Research On Modeling For Electric-pneumatic Positioning System Of Actuator

Actuator, as the final control element in automation system, is an increasingly vital component of modern industry around world. Properly selected actuator can increase efficiency, safety, profitability and ecology. Pneumatic actuator is the most popular type in use. The development of pneumatic actuator depends on advancing techniques level such as material technic, structure design, etc., more importantly, it depends on modeling the pneumatic position system of actuator. It is also important to say that the availability of a reliable analytical model forms the basis for intelligent valve positioner algorithm design, valve optimization design and control valve diagnosis. In this study, the main achievements are as follows:First of all, based on the analysis of a new type of torque motor works, this research created some important equations: (1) Magnetic circuit analysis and circuit analysis of this type of torque motor were carried out, and then the dynamic equation of the torque motor was created; (2)a flow equation was created of fixed orifice nozzles and the weight of the gas nozzle mouth based on the knowledge and the laws of aerodynamic; (3) dynamic equation of loaded nozzle-flapper mechanism was established with certain assumptions and approximations. Then, motion process of pneumatic actuator was divided into two parts during the study. Through the analysis of the working mechanism of thin-film gas chamber and the implementing agencies, combining the knowledge of thermodynamics and dynamics, Thermodynamic equation of thin-film chamber and force balance equation of actuator were built. Lastly, a test platform for measuring torque motor displacement of the movable iron piece in this research. The unknown parameters in the model were identified based on some experimental data. The comparison of simulation models and experimental data show the accuracy of this research. And the access to the unknown parameters has also been described in the paper.In this paper, for one thing, based on the study of the Electric - Pneumatic valve positioner (including torque motor, nozzle - flapper valve and pneumatic actuator) works, several equations were set up for each part of valve positioner. For another thing, thermodynamic equation of thin-film chamber and force balance equation of actuator were built according to the implementing agencies working principle. Then the unknown parameters were identified by the test plat built in the paper, and the analytical-experimental comparisons show the validity of the model.