Prediction of track misregistration due to disk flutter in hard disk drive

Disk runout consists of repeatable runout (RRO) and nonrepeatable runout (NRRO). NRRO is the main cause of track misregistration that prevents a high track density, whereas tracking servo control can compensate for most of RRO. An increase in the disk rotation speed increases the amplitude of disk flutter and, hence, causes head position error. Disk flutter is mainly caused by air disturbance due to disk rotation. Many previous researches have intended to investigate the vibration characteristics of rotating disks and the head off-track mechanism. They have used the head position error signal in servo system and approximate solution of head and disk dynamics using finite element modeling for a stationary disk to investigate the head position error. In this paper, the displacement spectrum is obtained by integrating the velocity data and removing the low-frequency component associated with integration noise. The axial displacements are converted to radial track misregistration units by modal analysis, the reformed Barasch method, and experimental study of the disk. The interaction between head and disk is precisely solved, and it becomes possible to predict the track misregistration by analyzing the disk flutter and transfer ratio for various disks.