Robust identification of pneumatic servo actuators in the real situations

Abstract

Intensive research in the field of mathematical modelling of the pneumatic cylinder has shown that its mathematical model is nonlinear and that a lot of important details cannot be included in the model. Selection of the model and the identification method have been conditioned by the following facts:(a) The nonlinear model of the system can be approximated by a linear model with time-variant parameters. (b) There is the influence of the combination of heat coefficient, unknown discharge coefficient and change of temperature on the pneumatic cylinder model. Therefore it is assumed that the parameters of the pneumatic cylinder are random (stochastic parameters). (c) In practical conditions, observations have a non-Gaussian distribution.Due to the abovementioned reasons, it is assumed that the pneumatic cylinder model is a linear stochastic model with variable parameters. The Masreliez-Martin filter (robust Kalman filter) was used for identification of parameters of the model. For the purpose of increasing the practical value of the filter, the following two heuristic modifications were performed:(1) It was adopted that T (k) = 1 holds for the scalar transformation of residuals. (2) Fisher information was approximated by a derivative of the Huber's function.The proposed modifications were confirmed through intensive simulations. In order to provide persistent excitation, V. Filipovic · N. Nedic · V. Stojanovic ( ) the autocovariance function "1/f " of the signal was used.The behaviour of the new approach to identification of the pneumatic cylinder is illustrated by simulations. Robuste Identifikation von pneumatischen Servo-Aktuatoren in der realen SituationenZusammenfassung Intensive Forschung auf dem Gebiet der mathematischen Modellierung des pneumatischen Zylinders hat gezeigt, dass sein mathematisches Modell nichtlinear ist und dass viele wichtige Details nicht in das Modell einbezogen werden können. Die Auswahl des Modells und die Art der Identifikation werden durch folgende Tatsachen bedingt: (a) Das nichtlineare Modell des Systems kann durch ein lineares Modell mit zeitvarianten Parametern angenähert werden. (b) Es besteht ein Einfluss der Kombination von Wärme-durchgangs-Koeffizient, unbekanntem Durchflusskoeffizienten und Änderungen der Temperatur auf das pneumatischen Zylinder-Modell. Es wird daher angenommen, dass die Parameter des pneumatischen Zylinders zufälligen Charakters sind. (c) Unter praktischen Bedingungen haben die Beobachtungsergebnisse eine nicht-Gaußsche Verteilung. Aufgrund der vorgenannten Gründe wird davon ausgegangen, dass das Pneumatikzylinder Modell ein lineares, stochastisches Modell mit variablen Parametern sein muss. Der Masreliez-Martin-Filter (robust Kalman-Filter) wurde für die Identifizierung von Parametern des Modells verwendet. Zur Erhöhung des praktischen Werts des Filters, wurden die beiden folgenden heuristischen Modifikationen durchgeführt: 184 Forsch Ingenieurwes (2011) 75:183-196 (1) Es wird angenommen, dass T (k) = 1 für das skalare Transformation der Residuen hält. (2...

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