Re: Digitizing arms??

I agree,

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

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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