Mitutoyo Digital Strips

There is capacitive coupling between the parallelograms and
the opposite surface.
In the calipers (including those from China with a variety of
names on them), the technology is the same. Several years
back, a magazine called "Circuit Cellar INK" had an article
on interfacing to the digital output on an older model of
Mitu. caliper, and a robotics magazine (which I've not seen)
carried an article on how to build your own long spars that
could use the standard caliper heads. Using copper clad
pc board.

I haven't looked at the Mitu. DRO strips, but the Chinese
calipers use right (90 deg) parallelograms aligned
orthogonally with the axis of motion of the slide. Skewed
alignment might permit two or more sensors in the head to
increase resolution.

I suppose one could use Teflon or other zero coeff. of thermal
expansion as the substrate for the PCB spar. I was imagining
my (treasured but as yet unused) linear motor which has
12K steps per inch, as an engine to advance a cutter along the
spar being made.....

/mark


Message: 19
Date: Thu, 16 Mar 2000 00:16:18 -0000
From: "Ian Wright" <Ian@...>
Subject: Re: Re: low cost linear encoders

Hi,

At a slight tangent to these discussions, does anyone know how the
Mitutoyo
digital vernier works? Mine has a bit of the scale torn off at the very
end
and under it appears to be a length of something like printed circuit
board
with diagonal cuts across it. I assume they must use some form of
quadrature
sensing on these copper parallelograms but I can't think of either how
they
would sense the presence or absence of copper without touching it (it's
under the thin plastic adhesive scale) or how they would get the
required
resolution of better than .0001" with something which seems so crudely
made.
Perhaps this method could be adapted for our linear DROs? Making the
linear
strip would seem to be quite possible in the home shop, probably by
making
an indexing jig with a guide for a knife to cut the copper of thin PCB,
and
the fact that it is a non-contact method which is also non-optical
should
mean that it would be relatively immune to the mess around a machine -
certainly my vernier seems to work OK in such an environment as it is
usually lying under a pile of muck in the lathe drip tray and I have to
wipe
it off each time I want to use it (This one's only my rough measurer
which
cost me the princely sum of 5UKP at a boot sale - my other tools get
treated
better!)

Ian

--
Ian W. Wright
Sheffield UK