Tape burnish with monitoring device

Details Tape burnish with monitoring device Tape burnish with monitoring device

1999-08-23

2001-09-18

Eley, Timothy V. (Department: 3723)

Abrading

Precision device or process - or with condition responsive...

With indicating

C451S307000

Reexamination Certificate

active

06290573

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to burnishing the surfaces of a disk with a burnishing tape. More particularly, the present invention relates to using a monitoring device to sense the quality and effectiveness of the burnishing process.
BACKGROUND
Magnetic memory disks, such as the type typically used in a computer hard drive, have a smooth surface over which the read/write head flies during operation. The trend has been to reduce the fly height of the read/write head over the surface of the disk to increase the data recording density on the disk. While it is desirable for a read/write head to fly as close as possible to the surface of the disk, it is important that the read/write head does not contact the disk or defects on the surface of the disk. A defect on the surface of the disk that physically contacts the read/write head may damage the read/write head, the disk, or both. Consequently, care must be taken during the disk processing and testing to assure that there are no defects on the surface of the disk that are greater than the fly height of the read/write head, which today is approximately 1 &mgr;″ (microinch).
Typical magnetic disks include an aluminum, glass, or silicon substrate that is plated with a NiP (nickel phosphate) layer and then textured, e.g., for the contact start stop zone. An underlayer of Cr (chromium) or NiP is sputtered on the plated NiP layer, a thin film of magnetic recording material, typically a Co (cobalt) alloy, is sputtered on the underlayer, followed by the deposition of a protective coating and a lubrication layer. The disk is then burnished to remove any asperities prior to testing the disk to assure the disk meets the required surface specifications. Presently, some magnetic disks are specified to have a roughness less than or equal to about 30 angstroms (3 nanometers).
A conventional method of burnishing the surfaces of a disk includes the use of an abrasive burnishing tape.
FIG. 1
shows a portion of a conventional burnishing apparatus
10
including burnishing tape
12
. The burnishing tape
12
is pressed against the surfaces of a disk
14
by pressure applying elements, such as pads
16
. Pads
16
are mounted on mounting blocks
18
that are controlled by the burnishing apparatus to move towards or away from the surfaces of the disk
14
, as indicated by arrows
19
. Disk
14
is mounted on a spindle
20
that rotates disk
14
as indicated by arrow
22
. Disk
14
and pads
16
move relative to each other, as indicated by arrow
24
so that a desired amount of the surfaces of disk
14
are burnished.
While pads
16
are shown in
FIG. 1
, it is understood by those of ordinary skill in the art that burnishing tape
12
may be pressed against the surfaces of the disk using other pressure applying elements, such as air knives, rollers, or other similar devices.
Once the surfaces of the disk are burnished, the disk is then tested, for example, with a glide head or certifying head. Conventionally, if there is a problem with the burnishing machine or the burnishing tape, the problem may not be recognized until after the burnishing process and the disk is tested. Meanwhile, additional disks may be burnished on the same burnishing machine and with the same burnishing tape.
SUMMARY
A monitoring device is used to monitor the performance of a burnishing apparatus in accordance with the present invention. The monitoring device includes at least one sensor that monitors the contact between the burnishing tape and the rotating disk.
In one embodiment the monitoring device includes at least one sensor that monitors the elastic waves produced by the contact between the rotating disk and the burnishing tape. The sensor may be an acoustic emission sensor, e.g., a piezo-electric transducer, that is coupled to the pressure applying element. The sensor receives the elastic waves propagating through the pressure applying element and converts the elastic waves into an electric signal. In another embodiment the sensor may detect the elastic waves propagating through the disk. For example, a vibrometer may be used to detect the vibrations in the disk and in response produce an electric signal. In another embodiment, an acoustic emission sensor mounted on the spindle upon which the disk is mounted detects the vibrations in the disk and converts the elastic waves into an electric signal.
Other embodiments include measuring the tension on the burnishing tape and measuring the frictional force between the rotating disk and the burnishing tape. The tension may be measured with a tension gauge coupled to a guide roll for the burnishing tape. The frictional force may be determined by analyzing the current used by the spindle motor to rotate the disk, which indicates the torque applied to the disk. The torque applied to the disk is proportional to the frictional force between the disk and the burnishing tape and the radius of the disk where the frictional force is applied.
The signals from the monitoring device sensor is converted into an amplitude signal in the time domain using a filter or into a signal in the frequency domain by performing a fast fourier transform. The amplitude signal may be used into indicate characteristics such as alignment of the pressure applying element and the type of burnishing tape being used. The signals in the frequency domain indicate, e.g., the lubrication condition of the disk.


REFERENCES:
patent: 4532802 (1985-08-01), Yeack-Scranton et al.
patent: 5012618 (1991-05-01), Price et al.
patent: 5099615 (1992-03-01), Ruble et al.
patent: 5313352 (1994-05-01), Chikazawa et al.
patent: 5423207 (1995-06-01), Flechsig et al.
patent: 5443415 (1995-08-01), Shebanow et al.
patent: 5791969 (1998-08-01), Lund
patent: 5820446 (1998-10-01), Lu

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