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Control Systems Technology, IEEE Transactions on

Issue 2 • Date Jun 1994

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Displaying Results 1 - 10 of 10
  • On the maximum feedback delay in a linear/nonlinear control system with input disturbances caused by controller-computer failures

    Page(s): 110 - 122
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1036 KB)  

    Electromagnetic interferences or other environmental disturbances may cause transient failures to the controller computer of a real-time control system. Such a faulty controller either fails to update the control input for one or more sampling periods, or generates erroneous control inputs until the failure is handled properly or disappears. The goal of this paper is to derive the maximum duration of controller's faulty behavior, called the hard deadline, a real-time control system can tolerate without losing stability or leaving its allowed state space. For linear time-invariant control systems, one can derive hard deadlines by testing the stability of their state difference equations which account for the effects of stationary occurrences of disturbances to, as well as the random delays in, the control input. Similarly, one can derive deadlines for nonlinear time-invariant control systems by linearizing their nonlinear state equations and using the Lyapunov's first method. In addition to this stationary model, a one-shot event model is considered for linear/nonlinear time-invariant control systems by using their state trajectories and allowed state spaces. The hard deadline information that represents the knowledge of the controlled process's inertia and timing constraints is applied to the design and evaluation of controller computers View full abstract»

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  • Eigenstructure assignment and controller optimization for mechanical systems

    Page(s): 88 - 100
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    A technique to assign a desired eigensystem to an actively controlled structure and to optimize the controller and structural parameters is presented. The technique explicitly parametrizes the feedback gain matrices in terms of the eigensystem and structural matrices and then optimizes the closed-loop system by minimizing some norm related to the feedback gain matrices. The technique can optimize design criteria such as gain suppression, actuator and sensor placement, minimum number of sensors, structural stiffness, and system sensitivity to parameter variations. The technique is computationally efficient by being developed in second order form using real arithmetic and with an analytic gradient supplied for the design variables. Two analytical example problems are presented in which active control systems are designed using eigensystem assignment with parametric feedback. The first example assigns eigenvalues and optimizes the controller design for a three-story scale model building. The second example assigns decoupled vibration modes to eliminate rotation of a gyro box View full abstract»

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  • Robust controllers for the Middeck Active Control Experiment using Popov controller synthesis

    Page(s): 73 - 87
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    The purpose of this paper is to demonstrate robust compensators designed using Popov controller synthesis on the Middeck Active Control Experiment (MACE): a Shuttle program scheduled for flight in January, 1995. The experiment has been designed to investigate the extent to which the on-orbit behavior of a precision-controlled spacecraft can be predicted and controlled using analysis and ground testing prior to launch. Previous flight experiments indicate that, on-orbit, the structural dynamics can change significantly, and that these changes are very difficult to predict. Thus the need arises for robust control techniques that can guarantee on-orbit performance for flexible spacecraft even though the models have large parameter uncertainties. Such a technique is developed in this paper using the Popov stability criterion from absolute stability theory. A state space representation of the stability analysis test is combined with an ℋ2 performance objective to provide a powerful technique for robust controller synthesis. A numerical algorithm for optimizing the controller gains and stability multipliers is discussed. Several experimental results on MACE are used to demonstrate that Popov controller synthesis guarantees robustness to real parameter variations and yields good performance with respect to the reference LQG designs View full abstract»

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  • Projective control design for multi-zone crystal growth furnace

    Page(s): 142 - 147
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    This paper addresses the problem of controlling the temperature profile inside a multi-zone crystal growth furnace. A minimal discrete-time state-space model of the furnace is determined by the least squares identification of a multi-input/multi-output (MIMO) model. An integral control structure for the discrete-time model is derived to allow reference tracking, and a state-feedback control is designed for the system by solving a discrete linear quadratic regulator (DLQR) problem with a suitably chosen cost. This state feedback controller serves as a reference for designing an output feedback controller through the projective control approach. The resulting projective controller has a structure similar to a MIMO proportional-plus-integral controller. The projective controller is used to control a simulated and an actual furnace. The resulting control system achieves the necessary control objective, i.e. it maintains the required temperature with no steady-state error and a reasonable transient behavior in spite of the uncertainties associated with the identified model View full abstract»

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  • The design of H controllers for an experimental non-collocated flexible structure problem

    Page(s): 101 - 109
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    This paper describes results in applying robust control techniques to achieve vibration suppression of an active precision truss structure. The active structure incorporates piezoelectric members which serve as both structural and actuation elements. The problem considered is multiple-input, multiple-output with non-collocated actuators and sensors. Several characterizations of uncertainty are studied and the resulting controllers are compared experimentally. One characterization uses a novel approach involving eigenvalue perturbation descriptions View full abstract»

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  • Multi-variable sliding mode control of quantum boost SRC

    Page(s): 148 - 150
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    A simple discrete multi-variable sliding mode controller (MSMC) is proposed to improve the control performance of the quantum boost series resonant converter (SRC). Since the nonlinear terms are decoupled by the proposed MSMC, it is very simple to implement and the simple first order output voltage response robust to the load disturbance can also be obtained without an additional load current sensor View full abstract»

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  • Review of the damped least-squares inverse kinematics with experiments on an industrial robot manipulator

    Page(s): 123 - 134
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    The goal of this paper is to present experimental results on the implementation of the damped least-squares method for the six-joint ABB IRb2000 industrial robot manipulator. A number of inverse kinematics schemes are reviewed which allow robot control through kinematic singularities. The basic scheme adopts a damped least-squares inverse of the manipulator Jacobian with a varying damping factor acting in the neighborhood of singularities. The effect of a weighted damped least-squares solution is investigated to provide user-defined accuracy capabilities along prescribed end-effector space directions. An online estimation algorithm is employed to measure closeness to singular configurations. A feedback correction error term is introduced to ensure algorithm tracking convergence and its effect on the joint velocity solution is discussed. Computational aspects are discussed in view of real-time implementation of the proposed schemes. Experimental case studies are developed to investigate manipulator performance in the case of critical end-effector trajectories passing through and near the shoulder and wrist singularities of the structure View full abstract»

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  • Thermal pressure control: regulation of high-pressure gas by exploitation of temperature sensitivity

    Page(s): 151 - 153
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    Precise pressure regulation in high-pressure gas-filled vessels is made difficult by the pronounced temperature dependence of gas pressure. The paper proposes an unusual control system exploiting the gas pressure-temperature relationship to achieve unusually precise regulation in a 207 MPa (30,000 lbf/in2) gas-filled test vessel for rock physics measurements. Joule-Thomson cooling, a major dynamic effect, is also discussed. This paper is presented as a conceptual and theoretical development View full abstract»

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  • Adaptive schemes for the active control of helicopter structural response

    Page(s): 61 - 72
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    This paper describes a new method for the design of an adaptive controller for the reduction of vibration in helicopter structures. Two known approaches are described which can be used to implement an active vibration control system-a frequency domain controller or a time domain controller. Both strategies have a number of advantages and disadvantages, which are discussed in the paper. A new approach to the design of an adaptive controller for the reduction of helicopter vibration is described. This new technique is a hybrid time/frequency domain solution combining the advantages from both the time domain linear quadratic feedback controller and the frequency domain quasi-static controller. Both fixed gain and adaptive control designs have been implemented, and comparisons of the performance of the various control approaches to the problem of minimizing vibration in helicopter structures is made. The hybrid strategy has been studied extensively using computer simulations and its performance has been shown to equal that of the frequency domain approach, providing up to 90 percent vibration reduction at the blade-passing frequency. Results from experimental validation on a helicopter airframe test rig confirm the effectiveness of the strategy View full abstract»

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  • A specification of neural network applications in the load forecasting problem

    Page(s): 135 - 141
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    This paper investigates the effectiveness of the artificial neural network (ANN) approach to short term load forecasting in electrical power systems. Using examples, the learning process and capabilities of a neural network in the prediction of peak load of the day are demonstrated. Different data normalizing approaches and input patterns are employed to exploit the correlation between historical load and temperatures and expected load patterns. A number of ANN's are included with emphasis given to their practical implementation for electrical power system control and planning purposes. The networks have been trained on actual power utility load data using a backpropagation algorithm. The prospects for applying a combined solution using artificial neural networks and expert systems, called the expert network are also discussed. Consideration is given to expert networks as a more complete solution to the forecasting problem which neither system alone can provide View full abstract»

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