Enhanced convective voice coil cooling to improve the operational performance of a disc drive

Apparatus and method for enhancing the convective cooling of a voice coil motor (VCM) of a disc drive. A portion of an air flow established by the rotation of a disc of the disc drive is diverted from the disc and is directed through a channel to the VCM. In one embodiment, an air foil is provided to support first and second magnetic paths of the VCM, the air foil having a shroud surface adjacent portions of the circumference of the disc and a diverter surface angularly extending from the shroud surface, the diverter surface diverting the air to the VCM. Alternatively, a base deck of the disc drive is provided with a shroud circumferentially adjacent portions of the disc and the channel extends through the shroud to direct the air from the disc to the VCM.

FIELD OF THE INVENTION 
The present invention relates generally to the field of disc drive devices 
and more particularly, but without limitation, to enhancing the convective 
cooling of the coil of a disc drive voice coil motor so as to improve the 
operational performance of the disc drive. 
BACKGROUND 
Modern hard disc drives comprise one or more rigid discs that are coated 
with a magnetizable medium and mounted on the hub of a spindle motor for 
rotation at a constant high speed. Information is stored on the discs in a 
plurality of concentric circular tracks by an array of transducers 
("heads") mounted to a controllably positionable actuator for radial 
movement relative to the discs. 
Typically, such radial actuators employ a voice coil motor to position the 
heads with respect to the disc surfaces. The heads are mounted via 
flexures at the ends of a plurality of arms which project outward from an 
actuator body. The actuator body pivots about a cartridge bearing assembly 
mounted to the disc drive housing and normally disposed thereto at a 
position closely adjacent the outer extreme of the discs so that the heads 
move in a plane parallel with the surfaces of the discs. 
The voice coil motor includes a coil mounted radially outward from the 
cartridge bearing assembly, the coil being immersed in the magnetic field 
of a magnetic circuit of the voice coil motor. The magnetic circuit 
comprises one or more permanent magnets and magnetically permeable pole 
pieces. When current is passed through the coil, an electromagnetic field 
is established which interacts with the magnetic field of the magnetic 
circuit so that the coil moves 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. 
A closed loop digital servo system such as disclosed in U.S. Pat. No. 
5,262,907 issued Nov. 16, 1993 to Duffy et al., assigned to the assignee 
of the present invention, is typically utilized to maintain the position 
of the heads with respect to the tracks. Such a servo system obtains head 
position information from servo blocks written to the tracks during disc 
drive manufacturing to maintain a selected head over an associated track 
during a track following mode of operation. A seek mode of operation, 
which comprises the initial acceleration of a head away from an initial 
track and the subsequent deceleration of the head towards a destination 
track, is also controlled by the servo system. Such seek operations are 
typically velocity-controlled, in that the velocity of the head is 
repetitively measured and compared to a velocity profile, with the current 
applied to the coil being generally proportional to the difference between 
the actual and profile velocities as the head is moved toward the 
destination track. 
It will be recognized that a continuing trend in the industry is to provide 
disc drives with ever increasing data storage and transfer capabilities, 
which in turn has led to efforts to minimize the overall time required to 
perform a disc drive seek operation. A typical seek operation includes an 
initial overhead time during which the disc drive services its own 
internal operations, seek time during which the head is moved to and 
settled on the destination track, and latency time during which the drive 
waits until a particular sector on the destination track reaches the head 
as the discs rotate relative to the heads. 
Seek times have typically been minimized through the application of 
relatively large amounts of current to the coil during the acceleration 
and deceleration phases of a seek operation. Latency times have also been 
continually minimized through continued increases in the rotational speeds 
of the discs (which in some disc drives have reached 10,000 revolutions 
per minute). 
A problem resulting from these improvements in disc drive seek performance, 
however, is the increase in the amount of heat that is generated within 
the drive. Particularly, the spindle motor used to rotate the discs is 
typically one of the largest sources of heat in the drive, and the amount 
of heat dissipated within the drive generally increases with increases in 
rotational speed of the discs and the amount of drag upon the discs. 
Moreover, after repetitive seeking, resistive power losses in the actuator 
coil of the voice coil motor tend to also generate significant amounts of 
heat within the drive. Because the coil is mechanically isolated from the 
magnetic circuit of the voice coil motor, over time the temperature of the 
coil can exceed that of the rest of the disc drive by several degrees, 
creating a localized "hot spot" within the disc drive. 
It is well known that the amount of current that can be passed through an 
actuator coil is generally a function of the direct current (dc) 
resistance of the coil, which in turn generally increases proportionally 
with the temperature of the coil. Hence, as coil temperature increases, so 
does the resistance; thus, over time lesser amounts of current can be 
applied to the coil, which in turn generally increases the time required 
to move a selected head from an initial track to a destination track 
during a seek operation. Moreover, elevated voice coil motor temperatures 
with respect to ambient can further adversely affect the ability of the 
disc drive to achieve optimal levels of performance, as the field strength 
of the magnetic circuit of a voice coil motor is generally a function of 
temperature and generally weakens as temperature is increased. Thus, the 
localized heating of the magnetic circuit further tends to increase the 
seek time of a disc drive. 
Additionally, elevated voice coil motor temperatures can result in the 
degradation of adhesive and insulative materials used in the construction 
of the voice coil motor. Such degradation can lead to internal 
contamination of the disc drive as well as to the shorting of the coil. 
Accordingly, there is a continual need for improvements in the art whereby 
data transfer performance of a disc drive can be increased while 
accommodating problems associated with the generation of heat within the 
drive as higher levels of drive performance are obtained. 
SUMMARY OF THE INVENTION 
The present invention provides an apparatus and method for enhancing the 
convective cooling of a voice coil motor (VCM) of a disc drive in order to 
reduce the temperature of the VCM during extended periods of disc drive 
operation. Generally, in accordance with the preferred embodiments of the 
present invention a portion of an air flow established by the rotating 
discs of the disc drive is diverted from the discs and is directed so as 
to pass over the coil of the VCM. 
In accordance with a first preferred embodiment of the present invention, 
an air foil is provided to support first and second magnetic paths of the 
magnetic circuit of the VCM, the first and second magnetic paths each 
comprising a permanent magnet and a magnetically permeable pole piece. The 
air foil is provided with a leading edge positionable adjacent a disc 
stack of the disc drive, a shroud surface extending from the leading edge 
and adjacent a portion of the outer diameter of the disc stack and a 
diverter surface extending from the leading edge at an angle with respect 
to the shroud surface. 
During operation of the disc drive, the air foil operates to divert a 
portion of the air flow established by the rotation of the disc stack to 
the VCM to convectively cool the same. The disc drive preferably further 
comprises a base deck to which the disc stack and the magnetic circuit are 
mounted, the base deck including a shroud portion adjacent portions of the 
outer diameter of the disc stack. The shroud portion of the base deck 
further preferably includes a baffle point proximate to the air foil so 
that a gap is formed therebetween, the diverted air being directed through 
the gap to the VCM. 
An alignment fixture is also disclosed to facilitate assembly of the 
magnetic circuit. The alignment fixture generally comprises a base 
surface, an alignment drum and an alignment pin which are utilized to 
correctly align the air foil for use in the disc drive. 
In alternative preferred embodiments, a recirculation filter of the disc 
drive is disposed in the path of the diverted air between the VCM and the 
disc stack. Additionally, features in the form of ramps can be provided in 
the disc drive base deck and top cover to further define the path taken by 
the diverted air so that the air is more directly channeled to the coil. 
Finally, an alternative diversion channel is disclosed, the diversion 
channel passing through the shroud of the base deck so as to divert the 
air from the disc stack to the VCM. 
These and various other features as well as advantages which characterize 
the present invention will be apparent from a reading of the following 
detailed description and a review of the associated drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings and particularly to FIG. 1, shown therein is 
a disc drive 100 generally constructed in accordance with the first 
preferred embodiment of the present invention. It will be understood that 
a variety of alternative preferred embodiments for the disc drive 100 will 
be discussed below in turn and that several of the features disclosed may 
be readily combined as desired, depending upon the requirements of a given 
application. Accordingly, for purposes of clarity the reference numeral 
100 will be used throughout to identify the top level disc drive assembly 
for each of the disclosed embodiments. 
The disc drive 100 of FIG. 1 generally includes a disc stack 102 which, in 
turn, comprises a plurality of discs 104 upon which digital data is 
magnetically stored. To this end, the discs 104 are mounted to a spindle 
motor 106 for rotation relative to a base deck 108 about an axis that 
extends through the centers of the discs 104 so that the data can be 
stored as patterns of magnetization of a surface medium along circular 
tracks (not separately designated) that are defined on the discs 104. The 
magnetization of the tracks is effected by heads 110 that are mounted on 
the ends of flexures 112 of an actuator assembly 114. Although not shown 
in FIG. 1, it will be understood that each surface of the discs 104 has 
associated with it a corresponding head 110. Moreover, a top cover 116 
(shown in partial cut-away fashion) cooperates with the base deck 108 in a 
conventional manner to provide a nominally sealed internal environment for 
the disc drive 100. 
Each of the flexures 112 extends into the disc stack 102 to support the 
corresponding head 110 adjacent the surface of the associated disc 104 and 
positions the head 110 in radial alignment with a desired track. The 
actuator assembly 114 pivots about a bearing assembly 118 mounted to the 
base deck 108 so as to enable the positioning of the heads 110 at desired 
radial locations of the disc 104 accordingly. 
The pivotal movement of the actuator assembly 114 is controlled by a voice 
coil motor (VCM) 120 which comprises a coil 122 and a magnetic circuit 
(not separately designated) having a pair of permanent magnets and 
corresponding pole pieces, such as shown in FIG. 1 at 124 and 126, 
respectively. It will be readily understood that the magnetic circuit 
further includes a second permanent magnet and corresponding pole piece 
which are disposed above the first permanent magnet 124 and pole piece 
126, but such are not shown in FIG. 1 to more clearly facilitate the 
present discussion. 
As will be recognized, the coil 122 is immersed in the magnetic field 
established by the magnetic circuit. Thus, when current is passed through 
the coil 122, an electromagnetic field is set up which interacts with the 
magnetic field of the magnetic circuit so as to cause the coil 122 to move 
relative to the magnetic circuit. As the coil 122 moves, the actuator 
assembly 114 pivots about the bearing assembly 118 and the heads 110 
radially traverse the surfaces of the discs 104. 
At such time that operation of the disc drive 100 is suspended, the heads 
110 are moved to landing zones 128 at the inner diameters of the discs 104 
and the actuator assembly 114 is secured by a conventional latch assembly 
130. 
A flex assembly 132 provides the requisite electrical connection paths for 
the actuator assembly 114 while allowing pivotal movement of the actuator 
assembly 114 during operation. The flex assembly includes a printed 
circuit board 134 to which head wires (not shown) are connected, the head 
wires being routed along the flexures 112 to the heads 110. The printed 
circuit board 134 typically includes circuitry for controlling the write 
currents applied to the heads 110 during a write operation and for 
amplifying read signals generated by the heads 110 during a read 
operation. Wires for the coil 122 are also attached to the flex assembly 
132 as shown. 
The flex assembly 132 terminates at a flex bracket 136 for communication 
through the base deck 108 to a disc drive printed circuit board (not 
shown) mounted to the bottom side of the disc drive 100. 
During disc drive operation the spindle motor 106 rotates the discs 104 at 
a constant high speed so as to present all the data storage locations 
within a particular track to the heads 110 for the reading or writing of 
data. As the discs 104 spin, frictional forces impart a velocity to the 
boundary layer air surrounding the discs 104. This velocity propagates 
throughout the volume of air within the disc stack 102, inducing a general 
positive profile air flow from the rotating discs 104 in the direction of 
rotation of the discs 104. As will be recognized, the heads 110 are 
provided with aerodynamic features that cause the heads 110 to fly in 
close proximity to the surfaces of discs 104 as a result of this air flow. 
The air flow is generally constrained within a shroud 138 which is formed 
as a portion of the base deck 108, the shroud 138 providing an arcuate 
enclosure adjacent portions of the outer edge of the disc stack 102. Thus, 
the shroud 138 generally operates to minimize windage power losses of the 
spindle motor 106 and to present a more uniform air flow for the heads 
110. 
In accordance with the first preferred embodiment of the present invention, 
as shown in FIG. 1 the voice coil motor 120 is further provided with an 
air foil 140, which preferably comprises a generally triangularly shaped 
spacer member fabricated from a rigid, magnetic material such as steel. As 
discussed in greater detail below, the air foil 140 provides mechanical 
support for the magnetic circuit within the disc drive 100, operates as a 
shroud over a portion of the circumference of the disc stack 102 and 
diverts a portion of the air flow generated by the spinning discs 104 to 
the voice coil motor 120 in order to enhance the convective cooling of the 
coil 122 and the magnetic circuit. 
Referring now to FIG. 2, shown therein is an isometric, partially exploded 
view of the magnetic circuit of FIG. 1. More particularly, FIG. 2 shows 
the magnetic circuit to comprise the first permanent magnet and pole piece 
124, 126 of FIG. 1, as well as a second permanent magnet and pole piece 
144, 146 respectively (which as will be recalled were omitted from FIG. 1 
for purposes of clarity). The pole pieces 126, 146 are mechanically 
separated and supported by way of the air foil 140 as well as by a 
cylindrically shaped support piece 148. 
Fasteners 150 are thus inserted as shown through corresponding holes (not 
separately designated) in the pole pieces 126, 146, the air foil 140 and 
the support piece 148 to secure these components of the magnetic circuit 
into a completed subassembly. Although not shown in FIG. 2, fasteners are 
likewise inserted into holes (denoted at 152) of the pole pieces 126, 146 
to secure the pole pieces 126, 146 to the base deck 108 and top cover 116, 
respectively, in the disc drive 100. Tooling alignment holes (designated 
at 154) are also provided for use during the assembly process to 
facilitate proper alignment of the pole pieces 126, 146 and the air foil 
140, as discussed below. For reference, FIG. 3 provides an elevational 
view of the assembled magnetic circuit of FIG. 2 as would be generally 
viewed from a vantage point indicated along view 3--3 in FIG. 1 (it will 
be recognized that FIG. 3 includes the second permanent magnet and pole 
piece 144, 146 which were omitted from FIG. 1). 
From a review of FIGS. 1-3, it will be readily understood that the air foil 
140 is provided with a shroud surface 162 disposed closely adjacent the 
outer diameter of the disc stack 102, the shroud surface 162 operating to 
retain portions of the air flow generated by the rotating discs 104 within 
the disc stack 102 in a manner similar to that described above by the 
shroud 138 of the base deck 108. The air foil 140 further includes a 
diverter surface 164 which extends from a leading edge 166 of the air foil 
140 at an angle with respect to the shroud surface 162. 
Referring again to FIG. 1, the shroud 138 juttingly terminates to form a 
baffle 168 at a point proximate to the air foil 140. A gap is thereby 
formed between the baffle 168 and the leading edge 166 of the air foil 
140, the gap causing the channeling of a portion of the air flow of the 
disc stack 102 toward the VCM 120 along a path that is generally 
tangential to the disc stack and is denoted by arrow 170. More 
particularly, the shapes and relative locations of the air foil 140 and 
the baffle 168 are such as to form a channel to the VCM 120, the channel 
providing a pressure drop across the face of the gap in accordance with 
the well-known Venturi effect. As will be recognized, the diverted air 
will pass over the coil 122 and the magnetic circuit, convectively cooling 
the same. 
The amount of air diverted to the VCM 120 will depend upon a variety of 
factors, including the relative distance between the baffle 168 and the 
air foil 140 and the relative size and angles of the surfaces 162, 164 of 
the air foil (i.e., the "angle of attack" of the air foil 140 with respect 
to the air flow established by the disc stack 102). Generally, however, it 
will be recognized that there will be an optimal amount of air that can be 
diverted to cool the VCM 120. At some point, diverting too much air may 
actually make things worse; that is, diverting too much air can result in 
greater amounts of heat being dissipated by the spindle motor 106, as 
larger amounts of current will be required by the spindle motor 106 to 
rotate the disc stack 102 as additional amounts of drag are applied to the 
disc stack 102 through the diverted air. 
Referring now to FIG. 4, shown therein is a top plan view of the magnetic 
circuit of FIGS. 1-3, generally illustrating the preferred manner in which 
the magnetic circuit is assembled. For reference, FIG. 4 provides a 
representation of the second pole piece 146, under which are dotted-line 
representations of the air foil 140, the second permanent magnet 144, the 
support piece 148 and the fasteners 150 used to secure these components 
together as discussed above. 
The magnetic circuit is assembled using an alignment fixture (denoted 
generally at 180) comprising a base surface 182, an alignment drum (a 
portion of which is shown at 184) and an alignment pin 186. As described 
below, the alignment drum 184 is utilized to obtain the correct rotational 
alignment of the air foil 140 with respect to the pole pieces 126, 146. 
Moreover, for purposes of the following discussion, FIG. 5 provides a 
cross-sectional, elevational view of the magnetic circuit and the 
alignment fixture 180 of FIG. 4; FIG. 6 provides a generalized flow chart 
illustrating the assembly steps utilized to assemble the magnetic circuit. 
To assemble the magnetic circuit, as shown by block 200 of FIG. 6 the 
permanent magnets 124, 144 are first attached in a conventional manner to 
the corresponding pole pieces 126, 146 using an adhesive suitable for use 
within the disc drive 100. In the preferred embodiment, the permanent 
magnets 124, 144 are initially procured in a non-magnetized state and 
possess a neodymium-iron-boron composition; for reference, a suitable 
source is Shin Etsu of San Jose, Calif. Once the permanent magnets 124, 
144 are attached to the corresponding pole pieces 126, 146, the 
subassemblies are magnetized using a conventional magnetizer in which 
large electromagnetic fields are applied to the permanent magnets 124, 144 
and pole pieces 126, 146, as indicated by block 202 of FIG. 6. 
Once magnetized, the first permanent magnet 124 and pole piece 126 
(hereinafter "first magnetic path") are placed onto the alignment fixture 
180, as shown by block 204 of FIG. 6. That is, with reference to FIGS. 4 
and 5, the alignment pin 186 is inserted into the corresponding alignment 
hole 154 and the magnetic path is positioned so as to rest on the base 
surface 182. Although two alignment pins could be used, in the preferred 
embodiment only the one alignment pin 186 is used, so that the first 
magnetic path can be rotated until the first pole piece 126 comes to rest 
against the alignment drum 184. 
Next, as indicated by block 206 in FIG. 6, the air foil 140 and the support 
piece 148 are placed onto the respective locations on the first magnetic 
path, as generally shown in FIG. 2. Alignment of the second permanent 
magnet 124 and pole piece 126 (hereinafter "second magnetic path") then 
takes place through the insertion of the alignment pin 186 through the 
corresponding alignment hole 154 of the second pole piece 146 and the 
positioning of the second magnetic path onto the air foil 140 and the 
support piece 148, as indicated by block 208. 
The fasteners 150 (FIG. 2) are then installed, block 210. However, the 
fasteners 150 are not finally torqued until the desired alignment of the 
magnetic circuit, including the alignment of the shroud surface 162 of the 
air foil 140 against the alignment drum 184, is achieved. Once the 
fasteners have been finally torqued, the magnetic circuit is removed from 
the alignment fixture 180 for subsequent installation into the disc drive 
100. 
Having now concluded the discussion of the first preferred embodiment and 
the preferred manner for assembling the same with respect to FIGS. 1-6, 
reference is now made to FIG. 7 which illustrates the second preferred 
embodiment of the present invention. More particularly, FIG. 7 shows the 
disc drive 100 of FIG. 1 to be further provided with a diverter ramp 220 
which operates to further channel the diverted air to the coil 122 of the 
VCM 120. 
The diverter ramp 220 extends upwardly from the base deck 108 at an angle 
and terminates at an elevation substantially that of the top surface of 
the first permanent magnet 124. Thus, as air is diverted from the disc 
stack 102 along path 170, the air is both tangentially and axially 
diverted with respect to the disc stack 102. The diverter ramp 220 is 
disposed adjacent a portion of the shroud 138 as shown and can be provided 
as a separate part or can be integrated into the casting that forms the 
base deck 108. 
FIG. 8 illustrates the diverter ramp 220 (and immediately associated 
portions of the disc drive 100) in greater detail. FIG. 9 provides a 
partial cross-sectional, elevational view of the diverter ramp 220 as 
would be generally seen along view 9--9 in FIG. 7 (along with certain 
elements that were omitted from FIG. 7 for purposes of clarity). 
Additionally, a second diverter path 222 can be extended downwardly from 
the top cover 116 to further channel the air to the coil 122, as shown in 
FIG. 9. 
Having concluded the discussion of FIGS. 7-9, reference is now briefly made 
back to FIG. 1, wherein is shown a recirculation filter 224 adjacent the 
disc stack 102. As will be recognized, a portion of the air flow 
established by the rotation of the disc stack 102 of FIG. 1 is diverted 
around a recirculation support member 226 supporting the recirculation 
filter 224 and will be caused to pass through the recirculation filter 224 
in a conventional manner. The recirculation filter 224 operates to trap 
airborne contaminating particulates so as to prevent such from interfering 
with the operation of the disc drive 100. Although the recirculation 
support member 226 is provided with an inner shroud surface 228 disposed 
closely adjacent the disc stack 102 so as to minimize windage losses, it 
will be recognized that some amount of drag will be applied to the spindle 
motor 106 as a result of the air flow that passes around the recirculation 
support member 226 and through the recirculation filter 224. 
Accordingly, FIG. 10 shows another preferred embodiment of the present 
invention which can be advantageously implemented in conjunction with the 
previously discussed embodiments. Particularly, FIG. 10 illustrates the 
disc drive 100 with the additional placement of a recirculation filter 230 
in the path taken by the diverted air as it passes to the VCM 120. The 
recirculation filter 230 is generally similar in construction and 
operation to the recirculation filter 224 of FIG. 1, except that the 
recirculation filter 230 is sized to fit within the gap between the shroud 
138 and the air foil 140 as shown and attached to the base deck 108 in a 
suitable manner. An important advantage associated with the location of 
the recirculation filter 230 in FIG. 10 is that improved shrouding of the 
disc stack 102 can be achieved through the elimination of the shroud 
opening necessary to accommodate the conventional recirculation filter 224 
of FIG. 1. 
Referring now to FIG. 11, shown therein is yet another preferred embodiment 
of the present invention which comprises the use of a channel (denoted in 
broken lines at 240) extending through portions of the shroud 138 of the 
base deck 108, the channel directing a portion of the air flow (along path 
170) from the disc stack 102 to the VCM 120. The channel 240 can be cut or 
formed as a portion of the base deck casting, depending upon the 
requirements of a particular application. 
Further, as shown in FIG. 11 the shroud 138 extends to a point closely 
adjacent the air foil 140. A sealing material 242 (such as a gasket or the 
like) can be advantageously used to form a seal between the shroud 138 and 
the air foil 140 to further reduce windage losses at this point. Although 
not shown in FIG. 11, windage losses can be further decreased by placing 
the recirculation filter 230 (FIG. 10) at the terminal end of the channel 
240 so that the diverted air passes through the recirculation filter 230 
before reaching the VCM 120. 
It will be recognized that the air foil 140 discussed above with reference 
to FIGS. 1-10 is particularly suitable for use in the embodiment disclosed 
in FIG. 11, as the shroud surface 162 of the air foil 140 operates to 
shroud the disc stack 102 in the area adjacent the VCM 120 and the 
diverter surface 164 operates to further divert the air exiting the 
channel 240 towards the coil 122. However, other configurations are 
readily contemplated; for example, the base deck 108 could be 
alternatively provided with a shroud surface that extends around the disc 
stack 102 along the path of the shroud surface 162 of the air foil 140. 
This would eliminate the need to seal any gap between the shroud 138 and 
the air foil 140 and would allow the use of a more conventional support 
member (such as the cylindrical support piece 148) to support the magnetic 
circuit at this location. 
Accordingly, in view of the foregoing it will be recognized that the 
present invention provides an apparatus and method for enhancing the 
convective cooling of a VCM (such as 120) of a disc drive (such as 100) 
through the diverting of a portion of an air flow established by the 
rotation of a disc stack (such as 102) of the disc drive to the VCM. In 
one of the disclosed, preferred embodiments, an air foil (such as 140) is 
disposed adjacent a disc (such as 104) of the disc drive. The air foil 
includes a leading edge (such as 166) disposed adjacent the outer diameter 
of the disc, a shroud surface (such as 162) extending from the leading 
edge and along a portion of the outer diameter of the disc and a diverter 
surface (such as 164) extending from the leading edge at an angle with 
respect to the shroud surface, the air foil directing a portion of an air 
flow established by the rotation of the disc to the VCM in order to cool 
the same. 
In additional preferred embodiments, diverter ramps (such as 220, 222) are 
provided to further channel the diverted air to the coil (such as 122) of 
the VCM; a recirculation filter (such as 230) is disposed in the path 
(such as 170) of the diverted air; and a channel (such as 240) is 
alternatively provided through the side of the shroud wall (such as 138) 
of the base deck (such as 108) of the disc drive in order to pass a 
portion of the air flow over the VCM. 
For purposes of the appended claims, it will be recognized that the phrase 
"first magnetic path" includes a source of magnetic flux, such as the 
permanent magnet 124 described above. Moreover, it will be recognized that 
the phrase "second magnetic path" includes a magnetically permeable 
member, such as the second permanent magnet 144 or the second pole piece 
146 described above. Although a two magnet, two pole piece configuration 
has been disclosed herein, the claimed invention will be understood to 
cover other configurations, such as for example a one magnet, two pole 
piece configuration. 
Finally, it will be recognized that for purposes of the appended claims the 
phrase "disc stack" will be understood to cover just one disc as well as a 
plurality of discs. 
It will be clear that the present invention is well adapted to attain the 
ends and advantages mentioned as well as those inherent therein. While 
presently preferred embodiments have been described for purposes of this 
disclosure, numerous changes may be made which will readily suggest 
themselves to those skilled in the art and which are encompassed in the 
spirit of the invention disclosed and as defined in the appended claims.