Re: Encoders from Wirz

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