Implementing enhanced track following during read back using head asymmetry metrics in hard disk drives

Patent metadata

Field	Value
Publication number	US-10008229-B2
Application number	US-201614988651-A
Country	US
Kind code	B2
Filing date	Jan 5, 2016
Priority date	Jan 5, 2016
Publication date	Jun 26, 2018
Grant date	Jun 26, 2018

Abstract

A method, apparatus, and system are provided for implementing track following using signal asymmetry metrics monitored during read back in hard disk drives (HDDs). Signal asymmetry metrics monitored during read back are used together with a position error signal (PES) to correct and guide the position of a read sensor with respect to a written track in the HDD.

First claim

What is claimed is:

1. A method for implementing track following in hard disk drives (HDDs), comprising:
monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics; and
using the estimate of position error from the monitored signal asymmetry metrics together with a servo position error signal (PES) estimate to correct and guide position of a read sensor with respect to a written track in the HDD, wherein monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics includes monitoring signal asymmetry metrics during read back of a written data track and during a data recovery procedure.

2. The method as recited in claim 1 , wherein the monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics includes monitoring signal asymmetry with respect to a head bias direction during read back of a written data track.

3. The method as recited in claim 1 , wherein the monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics further includes detecting change in signal resolution for shingled magnetic recorded (SMR) data tracks with reference to a shingle direction.

4. A method for implementing track following in hard disk drives (HDDs), comprising:
monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics; and
using the estimate of position error from the monitored signal asymmetry metrics together with a servo position error signal (PES) estimate to correct and guide position of a read sensor with respect to a written track in the HDD, wherein monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics includes monitoring signal asymmetry and noise asymmetry with respect to a head bias direction during read back of a written data track.

5. A method for implementing track following in hard disk drives (HDDs), comprising:
monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics; and
using the estimate of position error from the monitored signal asymmetry metrics together with a servo position error signal (PES) estimate to correct and guide position of a read sensor with respect to a written track in the HDD, wherein monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics further includes accumulating a metric E{y|y|} normalized by a second moment E(y^2) or E{y|y|}/E(y^2) of asymmetry y(t) waveform.

6. An apparatus for implementing track following in hard disk drives (HDDs), comprising:
a controller; and
at least one disk; said disk including a disk media including data tracks for storing data;
wherein said controller is configured to perform at least:
monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics; and
using the estimate of position error from the monitored signal asymmetry metrics together with a servo position error signal (PES) estimate to correct and guide position of a read sensor with respect to a written track in the HDD, wherein said monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics includes monitoring noise asymmetry with respect to a head bias direction during read back of a written data track.

7. The apparatus as recited in claim 6 , wherein the monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics further includes using control code for generating an estimate of position error from the monitored signal asymmetry metrics to implement track following.

8. The apparatus as recited in claim 6 , wherein the monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics further includes monitoring signal asymmetry with respect to a head bias direction during read back of a written data track.

9. The apparatus as recited in claim 6 , wherein the monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics further includes detecting change in signal resolution for shingled magnetic recorded (SMR) data tracks with reference to a shingle direction.

10. A system comprising a hard disk drive (HDD) comprising the apparatus as recited in claim 6 .

11. An apparatus for implementing track following in hard disk drives (HDDs), comprising:
a controller; and
at least one disk; said disk including a disk media including written data tracks for storing data;
wherein said controller is configured to perform at least:
monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics; and
using the estimate of position error from the monitored signal asymmetry metrics together with a servo position error signal (PES) estimate to correct and guide position of a read sensor with respect to a written track in the HDD, wherein said monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics includes accumulating a metric E{y|y|} normalized by a second moment E(y^2) or E{y|y|}/E(y^2) of asymmetry signal waveform y (t).

12. A system comprising a hard disk drive (HDD) comprising the apparatus as recited in claim 11 .

13. An apparatus for implementing track following in hard disk drives (HDDs), comprising:
a controller; and
at least one disk; said disk including a disk media including written data tracks for storing data;
wherein said controller is configured to perform at least:
monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics; and
using the estimate of position error from the monitored signal asymmetry metrics together with a servo position error signal (PES) estimate to correct and guide position of a read sensor with respect to a written track in the HDD, wherein said monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics includes monitoring signal asymmetry metrics during read back of a written data track and during a data recovery procedure.

14. A system comprising a hard disk drive (HDD) comprising the apparatus as recited in claim 13 .

15. An apparatus for implementing track following in hard disk drives (HDDs), comprising:
a controller; and
at least one disk; said disk including a disk media including written data tracks for storing data;
wherein said controller is configured to perform at least:
monitoring signal asymmetry metrics during read back and generating an estimate of position error from the monitored signal asymmetry metrics; and
using the estimate of position error from the monitored signal asymmetry metrics together with a servo position error signal (PES) estimate to correct and guide position of a read sensor with respect to a written track in the HDD, wherein said monitoring signal asymmet

Assignees

• Western Digital Tech Inc
• Western Digital Tech Inc

Inventors

• Galbraith Richard Leo
• Hanson Weldon Mark
• Nichols Mark A
• Taratorin Alexander
• Wood Roger William

Classifications

• G11B5/59683 Primary

  for magnetoresistive heads · CPC title

• G11B5/59627 Primary

  Aligning for runout, eccentricity or offset compensation (G11B5/5534, G11B5/59677, G11B5/59688 take precedence) · CPC title