<p>In this paper it will be presented 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. The analysis is based on a validated dynamic model of a standard actuation system composed of a directional valve and a linear actuator. The simulation data 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 emptying time is mainly caused by the backpressure chamber that needs to be unfilled until the driving chamber is capable to overcome the static friction, the load force, and the backpressure force. The transient-state time is caused due to the acceleration of the piston rod, which is the result of the reduction of the friction force after the static friction is overcame and represents the biggest portion of the total displacement time. The steady-state time occurs at the end of the piston displacement as a consequence of the reduction of the available pneumatic force caused by the increase of the viscous friction, resulting in a small variation in the chambers pressures and a constant speed displacement. The results also indicate that there is a close correlation between the displacement time and the relative size of the piston area, where undersized systems present a long emptying and steady-state time, whereas oversized actuators present mostly transient-state time. On the other side, when the piston is correctly sized the predominant times are the emptying and the transient-state time, while the steady-state time might be negligible. Since the emptying process of the backpressure chamber occurs predominantly with choked mass flow rate and the chamber volume is constant, an analytical equation to estimate the emptying time has been developed. Moreover, during the transient-state time, the velocity profile might be modeled as a first-order system, therefore, the acceleration time might be estimated as well. The proposed equations were evaluated along with simulation and experimental results, demonstrating their validity. 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, therefore, the main result from this research is a set of equations, developed based on the characteristic dynamic behavior of pneumatic actuation system, that can be used to size the directional valve using design parameters such as displacement time, piston volume, load force, and supply pressure.</p>

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

Paper Proceedings: https://asmedigitalcollection.asme.org/FPST/FPMC2021/volume/85239

2021 ASME/BATH Symposium on Fluid Power and Motion Control (FPMC2021)

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