> Gray code encoders, if cheap enough, usually are rotary (I never saw one =
linear
> at least). Pretty expensive anyway.

Gray code encoder can be optical or use other sensors
Gray code can be a SINGLE track with multiple sensors spaced along it
in such a way that they between them "see" a gray code. Mathematicians
used to say it was impossible. Nowadays its done. I don't know how
hard it is to get 6 or 7 bits.
BUT if you can use and end of track detector then you need simply two
detectors in quadrature on a single track. Very standard. cf eg
mechanical wheeled mouse. Each axis ha one "track" and two sensors.

36mm / 6 bits is about 0.5 mm/bit. Somewhat fine.

An optical "window" with width affected by position would probably be
easy enough. read light level shining through "window" to get
position.


     Russell



>
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