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 02:14:29 GMT
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Original-From:
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Steve Baker <SJBAKER1@AIRMAILihatespam.NET>
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Viewed:
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1397 times
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Jennifer Clark writes:
> This reminds me of an argument I've had several times, and to • >be honest have yet to come to a definitive answer. The
> maximum number of degrees of freedom an object can have in
> three dimensional space is six; translation in the X, Y, and
> Z planes and rotation about in the X, Y, and Z axes. Giving a
> device more points of articulation does not necessarily
> increase the degrees of freedom, although it can increase the
> envelope or ability of the device to, for example, work round corners.
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 that the total number of degrees of freedom of a mechanism
could never be more than six. You could have a mechanism like
a bicycle chain that has hundreds of 1 DOF links - and the
total mechanism would have three degrees of freedom because
it can move in X, Y and one rotation axis. I think that's
a USEFUL measure of a mechanism.
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.
According to the Internet glossary of Statistical terms:
http://www.animatedsoftware.com/statglos/sgdegree.htm
"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.
According to Professor B J Stone at the University of Western
Australia (who is talking about vibrational modes of a system):
http://www.animatedsoftware.com/statglos/sgdegree.htm
"A simple definition of "degrees of freedom" is - the number
of coordinates that it takes to uniquely specify the position
of a system."
...which fits with my definition.
The Free Online Dictionary of Computing says:
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."
I conclude that this term is too vague to argue about!
---------------------------- Steve Baker -------------------------
HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sf.net http://tuxaqfh.sf.net
http://tuxkart.sf.net http://prettypoly.sf.net
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Message has 1 Reply:
 | | Re: articulation points?
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| "Steve Baker" <lego-robotics@crynwr.com> skrev i meddelandet news:3DDC4185.404050...ail.net... (...) Agreed. (...) Not agreed. In mathematics (and statistics is just a part of math), you are not limited to 3D space, and higher spaces need more (...) (22 years ago, 21-Nov-02, to lugnet.robotics)
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Message is in Reply To:
| | RE: articulation points?
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| (...) However, a device is made up of several objects. Each component, if treated separately, has six degrees of freedom. Thus each component of, for example, the human arm (reduced to an upper arm, lower arm, and hand) has 6 DOF, for a total of 18. (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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