Transient characteristics of the cylinder, speed characteristics of the cylinder

For the transient characteristics of the cylinder, we can take the single-rod double-acting unbuffered cylinder as an example to analyze the motion state of the cylinder, as shown in the figure below. The solenoid valve reverses direction, the air source inflates the rodless cavity of the cylinder through port A, and the pressure P1 rises. The gas in the rod cavity is exhausted through port B and the exhaust port of the reversing valve, and the pressure P2 drops. When the pressure difference between the rodless side and the rod side of the piston reaches above the minimum operating pressure of the cylinder, the piston starts to move. Once the piston is started, the friction in the piston and other places suddenly drops from static friction to kinetic friction, and the piston shakes slightly. After the piston is started, the rodless cavity is in an inflated state with an increased volume, and the rodded cavity is in an exhaust state with a reduced volume. With factors such as the size of the external load and the impedance of the charging and exhausting circuits, the changing rules of the pressures P1 and P2 on both sides of the piston are also different, which leads to the changing rules of the piston's movement speed and the effective output force of the cylinder. The figure below is a schematic diagram of the transient characteristic curve of the cylinder. The time from when the solenoid valve is energized to when the piston starts to move is the delay time. The time from when the solenoid valve is energized to when the piston reaches the end of its stroke is the arrival time. As can be seen from the above figure, during the entire movement of the piston, the pressures P1 and P2 in the chambers on both sides of the piston and the movement speed U of the piston are changing. This is because although the rod cavity is exhausted, its volume is decreasing, and the downward trend of p2 is slowing down. If the exhaust is not smooth, p2 may also rise. Although the rodless cavity is inflated, its volume is increasing. If the air supply is insufficient or the piston moves too fast, the p1 page may decrease. Since the pressure difference in the chambers on both sides of the piston is changing, it affects the effective output force and the change of the piston movement speed. If the external load force and friction force are unstable, the changes in the pressure of the two chambers of the cylinder and the piston movement speed will be more complicated. Speed ​​characteristics of the cylinder The speed of the piston changes during the entire movement. The maximum value of the speed is called the maximum speed, recorded as um. For non-air-cushioned cylinders, the maximum speed is usually at the end of the stroke. For pneumatic buffer cylinders, the maximum speed is usually at the stroke position before entering the buffer. When the cylinder has no external load force, and it is assumed that the exhaust side of the cylinder is exhausting at the speed of sound, and the air source pressure is not too low, the calculated cylinder speed is called the theoretical reference speed. u0=1920*S/A where, u0 is the theoretical reference speed, S is the synthetic effective cross-sectional area of ​​the exhaust circuit, and A is the effective cross-sectional area of ​​the exhaust side piston. The theoretical speed is very close to the maximum speed of the cylinder without load, so the maximum speed of the cylinder without load is equal to u0. .As the load increases, the maximum speed um of the cylinder will decrease. The average speed v of the cylinder is the movement stroke L of the cylinder divided by the action time of the cylinder (usually calculated as the arrival time) t. Usually the speed of the cylinder refers to the average speed. In rough calculation, the maximum speed of the cylinder is generally 1.4 times the average speed. The speed range of standard cylinders is mostly 50~500mm/s. When the speed is less than 50mm/s, due to the increased influence of cylinder friction resistance and the compressibility of the gas, the piston cannot be guaranteed to move smoothly, and there will be a phenomenon of walking and stopping, which is called "crawling". When the speed is higher than 500mm/s, the friction and heat generation of the cylinder seal ring intensifies, accelerating the wear of the seal, causing air leakage, shortening the service life, and increasing the impact force at the end of the stroke, affecting the mechanical life. If you want the cylinder to work at low speed, you should use a gas-liquid damping cylinder, or use a gas-liquid combined cylinder for low-speed control through a gas-liquid converter. In order to work at higher speeds, it is necessary to lengthen the length of the cylinder barrel, improve the machining accuracy of the cylinder barrel, improve the material of the sealing ring to reduce frictional resistance, and improve the buffering performance. The above is an introduction to the transient characteristics of the cylinder and the speed characteristics of the cylinder. If you want to know more related information, please log in to Sunway Pneumatic www.diancifa.cc.