ISSN:1049-8923    

DOI:10.1002/rnc.4590040102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:1049-8923    

DOI:10.1002/rnc.4590040103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractQuantitative feedback theory (QFT) has received much criticism for a lack of clearly stated mathematical results to support its claims. Considered in this paper are two important fundamental questions: (i) whether or not a QFT design is robustly stable, and (ii) does a robust stabilizer exist. Both these are precursors for synthesizing controllers for performance robustness. Necessary and sufficient conditions are given to resolve unambiguously the question of robust stability in SISO systems, which in fact confirms that a properly executed QFT design is automatically robustly stable. This Nyquist‐type stability result is based on the so‐called zero exclusion condition and is applicable to a large class of problems under some simple continuity assumptions. In particular, the class of uncertain plants include those in which there are no right‐half plane pole‐zero cancellations over all plant uncertainties. A sufficiency condition for a robust stabilizer to exist is derived from the well‐known Nevanlinna‐Pick theory in classical analysis. Essentially the same condition may be used to answer the question of existence of a QFT controller for the general robust performance problem. These existence results are based on an upper bound on the nominal sensitivity function. Also considered is QFT design for a special class of interval plants in which only the poles and the DC gain are assumed uncertain. The latter problem lends itself to certain explicit computations that considerably simplify the QFT des

ISSN:1049-8923    

DOI:10.1002/rnc.4590040104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractNew formulations are presented for quantitative feedback theory that do not require the direct manipulation of templates in the classical sense. This enables the explicit incorporation of high‐frequency unstructured uncertainty into the problem statement, and allows for constructive existence conditions for the solvability of the QFT problem. Necessary and sufficient conditions for robust stability and robust performance are presented for plants with both parametric and high‐frequency unstructured uncertainty, that parallel their correspondingH∞counterparts. This work extends the recent contribution of Jayasuriya and Zhao to plants with more general non‐minimum phase characteristics such as RHP poles and zeros and time

ISSN:1049-8923    

DOI:10.1002/rnc.4590040105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper addresses the existence of loop gain‐phase shaping (LGPS) solutions for the design of robust digital control systems for SISO, minimum‐phase, continuous‐time processes with parametric uncertainty. We develop the frequency response properties of LGPS for discrete‐time systems using the Δ‐transform, a transform method that applies to both continuous‐time and discrete‐time systems. A theorem is presented which demonstrates that for reasonable specifications there always exists a sampling period such that the robust digital control problem has a solution. Finally, we offer a procedure for estimating the maximum feasible sampling period for LGPS solutions to robust digital co

ISSN:1049-8923    

DOI:10.1002/rnc.4590040106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper introduces some recently developed frequency‐domain design techniques that are effective in the design of control systems that are required to be robust under parametric uncertainty. We have extended the well‐known classical control tools (i.e., Nyquist plot, Bode plot, and Nichols chart) developed for a fixed plant to the domain offamiliesof plants where the uncertain parameter varies in intervals. Using this new family of plots, classical control design techniques can be used to design robust control systems. The technique is illustrated by examp

ISSN:1049-8923    

DOI:10.1002/rnc.4590040107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper considers the case in which a linear time‐invariant (LTI) but uncertain plant suffers from nonlinearities y=n(x) which can be expressed as y=Kn+η(x), |η(x)|≤M, withK, a possibly uncertain scalar. This covers a large and very important class of nonlinearities encountered in practice such as friction, backlash, dead zone and quantization.Quantitative design techniques are presented for this class for the satisfaction of specifications. Special attention is paid to the avoidance of limit cycles using describing function theory, although the design method is also amenable of application using other stability criteria such as the circle criteria. Numerical examples are developed illustrating the design proc

ISSN:1049-8923    

DOI:10.1002/rnc.4590040108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractTwo different control systems were developed using quantitative feedback theory for weld quality improvement. The first application to be discussed was designed for the resistancepinchwelding process and uses electrode displacement and force as feedback parameters. A correlation between weld quality and electrode displacement is established for constant electrode force. The system is capable of producing repeatable welds of consistent quality, with wide variations in weld parameters. This is the first time feedback control has been successfully applied to pinch welding. The second example presented in this paper was developed for penetration control of thegas‐tungsten‐arcwelding process. The feedback signal is obtained by measuring the amount of light emitted from the back side of the weld. Welds of constant penetration have been demonstrated in tests with travel speeds varying from 1.5 to 6 inches per minute and with 200 per cent changes in part thickn

ISSN:1049-8923    

DOI:10.1002/rnc.4590040109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractControl law design for rotorcraft fly‐by‐wire systems normally attempts to decouple the angular responses using fixed‐gain crossfeeds. This approach can lead to poor decoupling over the frequency range of pilot inputs and increase the load on the feedback loops. In order to improve the decoupling performance, dynamic crossfeeds should be adopted. Moreover, because of the large changes that occur in the aircraft dynamics due to small changes about the nominal design condition, especially for near‐hovering flight, the crossfeed design must be ‘robust’. A new low‐order matching method is presented here to design robust crossfeed compensators for multi‐input, multi‐output (MIMO) systems. The technique minimizes cross‐coupling given an anticipated set of parameter variations for the range of flight conditions of concern. Results are presented in this paper of an analysis of the pitch/roll coupling of the UH‐60 Black Hawk helicopter in near‐hovering flight. A robust crossfeed is designed that shows significant improvement in decoupling perfomance and robustness over the fixed‐gain or single point dynamic compensators. The design method and results are presented in an easily used graphical format that lends significant physical insight to the design procedure. This plant precompensation technique is an appropriate preliminary step to the design of robust feedback co

ISSN:1049-8923    

DOI:10.1002/rnc.4590040110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA new decentralized robust control design framework, model reference quantitative feedback design (MRQFD), is developed for the design of the MIMO parametric uncertain control systems. An internal model reference loop is proposed to obtain the achievement of generalized diagonal dominance (GDD) and the reduction of uncertainty in the resultant compensated internal loop system. Based on nonnegative matrix theory, a useful design guide is derived to achieve the GDD condition for the internal model reference loop. Then a sensitivity‐based quantitative feedback design (QFD) method is developed and used to solve the resulting series of single‐loop QFD problems. The MIMO quantitative specifications are guaranteed to be satisfied by the proposed design framework for largely uncertain systems. A successful application to the design of a robust multivariable controller for the Allison PD‐514 aircraft turbine engine is presented to demonstrate the effectiveness of the methodology developed

ISSN:1049-8923    

DOI:10.1002/rnc.4590040111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY