Subject:
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Re: articulation points?
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 21 Nov 2002 20:52:26 GMT
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Viewed:
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1534 times
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"Steve Baker" <lego-robotics@crynwr.com> skrev i meddelandet
news:3DDC4185.4040500@airmail.net...
>
> However, according to the Robotics Research Group at UTA:
>
> http://www.robotics.utexas.edu/rrg/learn_more/low_ed/dof/
>
> You add up the number of degrees of freedom of each
> joint (between zero and six) to get the total number
> of degrees of freedom for a mechanism.
>
> ...that doesn't seem a useful thing to measure because it
> tells you very little about the ability of the mechanism
> as a whole.
Agreed.
> According to the Internet glossary of Statistical terms:
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> http://www.animatedsoftware.com/statglos/sgdegree.htm
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> "Statistians use the terms "degrees of freedom" to
> describe the number of values in the final calculation
> of a statistic that are free to vary."
>
> Mathematicians (http://mathworld.wolfram.com) talk about:
>
> "The number of degrees of freedom in a problem, distribution,
> etc., is the number of parameters which may be independently
> varied."
>
> Those two definitions sound just like the UTA Robotics group
> definition.
Not agreed. In mathematics (and statistics is just a part of math), you are
not limited to 3D space, and higher spaces need more degrees of freedom to
be completely covered.
> The Free Online Dictionary of Computing says:
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> http://foldoc.doc.ic.ac.uk/foldoc/index.html
>
> "<robotics> The number of independent parameters required to
> specify the position and orientation of an object. Often used
> to classify robot arms. For example, an arm with six degrees of
> freedom could reach any position close enough and could orient
> it's end effector (grip or tool etc.) at any angle about the
> three perpendicular axes."
This one covers it pretty well, in theory.
The easy interpretation is:
With three coordinates you can _be_ anywhere, with three rotation axes you
can _point_ anywhere, what more do you want?
But as a (industrial) robot not only has to be at a given point, in a given
orientation, but also must be able to interact with the environment, those 6
DOF are not always enough.
It might need an extra joint to be able to reach _into_ a hole, and then
grab something at an angle there, should this be called another degree of
freedom, or just a count of joints?
Take a Gastroscope (for looking down your throat into the stomach) for
example - it's not enough for one end of it to be at the doctors eya, and
the other inside my stomach, but it must follow the throat etc. all the way
down, else I will be quite upset! (I was anyway, but that's another story)
Hmm, I'd better stop. I started out with defending 6DOF being the definitive
*it*, and now it seems I've gone off in the other direction...
--
Anders Isaksson, Sweden
BlockCAD: http://user.tninet.se/~hbh828t/proglego.htm
Gallery: http://user.tninet.se/~hbh828t/gallery/index.htm
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Message is in Reply To:
 | | Re: articulation points?
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| (...) >be honest have yet to come to a definitive answer. The (...) Opinion seems to be divided on the meaning of this term. In my field (computer graphics), I'd say that each joint in the mechanism had between zero and six degrees of freedom, but (...) (22 years ago, 21-Nov-02, to lugnet.robotics)
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