Gray-Box Modeling of a Pneumatic Servo-Valve

This paper presents the evaluation as well as the combined analytical andexperimental identification (gray box identification) of a servo-valve torque motor as thedirectional valve applied in a pneumatic actuator. Based on analytical modelling, a simplelinear parametric model with transfer function and block diagram is developed. Next, thestatic and dynamic characteristics of the torque motor are obtained from experimentalobservations. The characteristics confirm the desired linear behaviour of the torque motor.Hence, linearized coefficients from a best curve fitting of static characteristics can bederived. Classical methods of identification are applied on the frequency and stepresponses obtained from a set of tests on the torque motor. Obtained tests results based onparsimony principle and model order of analytical investigations are then implemented toderive the best identified transfer function to describe the performance of the servo-valvetorque motor. Design parameters are estimated with the comparison of the experimentaland analytical models. These parameters can be implemented with acceptable accuracy forservo control studies of pneumatic actuators.