Arduino Forum

Forum 2005-2010 (read only) => Hardware => Interfacing => Topic started by: aweida on Nov 11, 2010, 11:22 pm

Title: Pneumatic cylinder
Post by: aweida on Nov 11, 2010, 11:22 pm
Hello all, I am interested in interfacing my arduino mega with a small Pneumatic cylinder. I have yet to find much information on the subject(is this possible?). I am trying to emulate a push/pull motion for a side project. I wanted to see if anyone had any information/tutorials. It would be great if someone could point me in the right direction. Thanks much!
Title: Re: Pneumatic cylinder
Post by: gardner on Nov 12, 2010, 12:02 am
You will need a source of air pressure and some solenoid valves.  I think a good bet for small low power solenoid valves would be to scavenge some from battery-operated sprinkler timers.

Solenoid valves will have similar interface electronics requirements as relays, and you will find a mountain of information regarding hooking a relay to an Arduino courtesy of Google.
Title: Re: Pneumatic cylinder
Post by: graynomad on Nov 12, 2010, 12:28 am
Also with phneumatics it's difficult to get much control, it's just bang in, bang out. Unless you really need to use air for some reason (spark hazard for example) a linear actuator might be more appropriate.

______
Rob

Title: Re: Pneumatic cylinder
Post by: triath5147 on Nov 12, 2010, 01:10 am
If your building a ground breaker or other type of Halloween prop than pneumatic is the way to go, They are very fast acting. The pneumatic valves come in 12/24 and 120 volts and would be easy to implement using just a sketch turning the relays on and off with delays to match sound effects or whatever your doing with it.
Title: Re: Pneumatic cylinder
Post by: keeper63 on Nov 12, 2010, 04:07 am
Quote
Also with phneumatics it's difficult to get much control, it's just bang in, bang out.


I don't think this is true - I think with careful PWM control of the valves (on both the input and output sides, whatever direction), coupled with some form of positional feedback, and perhaps a PID loop - it could be done.
Title: Re: Pneumatic cylinder
Post by: graynomad on Nov 12, 2010, 04:44 am
As I understand it because air is compressable you have to build up a certain pressure to overcome whatever frictions there are in the system, having done so the ram starts to move, at which point you have far too much pressure so it moves too fast.

I suppose with a really quick PID response time you could control the pressure fast enough, but you can't take the pressure back, you can only stop adding to it. So if it's too high there's nothing you can do without another mechanism like a brake or as I think you referred to, modulating pressure to the other side of the ram.

I suppose another way would be to have the ram working against a spring so the stiction is a small proportion of the total force needed. Of course the load may also provide this function depending on its weight. For example air bags in vehicles rise slowly, they have next to no stiction and a large mass to move.

______
Rob

Title: Re: Pneumatic cylinder
Post by: aweida on Nov 12, 2010, 04:45 am
Thanks for the reply guys, I dont specifically need a pneumatic cylinder, as i stated earlier i am just trying to mimic a push and pull motion. Richard stated that there are electrical gadgets that simulate pneumatic cylinders. Can you recommend any for me. Thanks allot guys.
Title: Re: Pneumatic cylinder
Post by: graynomad on Nov 12, 2010, 04:47 am
Quote
I dont specifically need a pneumatic cylinder

OK that's easy then, search for "linear actuator". Or DIY with some threaded rod and a motor.

Another option is "electronic muscle", see

http://www.sparkfun.com/commerce/product_info.php?products_id=8751

I don't know how strong it is or what the travel is though.
______
Rob
Title: Re: Pneumatic cylinder
Post by: aweida on Nov 12, 2010, 04:50 am
Thanks, that is exactly what i needed, sorry for the confusion guys.
Title: Re: Pneumatic cylinder
Post by: wediggers on Nov 12, 2010, 05:22 am
if you don't need more then an inch of movement check out automotive door locks as they run about $10 and the speed/power can be adjusted by changing the voltage

as for pneumatic you can easily control the speed a needle valve on each end of the cylinder and the pressure with a and regulator
the valves can be a bit expensive $50-$100 but if you luck out you can find some on ebay for $10-$20 or you can make your own for about $10
using some manual toggle valves and a electric solenoid  
 
Title: Re: Pneumatic cylinder
Post by: retrolefty on Nov 12, 2010, 10:39 am
Just for background information Pneumatic actuators can and do exist in both on/off and linear forms, just like hydraulic actuators. Both require position feedback and some form of control like PID to work in linear operation. In a refinery or chemical plant there might be hundreds of control values in use that are pneumatic and linear in operation. This are typical driven with a linear 4-20ma control loop with an on-valve controller called a valve positioner that has position feedback and internal PID control action at the valve.

Lefty
Title: Re: Pneumatic cylinder
Post by: zoomkat on Nov 12, 2010, 06:39 pm
Quote
Thanks for the reply guys, I dont specifically need a pneumatic cylinder, as i stated earlier i am just trying to mimic a push and pull motion. Richard stated that there are electrical gadgets that simulate pneumatic cylinders. Can you recommend any for me. Thanks allot guys.


Using pneumatics for push/pull may be somewhat like push/pull using a sponge. Depending on your application, you might be able to use a hobby servo.
Title: Re: Pneumatic cylinder
Post by: keeper63 on Nov 12, 2010, 08:10 pm
Quote
So if it's too high there's nothing you can do without another mechanism like a brake or as I think you referred to, modulating pressure to the other side of the ram.


That is what I was referring to; you would have to carefully control the cylinder pressure on both sides of the ram to, with position feedback - for this to have any hope of working. I know its possible, as retrolefty noted, it is used in industry (and used to be common in industrial robots - but linear actuators seem to have taken over) all the time.

Though I agree that this is likely waaay outside the OP's original needs and/or capabilities (not too mention, possibly the wallet!) - so going with regular DC electric linear actuators might be the best choice...

:)

Title: Re: Pneumatic cylinder
Post by: aweida on Nov 12, 2010, 11:27 pm
Thanks for all the input, ive learned allot, this is great advice.