Re: Encoders from Wirz

Jon,

If I am following your description correctly you are calculating this based
upon attaching the encoder to the leadscrew?

Assuming you are using a 4 to 1 reduction to the leadscrew how would this
work out if you attached the encoders to the motor instead? Seems to me that
you would then get 9600 counts per inch using your scenario. Would that be
usable?


Tim
[Denver, CO]

> -----Original Message-----
> From: Jon Elson [mailto:jmelson@...]
> Sent: Saturday, June 26, 1999 9:44 PM
> To: CAD_CAM_EDM_DRO@onelist.com
> Subject: Re: [CAD_CAM_EDM_DRO] Encoders from Wirz
>
>
> From: Jon Elson <jmelson@...>
>
>
>
> Roger Brower wrote:
>
> > From: Roger Brower <rbrower@...>
> >
> > I found: @ http://wirz.com/surplus/index.html
> > QUBE Encoders from Danaher Controls
> > We have a very limited supply of these high qualtity incremental
> > industrial encoders from Danaher Controls,Model# 320120300000. The
> > encoders use a magnetic technology with a 120 ppr TTL current sink
> > quadatureoutput. The 1/4" x 3/4" shaft is on ABEC precison bearings with
> > 30 lb axial load rating. Data sheet included.$25.00, similar units sold
> > in industrial magazines for over $200.
> >
> > Are these going to be suitable for our servo systems? Those who know,
> > Let me know, and Save me three!
>
> Not likely. The 120 PPR is a bit low resolution. There is some variation
> on how they specify this, but, most likely that is 120 cycles of
> the quadrature
> waveform, also known as 120 cycles. If that is how it is rated, you get
> 480 quadrature transitions per revolution, which is still awfully low.
> With a .2" pitch (5 TPI) leadscrew, that is 480 * 5 = 2400 counts/inch,
> which comes out to .000416667" / count. That is just a little too coarse
> to have a machine that can move in .001" increments. I think there would
> be a lot of servo 'hunting' with this setup, since flickering only +/- one
> count would move almost .001".
>
> I paid $75 each for some Sumtak miniature encoders with 1000 cycle
> resolution, plus index. (No, I bought all 3 of them.) Good encoders
> do show up from time to time, if you know where to look. These give
> 4000 counts/rev, and on a .2" pitch screw, you get resolution of 1/20000"
> or .00005". That gives 20 counts for every thousandth, so you just can't
> even feel the motors hunting at all.
>
> Jon
>
>
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