Abstract
Many pneumatic cylinders are utilized for automation and usually driven by a meter-out circuit, because the cylinder velocity can be determined by adjusting the effective area of the exhaust restriction and the motion time is the same even if the load force is changed. That is, speed control is realized by using only a restriction. This characteristic is verified by numerical analysis of cylinder physical equations. However, the principle of speed control has been unknown despite of the basis on cylinder selection. Although, one of the researchers explained constant motion time by feedback qualitatively, feedback mechanism is not explained till now.
The purpose of this study is to clarify the speed control mechanism through the block diagram and the transfer function of the cylinder system, which are determined from linearizing fundamental equations. As a result, the following are found: 1) The air compressibility makes the feedback loop. The terminal velocity is unique since the transfer function from the load force to the cylinder velocity is one type. 2) Changing the load force, each change of air mass swept by the piston and exhausting flow rate is just canceled. This is the cause for minus one type transfer function. 3) The relation between initial (when motion starts) and equilibrium condition is fixed for any load force change. Therefore, not only terminal velocity but transient response is the same and moving time is unchanged. By this study, the principle of speed control is proved theoretically.
