Transient characteristics of the cylinder, velocity characteristics of the cylinder
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 following figure.
The solenoid valve reverses the direction, and the air source is filled into the rodless cavity of the cylinder through port A, causing the pressure P1 to rise. The gas in the rod cavity is discharged through the exhaust port of the reversing valve via port B, and the pressure P2 drops. When the pressure difference between the rodless side and the robed side of the piston reaches above the minimum operating pressure of the cylinder, the piston begins to move. Once the piston starts, the frictional force at the piston and other parts suddenly drops from static friction to dynamic friction, causing the piston to shake slightly. After the piston starts, the rodless chamber is in an inflated state with an increased volume, while the rod-bearing chamber is in an exhaust state with a decreased volume. With the differences in factors such as the size of the external load and the impedance of the charging and exhaust circuits, the variation patterns of the pressures P1 and P2 on both sides of the piston are also different, which leads to different variation patterns of the piston's movement speed and the effective output force of the cylinder. The following figure is a schematic diagram of the transient characteristic curve of the cylinder. The time from the energization of the solenoid valve to the start of the piston's movement is the delay time. The time from when the solenoid valve is energized to when the piston reaches the end of the stroke is the arrival time.
As can be seen from the above figure, throughout the entire movement of the piston, the pressures P1 and P2 in the chambers on both sides of the piston as well as the movement speed U of the piston are all changing. This is because although the rod cavity has exhaust, its volume is decreasing, so the downward trend of p2 slows down. If the exhaust is not smooth, p2 may still 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 drop. Due to the changing pressure difference in the chambers on both sides of the piston, it affects the effective output force and the variation of the piston's movement speed. If the external load force and friction force are unstable, the changes in the pressure between the two chambers of the cylinder and the movement speed of the piston will be more complex.
The speed characteristics of the cylinder
The speed of the piston varies throughout its entire movement. The maximum value of speed is called the maximum speed and is denoted as um. For non-gas buffer cylinders, the maximum speed is usually at the end of the stroke. The maximum speed of the gas buffer cylinder 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 sound velocity exhaust and the air source pressure is not too low, the calculated cylinder speed is called the theoretical reference speed.
u0=1920*S/A
Among them, u0 is the theoretical reference speed
S represents the combined effective cross-sectional area of the exhaust circuit
A represents the effective cross-sectional area of the piston on the exhaust side.
The theoretical speed is very close to the maximum speed of the cylinder when there is no load, so the maximum speed of the cylinder when there is no load is equal to u0. As the load increases, the maximum speed um of the cylinder will decrease.
The average speed v of a cylinder is the stroke L of the cylinder divided by the action time t of the cylinder (usually calculated as the arrival time). The speed of a cylinder usually referred to is the average speed. In rough calculations, the maximum speed of the cylinder is generally taken as 1.4 times the average speed.
The operating speed range of standard cylinders is mostly 50 to 500mm/s. When the speed is less than 50mm/s, due to the increased frictional resistance of the cylinder and the compressibility of the gas, the smooth movement of the piston cannot be guaranteed, and the phenomenon of intermittent movement will occur, which is called "crawling". When the speed exceeds 500mm/s, the frictional heat generation of the cylinder sealing ring intensifies, accelerating the wear of the sealing parts, causing air leakage, shortening the service life, and also increasing the impact force at the end of the stroke, affecting the mechanical life. To ensure that the cylinder operates at low speeds, it is advisable to use a pneumatic-hydraulic damping cylinder or, through a pneumatic-hydraulic converter, utilize a pneumatic-hydraulic combined cylinder for low-speed control. To operate at higher speeds, it is necessary to increase the length of the cylinder barrel, improve the processing accuracy of the cylinder barrel, enhance the material of the sealing ring to reduce frictional resistance, and improve the buffering performance, etc.
Above are Transient characteristics of the cylinder, the velocity characteristics of the cylinder content, to learn more related information are available at https://www.joosungauto.com/.
