An electrophotographic printing apparatus includes a laser or comparable image-forming apparatus which produces an image on a rotating drum having a metal core. Electrostatic images formed by the laser or the like are toned by a toning mechanism that includes a rapidly rotating magnetic core. To prevent...http://www.google.de/patents/US5063399?utm_source=gb-gplus-sharePatent US5063399 - Electrophotographic apparatus having reduced drum drive flutter
