Displacement probe

Flexure mechanism that helps turn a cheap photo-interrupter and a razor blade into a repeatable displacement sensor. The dual diaphragm flexures constrain the motion of the razor blade such that it moves in a very repeatable linear motion....aka good stuff :)

For less than $10, I've consistently seen on the order of 1 micron of repeatability…granted, this also requires some care on the electronics side of things. Also, if you don't have some pricey calibration gear on hand, it may be tricky to actually make use of that repeatability, since these photo-interrupters aren't always all that linear.

I'm not sure how much interest there is in these sorts of things, so I didn't think it worth a detailed "how to", but if anyone is interested in knowing more, hit me up!

When constructing the finished probe, the easiest way I've found is to go ahead and secure the razor blade into place (I use CA/super glue, but I'm sure there are plenty of great options, if you find one, please let me know!)

Then go ahead and wire up the photo-interrupter (yes, even though it's not installed.) You're going to want to be able to watch the output voltage from the sensor 'live'.

You can then position the sensor in its groove and slide it forward until it's positioned at the edge of the travel range (make sure it's the right edge :) ) Then glue down the sensor while being careful to hold it in place (may want to make a little jig if you're using a slower cure adhesive, but make sure it's a stable jig!)