JP2002536947A - Particle-free shield assembly for spindle motor - Google Patents

Abstract

  (57) [Summary] In a motor having a fixed shaft and a ball bearing having inner and outer races mounted near one end of the shaft, supported from a seal support integral with or bonded to a backing iron rotating with the hub. A magnetic seal is provided, wherein the pole piece of the seal extends around the shaft and retains ferrofluid between the ends of the pole piece extending around the shaft, and between the pole piece end and the shaft end. Hold the ferrofluid. A vacuum press holds the shield piece and heats the shield to a temperature such that the inner radius of the washer-shaped seal piece is greater than the outer diameter of the shaft. The press then lowers the shield on the outer diameter of the shaft. The shield is positioned by providing a positioning surface on the vacuum press that abuts against said end of the shaft. To place the shield on the outer surface of the shaft, the vacuum holding portion of the press extends below this alignment surface. When the shield cools, it pushes against the outer surface of the shaft and is fixed in place. The seal support includes a capture recess oriented toward the shaft and positioned to capture stray metal particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] This application is related to US Provisional Application No. 60/117822, filed Jan. 29, 1999.
Claim priority from the issue. FIELD OF THE INVENTION The present invention relates generally to the field of disk drives and, more particularly, to a shield that protects a ferrofluid seal from particles during assembly, and a method of placing the shield.

BACKGROUND OF THE INVENTION Disk drives, including magnetic drives, optical drives, and magneto-optical disk drives
Drives are widely used for storing information. General disk
The drive has one or several disks that store information in a plurality of concentric circular tracks. This information is written to and read from the disk using a read / write head mounted on an actuator arm that moves the surface of the disk from track to track by an actuator mechanism. The disk is mounted on a spindle that is rotated by a spindle motor so that the surface of the disk passes under the read / write head. Spindle motors generally include a shaft fixed to a base plate and a hub to which the spindle is mounted, the hub having 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 relative to the shaft. One or more bearings between the hub and the shaft facilitate rotation of the hub.

[0003] Spindle motors also typically include a reject seal that seals the interface space between the hub and the shaft. This is necessary because the lubricating fluid or grease used in the bearings tends to generate aerosol or vapor components that migrate or diffuse from the spindle motor into the disk chamber where the disk is held. . This vapor often carries other particles into the disk chamber, such as material scraped from bearings or other components of the spindle motor. These vapors and particles adhere to and damage the read / write head and the surface of the disk and damage the read / write head as the read / write head passes over the disk. Therefore, migration of these contaminants into the disk chamber must be prevented.

To prevent the transfer of these contaminants into the disk chamber, the latest generation of spindle motors utilizes a ferrofluid seal between the shaft and the hub. Ferrofluid seals are described, for example, in US Pat. No. 5,473,484, which is incorporated herein by reference. A typical ferrofluid seal consists of a ferrofluid, an axially polarized annular magnet, and two permeable annular pole pieces mounted on opposite sides of the magnet. Ferrofluids usually consist of a suspension of permeable particles suspended in a fluid carrier. The magnets and pole pieces are typically fixed to the hub and extend close to the shaft. However, it does not contact the shaft. The magnetic flux created by the magnet passes through the pole piece and the shaft, which is also permeable, and magnetically retains the ferrofluid in the magnetic gap between the pole piece and the shaft, thereby forming a seal.

[0005] However, problems arise when particles or the like are present or created during motor assembly. For example, a common fixed shaft has a center hole into which is threaded. When the screw is removed from this hole, very small magnetic particles can be created, which can fall into the ferrofluid.

[0006] In the past, efforts have been made to press a shield against the outer surface of the shaft, which acts as a cover over the ferrofluid and prevents the falling of particles. However, due to the interference fit between the shaft and the seal immediately above the magnetic fluid, burrs were generated, and particles could be removed and fall into the fluid. Particles with a size of 50 microns or more repel the magnetic fluid from its field. Further, when protruded into the seal, metal flaws that could move the ferrofluid out of the gap could be created. In addition to reducing the effectiveness of the seal, fluid may be splashed or moved from the motor area to the head-disk area during motor operation after installation in the disk drive, resulting in disk drive failure. was there. Therefore, there is a need for a way to solve these problems.

[0007] Other features and advantages of the invention will be apparent to those skilled in the art upon reviewing the exemplary disclosure set forth below in connection with the related figures.

SUMMARY OF THE INVENTION The present invention provides an apparatus for protecting a ferrofluid of a magnetic seal from particles or the like falling into the fluid. The present invention further provides devices and methods for attaching such shields without creating particles or burrs.

In accordance with one preferred form of the invention, a motor having a fixed shaft and a ball bearing having inner and outer races mounted near one end of the shaft, wherein the motor is integral with a backing iron that rotates with the hub. Or provided a magnetic seal supported from a seal support glued to the backing iron, the pole pieces of the seal extend around the shaft and hold the ferrofluid between the pole piece end and the shaft end I do. A vacuum press holds the shield piece and heats the shield to a temperature such that the inner radius of the washer-shaped seal piece is greater than the outer diameter of the shaft. The press then lowers the shield on the outer diameter of the shaft. The shield is positioned by providing a positioning surface on the vacuum press that abuts against said end of the shaft. To place the shield on the outer surface of the shaft, the vacuum holding portion of the press extends below this alignment surface. When the shield cools, it pushes against the outer surface of the shaft and locks in place without producing particles, while an interference fit is established between the shaft and the shield.

In another aspect of the invention, a seal support for supporting a radially outer edge of the magnetic seal is added toward the shaft and present in an air gap between the shield piece and the magnetic seal. Includes a capture recess positioned to capture stray metal particles.

In a preferred embodiment of the present invention, the assembly press is modified to include a closed loop heating system to preheat the shield, in addition to including a vacuum to hold the shield in place.

The features and advantages that characterize the present invention will become 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 ferrofluid seal according to the present invention is particularly useful. Referring to FIG.
Drive 100 generally includes a housing 105 having a base 110 joined to a cover 115. A plurality of disks 130 having a surface 135 covered with a magnetic medium (not shown) for magnetically storing information are mounted on a spindle 140. A spindle motor (not shown in this figure) rotates the spindle 140, thereby causing the disk 130 to move across the read / write head 145 suspended above the surface 135 of the disk by the suspension arm assembly 150. Rotates. In operation, the disk 130 rotates at high speed across the read / write head 145 and the suspension arm assembly 150
Moves the read / write head in an arc over a plurality of radially spaced tracks (not shown) on the surface 135 of the disk 130. Therefore,
The read / write head 145 is capable of magnetically reading and writing encoded information at selected locations on the magnetic media on the surface 135 of the disk 130.

FIG. 2 is a cross-sectional side view of a spindle motor 155 of a type that is particularly useful for disk drive 100. The spindle motor 155 is generally a shaft 175
A rotatable hub 160 having an inner surface 165 disposed about an outer surface 170 of the hub. The ferrofluid seal 185 in accordance with the present invention can
Are sealed to the inner surface 165 of the hub 160 and are electrically connected. Outer circumference 1 of hub 160
One or more magnets 190 attached to 95 interact with stator windings 205 attached to base 110 to rotate hub 160. Hub 160
Is supported on the shaft 175 by one or more bearings 215. Bearing 2
15 is a ball bearing (shown) or a fluid dynamic pressure bearing (fluid-dynamic b);
earing) (not shown). Ball bearings are generally
25 includes one or more balls 220 loosely held between the inner race 230 and the outer race 235. To facilitate the movement of the ball 220, the interface space 24 between the ball 220, the retainer 225 and the inner and outer races 230, 235
5 is filled with a lubricating fluid or grease. In a fluid dynamic bearing, a lubricating fluid, such as a gas or liquid, provides a bearing surface between the hub 160 and the shaft 175. A dynamic pressure generating groove (not shown) formed in the race of the inner surface 165 of the hub 160 or the outer surface 170 of the shaft 175 creates a local high pressure area that radially supports the hub. Regardless of the type of bearing 215 used, the outer race 235 preferably forms a protruding annular shoulder or shelf 250 around the inner surface 165 of the hub 160 that holds the ferrofluid seal 185.

Reference is made in detail to the improved shield design of FIG. This figure shows a shaft 300, in this example in the form of a fixed shaft, surrounded by a rotating hub 302 supported by a rotating backing iron 304 supporting a magnet 306 rotating outside the stator 308. When the stator is activated, the hub and the disk supported by the hub rotate at a constant high speed. In this example, the ball bearing indicated at 310 includes an inner race 312 and an outer race 314. Outer race 314 supports seal support 316, which supports locating ring 328 and magnetic seal 318. The magnetic seal 318 includes the pole pieces 320, 322 and the magnet 3
24. The magnetic seal provides the magnetic attraction required to hold the ferrofluid 326 in the region between the ends of the pole pieces 320, 322 and the outer surface of the shaft 300. However, in order to maintain this fluid in this position, especially under long-term high-speed operating conditions, measures must be taken to prevent small particles from falling into the ferrofluid 326. Therefore, it is important to place the shield 330 adjacent the end of the shaft 300 with a small gap 332 from the upper pole of the magnetic seal.

The problem created by this shield is that an interference fit is required between the outer surface of the shaft 300 and the inner surface of the shield to prevent undo costs when installing the shield on the shaft. However, these two parts, when pressed together, can create buffs and loose particles due to gauging. These particles can fall into the magnetic fluid. Buffs or particles larger than 50 μm in contact with the fluid will repel magnetic fluid from the ferrofluid seal 318. The flash or other long piece extending into the magnetic fluid allows the fluid to be easily spit out of this area. The ferrofluid then migrates to the head disk area and can cause disk drive failure. Splashing or movement of the ferrofluid further reduces the pressurizing capacity of the seal and causes long-term leakage into the motor, resulting in drive failure.

Therefore, a method using the press 400 shown in FIG. 4 was adopted. In this method, a heater is incorporated into the press, or the press cooperates with the heater to heat the shield. Preferably, a closed loop heating system is incorporated into the press to preheat the shield 330. For the shaft 300, stainless steel is generally used, whereas aluminum is selected for the material of the shield. I chose this material because
Due to the ease of heating and the expansion of the inner diameter 350 indicated at 350 in response to the heating. When the inner diameter is expanded to be greater than the outer diameter of the shaft while holding the shield in place, preferably by a vacuum against the underside of the press, the press lowers the shield 330 along the outer diameter of the shaft. The position of the shield relative to the shaft is established by having a fiducial, preferably a surface 410, defined on the area of the press that strikes the upper surface 420 of the shaft 300.
After being properly placed in place, the shield 330 rapidly loses its heat due to the high conductivity of the aluminum, and the heat is carried away through the shaft. The shield shrinks and fits snugly against the outer surface of the shaft without producing burrs or other metal particles. After the shield has cooled sufficiently, the vacuum applied via source 420 is released and the press is pulled away in the direction of arrow 415, leaving the shield in place.

In summary, a closed-loop heating system that changes the shield material to preferably aluminum and heats the shield to the desired target temperature and achieves the expansion required to smoothly slide over the outer surface of the shaft is provided. Changing the assembly press to include expands the inner diameter of the shield, thereby eliminating the interference between parts during the assembly process. As a result, the generation of particles due to prying is eliminated, and finally an interference fit is achieved.

It is further noted that other features of the present invention further provide or define a particle capture area 332 on shield support strip 328. As the hub 302 rotates about the shaft at high speed, particles trapped between the shield 330 and the seal 318 tend to be in the gap 360. Due to the centrifugal force created by the high speed rotation of the seal, which rotates with the hub and shaft, loose particles are blown outwardly toward the trapping region 332 and are retained in this depression. As such, particles cannot escape from the gap between the shield 330 and the protruding edge 362 of the seal support component 316.

[0020] Other features and advantages of the invention will be apparent to those skilled in the art upon reviewing the present disclosure. Therefore, the scope of the present invention is limited only by the claims.

[Brief description of the drawings]

FIG. 1 is a plan view of a disk drive in which a spindle motor incorporating a ferrofluid seal and shield according to one embodiment of the present invention is particularly useful.

FIG. 2 is a cross-sectional side view of one embodiment of a spindle motor incorporating a ferrofluid seal supported in the prior art.

FIG. 3 is a partial cross-sectional view of the spindle motor of FIG. 2 modified to show the seal support and shield of the present invention.

FIG. 4 is a schematic partial cross-sectional view of the motor of FIG. 3, showing the press shield and shaft used to position the shield.

──────────────────────────────────────────────────続 き Continued on the front page F term (reference)

Claims (5)

[Claims] 1. A shaft having one or more ball bearings, wherein each of the ball bearings has an inner and outer race supported by the shaft and supports a hub rotating with respect to the shaft from the outer race. And a magnetic seal adjacent to the ball bearing and closer to one end of the shaft than the ball bearing; and a shield supported by an interference fit near one end of the shaft between the magnetic seal and one end of the shaft. A method of placing a shield around a shaft near a magnetic seal in a spindle motor, the method comprising: heating the shield so that the inner diameter of the shield is greater than the outer diameter of the shaft; holding the shield on a press Operating the press to position the shield at the outer diameter of the shaft; and Instead, holding the shield in place until an interference fit occurs between the inner diameter of the shield and the outer diameter of the shaft. 2. The method of claim 1, wherein the press includes a heating system that heats the shield such that the inner diameter of the shield is greater than the outer diameter of the shaft. 3. The method according to claim 2, wherein the shield is aluminum and the shaft is steel, so that the shield can be easily heated so that the inner diameter of the shield is larger than the outer diameter of the shaft. The described method. 4. The method of claim 3, wherein the shield is heated to about 400 degrees Fahrenheit (about 200 degrees Celsius). 5. The press of claim 4, wherein the press has a reference surface that abuts a reference on the shaft such that the shield is co-located consistently with one end of the shaft. The described method.