Axial Transient Vibration of Polygonal Mirror Scanner Motor Supported by Thrust Magnetic Bearing and Radial Air Bearing

This paper describes an axial transient vibration of a polygonal mirror scanner rotor driven by a flat type brushless DC motor and supported by an axial magnetic beaing and a radial air bearing. From results of theoretical and experimental investigations, the following characteristics of the vibration and measures to suppress a static displacement and the transient vibration have been deduced: (1) Repulsive magnetic force is induced between the stator coils and rotor magnet under current passage. The force causes axial static displacement and axial transient vibration. (2) Parametric investigation deduced that; (a) high stiffness of the magnetic bearing and low acceleration current linearly reduce both the static displacement and the transient vibration, however, the former may reduce a lifetime of the air bearing due to a dry contact at the start and stop operation and the later prolongs the startup time ; (b) soft start-stop scheme of the motor current is effective to reduce the vibration.