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Automatic Control, IRE Transactions on

Issue 1 • Date January 1962

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Displaying Results 1 - 23 of 23
  • [Front cover and table of contents]

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  • The issue in brief

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  • Corrections

    Page(s): 72
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  • [Back cover]

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  • Asymmetric non-mean-square error criteria

    Page(s): 64 - 66
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    In the theory of linear prediction and/or filtering, it is well known that the optimum linear device obtained using the minimum mean-square error criterion is also optimum for a much wider class of symmetric error criteria if the input process is Gaussian. This result is extended here to include nonsymmetric error criteria as well as the case of nonstationary Gaussian inputs. A simple direct proof is given which exploits the fact that the probability density function of the error is known explicitly. The method consists of showing that the expected value of the generalized error weighting function \phi(\epsilon) is a monotonic (nondecreasing) function of the mean-squared error. View full abstract»

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  • Adaptive sampling frequency for sampled-data control systems

    Page(s): 38 - 47
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    Sampled-data control systems generally have fixed sampling frequencies which must be set high enough to give satisfactory performance for all anticipated conditions. A study is made here of an adaptive system which varies the sampling frequency by measuring a system parameter. It is shown that a sampler followed by a zero-order hold whose sampling period is controlled by the absolute value of the first derivative of the error signal will be a more "efficient" sampler than a fixed-frequency sampler. That is, over a given time interval, fewer samples are needed with the variable-frequency system than with a fixed-frequency system while maintaining essentially the same response characteristics. Analog computer studies of simple Type I and Type II sampled-data servo systems with error sampling and unity feedback verified the method. Standard analog computer components were used to set up a simulated servo system, a rate detector, absolute-value detector, a voltage-controlled oscillator, and a sampler and zero-order hold. The system described reduced the number of samples required for response to a step input to about three-quarters that required in a fixed-sampling-frequency system. Over a long period of time savings in the number of samples required can be expected to be between 25 and 50 per cent. In many applications the savings produced by reducing the over-all number of samples required may outweigh the added complexity of the adaptive-sampling-frequency system. View full abstract»

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  • A self-adjusting control system with large initial error

    Page(s): 33 - 38
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    A performance measuring, plant-adaptive control system is described. A linear plant having two variable parameters induces a large system error which is reduced by adjustments made in two controller parameters. An adaptive computer, the logical design of which is based on a modification of Newton's method of descent, generates the controller-parameter changes from measurements of the integral-of-error squared (ISE). This method is evaluated with regard to the time interval required to reduce ISE from a large initial value to a small prescribed limit. The average adaptation time for this system is shown to be approximately sixty times the response time of the system when the system error is zero. View full abstract»

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  • Decision-making in adaptive control systems

    Page(s): 24 - 32
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    An approach to the analysis and synthesis of adaptive control systems taking into account the effect of inexact measurements is presented here. The approach is based on the method of generalized quantized compensation. The mathematical tools needed for the analysis are adapted from the discipline of statistical inference. In particular, decision theory is used. An important consequence of inexact measurement is that the problems of identification and of control cannot be considered separately. Decision theory is used as the link that logically relates the two. Current application of decision functions has mostly been limited to cases where the unknown parameters to be determined can take on only discrete values. In view of the continuous variation of the parameters, assumptions that they take on discrete values lead to results whose optimality is not justifiable. Several possible extensions are presented. In addition, a sequential decision scheme that can be applied to reduce expected measurement time is presented. An attempt is made to make the statistical analysis largely self-contained and lucid to those not familiar with statistical inference procedures. View full abstract»

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  • A note on root-locus synthesis

    Page(s): 84
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  • Stability of nonlinear sampled-data control systems

    Page(s): 15 - 23
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    With regard to the asymptotic stability in the large of nonlinear, autonomous sampled-data systems, the following conjecture has been quoted frequently in the literature. Namely, "if the lineafized system is stable for all points of the state space, the original nonlinear system is asymptotically stable in the large" (henceforth abbreviated a.s.i.l.). This paper shows by counter examples that the statement is not true in general. Both total and incremental linearizations are considered and in both cases the conjecture is false. Finally, a sufficient condition for a a.s.i.l, is given. View full abstract»

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  • Convolution z -transform method applied to certain nonlinear discrete systems

    Page(s): 57 - 64
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    This paper extends to discrete systems the method of complex convolution developed by Weber [6] for continuous systems. In this paper the convolution z -transform method is applied to obtain an explicit solution of certain nonlinear difference equations. The explicit solution is often desired for system design as well as for obtaining the response for large intervals of time. In these difference equations which describe the physical discrete systems, it is assumed that the nonlinearities are "small." This is necessitated by the form of solution applicable to the use of the convolution method. The advantage of the method is to systematize the procedure for the solution as well as to obtain results in a closed form. The convergence of the solution is discussed as well as applications to certain examples. Two numerical examples are worked out to illustrate the method. Explicit approximate solution is obtained and the results compare favorably with the numerical solution of the nonlinear difference equation as a recurrence relationship. View full abstract»

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  • Stability analysis of nonlinear control systems by the second method of Liapunov

    Page(s): 3 - 15
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    The second method of Liapunov is used to study asymptotic stability of feedback control systems with single non-linear elements. The paper aims at a systematic development of Liapunov functions in terms of canonic transformations of state variables. This approach yields various simplified stability criteria; a rather complete table of such criteria is included. Several insights believed novel concerning the failure of the method in certain practical cases are presented. The root locus of the linear portion of the system is used to predict the applicability of the method. The proposed pole- and zero-shifting techniques extend the applicability of the method to many practical systems in which the method would fail without these techniques. View full abstract»

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  • Plant adaptive systems versus ordinary feedback systems

    Page(s): 48 - 56
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    The limitations in classical feedback that might justify the more complex plant or process adaptive systems are studied. Some of the limitations cited in the adaptive literature apply only to the classical single-degree-of-freedom configuration and not to the classical two-degree-of-freedom structures. Model and conditional feedback configurations are not superior to ordinary two-degree-of-freedom configurations. Time invariant (classical) compensation is adequate for coping with the sensitivity and disturbance problem in lightly damped and drifting plant poles. Two significant limitations in ordinary linear feedback systems that may justify the adaptive approach are: a) Their susceptibility to feedback transducer noise when the plant by itself does not have the loop gain area required for the desired sensitivity properties of the system; b) The limited sensitivity reduction achievable in nonminimum phase and unstable plants. The first of these may be eased by a multiple-loop design and the second by a parallel plant design. However, it has not been shown how the adaptive systems overcome the limitations of ordinary feedback systems. View full abstract»

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  • Knowledge in the large

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  • Compatibility of a two-degree-of-freedom system with a set of independent specifications

    Page(s): 67 - 72
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    In feedback control systems in which more than one transfer function must be specified, a multi-degree-of-freedom configuration is required. In many practical situations a two-degree-of-freedom configuration is of interest. This paper deals with the conditions that must be fulfilled in the choice of transfer functions so that two sets of specifications can be fulfilled by a given configuration. The possibility of implementing two sets of specifications independently is determined by the degree of complexity allowed in the individual transfer functions of the system. A method is described by which the compatibility of a given structure with a set of specifications can be insured. With the aid of a procedure which is illustrated in two examples, the minimum degree of complexity in the individual blocks is determined in relation with the high-frequency behavior of the system. View full abstract»

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Aims & Scope

The theory, design and application of Control Systems. It shall encompass components, and the integration of these components, as are necessary for the construction of such systems. The latest title for this publication is IEEE Transactions on Automatic Control.

 

This Transactions ceased publication in 1958. The current retitled publication is IEEE Transactions on Automatic Control.

Full Aims & Scope