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`g;g,,.,..ess Mail" mailing label number EL669269646US.
`~~ of Deposit March 2, 2001
`
`A
`
`Case No. 8864/20
`
`PATENT APPLICATION TRANSMITTAL LETTER
`
`To the Commissioner for Patents:
`
`Transmitted herewith for filing is the patent application of: Griffith D. Neal for: STATOR ASSEMBLY MADE FROM A PLURALITY OF
`
`TOROIDAL CORE ARC SEGMENTS ANDMOTOR USING SAME. Enclosed are:
`
`~ Six (6) sheet(s) of drawings, twenty-four (24) pages of application (including title page), and the following Appendices: __ .
`
`~ Declaration.
`
`Power of Attorney.
`
`Verified statement to establish small entity status under 37 CFR §§ 1.9 and 1.27.
`
`Assignment transmittal letter and Assignment of the invention to: Encap Motor Corporation.
`
`~
`0
`~
`D
`
`Col.2
`No. Extra
`
`Col.1
`No. Filed
`
`C.laims as Filed
`GG>i.
`E}iwic Fee
`9
`29-20
`t:ofal Claims
`5.3
`2
`lnae . Claims
`Mufti le De endent Claims Present
`*}f~he difference in col. 1 is less than zero,
`€1.nter "O" in col. 2.
`
`Small Entit
`Rate
`
`x$9=
`x$40=
`+$135=
`
`Total
`
`or
`Fee
`$ 355 or
`$81
`or
`or
`$40
`or
`or
`
`$
`
`$516
`
`Other Than
`Small Enti
`
`Rate
`
`x$18=
`x$80=
`+$270=
`
`Fee
`$ 710
`$
`$
`$
`
`Total
`
`$
`
`Please charge my Deposit Account No. 23-1925 in the amount of$:
`
`A duplicate copy of this sheet is enclosed.
`
`A check in the amount of$: 516 to cover the filing fee is enclosed.
`
`The Commissioner is hereby authorized to charge payment of the following fees associated with this communication or credit
`any overpayment to Deposit Account No. 23-1925. A duplicate copy of this sheet is enclosed.
`
`~ Any additional filing fees required under 37 CFR § 1.16.
`
`~ Any patent application processing fees under 37 CFR § 1.17.
`
`D
`
`Date
`
`The Commissioner is hereby authorized to charge payment of the following fees during the pendency of this application or
`credit any overpayment to Deposit Account No. 23-1925. A duplicate copy of this sheet is enclosed.
`D
`D
`
`Any filing fees under 37 CFR § 1.16 for presentation of extra claims.
`
`Any patent application processing fees under 37 CFR § 1.17.
`
`~ lo T~e issue fee set in 37 CFR § 1.18 at or ~nee , pursuant to 37 CFR § 1 _311 (b).
`3
`I
`
`(
`
`Sailesh K. Patel
`BRINKS HOFER GILSON & LIONE
`Registration No. 46,982
`
`Rev. Nov-98
`F:\COMMON\SPatel\8864-20 Patent App Trans Ur.doc
`
`Mitsuba - 1008
`Page 1 of 312
`
`

`

`"Express Mail" mailing label number ____ _
`
`Date of Deposit: - - - - - - - - - -
`
`Our Case No. 8864/20
`
`IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
`APPLICATION FOR UNITED STATES LETTERS PATENT
`
`INVENTOR:
`
`GRIFFITH D. NEAL
`
`TITLE:
`
`ATTORNEYS:
`
`STATOR ASSEMBLY MADE FROM A
`PLURALITY OF TOROIDAL CORE
`ARC SEGMENTS AND MOTOR
`USING SAME
`
`STEVEN P. SHURTZ
`REG. NO. 31,424
`SAILESH K. PATEL
`REG. NO. 46,982
`BRINKS HOFER GILSON & LIONE
`P.O. BOX 10395
`CHICAGO, ILLINOIS 60610
`(312) 321-4200
`
`Mitsuba - 1008
`Page 2 of 312
`
`

`

`-1-
`
`STATOR ASSEMBLY MADE FROM A PLURALITY OF TOROIDAL
`CORE SEGMENTS AND MOTOR USING SAME
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to a stator assembly used in a
`
`5
`
`motor. It relates particularly to a spindle motor such as used in a hard disc
`
`drive, and to the construction and arrangement of a stator assembly made
`
`10
`
`15
`
`20
`
`25
`
`from a plurality of arc segments.
`
`BACKGROUND OF THE INVENTION
`
`Computers commonly use disc drives for memory storage purposes.
`
`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.
`
`In conventional spindle motors, stators have been made by laminating
`
`together stamped pieces of steel. These stamped pieces of steel are
`
`generally circular in nature, but also have "poles" extending either inwardly or
`outwardly, depending on whether the rotor is on the inside or surrounds the
`stator. The stamped pieces are laminated together and then coated with
`insulation. Wire is then wound around the poles to form stator windings.
`An example of a conventional spindle motor 1 is shown in FIG. 1. The
`
`motor 1 includes a base 2 which is usually made from die cast aluminum, a
`stator 4, a shaft 6, bearings 7 and a disc support member 8, also referred to
`
`as a hub. A magnet 3 and flux return ring 5 are attached to the disc support
`
`member 8. The stator 4 is separated from the base 2 using an insulator (not
`
`shown) and attached to the base 2 using a glue. Distinct structures are
`formed in the base 2 and the disc support member 8 to accommodate the
`
`bearings 7. One end of the shaft 6 is inserted into the bearing 7 positioned in
`
`the base 2 and the other end of the shaft 6 is placed in the bearing 7 located
`in the hub 8. A separate electrical connector 9 may also be inserted into the
`
`base 2.
`
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`Page 3 of 312
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`

`

`-2-
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`Each of these parts must be fixed at predefined tolerances with respect
`
`to one another. Accuracy in these tolerances can significantly enhance motor
`
`performance.
`
`In operation, the disc stack is placed upon the hub. The stator
`
`5
`
`windings are selectively energized and interact with the permanent magnet to
`
`cause a defined rotation of the hub. As hub 8 rotates, the head engages in
`
`reading or writing activities based upon instructions from the CPU in the
`
`computer.
`
`Manufacturers of disc drives are constantly seeking to improve the
`
`10
`
`speed with which data can be accessed. To an extent, this speed depends
`
`15
`
`20
`
`25
`
`upon the efficiency of the spindle motor, as existing magneto-resistive head
`
`technology is capable of accessing data at a rate greater than the speed
`
`offered by the highest speed spindle motor currently in production. The
`
`efficiency of the spindle motor is dependent upon the dimensional consistency
`
`or tolerances between the various components of the motor. Greater
`dimensional consistency between 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.
`
`The conventional method of forming stators has a number of
`drawbacks. First, most steel is manufactured in rolled sheets and thus has a
`
`grain orientation. The grain orientation has an effect on the magnetic flux
`
`properties of the steel. In circular stamped pieces of steel, the grain
`
`orientation at different points around the circle differs. Compared from the
`
`radius line of the circle, the grain orientation is sometimes aligned along the
`
`radius, sometimes transverse to it, and mostly at a varying angle to the radius.
`The un-aligned grain structure of conventional stators causes the magnetic
`
`flux values to differ in parts of the stator and thus the motor does not have
`
`consistent and uniform torque properties as it rotates.
`
`Another drawback with using circular steel pieces is that, especially for
`
`30
`
`inward facing poles, it has been difficult to wind the wire windings tightly
`
`because of the cramped space to work inside of the laminated stator core.
`The cramped working space creates a lower limit on the size of the stator and
`
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`Page 4 of 312
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`

`

`-3-
`
`thus the motor. The limited working space also results in a low packing
`
`density of wire. The packing density of wire coiled around the poles affects
`
`the amount of power generated by the motor. Increasing packing density
`
`increases the power and thus the efficiency of the spindle motor.
`
`5
`
`An important factor in motor design is to reduce stack up tolerances in
`
`the motor. Stack up tolerances reduce the overall dimensional consistency
`
`between the components. Stack up tolerances refer to the sum of the
`
`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. One source
`
`10
`
`of stack up tolerances is from the circular stator body. Generally, the
`
`thickness of rolled steel is not uniform across the width of the roll. Sometimes
`
`the edges are thicker or thinner than the center. In a stator made from
`
`circular stamped pieces, the thickness of individual laminations are thus
`
`different from one side to the other. When stacked together, this creates a
`
`stack up tolerance problem. Furthermore, the circular stampings leave a lot of
`
`wasted steel that is removed and must be recycled or discarded.
`
`Another 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,
`
`20
`
`resistive 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 expand, and the bearing cages get stressed and may deflect,
`
`25
`
`causing non-uniform rotation reducing bearing life. This non-uniform rotation
`
`causes a further problem of limiting the ability of the servo system controlling
`
`the read/write heads to follow data tracks on the magnetic media. 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
`
`30
`
`addition, in current motors the operating temperatures generally increase as
`
`the size of the motor is decreased.
`
`Mitsuba - 1008
`Page 5 of 312
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`

`

`RlllU/Wlll'-M!
`
`-4-
`
`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
`
`5
`
`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
`
`10
`
`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.
`
`An example of a spindle motor is shown in U.S. Patent No. 5,694,268
`(Dunfield et a/.) (incorporated herein by reference). Referring to FIG. 5 of this
`patent, a stator of the spindle motor is encapsulated with an overmold 42.
`The overmolded stator 40 contains openings through which mounting pins 44
`may be inserted for attaching the stator 200 to a base. 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 TE") than the corresponding metal 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)
`
`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.
`Further, none of these three prior art designs address the problem of variation
`
`in the thickness of steel used to make the stator cores and the non-uniform
`grain structure in the steel compared to the magnetic flux in the stator during
`
`15
`
`20
`
`25
`
`30
`
`Mitsuba - 1008
`Page 6 of 312
`
`

`

`-5-
`
`operation of the motor. Thus, a need exists for an improved high speed
`
`spindle motor, having properties that will be especially useful in a hard disc
`
`drive, overcoming the aforementioned problems.
`
`BRIEF SUMMARY OF THE INVENTION
`
`5
`
`A high speed motor has been invented which overcomes many of the
`
`foregoing problems. In addition, unique stator assemblies and other
`
`components of a high speed motor have been invented, as well as methods of
`
`manufacturing motors and hard disc drives. In one aspect, the invention is a
`
`motor comprising: a plurality of stator arc segments forming a toroidal core,
`
`10
`
`wherein each said stator arc segment has two end surfaces that are each in
`
`contact with an end surface of another stator arc segment to form a toroidal
`
`core; and a monolithic body of phase change material substantially
`
`encapsulating the stator arc segments and holding said toroidal core in place.
`
`In another aspect the invention is a method of making a motor
`
`15
`
`comprising: providing at least two stator arc segments each having a first end
`
`20
`
`25
`
`surface and a second end surface; aligning said stator arc segments to form a
`
`toroidal core, wherein each said end surface of one segment is in contact with
`
`an opposing end surface of another segment; and substantially encapsulating
`
`said toroidal core with a monolithic body of phase change material and
`solidifying the phase change material to hold the stator arc segments
`
`together.
`
`In another aspect the invention is a method of making a motor
`
`comprising: providing four stator arc segments, wherein each stator arc
`
`segment has a first end surface and a second end surface; aligning said
`
`stator arc segments to form a toroidal core, wherein each said end surface of
`
`one segment is in contact with an opposing end surface of another segment;
`
`and substantially encapsulating said toroidal core with a monolithic body of
`
`phase change material, wherein said substantially encapsulating is by
`
`injection molding said phase change material around said toroidal core.
`
`Mitsuba - 1008
`Page 7 of 312
`
`

`

`-6-
`
`In yet another aspect, the invention is a combination of stator arc
`
`segments and a carrier used to support said stator arc segments during a
`
`winding operation comprising a plurality of stator arc segments, and: a
`
`plurality of cavities to hold and support said stator arc segments, wherein said
`
`5
`
`cavities are spaced apart a distance X, wherein the distance X is the length of
`
`uncoiled wire necessary to align said stator arc segments to form a toroidal
`
`core.
`
`The invention provides the foregoing and other features, and the
`
`advantages of the invention will become further apparent from the following
`
`10
`
`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.
`
`BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
`
`15
`
`FIG. 1 is an exploded, partial cross-sectional and perspective view of a
`
`conventional high speed motor of the present invention.
`FIG. 2 is a perspective view of a stator arc segment.
`
`FIG. 3 is a perspective view of a combined carrier assembly and stator
`
`arc segments of FIG. 2.
`
`20
`
`FIG. 4 is a perspective view of stator arc segments of FIG. 2 with
`
`windings thereon ready to be formed into a toroidal core.
`
`FIG. 5 is a perspective view of an injection molded stator assembly
`
`using the stator arc segments of FIG. 4.
`
`FIG. 6a is a cross-sectional view of the toroidal core of FIG. 4 in an
`
`25
`
`injection mold assembly, prior to injecting a phase change material.
`
`FIG. 6b is a cross-sectional view of the toroidal core of FIG. 4 in an
`
`injection mold assembly, after injecting a phase change material.
`FIG. 7 is an exploded, partial cross-sectional and perspective view of a
`
`high speed motor using the encapsulated stator of FIG. 5.
`
`30
`
`FIG. 8 is an exploded, partial cross-sectional and perspective view of a
`
`high speed motor and disc assembly made with the motor of FIG. 7.
`
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`Page 8 of 312
`
`

`

`-7-
`
`FIG. 9 is a cross-sectional view of the motor of FIG. 8.
`
`DETAILED DESCRIPTION OF THE DRAWINGS AND PREFERRED
`EMBODIMENTS OF THE INVENTION
`
`A preferred embodiment of a high speed motor of the present invention
`
`5
`
`and portions of the motor at different stages of manufacture are shown in
`
`FIGS. 2-7 and 9. By "high speed" it is meant that the motor can operate at
`
`over 5,000 rpm. The spindle motor 100 is designed for rotating a disc or stack
`
`of discs in a computer hard drive. Motor 100 is formed by using an injection
`
`molded stator assembly 40, that is formed by injection molding a plurality of
`
`10
`
`stator arc segments 20 aligned to form a toroidal core 17. Although the
`
`embodiment described here uses four arc segments, one of ordinary skill in
`
`the art will understand that two, three or any greater number of arc segments
`
`may be used. The preferred motor of the present invention is smaller, has a
`
`grain structure that is more uniformly aligned, allows for greater packing
`
`15
`
`density of wire and reduces waste of steel in the manufacturing process as
`
`compared with conventional motors used for disc drives, thereby increasing
`
`power and reducing stack up tolerances and manufacturing costs and
`
`producing other advantages discussed below.
`
`Referring to FIG. 2, a stator arc segment 20 is first constructed, using
`
`20
`
`steel laminations 11. The stator arc segment 20 is made of steel pieces that
`
`are stamped out of rolled steel. The stamped steel pieces are arc segments,
`
`but also have poles 21 extending inwardly or outwardly depending on whether
`
`the rotor is inside or surrounds the stator. In the embodiment shown in
`
`FIG. 2, the poles 21 are shown extending inwardly. The stamped pieces are
`
`25
`
`then coated with epoxy which provides insulation and laminates the pieces
`
`together to form a stator arc segment 20.
`
`As shown in FIG. 3, the stator arc segments 20 are then preferably
`
`placed in a carrier 30. The carrier 30 has a plurality of cavities 32 that hold
`
`the stator arc segments 20 in place. In a preferred embodiment, the space
`
`30
`
`between the cavities is equivalent to the length of wire needed to travel from a
`
`point on one pole 21a to the next pole 21 bin the same phase of windings
`
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`

`

`-8-
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`following the arc of the stator arc segments 20. The carrier 30 shown in FIG.
`
`3 shows an alternative embodiment where the space between the cavities is
`
`not necessarily equivalent to the length of wire needed to travel from a point
`
`on one pole 21a to the next pole 21b. By precisely aligning the stator arc
`
`5
`
`segments 20, the carrier 30 greatly enhances the efficiency for winding wire
`
`10
`
`15
`
`20
`
`25
`
`15 around the poles 21 and manufacturing stators.
`
`Wire 15 is then wound around the poles 21 of the stator arc segments
`
`20 using a spool winder 34 that has a set of needles 35 that wind wire around
`
`the poles 21. The wire 15 is wound around one pole 21 and is then wound
`around another pole 21 in its phase until all poles 21 in the same phase are
`
`wound with the same wire 15. Poles 21 in other phases are also similarly
`wound. Having only arc segments, rather than a full toroidal core, and placing
`
`the arc segments 20 in the carrier 30 makes it much easier for needle 35 to
`
`wind wire 15 around poles 21. Using this method, a wire packing density of
`about 60 percent to about 80 percent can be achieved.
`
`As shown in FIG. 4, the stator arc segments 20 are then removed from
`the carrier and aligned to form a magnetically inducible toroidal core 17
`
`having a plurality of poles 21 thereon, and wire windings 15 which serve as
`conductors. To form the toroidal core 17, an end surface 16 of each stator arc
`segment 20 is aligned and brought into contact with a corresponding end
`surface 19 of another stator arc segment 20. The wire 15 between the poles
`21 of different stator arc segments 20 is also aligned in the toroidal core 17,
`
`following the arc of the stator arc segments 20. As a result, the wire in the
`
`toroidal core 17 is taught. After the wire is wound so that one set of three
`
`leads is terminated together to create the common ground 46, and the other
`ends of the wire, are for each of the three phases form the leads 47a, 47b and
`47c by which current is supplied to the windings. The conductors induce or
`
`otherwise create a plurality of magnetic fields in the core when electrical
`
`current is conducted through the conductors. In this embodiment, a magnetic
`
`30
`
`field is induced in each of the poles 21 .
`
`As shown in FIG. 5, the toroidal core 17 is then encapsulated in a body
`42. Together the toroidal core 17 and the body 42 make up an injection
`
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`Page 10 of 312
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`

`

`-9-
`
`molded stator assembly 40. The body 42 is preferably a monolithic body.
`
`Monolithic is defined as being formed as a single piece. The body 42
`
`substantially encapsulates the toroidal core 17. Substantial encapsulation
`
`means that the body 42 either entirely surrounds the toroidal core 17, or
`
`5
`
`surrounds almost all of it except for minor areas of the toroidal core 17 that
`
`may be exposed. However, substantial encapsulation means that the body
`
`42 and toroidal core 17 are rigidly fixed together, and behave as a single
`
`component with respect to harmonic oscillation vibration.
`
`The body 42 is preferably formed of a phase change material, meaning
`
`10
`
`a material that can be used in a liquid phase to envelope the stator, but which
`
`later changes to a solid phase. There are two types of phase change
`
`materials that will be most useful in practicing the invention: temperature
`
`activated and chemically activated. A temperature activated phase change
`
`material will become molten at a higher temperature, and then solidify at a
`
`lower temperature. However, in order to be practical, the phase change
`
`material must be molten at a temperature that is low enough that it can be
`
`used to encapsulate a toroidal core. Preferred phase change materials will be
`
`changed from a liquid to a solid in the range of about 200 °F to about 700 °F,
`
`more preferably in the range of about 550 °F to about 650 °F. The most
`
`preferred temperature activated phase change materials are thermoplastics.
`
`The preferred thermoplastic will become molten at a temperature at which it is
`
`injection-moldable, and then will be solid at normal operating temperatures for
`
`the motor. An example of a phase change material that changes phases due
`
`to a chemical reaction, and which could be used to form the body, is an
`
`25
`
`epoxy. Other suitable phase change materials may be classified as
`
`thermosetting materials.
`
`The preferred method of developing the monolithic body 42 comprises
`
`designing a phase change material to have a coefficient of linear thermal
`
`expansion such that the phase change material contracts and expands at
`
`30
`
`approximately the same rate as the metal laminations of the toroidal core 17.
`
`For example, the preferred phase change material should have a CL TE of
`
`between 70% and 130% of the CL TE of the core of the stator. The phase
`
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`

`

`-10-
`
`change material should have a CL TE that is intermediate the maximum and
`
`minimum CL TE of the toroidal core and other motor components where the
`
`body is in contact with those other components and they are made of a
`
`different material than the core. Also, the CL TE's of the body and toroidal
`
`5
`
`core should match throughout the temperature range of the motor during its
`
`operation. An advantage of this method is that a more accurate tolerance
`
`may be achieved between the body and the components of the toroidal core
`
`because the CL TE of the body matches the CL TE of the toroidal core
`
`components more closely. Most often the toroidal core components will be
`
`10
`
`metal, and most frequently steel and copper. Other motor parts are often
`
`made of aluminum and steel.
`
`Most thermoplastic materials have a relatively high CL TE. Some
`
`thermoplastic materials may have a CL TE at low temperatures that is similar
`
`to the CL TE of metal. However, at higher temperatures the CL TE does not
`
`match that of the metal. A preferred thermoplastic material will have a CL TE
`of less than 2 x 10-5 in/in/°F, more preferably less than 1.5 x 10-5 in/in/°F,
`throughout the expected operating temperature of the motor, and preferably
`
`throughout the range of 0-250°F. Most preferably, the CL TE will be between
`about 0.8 x 10-5 in/in/°F and about 1.2 x 10-5 in/in/°F throughout the range of
`0-250°F. (When the measured Cl TE of a material depends on the direction
`
`of measurement, the relevant CL TE for purposes of defining the present
`
`invention is the CL TE in the direction in which the CL TE is lowest.)
`
`The CL TE of common solid parts used in a motor are as follows:
`
`Steel
`
`Aluminum
`
`Ceramic
`
`23°c
`
`0.5
`
`0.8
`
`0.3
`
`(x10-5 in/in/°F)
`
`250°F
`
`0.8
`
`1.4
`
`0.4
`
`15
`
`20
`
`25
`
`Of course, if the motor is designed with two or more different solids,
`
`such as steel and aluminum components, the CL TE of the phase change
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`30
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`material would preferably be one that was intermediate, the maximum CL TE
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`and the minimum CL TE of the different solids, such as 0.65 in/in/°F at room
`temperature and 1.1 x10-5 in/in/°F at 250°F.
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`5
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`10
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`-11-
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`One preferred thermoplastic material, Konduit OTF-212-11, was made
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`into a thermoplastic body and tested for its coefficient of linear thermal
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`expansion by a standard ASTM test method. It was found to have a Cl TE in
`the range of -30 to 30°C of 1.09x10-5 in/in/°F in the X direction and 1.26x10-5
`in/in/°F in both the Y and Z directions, and a CL TE in the range of 100 to
`240°C of 1.28x10-5 in/in/°F in the X direction and 3.16x10-5 in/in/°F in both the
`Y and Z directions. (Hence, the relevant CL TEs for purposes of defining the
`invention are 1.09 x 10-5 in/in/°F and 1.28 x 10-5 in/in/°F.) Another similar
`material, Konduit POX -0-988, was found to have a CL TE in the range of -30
`to 30°C of 1.1x10-5 in/in/°F in the X direction and 1.46x10-5 in/in/°F in both the
`Y and Z directions, and a CL TE in the range of 100 to 240°C of 1.16x10-5
`in/in/°F in the X direction and 3.4x10-5 in/in/°F in both the Y and Z directions.
`By contrast, a PBS type polymer. (Fortran 4665) was likewise tested. While it
`had a low CL TE in the range of-30 to 30°C (1.05x10-5 in/in/°F in the X
`direction and 1.33x10-5 in/in/°F in both the Y and Z directions), it had a much
`higher CL TE in the range of 100 to 240°C (1.94x10-5 in/in/°F in the X direction
`and 4.17x10-5 in/in/°F in both the Y and Z directions).
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`In addition to having a desirable CL TE, the preferred phase change
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`material will also have a high thermal conductivity. A preferred thermoplastic
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`material will have a thermal conductivity of at least 0.7 watts/meter°K using
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`ASTM test procedure 0149 and tested at room temperature (23°C).
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`Stator assemblies made from arc segments held together by a body of
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`phase change material partially encapsulating the stator are themselves novel
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`and define another aspect of the present invention.
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`25
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`In the present embodiment, the phase change material used to make
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`the body 42 is preferably a thermally conductive but non-electrically
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`conductive plastic. In addition, the plastic preferably includes ceramic filler
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`particles that enhance the thermal conductivity, while reducing the coefficient
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`of linear thermal expansion of the plastic. A preferred form of plastic is
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`30
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`polyphenyl sulfide (PPS) sold under the tradename "Konduit" by LNP. Grade
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`OTF-212 PPS is particularly preferred. Examples of other suitable
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`thermoplastic resins include, but are not limited to, thermoplastic resins such
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`-12-
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`as 6,6-polyamide, 6-polyamide, 4,6-polyamide, 12, 12-polyamide,
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`6, 12-polyamide, and polyamides containing aromatic monomers, polybutylene
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`terephthalate, polyethylene terephthalate, polyethylene napththalate,
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`polybutylene napththalate, aromatic polyesters, liquid crystal polymers,
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`5
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`polycyclohexane dimethylol terephthalate, copolyetheresters, polyphenylene
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`sulfide, polyacylics, polypropylene, polyethylene, polyacetals,
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`polymethylpentene, polyetherimides, polycarbonate, polysulfone,
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`polyethersulfone, polyphenylene oxide, polystyrene, styrene copolymer,
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`mixtures and graft copolymers of styrene and rubber, and glass reinforced or
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`10
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`impact modified versions of such resins. Blends of these resins such as
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`polyphenylene oxide and polyamide blends, and polycarbonate and
`polybutylene terephthalate, may also be used in this invention.
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`As shown in FIG. 6a, to encapsulate the toroidal core 17 and form body
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`42, the toroidal core 17 is first clamped and held in place by pins 61 in an
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`injection mold cavity 66. The injection mold cavity 66 is very effective and
`maintains the toroidal shape of the toroidal core 17. Molten phase-change
`material is then injected into the molding cavity 66 with an extrusion screw
`(not shown) until the pressure inside the cavity reaches a predetermined
`molding pressure. After injecting the molten phase change material, the pins
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`61 retract as shown in FIG. 6b. The phase change material is then allowed to
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`cool and solidify into a monolithic body 42 that substantially encapsulates the
`toroidal core 17. The preferred thickness of the body 42 depends on the
`aspect ratio of the toroidal core 17.
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`The injection molded stator assembly 40 is then used to construct the
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`rest of the spindle motor 100 (FIG. 7). The spindle motor 100 includes a hub
`108, which serves as a disc support member, the stator assembly 40, a base
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`102, a shaft 106 and bearings 107.
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`As shown in FIG. 7, a shaft 106 is connected to the hub or disc support
`member 108 and is surrounded by bearings 107, which are adjacent against
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`the base 102 of the motor. A rotor or magnet 103 is fixed to the inside of the
`hub 108 on a flange so as to be in operable proximity to the stator assembly.
`The magnet 103 is preferably a permanent magnet, as described below.
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`Referring to FIG. 7, the bearings 107 include an upper bearing 46 and
`a lower bearing 48. Also, each bearing 107 has an outer surface 50 and an
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`inner surface 52. The outer surface 50 of the upper bearing contacts the hub
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`108 and the outer surface 50 of the lower bearing 48 contacts the lower
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`5
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`support base 102. The inner surfaces 52 of the bearings 107 contact the
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`shaft 116. The bearings are preferably annular shaped. The inner
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`surfaces 52 of the bearings 107 may be press fit onto the shaft 16. A glue
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`may also be used. The outer surface 50 of the bearings 107 may be press fit
`into the interior portion of the base 102. A glue may also be used. The
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`10
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`bearings in the embodiment shown in FIG. 7 are ball bearings. Alternatively
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`other types of bearings, such as hydrodynamic or combinations of
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`hydrodynamic and magnetic bearings, may be used. The bearings are
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`typically made of stainless steel.
`The shaft 106 is concentrically disposed within the interior portion of
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`the stator assembly 40 and the base 102. The bearings 107 surround
`portions of the shaft 106. As described above, the inner surfaces 52 of the
`bearings are in contact with the shaft 106. The shaft 106 includes a top
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`portion 54 and a bottom portion 56. The top portion 54 of the shaft 106 is
`fixed to the hub 108. The bottom portion 54 of the shaft 106 is free to rotate
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`inside the lower bearing. Thus, in this embodiment, the shaft 106 is freely
`rotatable relative to the base 102. The shaft 106 is preferably cylindrical
`
`shaped. The shaft 106 may be made of stainless steel.
`Referring to FIGS. 7 and 9, the hub 108 is concentrically disposed
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`around the stator assembly 40 and the base 102. The hub 108 is fixed to the
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`shaft 106 and is spaced apart from the stator assembly 40 and the base 102.
`The hub 108 includes a flux return ring 58 and the magnet 103. The flux
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`return ring 58 is glued to the disc support member. The magnet 103 is glued
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`to the hub 108. As shown in FIG. 7, the magnet 103 concentrically surrounds
`the stator assembly 40. In this embodiment the magnet 103 and stator
`assembly 40 are generally coplanar when the motor 100 is assembled.
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`The m