Abstract
A rotating shaft supported by a repulsive magnetic bearing may contact with a backup bearing during the passage of the critical speed as a damping coefficient of the repulsive magnetic bearing is small. This paper introduced the freedom of inner ring rotation of the backup bearing and developed a model of contact whirling motion between the shaft and the backup bearing which considers both slipping and rolling conditions and transition between them. The contact vibration is investigated and it is clarified that the slipping forward whirling motion occurs in the case that the inner ring is not rotatable, the rolling forward whirling motion occurs in the case that a damping of the inner ring rotation is small. On the other hand, in the case that a damping of the inner ring rotation is large, the rolling backward whirling motion occurs with high whirling speed, and this backward whirling motion keeps existing when the rotational speed reaches to the lower side of the critical speed during deceleration. This result is validated experimentally. Furthermore, it is clarified that the rotational speeds of the escapement from the contact vibration change along with an axial displacement of the repulsive magnetic bearing.
