Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1999-08-11
2002-05-28
Neal, Regina Y. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S073030
Reexamination Certificate
active
06396652
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method applied to a head loading/unloading type disk drive to control unloading operation of retracting a head upon power down of the main power supply of a drive.
A hard disk drive (HDD) comprises a mechanism of retracting a head (slider on which a read/write element is mounted) to a designated retract position when a disk stops rotating, and a data read/write is disabled.
A CSS (Contact Start and Stop) type disk drive uses, as a retract position, a CSS area set on the innermost side on the disk, and retracts the head to the CSS area. When the disk stops rotating, the head comes into contact with the disk surface and is standby in contact with the CSS area. In the CSS type drive, the head slides on the disk surface at the rotation start and stop of the disk, and may damage (scratch) a data area on the disk.
To avoid this, the CSS area is set in a dedicated retract zone (to be also referred to as a dedicated landing zone) ensured separately from the data zone. When the drive is powered to rotate the disk by a spindle motor at a constant high speed, the head floats on the disk surface by air bearing generated with the rotation. Then, the head is moved to the data zone on the disk and positioned at a target position (target access track).
If the drive is powered down, or a host system issues a spindle motor stop instruction while the head is in the data zone, the drive retracts the head to the CSS area and stops the spindle motor. When the head retracts to the CSS area, the actuator collides against the stopper to prevent the head from projecting from the CSS area. The head is mounted on the actuator and moves radially along the disk by the driving force of a voice coil motor (VCM). The VCM drives the actuator by a driving current supplied from a VCM driver under the control of the microprocessor (CPU) of the drive.
When the drive is suddenly powered down during operation of the disk drive, the head must retract to the CSS area before the spindle motor stops. That is, if the disk stops rotating while the head floats on the data zone of the disk, the head collides against the disk. However, if power supply to the drive stops, supply of the driving current from the VCM driver to the VCM also stops to disable operation of the actuator.
Hence, the drive requires a system for urgently executing retract operation of moving the head to the CSS area. This system will be explained with reference to FIG.
13
.
As shown in
FIG. 13
, this system is roughly made up of a retract circuit
22
, rectifier
23
, and switches
26
and
27
. The rectifier
23
rectifies an AC back electromotive force (back EMF) induced by the coil of a spindle motor (SPM)
15
. The SPM
15
receives a driving current from an SPM driver
21
to rotate a disk as a recording medium when the power supply (main power supply) of the drive is turned on. The SPM driver
21
rotates the SPM
15
at a predetermined speed by executing control of the driving phase of the SPM
15
and control of a current flowing through the coil of the SPM
15
.
The retract circuit
22
monitors the voltage of the main power supply of the drive, and controls to turn on the switches
26
and
27
in accordance with detection of a power-off state. In accordance with operation of the switches
26
and
27
, the rectifier
23
supplies a DC driving current to a voice coil motor (VCM)
16
in the power-off state. In the power-on state of the drive, the VCM
16
receives a driving current from a VCM driver
24
to drive the actuator on which the head is mounted. The actuator is a head moving mechanism of moving the head radially along the disk.
When the disk drive is powered down, the SPM driver
21
and VCM driver
24
are equivalently disconnected from the corresponding motors
15
and
16
. The SPM
15
inertially rotates for a while even upon power down. At this time, the coil of the SPM
15
generates an AC back EMF. The rectifier
23
rectifies this back EMF into a DC voltage.
The retract circuit
22
monitors the power supply voltage, as described above. When the drive is powered down, the retract circuit
22
turns on the switches
26
and
27
. In the power-off state, the back EMF from the rectifier
23
flows a DC current through the VCM
16
via a current limiting resistor
25
. The driving VCM
16
automatically moves (retracts) the head to the CSS area on the disk even upon power down in the drive.
In this retract system, the SPM
15
and rectifier
23
correspond to so-called emergency reserve power supplies for the main power supply of the drive.
However, the retract system applied to the CSS type disk drive suffers the following problems.
As shown in
FIG. 13
, this system rectifies a back EMF from the SPM
15
by the rectifier
23
, and limits a current supplied to the VCM
16
via the series resistor
25
. For this reason, the current supplied to the VCM
16
is determined by the back EMF and current limiting resistor
25
. The back EMF decreases as the rotational speed of the SPM
15
decreases. However, a time (several sec) required to stop the SPM
15
and a time (several ten &mgr;sec) required to move the head to the CSS area are different by one or more orders of magnitude. Until the head reaches the CSS area, a predetermined current determined by the series resistor
25
is assumed to flow through the VCM
16
.
Since the predetermined current flows through the VCM
16
until the head moves to the CSS area in the power-off state, the head moving speed by the VCM
16
is proportional to the time and to the 1/2nd power of the moving distance.
Assume that the radii of the CSS area, innermost track, and outer most track are 15 mm, 16 mm, and 31 mm, respectively. The collision speed of the actuator against the stopper when the head retracts from the outermost track to the CSS area is almost four times the collision speed when the head retracts from the innermost track. In the CSS type disk drive, however, since the actuator can be driven by a relatively small current, the collision speed against the stopper can be set to such a degree as not to damage the head or disk by a collision shock. This speed suffices to generate a force larger than the offset force of an FPC (Flexible Printed Circuit board) having a group of terminals connected to the head. Note that a head amplifier circuit for amplifying a reproduction output from the head or the like is mounted on the FPC. For stable operation, the driving current of the VCM is desirably set smaller when the head retracts from the outermost track to the CSS area than when the head retracts from the innermost track.
On the other hand, head loading/unloading type disk drives have been developed. The loading/unloading mechanism retracts (unloads) the head to a retract location outside the disk when the disk stops rotating. The retract location has a ramp for supporting the suspension of the actuator. At the rotation start of the disk, the loading/unloading mechanism moves (loads) the head from the retract location onto the disk after the rotational speed reaches a steady speed. Since the loading/unloading type drive can avoid contact between the head and disk, it can improve a smooth disk surface, reduce the head flying height, and increase the recording density, compared to the CSS type drive.
More specifically, as shown in
FIGS. 2A and 2B
, the loading/unloading mechanism has a ramp (retract location)
14
arranged outside and near a disk
11
. Retract operation (unloading) moves a head (slider)
12
supported by a suspension
131
to the ramp
14
by driving of an actuator
13
. The distal end (having a tab; not shown) of the suspension
131
slides onto a ramp surface
141
of the ramp
14
. The head (slider)
12
is lifted up and unloaded from the surface of the disk
11
. The actuator
13
stops at a predetermined position on the outer side of the disk
11
by a stopper (not shown).
In a normal operation state when the drive is powered on, unloading operation of the head
12
is controlled by a microproc
Kawachi Hidetoshi
Osafune Koji
Gray Cary Ware & Freidenrich LLP
Kabushiki Kaisha Toshiba
Neal Regina Y.
LandOfFree
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