Re: Digitizing arm - CMM

>Appears so for the Microscribe arm. If I understand it's construction
>aright, it has 5 degrees of rotary freedom: one for the base table
>rotation, one for the first joint in pitch only, two for the next joint
>in pitch and roll (twist), and one in pitch for the joint that
>terminates in the probe. The Faro arms appear to have 6 (or more!).

Oops, it's a 5-axis. I didn't know that the wrist had 2 DOF. This
makes it more difficult, at least from a hardware point of view. The
DRO card on my webpage could be re-done to handle up to 6 DOF, but
that pushes up the cost, too. Not to mention the effect it will have
on resolution. Still, we should be able to get by without having the
full-motion wrist. It will kind of limit the shape and type of stuff
that can be scanned, though.

>Figure 1 in the Microscribe patent (# 5724262) is easier to understand
>than my description above. B)

Can that be looked up at IBM's patent page? And does anyone have the
URL close at hand? I can't find it at the moment.

>Ahh, yup. Sanity check me by a visit to their site, and a quick read of
>the described support for the Microscribe and Faro digitizing arms:
> www.rhino3d.com

The Rhino page says that the software directly interfaces with the
digitizing arm. That tells me how they do the surfacing stuff, but
I'll need to get info from Rhino as to just how the arm needs to
communicate with the program. It would be much easier to just dump
the data into a file and feed that into Rhino if I could, but maybe
we'll need to do a little more work than that.

>BTW, I thot I should mention in passing some details on what some might
>be squeemish about, this bit of "reverse engineering" and patent
>sleuthing.

<snip good patent use info>

Understood and agreed. The charter (is that the right term for a
mail list?) that Bill started this group with specifies that this
list is for hobbyists, not for commercial interests, so I don't think
that anyone reading will disagree either. It is nice to know,
however, that we're perfectly legal when using patents to do this
sort of thing. I wasn't aware of most of the things you mentioned.
Thanks for bringing this up. Perhaps we ought to add that info to
the download section for this list, since we'll probably be treading
in this territory again.

We need to stipulate that Gar's advice ain't the law, it's not the
advice of proper legal counsel, and you follow it at your own risk.

Thought I'd add that last line after I saw that Gar didn't cover his
butt in his last post. (That's one ya owe me there, pal ;)

A side thought I had about this involves the initial setup of the arm
and how it might be tricky. I was thinking that if we could build a
fixture that held the arm in a known position, you could put the arm
into the fixture when you started the program, and know exactly what
the joint angles were. Of course, this is dependant on what Rhino
needs from the arm, so I might be way off here. Anyone have a good
friend at Rhino, or do you know if they'd share the required info
with mere hobbyists? I'll drop them an email if I have to, but if
we've got someone with an "in", we'd be best to use it.

-Tom Kulaga