Control Scheme of RRO Compensation for Track Mis-registration in HDDs

Abstract

Hard disk drives (HDDs) which can store of large amount of digital data are supporting information society. To read/write the digital data on the disk, the magnetic head must be controlled precisely. The data is recorded as concentric orbits called as tracks on the disk. In the controller design, servo engineer must evaluate track mis-registration (TMR) for the reliability. The TMR is one of criteria of relative positioning accuracy for the tracks for risk assessment of data incorrectly writing. The risk means that the magnetic heads write on the different track from the target track. The relative positioning accuracy in the tracks should be improved to decrease the risk. In this paper, we have proposed a control scheme to compensate of repeatable runout (RRO) for the TMR. In the proposed control system, we distinguished the RRO by “synchronous RRO” and “asynchronous RRO”. Two types of RROs are compensated by using an adaptive feedforward cancellation (AFC). The AFC is designed to generate the suitable compensation signal for each type of RRO, and the proposed control system improves the relative positioning accuracy. The effectiveness of the proposed scheme has been verified by using a HDD benchmark model developed by IEEJ Industry Applications Society.