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Online ISSN 1751-8652 Print ISSN 1751-8644

IET Control Theory & Applications

Volume 5, Issue 8, 19 May 2011

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Volume 5, Issue 8

19 May 2011

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    • Exponential stability of static neural networks with time delay and impulses
      • Author(s): S.L. Wu ; K.-L. Li ; T.Z. Huang
      • Source: IET Control Theory & Applications, Volume 5, Issue 8, p. 943 –951
      • DOI:  10.1049/iet-cta.2010.0329
      • Type: Article
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      • p. 943 –951 (9)
        In this study, the authors investigate the problem of global exponential stability of static neural networks with time delay and impulses. Three types of impulses are studied: the impulses are input disturbances; the impulses are ‘neutral’ type, that is, they are neither helpful for stability of neural networks nor destabilising; and the impulses are stabilising. For each type of impulses, by using Lyapunov function and Razumikhin-type techniques, sufficient conditions for global exponential stability are established in terms of linear matrix inequalities with respect to suitable classes of impulse time sequences. The new sufficient conditions can explicitly reveal the effects of time delay, impulses etc., on the stability. Numerical results are given to show the less conservatism of the obtained criteria compared with the existing ones.
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      Realisation of a bilaterally teleoperated robotic vehicle platform with passivity control
      • Author(s): J. Ware  and  Y.-J. Pan
      • Source: IET Control Theory & Applications, Volume 5, Issue 8, p. 952 –962
      • DOI:  10.1049/iet-cta.2010.0265
      • Type: Article
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      • p. 952 –962 (11)
        In this study, a new bilateral teleoperated vehicle testing platform is proposed. In the platform, the authors apply a new power-based time domain passivity control (PTDPC) method in an effort to improve the transparency. A new bilateral teleoperation platform is realised where steering angle commands were transmitted from a steering wheel interface to a remote vehicle, and road surface forces are sent back from the vehicle to the steering wheel interface. The communication channel between the steering wheel (master side) and the remote vehicle (slave side) introduces time-varying delays in the transmitted signals. To ensure the stability of the whole system, PTDPCs are applied to each side of the communication channel, which further improve the tracking performance as well as reduce the overall effort required of the human operator. The alternative advantage of the passivity control is the simplicity: the dynamic models of both master and slave side systems are not required to be known. The algorithms, hardware and software realisations are described thoroughly in the study. Finally, experimental results are demonstrated to show the effectiveness of the proposed approach as well as the functionality of the new testing platform.
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      Distributed control of a class of interconnected systems in a string
      • Author(s): B.B. Sharma  and  I.N. Kar
      • Source: IET Control Theory & Applications, Volume 5, Issue 8, p. 963 –975
      • DOI:  10.1049/iet-cta.2010.0031
      • Type: Article
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      • p. 963 –975 (13)
        The study addresses the stabilisation problem of interconnected systems, using the contraction theory framework. A sufficient condition for the stability of closed loop system is derived using contraction. Neighbouring systems in the string arrangement are considered to have a physical interconnection between them. The proposed decentralised control technique presents a simple-way of establishing the stability of the overall system in comparison to the existing Lyapunov-based approaches. Here, the conditions for stability are reflected in terms of bounds on controller parameters. The uniform negative definiteness of the associated Jacobian of the system in a differential framework is ensured by identifying the location of eigenvalues, using the Gerschgorin theorem. Results are verified by considering the case of a mass-spring interconnected system in a string, where controllers of individual systems are designed using its local information and information from its nearest neighbours. Numerical results establish the efficacy of the proposed approach. The analysis presented here could be useful in addressing the stabilisation and coordination behaviour of complex physically interconnected systems.
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      High-order multi-agent consensus with dynamically changing topologies and time-delays
      • Author(s): P. Lin ; Z. Li ; Y. Jia ; M. Sun
      • Source: IET Control Theory & Applications, Volume 5, Issue 8, p. 976 –981
      • DOI:  10.1049/iet-cta.2009.0649
      • Type: Article
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      • p. 976 –981 (6)
        This study is concerned with consensus problems of a class of high-order multi-agent systems with dynamically changing topologies and time-delays. A nearest-neighbour rule is introduced for these high-order discrete-time agents with the consideration of communication time-delays. It is shown that consensus can be reached, even when the communication topologies are dynamically changing and the corresponding communication graphs have no spanning trees. It is also shown that the communication time-delays do not affect the stability of the multi-agent systems. Finally, a numerical example is included to illustrate the obtained results.
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      Stabilisation of quantised linear systems with packet dropout
      Stability intricacies of two-delay linear systems in the presence of delay cross-talk
      • Author(s): R. Sipahi  and  N. Olgac
      • Source: IET Control Theory & Applications, Volume 5, Issue 8, p. 990 –998
      • DOI:  10.1049/iet-cta.2010.0162
      • Type: Article
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      • p. 990 –998 (9)
        An improved technique to stabilise a class of first-order linear time-invariant dynamics with two delays is presented. It proposes to design a controller in which delay cross-talk feature (or delay coupling) is utilised to enhance the system's stability characteristics. The authors present some comparative observations vis-à-vis an earlier pioneering study, which is a widely used point of reference for this class of systems, however, without the delay cross-talk effect. Furthermore, the treatment here profits from a recently introduced methodology, called the ‘cluster treatment of characteristic roots (CTCR)’, for the stability assessment of these systems, differently from the earlier suggested procedures. With the introduction of the delay cross-talk term, the authors show that the new system may become stable for larger delay zones, which is otherwise impossible. In the text, we present several case studies to display the outcome of such a tool.
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      Comparison of control techniques for a robotic manipulator with base disturbances
      • Author(s): M.W. Dunnigan  and  C.M. Wronka
      • Source: IET Control Theory & Applications, Volume 5, Issue 8, p. 999 –1012
      • DOI:  10.1049/iet-cta.2010.0331
      • Type: Article
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      • p. 999 –1012 (14)
        A dynamic model of a robotic manipulator mounted on a moving base is derived using the Euler–Lagrange approach to design controllers that compensate for the base movement. It is assumed that the base inertia is large enough not to be influenced by the manipulator motion and therefore the base trajectory can be treated as a time-varying parameter in the dynamic equations. An adaptive controller compensating for the time-varying gravity vector is proposed based on existing schemes. Various controllers are analysed by quantitative comparisons of trajectory tracking performance and high-frequency torque content. The presented derivation is applied to a Mitsubishi PA10-6CE robotic manipulator mounted on a 6-DOF (degrees of freedom) platform.
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      Formal theory of state loss of Siphon-based deadlock prevention
      • Author(s): D.Y. Chao
      • Source: IET Control Theory & Applications, Volume 5, Issue 8, p. 1013 –1021
      • DOI:  10.1049/iet-cta.2010.0113
      • Type: Article
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      • p. 1013 –1021 (9)
        Deadlocks stop a system completely, leading to significant financial loss to a company. Uzam and Zhou propose selecting first-met bad marking (FBM) from the reachability graph of a given Petri net model. A monitor (hence a P-invariant) is added and marked with the number of tokens less than the sum of tokens in all marked operation places. This causes some live states to no longer be reachable. Piroddi et al. further increase it to maximally permissive states using the set-covering approach. However, there are weighted control (WC) arcs, which are more difficult to analyse than the ordinary control net by Uzam and Zhou. Huang et al. also employ WC near the end of the mixed integer programming (MIP) iteration steps and avoid reachability analysis (unlike the above two approaches). Experimentally, it runs faster than the above two approaches. However, all WC places are redundant. To avoid WC while not losing live states, the authors need to understand why state loss occurs. This study proposes developing a formal theory for state loss.
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      Chain-scattering description approach to characterise stabilising controllers and optimal H2 solution
      • Author(s): M.-C. Tsai  and  F.-Y. Yang
      • Source: IET Control Theory & Applications, Volume 5, Issue 8, p. 1022 –1032
      • DOI:  10.1049/iet-cta.2010.0130
      • Type: Article
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      • p. 1022 –1032 (11)
        This study presents an alternative method for solving a general class of control synthesis problems by employing chain-scattering matrix descriptions and coprime factorisations. Extended from Kimura's approach, the proposed method follows an abridged development without the need for any plant augmentation or the conjugation technique in its solution process. It is shown that general control synthesis problems, including those for stabilising controllers or further for H2 controllers, can be represented via two associated chain-scattering matrix descriptions and solved by means of two coprime factorisations. In the two-port chain description framework, the coprime factorisation is utilised as the fundamental idea instead of J-spectrum factorisation from the perspective of facilitating the process of guaranteeing no unstable pole-zero cancellation. A significant contribution of this study is its transparency and intuitive nature, providing a systematic theory of control and allowing practicing control engineers to learn this approach more easily and apply it to advanced control systems. Related graphic network representations are also presented to help explain the whole concept which will benefit engineering readers.
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      Introduction to single-input, single-output fractional control
      • Author(s): D. Valério  and  J. Sà da Costa
      • Source: IET Control Theory & Applications, Volume 5, Issue 8, p. 1033 –1057
      • DOI:  10.1049/iet-cta.2010.0332
      • Type: Article
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      • p. 1033 –1057 (25)
        This is a tutorial study to introduce fractional control to a reader with a background in control theory. Fractional controllers are those making use of fractional-order derivatives and integrals, and have been receiving increased attention over the last few years because of the robust performance (in the face of plant gain variations and even plant uncertainties in general) they can achieve. The study covers the fundamentals of the theory of derivatives and integrals with arbitrary real or complex orders, fractional transfer functions and their approximations, identification of fractional transfer function models from experimental data, first- and second-generation Crone controller, fractional proportional-integral-derivative (PID) control and third-generation Crone control.
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