Pneumatic valves for robot grippers or spot weld ?

Milacron · Apr 14, 2009

Say you want to plumb robot spot welder gun for the open and close of it's electrodes (accomplished via double acting air cylinder), is it typical for the air output for open and close, to be done with one air solenoid with "double solenoid, center off position" (3 postion directional control valve with exhaust ports)...or more typical to be done with two "spring return to off" type solenoids (2 position valve with exhaust port) ?

My impression, from looking at fuzzy photos of robots, is that it's more typical to use two (2 position) valves mouned on a common manifold.... but if so, I wonder why, as it seems like one 3 position valve would be simplier.

Tonytn36 · Apr 14, 2009

All I've seen are double solenoid single valves (i.e. 5/2) All of ours for material handling are ordered equipped with 2 valves for a total of 4 ports available. If only 1 valve (2 ports is used) you just turn the other one off in the controller. One reason to use a double coil valve vs. single is actuation time. A coil can pull the spool a lot faster than a spring return can push it back.

Milacron · Apr 14, 2009

Tonytn36 said:
One reason to use a double coil valve vs. single is actuation time. A coil can pull the spool a lot faster than a spring return can push it back.

That's what I was thinking too... a spring return type just didn't make any sense...and yet all the photos I saw showed two valves in place, which would imply two spring return valves if both were utilized for one double acting cylinder.

But maybe the situation at your plant answers the mystery...perhaps they are both 3 way type valves but really only one of the two valves is being used per air cylinder... :scratchchin:

Having said that, at below link are some closeup pictures of a pneumatic activated robot spot welder which clearly shows two valves... which appear to be 2 way type valves....so now I don't know what to think.. :confused:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=370180768897

Tonytn36 · Apr 14, 2009

There are 2 pneumatic devices on that unit. Notice the black air line going in the banjo fitting on the side of the unit? (3rd pic down, right column) That isn't going to the pneumatic cylinder...

Jburgess · Apr 14, 2009

Another reason to use the center off, 3 position valve is so in the event of an e-stop air pressure is removed from the cylinder. Keeps the jaws from moving unexpectedly when freeing a stuck part.

Milacron · Apr 14, 2009

Tonytn36 said:
There are 2 pneumatic devices on that unit. Notice the black air line going in the banjo fitting on the side of the unit? (3rd pic down, right column) That isn't going to the pneumatic cylinder...

Maybe, but don't know how you know that for sure. I can't even see how the air cylinder is connected to the air manifold really, so how do we know that black line doesn't take off from the other side of that bracket and connect to the air cylinder ? And what would the second cylinder be for anyway ? Might be one for open/close of coolant water flow but why not a direct solenoid for that instead of electric to air to water ?

And the clincher being they just look like 2 position spring return valves to me...only one solenoid on each.

Tonytn36 · Apr 14, 2009

The cylinder is direct ported from the manifold. 2nd pic down left column. See the little aluminum block with the pipe going to the manifold?
What is odd, is that black line actually runs over to that yellow box with the ARO on it, and that looks like a pneumatic water valve, but I don't see how the air gets to that from the valves.
Another oddity is that there are 3 exhaust silencers. Almost like one valve is a single position (2nd port blocked). It could also be that they needed 3 of that size to get the exhaust volume needed.
The second valve could also be a safety lock for the cylinder, which makes a lot of sense with a blocked secondary port.
It does look like two plain-jane spring-return valves though.

Limy Sami · Apr 14, 2009

Milacron said:
My impression, from looking at fuzzy photos of robots, is that it's more typical to use two (2 position) valves mouned on a common manifold.... but if so, I wonder why, as it seems like one 3 position valve would be simplier.

Suggestion ;- even with spring return, 2 seperate valves could be faster as one could open before the others fully closed (or vice versa)............ as opposed to waiting for a single valve to go from one port across centre to the other ??

Mark McGrath · Apr 15, 2009

It is usual to have two clamping pressures on the big spot welders I`ve worked on.Squeeze and hold.Easy way to do it is with two valves fed at different pressures.You need the highest pressure first so energise both valves,to change to holding pressure,de-energise high pressure valve.

irontoys · Apr 15, 2009

Milicron: Those appear to be plain Numatics air valves. http://www.numatics.com/common/deliverables/catalogs/valves/iso5599-2.pdf They do not appear to be a pilot control, just direct acting, 2 position, spring return solenoid valves. We frequently use 2 valves like this in motion control for speed controlling. That is ,we cascade them for a 2 speed exhaust. Might be the same here. The aluminum tube looks ported to the cylinder. That cylinder also appears to be single acting, with spring return open. Note smaller black cylinder with stud and nuts at end. To preload return (open clamp).Hope this helps

Milacron · Apr 15, 2009

irontoys said:
That cylinder also appears to be single acting, with spring return open. Note smaller black cylinder with stud and nuts at end. To preload return (open clamp).Hope this helps

I suppose that is possible, but the ARO spot weld gun I have here has double action cylinder..but mine is a different model number. (and unlike that one, mine is not "dressed"....i.e. mine has no valves, thus the need to install some. It seems these things can go either way...either the valving is installed on the robot arm or on the spot welder itself)

Milacron · Apr 15, 2009

FWIW, I corresponded today with an independant robot tech who confirms one 3 position valve would be fine for my setup.

Still a mystery why two 2 postion valves on the ARO gun on eBay... I was so curious I called the owner and even though he seemed pretty knowledgable about that sort of equipment, he didn't know either...so now he's curious too and is supposed to be "investigating"

Milacron · Apr 16, 2009

Milacron said:
... I was so curious I called the owner and even though he seemed pretty knowledgable about that sort of equipment, he didn't know either...so now he's curious too and is supposed to be "investigating"

He called back. One valve goes to what he called an "equalization" cylinder and the other to the actual cylinder. So maybe one valve closes the electrodes via the cylinder and the other valve opens it via the smaller cylinder...or maybe just the opposite...beats me...

atomarc · Apr 16, 2009

If you look at the pictures you can see that the clamping cylinder rides in a yoke on a common pivot with all rest of the apparatus. This would allow the welding clamp to pinch the material to be welded in a self centering fashion.

While I have never seen one of these things, my bet would be that only a single clamp, or tong moves while the other is fixed. This would be another reason why the entire cylinder/clamp mechanism should also pivot. The seller mentioned a 'equalization cylinder'. This would be the cylinder that is tied to the large yoke that shares a common pivot point with the clamp assembly and its air cylinder.

Unless the clamping assembly had some float or self centering capablity, high clamping pressure could shove the material out of position. Does this sound possible?

Stuart

Search

Largest Manufacturing Technology Community on the Web

Search

Pneumatic valves for robot grippers or spot weld ?

Milacron

Administrator

Tonytn36

Diamond

Milacron

Administrator

Tonytn36

Diamond

Jburgess

Aluminum

Milacron

Administrator

Tonytn36

Diamond

Limy Sami

Diamond

Mark McGrath

Diamond

irontoys

Aluminum

Milacron

Administrator

Milacron

Administrator

Milacron

Administrator

atomarc

Diamond

Similar threads