Digital sector servo incorporating repeatable run out tracking

Details Digital sector servo incorporating repeatable run out tracking Digital sector servo incorporating repeatable run out tracking

1994-06-22

1996-12-17

Psitos, Aristotelis

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

360 7809, G11B 5596

Patent

active

055859763

ABSTRACT:
A digital servo control system for controlling a disk file head includes a main control loop at least one head for reading servo information; a voice coil motor (VCM) attached to the head for positioning the head relative to the target track centerline of a track in response to a VCM control signal; means for deriving from the servo information a digital head position error signal (PES); and a processor employing an estimator model for estimating parameters of the VCM and for generating from the estimated parameters and the digital VCM control signal. A secondary control loop receives the PES and provides a compensation signal for repeatable runout (RRO) by providing high open-loop gain near the spindle rotation frequency of said disk. The compensation signal for repeatable runout (RRO) is added to VCM control signal. The secondary control loop includes two states x.sub.a and x.sub.b with state equations x.sub.a (k)=x.sub.b (k-1)-k.sub.1r e(k) and x.sub.b (k)=2 cos .omega.Tx.sub.a (k)-x.sub.a (k-1)-k.sub.2r e(k), where k.sub.1r and k.sub.2r are the feedback coefficients for the states e(k) and e(k-1) respectively and the control signal u(k) is the summation of the VCM control signal and x.sub.a (k-1), which is written as u(k)=VCM control signal+x.sub.a (k-1). A compensation module for repeatable runout error includes: a first feedback scaling block having a gain coefficient of k.sub.2r ; second feedback scaling block having a gain coefficient of k.sub.1r ; a first feedback block having a value of 2 cos .omega.T; a second feedback block having a gain of -1; a first unit delay for delaying x.sub.b (k); a second unit delay for delaying x.sub.a (k); a first summer having an output x.sub.b (k)=2 cos .omega.Tx.sub.a (k)-x.sub.a (k-1)-k.sub.2r e(k); a second summer having an output x.sub.a (k)=x.sub.b (k-1)-k.sub.1r e(k); a third summer for combining the VCM control signal with the output of the second unit delay to provide a modified VCM control signal which includes compensation for repeatable runout.

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"Magnetics Technology Centre" Singapore Publication entitled Learning and Compensating for Repeatable Runout of a Disk Drive Servo Using a Recurrent Neural Network by Siri Weerasooriya, Magnetics Technology Center, National University of Singapore ISSN 0218-4877 AC/1/93 1993.

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