Linear Motion

I'm trying to find a way to precisely measure one dimensional linear movement, resolution of at least 0.01 mm over a 1 m range.

I will demonstrate my lack of understanding of electronic principles, I know some, but not near enough, and application is difficult.

I had first envisioned using an infrared diode transceiver to send a carrier signal to my device in motion, which would bounce the signal back to the receiver. I was expecting that at every 1/2 wavelength of the carrier, I would take advantage of the superposition principle of the incoming and outgoing waves and be able to use Arduino to count the nulls and maximas at the receiving diode. Of course this turned out to be silly. It's probably silly for more reasons than I can imagin, but I suspect that the receiving diode will not experience the superposition of carrier waves and will just receive the fully reflected signal.

Then I had thought that I would send a pulse IR signal in the same manner as above, this time measuring the phase change of the pulse signal. Again, this is silly, but might actually be a viable means of measure, if the equipment was capable. I would still really like to understand how phase or even short timing differences between a generated pulse and pulse reception on another pin...

So now I am left at square one looking for ideas on how to measure these small changes in distances.

The diode will see the superposition but only if the IR is coherent, which it will not be unless it is a laser. Also the dimensions of the sensing junction has to be small compared to the wavelength of the radiation which it is not.

That sort of precision over that sort of distance is by no means an easy thing to acheave.

Wow, thanks for the quick reply. By coherent, I think you mean the signal would need to have a constant phase relationship, and/or be a single frequency?

When I started looking into this, I came across some theories in interferometry and realized that I'd need to be able to measure the incident signal and not the detected signal.

I've got a 6-inch digital caliper (about 150 mm). It reads down to 1/1000th of an inch, which should be 0.025mm if I've done the math correctly. It probably doesn't have 1/1000 accuracy over the entire distance (espeically since I've never had it calibrated), but it does have 1/1000th resolution.

It works mechanically with a gear (or wheel), so something inside is counting rotations. If you can get the mechanical accuracy, that same concept could be extended to 1M. In fact, you can buy a [u]1M caliper[/u] if you have the budget...

It shouldn't be too hard to build a wheel/gear system with 0.01mm resolution, especially if you can move in one direction after zeroing to eliminate play & backlash. But getting 0.01mm accruacy over a 1M range might be beyond anything the average machine shop can build... Which means you probably don't really need that kind of accuracy over that distance...

The Starrett caliper is about the cost of 50 Arduinos! While it is a good name brand product, it's accuracy over range is 0.40 mm (and yours would be 0.30 mm, or about 0.012"), best case.

Nevertheless, I likely would be happy with even 1 mm of overall accuracy, and I could most likely program a correction.

DVDdoug:
It works mechanically with a gear (or wheel), so something inside is counting rotations.

Electronic calipers measure capacitance change as they move, not count rotations.

Indeed, they are a clever technology - but the device you are looking for is a "electronic scale"
or "linear encoder" - they use several possible technologies from capacitance, optical moire fringes, some
use a magnetic method.

I think I've seen both kinds, but I'm not an expert on those. I have an older fashioned one with gears and a needle - never needs a battery and seems to repeat very well.