Re: [CAD_CAM_EDM_DRO] Re: Encoder Indexer Option

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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