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Any Time Control

TitleAny Time Control
Publication TypeMiscellaneous
Year of Publication2006
AuthorsFontanelli, D, Greco, L
KeywordsEmbedded Control, Robotics
Abstract

It is widely accepted in the control community that the Computer Controlled Systems (briefly, CCSs), have a lot of advantages based primarily on the high reconfigurability of the controller platform and the ability of making complex yet fast decisions. Such positive features make the CCS a useful platform for multitasking control, i.e. using only one single-processor platform to control several plants. Within this framework, the computer has to share its computational time to solve several critical tasks, each one with its priority. Taking into account schedulability and real time operating systems problems, it is just a step forward to realize that tasks with low priority could be interrupted any time, with unpredictable distributions, and it is just a logical intuition that not all the tasks can be at the highest priority. From a control point of view, each control task should compute a control input to the controlled system to prevent instability or to ensure the performances. This field seems to be at the border between the control community and the computer science community and it has not been widely investigated. Some work has been presented introducing more general scheduling models and methods for control systems, where control design methodology takes the availability of computing resources into account and allows the trade–offs between control performance and computer resources utilization, and also introducing the idea of any time CCS without solutions. In literature, the Control Server is introduced, allowing the separation between scheduling and control design by treating the controllers as scalable real–time components. Jitter and latency is included in the model and cannot be taken over. Furthermore, the interrupt time, the I/O operations and the overrun handling are not taken into account, simply imposing only soft real time control tasks. Useful tools for the analysis of real time control performance are the Jitterbug and the True Time that analyze the control performance once the control tasks are implemented as soft real time tasks.

Estim

TitleEstim
Publication TypeConference Paper
Year of Publication2006
Conference NameCIFA 2006
Date PublishedJune
Publication Languageeng
AuthorsChaillet, A
Conference LocationBordeaux, France
AbstractPour les systèmes non-linéaires, il est connu que la propriété de stabilité asymptotique est conservée par la structure de cascade. Le pr
NotesIn French

Probabilistic verification of a decentralized policy for conflict resolution in multi-agent systems

TitleProbabilistic verification of a decentralized policy for conflict resolution in multi-agent systems
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. IEEE Int. Conf. on Robotics and Automation
Pagination2448-2453
Publication Languageeng
AuthorsPallottino, L, Scordio, VG, Frazzoli, E, Bicchi, A
KeywordsEmbedded Control, Robotics
Abstract

In this paper, we consider a decentralized cooperative control policy proposed recently for steering multiple non-holonomic vehicles between assigned start and goal configurations while avoiding collisions. The policy is known to ensure safety (i.e., collision avoidance) for an arbitrarily large number of vehicles, if initial configurations satisfy certain conditions. The method is highly scalable, and effective solutions can be obtained for several tens of autonomous agents. On the other hand, the liveness property of the policy, i.e. the capability of negotiating a solution in finite time, is not yet completely understood. In this paper, we introduce a condition on the final vehicle configurations, which we conjecture to be sufficient for guaranteeing liveness. Because of the overwhelming complexity of proving the sufficiency of such condition, we assess the correctness of the conjecture in probability through the analysis of the results of a large number of randomized experiments.

Notes

Correct version

Integral Input to State Stability for cascaded systems

TitleIntegral Input to State Stability for cascaded systems
Publication TypeConference Paper
Year of Publication2006
Conference NameMTNS 2006
Date PublishedJuly
Publication Languageeng
AuthorsChaillet, A, Angeli, D
Conference LocationKyoto, Japan
KeywordsRobotics
Abstract

The Integral Input to State Stability (iISS) property is studied is the context of nonlinear time-invariant systems in cascade. A sufficient condition is given, in terms of the storage function of each subsystem, to ensure that the cascade composed of an iISS system driven by a Globally Asymptotically Stable (GAS) one remains GAS. Some sufficient conditions for the preservation of the iISS property under a cascade interconnection are also presented.

Practical stabilization of LTI SISO systems under assigned Input and Output quantization

TitlePractical stabilization of LTI SISO systems under assigned Input and Output quantization
Publication TypeConference Paper
Year of Publication2006
Pagination353-358
Date PublishedJuly
Publication Languageeng
AuthorsPicasso, B, Bicchi, A
KeywordsEmbedded Control, Robotics
Abstract

This work is concerned with the practical stabilization of discrete–time SISO linear systems under assigned quantization of the input and output spaces. A controller is designed which guarantees effective practical stability properties. Unlike most of the existing literature, quantization is supposed to be a problem datum rather than a degree of freedom in design. Moreover, in the framework of control under assigned quantization, results are concerned with state quantization only and do not include the quantized output feedback case considered here. While standard stability analysis techniques are based on Lyapunov theory and invariant ellipsoids, our study of the closed loop dynamics involves a particularly suitable family of sets, which are hypercubes in controller form coordinates.

Notes

ADHS'06

A converse Lyapunov theorem for semiglobal practical asymptotic stability and application to cascades-based control

TitleA converse Lyapunov theorem for semiglobal practical asymptotic stability and application to cascades-based control
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. IEEE Int. Conf. on Decision and Control
Date PublishedDecember
Publication Languageeng
AuthorsChaillet, A, Lor, A
Conference LocationSan Diego, USA
KeywordsRobotics
Abstract

We present a converse Lyapunov result for nonlinear time-varying systems that are uniformly semiglobally asymptotically stable. This stability property pertains to the case when the size of initial conditions may be arbitrarily enlarged and the solutions of the system converge, in a stable way, to a closed ball that may be arbitrarily diminished by tuning a design parameter of the system (typically but not exclusively, a control gain). This result is notably useful in cascaded-based control when uniform practical asymptotic stability is established without a Lyapunov function, , ıt e.g.} via averaging. We provide a concrete example by solving the stabilization problem of a hovercraft.

Brain response to visual, tactile and auditory flow in sighted and blind individuals supports a supramodal functional organization in hMT complex

TitleBrain response to visual, tactile and auditory flow in sighted and blind individuals supports a supramodal functional organization in hMT complex
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. 12th International Conference on Functional Mapping of Human Brain Mapping
Edited Volume31
Pagination512 TH-P
Publication Languageeng
AuthorsRicciardi, E, Sani, L, Gentili, C, Bonino, D, Vanello, N, Haxby, JV, Seifritz, E, Guazzelli, M, Landini, L, Bicchi, A, Di Salle, F, Pietrini, P
PublisherElsevier
KeywordsHaptics
Notes

Florence

Uniform Global Practical Stability for non-autonomous cascaded systems

TitleUniform Global Practical Stability for non-autonomous cascaded systems
Publication TypeConference Paper
Year of Publication2006
Conference NameMTNS 2006
Date PublishedJuly
Publication Languageeng
AuthorsChaillet, A, Lor, A
Conference LocationKyoto, Japan
KeywordsRobotics
Abstract

This paper aims to give sufficient conditions for a cascade composed of nonlinear time-varying systems that are uniformly globally practically asymptotically stable (UGPAS) to be UGPAS. These conditions are expressed as relations between the Lyapunov function of the driven subsystem and the interconnection term. Our results generalize previous theorems that establish the uniform global asymptotic stability of cascades.

Free Hand Haptic Interfaces Based on Magnetorheological Fluids

TitleFree Hand Haptic Interfaces Based on Magnetorheological Fluids
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. 14th Symp. on Haptic Interfaces for Virtual Environment and Teleoperator Systems
Pagination367-371
Date PublishedMarch
Publication Languageeng
AuthorsSgambelluri, N, Rizzo, R, Scilingo, EP, Raugi, M, Bicchi, A
KeywordsHaptics
Abstract

This paper is concerned with exploring the possibility of using Magneto-Rheological Fluids (MRF) as haptic interface. MRF are special materials capable of changing their rheological behaviour with an external magnetic field. This property suggested us to use MRF to mimic virtual objects whose compliance can be gradually modulated. Several architectures of prototypes have been envisaged. The general scheme of both prototypes refers to a Haptic Black Box (HBB) concept, intended as a box where the operator can poke his/her bare hand, and interact with the virtual object by freely moving the hand without mechanical constraints. In this way sensory receptors on the whole operator

Notes

Poster presentation

Robustness of PID controlled manipulators with respect to external disturbances

TitleRobustness of PID controlled manipulators with respect to external disturbances
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. IEEE Int. Conf. on Decision and Control
Date PublishedDecember
Publication Languageeng
AuthorsChaillet, A, Lor, A, Kelly, R
Conference LocationSan Diego, USA
KeywordsRobotics
Abstract

We present a robustness analysis for PID-controlled robot manipulators. For robot manipulators under the influence of external disturbances we provide a proof, and a tuning procedure, to establish uniform semiglobal practical asymptotic stability. In particular, in contrasts to other works on robust stability of PIDs, we do not use La Salle's principle but provide a strict Lyapunov function. The perturbations that we consider include discontinuous functions of the state, such as Coulomb friction. As corollaries of our main results, one may conclude the same stability property for the case of motion control using linear PID.

Advanced Modeling and preliminary psychophysical experiments for a free-hand haptic device

TitleAdvanced Modeling and preliminary psychophysical experiments for a free-hand haptic device
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. IEEE/RSJ Int. Conf. on Robots and Intelligent Systems - IROS06
Pagination1558-1563
Date PublishedOctober
Publication Languageeng
AuthorsSgambelluri, N, Scilingo, EP, Bicchi, A, Rizzo, R, Raugi, M
KeywordsHaptics
AbstractIn this paper we report on a new improved free-hand haptic interface based on magnetorheological fluids (MRFs). MRFs are smart materials which change their rheology according to an external magnetic field. The new architecture here proposed results from the development and improvement of earlier prototypes. The innovative idea behind this device is to allow subjects interacting directly with an object, whose rheology is rapidly and easily changeable, freely moving their hands without rigid mechanical linkages. Numerical advanced simulation tests using algorithms based on finite element methods have been implemented, in order to analyze and predict the spatial distribution of the magnetic field. A special focus was laid on investigating on how the magnetic filed profile is altered by the introduction of the hand. Possible solutions were proposed to overcome this perturbation. Finally some preliminary psychophysical tests in order to assess the performance of the device are reported and discussed.

Stability of sets for nonlinear systems in cascade

TitleStability of sets for nonlinear systems in cascade
Publication TypeConference Paper
Year of Publication2006
Conference NameMTNS 2006
Date PublishedJuly
Publication Languageeng
AuthorsChaillet, A, Panteley, E
Conference LocationKyoto, Japan
KeywordsRobotics
Abstract

The stability of (not necessarily compact) sets for nonlinear systems in cascade is addressed. It is proved that if two sets are globally asymptotically stable (GAS) for the subsystems taken separately then their cross-product is GAS for the corresponding cascade, provided that the solutions of the latter are globally bounded. In the case of a suitable growth rate of the interconnection in the state of the driven subsystem, we show that this latter requirement can be relaxed to just forward completeness of the cascade. Our results extend similar results on the stability analysis of cascaded systems and find applications in partial stability analysis and adaptive control.

Cascaded lemma for set-stable systems

TitleCascaded lemma for set-stable systems
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. IEEE Int. Conf. on Decision and Control
Date PublishedDecember
Publication Languageeng
AuthorsTsonnas, J, Chaillet, A, Panteley, E, Johansen, TA
Conference LocationSan Diego, USA
KeywordsRobotics
Abstract

A previous result about uniform global asymptotic stability (UGAS) of the equilibrium of a cascaded time-varying systems, is here also shown to hold for closed (not necessarily compact) sets composed by set-stable subsystems of a cascade. In view of this result an optimal control allocation approach is discussed.

A scalable platform for safe and secure decentralized traffic management of multiagent mobile systems

TitleA scalable platform for safe and secure decentralized traffic management of multiagent mobile systems
Publication TypeConference Paper
Year of Publication2006
Conference NameACM Workshop on Real-World Wireless Sensor Networks
Publication Languageeng
AuthorsDanesi, A, Fagiolini, A, Savino, I, Pallottino, L, Schiavi, R, Dini, G, Bicchi, A
KeywordsEmbedded Control, Robotics
Abstract

In this paper we describe the application of wireless sensor networking techniques to address the realization of a safe and secure decentralized traffic management system. We consider systems of many heterogeneous autonomous vehicles moving in a shared environment. Each vehicle is assumed to have different and possibly unspecified tasks, but they cooperate to avoid collisions. We are interested in designing a scalable architecture capable of accommodating a very large and dynamically changing number of vehicles, guaranteeing their safety (i.e., collision avoidance), the achievement of their goals, and security against potential adversaries. By properly distributing and revoking cryptographic keys we are able to protect communications from an external adversary as well as to detect non-cooperative, possibly malicious vehicles and trigger suitable countermeasures. In our architecture, scalability is obtained by decentralization, i.e. each vehicle is regarded as an autonomous agent capable of processing information concerning its own state and the state of only a fixed, small number of ``neighboring'' agents. Ad-hoc wireless sensor networks are employed to provide support for this architecture.

Security and Advanced Control Issues in a Robotic Platform for Monitoring and Relief

TitleSecurity and Advanced Control Issues in a Robotic Platform for Monitoring and Relief
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. of EWSN 2006 February 13-15, ETH Zurich
Publication Languageeng
AuthorsDanesi, A, Savino, IM, Schiavi, R, Bicchi, A, Dini, G
KeywordsEmbedded Control, Robotics
Abstract

This paper provides an architectural overview and a first implementation of an heterogeneous agent network composed by mobile robots of di

Symbolic Control for Underactuated Differentially Flat Systems

TitleSymbolic Control for Underactuated Differentially Flat Systems
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. IEEE Int. Conf. on Robotics and Automation
Pagination1649-1654
Publication Languageeng
AuthorsFagiolini, A, Greco, L, Bicchi, A, Piccoli, B, Marigo, A
KeywordsEmbedded Control, Robotics
Abstract

In this paper we address the problem of generating input plans to steer complex dynamical systems in an obstacle-free environment. Plans considered admit a finite description length and are constructed by words on an alphabet of input symbols, which could be e.g. transmitted through a limited capacity channel to a remote system, where they can be decoded in suitable control actions. We show that, by suitable choice of the control encoding, finite plans can be efficiently built for a wide class of dynamical systems, computing arbitrarily close approximations of a desired equilibrium in polynomial time. Moreover, we illustrate by simulations the power of the proposed method, solving the steering problem for two examples in the class of underactuated systems, which have attracted wide attention in the recent literature.

Adaptive non Linear Control of Dynamic Mobile Robots with Parameters Uncertainty

TitleAdaptive non Linear Control of Dynamic Mobile Robots with Parameters Uncertainty
Publication TypeConference Paper
Year of Publication2006
Conference NameInt. IFAC Symp. on Robot Control
Date PublishedSeptember
Publication Languageeng
AuthorsFontanelli, D, Viviani, R, Greco, L, Caiti, A, Bicchi, A
Conference LocationBologna, Italy
KeywordsEmbedded Control, Robotics
Abstract

Research of a modular stabilizing control law for uncertain, nonholonomic mobile systems with actuators limitation has been investigated. Modular design allows the definition of a stabilizing control law for the kinematic model. The presence of uncertainties in the actuators parameters or in the vehicle dynamics has been treated both adding suitable components to the Lyapunov function and using parameters adaptation laws (e.g. adaptive control and backstepping techniques). Simulations are reported for the set point stabilization of a unicycle like vehicle showing the feasibility of the proposed approach. Torque limitations for a unicycle like vehicle has been investigated using backstepping techniques for the vehicle tracking problem. Simulations are reported.

Active Mechatronic Interface for Haptic Perception Studies with Functional Magnetic Resonance Imaging: Compatibility and Design Criteria

TitleActive Mechatronic Interface for Haptic Perception Studies with Functional Magnetic Resonance Imaging: Compatibility and Design Criteria
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. IEEE Int. Conf. on Robotics and Automation
Pagination3832-3837
Publication Languageeng
AuthorsGassert, R, Vanello, N, Chapuis, D, Hartwig, V, Scilingo, EP, Bicchi, A, Landini, L, Burdet, E, Bleuler, H
KeywordsHaptics
Abstract

Functional brain exploration methodologies such as functional magnetic resonance imaging (fMRI), are critical tools to study perceptual and cognitive processes. In order to develop complex and well controlled fMRI paradigms, researchers are interested in using active interfaces with electrically powered actuators and sensors. Due to the particularity of the MR environment, safety and compatibility criteria have to be strictly followed in order to avoid risks to the subject under test, to the operators or to the environment, as well as to avoid artifacts in the images. This paper describes the design of an fMRI compatible mechatronic interface based on MR compatibility tests of materials and actuators. In particular, a new statistical test looks at the mean and variations of activity as a time series. The device with two degrees of freedom, allowing one translation with positionfeedback along a horizontal axis and one rotation about a vertical axis linked to the translation, was realized to investigate the brain mechanisms of dynamic tactile perception tasks. It can be used to move and orient various objects below the finger for controlled tactile stimulation. The MR compatibility of the complete interface is shown using the same statistical test as well as a functional study with a human subject.

On the Design and Control of Wireless Networked Embedded Systems

TitleOn the Design and Control of Wireless Networked Embedded Systems
Publication TypeConference Paper
Year of Publication2006
Conference NameInt. Conf. on Computer Aided Control System Design - CACSD'06
Pagination440-445
Publication Languageeng
AuthorsArzén, K-E, Bicchi, A, Hailes, S, Johansson, KH, Lygeros, J
PublisherIEEE
KeywordsEmbedded Control, Robotics
Abstract

Wireless networked embedded systems are becoming increasingly important in a wide area of technical fields. In this tutorial paper we present recent results on design and control of these systems developed within the project Reconfigurable Ubiquitous Networked Embedded Systems (RUNES), which is an European Integrated Project with the aim to control complexity in networked embedded systems by developing robust and scalable middleware systems. New components for control under varying network conditions are discussed for the RUNES architecture. The complexity of the closed-loop system is increased due to the coupling with the disturbances introduced by the communication system. The network may introduce additional delays, jitter, data rate limitations, packet losses etc. Experimental work on integration test beds that demonstrates these results is shown together with motivating links to the RUNES disaster relief tunnel scenario.

A Compatible Electrocutaneous Display for functional Magnetic Resonance Imaging application

TitleA Compatible Electrocutaneous Display for functional Magnetic Resonance Imaging application
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. 28th IEEE Engineering in Medicine and Biology Conference
Pagination100-102
Publication Languageeng
AuthorsHartwig, V, Cappelli, C, Vanello, N, Ricciardi, E, Scilingo, EP, Giovannetti, G, Santarelli, MF, Positano, V, Landini, L, Bicchi, A
KeywordsHaptics
AbstractIn this paper we propose an MR (Magnetic Resonance) compatible electrocutaneous stimulator able to inject an electric current, variable in amplitude and frequency, into the fingertips in order to elicit tactile skin receptors (mechanoreceptors). The desired goal is to evoke specific tactile sensations selectively stimulating skin receptors by means of an electric current in place of mechanical stimuli. The field of application ranges from functional Magnetic Resonance Imaging (fMRI) tactile studies to augmented reality technology. The device here proposed is designed using safety criteria in order to comply with the threshold of voltage and current permitted by regulations. Moreover, MR safety and compatibility criteria were considered in order to perform experiments inside the MR scanner during an fMRI acquisition for functional brain activation analysis. Psychophysical laboratory tests are performed in order to define the different evoked tactile sensation. After verifying the device MR safety and compatibility on a phantom, a test on a human subject during fMRI acquisition is performed to visualize the brain areas activated by the simulated tactile sensation.
Notes(poster presentation)

Safe and Dependable Physical Human-Robot Interaction in Anthropic Domains: State of the Art and Challenges

TitleSafe and Dependable Physical Human-Robot Interaction in Anthropic Domains: State of the Art and Challenges
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. IROS'06 Workshop on pHRI - Physical Human-Robot Interaction in Anthropic Domains
Publication Languageeng
AuthorsAlami, R, Albu-Schaeffer, A, Bicchi, A, Bischoff, R, Chatila, R, De Luca, A, De Santis, A, Giralt, G, Guiochet, J, Hirzinger, G, Ingrand, F, Lippiello, V, Mattone, R, Powell, D, Sen, S, Siciliano, B, Tonietti, G, Villani, L
EditorBicchi, A, De Luca, A
PublisherIEEE
KeywordsRobotics

Adaptive output feedback control of spacecraft relative translation

TitleAdaptive output feedback control of spacecraft relative translation
Publication TypeConference Paper
Year of Publication2006
Conference NameProc. IEEE Int. Conf. on Decision and Control
Date PublishedDecember
Publication Languageeng
AuthorsKristiansen, R, Lor, A, Chaillet, A, Nicklasson, PJ
Conference LocationSan Diego, USA
KeywordsRobotics
Abstract

We address the problem of tracking relative translation in a leader-follower spacecraft formation using feedback from relative position only and under parameter uncertainty (spacecraft mass) and uncertainty in the leader variables (true anomaly rate and rate of change). We only assume boundedness of orbital perturbations and the leader control force but with unknown bounds. Under these conditions we propose a controller that renders the closed-loop system, uniformly semiglobally practically asymptotically stable. In particular, the domain of attraction can be made arbitrarily large by picking convenient gains, and the state errors in the closed-loop system are proved to converge from any initial condition within the domain of attraction to a ball in close vicinity of the origin in a stable way; moreover, this ball can be diminished arbitrarily by increasing the gains in the control law. Simulation results of a leader-follower spacecraft formation using the proposed controller are presented.

Hybrid Modelling and Control of the Common Rail Injection System

TitleHybrid Modelling and Control of the Common Rail Injection System
Publication TypeConference Paper
Year of Publication2006
Conference NameHybrid Systems: Computation and Control
Edited Volume3927 / 2006
Pagination79-92
Publication Languageeng
AuthorsBalluchi, A, Bicchi, A, Mazzi, E, Vincentelli, SA, Serra, G
EditorHespanha, J, Tiwari, A
PublisherSpringer-Verlag
KeywordsEmbedded Control, Robotics
Abstract

We present an industrial case study in automotive control of significant complexity: the new common rail fuel injection system for Diesel engines, currently under production by Magneti Marelli Powertrain. In this system, a flow-rate valve, introduced before the High Pressure (HP) pump, regulates the fuel flow that supplies the common rail according to the engine operating point. The standard approach followed in automotive control is to use a mean-value model for the plant and to develop a controller based on this model. In this particular case, this approach does not provide a satisfactory solution as the discrete-continuous interactions in the fuel injection system, due to the slow time-varying frequency of the HP pump cycles and the fast sampling frequency of sensing and actuation, play a fundamental role. We present a design approach based on a hybrid model of the Magneti Marelli Powertrain common-rail fuel-injection system for four-cylinder multi-jet engines and a hybrid approach to the design of a rail pressure controller. The hybrid controller is compared with a classical mean-value based approach to automotive control design whereby the quality of the hybrid solution is demonstrated.

Improving efficiency of finite plans by optimal choice of input sets

TitleImproving efficiency of finite plans by optimal choice of input sets
Publication TypeConference Paper
Year of Publication2006
Conference NameHybrid Systems: Computation and Control
Edited Volume3927 / 2006
Pagination108-122
Publication Languageeng
AuthorsBicchi, A, Marigo, A, Piccoli, B
EditorHespanha, J, Tiwari, A
PublisherSpringer-Verlag
KeywordsEmbedded Control, Robotics
Abstract

Finite plans proved to be an efficient method to steer complex control systems via feedback quantization. Such finite plans can be encoded by finite–length words constructed on suitable alphabets, thus permitting transmission on limited capacity channels. In particular flat systems can be steered computing arbitrarily close approximations of a desired equilibrium in polynomial time. The paper investigates how the efficiency of planning is affected by the choice of inputs, and provides some results as to optimal performance in terms of accuracy and range. Efficiency is here measured in terms of computational complexity and description length (in number of bits) of finite plans.

Decentralized and scalable conflict resolution strategy for multi-agents systems

TitleDecentralized and scalable conflict resolution strategy for multi-agents systems
Publication TypeConference Paper
Year of Publication2006
Conference NameInt. Symp. on Mathematical Theory of Networks and Systems
Publication Languageeng
AuthorsPallottino, L, Scordio, VG, Frazzoli, E, Bicchi, A
KeywordsEmbedded Control, Robotics
Abstract

A decentralized cooperative collision avoidance control policy for planar vehicle recently proposed is herein considered. Given some simple conditions on initial configurations of agents, the policy is known to ensure safety (i.e., collision avoidance) for an arbitrarily large number of vehicles. The method is highly scalable, and effective solutions can be obtained for several tens of autonomous agents. On the other hand, the liveness property of the policy, i.e. the capability of negotiating a solution in finite time, is not yet completely understood. First a 3D workspace extension is proposed. Furthermore, based on a condition on target configuration previously proposed, some general results on the liveness property are reported. Finally, qualitative evaluations on the strategy and on the proposed target sparsity condition are pointed out.

Necessary and sufficient conditions for uniform semiglobal practical asymptotic stability: Application to cascaded systems

TitleNecessary and sufficient conditions for uniform semiglobal practical asymptotic stability: Application to cascaded systems
Publication TypeJournal Article
Year of Publication2006
AuthorsChaillet, A, Lor, A
JournalAutomatica
Volume42
Pagination1899-1906
Date PublishedNovember
KeywordsRobotics
Abstract

It is well established that for a cascade of two uniformly globally asymptotically stable (UGAS) systems, the origin remains UGAS provided that the solutions of the cascade are uniformly globally bounded. While this result has met considerable popularity in specific applications it remains restrictive since, in practice, it is often the case that the decoupled subsystems are only uniformly \emph{semiglobally} \emph{practically} asymptotically stable (USPAS). Recently, we established that the cascade of USPAS systems is USPAS under a local boundedness assumption and the hypothesis that one knows a Lyapunov function for the driven subsystem. The contribution of this paper is twofold: 1) we establish USPAS of cascaded systems without the requirement of a Lyapunov function and 2) we present a converse theorem for USPAS. While other converse theorems in the literature cover the case of USPAS ours has the advantage of providing a bound on the gradient of the Lyapunov function, which is fundamental to establish theorems for cascades.

Uniform global practical asymptotic stability for non-autonomous cascaded systems

TitleUniform global practical asymptotic stability for non-autonomous cascaded systems
Publication TypeJournal Article
Year of Publication2006
AuthorsChaillet, A, Lor, A
JournalEuropean Journal of Control
Volume12
KeywordsRobotics
Abstract

This paper aims to give sufficient conditions for a cascade composed of nonlinear time-varying systems that are uniformly globally practically asymptotically stable (UGPAS) to be UGPAS. These conditions are expressed as relations between the Lyapunov function of the driven subsystem and the interconnection term. Our results generalise previous theorems that establish the uniform global asymptotic stability of cascades.

Tools for semiglobal practical stability analysis of cascaded systems and applications

TitleTools for semiglobal practical stability analysis of cascaded systems and applications
Publication TypeBook Chapter
Year of Publication2006
AuthorsChaillet, A
Series TitleInternational Scientific and Technical Encyclopedia
Chapterin Proceedings of the CTS–HYCON Workshop
CityParis, France
KeywordsRobotics
Abstract

We present sufficient conditions for semiglobal and/or practical stability in terms of Lyapunov-like functions. Based on this, we provide a result for the stability analysis of cascaded systems. A converse result is also presented for a particular class of uniformly semiglobally practically asymptotically stable systems. We briefly show the usefulness of these results through various applications in the control of mechanical systems.