Candidate: Agnelo Dênis Vieira
Program: CPGEM / UFSC
Date: August, 1998
Advisor: Arno Bollmann
Abstract: The present work refers to the nonlinear modeling of a pneumatic position servo system constituted of a electropneumatic servovalve and a linear actuator without ram. For obtaining the mathematical model, the physical phenomenon´s that happen in the flow of fluids through orifices must be represented and applied the principle of the mass conservation and the 2nd Law of Newton in the actuator. Furthermore, is presented and discussed the state of the art in the modeling of friction forces in pneumatic actuators. One of the main contributions of this work says respect to the consideration of the effects of the leaks in the electropneumatic servovalve in the modeling of mass flow through orifices. The concept of “effective relative opening” of the variation of the control orifice superposed to the contraction and irreversibility effects of the mass flow through orifices. The consideration of the effects of the leaks is accomplished by considering two experimental parameters: the pressure / signal relationship of the servovalve and its effective relative opening. As a result of this modeling it is possible to represent the steady-state pressures in the actuators chambers in closed loop positioning servo systems, which determine the precision of positioning of the servo system. In the mass flow modeling it is considered the flow capacity of the servovalve, which is the parameter available in the manufacture´s catalogs. It is accomplished a comparison among the normalized coefficients usually employed for this description. As methodology of validation of the proposed mathematical model, the comparison of experimental data is accomplished with the results obtained from the numeric simulation of processes that reproduce the experimental conditions. Due to of the excellent reproduction of the behavior of the several variables analyzed during the validation of the mathematical model, great possibility of application of the model is verified in the project of pneumatic position servo systems, as well as for didactic purposes.
VIEIRA, A. D. Análise Teórico-Experimental de Servoposicionadores Lineares Pneumáticos. 1998. Dissertação (Mestrado em Engenharia Mecânica). Universidade Federal de Santa Catarina, Florianópolis.