NIDEC and HONDA - Ex. 1010
`Nidec Corporation and American Honda
`Motor Co., Inc. - Petitioners
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`U-S- Patent
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`Dec' 29 1997
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`5,694,268
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`1
`SPINDLE MOTOR HAVING OVERMOLDED
`STATOR
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application is a continuation—in-part of US. Ser. No.
`08/386383. filed Feb. 10. 1995.
`BACKGROUND OF THE INVENTION
`
`The present invention relates generally to the field of disc
`drive spindle motors for data storage devices and. more
`particularly. to a spindle motor in which the stator has a
`resilient overmold to isolate the stator from a base of the
`storage device.
`Disc drive data storage devices. known as “Winchester”
`type disc drives. are well-known in the industry. In a
`Winchester disc drive. digital data are written to and read
`from a thin layer of magnetizable material on the surface of
`rotating discs. Write and read operations are performed
`through a transducer which is carried in a slider body. The
`slider and transducer are sometimes collectively referred to
`as a head. and typically a single head is associated with each
`disc surface. The heads are selectively moved under the
`control of electronic circuitry to any one of a plurality of
`circular. concentric data tracks on the disc surface by an
`actuator device. Each slider body includes a self-acting
`hydrodynamic air bearing surface. As the disc rotates. the
`disc drags air beneath the air bearing surface. which devel-
`ops a lifting force that causes the slider to lift and fly sevm'al
`microinches above the disc surface.
`
`In the current generation of disc drive products. the most
`commonly used type of actuator is a rotary moving coil
`actuator. The discs themselves are typically mounted in a
`“stack” on the hub structure of a brushless DC spindle
`motor. The rotational speed of the spindle motor is precisely
`controlled by motor drive circuitry which controls both the
`timing and the power of commutation signals directed to the
`stator windings of the motor.
`The first Winchester disc drives to be produced were large
`cabinet models which included discs having a diameter of 14
`inches and AC induction spindle motors. These types of disc
`drives were commonly located in dedicated “computer
`rooms” with large mainframe computers. where environ—
`mental factors such as temperature and humidity could be
`carefully controlled. In this type of environment. the acous-
`tic noise generated by cooling fans and disc drive motors
`was of little concern. since the only persons directly in
`contact with the systems were maintenance personnel. who
`were generally not in the computer rooms for extended
`periods of time. The users of such systems were typically
`located at a remote location and communicated with the
`computer system via keyboards and display terminals which
`did not generate excessive amounts of acoustic noise.
`More recently, personal computers have become more
`popular and are commonly located within the work space of
`the system user. This has prompted an increase in awareness
`of acoustic noise generated by the disc drives located within
`the personal computers. In certain markets. such as Europe.
`the amount of acoustic noise allowable in the work place is
`closely regulated. With this in mind. it has become common
`for system manufacturers to impose a “noise budget” on
`manufacturers of major system components. such as disc
`drives. which limits the amount of acoustic noise that such
`components can contribute to the overall noise of the
`system.
`One of the principal sources of noise in disc drive data
`storage devices is the spindle motor which drives the discs
`
`2
`at a constant speed. Typical spindle motor speeds have been
`in the range of 3600 RPM. Current technology has increased
`spindle motor speeds to 4800 RPM. 7200 RPM and above.
`Analysis of various types of disc drives has brought to light
`several diflerent modes of acoustic noise generation which
`are attributable to the spindle motor and its control logic.
`One mode of noise generation is sympathetic vibration of
`the disc drive housing in response to the rotating mass of the
`spindle motor. Another mode of acoustic noise generation is
`electromagnetic disturbances caused by the excitation of the
`stator mass by the application and removal of the commu-
`tation pulses that are used to drive the motor and control its
`speed. The commutation pulses are timed. polarization-
`selected DC current pulses which are directed to sequen-
`tially selected stator windings. The rapid rise and fall times
`of these pulses act as a striking force and set up sympathetic
`vibrations in the stator structure.
`
`If the stator structure is rigidly connected to the disc drive
`housing. either directly or through a rigid material. these
`vibrations are coupled to the housing and generate resonant
`vibrations in the housing causing unacceptable levels of
`acoustic noise.
`
`Prior art attempts to reduce or eliminate noise include
`controlling the resonant frequency of the housing. and
`damping the vibration of the housing. In US. Pat. No.
`5.376.850. acoustic noise is reduced by uncoupling the
`stator from hard contact with the stationary portion of the
`shaft. A plurality of O—rings interposed radially between the
`stator and the shaft of the spindle motor. Also. a non-metallic
`washer is positioned at one end of the shaft and an axial
`O—ring is positioned at the other end of the shaft.
`
`SUMMARY OF THE INVENTION
`
`The present invention is a disc drive spindle motor for
`rotating at least one disc in a data storage device. The motor
`includes a base. a stationary member. a rotor and a stator. A
`bearing interconnects the rotor with the stationary member
`and allows the rotor to rotate about the stationary member.
`An overmold encapsulates at least part of the stator and
`provides the stator with a smooth external surface. The
`overmold mechanically isolates the stator from the base and
`damps sympathetic vibrations in the stator structure to
`reduce the generation of acoustic noise in the storage device.
`The overmold provides a convenient structure for mount-
`ing the stator to the base. In one embodiment. the stator
`includes a plurality of phase windings which are disposed
`about the stator and spaced apart by gaps. The overmold fills
`the gaps and substantially encapsulates the stator. A plurality
`of mounting apertures extend in an axial direction through
`the overmold in the gaps between the phase windings. A
`mounu‘ng pin extends through each mounting aperture and
`has a distal end which can be attached to the base by
`heat—staking. for example.
`the overmold comprises at a
`In another embodiment.
`plurality of mounting ears extending from a circumference
`of the stator in a radial direction for connection to the base.
`The mounting ears can include a rigid material. such as
`plastic or metal. which is encapsulated by the overmold or
`exposed to provide a rigid yet isolated connection.
`In another embodiment. the overmold has a circumferen—
`tial side wall opposite to the rotor having an annular raised
`projection. The projection is compressed between the stator
`and the base to secure the stator within the base. In yet
`another embodiment.
`the stator is adhered to the base
`through a polyester plastic film having first and second
`surfaces which carry a pressure sensitive adhesive.
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`While the present invention is useful in disc drive spindle
`motors having ball bearings. the present invention is par-
`ticularly useful in hydrodynamic bearing motors to reduce or
`eliminate pure vibration tones which become more notice-
`able with lower levels of background vibration. The over-
`molded stator can have an axial position which is within or
`below the hub. and can have a radial position which is
`internal or external to the rotor. The overmold provides the
`stator with an environmental seal having a smooth external
`surface which is substantially free of apertures. The over-
`mold can be cleaned more easily during production than a
`bare stator and therefore reduces impurities in the disc drive.
`The overmold provides a large surface area over which
`vibrations can be damped to reduce acoustic noise genera-
`tion. The overmold also allows a greater integration of parts
`which reduces the number of parts that must be assembled
`in the disc drive.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a top plan view of a disc drive data storage
`device. in accordance with the present invention.
`FIG. 2 is a sectional view of an isolated hydrodynamic
`bearing spindle motor in accordance with the present inven-
`tion.
`
`FIG. 3 is a fragmentary sectional view of an alternative
`attachment between the stator and the base in which the
`stator is partially isolated from the disc.
`FIG. 4 is a fragmentary sectional view of an alternative
`attachment between the stator and the base which includes
`two O—rings for isolation.
`FIG. 5 is a fragmentary sectional view of another alter-
`native attachment between the stator and the base which
`includes an O-ring located radially between the stator and
`the base and an O—ring located axially between the stator and
`the base.
`
`FIG. 6 is a sectional view of a ball bearing spindle motor.
`in accordance with the present invention.
`FIG. 7 is a plan view of an overmolded stator in accor-
`dance with the present invention.
`FIG. 8 is a sectional view of the stator shown in FIG. 7.
`taken along lines 7—7.
`FIG. 9 is a fragmentary sectional view of a spindle motor
`having the stator shown in FIGS. 7 and 8.
`FIG. 10 is a sectional view of a fully encapsulated stator.
`FIG. 11 is a sectional view of a overmolded stator having
`flux shields.
`
`FIG. 12 is a plan view of an overmolded stator having
`mounting ears.
`FIG. 13 is a sectional view of the stator shown in FIG. 12.
`taken along line 13—13.
`FIG. 14 is a fragmentary sectional view of a spindle motor
`having the stator shown in FIGS. 12 and 13.
`FIG. 15 is a plan view of a overmolded stator having a
`rigid mounting ring formed within the overmolding.
`FIG. 16 is a sectional view of the stator shown in FIG. 15,
`taken along lines 16—16.
`FIG. 17 is a fragmentary sectional view of a spindle motor
`having the stator shown in FIGS. 15 and 16.
`FIG. 18 is a sectional view of an overmolded stator with
`an annular projection.
`FIG. 19 is a fragmentary sectional View of a spindle motor
`having the stator shown in FIG. 18.
`FIG. 20 is a fragmentary sectional view of a spindle motor
`in which an overmolded stator is adhered to the base through
`a polyester plastic film.
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`4
`FIG. 21 is a sectional view of an overmolded stator in
`which the overmold is limited to an outer diameter of the
`stator.
`
`FIG. 22 is a fragmentary sectional view of a spindle motor
`having an overmolded stator with a radial position that is
`internal to the rotor.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The present invention is a spindle motor for a disc drive
`data storage device in which the stator is isolated from the
`base to reduce acoustic levels in the storage device. FIG. 1
`is a plan view of a typical disc drive 10 in which the present
`invention is useful. Disc drive 10 includes a housing base 12
`and a top cover 14. The housing base 12 is combined with
`top cover 14 to form a sealed environment to protect the
`internal components from contamination by elements from
`outside the sealed environment.
`
`The base and top cover arrangement shown in FIG. 1 is
`common in the industry. However. other arrangements of the
`housing components have been frequently used. and the
`present invention is not limited to the configuration of the
`disc drive housing. For example. disc drives have been
`manufactured using a vertical split between two housing
`members. In such drives. that portion of the housing half
`which connects to the lower end of the spindle motor is
`analogous to base 12. while the opposite side of the same
`housing member. which is connected to or adjacent the top
`of the spindle motor. is functionally the same as the top
`cover 14.
`
`Disc drive 10 further includes a disc pack 16 which is
`mounted for rotation on a spindle motor (not shown) by a
`disc clamp 18. Disc pack 16 includes a plurality of indi-
`vidual discs which are mounted for co—rotation about a
`central axis. Each disc surface has an associated head 20
`which is mounted to disc drive 10 for communicating with
`the disc surface. In the example shown in FIG. 1. heads 20
`are supported by flexures 22 which are in turn attached to
`head mounting arms 24 of an actuator body 26. The actuator
`shown in FIG. I is of the type known as a rotary moving coil
`actuator and includes a voice coil motor (VCM). shown
`generally at 28. Voice coil motor 28 rotates actuator body 26
`with its attached heads 20 about a pivot shaft 30 to position
`heads 20 over a desired data track along an arcuate path 32.
`While a rotary actuator is shown in FIG. 1. the present
`invention is also useful in disc drives having other types of
`actuators. such as linear actuators.
`
`FIG. 2 is a sectional view of a hydrodynamic bearing
`spindle motor 32 in accordance with the present invention.
`Spindle motor 32 includes a stationary member 34. a hub or
`sleeve 36 and a stator 38. In the embodiment shown in FIG.
`2. the stationary member is a shaft which is fixed and
`attached to base 12 through a nut 40 and a washer 42. Hub
`36 is interconnected with shaft 34 through a hydrodynamic
`bearing 37 for rotation about shaft 34. Bearing 37 includes
`a radial working surface 46 and axial working surfaces 48
`and 50. Shafl 34 includes fluid ports 54. 56 and 58 which
`supply hydrodynamic fluid 60 and assist in circulating the
`fluid along the working surfaces of the bearing. Hydrody-
`namic fluid 60 is supplied to shaft 34 by a fluid source (not
`shown) which is coupled to the interior of shaft 34 in a
`known manner.
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`Spindle motor 32 further includes a thrust bearing 45
`which forms the axial working surfaces 48 and 50 of
`hydrodynamic bearing 37. A counterplate 62 bears against
`working surface 48 to provide axial stability for the hydro-
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`dynamic bearing and to position hub 36 within spindle
`motor 32. An O-ring 64 is provided between counterplate 62
`and hub 36 to seal the hydrodynamic bearing. The seal
`prevents hydrodynamic fluid 60 from escaping between
`counterplate 62 and hub 36.
`Hub 36 includes a disc carrier member 66 which supports
`disc pack 16 (shown in FIG. 1) for rotation about shaft 34.
`Disc pack 16 is held on disc carrier member 66 by disc
`clamp 18 (also shown in FIG. 1). Apermanent magnet 70 is
`attached to the outer diameter of hub 36. which acts as a
`rotor for spindle motor 32.
`Stator 38 is formed of a stack of stator larninations 72 and
`associated stator windings 74. In accordance with the
`present invention. stator 38 is mechanically isolated from
`base 12 through a resilient coupling. It has been found
`through experiments that hydrodynamic bearing motors are
`much quieter and in general have lower background vibra-
`tion levels than motors having ball bearings. Because the
`background vibration levels are less in a hydrodynamic
`bearing motor. vibration responses to electromagnetic dis—
`turbances become more noticeable since the responses are
`no longer hidden in the background. Therefore. it is desirv
`able to reduce or eliminate as far as possible the transfer of
`vibrations resulting from electromagnetic disturbances from
`the stator to the base.
`
`As shown in FIG. 2. stator 38 is resiliently coupled to. but
`mechanically isolated from. base 12. Stator 38 is coupled to
`base 12 through an O-ring 80 and a resilient damping bridge
`82. O-ring 80 is compressed between a side surface 84 of
`stator 38 and a side surface 86 of base 12 such that stator 38
`and base 12 are adjacent to. but spaced from, one another in
`a radial direction with respect to a central axis 87. In one
`embodiment, O-ring 80 is integrated in stator 38 to form an
`assembly which facilitates a low-cost approach to mounting
`the stator within base 12. For example. O-ring 80 can be
`integrated in an indentation (not shown) in stator 38 through
`a vulcanizing process. O-ring 80 can also be integrated in
`stator 38 by over—molding the O-ring onto the stator. The
`O-ring material flows over the stator to form the desired
`O-ring features and is then hardened at a selected tempera-
`ture and pressure. The vulcanizing process and the over-
`molding process are controlled to provide the desired darnp—
`ing and stiffness characteristics.
`Base 12 includes a corresponding annular groove (not
`labeled) which retains O-ring 80 under compression when
`stator 38 is mounted within base 12. The annular groove
`within base 12 also assists in axially constraining O—ring 80.
`O—ring 80 can be formed as a continuous internal ring or as
`one or more individual pieces of O—ring material positioned
`between stator 38 and base 12. O—ring 80 can have any
`suitable cross section. such as circular or rectangular.
`O—ring 80 can be formed of a rubber-like or plastic—like
`material having high stifl’ness and high vibration damping
`characteristics. In a preferred embodiment, O-ring 80 is
`formed of an approximately 40—75 durometer (Shore A)
`material having a damping ratio of at least 2 decibels in an
`acoustic frequency range of approximawa 100 Hz to 10
`KHz. The material absorbs energy of acoustic vibrations and
`dissipates the energy as heat. In some embodiments. O—ring
`80 preferably has a damping ratio of at least 5 decibels. The
`preferred damping ratio depends on the type of bearing used,
`among other factors. With ball bearings. the background
`vibration level is higher. Electromagnetic disturbances are
`more hidden and require less damping. A damping ratio of
`2—3 decibels may be sufficient. With hydrodynamic
`bearings. electromagnetic disturbances are more noticeable.
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`A larger damping ratio is therefore preferred with hydrody-
`namic bearings.
`An example of a suitable material is a 70 durometer
`material such as Viton®. a patented polymer product of EL
`DuPont de Nemours Co.. of Wilmington. Del.. which is
`subjected to 0.009 inches of radial compression. Other
`materials which provide suitable isolation and stiffness may
`also be used to isolate stator 38 from base 12. It has been
`found that some rubber materials contain silicone or sulfur
`
`which can be harmful to the various components in a disc
`drive. Therefore. rubber or rubber-like materials not con-
`taining silicone and sulfur are preferred.
`Resilient bridge 82 extends between an upper mounting
`surface 90 of stator 38 and an upper mounting surface 92 of
`base 12. Bolts 94 and 96 secure bridge 82 to base 12 and
`compress bridge 82 against the upper mounting surfaces 90
`and 92 in an axial direction to provide additional vertical
`stilfness for the resilient coupling between stator 38 and base
`12. The combination of O-ring 80 and resilient bridge 82
`clamps stator 38 rotationally and vertically with respect to
`base 12. The O-ring preferably has enough torsional stiffness
`so that as spindle motor 32 begins to rotate. stator 38 is not
`allowed to rotate more than an insignificant amount. The
`combination of O-ring 80 and resilient bridge 82 provides
`suflicient vertical and torsional stiffness.
`
`Resilient bridge 82 is preferably formed of a material
`similar to that of O—ring 80. Resilient bridge 82 can be an
`annular ring. as shown in FIG. 2. or can include one or more
`individual bridge pieces which extend between stator 38 and
`base 12. In addition. bridge 82 can be formed as a washer
`which is secured to base 12 by a bolt. such as bolt 94 or 96.
`The washer would have a tab that would extend between
`
`base 12 and stator 38. Resilient bridge 82 can also be formed
`as a clamp of O—ring type material. Further. bridge 82 can be
`compressed against the upper mounting surfaces 90 and 92
`in several ways. For example. resilient bridge 82 can be
`compressed by bolt 94. as shown in FIG. 2. or can be
`compressed by a portion of top cover 14 (shown in FIG. 1).
`The mounting surfaces 90 and 92 can also include associated
`grooves for accepting resilient bridge 82. In addition. resil—
`ient bridge 82 can be integrated into the stator similar to
`O—ring 80.
`In the embodiment shown in FIG. 2. the spindle motor is
`a “below-hub” type motor in which stator 38 is positioned
`below hub 36. as opposed to within hub 36. In addition.
`stator 38 is located externally from hub 36 and is attached
`directly to base 12. In this embodiment. O-ring 80 and
`resilient damping bridge 82 are located at an outer diameter
`of stator 38.
`
`FIG. 3 is a fragmentary sectional view of a spindle motor
`which illustrates an alternative attachment between the
`stator and the base. In FIG. 3. stator 100 is attached to base
`102 through an O—ring 104 and a metallic C-clamp 106.
`C-clamp 106 provides sufficient vertical stiffness between
`stator 100 and base 102 but does not provide complete
`isolation between the stator and the base as does the embodi-
`ment shown in FIG. 2. Therefore. the embodiment shown in
`FIG. 2 is preferred over the embodiment shown in FIG. 3.
`FIG. 4 is a fragmentary sectional view of a spindle motor
`illustrating another alternative attachment between the stator
`and the base. In FIG. 4. stator 110 is attached to base 112
`through two O-rings 114 and 116. O-rings 114 and 116 are
`located radially between stator 110 and 112. O-rings 114 and
`116 are separated from one another by a radius such that they
`form a couple which contributes to the vertical and torsional
`stiflness of stator 110 with respect to base 112. If the stator
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`is rotated with respect to the base. the O—rings provide a
`restoring torque to overcome the rotation. The O-rings also
`maintain vertical alignment of the stator by providing a
`restoring force in a vertical direction in response to vertical
`movement of the stator with respect to the base. In the
`embodiment shown in FIG. 4. there is no need for a clamp
`or a bridge between stator 110 and base 112 since O-rings
`114 and 116 provide suflicient vertical and torsional stifl—
`ness.
`
`FIG. 5 is a fragmentary sectional view of a spindle motor
`which illustrates another embodiment of the present inven-
`tion. In FIG. 5. stator 120 is resiliently coupled to base 122
`through O-rings 124 and 126. O—ring 124 is located radially
`between stator 120 and base 122. O-ring 12A is compressed
`between the side walls of stator 120 and base 122 similar to
`the O-rings shown in FIGS. 2—4. O-ring 126 is located
`axially and compressed between a lower mounting surface
`128 of stator 120 and an opposing surface 130 of base 122.
`O-ring 126 provides additional stability and isolation. rect-
`angular.
`in
`invention is particularly useful
`While the present
`hydrodynamic bearing motors to reduce pure tone vibrations
`where the background vibration level is relatively low. the
`present invention is also useful in motors having ball bear-
`ings to reduce or eliminate the transfer of vibrations from the
`stator to the base.
`
`FIG. 6 illustrates a spindle motor having ball bearings. as
`opposed to a hydrodynamic bearing. Spindle motor 150
`includes a shaft 152. a hub 154 and a stator 156. Shaft 152
`is a stationary shaft which is fixedly attached to a base 158.
`Shaft 152 is also attached to the inner races of ball bearings
`160 and 162. Hub 154 is attached to the outer races of
`
`bearings 160 and 162 for rotation about shaft 152. Hub 154
`includes a disc carrying member 164 which carries a plu—
`rality of magnetic discs (not shown) for rotation about shaft
`152. Hub 154 also carries a permanent magnet 166 which
`forms a rotor for spindle motor 150.
`As in the embodiments shown in FIGS. 2—5. stator 156
`can be attached to base 158 through one or more resilient
`couplings. such as O-ring 168. Spindle motor 150 can also
`include a resilient damping ring or tab 170 for providing
`additional vertical stiffness between stator 156 and base 158.
`As discussed above, damping ring or tab 170 is optional.
`Alternatively. spindle motor 150 can be provided with a
`metallic C-clamp as shown in FIG. 3, two O—rings as shown
`in FIG. 4. or an additional O-ring located between the
`bottom of stator 156 and base 158.
`FIGS. 1—6 illustrate embodiments in which the stator is
`
`positioned external to the hub such that the O-rings are
`positioned along the outer diameter of the stator. However.
`the O—rings can also be positioned along the inner diameter
`of the stator in embodiments in which the stator is attached
`to the base about the stator’s inner diameter.
`
`FIG. 7 is a plan view of a stator in which the resilient
`coupling is integrated with the stator by overmolding the
`coupling onto the stator. FIG. 8 is a sectional view of the
`stator. taken along lines 8—8 of FIG. 7. Stator 200 includes
`a stator lamination 202 comprising a back-iron 204 and a
`plurality of teeth 206a—2061. which extend inward from
`back-iron 204 toward a central axis 207. Teeth 20641—2061
`
`are disposed about a circumference 222 of stator 200. A
`plurality of phase windings 208a—2081 are wound on stator
`teeth 206a—206l. respectively, for magnetic communication
`with an internal rotor (not shown). Phase windings
`208a—208l can have a number of winding configurations,
`such as those discussed in Dunfield et al. U.S. Ser. No.
`
`8
`08/469.643. entitled IRONLESS HYDRODYNAMIC
`SPINDLE MOTOR. filed Jun. 6. 1995, and Dunfield et al.
`U.S. Ser. No. 08/400,661. entitled HYDRODYNAMIC
`SPINDLE MOTOR HAVING DISTRIBUTED
`WINDINGS, filed Mar. 8. 1995. which are hereby incorpo-
`rated by reference.
`A flexible printed circuit (FPC 210 carries a plurality of
`conductors 212 which are electrically connected to start and
`finish winding terminations 214. 216.218 and 220. Termi-
`nations 214.216. and 218 and 220 are electrically connected
`to phase windings 208a—2081. in a lmown manner.
`Back-iron 204. stator teeth 206a—206l and windings
`208a—2081 are overmolded by a resilient rubber-like or
`plastic-like material. Gaps 224a—224l are formed between
`each phase winding 208a—208L Overmold 209 substantially
`encapsulates stator 200 and fills gaps 224a—2241 such that
`stator 200 has a smooth external surface which is substan-
`
`tially free of apertures. indentations or open cavities. This
`provides an environmental seal and a smface which can be
`cleaned much more easily during assembly than a rough and
`uneven surface provided by an exposed stator. Each of the
`stator lamination teeth 206a—206l remain exposed at an
`inner diameter surface 236 along circumference 222 for
`closer communication with the rotor. In one embodiment,
`overmold 209 has a minimum thickness of approximately
`0.25 mm around the various features of stator 200.
`
`the overmold material
`In a preferred embodiment,
`includes a 70 dtn'ometer rubber-like material having char-
`acteristics similar to the O-rings discussed with reference to
`FIG. 2. Other rubber-like and plastic-like materials can also
`be used in the present invention. The overrnolding process
`integrates the resilient coupling with the stator. The over-
`mold material flows over the stator to form the desired
`
`overmolding features and is then hardened at a selected
`temperature and pressure. The overmolding and vulcanizing
`processes are controlled to provide desired damping and
`stiffness characteristics. High loss and stiffness characteris-
`tics are preferred such that the overmold material damps
`acoustic vibrations and yet provides structural
`integrity
`within the extremely small spacial constraints of a disc
`drive.
`
`Overmolding stator 200 provides a variety of mounting
`possibilities. In the embodiment shown in FIGS. 7 and 80
`stator 200 includes mounting apertures 230. 232 and 234
`which extend through overmold 209 within gaps 224d. 224k
`and 2241, respectively. Mounting apertures 232 and 234
`extend in an axial direction with respect to central axis 207.
`Spindle motor 200 can include any number of mounting
`apertures and each aperture can have any cross section. such
`as circular or rectangle.
`As shown in FIG. 8. mounting pins 240 and 242 are
`inserted into mounting apertures 230 and 232. respectively.
`Mounting pins 240 and 242 preferably have a cross section
`which mates with the cross section of mounting apertures
`230 and 232. Mounting pins 240 and 242 have a head 244
`which rests in a seat 246 within overmold 209 for engaging
`an upper surface 248 of overmold 209. Mounting pins 240
`and 242 have a distal end 250 which is secured to the base
`of the disc drive spindle motor as shown in greater detail in
`FIG. 9. Features 252 and 254. shown in FIG. 8. form part of
`a bobbin which assists in winding phase windings
`2080—2081 over stator lamination teeth 206a—206l.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`FIG. 9 is a fragmentary sectional view of a disc drive
`spindle motor having the stator shown in FIGS. 7 and 8. Disc
`drive spindle motor 260 includes a hub 262 and stator 200.
`Hub 262 carries a magnet 264 which forms a rotor for
`
`19
`
`19
`
`

`

`5,694,268
`
`9
`spindle motor 260. Stator 200 is coaxial with magnet 264
`and has a radial position that is external to magnet 264 with
`respect to central axis 207 (FIG. 7). Stator 200 is mounted
`to base 266 through mounting pin 242. Distal end 250 of pin
`242 is heat-staked to a lower surface 268 of base 266.
`
`Mounting pin 242 is preferably formed of a plastic material
`which melts at distal end 250 when heat is supplied to base
`266 (typically aluminum) at area 270. When distal end 250
`cools. it adheres to lower surface 268 of base 266. thereby
`securing stator 200 to base 266.
`Overmold 209 mechanically isolates the stator mass from
`mounting pin 242 and base 266 such that sympathetic
`vibrations generated in stator 200 are damped by overmold
`209 and are not transferred to base 266. Circumferential side
`wall 272 of overmold 209 can be spaced from corresponding
`circumferential side wall 274 of base 266 or compressed
`against side wall 274 to provide additional stability and
`additional surface area over which acoustic vibrations can be
`dissipated. Surface 236 is left exposed to the rotor magnet so
`that overmold 209 does not increase a magnetic gap between
`teeth 206a—206l and the rotor magnet.
`FIG. 10 is a sectional view of an overmolded stator which
`is fully encapsulated. FIG. 10 is similar to FIG. 8 and uses
`the same reference numerals for similar elements. Stator 280
`includes back—iron 204. stator lamination teeth 206a—2061.
`windings 208a—2081 and overmold 209. In FIG. 10. over—
`mold 209 encapsulates surface 236 of stator lamination teeth
`206a—206L
`
`FIG. 11 is a sectional view of a stator 290 having flux
`shields according to another embodiment of the present
`invention. Again, the same reference numerals are used in
`FIG. 11 as were used in FIGS. 7—10 for similar elements.
`
`Stator 290 includes a flux shield 292 positioned along a
`lower surface 294 and a flux shield 296 positioned along an
`upper surface 298 of overmold 209. Overrnold 209 encap—
`sulates flux shield 292 along lower surface 294. In an
`alternative embodiment. flux shield 292 can be attached
`externally to lower surface 294. Surface 294 is referred to as
`a “lower" surface since it is adjacent the lower surface 268
`of base 266 (FIG. 9). Flux shield 296 has a proximal end 299
`which is encapsulated by ova-mold 209. Flux shields 292
`and 296 are formed of a magnetic flux conducting metal to
`assist in focusing an electromagnetic field generated by
`windings 2080—2081 toward rotor magnet 264 (FIG. 9).
`FIG. 12 is a plan view of an overmolded stator 300 having
`alternative mounting features. In FIG. 12. overmold 209
`further includes mounting ears 302. 304 and 306 w