Dynamic magnetic information storage or retrieval – Head mounting – For shifting head between tracks
Reexamination Certificate
2001-04-17
2003-04-15
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
For shifting head between tracks
C310S013000
Reexamination Certificate
active
06549380
ABSTRACT:
FIELD OF THE INVENTION
This application relates generally to information handling systems and more particularly to a magnetic circuit of a voice coil motor in an information handling system.
BACKGROUND OF THE INVENTION
One function of a disc drive is reliable storage and retrieval of information. Using one common implementation of a disc drive as an example, data is stored on one or more discs coated with a magnetizable medium. Data is written to the discs by an array of transducers, typically referred to as read/write transducers, mounted to an actuator assembly for movement of the transducers relative to the discs. The information is stored on a plurality of concentric circular tracks on the discs until such time that the data is read from the discs by the read/write transducers. Each of the concentric tracks is typically divided into a plurality of separately addressable data sectors. The transducers are used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the transducer senses the data previously written on the disc track and transfers the information to the external environment. Critical to both of these operations is the accurate locating of the transducer over the center of the desired track.
Conventionally, the transducers are positioned with respect to the disc surfaces by one or more actuator arms controlled through a voice coil motor. The voice coil motor is responsible for pivoting the actuator arms about a pivot shaft, thus moving the transducers across the disc surfaces. The actuator arm thus allows the transducers to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs. The actuator arm is driven by a control signal fed to a voice coil motor coil coupled to the rear end of the actuator arm.
The coil is immersed in the magnetic field of a magnetic circuit of the voice coil motor. With respect to conventional voice coil motor implementations, the magnetic circuit comprises one or more permanent magnet pairs adjacent to magnetically permeable magnet plates. When current is passed through the coil, an electromagnetic field is established which interacts with the magnetic field of the magnetic circuit such that the coil, as well as the transducer(s), experience direct rotational forces or torques about an axis of a rotatable assembly. Such rotational forces selectively position the transducer over the desired new track or maintain the position of the transducer over the desired current track. A conventional implementation of the magnetic circuit of the voice coil motor is shown in
FIG. 3. A
second conventional implementation of the magnetic circuit of the voice coil motor is shown in FIG.
4
.
A servo control system is used to sense the position of the actuator arm and control the movement of the transducer above the disc using servo signals read from the servo segments on the disc surface in the disc drive. The servo control system relies on servo information stored on the disc. The signals from this information generally indicate the present position of the transducer with respect to the disc, i.e., the current track position. The servo control system uses the sensed information to maintain transducer position or determine how to optimally move the transducer to a new position centered above a desired track. The servo system then delivers a control signal to the coil of the voice coil motor to rotate the actuator arm to position the transducer over a desired new track or maintain the position over the desired current track.
As shown in
FIG. 3
, in a typical voice coil motor
324
employing two parallel magnet pairs
342
and
344
coupled to an upper magnetically permeable plate
343
and a lower magnetically permeable plate
345
, respectively, the lines of magnetic flux
346
generated by the permanent magnet pairs
342
and
344
tend to cross an air gap
348
located between an upper surface
350
of the lower magnet pair
342
and a lower surface
352
of the upper magnet pair
344
in a generally orthogonal direction to surfaces
350
and
352
of the permanent magnet pairs
342
and
344
. When these “orthogonal” lines of magnetic flux
346
interact with the flux generated by a coil
326
, the resultant torque induced in the VCM
324
is primarily of the direct type, as described above. Put another way, when the flux generated by the parallel magnet pairs
342
and
344
of the VCM
324
, interacts with the flux generated by current in the coil
326
, balanced forces or torques act upon the VCM
324
.
The orthogonal orientation of the flux lines
346
relative to the surfaces
350
and
352
of the permanent magnet pairs
342
and
344
is thought to be due to a “steering” effect the oppositely facing north and south facing magnetic poles
362
and
364
of the permanent magnet pairs
342
and
344
have on the magnetic flux
346
. That is, the oppositely facing north and south facing magnetic poles
362
and
364
of the permanent magnet pairs
342
and
344
tend to guide the lines of magnetic flux
346
across the air gap
348
located between the permanent magnet pairs
342
and
344
in a generally orthogonal direction to the surfaces
350
and
352
of the permanent magnet pairs
342
and
344
.
In contrast, as shown in
FIG. 4
, it has been observed that without the guiding influence of the oppositely facing south and north magnetic poles, lines of magnetic flux
446
generated in a VCM
424
having a single magnet pair
444
tend to “fringe” as they cross the air gap
448
between the permanent magnet pair
444
and the upper magnetically permeable plate
440
. That is, the lines of magnetic flux
446
generated in the VCM
424
employing a single magnet pair
444
do not typically remain orthogonal to the upper surface
450
of the permanent magnet pair
444
. It is believed that when these “non-orthogonal” flux lines interact with the flux generated by the coil
426
, the result is unbalanced forces and moments acting on the coil
426
. Such unbalanced forces and moments typically lead to an undesirable increase in pitch torque and roll torque in the VCM
424
.
Although the conventional implementation shown in
FIG. 3
is desirable to somewhat alleviate unbalanced forces and moments associated with non-orthogonal flux lines, the parallel magnet design in
FIG. 3
is associated with relatively greater manufacturing costs than the design shown in FIG.
4
. In contrast, even though the magnetic circuit implementation shown in
FIG. 4
is relatively inexpensive to manufacture when compared to the conventional implementation shown
FIG. 3
, the design shown in
FIG. 4
is associated with potentially unbalanced forces and moments.
SUMMARY OF THE INVENTION
Against this backdrop the present invention has been developed. The present invention relates to a magnetic circuit of a voice coil motor incorporating a single permanent magnetic portion extending from a first plate and a raised plate portion protruding toward the first plate from a second plate. The raised plate portion protrudes from the second plate to interact with the magnetic portion extending from the first plate in order to reduce the occurrence of non-orthogonal flux lines in the voice coil motor. Accordingly, the voice coil motor employs a single magnetic portion and an opposite pole piece shaped to generate orthogonal, as opposed to non-orthogonal, flux lines relative to the surface of the permanent magnetic portion to ensure relatively balanced forces and moments acting upon the coil of the voice coil motor.
In accordance with one embodiment, a disc drive includes a voice coil motor for positioning a transducer over a data disc surface of a data storage disc rotatably mounted on a base plate. An actuator, which is coupled to the voice coil motor, is mounted on the base plate adjacent the disc for moving the transducer over the disc surface. The voice coil motor includes a voice coil, a first plate, a permanent magnet pair coupled
Merchant & Gould P.C.
Miller Brian E.
Nguyen Dzung C.
Seagate Technology LLC
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