Can you pass a small current through the screws and detect when the longer ones touch a metallic surface and complete the circuit?Is it possible that the disturbance of the head of the longer screw (as shown in your image) could detected by a camera because it would reflect differently....R
Put a small leaf spring over the track that only touches the head of the screw under test and lightly holds it down. Pass the current through the spring to the head.
I would go for an optical sensor under the screws. The QRE113 is really easy to use and easy to calibrate looking end-on (vertical-up) to the screws.The picture is helpful because it shows you have pointed screws. That won't work so well with an end-on looking sensor. A beam-break type sensor will work. Something like the laser beams you see in heist movie vaults. You don't need a laser. Just a thin slit to control the dispersion of the light.Beam-break sensors can be bought with both halves embedded in a housing. There's a slot that you pass the thing to be detected. Just set it up with an adjustable height and calibrate with known screws.
First off thanks for the image thing. I'm new around here obviously but I'll try and pick up on the SOP. These are both interesting suggestions. My initial reaction to the low current (how many volts do you think?) is that it shouldn't be a problem, as in should not damage the parts, I would just need a way to attach something wires or something else charged to the track of the belt, or make a metal belt system. The second option seems a little more difficult, only because the change is still pretty small, and I don't know much about measuring / detecting reflections?
So you're suggesting something like the KY-010 sensor? Or am I thinking this is something different than it is? https://tkkrlab.nl/wiki/Arduino_KY-010_Optical_broken_module
bluejets, the hall effect sensor looks interesting, but I don't know much about it or how it would work? Could you describe why I need to mount a magnet on the back face? And when you say specific range is this like 1mm or 1 inch? Or is it a trial by fire thing once you get it setup?
(I'm guessing steel)
The Original Post mentions Titanium. I can't see anyone taking this trouble with steel screws Of course, if this is a quality control issue I wonder why not reduce the manufacturing size by 0.5mm so they are all between 3.0 and 3.5mm - or increase it so they are all at least 4.0mm...R