Not Plc related, but it is engineering related

Stig · Sep 23, 2016

This sight is a pleathora of knowledge, perhaps someone can help me come up with the solution.

I have an air cylinder with a stroke length of 3 inches, it rotates a shaft with a pivot arm, the center to center length of the arm is 2.25 inches. This rotates the shaft more than 90 degrees. What im trying to figue out is what length the arm needs to be to get it to rotate only 90 degrees. My Math is a bit rusty, and this is not for a class.

I would prefer to be led in the proper direction and find the solution myself, rather than have the answer handed to me. If anybody can steer me to the equation, I would much appreciate it.

Thank you
Stig

Peter Nachtwey · Sep 23, 2016

Easy, the motion describes a right triangle.
I calculate 2.121 but that makes an an assumption and does fit your description.
sqrt(2.25^2+2.25^2)=3.18
It would take a 3.18 inch stroke to move a level arm of length 2.25 90 degrees. Something you are saying isn't right.

Highland Controls · Sep 23, 2016

Wouldn't it be arc length instead of a straight shot? Probably not much of a difference for this size, though.

Highland Controls · Sep 23, 2016

3.54" for arc length, so as Peter said, something isn't right with original numbers.

shooter · Sep 23, 2016

It depends on the connection points, so draw 2 triangles with all lengths in it and then calculate them, or use a cad program, when lazy.

James Mcquade · Sep 23, 2016

Your best bet is to use a cad program and draw the system you are trying to move.
position #1 - retracted position.
#2 - 90 degree position.

More than likely you will have to install stops at the 90 degree travel.
also, is there a force limitation on the system?

regards,
james

GTUnit · Sep 23, 2016

Just install some positive stops.
You can also make the arm length adjustable and fiddle with the point where the cylinder ball joint attaches till you get the motion you want.
Thinking 80/20 aluminum channel or something similar.

John Morris · Sep 23, 2016

IF The cylinder is accessible (can be taken apart), use internal stop/spacers,

Mill_Control · Sep 23, 2016

Peters answer is correct assuming the cylinder is at 90* to the arm at mid stroke. That or we're both wrong LOL

Playing around in CAD it's easy to determine where the cylinder fixed clevis C/L needs to be relative to the shaft C/L for the existing pivot arm. Once you realise you need the cylinder extended and retracted lengths rather than the stroke. But looking at it all on the screen I don't see an easy way to calculate anything besides the 90* at mid stroke arm length.

Stig · Sep 23, 2016

I will post a pic of the mechanism shortly.

Highland Controls · Sep 24, 2016

Mill Control-Please explain why it wouldn't be arc length? Am I missing something?

ndzied1 · Sep 24, 2016

When I read the description, this is what I am visualizing (attached). I think it's the same as Peter.

mendonsy · Sep 24, 2016

The position of the cylinder pivot point is also a factor. For the triangle calculation to work the cylinder pivot must line up with the retracted and extended points.

g.mccormick · Sep 24, 2016

Highland Controls said:
Mill Control-Please explain why it wouldn't be arc length? Am I missing something?

I believe the motion is arc , but start to end point is straight line.

Highland Controls · Sep 24, 2016

Yes, looking at the picture, it is clear that mounting point of cylinder affects travel distance. By the way, as drawn would be a bad choice. More than likely the rod would just try to pull back when retracting but not move.

Not Plc related, but it is engineering related

Stig

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