Re: Digitizing arm - CMM

>>The way you describe it, it only uses 4 encoders? That shouldn't
>>be too difficult to do, I'd think. Using 2000cpr encoders you
>>could probably get pretty darn accurate too.
>
>Not sure; did you check my short math doodle I posted recently. Looks
>like with 2048 cpr X 4 in quad, with even a short 10" single arm (just
>for purposes of illustration), the resolution per count is about 0.007",
>and that's just for the first joint.

Well, my understanding is that there's a rotary table, and an attached
arm with a shoulder, elbow, and wrist. Is that about right?

I just did a quickie calculation, it backs up your numbers. So,
being only slightly optimistic, we could probably hit .015"
resolution staying on the cheap side and doing the best machine and
measuring job we can. We could spend more, but I got a hunch it
would be a big price jump before there was any real improvement in
performance. Does this sound useful?

>Think Rhino ... presto, done deal. If you look on the Rhino3D site
>(www.rhino3d.com), under the topic of 3D-digitization, you'll see that
>Rhino provides the model creation poof, from the point cloud. That's why
>I suggested earlier that I'm sure them guys would provide the necessary
>info to make such a DIY gizmo compatible with say their Microscribe
>driver, or some such.

Wow, Rhino does that? I was sort of playing around with the beta a
long time ago, but with Pro/E, Solidworks, and AutoCAD easily
available, I couldn't really spare the time to learn another package.
I was once contemplating involvement with a project similar to this,
taking CAT scan data and creating rapid prototyping models of bones
(mostly damaged skulls and such). I dropped out due to the serious
math headaches involved. However, knowing that each point HAD to be
a surface point, I guess it would get easier.

>Sounds GREAT. An intrepid experimenter! Goodie. I trust the factoids I
>mentioned above regarding Rhino3D providing the surface model creation,
>are sufficient to stimulate your cerebral cortex further? B)

You bet, I'll look into it. I also need to get a few spare hours on
the machines at work to throw together some mechanicals to play with.
This can be difficult, since the guys in the toolroom get *really*
nervous when an engineer starts cranking handles. ;)

-Tom Kulaga