Doug and Eric
Don't know how heavy your set up is, but you might also be able to move the bug and get satisfactory results. Some of these positioners will work with big loads
I am a design, test and development, agricultural, electronic and software engineer, and once contemplated a career in the robotics industry. I am now setting myself up as a photographic solutions provider, specializing in "anything you cannot do with a DSLR".
When the subject is smaller than the camera, move the subject... and this avoids false perspective through changing the magnification
You do not even need a good tripod, as you can use a Sinar monorail system as an optical bench: you can mount a small subject like a slide copier attachment on a spare rear standard.
There are countless cheap and simple ways of producing the small movements you want, and a simple G-clamp type digital or mechanical micrometer (with the spare jaw cut off), would let you produce and measure the movements.
If you want smaller movements, you can use an epicyclic reduction gear box (or clock mechanism) to drive the micrometer or Sinar focusing knob.
You can use a standard mechanism that produces very slow movements, and control the focus slice size with a timer: a grandfather (long case) clock weight moves about a meter in about eight days - this would be slow enough for most applications!
A ratchet system (or clock escapement mechanism) might help, or a Weston differential pulley system could produce the required high velocity ratio, small movements.
