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Compensation of Resistance Imbalance in the Actuator Back-Electromotive Force Sense Circuitry

IP.com Disclosure Number: IPCOM000118780D
Original Publication Date: 1997-Jul-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Amano, Y: AUTHOR [+3]

Abstract

Disclosed is a technique to cancel the thermal drift in back-Electromotive Force (back-EMF) detection circuit of the Voice coil Motor (VCM) of the head actuator in the Hard Disk Drive (HDD) using ramp loading/unloading.

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Compensation of Resistance Imbalance in the Actuator Back-Electromotive
Force Sense Circuitry

      Disclosed is a technique to cancel the thermal drift in
back-Electromotive Force (back-EMF) detection circuit of the Voice
coil Motor (VCM) of the head actuator in the Hard Disk Drive (HDD)
using ramp loading/unloading.

      Actuator Loading and Unloading (L/UL) with ramp is now used
instead of conventional Contact Start Stop (CSS) in advanced HDDs.
In these HDDs, actuator back-EMF associated with its motion in the
magnetic field of a VCM is measured and utilized to control the
actuator velocity to enable the descent loading and unloading of the
head on the disk.  However, the back-EMF in the coil is much smaller
than the voltage across the VCM caused by the supplied current to
move the actuator and this voltage should be subtracted from the
sensed voltage across the VCM coil to get the back-EMF due to coil
motion.  A circuitry was devised (*)  to perform this subtraction, as
depicted in the Figure,

                            (Image Omitted)

  and Vout is equivalent to VbEMF, which is proportional to the
actuator velocity to be used in the control of actuator L/UL.
Deviation from eq. (2) can cause a significant amount of dR x I among
Vout. One  of the major factors which causes this deviation is the
HDD operating temperature change that mainly changes of Rcoil whose
temperature coefficient is usually different from resistors used in
...