I have to detect the position of a plastic bottle tap in a tray. The tray is 60 x 60 cm (2ft x 2 ft). The bottle tap is 1 cm (0.4 inch) diameter and is always in the correct position, that is with the internal threaded mouth to the tray.
I can manufacture the tap with any component inside or any drawing in the external surface.
The question is: which is the most economical technology to locate the position of the tap? magnetic? code bars and laser beam reader like in the supermarket? black and white vision? others?

 

If you only want to know if it's in a certain spot, a regular fixed focus photoeye would probably work. I know Allen Bradley makes a one called a minisight.