Re: [CAD_CAM_EDM_DRO] Re: How to establish repeatable home position w/steppers?

Rick: I guess that I was not clear in my description. One switch is
triggered by table movement and once that switch is triggered it looks
for the next index pulse from the encoder. That index pulse will only
register at one point and that is when the table has moved to the
position that trips the first switch. It does not count any pulses.It
will be the same place every time unless your belt skips a tooth.Does
that make more sense?
Carey

Rick Dulas wrote:

> Howdy! It occurs to me that using an encoder on the motorshaft as the
> reference for the home position doesn't tie home to any particular
> point
> in space. Wouldn't it be better to have "home" be an independently
> located point? Imagine that we move out 30 steps in the X dir and then
>
> return those 30 steps back to our departure point. We then declare
> that
> we are back where we started from because we counted our steps. This
> lacks what cartographers call "ground truth".
>
> I would prefer to establish "home" independently of the means of
> movement, and check that my 30 steps really brought me back "home".
> But
> maybe I don't have enough faith. <G>
>
> Rick Dulas
>
> dougrasmussen@... wrote:
>
> > Dave,
> >
> > .0002" is getting into the ballpark. .000125" is my theoretical
> > resolution so that's what I'm shooting for.
> >
> > Maybe some sort of encoder device on the motor shaft would be the
> way
> > to go?
> >
> > thanks,
> >
> > Doug
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@egroups.com, dave engvall <dengvall@n...>
> > wrote:
> > >
> > >
> > > There has been some discussion of limit switchs/home on the list
> in
> > the last month or so. One person was getting a thou or so out
> > > of micro-switches ( he did not state his limit of resolution) and
> I
> > get 0.0002"repeatibiliity from hall effect devices. They might
> > > be better than that but that is my resolution limit. :-)
> > >
> > >
> > > Dave
> > >
> > > dougrasmussen@c... wrote:
> > >
> > >
> > > > Group,
> > > >
> > > > On an open loop stepper system how do you establish a repeatable
>
> > home
> > > > position? I'm thinking of a home position that will repeat to
> > within
> > > > the resolution of the machine.
> > > >
> > > > I can't see that normal, every day limit switches will do the
> job.
> >
> > > > Dial indicators would be a pain, but would work provided they
> > didn't
> > > > get bumped or readjusted. Some very old machines used a vernier
>
> > dial
> > > > which was manually stepped to position.
> > > >
> > > > So, what method are most of you using?
> > > >
> > > > thanks,
> > > >
> > > > Doug
> > > >
> > > >
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> Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the
> discussion of shop built systems, for CAD, CAM, EDM, and DRO.
>
> Addresses:
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