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Control Theory and Applications, IEE Proceedings -

Issue 5 • Date Sep 2002

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Displaying Results 1 - 15 of 15
  • Stable adaptive fuzzy control of the molten steel level in the strip casting process

    Page(s): 357 - 364
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (573 KB)  

    A fuzzy control scheme to regulate the molten steel level in the strip casting process is presented, where the parameters of the fuzzy controller are stably adapted by using Lyapunov stability theory. A switching controller is also used to deal with the approximation error of the fuzzy logic system. The error in the molten steel level is proved to converge to zero asymptotically. In the simulation, the clogging/unclogging of the stopper nozzle is considered and is shown to be overcome by the proposed controller. The robustness to uncertainty is shown to be superior to that of the conventional proportional integral controller. View full abstract»

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  • Closed-loop identification with MPC for an industrial scale CD-control problem

    Page(s): 448 - 456
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (894 KB)  

    An approach to implementing closed-loop identification in a model predictive-control framework for the cross-direction control of basis weight is proposed. The closed-loop-identification technique uses the concepts of Markov parameters to determine a step-response model that can then be used within a model predictive controller. The technique is applied to an industrial-scale paper-machine-simulation benchmark problem for cases of varying degrees of shrinkage. The performance of wet- and dry-end full-array sensors are compared. Also, the performance of the closed-loop identification is compared for a nominal case and two cases in which shrinkage occurs in the drying process. View full abstract»

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  • Spatial frequency antiwindup strategy for cross-directional control problems

    Page(s): 414 - 422
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (910 KB)  

    A MIMO antiwindup strategy for cross-directional control of web forming processes is presented. The scheme relies on a basis function expansion of the system interaction matrix which allows one to analyse the problem in terms of the spatial frequency components of the web profile. Antiwindup protection is achieved by prioritising the control directions in which the available control authority is employed. In particular, disturbance compensation is first sought in those spatial frequency components associated with the largest gain, that is, where the required control effort is smaller. Stability of the scheme is analysed for the case in which complete knowledge of the input and output rotation matrices is assumed. Simulation results show that the steady-state performance attained with the proposed strategy is superior to that achieved by traditional MIMO antiwindup schemes and is close to an optimal QP solution to the problem. View full abstract»

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  • Quantifying the potential benefits of constrained control for a large-scale system

    Page(s): 423 - 432
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (987 KB)  

    It is of practical interest to identify which processes will benefit significantly from the use of constrained control algorithms such as model predictive control, and which will not. Explicit conditions are derived that identify whether a particular process may benefit from constraint handling. These conditions are also useful for understanding the interactions between design and control for a particular system, especially for actuator placement and selection. The conditions are computable for a large-scale system directly from its transfer function model, a simulation model (e.g. defined by a set of ordinary/partial-differential equations and algebraic conditions), or experimental input-output data. The formulation considers the effects of measurement noise, process disturbances, model uncertainties, plant directionality and the quantity of experimental data. The conditions are illustrated by application to a paper-machine model constructed from industrial data. View full abstract»

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  • Co-ordinated control of profile and shape in hot strip finishing mills with nonlinear dynamics

    Page(s): 471 - 480
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (817 KB)  

    A method of modelling and controlling profile and flatness in hot strip tandem rolling mills is described. The method for controlling the profile is based on explicit manipulation of the strip thickness across its width. The flatness is controlled by appropriately distributing and constraining the profile actuators, so that defects do not occur. Model-based predictive control is employed to generate the control signal for each stand and to co-ordinate the stands for optimal profile and shape control. Simulation results are presented to demonstrate the performance of the proposed co-ordinated control scheme. View full abstract»

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  • Two-dimensional and EM techniques for cross directional estimation and control

    Page(s): 457 - 462
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (627 KB)  

    Cross directional monitoring and the control of sheet forming processes are treated as a two-dimensional (2D) dynamical systems issue. However, the sensors used in sheet forming processes do not usually collect the full two-dimensional information. Instead, a scanning sensor moves across the sheet in a zigzag manner, and it is this sparse data that must be used for monitoring and control. It is shown that EM methods can be used with a two-dimensional model for estimation and control by treating the unscanned area of the sheet as 'missing' data. Particular attention is given to the efficient representation of the sheet forming process using state space models with suitable model order testing methods. Finally, it is shown how the EM model update is linked to a corresponding control algorithm. View full abstract»

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  • Delay-dependent stability and output feedback stabilisation of Markov jump system with time-delay

    Page(s): 379 - 386
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (597 KB)  

    The stochastic stability and stabilisation problems of a Markov jump system (MJS) with time-delay under a dynamical output feedback control law is considered. LMI-based sufficient conditions are established for the system to be stochastic stable and exponentially stable. A sufficient and necessary condition for the MJS to be stabilisable in the mean square quadratic stable sense, which implies stochastic stability of the system, is established. An LMI-based control design method is proposed and a numerical example is included to show the usefulness of the theoretical results. View full abstract»

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  • Two-degree-of-freedom design method of state-predictive LQI servo systems

    Page(s): 365 - 378
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1078 KB)  

    A method has been proposed for designing an LQI servosystem in which reference characteristics and disturbance characteristics can be adjusted separately. The paper extends the method to the case in which the plant has a cascaded pure delay. It is proved that the resulting optimal compensator is the same as that for the plant with the delay removed, except for the existence of a state-prediction mechanism to cope with the delay, and that all the fundamental desirable features are inherited from the delay-free case. From the results of the paper, a complete solution to the optimal-design problem of state-predictive two-degree-of-freedom LQI servosystems for step references and step disturbances is obtained. View full abstract»

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  • Robust control of cars with front and rear wheel steering

    Page(s): 394 - 404
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (869 KB)  

    A steering performance enhancement system for a 4WS car designed to improve the ability of the driver to keep the vehicle on the desired path is described. The system is commanded by the driver to control the front and rear wheel steering. The system is developed on the basis of a single-gain design approach having three goals: first, to guarantee that the lateral acceleration follows the driver's command, second to achieve robust relaxation of the sideslip angle, and third to preserve robust stability. The system designed is independent of the major uncertainties of the car model, namely the car's mass and the road characteristics. The system utilises the general robust triangular decoupling controller, achieving robust decoupling of the front lateral acceleration from the yaw dynamics, and a prefilter that activates the yaw dynamics according to the driver's commands guaranteeing the robust relaxation (reduction) of the sideslip angle. View full abstract»

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  • Identifying temporal and spatial responses of cross machine actuators for sheet-forming processes

    Page(s): 441 - 447
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1408 KB)  

    The cross-machine direction (CD) control performance for sheet-forming processes is heavily dependent on the accuracy of the models that characterise the responses of all CD actuators. Adjustment of each CD actuator generally affects a portion of sheet in both machine (temporal) direction and cross-machine (spatial) direction. A method to identify CD actuator responses in both directions by utilising two-dimensional sheet variation measurements is described. The new modelling method allows simultaneous identification. of individual two-dimensional responses for all CD actuators and avoids the severe impacts of conventional simple step tests. View full abstract»

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  • Model-based evaluation of the effect of horizontal roll offset on cross-directional control performance in cold-strip rolling

    Page(s): 463 - 470
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (967 KB)  

    Some modern rolling mills allow for the work and intermediate rolls to be offset in the plane of the strip, allowing three-dimensional roll deformation. A generalised extension to existing roll-stack models is proposed in order to characterise this effect. The model is used to explore the influence of three-dimensional roll deformation on the prediction of actuator sensitivities used in cross-directional control systems in cold rolling. It is shown that horizontal work-roll offset alters the magnitude and form of all existing actuator responses. The effect is dependent on the degree of offset and on the work-roll diameter and is most pronounced in the parabolic component of bulk actuators. Further, the horizontal roll offset can itself be used as an actuator, although the magnitude of its sensitivity varies significantly with the degree of offset. View full abstract»

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  • Delay-dependent stabilisation and disturbance tolerance for time-delay systems subject to actuator saturation

    Page(s): 387 - 393
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (682 KB)  

    The problem of delay-dependent stabilisation of linear continuous-time systems with time delay in the state, additive bounded disturbances and limited actuators is presented. A design procedure based on the solution of coupled matrix inequalities and the use of the S-procedure is proposed. The links and the trade-offs between tolerance to both disturbance and delay, and the size of the region inside which the stability of the closed-loop saturated system is assured, are discussed. View full abstract»

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  • Analysis of steady-state performance for cross-directional control

    Page(s): 433 - 440
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (813 KB)  

    The authors analyse the steady-state behaviour of a class of cross-directional controllers that are pertinent to general web-forming processes. Their analysis is framed in terms of the controllable space prescribed by the interaction matrix and general discrete orthonormal basis descriptions of both the input and output space under the assumption of closed-loop stability. The specific choice of controller defines (whether explicitly or implicitly) an additional assumed controlled space. It is well known that the controllable space determines a lower bound on output variation. They examine the implications of integral action and provide sufficient conditions for the steady-state output variation to achieve this lower bound. They confirm some intuitive results that connect the optimal constrained and unconstrained steady-state solutions for model-based control with no model mismatch. Model mismatch is usually detrimental to steady-state performance. This effect is interpreted in terms of leakage between the controllable and assumed controlled spaces, as well as their respective orthogonal complements. View full abstract»

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  • Optimal dynamic-inversion-based control of an overhead crane

    Page(s): 405 - 411
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (683 KB)  

    A methodology is proposed to control the transient sway and residual oscillation of a payload carried by an overhead crane. The design approach is based on a linearised model of the crane and consists of damping the linearised system by an observer-based controller and applying a dynamic inversion procedure in order to assure a predetermined oscillation free polynomial motion law for the payload. Polynomial functions are adopted in order to guarantee that the input function has a continuous derivative of an arbitrary order. Moreover, the motion time can be minimised, taking into account constraints on the actuators, by means of a simple bisection algorithm. Parameter uncertainties are taken into account during the whole design procedure. Simulation results, based on a nonlinear crane model, show how the method is also effective when the payload is hoisted or lowered during the motion, and when friction effects are considered. View full abstract»

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