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# PES Stability Detect Algorithm to Prevent Off Track Write After Shock

IP.com Disclosure Number: IPCOM000123427D
Original Publication Date: 1998-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 71K

IBM

## Related People

Kitazaki, N: AUTHOR [+4]

## Abstract

This article describes an algorithm to prevent 'Off Track Write' after external shock.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

PES Stability Detect Algorithm to Prevent Off Track Write After Shock

This article describes an algorithm to prevent 'Off Track
Write' after external shock.

When external shock is added during write operation, head
moves around nearby the target track, and if the write operation is
continued, the data of nearby tracks will be overwritten (Off Track
Write).

To prevent this, several methods have been implemented,
which are shock detection by sensor, write abort by PES (position
error signal), and so on.

Our new method uses an additional parameter 'SPE (summation
of position error)' which is defined as SPE{i} =
u*SPE{i-1}+(1-u)*|PE{i}| where 0<u<1 (we use u=15/16 as sensitivity
coefficient), and |PE{i}| is absolute value of position error of i'th
servo sector.  And the write operation is terminated at the servo
sector 'i' if SPE{i} is over the criteria.

Fig 1 shows a behavior of the head motion after
shock.  Top trace is position error and bottom trace is SPE.  If the
sensitivity coefficient 'u' is set properly, SPE value increases
immediately after shock and keeps large value while head position is
unstable.  After head position becomes stable, write operation is
permitted.

Fig 2 shows the experimental data of off track write
amount.  Upper is the conventional method and lower is the case
using new algorithm.  The amount of off track write is depressed
extremely.