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Posted by on October 1, 2005, 8:58 am
Here's the problem;
Say you have a robot arm which has several joints along it's length,
each one is driven by a pair of steel cables. The other ends of the
cables are connected to gearmotors which are located off the arm, to
keep the weight down. So the cables which drive the farmost joints need
to run through the preceding moveable joints, but the path length of
each cable must not change. ie, if the cable were to stretch or become
slack 'round the bends' it would affect the positioning of joints
further along the arm.
It can be done using bowden-type cables of course, with an inner cable
and an outer sheath, but this is not a very elegant solution. You can
also try and route the cables through the centre of each joint, but
unless they will bend to a very tight radius, the length still changes.
Is there a simple geometric solution to this, whereby cables can be
routed around a joint, and as it flexes the path length remains
constant? The Barrett Technology WAM arm appears to work this way, but I
can't see how. I have thought up one solution using a pair of
counter-rotating rollers, but I don't think the WAM works this way, and
I'm sure there's a better way.
Any descriptions or links, especially with diagrams, much appreciated.
Andy.
--
Posted by steamer on October 1, 2005, 12:37 pm
--Go to carlpisaturo.com and see how he's done it. Saw a drawing
he'd made in the class I took; the solution is non-obvious; i.e. there
*is* a trick to it..
--
"Steamboat Ed" Haas : You just can't beat
Hacking the Trailing Edge! : cruisin' in a steamboat
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---
Posted by MetalHead on October 1, 2005, 3:02 pm
steamer wrote:
> --Go to carlpisaturo.com and see how he's done it. Saw a drawing > he'd made in the class I took; the solution is non-obvious; i.e. there > *is* a trick to it.. >
Thanks for the pointer on this site, it is EXTREMELY cool!
Bob
Posted by on October 1, 2005, 3:08 pm
> --Go to carlpisaturo.com and see how he's done it. Saw a drawing >he'd made in the class I took; the solution is non-obvious; i.e. there >*is* a trick to it..
Thanks, I'd actually already seen this site. His solution is to run the
cables straight through the centre of the joint and bend them round as
small a radius as possible when the joint moves. He admits this is not a
perfect solution.
What I'm looking for is a mechanism that moves with the joint,
compensating for the path-length difference.
Andy.
--
Posted by on October 3, 2005, 6:54 am
Andy wrote:
> What I'm looking for is a mechanism that moves with the joint, > compensating for the path-length difference.
Can't you just do it programmatically? What's an importance of hardware
solution?
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> he'd made in the class I took; the solution is non-obvious; i.e. there
> *is* a trick to it..
>