Analytical model of the flow stage of a pneumatic servo-distributor for simulation and nonlinear control

A typical electropneumatic control system consists of one or two servo-distributors and a simple or double effect jack. The nonlinearities of such systems are chiefly due to the mass flow rate of the fluid through the restrictions which vary with the control input. The modelling objective for simulation is to enable an accurate representation of the physical system, generally in an analytical form, to be obtained, this form enables easier analysis and control laws synthesis. In this paper we have studied the Servotronic servo-distributor (Asco-Joucomatic Company). An approximation of the flow stage characteristic of this servo-distributor by several polynomial functions is described. We have developed analytical models for both simulation and control purposes. The choice of the polynomial functions and their degrees are discussed. Comparative results are presented and discussed.