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Online ISSN 1751-8652 Print ISSN 1751-8644

IET Control Theory & Applications

Volume 3, Issue 12, December 2009

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Volume 3, Issue 12

December 2009

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  • Regular Papers

    • Analogue input shaper for haptic interfaces
      • Author(s): Y.-A. Lim ; H.-S. Ahn ; J. Ryu
      • Source: IET Control Theory & Applications, Volume 3, Issue 12, p. 1553 –1564
      • DOI:  10.1049/iet-cta.2008.0231
      • Type: Article
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      • p. 1553 –1564 (12)
        An analogue input shaper (AIS) is proposed as a means for stably increasing the displayable impedance range of haptic interfaces. Usually, high-frequency inputs can occur during collisions with very stiff virtual objects and induce instabilities. The proposed AIS is basically a nonlinear low-pass filter and acts as a frequency-dependent dissipative element, which can eliminate unwanted high-frequency inputs to haptic interfaces. The proposed AIS is not placed in the power stage but in the signal stage, so that the AIS can be designed independent of motor parameters and does not affect transparency in free motion. In addition, two linear half-wave rectifiers are incorporated into the AIS to allow for a fast decrease of impedance and no negative input to the haptic interface when a haptic pointer leaves a virtual object. Through virtual wall experiments using two different haptic interfaces, the effectiveness of the proposed AIS is shown.
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      Control approach for tracking a moving target by a wheeled mobile robot with limited velocities
      • Author(s): L. Huang
      • Source: IET Control Theory & Applications, Volume 3, Issue 12, p. 1565 –1577
      • DOI:  10.1049/iet-cta.2009.0052
      • Type: Article
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      • p. 1565 –1577 (13)
        A mobile robot's motion is directly affected by the maximum velocity its actuators can provide. This problem becomes more serious when the robot tracks a moving target which imposes demanding requirements on the robot's driving capabilities. To find a solution to this problem, this paper extends the conventional Lyapunov-based motion controller while taking the limit on the robot's velocity into consideration. The effects of the target's motion are explicitly addressed in the controller design. The control outputs are attenuated by selected sinusoidal functions of the states without compromising the asymptotic stability of the controlled system. Next, a new Lyapunov function reflecting the priority of the tracking objectives is chosen to develop the controller which further reduces the surges and fluctuations of the controller outputs. The smoothness of the robot motion is improved, the reasonable magnitudes of the robot velocities and a better target tracking performance are achieved. Extensive simulation and experimental results in various situations are provided to verify the effectiveness of the proposed approaches.
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      Robust identification of switched regression models
      • Author(s): E. Domlan ; B. Huang ; J. Ragot ; D. Maquin
      • Source: IET Control Theory & Applications, Volume 3, Issue 12, p. 1578 –1590
      • DOI:  10.1049/iet-cta.2008.0274
      • Type: Article
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      • p. 1578 –1590 (13)
        This study addresses the problem of parameters estimation for switched regression models used to represent systems with multiple operating modes or regimes. For the identification of such models, the collected data are from different operating modes and there is no a priori information holding on the partitioning of the data in regard to the different operating modes. The essential contributions of this study lie first in the estimation procedure of the model parameters that provides an analytical solution, second in the simultaneous resolution of the problem of estimating the model parameters and allocating the data points to the different local models and finally the robustness of the estimation procedure regarding the presence of outliers in the identification dataset.
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      H∞ disturbance observer design for high precision track following in hard disk drives
      • Author(s): C.K. Thum ; C. Du ; F.L. Lewis ; B.M. Chen ; E.H. Ong
      • Source: IET Control Theory & Applications, Volume 3, Issue 12, p. 1591 –1598
      • DOI:  10.1049/iet-cta.2008.0317
      • Type: Article
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      • p. 1591 –1598 (8)
        Contrary to the conventional method of disturbance observers (DOB) where Q-filter is designed to be a low-pass filter with unity DC gain, the optimal H∞ method has been proposed to design the Q-filter and applied in the servo control system of hard disk drives in track following. Simulation and implementation results have shown that the resultant H∞ DOB improves low-frequency disturbance attenuation without compromising the disturbances attenuation performance at higher frequency region achieved by the nominal feedback controller. In terms of track-following precision, the proposed method is approximately 5% more accurate than the conventional method.
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      Switched delay-dependent control policy for water-quality systems
      • Author(s): M.S. Mahmoud
      • Source: IET Control Theory & Applications, Volume 3, Issue 12, p. 1599 –1610
      • DOI:  10.1049/iet-cta.2008.0474
      • Type: Article
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      • p. 1599 –1610 (12)
        A delay-dependent analysis and synthesis approach is established for a class of linear discrete-time switched systems with time-varying delays using switched Lyapunov–Krasovskii functionals (SLKFs). The problem of water-quality control is cast as the problem of delay-dependent ℒ2 gain analysis and synthesis. New delay-dependent asymptotic stability criteria are developed under arbitrary switching based on appropriately constructed SLKFs. Delay-dependent switched control feedback is then designed, based on state- and output-measurements, to render the corresponding switched closed-loop system delay-dependent asymptotically stable with a prescribed ℒ2 gain measure. The developed results are cast as linear matrix inequalities and tested by Matlab simulation on a representative water-quality example.
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      Sliding-mode control design applied to parallel-connected modular inverters through FPGA-based implementation
      • Author(s): R. Ramos ; D. Biel ; E. Fossas ; F. Guinjoan
      • Source: IET Control Theory & Applications, Volume 3, Issue 12, p. 1611 –1624
      • DOI:  10.1049/iet-cta.2008.0187
      • Type: Article
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      • p. 1611 –1624 (14)
        A sliding-mode control strategy based on a Lyapunov function approach is reported and applied to the design of a modular system of m parallel-connected single-phase inverters. This strategy is implemented by means of a field programmable gate array (FPGA) device which also includes a module operation supervision (MOS) block supporting power management, fault-tolerant and module operating time-sharing algorithms. Experimental results for three parallel-connected inverters are presented to illustrate the design features in terms of AC output voltage regulation, inverters current distribution, robustness in the presence of load variations and to show the proper operation of the MOS block.
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      Stability Feeler: a tool for parametric robust stability analysis and its applications
      • Author(s): T. Matsuda  and  T. Mori
      • Source: IET Control Theory & Applications, Volume 3, Issue 12, p. 1625 –1633
      • DOI:  10.1049/iet-cta.2008.0462
      • Type: Article
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      • p. 1625 –1633 (9)
        In this study the authors propose a new tool for robust stability analysis. This tool gives D-stability intervals along a given line in the polynomial coefficient space. D-stability means that all the zeros of characteristic polynomials are in a prescribed connected open region and therefore, besides continuous-time systems or discrete-time systems, any systems having such a pole location can be analysed by utilising this tool. The tool is referred to as ‘Stability Feeler’, named after a feeler of insects. It is shown that Stability Feeler can be systematically computed by using standard numerical calculations. The authors also show two applications of Stability Feeler. One is the design of robust controllers for linear uncertain systems. The other is robust absolute stability analysis of Lur'e systems. For the robust controller design, it is often necessary to analyse stability of systems with the designed controllers. However, by the support of Stability Feeler, the authors can directly obtain a class of stabilising controllers. For robust absolute stability of interval Lur'e systems, a sufficient condition has already been proposed, while Stability Feeler enables one to analyse stability of both continuous-time and discrete-time Lur'e systems with affine linear uncertainties, which are more general than interval ones. Moreover, sharpness of any robust absolute stability criteria for uncertain Lur'e systems can be assessed.
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