Re: CCD

I suggested this a while ago and the opinion then was that the resolution
would not be fine enough - however, I still think it would work and could
even give enough resolution using phototransistors with slit apertures.

Ian
--
Ian W. Wright
Sheffield UK

> Hi Arnie & Jon
>
> I've played around with some ideas on encoders - I was trying to resolve
> angular position, but the idea will apply equally to linear sensors. If

you

> take two films, both with lines at the same pitch and at a slight angle,

one

> film fixed and the other free to move with the slide. If the lines are

arranged

> at equal and opposite angles, you will get ' moire fringes ' set up, as

the

> films move relative to each other so do the moire fringes. All that is

needed,

> is to count the fringes as they pass a fixed sensor. The resultant number

of

> pulse are greater than the number of lines on each film, and by using a

simple

> 64 bit CCD ( TI no. TSL214 ) it should be possible to resolve the position

to a

> few microns. But as the sensor ihas a serial output, the speed would be

rather

> slow.
>
> Regards, Paul.