Re: [CAD_CAM_EDM_DRO] Closed-loop steppers, was: breakout boards plus - hard choice

Right again,
I think I'll just leave it up to people with just a bit more experience in
this area
I completely forgot about the limitations of the serial connector (drat...I
had a cool project with that, but it looks like I'm back to the
drawing board on that one)

Thanks for keeping me on the straight and narrow

On 8/1/07, Jon Elson <elson@...> wrote:
>
> Michael Fagan wrote:
> >
> > Right. I knew about the balls (I've got a set on the BP) but I didn't
> know
> > how they gathered data from them. I know they are advertised to have a
> > faster "refresh rate" than optical ones but other than that I don't know
> the
> > exact specs.
> > The newall dro unit does have a serial port output on the back that
> gives
> > real inch measurements for each axis regularly (don't know the exact
> timing)
> > so I think it can be interfaced for some things.
> I don't know how the Newall can have a FASTER refresh than
> direct-reading optical encoders. Most can produce 100,000
> quadrature counts per second with ease, and many of the models
> have a high speed readout option, mostly just faster
> differential line drivers. Then, they can go to 250,000
> counts/second and higher. If they are comparing their
> interpolator to other interpolated scales, then I think they are
> playing word games, as well as comparing what they make NOW with
> what others made 20 years ago. I know some of the outboard
> interpolators (Renishaw, Heidenhain, etc.) can go to several
> hundred thousand counts/second without introducing lag.
>
> The serial output is definitely going to be limited to a few
> hundred updates a second. 9600 Baud is roughly 1000 characters
> a second. If you are reading out 3 axes with 6 digits each, or
> 18 digits at 1000 chars/sec, that is 55 full updates a second,
> neglecting any format chars to tell which is which. Again,
> totally useless for a servo system, unless your bandwidth is
> about one Hz. That would be about as sluggish as your watching
> a display and moving by hand.
>
> Jon
>
>


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