Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism
Reexamination Certificate
1998-07-01
2001-01-30
Nguyen, Hoa T. (Department: 2753)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
C360S075000, C360S078040
Reexamination Certificate
active
06181502
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to reducing data access time in disk drives, and more particularly to an apparatus and method for reducing data access time during seek operations in disk drives by increasing a voltage supplied to a voice coil motor (VCM) of the disk drive.
2. Description of the Prior Art
In hard disk drives, data is stored on magnetic media disks in concentric data tracks, which are divided into groups of data sectors. Servo information including track number, sector number, and tracking information is recorded in radially continuous narrow wedges between the groups of data sectors. The disk drive includes an actuator assembly having a voice coil motor (VCM), an actuator arm extending from the VCM, and a transducer head disposed at the end of the actuator arm. One way of improving disk drive performance is to reduce data access time, including the time required to move the transducer head of the actuator assembly from a current data track to a selected target data track.
The disk drive performs a seek operation to move the transducer head from a present data track to a target data track. The disk drive includes a servo system employed to seek to the target data track and thereafter follow the target data track on the disk. The servo system controls the VCM so that the VCM swings the actuator and its attached transducer head to access the target data track. Therefore, if the torque developed (T
d
) by the VCM could be increased, a corresponding reduction in data access time could be achieved. T
d
is given by the following Equations I:
Equations I
T
d
=Kt*I
coil
Kt=Ke
(
Kt
in
Nm/A; Ke
in
V/
rad/sec)
Bemf=Ke*Vel
motor
(
Vel
motor
in rad/sec)
V
applied
=V
source
−Bemf=I
coil
*R
coil
I
coil
=(
V
source
−Ke*Vel
motor
)/
R
coil
Where:
T
d
is the torque developed by the VCM;
Kt is the Torque constant of the VCM;
I
coil
is VCM coil current;
Ke is the Voltage constant of the VCM i.e. the Bemf factor;
Bemf is the back emf of the VCM;
Vel
motor
is the velocity of the VCM;
V
applied
is the voltage applied to the VCM coil;
V
source
is the voltage of the VCM power source supplying power to the VCM; and
R
coil
is the total resistance of the VCM coil from the VCM power source to ground
As can be shown by Equations I above, T
d
can be increased by increasing Kt and/or I
coil
. Unfortunately, increasing I
coil
causes a corresponding heating of the VCM coil, proportional to the square of the current, which can result in heat related breakdown of VCM components, including the VCM coil itself. In particular, seek operations require the highest current to be supplied to the VCM in order to achieve competitive access times. Conversely, increasing Kt equates to an equal increase in Ke which increases the Bemf of the VCM. Therefore, the Bemf approaches V
source
as Kt is increased. Consequently, if V
source
cannot be increased, less voltage V
applied
is available and I
coil
is reduced as Kt is increased thereby limiting the performance of the VCM. The V
source
supplied to the VCM in disk drives, however, is fixed because, for compatibility with host systems, a standard power supply having a fixed voltage is used to supply power to the VCM. This fixed voltage power supply to the VCM therefore limits how much effect the VCM can have on reducing access times.
For reasons stated above and for other reasons presented in greater detail in the detailed description of the present specification, there is a desire to reduce data access time during seek operations in disk drives. In particular, there is a need to improve VCM performance by increasing the torque constant of the VCM to achieve a corresponding decrease in data access time in seek operations in disk drives. It would also be desirable to increase the torque constant of the VCM to permit a reduction in VCM coil current to reduce I
2
R power losses in the system while still maintaining a given torque in the VCM.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method of supplying power to a voice coil motor (VCM) in a disk drive. A VCM power source circuit receives a standard power supply having a fixed voltage and provides a boosted voltage VCM power source having a boosted voltage greater than the fixed voltage. The boosted voltage VCM power source is supplied to the VCM. The VCM power source circuit provides the boosted voltage VCM power source independently from the voice coil motor.
In one embodiment of the present invention, a boosted voltage VCM power source supplies power to the VCM at a first time and the standard power supply supplies power to the VCM at a second time. In one embodiment, a switch switches between the boosted voltage VCM power source and the standard power supply when supplying power to the VCM during a seek operation of the disk drive.
In one embodiment, the VCM power source circuit includes a stored power source for providing the boosted voltage VCM power source. For example, a charge pump can be used to store energy in a capacitor, and the stored energy in the capacitor can then be used as the boosted voltage VCM power source by discharging the capacitor. In one embodiment, two capacitors are employed to supply boosted voltage power to the VCM. In this embodiment, the disk drive performs a seek operation and a first capacitor is discharged and a second capacitor is charged during an acceleration mode of the seek operation, and the second capacitor is discharged and the first capacitor is charged during a deceleration mode of the seek operation.
In one embodiment, the VCM power source circuit includes a regulated DC power supply for continuously providing the boosted voltage VCM power source.
A disk drive constructed according to the present invention includes a VCM power source circuit to provide a boosted voltage VCM power source to the VCM of the disk drive. This boosted VCM voltage permits the torque constant of the VCM to be increased to allow greater torque to be developed by the VCM resulting in reduced data access times during seek operations in the disk drive.
The boosted VCM voltage advantageously permits the torque constant of the VCM to be increased while allowing for a corresponding reduction in VCM coil current to reduce I
2
R power losses in the system while still maintaining a given torque in the VCM.
REFERENCES:
patent: 4991129 (1991-02-01), Swartz
patent: 5204593 (1993-04-01), Ueki
patent: 5208518 (1993-05-01), Grapenthin et al.
patent: 5495372 (1996-02-01), Bahlmann et al.
patent: 5504402 (1996-04-01), Menegoli
patent: 5566369 (1996-10-01), Carobolante
patent: 5592353 (1997-01-01), Shinohara et al.
patent: 5631527 (1997-05-01), Canclini
patent: 5737144 (1998-04-01), Ataee et al.
patent: 6008690 (1999-12-01), Takeshima et al.
patent: 6011667 (2000-01-01), Dunn et al.
Hussein Hakam D.
Oettinger Eric Gregory
Stich Michael C.
Davidson Dan I.
Nguyen Hoa T.
Shara Milad G.
Western Digital Corporation
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