Gripping force

[arcka]

Hello Guys,

I need help in calculating the gripping force. I have to use a pneumatic cylinder which has linear mition and I am planning to use scissor tongs to carry this motion into gripping force. Can anybody help me with the selection of cylinder w.r.t displacement or force?

Thanks in advance
Arcka

 

[telecomguy]

On a smaller scale, I would use springs to create a controlled clamping force to avoid crushing. Then I'd use the cylinder to just open the claw. With the forces you are looking at, this might not be practical. And now you've reframed the problem with a predefined mechanism. Just thought I'd mention that in case it gave you some other ideas for addressing the challenge.

-tg

http://xternal.me

 

[mcgyvr]

Just some links for the OP to bring it back to the basics.

http://www.engineeringtoolbox.com/levers-d_1304.html

http://iqa.evergreenps.org/science/phy_science/ma.html

 

[LittleInch]

arcka,

As a few people here are telling you, there is no single force because it changes as the cylinder moves from nearly zero to the maximum when the tan coloured links are nearly at 90 degrees to the cylinder.

The key dimensions you need are the fixed or stated distance your jaws are apart / diameter of the rod, the distance between the pins at the end of the tan coloured links and the length of the tan coloured links and their distance from each other plus how the distance between the tan coloured links and the jaws vary (e.g.130mm links gap = 25mm jaw gap, 131 = 24.75 or whatever)

Then if you have a fixed rod diameter, just draw out the centreline between the pins, work out the angle of the tan links to the cylinder and you can get your force. If you have a variety of rod diameters then draw a variety of diagrams and get a variance in force. If the rod is thicker than you've shown on the drawing then the force will be less.

Of course this ignores any compression of the rod or embedment of any teeth, but this should be relatively small in comparison to the jaw movement. Of course if your rod is too small then force is zero....

I can only assume you have a fully dimensioned drawing or can interrogate your drawing to discover all these dimensions.

Good luck and let us know how you worked it out.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[dwallace1971]

Of what material are the two bits actually in contact with the rod you're trying to lift?

"On the human scale, the laws of Newtonian Physics are non-negotiable"

 

[81buckeye]

Going back to your original simple sketch, this does not seem to be a difficult problem. You already have the beginnings of a free-body-diagram. I would flesh out your diagram with variables for everything and write out the force balance equations with the hydraulic cylinder pressure as the unknown. Then put these equations into Excel and play around with the various dimensions until you come up with a solution you like. This may seem rudimentary but often the simplest approach makes the most sense. I would also suggest a simple beam bending analysis of your final solution to determine if the linkage members will provide sufficient strength and not yield.