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CUSTOMIZED SERVO NOTCH FILTER

IP.com Disclosure Number: IPCOM000014034D
Original Publication Date: 2000-Feb-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Abstract

Described is a method to improve the performance of a hard disk drive in the presence of mechanical variation. The method consists of tuning a notch filter using a measurement of the dynamics of the actuator assembly. Data from the measurement is used to compute the best notch frequency for the drive. In manufacturing, this measurement and tuning is done on a drive-by-drive basis. The structural dynamics of the actuator can cause servo performance degradation in both the access time of the drive and its on-track capability after the seek. Both of these things degrade performance. In the extreme case, the dynamics can also cause servo/mechanical instability, which leads to complete performance failure; in a manufactuing sense, this results in a lower yield. A servo notch filter reduces the excitation of the actuator dynamics by removing the exciting frequency from the control signal. Generally a "narrow notch" is the preferred application because it has less negative impact at other frequencies in the servo control signal. However, use of a narrow notch dictates that the notch be placed very near the frequency of the problem structural mode in the actuator. If the frequency mismatch between the center of the notch and the mode is too large, the benefit of the notch is lost because it now removes the wrong frequency from the control signal. In addition, the structural modes of vibration vary from actuator to actuator. Therefore, if a narrow servo notch is designed at a fixed frequency, it is imperative that the dynamics of all the actuators that are manufactured have a tight frequency distribution. In reality, it is common to have mean shifts in the actuator frequencies through the life of the program due to various tolerance shifts, manufacturing issues, etc.

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CUSTOMIZED SERVO NOTCH FILTER

   Described is a method to improve the performance of a hard disk drive in the
presence
of mechanical variation. The method consists of tuning a notch filter using a
measurement of
the dynamics of the actuator assembly. Data from the measurement is used to
compute
the best notch frequency for the drive. In manufacturing, this measurement and
tuning is done
on a drive-by-drive basis.

The structural dynamics of the actuator can cause servo performance degradation
in both the access time of the drive and its on-track capability after the seek.
Both of these things degrade performance. In the extreme case, the dynamics can
also cause servo/mechanical instability, which leads to complete performance
failure; in a manufactuing sense, this results in a lower yield.

A servo notch filter reduces the excitation of the actuator dynamics by removing
the exciting frequency
from the control signal. Generally a "narrow notch" is the preferred application
because it has less negative impact at other frequencies in the servo control
signal. However, use of a narrow notch dictates that the notch be placed very
near the frequency of the problem structural mode in the actuator. If the
frequency mismatch between the center of the notch and the mode is too large, the
benefit of the notch is lost because it now removes the wrong frequency from the
control signal.

In addition, the structural modes of vibration vary from actuator to actuator.
Therefore, if a narrow servo notch is designed at a fixed frequency, it is
imperative that the dynamics of all the actuator...