Re: Encoders

Hello, your analysis seems accurate if you are going direct drive
to the lead screws, so either one will work. You can not switch
quadrature on and off because that is how the drive determines
direction of rotation.
Not sure what your servos are like but one thing to keep in mind
is that you must have high torque servos to directly drive a .2
leadscrew on a milling machine. Smaller servos that run at say >
2000rpm may need reduction. Any reduction will multiply your
resolution as well. So a 500 line encoder(2000 cpr) and a 2:1
reduction will produce the same resolution as 1000 lines with no
reduction. But you will have twice the torque. You will still only
reach 135ipm at 45kHz. Reduction is often used with servos to bring
them closer to thier most efficient rpm range. In your analysis, you
would demand only 675rpm at the leadscrew. Thats pretty slow for a
servo.
US digital's E2 encoder is a good choice. If your motors have a
large bearing at the back, you may consider the "g" option which adds
molded ears to the encoder base. The larger mounting circle will
prevent you from drilling into the bearing.
Dean

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "C.S. Mo" <cs@v...> wrote:
> I'm looking to get some encoders for my mill conversion. I have
.200"
> lead ballscrews - it looks like my reasonable choices are 500cpr,
which
> gives me 0.0004"/0.0001" resolution (w/quadrature), or 1000cpr which
> gives me 0.0002"/0.00005" resolution.
>
> If my calculations are correct, with 1000cpr w/quadrature, I should
be
> able to get a maximum of 135ipm rapids using Mach2 (45,000hz pulse
stream).
>
> Assuming that 135ipm is satisfactory, is there any reason NOT to use
> 1000cpr encoders?
>
> Is it possible to switch quadrature on/off on the fly? Or even
without
> too much trouble manually? It might be interesting to have a machine
> setup with high and low resolution depending on what you were
working on.
>
> I'm currently looking at US Digital encoders - any other
recommendations?
>
> Thanks,
>
> --C.S.