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Control Theory & Applications, IET

Issue 17 • Date Nov. 17 2011

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Displaying Results 1 - 12 of 12
  • Note on observer for lur'e differential inclusion systems

    Page(s): 1939 - 1944
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    This note considers the reduced-order observer of Lur'e differential inclusion systems. The set-valued mappings in the differential inclusions are maximal monotone, but may not be compact and bounded. It is verified that if there exists a full-order observer, then there is also a reduced-order observer. The construction of the observer as well as the convergence and well-posedness of the observer are presented. An example is provided to illustrate the validation of the reduced-order observer. View full abstract»

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  • Robust Kalman filtering for uncertain state delay systems with random observation delays and missing measurements

    Page(s): 1945 - 1954
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    The robust Kalman filtering problem is investigated for uncertain stochastic systems with time-invariant state delay d0, bounded random observation delays and missing measurements. The described model is generalised to the case that d0d1, where d1 denotes the upper bound of random observation delays. The random delays and missing measurements are described by multiple Bernoulli random processes and their probabilities are assumed to be known. For robust performance, stochastic parameter perturbations are considered. Unlike the system augmentation approach, the robust Kalman filtering is derived in the linear minimum variance sense by using the innovation analysis approach, and the dimension of the designed filter is the same as the original systems. Moreover, the performance of the designed filter is dependent on the probabilities of delays and missing measurements at each step. An illustrative example is presented to demonstrate the effectiveness of the proposed design method. View full abstract»

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  • Robust quantised control for active suspension systems

    Page(s): 1955 - 1969
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (487 KB)  

    This study investigates the robust quantised H control problem for active suspension systems. First, based on the half-vehicle suspension model, the dynamical system with polytopic parameter uncertainties, which are caused by vehicle load variation, is established. In the meanwhile, the active suspension system performance, namely ride comfort, road holding and suspension deflection, are taken into account for the control design aim. Secondly, an input delay approach is utilised to transform the resulting active vehicle suspension system with sampling and quantisation measurements into a continuous-time system with a delay in the input sector bound uncertainty. Thirdly, robust quantised H performance analysis and controller synthesis criteria are presented in the form of convex optimisation problem by exploiting the Lyapunov functional approach. The existing robust quantised H controller condition not only guarantees the robust asymptotical stability of the closed-loop system, but also satisfies the output constrained performance. Finally, the effectiveness and application of the proposed method can be demonstrated by providing a design example. View full abstract»

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  • Switched manual pursuit tracking to measure motor performance in Parkinson's disease

    Page(s): 1970 - 1977
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (425 KB)  

    Control theoretic measures are proposed to assess motor performance in Parkinson's disease (PD), a neuro-degenerative disorder that impairs motor skills, speech, and aspects of cognition. Ten normal and 14 PD subjects performed a series of manual pursuit tracking tasks: three tasks were first performed separately, then as a merged sequence with sudden, unenunciated task changes. The tasks differed in whether the tracking errors appeared amplified, attenuated or unaltered. From the discrete block experiments, subject- and task-specific second-order, linear time invariant models were derived, with the trajectory subjects are asked to track as input and the subject's motor response as output. Multiple model adaptive estimation was employed on the merged sequences to determine whether, and with what delay, each subject modified their performance after a task change. Although all normal subjects detected the task change, less than one-third of PD subjects did (and with longer delay). Further, those PD subjects who detected the task change had estimators with higher damping ratio than those PD subjects who did not. Since cerebellar structures may affect damping ratio, and the basal ganglia are often associated with switching behaviour, the proposed method provides a comprehensive assessment of motor structures that may be affected in PD. View full abstract»

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  • Note on fractional-order proportional-integral-differential controller design

    Page(s): 1978 - 1989
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1293 KB)  

    This study deals with the design of fractional-order proportional-integral-differential (PID) controllers. Two design techniques are presented for tuning the parameters of the controller. The first method uses the idea of the Ziegler-Nichols and the A-stro-m-Ha-gglund methods. In order to achieve required performances, two non-linear equations are derived and solved to obtain the fractional orders of the integral term and the derivative term of the fractional-order PID controller. Then, an optimisation strategy is applied to obtain new values of the controller parameters, which give improved step response. The second method is related with the robust fractional-order PID controllers. A design procedure is given using the Bode envelopes of the control systems with parametric uncertainty. Five non-linear equations are derived using the worst-case values obtained from the Bode envelopes. Robust fractional-order PID controller is designed from the solution of these equations. Simulation examples are provided to show the benefits of the methods presented. View full abstract»

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  • Adaptive coordinated path following control of non-holonomic mobile robots with quantised communication

    Page(s): 1990 - 2004
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (751 KB)  

    In this study, Lyapunov-based technique and graph theory are combined to address the problem of coordinated path following where multiple mobile robots are required to follow some prescribed paths while maintaining a desired inter-robot formation pattern. The authors address this problem by developing decentralised feedback law that drives each robot to its desired path while adjusting its speed to the nominal velocity profile based on the exchange of information with its neighbours. The decentralised feedback law builds upon a non-linear control strategy with integral actions, that decouples the path following from the coordination control problem, the obtained subsystems are shown to be in a cascade connection of each other and therefore the stability of the entire closed-loop system is guaranteed by the small-gain theorem. The authors explicitly address the situation where the exchange of information among mobile robots takes place according to a quantised communication network and provide conditions under which the complete coordinated path-following closed-loop system is stable. Finally, the theoretical results are validated by simulations on a platform of three mobile robots. View full abstract»

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  • Local feedback pareto strategy for weakly coupled large-scale discrete-time stochastic systems

    Page(s): 2005 - 2014
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (189 KB)  

    In this study, the author discusses a Pareto strategy implemented via state and static output feedback for a class of weakly coupled large-scale discrete-time stochastic systems with state- and control-dependent noise. The asymptotic structure along with the uniqueness and positive semi-definiteness of the solutions of cross-coupled non-linear matrix equations (CNMEs) is newly established via the implicit function theorem. The main contribution of this study is the proposal of a parameter-independent local state and static output feedback Pareto strategy. Moreover, a computational approach for solving the CNMEs is also considered if the information about the small parameter is available. Particularly, a new iterative algorithm based on the linear matrix inequality is established to design a Pareto strategy. Finally, in order to demonstrate the effectiveness of the proposed design method, a numerical example is provided for practical aircraft control problems. View full abstract»

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  • Cooperative box-pushing with multiple autonomous robotic fish in underwater environment

    Page(s): 2015 - 2022
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (413 KB)  

    This study presents a cooperative underwater box-pushing scenario, in which three autonomous robotic fish that sense, plan and act on its own move an elongated box from some initial location to a goal location. With the onboard monocular camera, the robotic fish can estimate the pose of the object in the swimming tank. Considering the complexity of the underwater environment and the limited capability of a single robotic fish, the authors address the task by decomposing it into three subtasks and assigning them to capable robotic fish. With one robotic fish observing the box at the goal location and two robotic fish pushing the left and right ends of the box, the box can be moved gradually towards the goal location. The subtask consists of a series of behaviours, each designed to fulfil one step of the subtask. The robotic fish coordinate through explicit communications and distribute the subtasks with a market-based dynamic task allocation method. Task reallocation mechanism that permits robotic fish to auction its assigned task to capable ones is used to cope with unexpected changes in the environment and the limited sensing range of the robotic fish. Experiments are conducted to verify the feasibility of the proposed methods. View full abstract»

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  • H2 filtering for non-linear singularly perturbed systems

    Page(s): 2023 - 2032
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    In this study, the authors consider the H2 (or Kalman)-filtering problem for singularly perturbed (two-timescale) non-linear systems. Two types of filters, namely (i) decomposition and (ii) aggregate, are discussed, and sufficient conditions for the solvability of the problem in terms of Hamilton-Jacobi-Bellman equations (HJBEs) are presented. The results are also specialised to linear systems in which case the HJBEs reduce to a system of bilinear-matrix-inequalities. View full abstract»

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  • Simple proof of stability criterion for interval quasi-polynomials

    Page(s): 2033 - 2038
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    In this study, the authors study the stability of interval quasi-polynomials with fixed delay and interval delay. The stability of quasi-polynomial with a fixed coefficient can be checked by a frequency characteristic plot. The vertex quasi-polynomials with fixed coefficients are defined. Two theorems are presented to determine the stability of interval quasi-polynomials. Stability of interval quasi-polynomials with fixed delay or interval delay may be determined by eight or 16 vertex quasi-polynomials. The example is given to illustrate the proposed method. View full abstract»

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  • Brief paper - Improved zonotopic method to set membership identification for systems with time-varying parameters

    Page(s): 2039 - 2044
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (286 KB)  

    This study proposes an improved zonotopic method to set membership identification for linear discrete-time systems with a bounded description of noise and parameter expansion. As in the previous method, the time-varying nature of parameters is taken into account in a non-conservative way by a zonotope. A new family of zonotopes containing the intersection of a zonotope with a strip is constructed in the observation update procedure. The minimal volume zonotope in this family is selected as the outer bound of the feasible solution set of parameters. It can be proven that this minimal volume zonotope is not larger than the one obtained by means of the previous method. Simulation experiments are conducted showing the performance of the improved method as compared to the previous method and the parallelotopic method. Two types of distribution of the parameter expansion are considered. The results expose the weakness of the previous method and illustrate the effectiveness of the improvement. View full abstract»

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  • Brief paper repetitive learning control for triangular systems with unknown control directions

    Page(s): 2045 - 2051
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    A backstepping repetitive learning control method is proposed for a class of high-order non-linear systems with triangular structure with unknown control coefficients. The Nussbaum-gain method is incorporated into the control design to counteract the lack of a priori knowledge of the control directions. A differential-difference repetitive control law is presented to avoid the difficulties encountered in the derivation of the fictitious control. It is proved that the output of controlled system converges to the desired trajectory asymptotically along the iterative learning axis through repetitive learning. Simulation is carried out to show the validity of the proposed control method. View full abstract»

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IET Control Theory & Applications is devoted to control systems in the broadest sense, covering new theoretical results and the applications of new and established control methods.

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