Re: [CAD_CAM_EDM_DRO] Re: Digitizing arms??

On Thu, 24 Jun 2004 14:54:54 -0000, you wrote:

>I agree,
>
>Get one of those summagraphics tablets on ebay real cheap... those
>have a crosshair puck, most accurate hand-tracing you can get.

Before you get one of them, make sure that the drivers are available
for your operating system of choice. No drivers = no fun. Not all
drivers are available for all operating systems depending on the model
of the tablet.

Harvey

>
>Jason
>
>> If your only after 2 axis, use a tablet and trace.
>>
>>
>>
>> ----- Original Message -----
>> From: "Jon Elson" <elson@p...>
>> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
>> Sent: Wednesday, June 23, 2004 9:09 PM
>> Subject: Re: [CAD_CAM_EDM_DRO] Digitizing arms??
>>
>>
>> >
>> >
>> > doug98105 wrote:
>> >
>> > >Group,
>> > >
>> > >Looking for some ideas on making a two axis digitizing arm.
>> > >
>> > >Back in the days of Apple II computers I saw a couple of crude
>> > >digitizing arms built using potentiometers and inputting through the
>> > >game controller input. Position was determined by the resistance
>> > >readings.
>> > >
>> > >With high resolution encoder devices it seems like a much more
>> > >accurate digitizer could be made.
>> > >
>> > >Any thoughts?
>> > >
>> > >
>> > Yeah, look at Faro for how they did it. The problem with these things
>> > is that certain arm positions lead to poor accuracy, because a
>very small
>> > movement of one joint makes a big change in position.
>> >
>> > No doubt a 1000 cycle/rev, or even 2500 cycle/rev encoder would be
>> > a HUGE improvement over the ancient Apple digitizer with pots.
>> > Unless they used special pots, you couldn't possibly get better than
>> > 1% angular accuracy, and that is 3.6 degrees! Yikes!
>> >
>> > I worked for a medical computer company in the WAY distant past,
>> > and they made "Rho - Theta" and "Phi-Theta" digitizing arms using
>> > very expensive mil-spec rotary and linear pots, and had all sorts of
>> > trouble getting enough resolution with a 12-bit ADC to digitize
>> > the location of a patient's tumors, etc. Linearity was no problem, as
>> > the software had cal tables built for the individual digitizing arm.
>> >
>> > Jon
>> >
>> >
>> >
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>OFF Topic POSTS: General Machining
>If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble.
>http://www.metalworking.com/news_servers.html
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>http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list.
>
>NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
>bill
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