Am a student doing my masters....well me and my professor are designing a testing machine which is more like a milling machine but doesnt remove material but test few things.....what my question is...is there any mechanism in which the travell of Z direction is really low...that is in microns...if yes please lemme know....I request you people to help me out in this process

thanks in advance.....

The stepper motors most of us here deal with in converting our milling machines have a .001 inch movement per step(200 steps per revolution), .0005 per half step(using .200 pitch ballscrews). To build a machine that only moves 1 micron would need a 13 to 1 pulley ratio (using half step). A 10 tooth timing pulley on the motor with a 130 tooth pulley on the feedscrew. On paper this would work but hobby machines aren't anywhere near accurate enough to hold these tolerances. Using finer pitched feedscrews would lower the ratio. If you have the money these Nanostep Microstepping Motors from Oriental Motor would be what you are looking for.
http://catalog.orientalmotor.com/viewitems/stepping-motors-motor-driver-packages--1073/nanostep-cfkii-series?&plpver=11&forward=1&backtoname=&pane=
They have resolution settings up to 125,000 steps per revolution.
You might find something used in the medical field at a surplus site or Ebay.
Hoss

What force or speed is involved?
For example a servo motor with say a 2000p/rev encoder would give you a pulse resolution of 2000x4=8000p/rev at the motor, If you had a .25 lead ball screw coupled from the motor with a 4:1 timing belt reduction, this would give you a resolution of 7.8 microns, you could decrease this if you wish.
Al.

They might be too fine, but piezo-electric elements have been used for such things as tunneling electron microscopes and fringe locking circuits for lasers. In the microscope they use a stack of them to get range.

http://www.geocities.com/spm_stm/Disk_Scanner_Exp.html
http://sxm4.uni-muenster.de/stm-en/
http://www.xmission.com/~ralcon/whylock.html

Another method which might be too fine also is using thermal expansion of a rod between known temperatures. A system based on this is used in Microtomes for cutting very thin sample slices for transmission eletronmicroscopy.

Thanks alot guys for the responses u have given in this short span...i really thank you guys from the bottom of my heart....

The thing which we are testing are pretty much soft materials like a tissue paper etc.....so there may not be much force applied on it and using a belt will indeed increase the vibrations....so using a servo will serve our purpose but do you think its apt....if yes i need a servo which can traverse my z direction to a fine resolution 0.2 microns every interval(say 4 intervals)...is der any thing of this kind...if yes please do reply or do give us any new mechanism which we can go with...

i really appreciate u guys for helping me.....

Thanks...

I work on a Kern Micro Milling Machine at work that has a repeatability positional accuracy that is in the micron. It's servo driven with a heidenhein glass scale with an acurracy of .1 Micron. Kern also has a Nano Machine that has a positional accuracy at .3 microns and I believe that they utilize a hydrostatic drive system. Hope that helps.