Strain gauge force sensitivity

[CharleyK]

Hello, I'm new here and that's because I've run into a problem I can't reliable find anywhere else.
I guess I need some personal experience or input from someone.

I'm designing a force sensor for a project of mine, it will be measuring force in three orthogonal directions. Now, I'm confident I can design a platform with the required stiffness in all directions, but the problem is measuring.

I have several options, piezo-electric elements, strain gauges or laser interferometers.
I'm dealing with a force of a few tens of mN and I need a sensitivity of tens of μN. The force is also a very slowly changing force vector, so I guess piezo-electric won't be any good.

From what I gathered, piezo-resistive strain gauges have he highest sensitivity (save for capacitive methods), but most of the time the force sensitivity is a matter of signal amplification. I know a guy who could amplify a normal 2N load cell to a sensitivity of 0.1 mN, but does anyone know/think I can get strain gauges amplified with a 0.01 mN sensitivity without too much drift?

Or maybe know a site/source where I could find some guidelines for determining the force sensitivity of such a setup?

Thanks!
Charley

 

[Baluncore]

I believe you are operating below the sensitivity of most strain gauges.

I would consider using the voice coil assemblies from three loudspeakers. Remove the cone but not the suspension. By optically sensing the axial position of the voice coil you can maintain it's position with a DC current through the coil. Do that for each of the 3Ds and monitor the current needed to maintain position. Those currents are directly proportional to the force components.