A Novel in Field Method for Determining the Flow Rate Characteristics of Pneumatic Servo Axes

Several strategies, in order to improve an actuator's control and to increase the bandwidth, consider the relationship between the valve's driving signal and the air flow rate. Such an approach to the control strategy takes advantage of the evaluation of the valve's characteristic parameter, known as sonic conductance. The sonic conductance can be measured following the procedure stated by the standard ISO 6358. Nevertheless, the measurement carried out according to this standard is very expensive in terms of time and air consumption. In this paper, an alternative method to evaluate the sonic conductance is presented. The method is based on a new practical approach: the sonic conductance is evaluated leaving the valve mounted on the actuator and using only the piston's position transducer. The steady state piston's motion allows us to determine the sonic conductance. The new approach allows us to get the conductance in a very short time, without the need to use a proper test bench and pressure transducers. Moreover, performing the measurements directly on the pneumatic axis allows us to characterize not only the valve but the duct connecting the valve to the actuator's chamber too.