Re: [CAD_CAM_EDM_DRO] glass scale alignment

On Fri April 28 2006 23:53, you wrote:
Hi Jon,

> Denis Casserly wrote:
> >Hello,
> >I have a pair of ' Metric 01 MM ' glass scales and I can't get the reading
> >head aligned properly with the glass scale so that it will output a
> > reliable signal. I can move the head along the scale by hand and it
> > seems to read accurately but I can't find that sweet spot when I put it
> > back on to it's bracket. The bracket doesn't appear to be bent or loose.
> > Would anyone know how to set up the reader head alignment.
>
> If this is the typical glass scale encased in the aluminum extrusion

Yes, it looks like a glass scale in an aluminum extrusion and the glass is
clean and looks to be well protected by a pair of full length lip seals that
cover the slot where the read head goes in. The light source and the
photodetectors were really dirty and I've already cleaned them.

> then the external
> alignment is generally isolated from the internal alignment by some kind
> of wire
> or metal strip. > Would you know what the alignment procedure is for the
reader head? This allows slight misalignments between the spar and
> the machine
> slides without putting large forces on the read head. The read heads
> ride on teflon
> gliders or tiny ball bearings. Some cheap scales are actually designed
> to self-destruct
> after a certain amount of linear travel. The teflon sliders wear down
> until the
> read head scrapes the grating off the glass scale. Keeping the insides
> of the scale
> clean greatly extends the life of the unit.

The read head looks like it rides on white (teflon?) pads and I guess that
they have to ride on some sort of reference track inside the extrusion which
holds the scale - right? If that's the case I'll try to find that track that
the pads ride on. The alignment looks like it a set of 4 grub screws and 2
large clamp screws in an intermediate plate between the read head and the
read head mounting bracket on the travelling axis. The adjustment setup looks
like it will rock the head around relative to the scale.
>
> The analyzer grating in the read head needs to be VERY close to the
> scale, on the side with
Yes, I can get it the read head to output by detaching it's mount, moving it
around until I can get a reading, and moving it up and down the scale after I
get the relatonship correct. So I think the head will read and it's an
alignment issue between the head and the glass scale.
> the grating on it. Some scales can be assembled backwards with the
> analyzer on the
> plain side, and the light source on the side of the scale with the
> grating. This won't
> work. Most of the medium-resolution scales are not that critical on
> alignment, at least
> to just produce quadrature signals.
It hasn't been disassembled so I guess the scale is mounted right side up. It
worked OK for over 10 years the way it was.
>
> You don't give us much info to work with. No make or model, not even a
> description
> of how the read head is kept aligned with the scale. I've never seen a
> good scale
> for machine tool applications where the read head was simply mounted to
> one part
> of the machine and the scale mounted on the other. Accu-Rite, Sony,
> Mitutoyo, Teledyne/
> Gurley, etc. all use some scheme where the read head rides on something
> within the
> spar, and a link to the machine drives the read head back and forth.
> This scheme
> always allows a tiny bit of hysteresis, but if the link is stiff and
> straight, it allows the
> machine to not be quite perfectly aligned or even travel in a straight
> line without
> possibly ramming the head into the scale, and yet have the two move
> together in
> the machine's axis of travel.
I've never heard of the manufacturer before, the only information that I can
get off the scale is: ' METRIC 01 MM ' . Other than that there's nothing else
on the scale or the read head. Here's the nameplate data off the Anilam DRO
Model # 102-2, Serial # MW8121671, is that of any more help? I'll try to
locate the spot where the teflon pads contact, the wire or track that you
referred to earlier, perhaps it is broken and the read head can't get to the
location where it will read the glass and output reliable data. Is it
possible that the reference track is a tiny wire rope that's pulled taut
inside the extrusion. I think that there was one hanging off the machine from
the vicinity of the glass scale.


cheers,
Denis

>
> Jon
>
>
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