Dynamic magnetic information storage or retrieval – Head mounting – For shifting head between tracks
Reexamination Certificate
2000-11-29
2003-06-10
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
For shifting head between tracks
Reexamination Certificate
active
06577474
ABSTRACT:
FIELD OF THE INVENTION
This application relates generally to magnetic disc drives and more particularly to a voice coil motor assembly that is partially integrated with the top cover of a disc drive.
BACKGROUND OF THE INVENTION
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium, such as a disc. Modern disc drives include a head disc assembly comprising one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a drive motor for rotation at a constant high speed. Disc drive components within the head disc assembly, such as the hub of the drive motor, a flex assembly, and a voice coil motor, are mounted to a base plate. A top cover mounts on the base plate to internally seal the head disc assembly. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a radial actuator arm (E-block) for movement of the heads relative to the discs. The read/write transducer, e.g. a magneto resistive read/write head, is 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 head senses the data previously written on the disc track and transfers the information to the external environment.
The actuators employ a voice coil motor assembly to position the heads with respect to the disc surfaces. The voice coil motor assembly includes a coil and a magnetic circuit comprising one or more permanent magnet sets and magnetically permeable pole pieces. The coil is mounted on the side of the actuator arm opposite the head arms so as to be immersed in the magnetic field of the magnetic circuit. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces.
The heads are mounted via flexures at the ends of a plurality of actuator arms that project radially outward from the actuator body. The actuator body pivots about a bearing assembly mounted on the base plate at a position closely adjacent to the outer extreme of the discs. The head(s) read data and transfer it along the actuator arm to a preamplifier that amplifies the signals coming from the heads.
Typically, a magnetically permeable bottom pole is mounted to the base plate and a magnetically permeable top pole is mounted to the base plate via standoffs in spaced relation to the bottom pole and the top cover. The top pole is mounted such that it forms an air gap between the top pole and the top cover. At least one permanent magnet set is positioned between the two poles and attached to either pole. The coil is positioned between the magnet set and the opposite pole.
FIG. 1
shows a head disc assembly of a conventional disc drive
100
. The disc drive
100
includes a base plate
102
to which various components of the disc drive
100
are mounted. A top cover
104
, shown partially cut away, cooperates with the base
102
to form an internal, sealed environment for the disc drive
100
in a conventional manner. The components include a drive motor
106
which rotates one or more discs
108
at a constant high speed. Information is written to and read from tracks on the discs
108
through the use of an actuator assembly
110
, which rotates during a seek operation about a bearing shaft assembly
112
positioned adjacent the discs
108
. The actuator assembly
110
includes a plurality of actuator arms
114
which extend towards the discs
108
, with one or more flexures
116
extending from each of the actuator arms
114
. Mounted at the distal end of each of the flexures
116
is a head
118
which includes an air bearing slider enabling the head
118
to fly in close proximity above the corresponding surface of the associated disc
108
.
During a seek operation, the track position of the heads
118
is controlled through the use of a voice coil motor (VCM) assembly
120
, which typically includes a coil
126
attached to the actuator arm
114
, a top pole
122
, a bottom pole
124
(shown in FIG.
2
), and one or more permanent magnet sets
128
having a pair of magnets
129
and
131
with opposite polarity lying in a common plane which establish a magnetic field in which the coil
126
is immersed. The magnet could also be (rather than two pieces) a single part with a transition zone between the two faces of opposite polarity. The top pole
122
is attached in spaced relation to the bottom pole
124
with magnetically permeable standoffs
150
. The controlled application of current to the coil
126
causes magnetic interaction between the permanent magnet sets
128
and the coil
126
so that the coil
126
moves in accordance with the well known Lorentz relationship. The top pole
122
and the bottom pole
124
provide a return path for the magnetic field passing through the coil
126
. As the coil
126
moves, the actuator assembly
110
pivots about the bearing shaft assembly
112
, and the heads
118
are caused to move across the surfaces of the discs
108
.
FIG. 2
shows a sectional view of a conventional voice coil motor
120
along line
2
-
2
of FIG.
1
. The bottom pole
124
is mounted to the base plate
102
by any conventional method, such as screws or adhesive. The top pole
122
is mounted to the base plate
102
via standoffs (not shown) such that the top pole
122
is spaced apart from the bottom pole
124
. The top pole
122
and the top cover
104
typically form an air gap
123
therebetween. A permanent magnet set
128
is attached to the top pole
122
opposite the top cover
104
. The coil
126
is attached to the actuator assembly (not shown) and positioned between the magnet set
128
and the bottom pole
124
. An air gap
125
is formed between the magnet set
128
and the coil
126
. Another air gap
127
is formed between the coil
126
and the bottom pole
124
. One of the problems with this conventional design is that the overall height and size of the disc drive is increased because of the extra space created by the air gap
123
. In order to eliminate the air gap
123
, the top pole
122
must be adjacent to the top cover
104
and the magnet set
128
. A second problem with this conventional design is that it requires unnecessary parts, such as standoffs
150
, to mount the top pole
122
within the head disc assembly.
However, this conventional voice coil motor design has several potential areas for improvement. First, this design wastes space because the air gap between the top cover and the top pole is not required in order for the voice coil motor to function. One way to eliminate the air gap would be to mount the top pole directly to an inside surface of the top cover with an adhesive. However, adhesives may cause outgasing that can corrupt normal disc drive operation. A second way to eliminate the air gap would be to weld the top pole directly to the top cover, providing the two parts (cover and pole) are of similar materials and are able to be welded. The problem with welding is that the potential exists for a gap to form between the two parts. The gap may allow contaminates to be trapped and possibly escape to the interior of the head disc assembly. Contaminants that can be trapped even from a cleaning process. Another way to eliminate the air gap and save space is to create a recess in the top cover with an opening into the head disc assembly. The top pole is then mounted to an outside surface of the top cover and the magnet set is inserted into the head disc assembly via the opening in the recess. While this approach saves space by eliminating the air gap between the top pole and the top cover, the opening breaks the seal between the top cover and the base plate thereby increasing the possibility of contamination within the head disc as
Kazmierczak Frederick Frank
Maiers Michael Alan
Seagate Technology LLC
Stoll-DeBell Kirstin L.
Tupper Robert S.
Watko Julie Anne
LandOfFree
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