Code writing system for production of magnet-readable code on surface of cylindrical object involves laser producing intense switchable beam locally changing characteristics of magnetic surface layer

摘要

The cylindrical object (2) may be moved so that the code is written in a spiral resembling a screw thread. The switchable laser (6) produces an intense focused beam (8) which locally heats a surface layer of magnetically conducting material with low magnetic remanence. Heating by the laser beam transforms the material to a poorly magnetically conducting material with high magnetic remanence. A series of dots and dashes may form the magnet readable code (4).