U.S. patent application number 10/309436 was filed with the patent office on 2003-06-05 for spindle motor assembly with polymeric motor shaft and hub.
This patent application is currently assigned to Seagate Technology LLC, a Delaware corporation. Invention is credited to Boutaghou, Zine-Eddine.
Application Number | 20030102745 10/309436 |
Document ID | / |
Family ID | 22451287 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030102745 |
Kind Code |
A1 |
Boutaghou, Zine-Eddine |
June 5, 2003 |
Spindle motor assembly with polymeric motor shaft and hub
Abstract
A spindle motor assembly (18) includes a polymeric motor shaft
(20), a polymeric hub (22) to support a rotating disc (24), and a
stator (40) disposed in an internal cavity defined by the hub. A
resilient snap-in retainer (62) is molded to the motor shaft (20)
to hold the hub (22) in place. A surface of the polymeric hub and
an opposing surface of the polymeric motor shaft form a
hydrodynamic bearing.
Inventors: |
Boutaghou, Zine-Eddine;
(Vadnais Height, MN) |
Correspondence
Address: |
SEAGATE TECHNOLOGY LLC
INTELLECTUAL PROPERTY DEPARTMENT
920 DISC DRIVE, MS/SV15B1
SCOTTS VALLEY
CA
95066-4544
US
|
Assignee: |
Seagate Technology LLC, a Delaware
corporation
|
Family ID: |
22451287 |
Appl. No.: |
10/309436 |
Filed: |
December 4, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10309436 |
Dec 4, 2002 |
|
|
|
09600268 |
Jul 13, 2000 |
|
|
|
6519113 |
|
|
|
|
09600268 |
Jul 13, 2000 |
|
|
|
PCT/US00/11017 |
Apr 25, 2000 |
|
|
|
60131849 |
Apr 28, 1999 |
|
|
|
Current U.S.
Class: |
310/90 ;
G9B/19.028 |
Current CPC
Class: |
F16C 2370/12 20130101;
F16C 33/20 20130101; F16C 2220/04 20130101; F16C 17/107 20130101;
F16C 33/102 20130101; G11B 19/2009 20130101; F16C 2202/50 20130101;
F16C 33/107 20130101; F16C 2208/48 20130101; H02K 7/086
20130101 |
Class at
Publication: |
310/90 |
International
Class: |
H02K 005/16 |
Claims
What is claimed is:
1. A spindle motor assembly comprising a polymeric motor shaft, a
polymeric hub to support a rotating disc, and a stator disposed in
an internal cavity defined by the hub, wherein a surface of the
polymeric hub and an opposing surface of the polymeric motor shaft
form a hydrodynamic bearing.
2. The spindle motor assembly of claim 1 including a snap-in
retainer molded to the hub to hold the disc in place.
3. The spindle motor assembly of claim 1 including a fastener
molded to the hub to hold the disc in place.
4. The spindle motor assembly of claim 1 including a snap-in
retainer molded to the motor shaft to hold the hub in place.
5. The spindle motor assembly of claim 4 wherein the snap-in
retainer is resilient.
6. The spindle motor assembly of claim 1 wherein the stator
includes coils and wherein a magnet is connected to the hub such
that during operation of the disc drive, the magnet interacts with
the coils to cause rotational movement of the hub about the motor
shaft.
7. The spindle motor assembly of claim 6 wherein the magnet is
attached to a back-iron connected to the hub.
8. The spindle motor assembly of claim 7 including a flux
conducting ring disposed at an outer perimeter of a horizontal
extension of the motor shaft.
9. The spindle motor assembly of claim 1 including pressure
generating features formed in the polymeric motor shaft, wherein
during operation of the spindle motor assembly, the journal bearing
and pressure generating features create a pressure gradient in a
gap between the surface of the motor shaft and the opposing surface
of the hub.
10. The spindle motor assembly of claim 9 wherein the pattern of
pressure generating features includes spiral grooves formed in the
motor shaft.
11. The spindle motor assembly of claim 9 wherein the pattern of
pressure generating features includes Rayleigh steps formed in the
motor shaft.
12. The spindle motor assembly of claim 1 including a solid
lubricant disposed on a surface of the hub that comes into contacts
the motor shaft during operation during operation of the spindle
motor assembly.
13. The spindle motor assembly of claim 1 including a solid
lubricant disposed on a surface of the motor shaft that comes into
contact with the hub during operation of the spindle motor
assembly.
14. A computer disc drive comprising: a spindle motor assembly
including a polymeric motor shaft having a pattern of pressure
generating features, a polymeric hub to support a rotating disc,
and a stator disposed in an internal cavity defined by the hub,
wherein a surface of the polymeric hub and an opposing surface of
the polymeric motor shaft form a hydrodynamic bearing, and wherein
during operation of the disc drive, the journal bearing and
pressure generating features create a pressure gradient in a gap
between the surface of the motor shaft and the opposing surface of
the hub.
15. The disc drive of claim 14 including a snap-in retainer molded
to the motor shaft to hold the hub in place.
16. The disc drive of claim 14 wherein the stator includes coils
and wherein a magnet is connected to a back-iron attached to the
hub and a flux conducting ring is disposed at an outer perimeter of
a horizontal extension of the motor shaft, wherein during operation
of the disc drive, the magnet interacts with the coils to cause
rotational movement of the hub about the motor shaft, and the flux
conducting ring forms a thrust bearing.
17. A method of assembling a spindle motor assembly for a computer
disc drive, the method comprising: positioning a hub over a motor
shaft; pressing the hub downward so that an extension on the hub
contacts a snap-in retainer molded to the motor shaft; and allowing
the snap-in retainer to spring back to hold the hub in place.
18. The method of claim 17 further including: holding a disc in
place with a snap-in retainer molded to the hub.
19. The method of claim 17 wherein the hub defines an internal
cavity for a stator when the hub is held in place by the snap-in
retainer.
20. A spindle motor assembly comprising a polymeric motor shaft, a
polymeric hub to support a rotating disc, a stator disposed in an
internal cavity defined by the hub, and means for holding the hub
in place with respect to the motor shaft.
21. A spindle motor assembly comprising a motor shaft, a hub to
support a rotating disc, a stator disposed in an internal cavity
defined by the hub, a hydrodynamic bearing between a surface of the
motor shaft and an opposing surface of the hub and means for
creating a pressure gradient in a gap between the surface of the
motor shaft and the opposing surface of the hub.
Description
BACKGROUND
[0001] The invention relates generally to hydrodynamic bearing
assemblies of the type that provide support and rotation for
high-speed spindle elements. Such hydrodynamic bearing assemblies
can be utilized, for example, in computer disc drive recording
systems.
[0002] Disc drive memory systems are used in computers for storage
of digital information that can be recorded on concentric tracks of
a magnetic disc medium. One or more discs are rotatably mounted on
a spindle, and the information, which can be stored in the form of
magnetic transitions within the discs, is accessed using read/write
heads or transducers. The read/write heads are located on a
pivoting arm which moves radially over the surface of the disc. The
read/write heads must be accurately aligned with the storage tracks
on the disc to ensure the proper reading and writing of
information.
[0003] During operation, the discs are rotated at high speeds
within an enclosed housing using an electric motor located inside a
hub or below the discs. One type of motor in known as an in-hub or
in-spindle motor. Such motors typically have a spindle mounted by
means of two ball bearing systems to a motor shaft disposed in the
center of the hub. One of the bearings is located near the top of
the spindle and the other near the bottom. The bearings permit
rotational movement between the shaft and the hub while maintaining
proper alignment of the spindle to the shaft. The bearings can be
lubricated with grease or oil.
[0004] The conventional bearing system described above is prone to
several problems, including vibrations generated by the balls
rolling on the associated raceways. The strict requirements of
shock resistance for hard disc drives in portable computer
equipment also makes the use of such conventional systems less
desirable. Another problem relates to the fact that mechanical
bearings are not always scalable to smaller dimensions. That is a
significant drawback because the trend in the disc drive industry
has been to continually reduce the physical dimensions of the disc
drive unit.
[0005] As an alternative to the conventional ball bearing systems,
hydrodynamic bearing systems have been developed. In a hydrodynamic
bearing system, a lubricating fluid, such as a gas or liquid,
serves as the bearing surface between a stationary base or housing
and the rotating spindle or rotating hub. The size of the gap
between the rotating hub and the stationary portion of the motor
must be tightly controlled to obtain good dynamic performance.
[0006] Unfortunately, the control required for the dimensions of
the gap makes machining those sections costly. Furthermore,
variations in the manufacturing process that result from machining
metal sections of the disc drive system make it difficult to obtain
a gap with specified dimensions in a repeatable fashion.
SUMMARY
[0007] In general, a spindle motor assembly includes a polymeric
motor shaft, a polymeric hub to support a rotating disc, and a
stator disposed in an internal cavity defined by the hub. An outer
surface of the motor shaft and an opposing surface of the hub form
a hydrodynamic journal bearing.
[0008] One or more of the following features may be included in
various implementations. A resilient snap-in retainer can be molded
to the hub to hold the disc in place. Alternatively, a fastener
molded to the hub can hold the disc in place. A resilient snap-in
retainer can be molded to the motor shaft to hold the hub in
place.
[0009] The stator can include coils and one or more magnets can be
connected to the hub such that during operation of the disc drive,
the magnets interact with the coils to cause rotational movement of
the hub about the motor shaft. The magnets can be attached to a
back-iron that is attached to the hub. Additionally, a flux
conducting ring can be disposed at an outer perimeter of a
horizontal extension of the motor shaft. The flux conducting ring
can provide a thrust bearing to facilitate operation of the spindle
motor assembly.
[0010] Pressure generating features can be formed in the polymeric
motor shaft. During operation, the journal bearing and pressure
generating features create a pressure gradient in a gap between the
surface of the motor shaft and the opposing surface of the hub. The
pressure generating features can include, for example, spiral
grooves formed in the motor shaft or Rayleigh steps formed in the
motor shaft.
[0011] A solid lubricant can be disposed on the hub on a surface
where the hub contacts the motor shaft during operation of the
spindle motor assembly. Similarly, a solid lubricant can be
disposed on a surface of the motor shaft that contacts the hub
during operation of the spindle motor assembly.
[0012] The spindle motor assembly can form, for example, part of a
computer disc drive.
[0013] According to another aspect, a method of assembling a
spindle motor assembly for a computer disc drive includes
positioning a hub over a motor shaft, pressing the hub downward so
that an extension on the hub contacts a snap-in retainer molded to
the motor shaft, and allowing the snap-in retainer to spring back
to hold the hub in place.
[0014] In some implementations, the hub defines an internal cavity
for a stator when the hub is held in place by the snap-in retainer.
A disc can be held in place with a snap-in retainer molded to the
hub.
[0015] Some implementations include one or more of the following
advantages. Forming the hub and/or motor shaft with a polymeric
material can facilitate the achievement of tight control of
dimensions of those components during fabrication to obtain
improved dynamic performance. Use of polymeric materials also can
result in more repeatable manufacturing techniques. Known
techniques, such a mold injection, can be incorporated into the
manufacturing process to make the hub and motor shaft, and other
components can easily be molded or otherwise connected as part of
the spindle motor assembly. Similarly, a pattern of grooves,
Rayleigh steps or other features can be formed on the motor shaft
during the mold injection process to provide the appropriate
pressure gradients for stabilizing the spindle motor during
operation of the disc drive.
[0016] Use of polymeric materials for the hub and/or motor shaft
also can facilitate the assembly process of the disc drive using
snap-in features that easily can be formed by injection molding or
other techniques. Such snap-in features can be used, for example,
to hold the hub in place with respect to the motor shaft and to
hold a disc in place.
[0017] Use of polymeric materials can, in some cases, provide a
significant reduction in manufacturing and assembly costs because
the various components can be made smaller.
[0018] Providing solid lubricants on selected areas of the of the
surface of the hub and/or motor shaft can improve the tribology and
reduce the amount of liquid lubricant that might otherwise be
required as a result of absorption of the liquid lubricant by the
polymeric hub or motor shaft.
[0019] Other features and advantages will be readily apparent from
the following detailed description, the accompanying drawings, and
the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a top plan view of an exemplary disc drive.
[0021] FIG. 2A is a partial cross-sectional view of one
implementation of a spindle motor assembly according to the
invention.
[0022] FIG. 2B shows details of the polymeric hub for holding a
disc according to another implementation
[0023] FIG. 3A shows further details of a polymeric motor shaft and
polymeric hub according to the invention.
[0024] FIG. 4 illustrates an exemplary pattern of pressure
generating features formed on the polymeric motor shaft.
[0025] FIGS. 5A, 5B and 5C illustrate assembly of the polymeric hub
and motor shaft according to the invention.
[0026] FIG. 6 illustrates a hub and shaft with solid lubricant
provided in areas of contact.
DETAILED DESCRIPTION
[0027] As shown in FIG. 1, a disc drive 1 includes a disc 2 that is
rotated by the spindle 4 of a spindle motor. As the disc 2 rotate,
a transducer 5 mounted on the end of an actuator arm 6 is
selectively positioned by a voice coil motor 8. The voice coil
motor 8 moves the transducer from track to track over the surface
of the disc. The foregoing elements can be mounted in an air-tight
housing 10.
[0028] As indicated by FIG. 2A, the spindle motor assembly 18 is
substantially symmetrical about the axis 32 and includes a motor
shaft 20 over which a hub 22 is positioned. The motor shaft 20 and
hub 22 can be formed as separate pieces each of which can comprise
a polymer such as a liquid crystal polymer and which can be formed,
for example, by an injection molding technique. The hub 22 supports
a data storage disc 24 having a central aperture and which is held
in place by a resilient snap-in retainer 30. In an alternative
implementation, the disc 24 can be held in place by a fastener 80
that is connected to the hub 22, as shown in FIG. 2B. A screw 82 or
similar insert can clamp the fastener 80 to hold the disc 24 in
place.
[0029] A gap 28 exists between the two opposing surfaces formed by
the hub 22 and the shaft 20. In some implementations, the width of
the gap 28 is on the order of several microns. As described in
greater detail below, the outer surface of the shaft 20 and an
opposing surface of the hub 22 form one or more hydrodynamic
journal bearings that are self-pressurizing air-bearings. During
operation, the hub 22 rotates about the shaft 20 while holding the
disc 24.
[0030] FIG. 3 shows further details of the polymeric motor shaft 20
and polymeric hub 22. The hub 22 includes an inner vertical section
34 that extends downward from a horizontal upper section 36 and
which surrounds the motor shaft 20. The hub 22 also includes an
outer vertical section 38 that extends downward from the horizontal
upper section 36. The polymeric snap-in retainer 30 that holds the
disc 24 in place can be molded to the outer vertical section 38 of
the hub 22 during the mold injection process.
[0031] The upper horizontal section 36 and the inner and outer
vertical sections 34, 38 of the hub 22 define an internal cavity
within which a stator 40 is disposed. The stator 40 includes a
series of coils 42 positioned around a laminated core (not shown).
The stator 40 is supported by a vertical member 46 extending upward
from a lower horizontal extension 48 of the shaft 20. The vertical
member 46 that supports the stator 40 can be molded to the lower
horizontal extension 48 and can be formed during mold injection of
the shaft 20.
[0032] As further shown in FIG. 3, one or more permanent magnets 50
are attached to a back-iron 52 which, in turn, is attached to the
inner surface of the hub's outer vertical section 38. The magnet(s)
50 interacts electro-magnetically with the coils 42 to cause
rotational movement of the hub 22 about the motor shaft 20 during
normal operation. Electrical activation of the coils 42 can be
achieved by providing terminal leads to the stator 40.
[0033] The back-iron directs flux away from the magnet 50. An
additional flux conducting ring 54 can be provided at or near the
outer perimeter of the lower horizontal extension 48 of the shaft
20. Such a flux conducting ring 54, which can be formed, for
example, from a metal such as stainless steel, serves as a magnetic
preload to help maintain the hub 22 and shaft 20 in the proper
relationship. The preload 54 forms a thrust bearing that helps
overcome the weight of the disc and hub assembly.
[0034] A pattern of pressure generating features, such as a
herringbone or similar pattern 56, is formed on the polymeric shaft
20 during the mold injection process. The self-pressurizing journal
bearings that establish the stability of the spindle motor use the
pattern of pressure generating features 56 on the shaft 20 to
create pressure gradients in the gap 28 in order to provide radial
stiffness. The herringbone pattern can include spiral grooves 58
(FIG. 4) formed in cylindrical sections of the shaft 20. Instead of
a pattern of herringbone grooves, Rayleigh steps or other chevron
patterns can be used. The depth and geometries of the grooves 58 or
steps can be formed during the molding process.
[0035] As shown in FIG. 3, the shaft 20 also includes pressure
generating features which form a thrust plate 60 in the lower
horizontal extension 48 of the shaft. The thrust plate 60 provides
axial stiffness for the hydrodynamic journal bearings.
[0036] As previously noted, the motor shaft 20 and hub 22 are
polymeric components that can be formed separately by a mold
injection technique. The back-iron 52 and magnet 50 can be attached
to the hub 22 after it is molded. Alternatively, the back-iron 52
and magnet 50 can be provided as inserts to the mold during the
mold injection process. Similarly, the stator 40 and flux
conducting ring 54 can be attached to the shaft 20 after it is
molded. Alternatively, the stator 40 and flux conducting ring 54
can be provided as inserts and molded to the shaft 20 during the
mold injection process.
[0037] To facilitate positioning of the hub 22 with respect to the
motor shaft 20, a resilient snap-in polymeric retainer 62 extends
upward from the lower horizontal extension 48 of the shaft. An
annular lip portion 64 near the bottom of the inner vertical
section 34 of the hub 22 extends outward. When properly positioned,
the snap-in retainer 62 extends partially over the annular lip
portion 64 to hold the hub 22 in place. The snap-in retainer 62 can
be molded to the lower horizontal extension 48 during formation of
the shaft 20.
[0038] FIGS. 5A, 5B and 5C illustrate assembly of the hub 22 and
the motor shaft 20. Initially, the hub 22 is positioned over the
shaft 20 as shown in FIG. 5A so that the inner vertical section 34
surrounds the outer surface of the shaft. Downward pressure is
exerted on the hub 22 until the annular lip portion 64 contacts the
snap-in retainer 62 and pushes it outward (FIG. 5B). Next, the hub
22 is pressed downward until the annular lip portion 64 rests above
the upper surface of the horizontal extension 48. The snap-in
retainer 62 resiliently springs back to it original position (FIG.
5C) to hold the hub in place. A disc 24 then can be placed over the
hub 22 and held in place by the resilient snap-in retainer 30 or,
alternatively, by use of the fastener 80 (FIG. 3B).
[0039] A liquid lubricant such as Z-dol (PFPFE lubricant) can be
provided on the regions of the hub 22 and shaft 20 which contact
one another. To improve the tribology and to reduce the amount of
liquid lubricant that may be absorbed by the polymeric hub and/or
shaft, a solid lubricant can be provided on the hub 22 and shaft 20
prior to the liquid lubricant. For example, as shown in FIG. 6, a
diamond-like carbon (dlc) solid lubricant 66 such as a graphite
film can be vacuum deposited on contact areas between the hub 22
and shaft 20. Such contact areas include the regions near the
pressure generating features 56 formed on the shaft 20 as well as
regions near the pressure generating features that form the thrust
plate 60. The solid lubricant 66 can take the form of a dlc coating
or dlc pads. Other solid lubricants, such as molybdenum sulfide
(MoS.sub.2) also can be used. The use of a solid lubricant can help
reduce the wear and degradation of the liquid lubricant.
[0040] Other implementations are within the scope of the following
claims.
* * * * *