pegasixi:
I want to come up with a digital or gentle mechanical solution to finding the edges of the foil as it winds up. The sensing needs to be done on the foil plane BEFORE its wound into the roll.
(so that I can ensure that the strip stays perfectly centered)
I'm guessing that the underlying requirement is to end up with the material centered on the roll after it is wound up, and I wonder whether it may be possible to come up with a scheme to make the foil self-center rather than measure whether it's off-center and then try to do something (what?) about it.
Unfortunately, without having any idea of where the foil is coming from or to or what the physical properties are, I can't begin to guess how you'd achieve that.