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

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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