Re: [CAD_CAM_EDM_DRO] Just How Accurate Is CNC?

> I can well understand the cost issue, but motion measurement has
> changed in the last few years. Much has been done with inexpensive
> lasers. I do not know a whole lot about it, but it seems that if I
> can buy a optical mouse for $5, there might be a more precise version
> of a laser measuring device that could be mounted to the bottom of a
> table to precisely read table movement. The optical mouse is not that

The motion tracking of an optical mouse is nowhere near linear, and
certainly not reproducible. You'll need a high-quality high-resolution
reference which spans the entire length of the linear actuator, and
new detection software as well. It gets very tricky to say the least,
especially if you're looking for resolutions of 0.001" or better.

> surface could be much more consistent. Or you might use a laser in
> the saddle reflecting off the end of the table and measure the
> trip-time per pulse.

Not really. To resolve 0.001" of saddle movement, you'd need a time
resolution of about 150fs (1fs = 0.000001 ns). Good luck...

You can use interferometry, but that gets very expensive because you
not only need a very good laser for it (coherence length much bigger
than saddle travel) but a complementary method for course measurement,
unless you always want to move your saddle at about 0.1 IPM or
slower.

Andras