JP2003526761A - Ferrofluid seal between shaft and hub for disk hard drive - Google Patents

Abstract

SUMMARY An apparatus and method are provided for sealing an outer surface (170) of a shaft (175) to an inner surface (165) of a hub (160). The seal includes a magnet (155) and a magnetic field in the top and bottom pole pieces (260 and 265) and the gap (275) between the pole pieces (260 and 265) and the hub (160) or shaft (175). And a ferrofluid (270) held in the container. The top pole piece (260) has an L-shaped cross section, with a horizontal portion (260a) parallel to the magnet (155) and a shorter vertical portion (260b) facing the shaft (175). In one embodiment, the vertical portion (260b) or the portion of the shaft (175) facing it is contoured to provide a magnetic flux gradient that axially concentrates the ferrofluid (270) in the gap (275). Have been. In another aspect, a catcher (335) is provided to reduce ferrofluid (270) loss when forming an outer seal using a ferrofluid seal (185). In another aspect, a static ferrofluid seal (345) is provided for sealing a stationary shaft (350) to a rotating hub (355).

Description

Detailed Description of the Invention

(Cross Reference of Related Applications) This application is US provisional patent application 60/116758 filed January 22, 1999, 60/117826 filed January 29, 1999, February 25, 1999. Application 60/121687, and application March 16, 1999 60/1246
Claiming priority by No. 29. FIELD OF THE INVENTION The present invention relates generally to the field of disk drives, and more particularly to an apparatus and method for providing a reliable magnetic fluid seal between a spindle motor hub and shaft in a disk drive. Regarding

BACKGROUND OF THE INVENTION Disk drives, including magnetic disk drives, optical disk drives, and magneto-optical disk drives, are widely used to store information. A typical disk drive has one or more disks that store information in the form of concentric tracks. This information is written to the disc using a read / write head attached to an actuator arm that moves from track to track across the surface of the disc by an actuator mechanism,
And read from the disc. The disk is mounted on a spindle that is rotated by a spindle motor to pass over the surface of the disk below the read / write head. Spindle motors typically include a shaft fixed to a base plate and a hub to which the spindle is attached and which has a sleeve into which the shaft is inserted. Permanent magnets attached to the hub interact with the stator windings on the base plate to rotate the hub with respect to the shaft. One or more bearings between the hub and shaft facilitate rotation of the hub.

Spindle motors also typically include exclusive seals to seal the interface space between the hub and shaft. This is necessary because the lubricating fluid or grease used in the bearing tends to release aerosol or vapor components that move or diffuse out of the spindle motor and into the disc chamber where the disc is maintained. is there. This vapor often transfers other particles into the disk chamber, such as material scraped from bearings and other components of the spindle motor. These vapors and particles deposit on the surface of the read / write head and the disk, which causes damage to the disk and read / write head as the read / write head passes over the disk. Therefore, the transfer of these contaminants into the disk chamber must be prevented.

To prevent the transfer of these contaminants into the disk chamber, the final product of the spindle motor utilizes a ferrofluidic seal between the shaft and the hub. Ferrofluidic seals are disclosed, for example, in US Pat.
No. 73484. A typical ferrofluid seal is a ferrofluid,
It consists of an axially polarized annular magnet and two magnetically permeable annular pole pieces mounted on opposite faces of the magnet. Ferrofluids conventionally consist of a suspension of magnetically permeable particles suspended in a fluid carrier. Generally, the magnets and pole pieces are fixed to the hub,
Extends close to the shaft, but does not touch the shaft. The magnetic flux generated by the magnet passes through the pole pieces and the shaft, which is also magnetically permeable, to magnetically retain the ferrofluid in the gap between the pole pieces and the shaft, thereby forming a seal. .

As mentioned above, current ferrofluidic seals use a rotating design in which the magnet and pole pieces are mounted on the hub and the ferrofluid seals with the stationary shaft. While this design works well with conventional spindle motors, the final product of the motor rotates at high speeds, often above 1300 revolutions per minute (rpm). Such high-speed centrifugal forces often exceed the ability of the ferrofluid seal's magnetic flux to hold the ferrofluid to the shaft due to the velocity gradient across the ferrofluid, resulting in It becomes impossible to maintain an airtight seal.

Therefore, there is a need for a ferrofluidic seal that seals the outer surface of a shaft to the inner surface of a hub disposed around the shaft. It is desirable for ferrofluidic seals to provide a reliable structure at high rotational speeds. There is also a need for a method of forming such a ferrofluidic seal without increasing the manufacturing time or cost of assembling the spindle motor in which the seal is used.

The present invention provides a solution to these and other problems and provides other advantages over the prior art.

SUMMARY OF THE INVENTION The present invention is directed to a device for sealing the outer surface of a shaft to the inner surface of a hub disposed around the shaft, which solves the above problems.

According to one embodiment, there is provided a seal having an annular magnet, the top and bottom pole pieces of which are coupled to opposite poles thereof. The pole pieces have an annular shape and have an inner radius that is larger than the radius of the outer surface of the shaft. The top pole piece includes an L-shaped cross-sectional area with a long horizontal portion parallel to the surface of the magnet poles and a shorter vertical portion parallel to the outer surface of the shaft. The ferrofluid is magnetically retained between the vertical portion of the top pole piece and the outer surface of the shaft to form a seal therebetween. In general, the top pole piece is separated from the outer surface of the shaft by a gap that is less than the distance separating the top pole piece from the bottom pole piece. In one embodiment, the hub is rotatably supported about the shaft by a bearing that includes an inner race on the shaft and an outer race mounted on the hub and the gap includes the top pole piece on the inner race of the bearing. Less than a distance away from the race. Preferably, the top pole piece is
The vertical portion has a curved corner that joins the horizontal portion to spread the magnetic flux gradient over a larger area, thereby allowing the ferrofluid to be retained over a larger area. More preferably, the vertical portion also includes a curved tip at its lower end.

In another embodiment, a seal is provided for sealing the outer surface of the magnetically permeable shaft to the inner surface of a hub disposed around the shaft. The seal has an annular magnet,
Top and bottom pole pieces are coupled to the opposing poles, the top and bottom pole pieces facing the contoured portion of the outer surface of the shaft. More specifically, the contoured portion is in face-to-face relationship with the inner radius of the top pole piece. The ferrofluid is magnetically retained in the gap separating the top pole piece from the outer surface of the shaft, forming a seal therebetween. The contoured portion introduces a magnetic flux gradient that axially concentrates the ferrofluid in the gap between the top pole piece and the shaft. In one version of this embodiment, the contoured portion includes a raised curved surface in facing relationship with the top pole piece. The curved surface can be formed by a pair of axially spaced grooves machined circumferentially around the outer surface of the shaft, with curved surfaces raised relative to the grooves formed between the grooves. Alternatively, the contoured portion may include two beveled surfaces that intersect at an angle to form the tip of the ring around the shaft. Ring
It may be a separating element that is coaxial with the shaft and is attached to the shaft, or it may be an integral part of the shaft itself. In a preferred version of this embodiment, the top pole piece has a generally L-shaped cross-sectional area with the long horizontal portion parallel to the surface of the magnet poles and the shorter vertical portion substantially parallel to the outer surface of the shaft. . The top pole piece is positioned so that the vertical portion is in face-to-face relationship with the contoured portion.

In another aspect, the invention is directed to a seal for sealing an outer surface of a shaft to an inner surface of a magnetically permeable hub disposed around the shaft. The seal includes annular magnets having opposite poles coupled to a pair of annular pole pieces positioned between the shaft and the hub. The pole pieces are made of a magnetically permeable material and have an outer radius that is smaller than the radius of the inner surface of the hub. The seal further includes a catcher mounted on the inner surface of the hub. The catcher is an annular ring of magnetically permeable material having a curved surface that is in facing relationship with the outer radius of the pole pieces. The ferrofluid is magnetically retained in the gap separating the pole pieces from the catcher and forms a seal between them, which causes the ferrofluid to splatter and outward when the hub is rotated with respect to the shaft. Movement is greatly reduced. Preferably, the curved surface has a cross-sectional area having a U-shape, U
The open ends of the V-shape are oriented with respect to the outer radius of the pole pieces so that they extend radially inward beyond the outer radius of the pole pieces. The catcher can be formed from a single piece, or it can have top and bottom portions joined to form a curved surface, one of which can be integrally formed with the hub. .
The catcher is attached to the hub with an adhesive, an O-ring, or a plastic adhesive. In one preferred embodiment, the pole pieces, ferrofluid, catcher, and hub are made of an electrically conductive material so that the pole pieces are electrically coupled to the shaft and the ferrofluid electrically connects the pole pieces and the catcher. Coupled, the catcher is electrically coupled to the hub. More preferably, the outer radius of the pole pieces and the inner radius of the hub are about 1 × the surface area of the ferrofluid that electrically couples the pole pieces to the catcher.
It is selected to provide a resistance value of less than 10 ⁹ ohms.

In another aspect, the invention is directed to a stationary ferrofluidic seal for sealing a stationary shaft to a rotating hub. The effect of centrifugal force, which tends to force ferrofluids away from the magnets of conventional ferrofluidic seals, and the magnetic flux of the seals exceeds the ability of the fluid to hold the fluid against the shaft is that the seal itself is mounted on a stationary shaft Canceled by. The formed magnetic shield arm is mounted on the rotating hub, so that the magnetic shield arm projects upward through the inner diameter of the magnet and the pole piece of the seal. Thus, the rotating magnetic shield arm extends radially inward from the hub to a point between the magnet and the shaft, which causes the velocity gradient of the ferrofluid to flow from the rotating surface of the magnetic shield arm to the current stationary surface of the seal. Toward the outside. By utilizing this approach, the ferrofluid closest to the shaft approaches the motor RPM, but at a lower velocity, and the ferrofluid velocity near the seal magnet and pole pieces approaches zero. The reduced velocity of the ferrofluid in the shaft reduces the forces that would normally tend to diffuse the fluid and maintains the integrity of the seal.

The present invention is particularly useful for spindle motors such as those used in disk drives. Spindle motors typically have a base to which a shaft is coupled and a hub having an inner surface disposed around the outer surface of the shaft. One embodiment of the seal according to the present invention is positioned between the shaft and the hub to seal the outer surface of the shaft to the inner surface of the hub and electrically couple the shaft to the hub.

These and various other features, as well as advantages, which characterize the present invention, will be more apparent from a reading of the following detailed description and a review of the associated drawings.

DETAILED DESCRIPTION FIG. 1 is a plan view of a magnetic disk drive in which a spindle motor having a ferrofluidic seal according to the present invention is particularly useful. Referring to FIG. 1, a disk drive 100 typically includes a housing 1 having a base 110 joined to a cover 115.
Including 05. Surface 13 covered with a magnetic medium (not shown) for magnetically recording information
One or more disks 130 having 5 are mounted on a shaft 140. A spindle motor (not shown in this figure) rotates shaft 140 to rotate disk 130 past a read / write head 145 suspended on disk surface 135 by suspension arm assembly 150. . In operation, disk 130 rotates at high speeds past read / write head 145, while suspension arm assembly 150 is radially spaced on surface 135 of disk 130. Moving the read / write head in an arc over a plurality of tracks being opened. The read / write head 145 can thus read and write magnetically encoded information at selected locations on the magnetic medium on the surface 135 of the disk 130.

FIG. 2 illustrates a type of spindle drive that is particularly useful in disk drive 100.
It is a sectional side view of a motor 155. Typically, the spindle motor 155 is the shaft 1
A rotatable hub 160 having an inner surface 165 disposed about an outer surface 170 of 75. The ferrofluidic seal 185 connects the outer surface 170 of the shaft 175 to the hub 160.
The inner surface 165 of the seal. One or more magnets 190 mounted on the perimeter 195 of the hub 160 interact with the stator windings 205 mounted on the base 110 to rotate the hub 160. Hub 160 is supported on shaft 175 by one or more bearings 215, such as hydrodynamic bearings (not shown) or ball bearings 215 shown in FIG. Ball bearings are generally inner race 23
Includes one or more balls loosely held by a retainer 225 between the O and the outer race 235. The two-sided space (not shown) between the ball 220, the retainer 225 and the inner race 230 and the outer race 235 may be filled with a lubricating liquid or oil to facilitate the movement of the ball 220. it can.
The structure of bearing 215 is not relevant to the present invention. The important thing is the bearing 21
The ferrofluidic seal 185 must maintain a hermetic seal between the outer surface 170 of the shaft 175 and the inner surface 165 of the hub 160 so that fluids, oils, and other loose particles associated with No. 5 do not reach the disk 130. That is not the case.

A typical ferrofluidic seal 185, as shown in FIG. 2, includes a laminated plate 250 consisting of an annular magnet 255 having a top pole piece 260 and a bottom pole piece 265 coupled to opposite poles. The magnet 255 and pole pieces 260, 265 are attached and sealed to the inner surface 165 of the hub 160 or the outer surface 170 of the shaft 175 using epoxy or solder. Ferrofluid 270 is magnetically retained between pole pieces 260, 265 and outer surface 170 of shaft 175 or inner surface 165 of hub 160 to seal the shaft to the inner surface of the hub. Ferrofluid 270 is typically Fe ₃ O suspended colloidally in a dispersion medium such as a hydrocarbon or synthetic ester-based fluid.
Or it contains ferromagnetic particles such as magnetite. In the conventional ferrofluidic seal 185, the ferrofluid 270 forms a top meniscus 280, as shown in FIG. 2, which is the centrifugal force exerted on the ferrofluid of the ferrofluidic seal that rotates at high speed during dynamic operation. Forces can cause ferrofluids to scatter and move. This splattering and movement can result in contamination of the disk 130 and loss of the hermetic seal.

An embodiment of a ferrofluidic seal 185 according to the present invention that solves these problems will now be described in detail with reference to FIG. In this particular embodiment, the ferrofluidic seal 185 is mounted on the inner surface 165 of the hub 160 and is in face-to-face relationship with the outer surface 170 of the shaft 175. The ferrofluidic seal 185 can be attached to the inner surface 165 by any suitable means such as an adhesive (as shown here), a force fit, or a retaining ring (not shown). Ferrofluidic seal 185 includes an annular magnet 255 having a top pole piece 260 and a bottom pole piece 265 coupled to opposite poles. Ferrofluid 270 is magnetically retained between the pole pieces and outer surface 170 of shaft 175, sealingly sealing the shaft to inner surface 165 of hub 160. The pole pieces 260, 265 have a generally annular shape and have an inner radius that is greater than the radius of the outer surface 170 of the shaft 175. According to the present invention, the top pole piece 260 includes a flat annular disk having a cylinder joined to its inner radius to form a substantially L-shaped cross-sectional area. This L-shaped cross-sectional area is
A long horizontal portion 260a extending radially parallel to the surface of the pole of 5, and the shaft 17
5 has a short vertical portion 260b parallel to the outer surface 170.

Top pole piece 260 and bottom pole piece 265 are typically formed from a magnetically permeable material using a stamping process. Since the stamping process often leaves marks or scratches on the surface of the pole pieces 260, 265, a thin layer of material such as nickel or cladding 285 is applied to the surface of the pole pieces. The cladding 285 may be applied using any suitable technique such as electroplating, spattering, and sputtering or evaporation deposition processes. Cladding 28
5 enhances the operation of the ferrofluidic seal 185 by providing a smooth and uniform surface on which the ferrofluid 270 can seal.

The top pole piece 260 is separated from the outer surface 170 of the shaft 175 by a gap 275 that is shorter than the distance separating the top pole piece from the bottom pole piece 265. Figure 3
Bearing 215, which includes an inner race 230 on the shaft and an outer race 235 attached to the hub, as shown in FIG.
The gap 275 that separates the top pole piece 260 from the outer surface 170 of the shaft when separated from zero is also small compared to the distance separating the top pole piece from the inner race 230 of the bearing 215.

The surface of the vertical portion 260 b facing the outer surface 170 of the shaft 175 is preferably curved or curved at the portion where it joins the horizontal portion 260 a and its lower end or tip 290. The sharp corners produce a region of high flux density, which results in lower magnetic forces or pressures just above the corners than needed to keep the ferrofluid in place in this region. The rounded corners allow the magnetic flux gradient to spread over a wider range, which allows the ferrofluid to be retained over a wider range. This allows more ferrofluid 270 to be initially injected into the ferromagnetic seal 185, thereby extending the seal life.
This is because the ferrofluid is lost over time due to e.g. evaporation and cannot maintain a hermetic seal below a certain amount. Further, from a manufacturing point of view, the pole pieces 260, 265 are easier to form rounded corners because they are manufactured by stamping and are therefore more economical.

Since the surface area of the seal with the outer surface 170 of the shaft 175 is directly proportional to the surface area of the vertical portion 260b of the top pole piece 260, it is desirable to maximize the portion of the top pole piece having a vertical cross-sectional area. One way to achieve this is to reduce the inner radius of the bottom pole piece 265 so that the vertical portion 260b of the top pole piece 260 can expand between the bottom pole piece and the outer surface 170 of the shaft 175. . To do this, in order to maintain a distance between the top pole piece and the bottom pole piece 265 that is longer than the gap 275, the vertical portion 260b of the top pole piece 260 is moved to the horizontal portion 2.
The portion to be joined with 60a is tapered toward its tip 290.

To further reduce radial migration of the ferrofluid 270 from the outer surface 170 of the shaft 175, a barrier film 295 is applied to the horizontal portion 260a of the top pole piece 260. The barrier film is hydrophilic (o) having a surface energy lower than that of the top pole piece material and lower than the surface tension of the ferrofluid 270.
Fluorophyc) and hydrophobic fluoropolymers. One suitable commercially available polymer for this is New Bedford, Massachusetts-Sets (New).
Nyeb from Nye Lubricants, Inc. (Bedford)
ar (registered trademark).

The barrier film 295 can be formed by applying a thin layer or coating of fluoropolymer using any suitable technique such as spin coating, spattering, sputter deposition, photolithography. In the preferred embodiment, the fluoropolymer is applied by dipping the top pole piece 260 in a solution of fluoropolymer material to form a thin layer bonded to the horizontal portion 260a of the top pole piece 260. The excess material is then removed using solution dipping and the top pole piece 26 using vaporized solvent.
Degrease 0. The fluoropolymer is then cured using air or oven drying to form a strong barrier film that is firmly bonded to the horizontal portion 260a of the top pole piece 260.

In another embodiment, as shown in FIG. 4, the outer surface 170 of the shaft 175 that faces the top pole piece 260 axially concentrates the ferrofluid 270 in the gap 275 between the top pole piece and the shaft. Contoured portion 300 that produces a magnetic flux gradient
Have. This is desirable because fluid can move within this gap when the magnetic flux along the gap 275 between the top pole piece 260 and the shaft 175 is uniform. Since the volume of fluid 270 gradually decreases as the spindle motor 155 ages, it gaps the ferrofluid in such a way as to provide a perfect seal even if there is still a sufficient amount of ferrofluid. It is never placed inside 275. Thus, creating a magnetic flux gradient allows the ferrofluid 270 in the gap 275 to be axially concentrated near a point, typically near the axial center of the vertical portion 260b. The contoured portion 300 faces the inner radius of the top pole piece 260 and the ferrofluid 270 is magnetically retained in the gap 275 to separate the top pole piece from the outer surface 170 of the shaft 175 therebetween. Form a seal. In one version of this embodiment, the contoured portion 300 has a raised curve formed by a set of axially separated grooves 305 machined circumferentially around the outer surface 170 of the shaft 175. Including.

Alternatively, as shown in FIG. 5, the contoured portion 300 can include two beveled surfaces that intersect at an angle to form the apex of the ring 310 around the shaft 175. The ring 310 is an integral part of the shaft itself (not shown),
Alternatively, as shown in FIG. 5, it can be a separate element coaxial with the shaft 175 and mounted on the shaft. The latter version requires only the ring 310 to be made of a magnetically permeable material, which allows the shaft to be made of a non-magnetic material such as stainless steel, which has high strength, high conductivity,
It has further advantages in having other desirable properties such as low cost and ease of machining.

In a preferred version of this embodiment, the top pole piece 260 has a substantially L-shaped cross-sectional area as described above, with the vertical portion 260 b arranged in facing relationship with the contoured portion 300. To be done.

FIG. 6 is a graph showing the magnetic flux gradient created in the ferrofluidic seal 185 using the top pole piece 260 having the L-shaped cross-sectional area shown in FIG. 4 and having the contoured portion 300. Is.

Alternatively, as shown in FIG. 7, the surface 315 of the vertical portion 260a of the top pole piece 260 that faces the straight shaft 175 can also be contoured to produce the desired magnetic flux gradient. In this version, the surface of the vertical portion 260b facing the shaft 175 is curved or convex to concentrate the lines of magnetic flux at a point near the axial center of the vertical portion of the top pole piece 255.

In yet another alternative, shown in FIG. 8, the vertical portion 260 b has a straight outer surface 17.
The L-shaped top pole piece 260 may be bent to form an angle 320 with the shaft 175 having a zero. In this embodiment, the magnetic flux is concentrated at the lower end or tip 290 of the vertical portion 260b closer to the shaft 175. FIG. 9 is a graph showing the gradient in the magnetic flux introduced into the ferrofluidic seal 185 using the top pole piece whose vertical portion forms various angles 320 with the outer surface 170 of the shaft 175. Lines 330, 331, 333 and 334 show the magnetic flux gradients for the bent top pole pieces forming angles 320 of 0 degrees, 10 degrees, 30 degrees and 40 degrees, respectively.

In another aspect, shown in FIG. 10, the present invention provides a catcher 335 for reducing splattering or outward movement of ferrofluid 270 when using a ferrofluidic seal to form an outer seal. It is directed to a ferrofluidic seal 185 having. In this embodiment, the ferrofluidic seal 185 includes an annular magnet 255 with a pair of annular pole pieces 260, 265 coupled to its opposite pole located between the shaft 175 and the hub 160. The pole pieces 260, 265 are made of a magnetically permeable material and have an outer radius that is smaller than the radius of the inner surface 165 of the hub 160. Catcher 335
Is mounted on the inner surface 165 of the hub 160. The catcher 335 includes an annular ring made of a magnetically permeable material and has a curved surface that faces the outer radii of the pole pieces 260, 265. The ferrofluid 270 is magnetically retained in the gap 275, separating the pole pieces 260, 265 from the catcher 335 and forming a seal therebetween, and the ferrofluid as the hub 160 rotates relative to the shaft 175. 270
Dramatically reduce the scattering and movement to the outside. The cross-sectional area of the curved surface is semicircular or U
And is oriented with respect to the outer radius of the pole pieces 260, 265, U
Preferably, the open ends of the V-shape extend radially inward through the outer radius of the pole pieces. The catcher 335 may be manufactured from a single piece or have top and bottom portions (not shown) that join to form a curved surface, one of the two portions being integrally formed with the hub 160. You can The catcher 335 can be attached to the hub 160 by any suitable means including an adhesive such as an epoxy, O-ring or plastic bonder.

In one embodiment, shaft 175, pole pieces 260, 265, ferrofluid 270.
, The catcher 335 and the hub 160 can be made of electrically conductive material, the pole pieces are electrically coupled to the shaft, the ferrofluid is electrically coupled to the pole pieces and the catcher, and the catcher is electrically coupled. Coupled to the hub. The pole piece 260,
The outer radius of 265 and the inner radius of hub 160 are preferably selected so that the surface area of ferrofluid 270 that electrically couples the pole pieces to catcher 335 provides a resistance of about 1 × 10 ⁹ ohms or less. . More preferably, the surface area is selected to provide a resistance of 0.4 × 10 ⁹ ohms or less, most preferably 0.22 × 10 ⁹ ohms or less. The pole pieces 260, 265 can be electrically coupled to the shaft 175 by a conductive epoxy or pressure fit between the pole pieces and the shaft.

In yet another aspect, the invention is directed to a static ferrofluidic seal that seals a stationary shaft to a rotating hub. In conventional ferrofluidic seals, the magnets and pole pieces are mounted directly on the inner surface of the hub or on the outer surface of the shaft and are positioned opposite the corresponding surfaces. Typically, the ferrofluidic seal is attached to the hub and rotates with the hub about the shaft. As noted above, this rotation creates a velocity gradient across the magnetically retained ferrofluid between the pole pieces and the outer surface of the shaft. Centrifugal forces that occur in ferrofluids at high speeds often exceed the magnetic flux's ability to keep the ferrofluid on the shaft, which can result in the ferrofluid seal failing to maintain a hermetic seal.

An embodiment of a static ferrofluidic seal 345 for sealing a stationary shaft 350 to a rotating hub 355 according to the present invention will now be described with reference to FIG. In the present invention, it is attached at its inner or proximal end 365 to the outer surface 370 of the stationary shaft 350, and at its distal end 375 to the laminate 380 of the magnet 385, the top pole piece 390,
A support arm 360 is provided with a bottom pole piece 395 coupled to the opposite pole. The support arm 360 extends radially approximately to the inner surface of the hub 355, leaving only a small amount of space for the hub to rotate freely past the stationary support arm. Generally, support arm 360 is formed of a non-magnetic material to eliminate magnetic coupling with top pole piece 390. Laminate 380 is integrally formed with any suitable means, including solder, adhesive or epoxy, and support arms, and is folded over the outer radius of the laminate to secure the tabs in place (not shown). It can be fixed to the support arm 360 by mechanical means such as ().

The other main element in this design is the hub 355 or bearing 21.
5 is a magnetic shield arm 400 that rotates with the hub attached to components mounted therein, such as the outer race 235 of FIG. Magnetic shield arm 400
Hub 355 (by any suitable means including solder, adhesive or epoxy.
Or the components attached to it) can be fixed. The magnetic shield arm 400 generally comprises a flat annular disk with a cylinder joined to its inner radius and having an L-shaped cross-sectional area, which from the hub 355 to the inner radius of the laminate and the outer surface 370 of the shaft 350. A radially extending section 400a extending to the midpoint of the, and an axially extending shield portion 400b.

The magnetic shield arm 400 is formed of a magnetically permeable material, and the ferrofluid 270 is a gap 405 between the pole pieces 390, 395 of the laminate and the inner surface of the shield portion 400b.
Magnetically retained therein to complete the seal between shaft 350 and hub 355. In a preferred embodiment, the magnetic shield arm 400 includes a layer of nickel or cladding 285 on its surface to provide a sufficiently smooth surface to enhance the ferrofluidic seal as described above. The shield portion 400a of the rotating magnetic shield arm 400 is inside the inner radius of the laminate 380 between the stationary magnet 385 and the shaft 350, which is also stationary, so that the velocity gradient acting on the ferrofluid 270. Decreases outward from the rotating surface of the magnetic shield arm 400 toward the stationary surface of the outer laminate 380. Therefore, the centrifugal forces that may act on ferrofluid 270 and propel it out of gap 405 are dramatically reduced. Further, the centrifugal force generated by the rotation of the shield portion 400b and acting on the ferrofluid 270 in this area, in turn, acts from the shield portion of the magnetic shield arm 400 toward the laminate 380, thereby causing the shield portion to move. And holds the ferrofluid between the and the laminate. Therefore, the integrity of the hermetic seal between the spindle motor 155 and the disk chamber is maintained even at high rotational speeds above 13,000 rpm.

In the embodiment shown in FIG. 11, the top pole piece has a generally Z-shaped cross-sectional area such as that used to concentrate the magnetic flux from the top pole piece 390. However, the top pole piece 390 can also have an L-shaped cross-sectional area as described above. Further, either the outer surface of the vertical portion 260b of the L-shaped top pole piece or the inner surface of the shield portion 400b is contoured portion 28 as also described above to concentrate the magnetic flux axially.
5 can be included, thereby extending the life of the ferrofluidic seal 345.

Additionally, all or part of the surface of the magnetic shield arm 400 can be coated with a fluoropolymer such as Nyebar® to form the barrier film 295 described above. The main area of placement of the barrier film 295 is the inner corner of the junction between the shield portion 400b and the radially extending portion 400a of the magnetic shield arm 400. Although not so critical, it has also been found desirable to apply a barrier film 295 to the outer surface of the shield portion 400b facing the shaft 350 or the distal end 365 of the support arm 360 and the lower surface of the bottom pole piece 395. . By applying the barrier film 295 to the outer surface of the shield portion 400b, movement of the ferrofluid 270 to the spindle motor 155 can be eliminated or reduced. By applying the barrier film 295 to the lower surface of the bottom pole piece 395, the movement of the ferrofluid 270 between the bottom pole piece and the magnetic shield arm 400 is further reduced. Generally, a ferrofluidic seal 345
The barrier film 295 is not applied to the inner sealing surface of the shield to avoid interference with the operation of the. However, the entire magnetic shield arm 400 can be dipped over its surface to form a barrier film 295 and it has been found that the fluoropolymer layer is sufficiently thin to not interfere with the operation of the ferrofluidic seal 345. .

Then some of the important aspects of the present invention are repeated in order to further emphasize its structure, function and advantage.

In one aspect, a seal is provided for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed around the shaft. The seal includes an annular magnet located between the shaft and the hub, with the top and bottom pole pieces coupled to opposite poles of the magnet, the top and bottom pole pieces made of a magnetically permeable material. And having an annular shape with an inner radius greater than the radius of the outer surface of the shaft, the top pole piece including a substantially L-shaped cross-sectional area, which is substantially parallel to the surface of the poles of the magnet. It has a long horizontal section and a short vertical section that faces the outer surface of the shaft without touching it, and a ferrofluid is magnetically retained between the vertical section of the top pole piece and the outer surface of the shaft. To form a seal.

In one embodiment, the top pole piece is separated from the outer surface of the shaft by a gap that is less than the distance separating the top pole piece from the bottom pole piece. In another embodiment, the shaft further includes a bearing inner race that separates the shaft from the hub, the gap being less than the distance separating the top pole piece from the bearing inner race. In yet another embodiment, the top pole piece includes a curved corner where the vertical portion joins the horizontal portion to spread the magnetic flux gradient over a larger area,
This allows the ferrofluid to be retained over a larger area. In yet another embodiment, the vertical portion of the top pole piece includes a curved tip at its lower end to spread the magnetic flux gradient over a larger area, which may hold ferrofluid over the larger area. I am trying. In another embodiment, the bottom pole piece includes an inner radius that is less than the inner radius of the top pole piece, and the vertical portion of the top pole piece is
It extends between the inner radius of the bottom pole piece and the outer surface of the shaft. In yet another embodiment, the vertical portion of the top pole piece is tapered, from which the horizontal portion is joined to the lower end of the vertical portion to increase the distance separating the top pole piece from the bottom pole piece. . In yet another embodiment, a Nyebar® coating is applied to the horizontal portion of the top pole piece to prevent radial migration of ferrofluid from the outer surface of the shaft. In another embodiment, a nickel coating is applied to the top pole piece to provide a substantially smooth surface in contact with the ferrofluid. In yet another embodiment, the shaft includes a contoured portion and a seal is disposed between the shaft and the hub such that the vertical portion of the top pole piece is in a relationship facing the contoured portion. It is supposed to be. In yet another embodiment, the vertical portion of the top pole piece forms an angle with the outer surface of the shaft to introduce a magnetic flux gradient between the top pole piece and the shaft that concentrates the ferrofluid axially therebetween. In another embodiment, the vertical portion of the top pole piece includes a contoured surface facing the outer surface of the shaft, and a ferromagnetic surface between the top pole piece and the shaft, between the center of the contoured surface of the vertical portion and the outer surface of the shaft. Concentrate the fluid in the axial direction,
Introduce a magnetic flux gradient. The seal of the present invention is particularly useful in spindle motors,
The motor includes a base having a shaft coupled thereto and a bearing capable of rotating and supporting a hub around the shaft, the inner race and the outer race fixed to the shaft and the hub, respectively. And a stator mounted on the hub and a stator wound on a base plate capable of interacting with the magnet on the hub and rotating it relative to the shaft.

In another aspect, a method is provided for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed around the shaft. The method comprises the steps of: (a) forming a laminate comprising an annular magnet having a top pole piece and a bottom pole piece connected to its opposite poles, the top pole piece and the bottom pole piece comprising: A substantially L-shaped cross section having the shape of an annulus whose inner radius is larger than the radius of the outer surface of the shaft, the top pole piece having a long horizontal portion substantially parallel to the surface of the poles of the magnet. And (b) disposing a laminate between the outer surface of the shaft and the inner surface of the hub such that the vertical portion of the top pole piece is substantially parallel to the outer surface of the shaft. And (c) injecting a ferrofluid between the top pole piece and the outer surface of the shaft to form a seal therebetween.

In one embodiment, step (b) comprises disposing the laminate such that the top pole piece is separated from the outer surface of the shaft by a gap that is less than the distance separating the top pole piece from the bottom pole piece. . In another embodiment, the shaft comprises an inner race of bearings separating the shaft from the hub, and step (b) comprises
The method further comprises arranging the laminate so that the gap is less than the distance separating the top pole piece from the inner race of the bearing. In yet another embodiment, step (a) has a curved corner where the vertical portion joins the horizontal portion there and spreads the magnetic flux gradient over a larger area at its lower end, which causes the ferrofluid to become more Forming a top pole piece with a curved tip that allows it to be retained over a large area.

In yet another aspect, a seal is provided for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed about the shaft. The seal is an annular magnet disposed between a shaft and a hub, the top and bottom annular pole pieces of which are secured to their opposing magnetic poles, the pole pieces of the outer surface of the shaft. A magnet including an inner radius greater than a radius, a ferrofluid magnetically retained in a gap separating the top pole piece from the outer surface of the shaft to form a seal therebetween, and spreading the magnetic flux gradient over a larger area. And means for allowing the ferrofluid to be retained on a larger area over the gap of the shaft.

In one embodiment, the means for spreading the magnetic flux gradient over a larger area comprises a cylindrical extension of the inner radius of the top pole piece, said cylindrical extension being in non-contact opposition with the outer surface of the shaft. Have a relationship. In another embodiment, the gap between the cylindrical extension and the outer surface of the shaft is less than the distance separating the cylindrical extension from the bottom pole piece. In yet another embodiment, the shaft further comprises an inner race of a bearing separating the shaft from the hub, and a gap between a cylindrical extension and an outer surface of the shaft includes the cylindrical extension in the bearing. Smaller than the distance from the inner race.

In yet another aspect, a seal is provided for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed about the shaft. The seal is an annular magnet disposed between a shaft and a hub, the top and bottom annular pole pieces of which are connected to their opposing magnetic poles, the pole pieces being made of a magnetically permeable material. A magnet having an inner radius larger than the outer radius of the shaft but smaller than the inner radius of the magnet, and a contoured portion of the outer surface of the shaft, wherein the inner radius of the top pole piece is And a ferrofluid that holds a top pole piece in a gap that separates the top pole piece from the outer surface of the shaft and forms a seal therebetween, whereby the contoured portion includes: A magnetic flux gradient that axially concentrates the ferrofluid is introduced into the gap between the top pole piece and the shaft.

In one embodiment, the top pole piece is substantially L-shaped with a long horizontal portion that is substantially parallel to the surface of the magnet poles and a shorter vertical portion that is substantially parallel to the outer surface of the shaft. And a top pole piece is disposed such that the vertical portion is in a facing relationship with the contoured portion. In another embodiment, the contoured portion of the outer surface of the shaft includes a raised curved surface in a relationship facing the top pole piece. In yet another embodiment, the contoured portion of the outer surface of the shaft intersects at an angle,
It includes two bevels that form the apex of the ring around the shaft. In yet another embodiment, the contoured portion of the outer surface of the shaft includes a pair of axially spaced grooves machined around the outer surface of the shaft to form a curved surface therebetween. In another embodiment, the contoured portion comprises a coaxial ring secured to the shaft. In yet another embodiment, the ring is made of a magnetically permeable material and the shaft is
It is non-magnetic.

In another aspect, a seal is provided for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed about the shaft. This method
a) forming a laminate comprising an annular magnet having a top pole piece and a bottom pole piece fixed to its opposing poles, wherein the top pole piece is larger than the radius of the outer surface of the shaft. Having a radius; (b) forming a contoured portion on the outer surface of the shaft; (c) disposing a laminate between the outer surface of the shaft and the inner surface of the hub; Allowing the inner radius of the top pole piece to be in a relationship facing the contoured portion and separated from it by a gap; and (d) the top pole piece and the contoured portion. Introducing a ferrofluid into the gap therebetween to form a seal therebetween.

In one embodiment, step (a) comprises a top pole piece with a substantially L-shaped cross section having a long horizontal portion substantially parallel to the surface of the magnet poles and a shorter vertical portion. Forming a laminated plate comprising: a step (c) such that the vertical portion of the top pole piece is in a relationship substantially parallel to the outer surface of the shaft and faces the contoured portion. Arranging the laminates on the. In another embodiment, step (b) comprises forming a contoured portion having a raised curved surface disposed around the shaft. In yet another embodiment, step (b) comprises forming angled intersections around the shaft to form a contoured portion having two bevels forming the apex of the ring. In yet another embodiment, step (b) comprises machining a pair of axially spaced grooves around the shaft to form a contoured portion therebetween to form a curved surface. Including. In another embodiment, step (b) comprises securing the coaxial ring to the shaft to form the contoured portion.

In yet another aspect, a seal is provided for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed around the shaft. A seal is an annular magnet disposed between a shaft and a hub, the top and bottom annular pole pieces of which are fixed to their opposing magnetic poles, the pole pieces having a radius of an outer surface of the shaft. A substantially L-shaped cross-section having a long horizontal portion having a larger inner radius and substantially parallel to the surface of the magnet poles and a shorter vertical portion substantially parallel to the outer surface of the shaft. A magnet including; a ferrofluid magnetically retained in a gap separating the top pole piece from the outer surface of the shaft to form a seal therebetween; and located between the center of the top pole piece and the outer surface of the shaft. Means for providing a magnetic flux gradient that axially concentrates the ferrofluid in the gap.

In another embodiment, a method for providing a magnetic flux gradient includes a contoured portion of the outer surface of the shaft in a relationship facing the vertical portion of the top pole piece. In another embodiment, the contoured portion includes a raised curved surface disposed around the outer surface of the shaft. In yet another embodiment, the contoured portion includes a pair of axially spaced grooves machined around the outer surface of the shaft to form a curved surface therebetween.

In another embodiment, a seal is provided for sealing the outer surface of a magnetically permeable shaft to the inner surface of a hub disposed around the shaft. The seal is an annular magnet disposed between a shaft and a hub, the top and bottom annular pole pieces of which are connected to their opposing magnetic poles, the pole pieces being made of a magnetically permeable material. A magnet having an outer radius smaller than the radius of the inner surface of the hub, and a catcher fixed to the inner surface of the hub, which is made of a magnetically permeable material and has a curved surface on its inner radius. An annular ring, the curved surface being magnetically retained in a gap separating the pole piece from a catcher in a relationship facing the outer radius of the pole piece and the catcher fixed to the inner surface of the hub, thereby
And a ferrofluid in which the ferrofluid is substantially prevented from bouncing, or outward movement, when the hub is rotated relative to the shaft.

In one embodiment, the curved surface comprises a cross-section having a U-shape, the U-shaped open end extending radially inward beyond the outer radius of the pole piece. In another embodiment,
The catcher includes a top and a bottom. In yet another embodiment, at least one of the top and bottom of the catcher is integrally formed with the hub. In yet another embodiment, the catcher is secured to the hub with glue, O-rings, or plastic bonders. In another embodiment, the pole piece, ferrofluid, catcher,
And the hub is made of an electrically conductive material, the pole pieces are electrically coupled to the shaft, the ferrofluid is electrically coupled to the pole pieces and the catcher, and the catcher is electrically coupled to the hub. , The outer radius of the pole pieces and the inner radius of the hub are selected so that the surface of the ferrofluid that electrically couples the pole pieces to the catcher provides a resistance of less than approximately 1 × 10 ⁹ ohms. . In yet another embodiment, the pole pieces are electrically coupled to the shaft via a conductive epoxy or a force fit between the pole pieces and the shaft.

In yet another aspect, a method is provided for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed around the shaft. The method comprises the steps of: (a) forming a laminated plate containing a magnet with a pair of annular pole pieces fixed to opposite poles thereof, wherein the pole pieces are larger than the inner radius of the inner surface of the hub. (C) providing a catcher made of a magnetically permeable material, the catcher comprising an annular ring having a curved surface on its inner radius; ) Disposing the laminate within the catcher, the catcher being disposed coaxially around the laminate such that the curved surface faces the outer radius of the pole piece, from which the gap And a catcher that holds the laminate therein, is secured to the inner surface of the hub.

In one embodiment, the method comprises introducing a ferrofluid into a gap between the pole pieces and the curved surface of the catcher so as to be magnetically retained therebetween to form a seal. Including further. In another embodiment, the step of introducing ferrofluid is performed before securing the catcher to the inner surface of the hub. In yet another embodiment, step (b) comprises providing a catcher having a top and a bottom that, when joined, forms a name curve, and step (c) comprises between the top and the bottom. Arranging a laminate on the top and joining the top and bottom.

In yet another aspect, a seal is provided for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed about the shaft. The seal is an annular magnet disposed between a shaft and a hub, the pair of annular magnetic pole pieces being connected to the opposite magnetic poles, the magnetic pole pieces being made of a magnetically permeable material. A magnet having an outer radius smaller than a radius of an inner surface of the hub; a ferrofluid magnetically retained in a gap between the pole pieces and the inner surface of the hub to form a seal therebetween; Contain a ferrofluid in the gap,
Means for causing substantially no bounce or outward movement of the ferrofluid when the hub rotates relative to the shaft.

In one embodiment, the means for containing the ferrofluid comprises a catcher fixed to the inner surface of the hub, the catcher comprising an annular ring having a curved surface on its inner radius, the curved surface comprising: There is a relationship facing the outer radius of the pole pieces. In another embodiment, the curved surface comprises a cross-section having a U-shape, the U-shaped open end extending radially inward beyond the outer radius of the pole piece. In yet another embodiment,
The catcher is fixed to the hub with glue, O-rings, or plastic bonders.

In another aspect, at least one bearing has an inner race and an outer race secured to a shaft and a hub, respectively,
A seal is provided for sealing the outer surface of the stationary shaft to the inner surface of the hub supported for rotation about the shaft. The seal includes an annular magnet disposed between the shaft and the hub, the pair of pole pieces being connected to the opposite poles, and the outer race, but beyond the inner race, but not to the inner race. A magnetic shield arm that extends to a position between the shaft, the magnet, and the magnetic pole piece without being coupled, and is magnetically held between the magnetic pole piece and the magnetic shield arm, and between the shaft and the hub. And a ferrofluid that forms a seal with.

In one embodiment, the magnet has an inner radius that is greater than the radius of the outer surface of the shaft, and the pole pieces have an inner radius that is greater than the radius of the outer surface of the shaft but less than the inner radius of the magnet. A radius and a magnetic shield arm extends between the inner radius of the pole piece and the shaft. In another embodiment, the magnetic shield arm comprises a substantially L-shaped cross section, a radial segment secured to an outer race extending a sufficient length inside the inner race, and a shaft. Substantially parallel, with axial segments extending between the shaft and the magnetic seal poles. In yet another embodiment, the seal comprises a support extending axially from the stationary shaft towards the hub and a distal region of the support arm from the shaft supporting the radially outer ends of the annular magnet and the annular pole pieces; And an annular magnet and an annular pole piece extending radially inward from the support arm toward the shaft. In yet another embodiment, a Nyebar® coating is applied to the magnetic shield to prevent radial movement of the ferrofluid away from the seal. In another embodiment, a nickel coating is applied to the magnetic shield to provide a substantially smooth surface in contact with the ferrofluid. In yet another embodiment, the top pole piece is a shorter horizontal portion that is substantially parallel to and faces the shield portion of the magnetic shield arm and a long horizontal portion that is substantially parallel to the surface of the poles of the magnet. A substantially L-shaped cross section having a substantially L-shaped cross section with a vertical portion. In yet another embodiment, the vertical portion of the top pole piece comprises a contoured surface facing the shield portion of the magnetic shield arm, the vertical portion contour being between the top pole piece and the shield portion. A magnetic flux gradient that axially concentrates the ferrofluid is introduced between the center of the applied surface and the shielded portion of the magnetic shield arm.

In yet another embodiment, a spindle for use in a disk drive
A motor is provided. The spindle motor includes a base, a stationary shaft coupled to the base, the shaft having an outer surface, and at least one bearing fixed to the shaft and the hub, respectively, an inner race and an outer race. By including a hub supported for rotation about the shaft and a seal for sealing an outer surface of the shaft to an inner surface of the hub. The seal comprises an annular magnet disposed between the outer surface of the shaft and an inner surface of the hub, the pair of annular pole pieces being connected to the opposing magnetic poles, and the outer race and the inner race and beyond. However, a magnetic shield arm that extends to a position between the shaft, the magnet, and the magnetic pole piece without being coupled thereto, and is magnetically held between the magnetic pole piece and the magnetic shield arm,
A ferrofluid forming a seal between the shaft and the hub.

In one embodiment, the magnet has an inner radius that is greater than the radius of the outer surface of the shaft,
The pole piece has an inner radius that is greater than the radius of the outer surface of the shaft but less than the inner radius of the magnet, and a magnetic shield arm extends between the pole piece and the shaft. In another embodiment, the magnetic shield arm comprises a substantially L-shaped cross-section, a radial segment secured to an outer race extending a sufficient length within the inner race, and a shaft and a substantially radial segment. Parallel to the shaft, there is an axial segment extending between the shaft and the magnetic pole of the magnetic seal. In yet another embodiment, the seal comprises a support arm extending radially from the stationary shaft toward the hub and a support arm from the shaft supporting the annular magnet and the annular pole piece.
The arm further includes a distal region of the arm and an annular magnet and an annular pole piece that extend radially inward from the support arm toward the shaft. In yet another embodiment, the support arm comprises a non-magnetic material. Another idea is that the magnetic shield arm is made of magnetic stainless steel material.

In yet another embodiment, at least one bearing has an inner race and an outer race secured to the shaft and hub, respectively, to allow the outer surface of the stationary shaft to rotate about the shaft. A seal is provided for sealing against the inner surface of the hub carried by the hub. This seal is
An annular magnet disposed between the shaft and the hub, the pair of annular pole pieces being coupled to the opposing magnetic poles, and an inner diameter of the radially extending annular magnet supported from the outer race, Shielding means projecting between the magnet and the stationary shaft, and a ferrofluid retained between the pole pieces and the magnetic shield to effectively form a seal between the shaft and the hub.

In another embodiment, at least one bearing has an inner race and an outer race secured to the shaft and hub, respectively, to allow the outer surface of the stationary shaft for rotation about the shaft. A seal is provided for sealing against the inner surface of the supported hub. The seal is supported from an outer ring of bearings and an outer ring of magnets disposed between the shaft and the hub, the pair of annular pole pieces connected to the opposite poles, and the outer race and the outer hub. Rotating with and including a shield means formed of a magnetic material and a ferrofluid supported between the shield means and the magnet, the relative rotation of the shield means with respect to the magnet causes the shield This results in a fluid velocity gradient decreasing outward from the rotating surface towards the stationary surface of the magnet and the pole pieces.

While numerous features and advantages of various embodiments of the invention have been set forth in the foregoing description, with details of the structure and function of the various embodiments of the invention, the disclosure is merely exemplary. Changes may be made in the details, particularly as to the construction of the structures and parts within the principles of the invention, to a sufficient extent as indicated by the broad general meaning in which the appended claims are expressed. it can. Therefore, the scope of the appended claims should not be limited to the preferred embodiments described herein.

[Brief description of drawings]

FIG. 1 is a plan view of a disk drive (prior art) in which a spindle motor incorporating a ferrofluidic seal according to an embodiment of the invention is particularly useful.

FIG. 2 is a side sectional view of an embodiment of a spindle motor (prior art) in which the present invention is useful, illustrating a ferrofluidic seal according to the prior art.

FIG. 3 is a partial side sectional view of a ferrofluidic seal having an L-shaped top pole piece, according to an embodiment of the invention.

FIG. 4 is a partial side cross-sectional view of a ferrofluidic seal having an L-shaped top pole piece in facing relationship with a contoured shaft, according to an embodiment of the invention.

FIG. 5 is a partial cross-sectional side view of a ferrofluidic seal having an L-shaped top pole piece in facing relationship with a contoured ring around a shaft, according to an embodiment of the invention.

FIG. 6 is a graph showing the gradient in the magnetic flux produced in a ferrofluidic seal using the arbitrarily contoured shaft shown in FIG.

FIG. 7 is a partial cross-sectional side view of a ferrofluidic seal having an L-shaped top pole piece with a contoured surface in opposed relation to a straight shaft, according to an embodiment of the invention.

FIG. 8 is a partial side cross-sectional view of a ferrofluidic seal having a bent L-shaped top pole piece in facing relationship with a straight shaft according to an embodiment of the present invention.

9 is a graph showing the gradient in the magnetic flux produced in a ferrofluidic seal using the bent top pole piece shown in FIG.

FIG. 10 is a partial cross-sectional side view of a spindle motor having an external ferrofluidic seal with a catcher, according to an embodiment of the invention.

FIG. 11 is a partial side sectional view of a spindle motor having a fixed shaft and a static ferrofluidic seal, according to an embodiment of the invention.

─────────────────────────────────────────────────── ─── Continued front page    (31) Priority claim number 60 / 121,678 (32) Priority date February 25, 1999 (February 25, 1999) (33) Priority claiming countries United States (US) (31) Priority claim number 60 / 124,629 (32) Priority date March 16, 1999 (March 16, 1999) (33) Priority claiming countries United States (US) (81) Designated countries DE, GB, JP, KR, SG (72) Inventor Bair, Marten, Fredrick             Los Angeles, California, United States             Toss, Miller Hill Road 24750 (72) Inventor Leblanc, Jeffrey, Arnold             United States California, Apt             Su, Oak Ridge Road 6565 (72) Inventor Pam, Tan, Hang             United States California, Scott             Tuvalu, Bean Creek Road             111 (72) Inventor Nottingham, Robert, Allen             United States California, Santa             Cruise, Hector Lane 1816 (72) Inventor Wittome, Michael, James             United States California, Scott             TUBBERRY, Meadow Way 24 A F term (reference) 3J042 AA03 AA08 AA16 BA04 CA01                       DA01                 5D109 BC01 BC02 BC12 BC14 BC17 [Continued summary] 5) is provided.

Claims (20)

[Claims] 1. A seal for sealing an outer surface of a magnetically permeable shaft to an inner surface of a hub disposed around the shaft, comprising: (a) an annular magnet positioned between the shaft and the hub; b) top and bottom pole pieces coupled to opposite poles of the magnet, comprising a magnetically permeable material, having an annular shape with an inner radius greater than the radius of the outer surface of the shaft, A top pole piece and a bottom portion, the pole piece having a substantially L-shaped cross-sectional area and having a long horizontal portion generally parallel to the surface of the magnet poles and a shorter vertical portion facing the outer surface of the shaft and in non-contact relationship. A seal comprising a pole piece, and (c) a ferrofluid that is magnetically retained between the vertical portion of the top pole piece and the outer surface of the shaft to form a seal therebetween. 2. The seal of claim 1, wherein the top pole piece is separated from the outer surface of the shaft by a gap that is less than the distance separating the top pole piece from the bottom pole piece. 3. The seal of claim 2 wherein the shaft further comprises a bearing inner race separating the shaft from the hub, the gap being less than the distance separating the top pole piece from the bearing inner race. 4. The top pole piece has a curved corner where the vertical portion joins the horizontal portion to spread the magnetic flux gradient over a larger area, thereby enabling the ferrofluid to be retained over a larger area. The seal according to claim 1, wherein 5. The seal of claim 1 wherein nickel cladding is applied to the top pole piece to provide a substantially smooth surface in contact with the ferrofluid. 6. The shaft comprises a contoured portion and the seal is positioned between the shaft and hub such that the vertical portion of the top pole piece is in face-to-face relationship with the contoured portion. The seal described in 1. 7. A spindle motor comprising the seal according to claim 1, further comprising: (a) a base to which the shaft is coupled, and (b) a hub rotatably supported about the shaft. Bearings that can be mounted on the shaft and hub, respectively.
A spindle with a bearing having a race, (c) a magnet mounted on the hub, and (d) a stator winding on a base plate that can interact with the magnet on the hub to rotate the hub with respect to the shaft. ·motor. 8. A seal for sealing an outer surface of a shaft to an inner surface of a magnetically permeable hub disposed around the shaft, comprising: (a) opposing annular magnets positioned between the shaft and the hub. An annular magnet comprising a pair of annular pole pieces coupled to a magnetic pole, the pole pieces comprising a magnetically permeable material and having an outer radius smaller than the radius of the inner surface of the hub; A catcher mounted on the inner surface of the magnetic disk, comprising an annular ring made of a magnetically permeable material and having a curved inner radius, the curved surface facing the outer radius of the pole piece; and (c) a hub. A ferrofluid magnetically retained in a gap separating the pole pieces from a catcher mounted on the inner surface of the ferrofluid, and when the hub is rotated with respect to the shaft Seal movement is substantially reduced. 9. The seal of claim 8, wherein the curved surface comprises a cross-sectional area having a U-shape, the U-shaped open end extending radially inward beyond an outer radius of the pole piece. 10. The pole piece, ferrofluid, catcher, and hub are made of a conductive material, the pole piece electrically couples to the shaft, and the ferrofluid electrically couples to the pole piece and catcher, the catcher comprising: Electrically coupled to the hub, the outer radius of the pole pieces and the inner radius of the hub provide a surface area of ferrofluid that electrically couples the pole pieces to the catcher provides a resistance value of less than about 1 × 10 ⁹ ohms. 9. The seal of claim 8 selected as: 11. To seal the outer surface of a stationary shaft to the inner surface of a hub supported for rotation about the shaft by at least one bearing having an inner race and an outer race mounted on the shaft and hub, respectively. And (b) an annular magnet positioned between the shaft and the hub, the annular magnet having a pair of annular pole pieces coupled to opposite magnetic poles of the annular magnet; and (b) an inner race from the outer race. A magnetic shield arm extending beyond the race, but not connected to it, to a position between the shaft and the magnet and pole piece, and (c) magnetically between the pole piece and the magnetic shield arm. A seal comprising a ferrofluid held and forming a seal between the shaft and the hub. 12. The magnetic shield wherein the magnet has an inner radius greater than the radius of the outer surface of the shaft, and the pole pieces have an inner radius greater than the radius of the outer surface of the shaft but less than the inner radius of the magnet. The seal of claim 11, wherein the arm extends between the inner radius of the pole piece and the shaft. 13. The magnetic shield arm comprises a substantially L-shaped cross-sectional area,
A radial segment fixed to the outer race long enough to extend inward beyond the race and axially extending generally parallel to the shaft and between the shaft and the magnetic seal poles. The seal of claim 11, having a segment. 14. A support arm extending axially from the stationary shaft toward the hub, the distal region of the support arm from the shaft supporting a radially outer end of the annular magnet and the annular pole piece, 14. The seal of claim 13, wherein the annular magnet and the annular pole piece extend radially inward from the support arm toward the shaft. 15. The seal of claim 11, wherein a Nyebar® coating is applied to the magnetic shield arm to reduce radial movement of the ferrofluid away from the seal. 16. Applying nickel cladding to the magnetic shield arm,
The seal of claim 11, which provides a substantially smooth surface that contacts the ferrofluid. 17. The top pole piece has a substantially L-shaped cross-sectional area and is in a face-to-face relationship with a long horizontal portion substantially parallel to the surface of the magnetic pole of the magnet and the shield portion of the magnetic shield arm, and is substantially parallel to the shield portion. 12. The seal of claim 11 having a shorter vertical portion that is 18. The vertical portion of the top pole piece comprises a contoured surface facing the shield portion of the magnetic shield arm, the center of the contoured surface of the vertical portion and the shield portion of the magnetic shield arm. 18. The seal of claim 17, wherein a magnetic flux gradient that axially concentrates the ferrofluid between is introduced between the top pole piece and the shield. 19. The seal according to claim 11, wherein the support arm is made of a non-magnetic material. 20. The magnetic shield arm comprises a magnetic stainless steel material.
The seal described in 1.