Holding the center position (less accurate)

If you simply want to stop the air cylinder in an intermediate position (not necessarily extremely accurate) you can use the valves below.

 

The 5/3-way valve

This valve has three positions. Extending, pulling and the middle position (resting position). You can choose the electrically controlled, pneumatic or manual valve.

Closed middle position:

• The air ports to the cylinder are closed. As a result, the air is trapped in the cylinder chamber(s) and the piston holds its center position. The disadvantage of this valve is that leakage can occur in the valve under heavy load. The cylinder can slowly shift because there is a difference in the surface area of the piston in the input and output stroke. With even load, the piston will always run through or back into the output side.

Open middle position:

• Both cylinder chambers are under pressure. This gives stability, but because there is a difference in surface area between the rod side and the piston side, the piston can still move if an external force is applied to it.

Use of Check Valves

A better way to keep the cylinder in position when there is an external force on it is by using air-operated check valves or stop valves.

When you turn off the air supply, the valves are closed. The air in the cylinder is completely blocked in this way. This ensures a safer and firmer stop than if you only work with the 5/3-way valve. This is an ideal solution for holding the cylinder in any place, for example when you want to clamp something with the air cylinder.

 

Precise positioning

If you want to stop and hold the cylinder accurately at a specific position, you need a more advanced technique.

Proportional control

The best way to get the air cylinder to be positioned accurately is with a proportional steering. Which means that you need a proportional valve and a position sensor on the cylinder. The valve regulates the airflow and pressure gradually by means of an electronic signal. The position sensor measures the actual position of the piston and sends it back to a controller. The regulator then adjusts the pressure and airflow through the valve until the desired position for the air cylinder is reached.

Cylinders with multiple fixed positions

With a tandem cylinder or several linked cylinders, you can stop the air cylinder at several fixed positions. The chambers are selectively aerated and therefore several intermediate positions are possible.

In short, although a standard air cylinder prefers the end positions, with the right components you can stop and hold it in any position, with the required accuracy determining the technical solution.

 

 

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