3 ms·
Very large digital scales for digital readouts (DROs) on machines like manual lathes and mills actually do use quadrature optical encoding via etched glass scal
by mk_stjames 4y ago
Very large digital scales for digital readouts (DROs) on machines like manual lathes and mills actually do use quadrature optical encoding via etched glass scales inside aluminum housings, similar to the light gate on a scroll wheel of a mouse, but instead detecting fringe pattern light/dark from the etching in the glass scale. The etching is typically 5 microns in spacing, so a resolution of 0.005mm, or sometimes smaller. Because the glass is very stable this can be pretty repeatable over large distances.
- jbay808 4y agoJust to expand on that, usually the etched scale pitch is 20 microns, but digital quadrature detection gives you 4x the resolution of the scale pitch, resulting in a 5 um distance between successive rising / falling edges of the quadrature signal. Analog measurement can be used to interpolate to much finer resolution, even 1 nm for good quality optical scales with good electronics.