🚀 go-pugleaf

"Cory Seligman" <coryms+google@azazel.eng.monash.edu.au> schreef in bericht
news:a64581c0.0309242126.7a4fe4ee@posting.google.com...
> Hi all.
>
> I've successfully made a linear optical encoder with a stroke of about
> 25cm using a flattened steel rod with a nice shiny surface, and gluing
> on a laser printed transparency with a pattern of stripes. This works
> find with a 1mm pattern, and a homemade detector. The detector is an
> IR LED, a small lense and a Honeywell HLC2701 encoder detector
> chip/opto thingy.
>
> No worries, except it's fiddly. The lense and detector and pattern
> have to be adjusted just right, and it's hard to put together.
>
> So I got some Agilent HEDR-8100 detector chips. they have the lenses
> built in and do all the hard work for you. The only problem is that
> they're 150 lines per inch, which is more than I can do reliably on a
> laser printer. So I'm looking for alternatives.
>
> Does anyone know of somewhere I can get stripes like that printed
> directly on the steel? Or etched?
>
> Any thoughts on producing a clear strip with black stripes
> photographically?
>
> Or maybe a replacement reflective optical encoder detector that works
> on a 1mm stripe spacing? As far as I can tell, the Agilent one is the
> only device of its type.

If you place a transparent filter on top, also printed with 1mm stripes,
you don't need a very well adjusted sensor. When the rod with the stripes
move behind the filter, even you can clearly see that it moves. Most
optical encoders work like that, makes them get away with pretty coarse leds
and fotodiodes.

Situation 1:
# # # # # # # # # # # # # # # # # ROD
   # # # # # FILTER

    ^^^ looks like 100% black from this point


Situation 1, rod moved a bit:
 # # # # # # # # # # # # # # # # # # ROD
   # # # # # FILTER

     ^^^ looks like 50% black from this point


Place two filters with the stripes 90 degrees apart for A & B signals.
The effect is named after Moire, it's inventor, I think.

-- 
Thanks,
Frank Bemelman
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