The magnetic induction line can produce a high frequency alternating magnetic field, non-ferrous metals is a good electrical conductivity, so to the magnetic roller surface when transported by belt inside the metal induced eddy current, the magnetic field produced by the eddy current magnetic field and the original direction is opposite, so will form a strong repulsive force, magnetic roller exclusion was to far away places, using magnetic roller circular cylinder shape can be separated in a fall, achieve the purpose of separation.