Abstract
As the recording track density increases in hard disk drives, the ball bearing in the actuator pivot would only rotate a few micro-degrees during track following and short seeks. In this paper, the behavior of the friction torque of the ball bearing under micro motion was studied. The investigation showed that the change in the direction of the rotation did not result in a reversal of the friction torque and hence, not forming the torque hysteresis loop when the ball bearing oscillation was less than a certain value. The friction torque was observed to keep to that value rather than dropping back to zero, though the direction of rotation of ball bearing changes frequently during track following. This impacts the servo controller design.
