DRO

> Thanks James,
>
> I knew about US Digital. I was hoping this was something
> else, as I was looking for a little higher resolution
> linear encoders. (cheap)
>

The USDigital strips CAN be used at much higher resolutions.

The trick here is to NOT use the HP "digital" decoders, but to use an
analog optical decoder ( of some custom design ).

Instead of sensing "fully black" or "fully white", one would
additionally sense intermediate light levels, e.g., "half white". The
number of intermediate levels available would depend on the edge
sharpness of the lines on the strip, but doubling the resolution of the
strips should present no real challenge and even tripling or
quadrupling it could be possible.

Some time would have to be spent aligning the two sensors and for this,
a dual trace scope makes life a lot easier. But alignment presents no
real difficulty, just tedium.

Ultimately, diffraction effects would start to rear its ugly head to
limit the information available via this simple means. Also, it might
be difficult to set up so that each "step" occurs at exactly the same
distance at higher "multiples" than just a doubling.

The thing is, it IS cheap, as you won't be buying the HP parts,
you'll be making your own.

Alan


--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta