Controlling the position of piston (programming pneumatics)

[Xavier M]

Hi all, is it possible to program the position of a pneumatic piston?

For example, if I wanted to stop a piston half way or a third of the way, how could I accomplish this? Are there any sensors which could possibly help?

I was thinking about a magnetic sensor which could read the position. Or instead of using a sensor, we could have a time factor, but I don't want to do dead reckoning by depending on time.

[nathand]

There is no way to do this reliably.  Standard pneumatics aren't designed to do what you're trying to do.  You would somehow need to balance the pressure on each side of the piston at exactly the point where you want it to stop, which would be very difficult to do reproducibly.

[A..P]

I disagree with Nathan. I've used the magnet collars that fit over the pneumatic cylinder to great success. When the piston gets to the magnet open the solenoid so that both sides are closed. In practice you will drift by a small degree depending on your bore size(maybe a 1/4" on a 1" bore). This works great if you have a couple discreet states you want your piston to go to. The drift is quite consistent, so if you are coming from the same direction every time you can simply move the collar back the drift distance.

Good luck!