Re: Building A Cheap DRO

Has anyone looked at the Agilent Optical mouse encoders?

For the ADNS-2051 they quote 800 Counts per Inch and a maximum linear
movement of 14 inches per second. The advantage might be it tracks x
and y from one sensor with no physical contact to the table and is
cheap. Downside is resolution might not be up to spec for some
situations - but for $15 what do you expect.

Richie

--- In CAD_CAM_EDM_DRO@y..., Russell Shaw <rjshaw@i...> wrote:
> Has anyone tried photographic methods to put lots of
> black lines around the circumference of a plastic disk
> to make an optical encoder? How are long linear encoders
> made?
>
> Raymond Heckert wrote:
> >
> > I'd be greatly concerned about the amount of tension you need to
have in
> > the wire that's wrapped around the encoder shaft. Most rotary
encoders are
> > designed to handle only very light "side-loads". Also, even at 1
inch of
> > wire wrapped per rev, how many turns of wire can you even put on
the
> > shaft?? You probably only get 20" of travel, max. And don't
forget about
> > the "sweep-angle" error that would be induced. Also what keeps
the wire
> > from "piling up" as the sweep angle gets greater. I'd worry more
about
> > these things than the dia of the "pulley" (shaft), or the
uniformity of the
> > wire dia. There must be better ways of doing this ...for what
it's worth.
> >
> > RayHex
> >
> > ----------
> > > From: cutsgems <chuknospam@a...>
> >
> > > I'd like to add a 3 axis DRO to my mini-mill. I've investigated
the
> > > Calareo/Wholesale tool import digital machine scales & readout
box,
> > > nearly $500 to cover all three axis. So what I had in mind was
some
> > > encoders from US Digital, something like 2000 PPR?? to get
0.0005"
> > > resolution, use a simple wire under tension wrapped around the
axle of
> > > the encoder to convert the linear motion to rotary. Use an old
laptop
> > > & printer port & available software for the readout.
> > >
> > > My questions are the mechanics for the encoder.
> > > Would a 1000 PPR encoder give me the resolution required if I
used
> > > 0.6369" diameter hub on the encoder as opposed to a .3183
diameter hub
> > > which would only yeild a .001" resolution. Or am I better off
using a
> > > 2000 PPR encoder with the .3183 hub? (The .3183 is a rough
calculation
> > > required to convert 1" of travel into 1 rev on the encoder).
> > >
> > > Secondly, when calculating the hub diameter, how do I account
for the
> > > wire diameter in the calculation? Is it 1/2 the wire diameter
+/- the
> > > hub diameter???? Thanks.