Are Computer Stereo Vision techniques appropriate for sub-millimetre measurements?
Stereo imaging

Given the large field of view you need in relation to the accuracy you want, and how close you want to be, I think that stereo imaging may be a challenging, so you need to somehow amplify the differences you are trying to measure.

Structured lighting

If you are essentially trying to measure the profile of an object, have you considered a single high resolution camera and structured lighting?



Thanks to looptechnology for this image, used without permission, but hopefully attribution will be enough.

Note, the shallower the grazing angle, the the greater accuracy you can measure, but the lower the supported depth of field would be, so for your application you would need to optimise for your needs or make your system adjustable (one laser angle for 0-500um, another for 500-1500um and so on). In this case though, you would probably have to calibrate each time you changed laser position.

Incidentally, a very cheap way to try this out would be to pick up a pair of Laser Scissors which include a basic line laser LED.

Finally, you can remove the vibration problem by sampling multiple times, rejecting outliers and then averaging. A better solution though would be to mount the whole test apparatus on a block of granite. This worked well for laser micro-machining tools I've worked with in the past, which require micron level position and depth of focus accuracy, even when located in factories.

Some back of the envelope calculations.

Lets assume an incident angle of 10 degree from horizontal, and a camera with a 640x480 resolution and a field of view of 87 x 65mm. If we place the beam so that it is right at the bottom of the portrait frame with no sample, and then place the sample with the beam crossing it, this should give us a maximum height of around 15mm and thus an uncorrected resolution of around 24um for each pixel the line walks up the screen. With this setup, a 0.1mm variation should be visible as a 4 pixel variation in position.

Similarly, if we use an incident angle of 2 degrees from horizontal then this should give us a maximum height of around 3mm (Tan(2deg)*87mm) and thus an uncorrected resolution of around 4.7um per pixel, for a much more noticeable 20 pixel jump. This would probably require a much more accurate line laser however.

Note, if the camera is close enough then the you may need to do a second trig calculation, using the camera height, to determine the the true position of the line relative to the base line.

Also note that if you don't need absolute accuracy, and local repeatability is enough (say you are profiling the flatness of a sample to ensure it is within given tolerances) then just being able to see the relative position of the laser line might be enough.