Browse Prior Art Database

# Torque Up Circuit

IP.com Disclosure Number: IPCOM000105481D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 46K

IBM

## Related People

Okutsu, K: AUTHOR

## Abstract

Disclosed is a new circuit to increase the spindle start up torque. When HDD (Hard Disk Drive) is powered on, sometimes the head sticks to the disk surface (called stiction) then spindle cannot rotate. The disclosed circuit ("Torque Up Circuit") can increase the armature current when "stiction" occurs, raises the spindle start up torque and starts rotation.

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Torque Up Circuit

Disclosed is a new circuit to increase the spindle start up
torque.  When HDD (Hard Disk Drive) is powered on, sometimes the head
sticks to the disk surface (called stiction) then spindle cannot
rotate.  The disclosed circuit ("Torque Up Circuit") can increase the
armature current when "stiction" occurs, raises the spindle start up
torque and starts rotation.

When a head sticks to the disk surface, the head is resonant
with the disk at a particular frequency.  If the spindle can be
vibrated at this resonant frequency, the head may be removed from the
disk.  This method has been already implemented and called "Torque
Amplification".  However a spindle torque cannot be increased by this
method.  So sometimes a head cannot be removed from the disk by this
method.  When a frequency of an armature current is changed, a head
is resonant with the disk at a particular frequency.  "Torque
Amplification" method tries to remove a head from the disk at this
"resonant frequency".

In accordance with the disclosed circuit, a spindle torque is
raised by increasing the armature current only when satiation occurs.
The following equation represents the relation between a spindle
torque (T) and an armature current (Ia).

T=Kt * Ia ...  (1)

where Kt is a torque constant.

In the Figure, Ra is a coil resistance, Rsns is a sense
resistance, and V is a voltage supplied to a driver.  The armature
current Ia is expresse...