Re: Optical film for use with DROs

>You don't need a HEDS unit if you can do what you have done. All you
>have to do is make 2 fixed gratings with the same line pitch as the
>scale but one offset from the other by 1/4 line pitch. Place two
>narrow angle LEDs above and two phototransistors underneath. The
>fixed gratings will act as a shutter to the movable scale grating as
>long as the distance between them is very small or the LED light beam
>is collimated (narrow angle output). The phototransistor outputs will
>be in quadrature.

I tried this when I worked for a company that wanted to produce joysticks for
use with Macs, using optics instead of pots.

We had ENORMOUS problems with scratching when placed emulsion to emulsion.
It didn't work at all when placed the other way 'round. Apparently, that
small difference in spacing was enough to mess up something optical.

This with much larger lines and spaces than we're talking about here.

We eventually ended up sending each roll of film to Hollywood ! where the
film was coated with something magic. It wasn't a forever solution, but
did last long enough for the average user.

I think the fact that USDigital is having so much trouble with their
500 line linear encoders and that no other manufacturer of encoders ever
came out with a product this fine is interesting, and should be noted.

Funny things start happening to light right around spacings like this ...

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