US 5,132,897 AGranted

Method and apparatus for improving the accuracy of closed loop controlled systems

AssigneeCarl Schenck AG

InventorBernd Allenberg

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Abstract

The precision of a closed loop control system, for example of a loss-in-weight feeder, having a controlled operating section and a closed loop controlling section, is improved by adjusting the closed loop controlling section with regard to at least two stochastic precision disturbing signals. One such signal may represent disturbances that affect a sensor for ascertaining the actual weight of the scale. The other value may represent estimated bulk material density variations or disturbances. A model generator (7) provides spectra representing these disturbing values. A noise parameter estimator (17) selects those spectra most closely resembling the spectra of the disturbing values for producing an adjusting signal that is used to adapt the closed loop controlling section (5) to an optimal control. The closed loop controlling section (5) has connected thereto an evaluating circuit (14) including the model generator (7) for performing the correction or adjustment.

Claims8

Dependent claims

A method for improving the control precision of a closed loop controlled system including a controlled operating section and a controlling section, comprising the following steps:

(a) sampling by a sensor an actual operational value of said controlled operating section and estimating another actual value from said sampled actual value;
(b) providing a set point signal and producing a closed loop control signal from said estimated actual operation signal and from said set point signal for controlling said closed loop controlled system,
(c) establishing mathematic models of at least two stochastic disturbance model spectra of said closed loop control system,
(d) producing control modifying signals for influencing said controlling section, said producing step comprising,
(e) forming, for a fixed length of time, from said actual operational value an estimated actual operation signal,
(f) forming from said estimated actual operation signal a power density spectrum,
(g) determining from said power density spectrum a stochastic disturbance spectrum based on first proportions of stochastic disturbances by disregarding second proportions of monochromatic disturbances,
(h) comparing said stochastic disturbance spectrum with said stochastic disturbance model spectra and selecting that model spectrum which fits said stochastic disturbance spectrum most closely,
(i) dividing said selected model spectrum into first parts corresponding to disturbances of said sensor and into second parts corresponding to variations of the controlled actual value, and
(j) using said first and second parts of said selected model spectrum as said control modification for said influencing of said controlling section to increase the accuracy of said closed loop controlled system.

7 more elements

An apparatus for improving the control precision of a closed loop control system, comprising a controlled operating section, a controller section (5) and signal evaluating circuit means (14) for minimizing at least two stochastic precision disturbing values by way of a model calculation, said signal evaluating circuit means (14) comprising a spectral analyzing circuit (15) for scanning or sampling, for a fixed length of time, an estimated signal representing the actual operational value of said controlled operating section to form a first power density spectrum, a spectrum identifying circuit (6) operatively connected to an output of said signal analyzing circuit for identifying frequencies where said first power density spectrum exceeds a fixed threshold power density value, a correction circuit (16) connected to said output of said spectral analyzing circuit (15) and to an output of said spectrum identifying circuit (6) for forming a second power density spectrum of stochastic disturbances (.phi..sub.2), a noise parameter estimating circuit (17) connected to an output of said correction circuit (16), a model generator (7) connected with an output to said noise parameter estimating circuit (17) for providing model spectra to said noise parameter estimating circuit (17) for selecting an approximation model spectrum which most closely approximates said second power density spectrum of stochastic disturbances, a closed loop controller adjustment circuit (18) having one input connected to said noise parameter estimating circuit (17) and a further input connected to an output of said model generator (7) for selecting from said approximation model spectrum a spectrum representing one of said two stochastic precision disturbing values and for selecting from model spectra supplied by said model computer the other of said two stochastic precision disturbing values, and a connector circuit (8) connecting an output of said controller adjustment circuit (18) to said closed loop controller section (5) for adjusting said closed loop controller section (5) to an optimal control of said controlled operating section.

Dependencies are inferred from the claim text.