HK1026976B - Disk drive with flow-by chemical breather filter - Google Patents

Description

Disk drive with surface flow type chemical breather filter

The present invention relates generally to data recording disk drives and, more particularly, to a magnetic recording disk drive with a breather filter that prevents chemical contaminants and particulate matter from entering the drive.

A disk drive, also known as a disk file, is an information storage device. Such information storage devices employ a rotatable magnetic disk, a read/write head or transducer and an actuator. A rotatable magnetic disk has a plurality of concentric data tracks containing various information. The read/write head is used to read data from different tracks and/or write data to the tracks. The actuator is connected to the read/write head carriage which moves the head to the desired track during a read/write operation and maintains the position of the track. The read/write head may be a single element inductive read/write head or a dual element inductive write/magnetoresistive read head. Generally, a plurality of magnetic disks are mounted on a housing rotated by a disk drive or spindle motor, and a plurality of read/write head supports connected to an actuator for accessing the surfaces of the magnetic disks. A housing is defined by the walls and includes a base and a cover, supports the disk drive motor and the read/write head actuator, and encloses the read/write head and the disk to form a substantially sealed environment. The housing has a vent hole for adjusting the pressure differential between the interior of the disk drive and the surrounding atmosphere and for providing the required regulated air supply to the housing to replenish the leaked air. A particulate filter is provided adjacent the vent to prevent particulate matter from entering the disk drive.

The read/write head support in a conventional magnetic recording disk drive is an air bearing slider that rides on an air bearing above the surface of the disk as the disk rotates at its operating speed. The slider is held in position adjacent the disk surface by the biasing force of a suspension connecting the slider to the actuator. The disk surface has a liquid lubricant film for minimizing damage to the read/write head and the disk due to inadvertent contact between the slider and the disk during operation, and for facilitating actuation of the disk drive slider while stationary on the disk surface.

In contrast to conventional air bearing disk drives, contact or near contact disk drives have been proposed. Such disk drives maintain the read/write head supports in contact with the disk or a liquid film thereon, either constantly or occasionally during read and write operations. Examples of these types of disk drives are described in U.S. patent 5,202,803 by IBM and published European patent application EP367510, U.S. patent 5,097,368 assigned to Conner Peripherals, Inc., and U.S. patent 5,041,932 assigned to transmitter, Inc.

Magnetic recording disk drives are very sensitive to chemical contaminants. The high molecular weight organic vapor adsorbs onto the very smooth surfaces of the magnetic disk and the slider, causing the liquid lubricant to change its properties. Other chemical contaminants, such as S0, can also cause metallographic corrosion of the disk and the read/write head, particularly the magnetoresistive read element. Therefore, many disk drives employ a chemical filter near the vent hole in addition to the particulate filter.

In conventional disk drives having a filter disposed adjacent to the vent, the pressure gradient between the ambient atmosphere and the interior of the disk drive forces air to flow through the filter. This is desirable because it maximizes the contact of the chemical vapor with the chemical filter material. The vent is typically positioned at the lowest pressure in the disk drive to ensure that all air enters the disk drive through a vent filter attached to the vent. But the addition of chemical filter media increases the combined flow resistance through the chemical and particulate filters. This can result in contaminants entering the disk drive through other leakage points or orifices.

What is needed is a disk drive breather filter assembly that maximizes the removal of chemical contaminants with as low flow resistance as possible.

The present invention is a disk drive having an improved breather filter assembly that filters both chemical contaminants and particles. The filter assembly includes a housing having an internal passage and a recess to support and contain the chemical and particulate filter elements, the passage in the filter housing providing a flow path between the vent opening and the sheet of chemical filter material. The filter housing is also provided with a baffle in the recess adjacent the side of the chemical filter plate not exposed to air from the channels. This baffle prevents the inflow of air through the chemical filter and redirects the air flow across the surface of the chemical filter plate. After passing through the chemical filter plate, the air is redirected through a particulate filter and into the disk drive housing. In the present invention, air entering the disk drive housing is generally not forced into the interior of the chemical filter by forced flow, but rather flows along the surface of the substance, thereby enabling the chemical filter to not significantly reduce the pressure drop across the entire filter assembly as in prior art breather filter assemblies. The air flow across the surface of the material diffuses contaminants into the inhalant for capture by the inhalant.

For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.

FIG. 1 is a side view of a magnetic recording disk drive of the present invention, and a cross-sectional view of the disk drive housing.

FIG. 2 is a cross-sectional view of an attached breather filter assembly of a portion of a disk drive cover.

FIG. 3 is a view taken along line 3-3 of FIG. 2 showing air passages in the breather filter assembly housing.

Figure 4 is a graph illustrating the improved chemical contaminant capture of the breather filter assembly of the present invention.

Referring to FIG. 1, there is shown a schematic cross-sectional view of a disk drive of the present invention. The disk drive comprises a housing having a base 10 and a cover 11. A disk drive motor 12 and actuator 14 are secured to the base 10. The base 10 and cover 11 substantially enclose the disk drive. The hub 18 connects the magnetic recording disk 16 with the disk drive motor 12, and the magnetic recording disk 10 is attached to the hub 18 for rotation by the disk drive motor 12. The surface of the disc 16 holds a thin film 50 of relatively high viscosity lubricant. The lubricant may be a conventional perfluoropolyether (PFPE) disk lubricant with the read/write or transducer 42 formed on the trailing end of the air bearing slider 20. The transducer 42 may be an inductive read and write transducer or an inductive write transducer with a Magnetoresistive (MR) read transducer formed by thin film deposition methods well known in the art. The slider 20 is connected to the actuator 14 by means of a fixed arm 22 and a cantilever arm 24, the cantilever arm 24 providing a biasing force that urges the slider 20 against the surface of the recording disk 16. During operation of the disk drive, the disk drive motor 12 drives the disk 16 at a constant speed. Actuator 14, typically a linear or rotary Voice Coil Motor (VCM), typically drives slider 20 across the surface of disk 16 so that the read/write head can access different data tracks on disk 16.

A sealing gasket 13 is arranged between the base 10 and the cover 11. A small vent 64 is located in the cover 11 for regulating the pressure between the interior of the disk drive and the external environment. The filter assembly 60 is mounted within one of the body walls of the disc drive housing, i.e. within the cover 11 in figure 1, and is aligned with the vent 64. The air vent 64 and filter assembly 60 are located in a low pressure region of the disk drive so that air will pass through the filter assembly and not enter the disk drive through other openings or leak points around the sealing pad 13.

Fig. 2 shows a detail of the filter assembly 60. The assembly 60 includes a cylindrical filter housing 62 mounted on the inner surface of the disk drive cover 11. The housing 62 is preferably made of a plastic material such as polycarbonate. The inlet 80 of the housing 62 is aligned with the vent 64 in the cover 11. The filter housing 62 is seated in a circular retaining ring 61 formed in the lid 11 and secured to the lid 11 by means of a double-sided adhesive tape 65, the tape 65 having a hole aligned with the vent 64 and the housing inlet 80. Alternatively, the filter housing 62 may be seated in a recessed or raised detent boss in the lid 11, secured to the lid 11 by means of double-sided adhesive tape 65.

A first air permeable, open mesh, insulation layer 70, an adsorbent chemical filter sheet 72, a baffle 74, and a second air permeable, open mesh insulation layer 76 are disposed within the central recess 66 of the filter housing 62. Chemical filter plate 72 is made of a gas permeable media containing activated carbon (e.g., commercially available Kynol activated carbon cloth) that removes chemical contaminants, including organic gases. The apertured mesh barrier is a thin three-dimensional mesh made of an inert material, such as Delnet, which is commercially available. The baffle 74 may be made of any non-porous material, such as Mylar, which prevents the passage of gases. A particle filter 78 is located at the end of the housing 62 and covers the recess 66 to secure the internal components within the housing 62. The particle filter 78 is preferably made of a stretched polytetrafluoroethylene film such as the commercially available Tetratex (available from Donaldson-Tetratec corporation) or an electrostatically charged nonwoven fabric such as the commercially available Filtreet (available from 3M corporation) and Donaldson electric (available from Donaldson corporation).

As can be seen in fig. 2, the filter housing 62 has a passage for air to pass from the air vent 64 to the chemical filter plate 72. The channel includes an inlet 80 aligned with the vent 64, a channel 81 for limiting the diffusion of foreign contaminants into the filter, a vertical channel 82, and an outlet channel 83. An annular adhesive ring 85 covers the channel 83 except for an outlet end 87 (see fig. 3). The outlet end 87 is generally concentrated through the open mesh barrier 70 in a direction perpendicular to the chemical filter plate 72. A cross-sectional view of the filter housing 62 taken along line 3-3 of FIG. 2 is shown in FIG. 3, and the air passages can be more clearly seen. The inlet 80 (the portion of the channel 81 that is concealed) directs air through the tortuous diffusion path formed by the channel 81. The channel ends at a vertical channel 82 communicating with an outlet 83, the elements 82 and 83 creating additional resistance to the diffusion fluid. The channel 83 terminates at an outlet end 87.

The operation of the filter assembly 60 will now be described with reference to fig. 2 and 3, which have been described above. When the pressure within the disk drive housing immediately adjacent the breather filter is less than the ambient atmospheric pressure, a pressure gradient is created across the breather filter assembly and air is drawn into the breather holes 64 and into the inlet 80 of the filter housing 62. As indicated by the directional arrows in fig. 2, the air flows through the channels 81, down through the vertical channels 82, and through the exit channels 83 through the exit holes 87 of the adhesive ring 85. Air is discharged through outlet 87 in the direction of the arrows generally perpendicular to mesh barrier layer 70 and chemical filter sheet 72. Because baffle 74 is disposed adjacent to surface 71 of chemical filter plate 72, air cannot be redirected across and generally parallel to back surface 73 of filter plate 72 by chemical filter plate 72. Any air entering the interior of filter plate 72 is introduced by diffusion rather than by forced flow guidance. Air enters the annular gap of the recess 66 after passing over the entire surface 73 of the chemical filter plate 72, then returns to the entire mesh insulation 76, and then flows into the interior of the disk drive through the particle filter 78.

In the present invention, air entering the disk drive housing typically does not enter the interior of the chemical filter by forced flow, but rather flows along the surface of the chemical filter, and thus the chemical filter does not substantially increase the flow resistance of the filter assembly as in prior art breather filter assemblies. As the gas stream passes over the surface of the filter, the contaminants can diffuse into the adsorbent material and be captured by the adsorbent material.

Figure 4 illustrates the advantage of the present invention, which is a plot of the ratio of the concentration of contaminant at the "outlet" to the concentration of contaminant at the "inlet" during accelerated chemical testing of various filter assemblies. The horizontal "clipping" line in FIG. 4 is the maximum contaminant concentration that a particular disk drive design allows. Curve a of fig. 4 is the characteristic curve of a conventional "flow-through" filter in which air is forced through the chemical filter by means of a pressure gradient. Curve B of figure 4 is a "flow along" filter assembly of the present invention. Clearly, the filter assembly of the present invention has a much lower chemical concentration ratio at the "outlet" to the "inlet" throughout the test, and thus better chemical capture performance. In addition, the filter assembly of the present invention still has sufficient chemical filtration capacity below the limiting line for a duration of about 50% longer than conventional filtration devices. That is, the filter assembly of the present invention required 1 half hour to reach the limiting line during the accelerated test, while the conventional "flow through" filter assembly required 1 hour. In this accelerated test, 1 hour corresponds to a service life of about 2.5 to 5 years.

While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to the invention may occur. For example, the filter assembly may have a second chemical filter plate, with the baffle being positioned between the two chemical filter plates so that air passes across one surface of each plate. It is to be understood that such changes and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims (4)

1. A filter assembly, comprising:

a filter assembly housing having an inlet for receiving air to be filtered and an outlet for discharging filtered air into the housing;

a panel of chemical filter material supported in said housing for adsorbing chemical contaminants, the panel having a first surface exposed perpendicularly to the direction of flow of air to be filtered, a second surface opposite said first surface, and an outer edge;

a baffle supported in the housing and held in contact with the second surface of the sheet of chemical filter material for preventing air from passing through the sheet of chemical filter material,

whereby air is forced to circulate across the first surface of the sheet of chemical filter material; and a layer of particulate filter material supported by the housing and located adjacent the outlet of the housing for filtering particulate matter from the air after the air has passed across the first surface of the sheet of chemical filter material and past the outer edge of the sheet of chemical filter material,

wherein the housing inlet comprises a channel with an inlet aligned with the vent, and an outlet at an intermediate position oriented perpendicular to the first surface of the sheet of chemical filter material such that air is channeled perpendicular to the first surface of the sheet of chemical filter material and redirected by the baffle to flow parallel to and across the first surface of the sheet of chemical filter material.

2. The filter assembly of claim 1, further comprising a gas permeable barrier layer positioned between the housing inlet and the sheet of chemical filter material within the housing.

3. The filter assembly of claim 1, further comprising a gas permeable barrier layer positioned within said housing between said baffle and said layer of particulate filter material.

4. The filter assembly of claim 1, wherein a diffuser passage is formed in the passage of the housing inlet.