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Pneumatic Cylinder

  1. Apr 9, 2006 #1
    I am tring to make a device that uses a spring loaded pneumatic cylinder, but I dont know anything about pneumatics, and havent found much on the net.
    I need a spring loaded cylinder to oscillate.
    I am not sure if the system needs a exaust valve and a cut off to the intake valve, or if it just needs the exhaust valve by itself.

    I wasnt sure if the intake valve wasnt shut off as well as the exhaust valve open if the head would just lift up to some level of bleeding the air out and sit there?

    Thanks guys
     
  2. jcsd
  3. Apr 9, 2006 #2

    Integral

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    What are you using to control in the input? IIRC you need a 3-2 solenoid valve to control a single action cylinder. With an electrically activated 3-2 solenoid you will be able to control when the cylinder is activated. If you wish to control the speed put a flow control on the exhaust port.
     
  4. Apr 9, 2006 #3
    I am trying to controll it all inside the unit similar to how a air body saw or air file work.
     
  5. Apr 9, 2006 #4

    Cliff_J

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    Both the air body saw and air file are rotary vane tools that spin a crankshaft and that creates the oscillating motion. No valves constantly opening/closing and no control system needed, just a pressure reduction valve to control the pressure present at the vanes.

    Do you need varying speed or power levels? If so, those are going to be quite challenging with a pneumatic cylinder, and speeds approaching an air saw are going to be very difficult unless the stroke is short.
     
  6. Apr 10, 2006 #5
    I concur with Integral. You require a 3/2 way solenoid valve. You can keep the exhaust valve open(spring side) or put a flow control valve to control the stroke. The exhaust from the air supply side will be taken care by the 3/2 way valve.
     
  7. Apr 10, 2006 #6
    it is going to be highspeed 40cycles per sec. +, actually I have a air file and saw that I use for car audio, I have taken them apart and they do not have a rotary system.they have opening and closing valves.the piston opens and closes the valves as it oscillates.
     
  8. Apr 10, 2006 #7
    very small stroke 5mm max.
     
  9. Apr 10, 2006 #8
    yes varying speed and power levels.
     
  10. Apr 10, 2006 #9
    http://img218.imageshack.us/my.php?image=pneumatic6fn.jpg
    here is what I had a couple months ago. will this work?
    Or would it work if the bottom part of the yello cylinder was removed to allow the air to push against the head?
    Does the cylinder(piston)need to cut off the air inlet?
    WIll th exhaust work?
    Does there need to be a exhaust on the spring side of the cylinder(piston)?
     
  11. Apr 10, 2006 #10

    Integral

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    I cannot tell from your drawing if it will work or not. My first reaction was no. I do not see where the expansion takes place.

    I have worked with Haskel pumps which do about what you want, but at perhaps a slower rate. If you go to products and poke around a bit they have some pretty good information.

    Are you planning on making this from scratch? Pretty ambitious project, you may do yourself well to learn something about pneumatics in addtion to having good machining skills and access to a lathe and milling machine. Pneumatics is not a trivial field, you may be able to find something in your local liberary. All I could find in my search efforts on the web were professional training courses which were not free.
     
  12. Apr 10, 2006 #11
    Yes I am building it from scratch, Im not doing the machining just the design. I got a copy of Solid Works yesterday for making the blueprints for the machinist. Thing is this system is really small so I dont think it will take thatmuch for it to work. The stroke length is only about 5mm max.
    piston is about .5-.75", I know pneumtics isnt trivial but it is just basic physics, Im just not familiar with the technicalities.
    In the picture if I reduce the lower part of the piston to say only half its diameter, it would be able to expand, compressing the spring, My unknowing is will the piston fire upwards at a rate that even w/ the inlet valve closed off will it continue upwards fractionally, and will the exhaust port(adjustable for stroke heigh) release any excess pressure causing it to not continue upwards with the added backpressure from the spring.

    Thing that sucks is with not knowing the out come I will just have to design multiple pistons, and possibly multiple heads.
    and test it.
     
  13. Apr 10, 2006 #12
    There seems to be few problems as far as my understanding of your drawing is concerned.

    1. Considering it as a two head piston, I don't see any reason as to why it should move at all if you let in compressed air in the middle of the two heads.

    2. As you move the piston, the exhaust port is closed and there is some compression at the spring side that will tend to stop the stroke.

    3. The output link, perpendicular to the piston movement, may rotate instead of sliding(unless you restrict the rotation).

    Rather than going for new designs, I would just select a compact pneumatic cylinder (check Festo or SMC). The speed of the stroke can be adjusted by a flow control valve in the exhaust, as already suggested earlier, no. of strokes can be controlled by no. of times you on and off the 3/2 solenoid and stroke length can be controlled by adjusting back pressure on the exhaust side.
     
  14. Apr 11, 2006 #13

    FredGarvin

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    Getting here a bit late...

    Quark is right on. The piston looks like it is never going to move since you have the same pressure on opposite faces. So you will need to get rid of that bottom face. Once you get rid of the bottom face, I'd consider moving the air inlet port to the bottom. It'd be easier to machine.

    It looks like you are adjusting the stroke by the placement of the exhaust port? Is that correct?

    The toughest part about cylinders is getting the piston seal to work in a high cyclic rate piece.
     
  15. Apr 11, 2006 #14
    Ok so as I said before Ill reduce the size of the bottom part of the piston.
    the release valve is actually threaded at the top of the head, and where it goes down through the head it is tight, I might need to add a spring at the top or something to the threads to keep it tight enough not to rotate during oscillation, like a spring loaded screw valve on a carburater.

    Also I was worried about the input as far as machineing it obviously wont bend like that but how can I get the bend at the bottom, they cant machine a 90 degree angle at the bottom of a 10-15mm cylinder hole?

    ALso the machine can only have one air inlet.
    so if I use a 3/2 valve to compress say 6-8ft of 1/8 or 1/4 clear tube will I be able to get 40hz+ cycle rates with a external valve that far away?

    that is why I want the system to open and close itself(speed)

    btw this is for a tattoo machine so you can imagine how small it needs to be, its a art tool/medical tool.
     
  16. Apr 11, 2006 #15

    FredGarvin

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    You can cross drill the holes. Machine the vertical hole down to the proper depth. Then drill a radial hole from the OD to the ID making sure it intersects the hole. Then go back after and weld shut the hole in the OD only. That gives you the right angle passage you need to the ID. Just make sure to do this BEFORE the final machining on the ID of the cylinder. If you do it after, the weld will distort the ID and your motion/sealing will go south on you.
     
  17. Apr 11, 2006 #16
    that wasnt what i wanted to hear.
     
  18. Apr 12, 2006 #17

    FredGarvin

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    Why not? It's a simple machining operation. I do it all the time for things like oil and buffer air passages.
     
  19. Apr 12, 2006 #18
    Can you see the weld? If not thats cool.
     
  20. Apr 12, 2006 #19
  21. Apr 12, 2006 #20

    FredGarvin

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    The weld can be buffed out. You wouldn't know it's there if done correctly.
     
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