Re: Encoder Indexer Option

Dave,
Thanks for expounding on this. I think that someone sells a board
that will take the index line and use it for a homing routine
independent of the servo driver. I will have to see if this is
justified for my setup.

-Brady

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "David A. Frantz"
<spinwizard@f...> wrote:

> Hi Brady;
>
> Hopefully I'm not about to duplicate somebodies else's efforts here

but

> I have comments to your questions.
>
> For #1
> The index feature or pulse happens once a revolution on most rotary
> encoders. Usually the index pulse is valid for a couple of pulses

from

> the sin and cosine signals. You need for the pulse is dependent

on the

> controls you are using. Unfortunately I can't comment on Mach2
> directly. In any event I'd get the encoders if you can with the

Index

> channel.
>
> For your information the index pules provides a high resolution
> reference when use in conjunction with a home limit switch. That

is

> the pulse is repeatable to a small fraction of a revolution which
> linearly can be a very small distance. It takes a very good switch
> indeed to reliably repeat reliably under 100th of an inch much less

a

> thousands.
>
> For #2
> That unfortunately is a very difficult question you ask. Many

things

> come into play including the quality of wiring and shielding.
> Unfortunately many encodes today have what are described as

differential

> outputs but I'd prefer to think of them as complementary. I'm not
> sure how the engineers on this board deal with this but my

perspective

> is that for differential to be of any use it needs to feed some

sort of

> differential buffer.
>
> The problem in many cases with single ended signals, even those with
> complementary outputs, is ground induced noise. It is very

important

> that care is taken to avoid ground loops. You especially want to
> maintain a star arrangement of ground runs. I did mis some of this
> thread but do realize that complimentary encoders may not solve many
> problems at all.
>
> For #3
> Technology with respect to encoders for a long while was changing
> rapidly so I'm not willing to state what the current limits are.
> Often (at least in the past) the leading edge was analog. At the

level

> that most projects here are done though I will go out on a limb and

say

> that there would be no difference other than cost. As to pulse

counts

> there is no difference. On the type of encoders I think you are
> talking about the extra signals are simply complements of what

would be

> considered the main signals.
>
> Dave
>
>
>
> On Mon, 2005-01-31 at 16:39 +0000, braidmeister wrote:
> >
> > 3 Questions still floating out there:
> >
> > 1. Is there any reason why I would need an Index feature on the
> > encoder for the Bridgeport? Doesn't this have something to do

with

> > threading/tapping? (I will be running Mach2...is this a moot

point?)

> >
> > 2. If running sheilded lines less than 8 feet long, is there

really

> > justification to go to a differential encoder? It seems to me

that in

> > the case of US Digital, that it would be a PITA to convert a

shaft-

> > type encoder to my motors...The ideal setup would be a hole-thru
> > design with a 5/8" encoder.
> >
> > 3. If I did select a differential encoder, is there any bearing

on

> > the CPR rating? I mean, would there be a difference between a

1000

> > CPR non-diff and a 1000 CPR differential?
> >
> > -Brady
> >
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, Stephen Wille Padnos
> > <spadnos@s...> wrote:
> > > Polaraligned wrote:
> > >
> > > >I don't know about the one you spec'd out. I did not look
> > > >yours up. Diff encoders have an inverted output also for each
> > channel.
> > > >
> > > >Check this out.
> > > >
> > > >http://www.rutex.com/home/index
> > > >
> > > >Go to bottom of page and download whole pdf document.
> > > >
> > > >It is a great source of info on setting up a servo system
> > > >using rutex hardware. It gives lots of encoder interfacing
> > > >info. Using diff encoders may save a headache. So if the
> > > >cost is small, which it should be, why not use them?
> > > >
> > > >Scott
> > > >
> > > >
> > > I think they changed their website around recently - there's no

PDF

> > > linked at the bottom of the page :)
> > > You might want to put in the name of the file you were

suggesting,

> > or a
> > > direct link to it.
> > >
> > > - Steve
> >
> >
> >
> >
> >
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