Re: Digitizing arm - CMM

On Wed, 12 May 1999 20:28:40 -0700, Tom Kulaga <tkulaga@...>
wrote:

>>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?

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!).

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

>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?

It SURE does to me, anyway. Perfectly acceptable accuracy for roughing
out models that you then refine within a 3D editor/modeling program. As
far as available sensors, etc. to "stay cheap", even their patent itself
refers to use of HP Optical Sensors and LS7166 chips with the sensors in
quad+index mode, so I think our own combined group USDigital/HP sensor
experiences are indeed adequate to the task.

>Wow, Rhino does that?

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

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. It's come up in other experimental venues I've been involved
in, so I've checked into it via counsel, and especially patent law
counsel, and it IS perfectly acceptable for a practitioner in the art
(that's us) to experiment with design concepts disclosed in issued
patents, as long as it's for the purpose of "examination of prior art,
and advancing the art". What ISN'T permissable is to do so for purpose
of selling or benefiting commercially from such experimentation and
testing, without a license of such patented art.

Just in brief, two examples, one obvious, the other not so obvious, but
ya understand it's a messy world when the lawyers get mixed into the
punch-bowl. First is obvious; you may not embody a patented device in
order to sell it without permission/license. Second (an example of the
"commercial benefit" prohibition) is that you may not embody a patented
device to use in the course of a business operation, where you benefit
monetarily (for example, as a result of using your "experimental
embodiment", you turn out parts faster in your business, say, than
without it).

Basically, if we wanna play within this field, we can. But don't play
with other's intellectual property if you intend to go beyond "play",
and make profit or other monetary or commercial gain. Really just that
simple. So please, no presumptuous hightoned albeit ignorant
folk-moralizing that somehow viewing and playing with these patents may
be unethical. It's not only NOT, the patent attorney I discussed this
with wisely pointed out that the system is set up to intentionally allow
such "trial" of patented material, so that workable art is proven and
the advancement of the art is encouraged/stimulated. To wit, you can
test and experiment with someone else's ideas and designs; but you
dasn't STEAL them. Pretty obvious and straightforward, really. Just
wanna head off any such concerns at the pass, sotaspeak.

Gar