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  • 1
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    Beyond singular values and loop shapes (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The status of singular value loop-shaping as a design paradigm for multivariable feedback systems is reviewed. It shows that this paradigm is an effective design tool whenever the problem specifications are spacially round. The tool can be arbitrarily conservative, however, when they are not. This happens because singular value conditions for robust performance are not tight (necessary and sufficient) and can severely overstate actual requirements. An alternate paradign is discussed which overcomes these limitations. The alternative includes a more general problem formulation, a new matrix function mu, and tight conditions for both robust stability and robust performance. The state of the art currently permits analysis of feedback systems within this new paradigm. Synthesis remains a subject of research.
    Keywords: CYBERNETICS
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 14; 5-16
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  • 2
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    Building brains for bodies (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We describe a project to capitalize on newly available levels of computational resources in order to understand human cognition. We will build an integrated physical system including vision, sound input and output, and dextrous manipulation, all controlled by a continuously operating large scale parallel MIMD computer. The resulting system will learn to 'think' by building on its bodily experiences to accomplish progressively more abstract tasks. Past experience suggests that in attempting to build such an integrated system we will have to fundamentally change the way artificial intelligence, cognitive science, linguistics, and philosophy think about the organization of intelligence. We expect to be able to better reconcile the theories that will be developed with current work in neuroscience.
    Keywords: CYBERNETICS
    Type: AIAA PAPER 94-1208-CP , NASA. Johnson Space Center, Conference on Intelligent Robotics in Field, Factory, Service, and Space (CIRFFSS 1994), Volume 1; p 253-263
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  • 3
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    Some design guidelines for discrete-time adaptive controllers (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: There have been many algorithms proposed for adaptive control which will provide globally asymptotically stable controllers if some stringent conditions on the plant are met. The conditions on the plant cannot be met in practice as all plants will contain high frequency unmolded dynamics therefore, blind implementation of the published algorithms can lead to disastrous results. This paper uses a linearization analysis of a non-linear adaptive controller to demonstrate analytically design guidelines which aleviate some of the problems associated with adaptive control in the presence of unmodeled dynamics.
    Keywords: CYBERNETICS
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  • 4
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    Beyond singular values and loop shapes (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The status of singular value loop-shaping as a design paradigm for multivariable feedback systems is reviewed. It shows that this paradigm is an effective design tool whenever the problem specifications are spacially round. The tool can be arbitrarily conservative, however, when they are not. This happens because singular value conditions for robust performance are not tight (necessary and sufficient) and can severely overstate actual requirements. An alternate paradign is discussed which overcomes these limitations. The alternative includes a more general problem formulation, a new matrix function mu, and tight conditions for both robust stability and robust performance. The state of the art currently permits analysis of feedback systems within this new paradigm. Synthesis remains a subject of research.
    Keywords: CYBERNETICS
    Type: NASA-CR-177018 , NAS 1.26:177018 , LIDS-P-1504
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  • 5
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    Robustness of continuous-time adaptive control algorithms in the presence of unmodeled dynamics (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper examines the robustness properties of existing adaptive control algorithms to unmodeled plant high-frequency dynamics and unmeasurable output disturbances. It is demonstrated that there exist two infinite-gain operators in the nonlinear dynamic system which determines the time-evolution of output and parameter errors. The pragmatic implications of the existence of such infinite-gain operators is that: (1) sinusoidal reference inputs at specific frequencies and/or (2) sinusoidal output disturbances at any frequency (including dc), can cause the loop gain to increase without bound, thereby exciting the unmodeled high-frequency dynamics, and yielding an unstable control system. Hence, it is concluded that existing adaptive control algorithms as they are presented in the literature referenced in this paper, cannot be used with confidence in practical designs where the plant contains unmodeled dynamics because instability is likely to result. Further understanding is required to ascertain how the currently implemented adaptive systems differ from the theoretical systems studied here and how further theoretical development can improve the robustness of adaptive controllers.
    Keywords: CYBERNETICS
    Type: IEEE Transactions on Automatic Control (ISSN 0018-9286); AC-30; 881-889;
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  • 6
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    Robustness of adaptive control algorithms in the presence of unmodeled dynamics (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper reports the outcome of an exhaustive analytical and numerical investigation of stability and robustness properties of a wide class of adaptive control algorithms in the presence of unmodeled dynamics and output disturbances. The class of adaptive algorithms considered are those commonly referred to as model-reference adaptive control algorithms, self-tuning controllers, and dead-beat adaptive controllers; they have been developed for both continuous-time systems and discrete-time systems. The existing adaptive control algorithms have been proven to be globally asymptotically stable under certain assumptions, the key ones being (1) that the number of poles and zeroes of the unknown plant are known, and (2) that the primary performance criterion is related to good command following. These theoretical assumptions are too restrictive from an engineering point of view. Real plants always contain unmodeled high-frequency dynamics and small delays, and hence no upper bound on the number of the plant poles and zeroes exists. Also real plants are always subject to unmeasurable output additive disturbances, although these may be guide small. Hence, it is important to critically examine the stability robustness properties of the existing adaptive algorithms when some of the theoretical assumptions are removed; in particular, their stability and performance properties in the presence of unmodeled dynamics and output disturbances. Previously announced in STAR as N83-16061
    Keywords: CYBERNETICS
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  • 7
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    Angles of multivariable root loci (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A generalized eigenvalue problem is demonstrated to be useful for computing the multivariable root locus, particularly when obtaining the arrival angles to finite transmission zeros. The multivariable root loci are found for a linear, time-invariant output feedback problem. The problem is then employed to compute a closed-loop eigenstructure. The method of computing angles on the root locus is demonstrated, and the method is extended to a multivariable optimal root locus.
    Keywords: CYBERNETICS
    Type: LIDS-P-1147 , IEEE Transactions on Automatic Control; AC-27; Dec. 198
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  • 8
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    Multivariable feedback design - Concepts for a classical/modern synthesis (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper presents a practical design perspective on multivariable feedback control problems. It reviews the basic issue - feedback design in the face of uncertainties - and generalizes known single-input, single-output (SISO) statements and constraints of the design problem to multiinput, multioutput (MIMO) cases. Two major MIMO design approaches are then evaluated in the context of these results.
    Keywords: CYBERNETICS
    Type: IEEE Transactions on Automatic Control; AC-26; Feb. 198
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  • 9
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    Asymptotic Eigenstructures (1980)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: The behavior of the closed loop eigenstructure of a linear system with output feedback is analyzed as a single parameter multiplying the feedback gain is varied. An algorithm is presented that computes the asymptotically infinite eigenstructure, and it is shown how a system with high gain, feedback decouples into single input, single output systems. Then a synthesis algorithm is presented which uses full state feedback to achieve a desired asymptotic eigenstructure.
    Keywords: CYBERNETICS
    Type: NASA-CR-162900 , LIDS-P-982
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  • 10
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    Robustness properties of discrete time regulators, LOG regulators and hybrid systems (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Robustness properites of sample-data LQ regulators are derived which show that these regulators have fundamentally inferior uncertainty tolerances when compared to their continuous-time counterparts. Results are also presented in stability theory, multivariable frequency domain analysis, LQG robustness, and mathematical representations of hybrid systems.
    Keywords: CYBERNETICS
    Type: LIDS-FR-960 , NASA-CR-163313
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