Pneumatic logic for gripper, on - off -on

I have a chuck that holds samples for metrology equipment.  It uses a pneumatic gripper (it's actually configured to push the sample into hard stops) to fine position and clamp samples.

We have a problem with the sample drifting after clamping and/or riding up in the chuck while clamping.  We've made a number of changes with some success but this issue still happens sometimes.

One thing that has been found to help is to clamp, unclamp, clamp again.  The first clamp basically positions it while the second holds it in place while the metrology equipment does its thing.

Trouble is our software people are massively backlogged and so far haven't undertaken to add this as a function to happen automatically.

I'm wondering if I could achieve this with pneumatic logic?  The software turns the air/N2 pressure on and the chuck clamps, opens, clamps again and stays clamped till the software turns the pressure off.

I did relatively little logic at school and nothing specifically on pneumatic logic.

1.    Does this seem like it's possible.

2.    Can anyone point me in a direction where I can learn a little about this and work it out.

I'll probably work with our main pneumatics vendor if it looks promising but I want to have some idea up front.  A quick google search turned up some vendor  pages and on this site thread404-217222: Timed pneumatic valves? but I was wondering if anyone more knowledgeable could point me to a good source of info.

Thanks,
 

KENAT, probably the least qualified checker you'll ever meet...

I don't know how accessible your control cabinet is, but you might also consider ordinary relay ladder logic.  If there is space on a DIN rail, you could add a couple of little timing relays to do it (time until unclamp; time until reclamp).

Don
Kansas City

KENAT we use SMC a fair amount, we are lucky as their UK headquarters are just down the road. I have no idea what they are like stateside but they offer fantastic technical support in the UK, they might be worth contacting.

http://www.smc.eu/portal/WebContent/corporative/products/products.jsp

Maybe something like this (I don't know how this diagram will turn out):


                             |
clamp output-->--+------(T1)-|
                 |           |
                 | T1        |
|                +-]/[-+-( )-| clamp
|                | T2  |     |
|                +-] [-+     |
|   T1                       |
|--] [------------------(T2)-|
|                            |
|                            |
H                            N

Don
Kansas City

1. Yes, it's possible.

2.  Some good resource links here:  thread404-217222: Timed pneumatic valves?

 

Duh - maybe I should read your entire post before I point you to a thread you already found.

 

Don's drawing is not clear but you can do it with two pneumatic timers as suggested. You can reset the two timers, for the new cycle, by switching off the compressed air supply to timers.

This Link gives you some control circuits. The penultimate one may be of interest to you.

Let's try that again.  Maybe this is a little easier to read.

Don
Kansas City

• http://files.engineering.com/getfile.aspx?folder=827ccc39-8dae-4aab-b940-0d

Thanks,

I was out of the office today but I'll look closer on Monday.

I was already thinking about timers so thanks for confirming I may be on the right track.

I think we may have a good SMC rep, that or Festo, it's been a couple of years since I looked at any pneumatics.

Thanks again,

Ken

KENAT, probably the least qualified checker you'll ever meet...

Take a lok at chapter 19 of the Basic Ebook and/or section 2 of the Fluid Power Circuits Explained book here for some training on Air Logic controls. At least it will give you an idea of what is available and some circuit design ideas.

http://www.hydraulicspneumatics.com/200/eBooks/
 

Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

So it appears I was on the right track.

Essentially 2 Timers in parallel.  One that closes a valve after say 'T1' seconds and a second one that opens a valve after 'T1+T2' seconds.

In my case the signal and supply would both be the same source, correct?

Sorry my terminology isn't quite right yet, I'm still reading through the ebook, however I wanted to thank you all for your input, it's answers like these that make this site so usefull.

 

KENAT, probably the least qualified checker you'll ever meet...

I'm assuming that the clamp is controlled by a 24Vdc solenoid valve that is connected to a sourcing output from some sort of controller.  You just need to locate the V+, the common, and the control wire to the valve (the solenoid will have one common and one control wire).  In my diagram, the left side of the ladder is +V, the right side is common.  

I've shown the clamp output as a contact point, but actually you would just run the controller output wire directly to the timer terminals as shown.

Maybe this diagram will make more sense:

Don
Kansas City

• http://files.engineering.com/getfile.aspx?folder=0f5b841b-19d4-4281-952a-35

Ah, now I think I see Don, I realized your first post was regarding the electric solution but thought your later ones were pneumatic, I was mistaken.  (Explains why I had trouble with a couple of the symbols in your sketch though when I was comparing to pneumatic symbols!)  

Tapping into our electrics/electronics is probably no more of an option than changing the software.  The Chuck can be exchanged with at least one other type of chuck, more or less 'invisible' to the rest of the tool.  The other chuck just uses the vacuum to hold the sample in place so the on/off/on wouldn't be appropriate.  I realize there could be a selector switch but it's starting to get well beyond my competancy.

Really appreciate the input though and I'll suggest it when we get together to discuss the problem.

KENAT, probably the least qualified checker you'll ever meet...