How to achieve accurate positioning of the cylinder? Eight position control methods to tell you

The cylinder can usually only be held in two positions: extended and retracted. If the cylinder is required to stop at an intermediate position during movement, the pneumatic system is required to have a position control function. Since the gas is compressible and the pneumatic system cannot guarantee no air leakage for a long time, it is difficult to obtain high positioning accuracy by only using a three-position five-way solenoid valve to control the position of the cylinder. Where higher positioning accuracy is required, methods such as mechanical auxiliary positioning, multi-position cylinders, brake cylinders or gas-liquid conversion units can be used. So today we will share with you the relevant basic knowledge for your reference.





1. Positioning method using external stops
In order to position the cylinder in the middle of the stroke, the most reliable method is to set a mechanical stop at the positioning point. This method requires high positioning accuracy and is difficult to adjust. The setting of the stopper must consider both strong stiffness and buffering ability to absorb shock.

2. Position control using multi-position cylinders
A single-rod double-stroke cylinder is used, which is composed of two single-rod double-acting cylinders with unequal strokes connected in series. When the valve positioning accuracy is high, methods such as mechanical auxiliary positioning, multi-position cylinders, brake cylinders or gas-liquid conversion units can be used.







3. Use the position control of the locking cylinder
The locking cylinder can be used to achieve intermediate positioning control. After the cylinder is locked, the forces on both sides of the piston should be in a balanced state to prevent the piston rod from rapidly extending due to the unbalanced force on the piston when unlocking, so as not to injure people or equipment. , so there is a pressure reducing valve with a one-way valve on the rodless side of the cylinder.

4. Use magnetic switches (or travel switches), machine-controlled valves, etc. to achieve position control
For a cylinder with a magnetic switch, if the distance between the two magnetic switches a0 and a1 on the cylinder is changed, the detection stroke of the piston will change. The mechanical control valve controls the continuous reciprocating circuit of the cylinder. If the distance between the two mechanical control valves changes, the telescopic stroke of the cylinder will also change.







5. Position control using gas-liquid conversion unit
In order to obtain higher positioning accuracy, the gas pressure can be used to push the liquid actuator (such as a gas-liquid combined cylinder and a gas-liquid combined swing cylinder) through the gas-liquid conversion unit. Of course, the speed of movement should not be high.

6. Use pneumatic position sensors to achieve position control
The use of pneumatic position sensors can ensure high positioning accuracy. In order to reduce the air consumption of the pneumatic sensor, a pressure reducing valve and a throttle valve can be installed.

7. Position control using pressure signals
When the cylinder drops to the point where the vacuum suction cup contacts the heavy object, once the vacuum in the vacuum suction cup reaches the set pressure of the vacuum pressure switch, the vacuum pressure switch acts, commanding the two-position five-way valve to reset, and the suction cup sucks the heavy object and is lifted by the cylinder. . Use a vacuum generator to maintain vacuum during lifting. When the heavy object is moved to the designated position, the solenoid valve is powered off, and the heavy object is separated from the suction cup.

8. Use the locator to locate
The cylinder is equipped with a positioner, which enables precise and stable position control of the cylinder. The cylinder is positioned proportional to the signal pressure. An electric-pneumatic positioner can also be used to control the opening of the valve and position the cylinder and swing cylinder. The input signal is current, and the current signal is proportionally converted into a pressure signal to control the position of the actuator.







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