(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`11111111111111111111111111111111111111111111111111111111111111111111111111111111
`
`(43) International Publication Date
`21 June 2001 (21.06.2001)
`
`peT
`
`(10) International Publication Number
`WO 01/45233 Al
`
`(51) International Patent Classification?:
`
`H02K 5/24
`
`(74) Agent: SHURTZ, Steven, P.; Brinks Hofer Gilson & Li(cid:173)
`one, P.O. Box 10087, Chicago, IL 60610 (US).
`
`(21) International Application Number: PCTfUSOO/34078
`
`(22) International Filing Date:
`15 December 2000 (15.12.2000)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`English
`
`(30) Priority Data:
`601172,287
`60/171,817
`
`17 December 1999 (17.12.1999) US
`21 December 1999 (21.12.1999) US
`
`EN CAP MOTOR CORPORATION
`(71) Applicant:
`[USfUS); 540 Delancy Street, Suite 3m, San Francisco,
`CA 94107 (US).
`
`(72) Inventors: LIEU, Dennis, K.; 1036 Wickham Drive, Mor(cid:173)
`aga, CA 94556 (US). NEAL, Griffith, D.; 1330 Bay Street,
`Alameda, CA 94501 (US).
`
`(81) Designated States (national): AE, AG, AL, AM, AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CR, CU, CZ,
`DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR,
`HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR,
`LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ,
`NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM,
`TR, TT, TZ, UA, UG, UZ, VN, YU, ZA, Zw.
`
`(84) Designated States (regional): ARIPO patent (GH, GM,
`KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), Eurasian
`patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), European
`patent (AT, BE, CH, CY, DE, DK, ES, Fl, FR, GB, GR, IE,
`IT, LU, MC, NL, PT, SE, TR), OAPI patent (BF, BJ, CF,
`CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG).
`
`Published:
`With international search report.
`Before the expiration of the time limit for amending the
`claims and to be republished in the event of receipt of
`amendments.
`
`[Continued on next page]
`
`------ --------------------------------------------------------------------------------------
`
`(54) Title: SPINDLE MOTOR WITH ENCAPSULATED STATOR AND METHOD OF MAKING SAME
`
`---------=
`
`51
`
`~
`~
`M
`tn
`:::t (57) Abstract: A spindle motor (20) comprises a baseplate (22), a shaft (26) supported by said baseplate (22), a stator assembly
`S (21) having windings (31), the stator (21) being rigidly attached to said baseplate (22), injection molded thermoplastic material (36)
`o in operable proximity to the stator assembly (21). In one embodiment, a stator (71) is cordless. In order embodiments, the stator
`
`encapsulating said windings (31), and a hub (28) supported on said shaft (26), said hub (28) having a magnet (23) connected thereto
`
`: , (21) has a core (24) and the core is substantially encapsulated by the thermoplastic material (36). In preferred embodiments, the
`~ thermoplastic material (36) secures the stator to the baseplate (22) or forms the baseplate (22).
`
`Page 1 of 41
`
`PETITIONERS' EXHIBIT 1008
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`

`

`WO 01/45233 Al
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`11111111111111111111111111111111111111111111111111111111111111111111111111111111
`
`For two-letter codes and other abbreviations, refer to the "Guid(cid:173)
`ance Notes on Codes and Abbreviations" appearing at the begin(cid:173)
`ning of each regular issue of the PCT Gazette.
`
`Page 2 of 41
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`

`WO 01145233
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`peT /uSOO/34078
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`-1-
`
`SPINDLE MOTOR WITH ENCAPSULATED
`STATOR AND METHOD OF MAKING SAME
`
`REFERENCE TO EARLIER FILED APPLICATION.
`
`The present application claims the benefit of the filing date under 35
`
`5
`
`U.S.C. §119(e) of provisional U.S. Patent Application Serial No. 60/172,287,
`
`filed December 17, 1999, and of provisional U.S. Patent Application Serial No.
`
`60/171,817, filed December 21, 1999, both of which are hereby incorporated
`
`by reference.
`
`FIELD OF THE INVENTION
`
`10
`
`The present invention relates to spindle motors. More particularly the
`
`invention relates to spindle motors with an encapsulated stator and methods
`
`of making the same, and hard drives utilizing the same.
`
`BACKGROUND OF THE INVENTION
`
`Computers commonly use disc drives for memory storage purposes.
`
`15
`
`Disc drives include a stack of one or more magnetic discs that rotate and are
`
`accessed using a head or read-write transducer. Typically, a high-speed
`
`motor such as a spindle motor is used to rotate the discs.
`
`An example of a conventional spindle motor 1 is shown in FIG. 1. The
`
`motor 1 includes a baseplate 2 which is usually made from machined
`
`20
`
`aluminum, a stator core 4, a shaft 6, bearings 7 and a disc support member 8,
`
`also referred to as a hub. A magnet 3 is attached to the disc support
`
`member or hub 8. The hub 8 may be made of steel so that it acts as a flux
`
`return ring. The stator core 4 is secured to the baseplate 2 using a support
`
`member 5. One end of the shaft 6 is inserted into the baseplate 2 and the
`
`25
`
`other end of the shaft 6 supports bearings 7, which are also attached to the
`
`hub 8. A flexible electrical cable 9 may be supported on the baseplate 2.
`
`Wires 12 from the cable exit through holes 15 in the baseplate. The flexible
`
`cable 9 is also used to seal the baseplate so that particulate material is not
`
`expelled from the motor 1. The wires 12 carry electric current to the wire
`
`30
`
`windings 11 wrapped around poles formed on the core 4. Mounting holes 14
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`Page 3 of 41
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`-2-
`
`on the baseplate are used to secure the motor to the baseplate of a housing
`
`for a hard disk drive or other electrical device. The hub 8 includes holes 13
`
`that are used to attach the media discs (not shown) to the hub 8.
`
`Each of these parts must be fixed at predefined tolerances with respect
`
`5
`
`to one another. Accuracy in these tolerances can significantly enhance motor
`
`performance.
`
`In operation, the disc stack is placed upon the hub. The stator
`
`windings 11 are selectively energized and interact with the permanent
`
`magnet 3 to cause a defined rotation of the hub. As hub 8 rotates, the head
`
`10
`
`engages in reading or writing activities baseplated upon instructions from the
`
`CPU in the computer.
`
`Manufacturers of disc drives are constantly seeking to improve the
`
`speed with which data can be accessed. To an extent, this speed depends
`
`upon the speed of the spindle motor, as existing magneto-resistive head
`
`15
`
`technology is capable of accessing data at a rate greater than the speed
`
`offered by the highest speed spindle motor currently in production. The speed
`
`of the spindle motor is dependent upon the dimensional consistency or
`
`tolerances between the various components of the motor and the rigidity of
`
`the parts. Greater dimensional consistency between components and rigidity
`
`20
`
`of the components leads to a smaller gap between the stator 4 and the
`
`magnet 3, producing more force, which provides more torque and enables
`
`faster acceleration and higher rotational speeds. In the design shown, the
`
`gap between the stator 4 and magnet 3 is located near the outside diameter
`
`of the hub 8. Thus the magnet 3 is attached to the most flexible part of the
`
`25
`
`hub, making the spindle vulnerable to vibration caused by misalignment of the
`
`motor. One,drawback of conventional spindle motors is that a number of
`
`separate parts are required to fix motor components to one another. This can
`
`lead to stack up tolerances which reduce the overall dimensional consistency
`
`between the components. Stack up tolerances refers to the sum of the
`
`30
`
`variation of all the tolerances of all the parts, as well as the overall tolerance
`
`that relates to the alignment of the parts relative to one another.
`
`Page 4 of 41
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`Another drawback to the conventional design is the cost of the
`
`machined baseplate 2. Unfortunately, die-casting or forging does not produce
`
`baseplates with sufficient precision. Therefore quality baseplates are made
`
`by machining the necessary surfaces and tolerances. The flexible cable 9
`
`5
`
`also adds to the cost. Steel hubs 8 are expensive and difficult to machine.
`
`Aluminum hubs 8 are less expensive, but still must be extensively machined
`
`in the bearing area. The stator 4 is a major source of acoustic noise. Also,
`
`the stator assembly is difficult to clean, so that particulates are not emitted
`
`from the motor.
`
`10
`
`In an effort to enable increased motor speed, some hard disc
`
`manufacturers have turned to the use of hydrodynamic bearings. These
`
`hydrodynamic bearings, however, have different aspect ratios from
`
`conventional bearings. An example of a different aspect ratio may be found in
`
`a cylindrical hydrodynamic bearing in which the length of the bearing is
`
`15
`
`greater than it's diameter. This results in more susceptibility to problems
`
`induced by differing coefficients of thermal expansion than other metals used
`
`in existing spindle motors, making it difficult to maintain dimensional
`
`consistency over the operating temperature that the drive sees between the
`
`hydrodynamic bearings and other metal parts of the motor. Hydrodynamic
`
`20
`
`bearings have less stiffness than conventional ball bearings so they are more
`
`susceptible to imprecise rotation when exposed to vibrations or shock.
`
`An important characteristic of a hard drive is the amount of information
`
`that can be stored on a disc. One method to store more information on a disc
`
`is to place data tracks more closely together. Presently this spacing between
`
`25
`
`portions of information is limited due to vibrations occurring during the
`
`operation of the motor. These vibrations can be caused when the stator
`
`windings are energized, which results in vibrations of a particular frequency.
`
`These vibrations also occur from harmonic oscillations in the hub and discs
`
`during rotation, caused primarily by non-uniform size media discs.
`
`30
`
`An important factor in motor design is the lowering of the operating
`
`temperature of the motor. Increased motor temperature affects the electrical
`
`efficiency of the motor and bearing life. As temperature increases, resistive
`
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`loses in wire increase, thereby reducing total motor power. Furthermore, the
`
`Arhennius equation predicts that the failure rate of an electrical device is
`
`exponentially related to its operating temperature. The frictional heat
`
`generated by bearings increases with speed. Also, as bearings get hot they
`
`5
`
`expand, and the bearing cages get stressed and may deflect, causing non(cid:173)
`
`uniform rotation and the resultant further heat increase, non-uniform rotation
`
`requiring greater spacing in data tracks, and reduced bearing life. One
`
`drawback with existing motor designs is their limited effective dissipation of
`
`the heat, and difficulty in incorporating heat sinks to aid in heat dissipation. In
`
`10
`
`the design of the motor 1 there is a small direct path between the stator and
`
`the core, which makes it difficult to cool the stator, which reduces motor
`
`efficiency the above reasons. Also 5x11 mm bearings commonly used are
`
`not sufficiently stable nor have a life required for desired high-speed operation
`
`(10,000 rpm and above). In addition, in current motors the operating
`
`15
`
`temperatures generally increase as the size of the motor is decreased.
`
`20
`
`25
`
`Manufacturers have established strict requirements on the outgassing
`
`of materials that are used inside a hard disc drive. These requirements are
`
`intended to reduce the emission of materials onto the magnetic media or
`
`heads during the operation of the drive. Of primary concern are glues used to
`
`attach components together, varnish used to insulate wire, and epoxy used to
`
`protect steel laminations from oxidation.
`
`In addition to such outgassed materials, airborne particulate in a drive
`
`may lead to head damage. Also, airborne particulates in the disc drive could
`
`interfere with signal transfer between the read/write head and the media. To
`
`reduce the effects of potential airborne particulate, hard drives are
`
`manufactured to exacting clean room standards and air filters are installed
`
`inside of the drive to reduce the contamination levels during operation.
`
`Heads used in disc drives are susceptible to damage from electrical
`
`shorts passing through a small air gap between the media and the head
`
`30
`
`surface. In order to prevent such shorts, some hard drives use a plastic or
`
`rubber ring to electrically isolate the spindle motor from the hard drive case.
`
`This rubber ring may also mechanically isolate the spindle motor from the
`
`Page 6 of 41
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`-5-
`
`hard drive case so that vibrations generated by the motor are not transmitted
`
`to other components in the hard drive. A drawback to this design is the
`
`requirement of an extra component.
`
`Another example of a spindle motor is shown in U.S. Patent
`
`5
`
`No. 5,694,268 (Dunfield et al.) (incorporated herein by reference). Referring
`
`to FIGS. 7 and 8 of this patent, a stator 200 of the spindle motor is
`
`encapsulated with an overmold 209. The overmolded stator contains
`
`openings through which mounting pins 242 may be inserted for attaching the
`
`stator 200 to a baseplate. One drawback to this design is that baseplate does
`
`10
`
`not receive any increased rigidity through this type of connection.
`
`U.S. Patent No. 5,672,972 (Viskochil) (incorporated herein by
`
`reference) also discloses a spindle motor having an overmolded stator. One
`
`drawback with the overmold used in these patents is that it has a different
`
`coefficient of linear thermal expansion ("CL TEn) than the corresponding metal
`
`15
`
`parts to which it is attached. Another drawback with the overmold is that it is
`
`not very effective at dissipating heat. Further, the overmolds shown in these
`
`patents are not effective in dampening some vibrations generated by
`
`energizing the stator windings.
`
`U.S. Patent No. 5,806,169 (Trago) (incorporated herein by reference)
`
`20
`
`discloses a method of fabricating an injection molded motor assembly.
`
`However, the motor disclosed in Trago is a step motor, not a high-speed
`
`spindle motor, and would not be used in applications such as hard disc drives.
`
`Thus, a need exists for an improved spindle motor, having properties that will
`
`be especially useful in a hard disc drive, overcoming the aforementioned
`
`25
`
`problems.
`
`BRIEF SUMMARY OF THE INVENTION
`
`A spindle motor has been invented which overcomes many of the
`
`foregoing problems. In addition, unique stator and baseplate assemblies and
`
`other components of a high-speed motor have been invented, as well as
`
`30
`
`methods of manufacturing such motors. In one aspect, the invention is a
`
`spindle motor comprising: a baseplate; a shaft supported by said baseplate; a
`
`Page 7 of 41
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`peT fUSOO/34078
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`-6-
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`stator assembly comprising a core having poles and windings around said
`
`poles, the stator core being rigidly attached to said baseplate; injection
`
`molded thermoplastic material encapsulating said windings, and a hub
`
`supported on said shaft, said hub having a magnet connected thereto in
`
`5
`
`operable proximity to the stator assembly.
`
`In a second aspect the invention is a spindle motor comprising: a
`
`baseplate; a shaft supported by said baseplate; a stator assembly comprising
`
`a core having poles and windings around said poles, the stator assembly
`
`being spaced from the baseplate; a hub supported on said shaft, said hub
`
`10
`
`having a magnet connected thereto in operable proximity to the stator
`
`assembly; and a thermoplastic material secured to the baseplate and
`
`encapsulating the stator windings, the thermoplastic material joining the stator
`
`assembly to the baseplate in the space between the stator assembly and the
`
`baseplate.
`
`15
`
`In another aspect the invention is a baseplate and stator combination
`
`comprising: a baseplate; a stator assembly comprising a core having poles,
`
`and windings around said poles; and an injection molded thermoplastic
`
`material encapsulating the windings and also locking the stator assembly to
`
`the baseplate, the baseplate and stator assembly not being in direct contact
`
`20
`
`with one another but rather having a space between them filled in by the
`
`thermoplastic material.
`
`In yet another aspect the invention is a spindle motor comprising:
`
`baseplate made of stiff thermoplastic material, having a modulus of elasticity
`
`of at least 1,000,000 psi, and a metal plate substantially encapsulated by the
`
`25
`
`stiff thermoplastic material; a shaft supported by said baseplate; a stator
`
`assembly comprising a core having poles and windings around said poles; a
`
`hub supported on said shaft, said hub having a magnet connected thereto in
`
`operable proximity to the stator assembly; and a vibration dampening
`
`thermoplastic material encapsulating the stator windings, the vibration
`
`30
`
`dampening thermoplastic material having a vibration dampening ratio of at
`
`least 0.05 in the range of 0-500 Hz and joining the stator assembly to the
`
`baseplate.
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`Page 8 of 41
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`-7-
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`In another aspect the invention is a method of manufacturing a spindle
`
`motor comprising the steps of: providing a baseplate, a hub having a magnet
`
`connected thereto and a stator assembly comprising a core having poles and
`
`windings around said poles; rigidly attaching the stator core to the baseplate;
`
`5
`
`injection molding a thermoplastic material to encapsulate the windings after
`
`the core is attached to the baseplate, and mounting the hub on a shaft
`
`supported on the baseplate so that the magnet on the hub is in operable
`
`proximity to the stator assembly and so that the hub can rotate with respect to
`
`the stator.
`
`10
`
`In another aspect the invention is a method of manufacturing a spindle
`
`motor comprising the steps of: providing a baseplate, a stator assembly
`
`comprising a core having poles and windings around said poles, and a hub
`
`having a magnet connected thereto; injection molding a thermoplastic material
`
`to encapsulate the windings and in between the baseplate and stator
`
`15
`
`assembly so as to secure the stator assembly to the baseplate sufficiently to
`
`allow the rigidity of the core to help stiffen the baseplate, and rotatably
`
`mounting the hub on a shaft rigidly supported on the baseplate so that the
`
`magnet on the hub is in operable proximity to the stator assembly.
`
`In another aspect the invention is a method of manufacturing a spindle
`
`20
`
`motor comprising the steps of: providing a metal baseplate insert, a hub
`
`having a magnet connected thereto and a stator assembly comprising a core
`
`having poles and windings around said poles; holding the baseplate insert
`
`and stator assembly in an injection mold and injection molding a thermoplastic
`
`material so as to substantially encapsulate the baseplate insert and the
`
`25
`
`windings and secure the stator assembly and baseplate insert together; and
`
`rotatably mounting the hub on a shaft rigidly supported on the combined
`
`encapsulated baseplate insert and stator assembly so that the magnet on the
`
`hub is in operable proximity to the stator assembly.
`
`In another aspect the invention is a spindle motor comprising: a
`
`30
`
`baseplate; a shaft supported by said baseplate; a coreless stator assembly
`
`comprising windings encapsulated in a thermoplastic material; and a hub
`
`rotatably supported on said shaft, said shaft having a magnet connected
`
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`-8-
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`thereto in operable proximity to the stator assembly, the hub also including a
`
`flux return ring supported opposite the magnet so that the stator assembly is
`
`located between the flux return ring and the magnet.
`
`The invention provides the foregoing and other features, and the
`
`5
`
`advantages of the invention will become further apparent from the following
`
`detailed description of the presently preferred embodiments, read in conjunction
`
`with the accompanying drawings. The detailed description and drawings are
`
`merely illustrative of the invention and do not limit the scope of the invention,
`
`which is defined by the appended claims and equivalents thereof.
`
`10
`
`BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
`
`FIG. 1 is a cross-sectional view of a prior art high-speed motor.
`
`FIG.2 is a cross-sectional view of a high-speed motor in accordance
`
`with the first embodiment of the present invention.
`
`FIG. 3 is a cross-sectional view of the encapsulated stator used in the
`
`15
`
`motor of FIG. 2.
`
`FIG.4 is a cross-sectional view of a high-speed motor in accordance
`
`with a second embodiment of the present invention.
`
`FIG. 5 is a plan view of a lamination used in the core of the stator of the
`
`high-speed motor of FIG. 4.
`
`FIG. 6 is a plan view of the stator of the high-speed motor of FIG. 4.
`
`FIG. 7 is a cross-sectional view of the stator shown in FIG. 6 taken
`
`along line 7-7.
`
`FIG. 8 is an elevational view of the ferrule used in the high-speed
`
`motor of FIG. 4.
`
`FIG. 9 is an elevational and partial cross-sectional view of the shaft
`
`used in the high-speed motor of FIG. 4.
`
`FIG. 10 is a top plan view of the baseplate used in the high-speed
`
`motor of FIG. 4.
`
`FIG. 11 is a cross-sectional view taken along line 11-11 of FIG. 10.
`
`FIG. 12 is a cross-sectional view of the hub used in the high-speed
`
`motor of FIG. 4.
`
`20
`
`25
`
`30
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`
`FIG. 13 is a cross-sectional view of a high-speed motor in accordance
`
`with a third embodiment of the present invention.
`
`FIG. 14 is a cross-sectional view of a high-speed motor in accordance
`
`with the fourth embodiment of the present invention.
`
`5
`
`FIG. 15 is an exploded view of a hard disc drive of the present
`
`invention.
`
`DETAILED DESCRIPTION OF THE DRAWINGS AND PREFERRED
`EMBODIMENTS OF THE INVENTION
`
`First Embodiment
`
`10
`
`A first embodiment of a high-speed motor of the present invention is
`
`shown in FIGS. 2-3. By "high-speed" it is meant that the motor can operate at
`
`over 5,000 rpm. The spindle motor 20 is designed for rotating a disc or stack
`
`of discs in a computer hard disc drive. Motor 20 is formed using an
`
`encapsulation method to encapsulate the stator windings.
`
`15
`
`Referring to FIGS. 2-3, a stator assembly 21 is first constructed, using
`
`conventional steel laminations 24a, 24b, etc forming a magnetically inducible
`
`core 24 having a plurality of poles thereon, and wire windings 31 which serve
`
`as conductors. The conductors induce or otherwise create a plurality of
`
`magnetic fields in the core when electrical current is conducted through the
`
`20
`
`conductors. In this embodiment, a magnetic field is induced in each of the
`
`poles. Once the windings are in place, the wire 31 is encapsulated with a
`
`thermoplastic material 36, described in more detail hereafter, and the core 24
`
`is substantially encapsulated by the material 36 (FIG. 3).
`
`Substantial encapsulation means that the material 36 either entirely
`
`25
`
`surrounds the core 24 or surrounds almost all of it except for minor areas of
`
`the core 24 that may be exposed, such as the face of the poles. However,
`
`substantial encapsulation means that the material 36, wire 31 and core 24 are
`
`rigidly fixed together, and behave as a single component with respect to
`
`harmonic oscillation vibration.
`
`30
`
`As shown in FIG. 2, a shaft 26 is connected to the baseplate 22 and is
`
`surrounded by bearings 27. A rotor or magnet 23 is fixed to the inside of the
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`hub 28 so as to be in operable proximity to the stator 21. The magnet 23 is
`
`preferably a permanent magnet, as described below. The baseplate 22
`
`includes a flex cable 29 as in the motor of FIG. 1. Wires 32 may be coupled
`
`to a control circuit board (not shown) for the motor 20. Alternatively the
`
`5
`
`connector may be a flexible circuit with copper pads allowing spring contact
`
`interconnection.
`
`The baseplate 22 is generally connected to the hard drive case (not
`
`shown). Connecting members (not shown), such as screws, may be used to
`
`fix the baseplate 22 to the hard drive case, using holes 34. Alternatively,
`
`10
`
`other types of mounting features such as connecting pins or legs may be
`
`formed as part of the baseplate 22. Alternatively, the baseplate of the motor
`
`may constitute the baseplate section of the hard drive housing.
`
`The thermoplastic material 36 is preferably a thermally conductive but
`
`non-electrically conductive plastic. In addition, the plastic preferably includes
`
`15
`
`ceramic filler particles that enhance the thermal conductivity of the plastic. A
`
`preferred form of plastic is polyphenyl sulfide (PPS) sold under the tradename
`
`"Konduit" by LNP. Grade OTF-212 PPS is particularly preferred. Another
`
`preferred thermoplastic material is a liquid crystal polymer sold by LNP.
`
`Examples of other suitable thermoplastic resins include, but are not limited to,
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`20
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`thermoplastic resins such as 6,6-polyamide, 6-polyamide,
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`4,6-polyamide, 12, 12-polyamide, 6, 12-polyamide, and polyamides containing
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`aromatic monomers, polybutylene terephthalate, polyethylene terephthalate,
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`polyethylene napththalate, polybutylene napththalate, aromatic polyesters,
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`liquid crystal polymers, polycyclohexane dimethylol terephthalate,
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`25
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`copolyetheresters, polyphenylene sulfide, polyacylics, polypropylene,
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`polyethylene, polyacetals, polymethylpentene, polyetherimides,
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`polycarbonate, polysulfone, polyethersulfone, polyphenylene oxide,
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`polystyrene, styrene copolymer, mixtures and graft copolymers of styrene and
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`rubber, and glass reinforced or impact modified versions of such resins.
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`30
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`Blends of these resins such as polyphenylene oxide and polyamide blends,
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`and polycarbonate and polybutylene terephthalate, may also be used in this
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`invention.
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`Page 12 of 41
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`WO 01145233
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`peT /uS00/34078
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`-11-
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`Referring to FIG. 2, the bearings 27 include an upper bearing and a
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`lower bearing. Also, each bearing 27 has an outer surface and an inner
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`surface. The outer surface of the bearings contacts the hub 28. The inner
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`surfaces of the bearings 27 contact the shaft 26. The bearings are preferably
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`5
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`annular shaped. The inner surfaces of the bearings 27 may be press fit onto
`
`the shaft 26. A glue may also be used. The outer surface of the bearings 27
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`may be press fit into the interior portion of the hub 28. A glue may also be
`
`used. The bearings in the embodiment shown in FIG. 2 are ball bearings.
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`Alternatively other types of bearings, such as hydrodynamic or combinations
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`10
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`of hydrodynamic and magnetic bearings, may be used. The bearings are
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`typically made of stainless steel.
`
`The shaft 26 is concentrically supported by the baseplate 22. The
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`shaft 26 includes a top portion and a bottom portion. The top portion of the
`
`shaft 26 supports the hub 28. The bottom portion of the shaft 26 is rigidly
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`15
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`fixed to the baseplate 22. Thus, in this embodiment, the hub 28 is freely
`
`rotatable relative to the shaft 26 and baseplate 22. The shaft 26 is preferably
`
`cylindrical shaped and may be made of stainless steel.
`
`The hub 28 is concentrically disposed around the shaft 26. The hub 28
`
`is spaced apart from the stator 21. The hub 28 is preferably made of steel so
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`20
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`that the portion of the hub 28 adjacent the magnet 23 provides a flux return
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`ring. The magnet 23 is glued to the hub 28. As shown in FIG. 2, the
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`magnet 23 concentrically surrounds the stator 21.
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`The magnet 23 is preferably a sintered part and is one solid piece. The
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`magnet 23 is placed in a magnetizer which puts a plurality of discrete North
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`25
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`and 'South poles onto the magnet 23, dependant on the number of poles on
`
`the stator 21. Holes 33 in the top of the hub 28 are used to attach the
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`magnetic media used in hard drive, just as with motor 10.
`
`Operation of the First Embodiment
`
`In operation, the spindle motor shown in FIGS. 2-3 is driven by
`
`30
`
`supplying electrical pulses to the wires 32. These pulses are used to
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`selectively energize the windings 31 around the stator poles. This results in a
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`moving magnetic field. This magnetic field interacts with the magnetic field
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`Page 13 of 41
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`WO 01145233
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`peT /uS00/34078
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`-12-
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`generated by the magnet 23 in a manner that causes the magnet 23 to rotate
`
`about the stator 21. As a result, the hub 28 begins to rotate about the
`
`shaft 26. The bearings 27 facilitate the rotation of the hub 28.
`
`Discs or a disc stack (not shown) that are placed upon the hub are
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`5
`
`caused to rotate as the hub 28 rotates. A head (not shown) then reads and
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`writes data to and from the discs.
`
`Method of Making the First Embodiment
`
`The encapsulated stator shown in FIGS. 2 and 3 is made in part using
`
`an encapsulation technique. This encapsulation technique involves the
`
`10
`
`following steps. First, a mold is constructed to produce a part with desired
`
`geometry. The mold has two halves. The stator core with windings 31
`
`thereon is placed within the mold and the two halves are closed. Core pins
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`hold the stator core 24 in its correct position. Second, using solid-state
`
`process controlled injection molding, plastic is injected through one or more
`
`15
`
`gates around the stator, so as to encapsulate the stator. As plastic flows in,
`
`core pins are withdrawn so that the plastic completely surrounds the windings
`
`31 and most if not all of the core 24, thus forming the stator assembly 21
`
`(FIG. 3).
`
`A core support 25 is used to support the core 24 and transfer the
`
`20
`
`rigidity of the encapsulated stator 21 to the baseplate 22. In other
`
`embodiments, the support 25 may simply be formed as part of the
`
`baseplate 22. The encapsulated stator 21 is press fit into the support 25.
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`The shaft 26 is press fit and possibly glued into the baseplate 22.
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`Next, glue is placed on the inner and outer bearing surfaces and the bearings
`
`25
`
`are press fit onto the shaft and into the interior portion of the hub 28.
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`After the spindle motor is assembled, it can be used to construct a hard
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`disc drive by using the holes 34 to mount the motor to the baseplate of the
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`hard disc drive. Thereafter, construction of the hard disc drive can follow
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`conventional methods.
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`Page 14 of 41
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`WO 01145233
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`peT /uSOO/34078
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`-13-
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`Advantages of the First Embodiment
`
`An advantageous feature of the first embodiment is provided by the
`
`fact that the thermoplastic material 36 is preferably a monolithic body or
`
`monolithically formed using an encapsulation technique. This monolithic body
`
`5
`
`provides a single structure that holds the core laminations 24a, 24b etc. and
`
`wire 31 together.
`
`The preferred thermoplastic material 36 is a type of thermoplastic with
`
`a CL TE similar to that of the steel hub 28. This in turn facilitates optimal fits
`
`between the stator and the hub 28.
`
`10
`
`Through the use of the present embodiment, a particular plastic may
`
`be chosen for the material 36 that has properties of vibration dampening ratio
`
`and modulus of elasticity, as well as rockwell hardness, flex modulus, and
`
`elongation, that are specifically designed to counteract the vibratory
`
`frequencies generated by the motor. Thus, the disclosed spindle motor
`
`15
`
`substantially reduces motor vibration. This reduced vibration allows
`
`information on a disc to be stored closer together, thereby enabling higher
`
`data density. The encapsulation also reduces acoustic emissions from the
`
`motor, making it quieter.
`
`As discussed above, controlling heat dissipation in conventional
`
`20
`
`spindle motors is difficult to achieve. A particular plastic may be chosen for
`
`encapsulating the stator 21 is designed to facilitate heat dissipation. By
`
`putting this material in intimate contact with the motor windings and then
`
`creating a solid thermal conductive pathway to the housing of the drive,
`
`overall motor temperature may be reduced.
`
`25
`
`The disclosed spindle motor also reduces the emission of materials
`
`from the motor components onto the magnetic media or heads of the disc
`
`drive. This is achieved because components such as the stator, which
`
`potentially emit such materials, are substantially encapsulated in plastic.
`
`In addition, the disclosed spindle motor obviates the necessity of a
`
`30
`
`separate plastic or rubber ring sometimes used to isolate the spindle motor
`
`from the hard drive in order to prevent shorts from being transferred to the
`
`magnetic media and ultimately the read-write heads. Because the stator 21 is
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`Page 15 of 41
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