, Superseded Departments, Signals, Sensors and Systems.
    A feedback control scheme for reversing a truck and trailer vehicle2001In: IEEE transactions on robotics and automation, ISSN 1042-296X, Vol. 17, no 6, p. 915-922Article in journal (Refereed)
    Abstract [en]

    A control scheme is proposed for stabilization of backward driving along simple paths for a miniaturized vehicle composed of a truck and a two-axle trailer. The paths chosen are straight lines and arcs of circles. When reversing, the truck and trailer under examination can be modeled as an unstable nonlinear system with state and input saturations. The simplified goal of stabilizing along a trajectory (instead of a point) allows us to consider a system with controllable linearization. Still, the combination of instability and saturations makes the task impossible with a single controller. In fact, the system cannot be driven backward from all initial states because of the jack-knife effects between the parts of the multibody vehicle; it is sometimes necessary to drive forward to enter into a specific region of attraction. This leads to the use of hybrid controllers. The scheme has been implemented and successfully used to reverse the radio-controlled vehicle.

  • 3. Borges De Sousa, João
    et al.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Silva, Jorge
    A control architecture for multiple submarines in coordinated search missions2005In: Proceedings of the 16th IFAC World Congress, IFAC , 2005, p. 109-114Conference paper (Refereed)
    Abstract [en]

    A control architecture for executing multi-vehicle search algorithms is presented. The proposed hierarchical structure consists of three control layers: maneuver controllers, vehicle supervisors and team controllers. The system model is described as a dynamic network of hybrid automata in the programming language Shift and allows reasoning about specification and dynamical properties in a formal setting. The particular search problem that is studied is that of finding the minimum of a scalar field using a team of autonomous submarines. As an illustration, a coordination scheme based on the Nelder-Mead simplex optimization algorithm is presented and illustrated through simulations.

  • 4. Carli, R.
    et al.
    Fagnani, F.
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Zampieri, S.
    Communication constraints in coordinated consensus problems2006In: Proc Am Control Conf, 2006, p. 4189-4194Conference paper (Refereed)
    Abstract [en]

    The interrelationship between control and communication theory is becoming of fundamental importance in many distributed control systems. Particular examples are systems comprised of multiple agents. When it comes to coordinately control a group of autonomous mobile agents in order to achieve a common task, communications constraints impose limits on the achievable control performance. Starting from an emerging problem, studied in the robotics and control communities, called consensus or state agreement problem, we characterize the relationship between the amount of information exchanged by the agents and the rate of convergence to the agreement. In particular we show that communication networks that exhibit particular symmetries yield slow convergence, if the amount of information exchanged does not scale with the number of agents. On the other hand, if we allow exchange of logarithmic quantized data, the control performance significantly improves with little growth of the required communication effort.

  • 5. Carli, Ruggero
    et al.
    Fagnani, Fabio
    Focoso, Marco
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Zampieri, Sandro
    Symmetries in the coordinated consensus problem2006In: Networked Embedded Sensing And Control / [ed] Antsaklis, PJ; Tabuada, P, Springer Berlin/Heidelberg, 2006, Vol. 331, p. 25-51Conference paper (Refereed)
    Abstract [en]

    In this paper we consider a widely studied problem in the robotics and control communities, called consensus problem. The aim of the paper is to characterize the relationship between the amount of information exchanged by the vehicles and the speed of convergence to the consensus. Time-invariant communication graphs that exhibit particular symmetries are shown to yield slow convergence if the amount of information exchanged does not scale with the number of vehicles. On the other hand, we show that retaining symmetries in time-varying communication networks allows to increase the speed of convergence even in the presence of limited information exchange.

  • 6. Carli, Ruggero
    et al.
    Fagnani, Fabio
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Zampieri, Sandro
    Communication constraints in the average consensus problem2008In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 44, no 3, p. 671-684Article in journal (Refereed)
    Abstract [en]

    The interrelationship between control and communication theory is becoming of fundamental importance in many distributed control systems, such as the coordination of a team of autonomous agents. In such a problem, communication constraints impose limits on the achievable control performance. We consider as instance of coordination the consensus problem. The aim of the paper is to characterize the relationship between the amount of information exchanged by the agents and the rate of convergence to the consensus. We show that time-invariant communication networks with circulant symmetries yield slow convergence if the amount of information exchanged by the agents does not scale well with their number. On the other hand, we show that randomly time-varying communication networks allow very fast convergence rates. We also show that by adding logarithmic quantized data links to time-invariant networks with symmetries, control performance significantly improves with little growth of the required communication effort.

  • 7. Fagnani, Fabio
    et al.
    Johansson, Karl Henrik
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Speranzon, Alberto
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Zampieri, Sandro
    On multi-vehicle rendezvous under quantized communication2004Conference paper (Refereed)
    Abstract [en]

    A rendezvous problem for a team of autonomous vehicles, which communicate over quantized channels, is analyzed. The paper illustrates how communication topologies based on uniform and logarithmic quantizations influence the performance. Since a logarithmic quantizer in general imposes fewer bits to be communicated compared to a uniform quantizer, the results indicate estimates of lower limits on the amount of information that needs to be exchanged in order for the vehicles to meet. Simulation examples illustrate the results.

  • 8.
    Fischione, Carlo
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sangiovanni-Vincentelli, Alberto
    Peer-to-peer Estimation over Wireless Sensor Networks via Lipschitz Optimization2009In: 2009 INTERNATIONAL CONFERENCE ON INFORMATION PROCESSING IN SENSOR NETWORKS (IPSN 2009), NEW YORK: IEEE , 2009, p. 241-252Conference paper (Refereed)
    Abstract [en]

    Motivated by a peer-to-peer estimation algorithm in which adaptive weights are optimized to minimize the estimation error variance, we formulate and solve a novel non-convex Lipschitz optimization problem that guarantees global stability of a large class of peer-to-peer consensus-based algorithms for wireless sensor network. Because of packet. losses, the solution of this optimization problem cannot be achieved efficiently with either traditional centralized methods or distributed Lagrangian message passing. The prove that the optimal solution can be obtained by solving a set of nonlinear equations. A fast distributed algorithm, which requires only local computations, is presented for solving these equations. Analysis and computer simulations illustrate the algorithm and its application to various network topologies.

  • 9.
    Johansson, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Distributed Model Predictive Consensus2006In: Proceedings of the 17th International Symposium on Mathematical Theory of Networks and Systems, 2006, p. 2438-2444Conference paper (Refereed)
    Abstract [en]

    In this paper we consider the problem of designing a distributed control strategy such that a linear combination of the states of a number of vehicles coincide at a given time. The vehicles are described by linear difference equations and are subject to convex input constraints. It is demonstrated how primal decomposition techniques and incremental subgradient methods allow us to find a solution in which each vehicle performs individual planning of its trajectory and exchanges critical information with neighbors only. We explore various communication, computation, and control structures, and demonstrate the performance of the algorithms by numerical examples.

  • 10.
    Johansson, Karl Henrik
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Zampieri, S.
    On quantization and communication topologies in multi-vehicle rendezvous2005Conference paper (Refereed)
    Abstract [en]

    A rendezvous problem for a team of autonomous vehicles that is communicating through quantized channels is considered. Communication topologies and feedback control law are presented that solves the rendezvous problem in the sense that a meeting point for the vehicles is practically stabilized. In particular, it is shown that uniform quantizers can sometimes be replaced by logarithmic quantizers and thus reduce the need for communication bandwidth.

  • 11.
    Mazo, Manuel
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Speranzon, Alberto
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Johansson, Karl Henrik
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Hu, Xiaoming
    KTH, Superseded Departments, Mathematics.
    Multi-robot tracking of a moving object using directional sensors2004In: 2004 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION, VOLS 1- 5, PROCEEDINGS, 2004, p. 1103-1108Conference paper (Refereed)
    Abstract [en]

    The problem of estimating and tracking the motion of a moving target by a team of mobile robots is studied in this paper. Each robot is assumed to have a directional sensor with limited range, thus more than one robot (sensor) is needed for solving the problem. A sensor fusion scheme based on inter-robot communication is proposed in order to obtain accurate real-time information of the target's position and motion. Accordingly a hierarchical control scheme is applied, in which a consecutive set of desired formations is planned through a discrete model and low-level continuous-time controls are executed to track the resulting references. The algorithm is illustrated through simulations and on an experimental platform.

  • 12. Silva, Jorge
    et al.
    Speranzon, Alberto
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Borges de Sousa, João
    Johansson, Karl Henrik
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Hierarchical search strategy for a team of autonomous vehicles2004In: Proceedings of the 5th IFAC symposium on intelligent autonomous vehicles, IFAC , 2004Conference paper (Refereed)
    Abstract [en]

    A multi-vehicle search strategy based on the simplex algorithm is proposed. The strategy is decomposed into a hierarchical scheme with three layers. The upper layer is described by a discrete-event system. The output of this layer is a set of way-points for the vehicles and it is used by the middle layer in order to coordinate the motion of the vehicles. The lower layer drives each vehicle to a way-point. The paper compares two possible discrete coordination strategies: one minimizes the travelled distance of the vehicles and the other avoids their trajectories to cross. Minimization of vehicle intercommunication is also studied.

  • 13.
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES).
    Coordination, Consensus and Communication in Multi-robot Control Systems2006Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    Analysis, design and implementation of cooperative control strategies for multi-robot systems under communication constraints is the topic of this thesis. Motivated by a rapidly growing number of applications with networked robots and other vehicles, fundamental limits on the achievable collaborative behavior are studied for large teams of autonomous agents. In particular, a problem is researched in detail in which the group of agents is supposed to agree on a common state without any centralized coordination. Due to the dynamics of the individual agents and their varying connectivity, this problemis an extension of the classical consensus problemin computer science. It captures a crucial component of many desirable features of multi-robot systems, such as formation, flocking, rendezvous, synchronizing and covering.

    Analytical bounds on the convergence rate to consensus are derived for several systemconfigurations. It is shown that static communication networks that exhibit particular symmetries yield slow convergence, if the connectivity of each agent does not scale with the total number of agents. On the other hand, some randomly varying networks allow fast convergence even if the connectivity is low. It is furthermore argued that if the data being exchanged between the agents are quantized, it may heavily degrade the performance. The extent to which certain quantization schemes are more suitable than others is quantified through relations between the number of agents and the required total network bit rate.

    The design of distributed coordination and estimation schemes based on the consensus algorithm is presented. A receding horizon coordination strategy utilizing subgradient optimization is developed. Robustness and implementation aspects are discussed. A new collaborative estimation method is also proposed.

    The implementation of multi-robot control systems is difficult due to the high systemcomplexity. In the final part of this thesis, a hierarchical control architecture appropriate for a class of coordination tasks is therefore suggested. It allows a formal verification of the correctness of the implemented control algorithms.

  • 14.
    Speranzon, Alberto
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On control under communicaiton constraints in autonomous multi-robot systems2004Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    Multi-robot systems have important applications, such as space explorations, underwater missions, and surveillance operations. In most of these cases robots need to exchange data through communication. Limitations in the communication system however impose constraints on the design of coordination strategies. In this thesis we present three papers on cooperative control problems in which different communication constraints are considered. The first paper describes a rendezvous problem for a team of robots that exchanges position information through communication. A local control law for each robot should steer the team to a common meeting point when communicated data are quantized. The robots are not equipped with any sensors so the positions of other teammates are not measured. Two different types of quantized communication are considered: uniform and logarithmic. Logarithmic quantization is often preferable since it requires that fewer bits are communicated compared to when uniform quantization is used. For a class of feasible communication topologies, control laws that solve the rendezvous problem are derived. A hierarchical control structure is proposed in the second paper, for modelling autonomous underwater vehicles employed in finding a minimum of a scalar field. The controller is composed of two layers. The upper layer is the team controller, which is modeled as discrete-event system. It generates waypoints based on the simplex search optimization algorithm. The waypoints are used as target points by the lower control layer, which continuously steers each vehicle from the current to the next waypoint. It is shown that the communication of measurements is needed at each step for the team controller to generate unique waypoints. A protocol is proposed to reduce the amount of data to be exchanged, motivated by that underwater communication is costly in terms of energy. In the third paper, a probabilistic pursuit{evasion game is considered as an example to study constrained communication in multi-robot systems. This system can be used to model search-and-rescue operations and multi-robot exploration. Communication protocols based on time-triggered and event-triggered synchronization schemes are considered. It is shown that by limiting the communication to events when the probabilistic map updated by the individual pursuer contains new information, as measured by a map entropy, the utilization of the communication link can be considerably improved compared to conventional time-triggered communication.

  • 15.
    Speranzon, Alberto
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A distributed estimation algorithm for tracking over wireless sensor networks2007In: 2007 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, 2007, p. 3088-3093Conference paper (Refereed)
    Abstract [en]

    A new distributed estimation algorithm for tracking using a wireless sensor network is presented. We investigate how to track a time varying signal, noisily sensed by the nodes of the network. The algorithm is distributed, meaning that it does not require a central coordination among the nodes. Moreover, the proposed approach is scalable with respect to the network size, which means that its complexity does not grow with respect to the total number of nodes. The algorithm designed turns out to be composed by a cascade structure. Local constraints are determined to guarantee the global asymptotic stability of the estimation error. The algorithm can be applied e.g., for the position estimation, temporal synchronization, as well as tracking of signals. Performance is illustrated by simulations, where our filter is shown to behave better than other distributed schemes proposed in the literature.

  • 16.
    Speranzon, Alberto
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Johansson, Karl Henrik
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On Localization and Communication Issues in Pursuit-Evader Game2002Conference paper (Refereed)
  • 17.
    Speranzon, Alberto
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Johansson, Karl Henrik
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On some communication schemes for distributed pursuit-evasion games2003In: 42ND IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-6, PROCEEDINGS, NEW YORK: IEEE , 2003, p. 1023-1028Conference paper (Refereed)
    Abstract [en]

    A probabilistic pursuit-evasion game from the literature is used as an example to study constrained communication in multi-robot systems. Communication protocols based on time-triggered and event-triggered synchronization schemes are considered. It is shown that by limiting the communication to events when the probabilistic map updated by the individual pursuer contains new information, as measured through a map entropy, the utilization of the communication link can be considerably improved compared to conventional time-triggered communication.

  • 18.
    Zurita Ares, Benigno
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Park, Pan Gun
    KTH, School of Electrical Engineering (EES).
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Speranzon, Alberto
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On power control for wireless sensor networks: System model, middleware component and experimental evaluation2015In: 2007 European Control Conference, ECC 2007, 2015, p. 4293-4300Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate strategies for radio power control for wireless sensor networks that guarantee a desired packet error probability. Efcient power control algorithms are of major concern for these networks, not only because the power consumption can be signicantly decreased but also because the interference can be reduced, allowing for higher throughput. An analytical model of the Received Signal Strength Indicator (RSSI), which is link quality metric, is proposed. The model relates the RSSI to the Signal to Interference plus Noise Ratio (SINR), and thus provides a connection between the powers and the packet error probability. Two power control mechanisms are studied: a Multiplicative-Increase Additive-Decrease (MIAD) power control described by a Markov chain, and a power control based on the average packet error rate. A component-based software implementation using the Contiki operating system is provided for both the power control mechanisms. Experimental results are reported for a test-bed with Telos motes.

1 - 18 of 18
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