Dead-zone Effect Research Articles

Design of new adaptive fuzzy logic controller for nonlinear plants with unknown or time-varying dead zones

An adaptive fuzzy logic controller (FLC) is designed for plants with unknown and/or time-varying dead zones. The steady-state control resolutions with perturbing action, which are different from the ones in the transient states, are used to cancel out the unknown and/or time-varying dead-zone effects. Automatically adjusted control resolutions play a key role as a fuzzy dead-zone inverse. The control resolutions of the control input variables are dependent on the scaling gains of the variables. Therefore, we can develop the fuzzy dead-zone inverse by reperturbing and adjusting the scaling gains adequately in the steady-states. The developed fuzzy logic controllers that are applied to the plants with unknown dead zones ensure their effectiveness even though the dead-zone characteristics are time varying.

A nonlinear universal servomechanism

A servomechanism problem of controlling a scalar output variable to /spl lambda/-track any reference signal from some prescribed function space R, whilst maintaining internal states bounded, is addressed for a class S of uncertain nonlinearly-perturbed, single-input, single-output, minimum-phase, relative-degree-one, linear systems with nonlinear actuator characteristics (encompassing, for example, hysteresis and dead-zone effects). The actuator characteristics are required only to be contained in the graph of a suitably regular set-valued map. The terminology "/spl lambda/-tracking" is used in the following sense: for arbitrary prescribed /spl lambda/>0, an (adaptive) feedback strategy is sought which, for every reference signal of class R and every system (unknown to the controller) of class S, ensures that the tracking error is asymptotic to the interval /spl lsqb//spl minus//spl lambda/,/spl lambda//spl rsqb//spl sub/R. The instantaneous values of the reference signal and scaler output only are available for feedback. Adopting the space W/sup 1,/spl infin//(R) as the set R of admissible reference signals and under fairly weak assumptions on the nature of the system nonlinearities, one such (R, S)-universal adaptive feedback solution to this servomechanism problem is constructed. The feedback is continuous and its construction does not invoke an internal model principle.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

General treatment of spatial light modulator dead-zone effects on optical correlation II Mathematical analysis

We present a general analytical treatment of optical correlation in correlators that use pixellated spatial light modulators with transmissive (or reflective) dead zones in both the input and filter planes. The active areas of the pixels modulate the light intensity while the dead zones transmit (or reflect) all of the light. Our model can predict the changes in the correlation peak and the signal-to-noise ratio with changes in dead zones, calculated in Part I [Appl. Opt. 32, 6527(1993)] from computer simulations. This model is also a general one: It applies to correlators in which one spatial light modulator contaions only opaque dead zones while the other contains only transmissive dead zones; it also applies to the case in which any one spatial light modulator contains both opaque and transmissive dead zones.

General treatment of spatial light modulator dead-zone effects on optical correlation I Computer simulations

In Part I we present an approximate mathematical analysis and exact computer simulations for optical correlation in correlators having pixellated spatial light modulators with transmissive (or reflective) dead zones in both the input and filter planes. We show that the correlation amplitude consists of four terms: a true correlation plus three different types of noise terms originating from the transmissive dead zones in both spatial light modulators; we describe the role that each of these terms plays in the correlation process. We calculate peak intensity, signal-to-noise ratio, and energy throughput efficiency as a function of dead-zone area in both spatial light modulators using either phase-only or matched filters. We utilize a dc block in the filter plane for noise reduction. We also use a filter reference image smaller than the input spatial light modulator size to reduce false correlation peaks. We discuss the effects of fabricating a filter from a filter reference image whose center has been offset rom optic axis. In Part II [Appl. Opt. 32,6536 (1993)] we present a general analytical treatment of our model that can justify the simulation results of Part I. This analysis is applicable even to mixed cases of opaque and transmissive dead zones.

The effect of dead zones on longitudinal dispersion in streams

Dead zones tend to hold back the downstream travel, to increase the longitudinal spreading and to provide a long tail of low concentration for passive contaminant releases in natural streams. Here it is shown how the presence of a random distribution of dead zones can be accommodated into the method of moments by choosing an appropriate composite averaging. The individual roles of the cross-stream velocity shear, the dead-zones mean volume fraction and the dead-zones probability distribution are clearly revealed in the longitudinal shear-dispersion coefficient. The inevitable deviations from Gaussianity are examined by means of skewness and kurtosis. Simple examples are used to quantify the effects of the dead zones upon contaminant dispersion in Couette flow, pipe and plane Poiseuille flows.

Closure to “Predicting Effects of Dead Zones on Stream Mixing”

Closure to “Predicting Effects of Dead Zones on Stream Mixing”

Erratum for “Predicting Effects of Dead Zones on Stream Mixing”

Erratum for “Predicting Effects of Dead Zones on Stream Mixing”

Discussion of “Predicting Effects of Dead Zones on Stream Mixing”

Discussion of “Predicting Effects of Dead Zones on Stream Mixing”

Predicting Effects of Dead Zones on Stream Mixing

Longitudinal mixing in open-channel flow is described by two coupled partial differential equations, the solution of which, in the frequency domain, is a function of four parameters: mean residence time; Peclet number or dimensionless dispersion coefficient; fraction of stream volume which is dead zone; and mean residence time in a dead zone. The solution is given and methods of estimating the parameters from hydraulic data are described. The fraction of stream volume which is dead zone is a function of the friction factor, and the ratio of mean dead zone residence time to mean residence time in a reach is essentially a constant. The effects of errors in estimating values of the parameters are discussed and illustrated.

Experimental Study of Hydrostatic Extrusion

An experimental investigation of hydrostatic extrusion through conical dies using commercially pure lead billets was carried out with two different hydrostatic pressure systems; namely, a ram-type extrusion system (with a forced predetermined extrusion rate), and an injection pump (constant-pressure) system. Pressure characteristics, flow patterns, and the cavity, piping, and dead-zone effects were investigated. Experimental pressure results for both types of pressure systems agreed well with analytical predictions. Furthermore, dead-zone, cavity, and piping effects were found to be dependent upon the semicone angle and the amount of area reduction of the billet.

A Graphical Method for the Analysis of Piecewise Linear Control Systems, With Particular Application to Relay Controls

Abstract A graphical method is described for the analysis of piecewise linear control systems. By means of it both transient and steady oscillations can be studied. After the “characteristic curves” of a system have been computed and plotted, it is shown that the effects of dead zone, solid friction, backlash, and various lead devices are easily taken into account, without further computation. The method is illustrated by a more detailed examination of the behavior of relay controls, and a few of the charts obtained by the method are given.