possible to have pneumatic cylinder as a replacement for spring?

[picksbendy]

Hi guys,

I'm having a machine that is sort of like a cam following mechanism, which is more of copying the circumference of a mold, and spring is used to control the extending and retracting action.
The fact is i'm really not familiar with pneumatic components, i tried to use an air regulator unit connected to port A and leaving port B of the actuator expose to atmospheric pressure. then in between port A and air regulator unit, i branched out to a pressure relief valve. Problem is the relief valve is not relieving any air when retracting and hence causing pressure to shoot high everytime the actuator retracted. I'm thinking i might need a gate to control the flow from regulator and to the relief valve so that when extending the relief valve opening is closed and regulator opening is opened and vice versa.
any suggestion to the parts or combination to achieve that? or it is not possible at all??? been flipping books and surfing net, still have no clue at all.
help desperately needed.
thanks,
best regards,
Picks

 

[tygerdawg]

Seems like it'd be easier with a spring. However...

The back pressure seen by the regulator depends on how much stroke the actuator undergoes during motion. May be significant, may not. I think the relief valve should be in parallel to the regulated supply, not in series. During retraction, pressure builds to a point then is relieved. Presure is applied on extension by the constant regulated supply.

You'd have to make sure all of your tubing is properly sized so that flow is not limited and motion is not optimal. Control speed of reaction & extension with flow controls on entry & exit ports all the way around.

Easier with a...ah, never mind.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[MikeHalloran]

OR, you could use a non-relieving regulator and put a volume chamber between it and the cylinder. The bigger the chamber, the lower the effective spring rate of the cylinder.
DO NOT use air for pressures over ~200 psi.



Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

Do as Mike suggests. You do not want to be constantly consuming air when you don't have to. The other problem with air cylinders for your application is stiction of the piston seal. Friction will add to the force during retraction and subtract during extension. Rolling diaphragm cylinders perform better in this regard.

Sometimes just using a weight can be best solution for obtaining constant force.