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Control Theory and Applications, IEE Proceedings -

Issue 6 • Date Nov 2000

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Displaying Results 1 - 19 of 19
  • Force control of a single-link flexible robot based on a collision detection mechanism

    Page(s): 588 - 595
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    The paper studies the use of flexible robots in tasks that require a contact with the environment. Here a flexible robot has the advantage that the energy of the collision can be absorbed by the robot structure instead of by the environment. First, a tip position control method of a single-link flexible robot for collision-free trajectories is presented. This method offers a behaviour of the flexible robot similar to that of a rigid robot under the same working conditions. We also make a comparison among different force control methods. Experimental results are shown that validate the study. The feasibility of the proposed force control is validated from the good collision detection results obtained. The result was made possible by the reliability of the position control method and the detailed analysis made of the reference signal. The approach presented can be generalised for the control of more complex arms View full abstract»

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  • Cancelling vibrations in flexible articulated structures using non-causal inverse dynamics

    Page(s): 596 - 604
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    Inverse dynamics is the process of computing actuator efforts to produce desired responses. An algorithm is presented which uses a non-causal inverse dynamics approach to cancel vibrations in a flexible manipulator or a flexible articulated structure. Solutions are obtained for individual modes and then combined them to obtain general solutions. This approach can be used for real time control since few computations are required for combining the solutions. The algorithm is demonstrated via computer simulations of a 60 m deployable boom on the Space Shuttle. The boom was used in the Shuttle radar topography mission on a Space Shuttle flight. An analytical study to demonstrate the advantages of using inverse dynamics in this type of articulated structure is presented View full abstract»

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  • SMVSC for a class of time-delay uncertain systems with mismatching uncertainties

    Page(s): 687 - 693
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    A sliding-mode control approach is proposed for a class of uncertain time-delay systems with mismatching uncertainties. It is based on the linear matrix inequality technique and the sliding-mode variable structure control method. A simulation study for a numerical example is given to illustrate the effectiveness of this approach in control design View full abstract»

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  • Parallel force and position control of flexible manipulators

    Page(s): 605 - 612
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The problem of controlling the interaction of a flexible link manipulator with a compliant environment is considered. The manipulator's tip is required to keep contact with a surface by applying a constant force and maintaining a prescribed position or following a desired path on the surface. Using singular perturbation theory, the system is decomposed into a slow subsystem associated with rigid motion and a fast subsystem associated with link flexible dynamics. A parallel force and position control developed for rigid robots is adopted for the slow subsystem while a fast control action is employed to stabilise the link deflections. Simulation results are presented for a two-link planar manipulator under gravity in contact with an elastically compliant surface View full abstract»

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  • Passivity/sliding mode control of a stand-alone hybrid generation system

    Page(s): 680 - 686
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    A variable structure controller for an electric generation hybrid system is proposed. The system is intended for variable alternate load and includes a wind turbine, photovoltaic generation and a battery bank. As a first step for the controller design, a dynamic model of the system is developed in a rotor reference frame. The control law is designed through the combination of passivity and sliding mode techniques. The objective is to control the operation of the wind subsystem to complement the photovoltaic generation, so the power demand is satisfied. During periods of scarce winds, the strategy is modified and the control objective becomes maximum wind generation View full abstract»

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  • Table online neural control of systems with closed kinematic chains

    Page(s): 619 - 632
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1208 KB)  

    The neural control of robotic systems with closed kinematic chains is discussed and theorems guaranteeing the control stability of such systems are developed. The first class of systems have a single serial chain with a prescribed contact force when moving across a surface, i.e. the problem of hybrid position/force neural control. The second class of systems considered includes hexapod walking machines, which have a varying topology of closed kinematic chains during walking. The equations of motion can be solved by optimising contact forces according to a predefined cost function, and so the hybrid/position neural controller is extended to this class. A novel control structure which makes no initial assumptions about the system is also presented, using the concept of `virtual neural networks'. This approach can be applied to a large number of different systems, and it is also extended to include neural networks implemented on digital microprocessors View full abstract»

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  • Periodic errors elimination in CVCF PWM DC/AC converter systems: repetitive control approach

    Page(s): 694 - 700
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A plug-in digital repetitive learning (RC) controller is proposed to eliminate periodic tracking errors in constant-voltage constant-frequency (CVCF) pulse-width modulated (PWM) DC/AC converter systems. The design of the RC controller is systematically developed and the stability analysis of the overall system is discussed. The periodic errors are forced toward zero asymptotically and the total harmonics distortion (THD) of the output voltage is substantially reduced under parameter uncertainties and load disturbances. Simulation and experimental results are provided to illustrate the validity of the proposed scheme View full abstract»

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  • Control strategies for hardware-in-the-loop simulation of flexible space robots

    Page(s): 569 - 579
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    As a partner in the International Space Station, Canada is responsible for the verification of all tasks involving the special purpose dextrous manipulator. Those verifications cannot be performed using software simulators only since the accuracy of existing contact dynamic models are yet to be confirmed, especially in the real-time mode required for verifying human operated processes. One option is to use a hardware-in-the-loop simulation (HLS), where the space hardware is simulated and the contact dynamics is emulated using a rigid robot performing the tasks. The main difficulty in this approach is the trade-off between the stability of the control loop and good performance. The control of the rigid robot in the HLS is investigated. Simplified linear systems are used to determine the limitations of the classical position-based control when contact occurs. A new control scheme in which the slave robot is driven in acceleration is proposed. Experimental results show the benefit of using this new acceleration control approach View full abstract»

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  • Robust H control for uncertain linear time invariant descriptor systems

    Page(s): 648 - 654
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    The H control problem for uncertain descriptor systems with time-invariant nonbound uncertainty in the state matrix is considered. Necessary and sufficient conditions for robust H control of descriptor systems by state feedback and dynamic output feedback are derived. The design results are expressed in terms of generalised algebraic Riccati inequalities, which may be considered an extension of results given in recent literature. Explicit formulae for controllers which solve the corresponding problems are provided. The generalised algebraic Riccati inequalities approach used is based on a version of the bounded real lemma for descriptor systems, thus making the given proofs simpler View full abstract»

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  • Robust Kalman filtering for discrete state-delay systems

    Page(s): 613 - 618
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    A robust estimator design methodology has been developed for a class of linear uncertain discrete-time systems. It extends the Kalman filter to the case in which the underlying system is subject to norm-bounded uncertainties and constant state delay. A linear state estimator is constructed via a systematic procedure such that the estimation error covariance is guaranteed to lie within a certain bound for all admissible uncertainties. The solution is given in terms of two Riccati equations involving scaling parameters. A numerical example is provided to illustrate the theory View full abstract»

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  • Methodology for control of a space robot with flexible links

    Page(s): 562 - 568
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    A methodology of stable manipulation-variable feedback control of space robots with flexible links for avoiding static target and continuous path tracking is discussed. The proposed methodology is effective for base-fixed robots with flexible links on the ground, as well as free-flying space robots. A virtual rigid manipulator (VRM) concept is introduced and a pseudo-resolved-motion rate control for flexible manipulators is derived. By using the VRM, other controls, including an extended local PD-control and a pseudo-resolved-acceleration control, are given. They can be transformed into joint-variable feedback controls and are robust stable. Combining those controls with a reduced-order modal control yields a composite control. The asymptotic stability of the static target is verified by the Lyapunov method. For path tracking control, the orbital stability is discussed in terms of the singular perturbation method. Numerical simulations demonstrate the effectiveness and feasibility of the proposed method View full abstract»

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  • Parametric linear quadratic control and random delays

    Page(s): 641 - 647
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    The authors derive the design equations for parametric linear quadratic control of continuous-time systems with random delays. This problem motivates a more general setup that is utilised for the development of efficient numerical algorithms. Systems with random delays are important in control problems over communication networks. The generalised setup allows robustness issues against modelling errors and statistically varying disturbances to be addressed. The results are illustrated with examples View full abstract»

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  • Subject Index

    Page(s): 702 - 705
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    First Page of the Article
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  • Fault detection in hot steel rolling using neural networks and multivariate statistics

    Page(s): 633 - 640
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (800 KB)  

    The paper addresses the issue of maintaining consistent high quality production in the steel industry by extending techniques emanating from the fields of neural networks and multivariate statistics. Process diagnostic methodologies based on these tools were developed and applied to a six-stand hot rolling mill. The objective was to achieve better mill setup parameters so that the manufactured coils consistently meet the required customer specifications. A wavelet neural network was successfully used for modelling the mill parameters and for detecting errors in the rolling stand settings. Model prediction accuracy and robustness were enhanced through stacked generalisation. Multivariate statistical performance monitoring techniques were then applied on top of the mill control systems to provide early warning of strips being badly rolled. Both approaches yielded comparable results on monitored data from a hot strip mill and, in combination, provided enhanced manufacturing performance View full abstract»

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  • Inferential control for rolling mills

    Page(s): 673 - 679
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    A robust inferential controller is developed for hot strip rolling mill tension control. Tension cannot be measured, therefore a nonlinear model is used to infer the tension from the looper angle. The model uses constant physical parameters while the actual physical system will be uncertain, therefore quantitative feedback theory is used to design a tension controller, which will provide robust performance despite uncertainty from both the physical system and the inference model or soft sensor View full abstract»

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  • Author Index

    Page(s): 701
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (48 KB)  

    First Page of the Article
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  • Shift and delta operator realisations for digital controllers with finite word length considerations

    Page(s): 664 - 672
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    The implementation issues of digital controllers with finite word length (FWL) considerations are addressed. Both the shift and delta operator parametrisations of a general controller structure are considered. A unified formulation is adopted to derive a computationally tractable stability related measure that describes FWL closed-loop stability characteristics of different controller realisations. Within a given operator parametrisation, the optimal FWL controller realisation, which maximises the proposed stability related measure, is the solution of a nonlinear optimisation problem. The relationship between the z-operator and δ-operator controller parametrisations is analysed, and it is shown that the δ parametrisation has a better FWL closed-loop stability margin than the z-domain approach under a mild condition. A design example is included to verify the theoretical analysis and to illustrate the proposed optimisation procedure View full abstract»

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  • Analysis and design of robust adaptive control for nonlinear output feedback systems under disturbances with unknown bounds

    Page(s): 655 - 663
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    Robust adaptive control of nonlinear output feedback systems under bounded disturbances whose bounds are unknown is considered. A new algorithm is proposed for estimation of unknown bounds and adaptive control of the uncertain nonlinear system. To carry out the backstepping design with the estimation of unknown bounds, a new Lyapunov function is introduced with a flat zone in the pre-specified neighbourhood of the origin. The adaptive law based on the Lyapunov function has a dead zone, whose size depends on the flat zone. The design procedure follows the standard backstepping with variations in dealing with the cross terms between different stages and the bound estimation. The stability analysis shows that all the variables of the closed-loop control system are bounded, and the output tracking error converges to the flat zone which can be arbitrarily small. The proposed method does not need any bound of uncertain parameters or unknown disturbances, and it prevents the bursting phenomena View full abstract»

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  • Tip-trajectory tracking control of single-link flexible robots by output re-definition

    Page(s): 580 - 587
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    Output re-definition techniques are proposed so that the transfer function of the system with the new output is minimum phase and this facilitates the design of trajectory tracking controllers. There are various output functions suggested in the literature. The authors show that the zero dynamics of a single-link flexible robot is exponentially stable with the newly defined output function. Asymptotic tracking of step input, linear and second-order polynomial trajectories are achieved using controllers designed based on this new technique and the link vibrations are damped out significantly. The unique feature of the controller design technique is that the poles of the zero dynamics can be placed at any desired locations in the left half of the s-plane. This enables the suppression of undesirable vibrations while the robot tip is tracking a prescribed tip-trajectory View full abstract»

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