Piezoelectric vibration damping for disk drives

Details Piezoelectric vibration damping for disk drives Piezoelectric vibration damping for disk drives

1999-06-23

2001-10-30

Heinz, A. J. (Department: 2652)

Dynamic magnetic information storage or retrieval

Record transport with head stationary during transducing

Disk record

C360S264000, C360S244200

Reexamination Certificate

active

06310746

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to magnetic disk data storage systems, and more particularly to the use of piezoelectric materials to damp vibrations within the same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In
FIGS. 1A and 1B
, a magnetic disk data storage system of the prior art includes a sealed enclosure
12
, a spindle motor
14
, a magnetic medium or disk
16
, supported for rotation by a drive spindle Si of the spindle motor
14
, a voice-coil actuator
18
and an arm
20
attached to an actuator spindle S
2
of voice-coil actuator
18
. A read/write head support system consists of a suspension
22
coupled at one end to the arm
20
, and at its other end to a read/write head
24
.
The read/write head
24
typically includes an inductive write element with a sensor read element. As the motor
14
rotates the magnetic disk
16
, as indicated by the arrow R, an air bearing is formed under the read/write head
24
causing it to lift slightly off of the surface of the magnetic disk
16
, or, as it is termed in the art, to “fly” above the magnetic disk
16
.
Discrete units of magnetic data, known as “bits,” are typically arranged sequentially in multiple concentric rings, or “tracks,” on the surface of the magnetic medium. Data can be written to and/or read from essentially any portion of the magnetic disk
16
as the voice-coil actuator
18
causes the read/write head
24
to pivot in a short arc, as indicated by the arrows P, over the surface of the spinning magnetic disk
16
. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
Fundamentally, magnetic disk drives are electro-mechanical devices incorporating rapidly moving or spinning components. The different motions within a drive may induce various components to vibrate. Vibrations can be deleterious to the performance of a disk drive and may increase data retrieval times, reduce accuracy, reduce total storage capacity, and lead to possible catastrophic failure. Therefore, controlling and minimizing vibrations have become critical to the magnetic disk drive industry.
FIG. 2
is a perspective view of a Voice-Coil Motor (VCM)
30
and Head Stack Assembly (HSA)
40
showing commonly used viscoelastic dampers according to the prior art. The VCM consists, in part, of two substantially parallel magnetic plates
32
and
32
′. A prior art viscoelastic VCM damper
34
is usually attached to the exterior surface of magnetic plate
32
.
The Head Stack Assembly
40
consists, in part, of an actuator arm,
20
, a suspension
22
, and a read/write head
24
. A prior art viscoelastic actuator arm damper
44
is normally attached to the actuator arm
20
, and a prior art viscoelastic suspension damper
46
is attached to the suspension
22
. Together, the VCM
30
and the HSA
40
control the positioning of the read/write head
24
relative to the magnetic storage medium. The disk drive control logic directs the movement of the read/write head
24
through a preamplifier
38
and a flexible cable
42
. A prior art viscoelastic flexible cable damper
48
is attached to the flexible cable
42
.
One of the key areas for vibration control in a disk drive
10
is the suspension
22
that holds the read/write head
24
out over the surface of the rapidly spinning magnetic disk
16
. One possible vibrational mode for the suspension
22
is a bending mode in which the suspension
22
flexes up and down bringing the read/write head
24
alternately closer and further away from the magnetic disk
16
. Such a vibration is undesirable for at least three reasons. Firstly, as the read/write head
24
moves further away from the surface of the magnetic disk
16
, its ability to read the magnetic information on the magnetic disk
16
diminishes rapidly. Secondly, as the read/write head
24
moves closer to the magnetic disk
16
the likelihood of the read/write head
24
inadvertently touching the surface of the magnetic disk
16
increases. Contact between the read/write head
24
and the magnetic disk
16
can create wear debris, and in some instances even lead to a catastrophic failure of the device frequently referred to as “head crash.” As designers build drives with ever lower “fly heights,” preventing unwanted contact between the read/write head
24
and the magnetic disk
16
becomes increasingly difficult and controlling vibrations becomes increasingly important. Thirdly, vibration of the suspension
22
causes modulation in the signal being read from or written to the magnetic disk
16
by the read/write head
24
.
Other vibrational modes of the suspension
22
can include torsional modes and side-to-side bending, sometimes referred to as sway. These vibrational modes can also create modulations in the signal being read from or written to the magnetic disk
16
. Side-to-side bending of the suspension
22
while writing to the magnetic disk
16
may also cause broadening of the trackwidth. Broadening the trackwidth may cause adjacent tracks to overlap, resulting in a loss of data. However, allowing extra space between tracks decreases the number of tracks that can be written on the surface of the magnetic disk
16
and therefore reduces its total storage capacity. Therefore, reducing vibrations could allow tracks to be placed closer together, leading to higher storage capacities.
Another problem associated with vibrations of the suspension
22
is the time it takes for the read/write head
24
to stabilize its position over a particular track after being moved between tracks, sometimes referred to as settling time. Delays in stabilization over a desired track may increase the delay before data can be accessed or written. In other words, damping the vibrations of suspension
22
will improve its dynamic characteristics, thereby enhancing disk drive overall access time.
Vibrations in other components connected to the suspension
22
also may contribute to unwanted vibrations in the suspension
22
. Therefore, it may be desirable to damp the vibrations of components such an actuator arm
20
, a Voice-Coil Motor (VCM)
30
, and a flexible cable
42
. Damping the vibrations of components, generally may be desirable for several additional reasons. Vibrations in a mechanical device may reduce the device's overall longevity by loosening connectors, seals, and filters, and creating excessive wear in moving parts. Vibrations can also lead to frayed wires, metal fatigue, and particle generation.
Vibration control in disk drives has commonly been achieved through the use of passive damping. In the prior art, passive damping has been accomplished by attaching constraining viscoelastic materials to components that are known to vibrate. Viscoelastic materials damp vibrations by creating passive resistance to bending and twisting motions. There are drawbacks, however, to the use of viscoelastic vibration dampers. One problem is that viscoelastic materials are frequently polymeric and tend to degrade as they age, loosing their damping effectiveness while outgassing and shedding particles. Outgassing and particle contamination may pollute the surface of the magnetic disk
16
and lead to problems such as “head crash” or the inability of the read/write head
24
to lift off of the surface of the magnetic disk
16
and “fly.” Additionally, viscoelastic materials typically loose damping efficiency with increasing temperature. Since the temperature within the disk drive
10
typically increases as it operates, vibrations of components within the disk drive
10
may worsen as the drive is used.
Accordingly, what is desired is a damping system for more efficiently reducing vibrations of components of data storage and retrieval systems. Also, a damping system is desired that can maintain its damping efficiency over a longer period of time, and over a greater range of temperatures, with less particle generation and outgassing than may be found in the prior art. A damping system is further desired that

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