HI guys, I'd like to know if someone has already done a capacitive sensor for detecting plastic objects (range 1-4cm), my intention is to build a robotic arm that holds plastic objects if it detects one, I'd be very grateful if you could show me a diagram that you may have used on any projects you have developed.
There is certainly no problem discriminating aluminum from plastic -- an inductive proximity sensor will do that. Here are some commercial examples (but you can make your own): Tubular Sensors | Allen-Bradley