Somewhat OT - Anyone know optical sensors?

Only 92 here in midcoast ME - just right for swimming all afternoon today .

The obvious questions are how accurate and how fast? And what sort of positioning system?

First off, I'd suggest looking at something more contrasty and sharper edged than paint, especially if you want to use an inexpensive photo- sensor. Some sort of tape flags are my first thought. There are photo- sensors with moderate range and depth of field that can discriminate position precisely on a good edge. Banner makes several sensors using what they call "convergent beam" technology that are inexpensive and can work well in positioning apps. They also make a laser sensor (Picodot?) that's very precise and has greater range.

I'd also look at the low end vision sensors, sometimes called pixel counters, that can locate an edge (light to dark transition) and return a value based on the position of the edge. This would allow faster positioning than a bang-bang system using a simple on-off sensor.

Best bet is get in touch with a couple of the sensor reps and see what they can do for you. I'd start with Banner, Keyence, and Omron, based on the good support I get in this area. There are several others that I'm sure can help, depending on the quality of the local reps.

As an aside, I did some R&D for a dowel mill that was sort of the opposite of your task. We were sensing color changes in the wood itself and trying to correlate that to certain defects which were then sprayed with dye. The dyed sections were culled in a later operation. In that case I was using a sensor that ouput the RGB values of the wood's color.

Ned Simmons

You might want to try:

use their sensors a *lot* and they work quite well (depending on what you actually expect to do). Everything from simple reflective sensors to diode-laser/fiber-optic coupled sensors. FO coupled sensors allow positioning in tight places, BTW.

Joe (in the South Carolina mountains, where it's only supposed to get to 96F today - with a heat index of 105F. Glad I'll be in the NC mountains tomorrow - only 85 forecast)