Sizing Directional Pneumatic Valves Based on the Characteristic Dynamic Behavior of Linear Actuators

In this paper, a novel approach to size directional pneumatic valves based on the analysis of the characteristic behavior of pneumatic actuators applied for pick and place tasks is presented. The study evidences the existence of three characteristic times in the displacement of a standard pneumatic actuation system, which are the emptying time, the transient-state time, and the steady-state time. The results also indicate that there is a close correlation between the velocity profile and the relative size of the piston area, where the steady-state time might be negligible when the piston is correctly sized. The emptying time, characterized by the depressurization of the counterpressure chamber, occurs predominantly with choked mass flow rate and constant volume. In this way, an analytical equation to estimate the emptying time has been determined. Moreover, during the transient-state time, the velocity profile is similar to the characteristic behavior of a first order system, therefore, the transient-state time is estimated by the time constant of the system, which was obtained by a linear first order model developed using the fundamental equations that govern the system behavior. The total displacement time, which is a design requirement to size directional valves, can be expressed as the sum of the emptying and transient-state time. Consequently, a set of equations are proposed to size the directional valve using design parameters such as displacement time, piston volume, load force, and supply pressure. The proposed equations were evaluated along with simulation and experimental results, demonstrating their validity and accuracy.