Re: [CAD_CAM_EDM_DRO] Re: Fresh run at homebrew DRO

"J. Mark Wolf" wrote:

>
> OK. I bought the digital scales from http://www.calaerosupply.com
> They call them "horizontal quill kits".

A warning: a measuring device with "SPC output" is not the same
as a "digital scale" in the DRO sense. Proper DRO scales have
continuous TTL quadrature output of two signals A & B
(or four signals A,/A,B,/B in the case of differential output)
capable of signal speeds in the hundreds of kiloHertz or even
low MegaHertz range.

Such a rapid output enables suitable electronics (ie quadrature
decoder chips) to track the position and velocity with great
resolution.

SPC output devices usually have a fixed length bit stream output,
capable of emitting only one or two positional reports per second.
This is fine for humans reading an LED output, useless for dynamic
CNC position feedback.

Although I don't know about your devices specifically, I would
think the Mitutoyo has quadrature A&B outputs (not clock & direction),
but I'm just guessing.

The "horizontal quill kits" are probably SPC output (ie a binary
stream of encoded digits), and thus the two are incompatable, and
the Calaero scale useless for quadrature feedback for closed loop
control.

If anyone started making long digital calipers with quadrature output
instead of SPC output, we cnc'ers should throw a party.

(The unstated assumption is that you are trying to use DRO output
for dynamic position feedback, not just 'Digital Read Out' of your
last position when the movement has stopped).

Doug Fortune
http://www.cncKITS.com