Separate drive and metrology structures

Has anyone here built a machine with separate drive and metrology
structures? I was just reading about a diamond turning lathe at Livermore
labs of quite large size, > 1 m swing, I think. It had separate structures
for the drives and laser metrology.
This makes a lot of sense to me. If the feedback was quick enough it could
act even though the drive structure was flexing, if the metrology structure
maintained its accuracy.
So vibration, constant load, and thermal strains would be less of a problem
with this sort of design.

Since most of us don't need microinch level accuracy, maybe the principle
could be used to make much lighter machines without comprimising accuracy
and finish.

Elliot Burke