On Fri, 22 Nov 2002, Chris Loiacono wrote:

*>Does anyone know what technology is used on the DRO's used on metalworking
*>machine tools?
*>The ones I had used what they called "glass slides", one for each axis. I
*>never took one apart to look closely, but I have searched for this and come
*>up short. I would think this would make an interesting PIC project for all
*>of us with home workshops....
*>Chris

A glass slide is a just what it says. A band of glass with lines scribed
on it at fixed intervals, usually 50 microns. There are several kinds
(absolute, relative etc). A specialised optical sensor reads these
encoder-like (sin, cos) with some models allowing for interpolation for
higher precision. A close equivalent is the device used for this purpose
in some HP (695C ?) printers which can be had for cheap surplus (due to
expensive ink). Interfacing to a PIC is no problem.

Other less often used DROs use potentiometer+string and encoder+string.
These work well but precision is limited. They are used when there is a
lot of gunk in the work area.

Peter

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