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Unread 10-01-2005, 19:04
Rickertsen2 Rickertsen2 is offline
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Re: Pneumatic Confusion

Quote:
Originally Posted by Cyberguy34000
Pneumatics are something that I thought I had a pretty good idea of how they worked, but as I'm reading more and more of the posts on this form I'm questioning if I know them as well I think I do. I'm considering proposing an arm design at tonight's meeting that involves 3 pneumatic pistons. One for the base, another for the elbow, and the final one for the grabber. As I understood it, pneumatics work by controlling the releasing of pressurized air to manipulate movable pistons which when they become pressurized, expand.

But is the process controllable enough to be used on something that needs a great deal of prison and control, such as a joint in an arm? Can you acurately control the joint of the arm or would it only have one of two extremes? Please help.
In most circumstances, pneumatics can only be positioned at their extremes. There are ways to position them midway, But i would not recommend it for an arm. Motors would be a much better way to go
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Unread 10-01-2005, 19:26
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Re: Pneumatic Confusion

Quote:
Originally Posted by Rickertsen2
In most circumstances, pneumatics can only be positioned at their extremes. There are ways to position them midway, But i would not recommend it for an arm. Motors would be a much better way to go
I dis, and do agree with this statement. Motors do work well at controlling positioning. In fact that is all Sparky has ever used for controlling an arm. Very evident in Sparky 2, and 5. Both used in manipulation of 2x multiplier balls. There is one way that you can very effectively control the positioning of a pnuematic cylinder. The catch is that with using it as a contorler for an arm, you might have some issues with pressure. In my opinion, I find that both ways can be very productive ways of controlling an arm. And if you really want to use air, just marry 2 pistons together to get the desired mid-position stop you want, just like Moe did last year.

ivey
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Unread 10-01-2005, 22:41
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Re: Pneumatic Confusion

If you choose to use pneumatics to do this, there are a few good discussion threads from January and February 2004.

Also, some other sources -

www.cyberblue234.com / go to the multimedia and there is a video of pneumatic staging (ie starting and stopping mid-point on the travel).

also check the white papers, technical section, for a slide on the pneumatic circuit layout to do this staging. the title is "Controlling Pneumatics - Sketch".
I am the author of the file upload if that helps the search. It was uploaded in January or February 2004.

Basically, you control the movement of the cylinder by controlling the exhaust of the solenoid valve. I believe the slide shows doing that with two switches - one to control the direction and one to start and stop the cylinder. We ended up finding a way to link the solenoids and control it with one 3 way switch (extend - hold - retract).

It is difficult to repeatedly go to the exact same stop point. Air is very compressible, so the cylinder might move a little. Most cylinders were more accurate in one direction - depending on how they were loaded.

Good Luck. Take some time to experiment.
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Unread 11-01-2005, 03:33
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Re: Pneumatic Confusion

I am not sure why more people do not know about this, but SMC offers a valve that looks just like the double solenoid but functions slightly differently.

The valve I am talking about has a center off/center pressure/center exhaust feature. Meaning you can have variable piston position using only one valve (not sure if you can get away with one relay quite yet).

The part number differs only slightly from the regular double solenoids. If you are interested, drop me a line. The only catch, currently (as of today) they are on a 4-6 week back/manufacturing order from SMC in japan as no one in the US has any in stock. This valve also fits on the manifold we used last year. (I should also note that those are not in stock either!) Argh
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