Nonlinear dynamic model of a pivot ball bearing in hard disk derive including the Hertzian contact force

Abstract

In the history of hard disk drive there are steadily increasing magnetic recording density. The head-positioning control should be more high accuracy because of the high magnetic density in hard disk drive. Previous studies of head-positioning control are considered pivot friction torque or dual actuator control system. These are not considered structural characteristics of pivot ball bearing. A nonlinear dynamic model of a pivot ball bearing is presented in this paper, considering contact between balls and an outer race when slider is seeking. The Hertzian contact equation is used at the contact points. The pivot ball bearing differs from other ball bearings in that it is combined an actuator and rotates at seeking velocity profile. Therefore, the modeling is considered a change of the center of mass and also seeking velocity. It is hard to measure directly displacement and velocity of the outer race by using laser-Doppler vibrometers because of actuator. Therefore, measurement location is replaced by a small cylinder which is adhered above the outer race to measure. To verify a new pivot ball bearing model, this paper makes a comparison between the modeling and this result which is compensated for motion of the cylinder at several seeking distance. © 2015 by ASME.