Disc drive anti-shock suspension cushions

Details Disc drive anti-shock suspension cushions Disc drive anti-shock suspension cushions

1999-11-17

2003-04-29

Miller, Brian E. (Department: 2652)

Dynamic magnetic information storage or retrieval

Head mounting

Disk record

Reexamination Certificate

active

06556383

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to disc drive storage devices. More particularly, the present invention relates to cushions placed on head suspensions of a disc drive to provide enhanced shock protection to the head by limiting vertical excursions and dampening motion of the suspension and the attached head.
BACKGROUND OF THE INVENTION
FIG. 1
illustrates a typical computer disc drive
20
that includes one or more discs
22
mounted on a hub
24
for rotation about a spindle axis
25
(FIG.
2
). The discs
22
are typically coated with a magnetic medium for storage of digital information in a plurality of circular, concentric data tracks. A spindle motor rotates the hub
24
and the attached discs
22
about the axis
25
to allow a head or “slider”
26
carrying electromagnetic transducers to pass over each disc surface and read information from or write information to the data tracks.
The slider
26
is typically formed from a ceramic block having a specially etched air bearing surface that forms an air “bearing” as the disc rotates beneath the slider. The hydrodynamic lifting force provided by the air bearing surface causes the slider
26
to lift off and “fly” a very small distance above the surface of the disc
22
as the disc spins up to its operating speed. Although the fly height of the slider
26
is only a fraction of a micron, this thin film of air between the slider
26
and the disc
22
prevents damage to the fragile magnetic coating on the surface of the disc.
The slider
26
is preferably moved between data tracks across the surface of the disc
22
by an actuator mechanism
28
such as a rotary voice coil motor. The actuator
28
includes arms
30
(
FIGS. 1 and 2
) attached to each of the sliders
26
by flexible suspensions
32
. Each suspension
32
essentially comprises a flat sheet metal spring that exerts a controlled preload force on the slider
26
in the vertical direction (i.e., against the surface of the disc
22
as shown in FIG.
2
). The preload force supplied by the suspension
32
effectively counters the hydrodynamic force generated by the slider
26
and prevents the slider from flying too far off the surface of the disc
22
. Although relatively flexible in the vertical direction, the suspension
32
is relatively stiff in the lateral direction in order to provide for precise lateral positioning of the slider
26
over the closely spaced data tracks.
The suspension
32
typically includes a relatively stiff load beam
34
(
FIG. 3
) and a relatively flexible gimbal
36
for attaching the slider
26
. A first or proximal end
38
of the load beam
34
is attached to the arm
30
(
FIG. 2
) of the rotary actuator
28
, and a relatively flexible region
40
(
FIG. 3
) of the load beam
34
adjacent the actuator arm
30
is typically bent downward toward the surface of the disc
22
to supply the aforementioned preload force. A second or distal end
42
of the load beam
34
opposite the actuator arm
30
is attached (such as by welding) to the more flexible gimbal
36
which, in turn, is fixed to the slider
26
. An end of the gimbal
36
includes a cutout region defining two parallel flexure beams
44
and a cross member
45
defining an attachment pad
46
. A tongue
48
of the load beam
34
typically protrudes within the cutout region of the gimbal
36
so that a dimple (not shown) on the bottom of the tongue
48
may contact a top surface of the slider
26
to transfer the preload force directly to the slider
26
. The attachment pad
46
of the gimbal
36
is secured to the top surface of the slider, such as by an adhesive, so that the flexure beams
44
provide a resilient connection between the slider
26
and the relatively stiff load beam
34
. The resilient connection provided by the gimbal
36
is important to allow the slider
26
to pitch and roll (i.e., “gimbal”) while following the topography of the rotating disc
22
. While
FIG. 3
illustrates the load beam
34
and gimbal
36
as separate components, it is understood that these components may be formed from a single piece of metal forming an integrated suspension
32
(not shown).
Although the preload supplied by the bend region
40
of the load beam
34
is effectively countered by the hydrodynamic force generated by the slider
26
during rotation of the disc
22
, that same preload force typically forces the slider
26
to rest on the surface of the disc
22
once the disc stops spinning and the hydrodynamic force dissipates (e.g., when the disc drive
20
is powered down). During these periods of inactivity, and particularly during assembly, shipping and handling of the disc drive
20
before the drive is assembled within a computer, the fragile magnetic coating on the surface of the disc
22
is susceptible to damage from accidental vertical displacement of the slider
26
, such as by a shock event.
Vertical displacement of the slider
26
may occur when a disc drive
20
is subjected to a shock of sufficient magnitude to cause the actuator arm
30
and the attached suspension
32
to move away from the disc surface (either on the initial shock or on a rebound from the initial shock). Although the bend region
40
in the load beam
34
and the resilient nature of the gimbal
36
tend to hold the slider
26
against the disc surface even as the actuator arm
30
moves away from the disc
22
, a sufficiently large shock (e.g., a shock 200 times the acceleration of gravity or 200 “Gs”) will typically overcome the preload force and cause the slider
26
to be pulled off the disc surface. The return impact of the slider
26
against the disc surface can cause severe damage to the thin magnetic coating on the surface of the disc. If the shock event occurs during operation of the disc drive, the damage to the disc coating may create an unusable portion or sector of the disc and a potential loss of data stored on that portion of the disc. However, most large shock events typically occur during periods of inactivity, as described above, when the slider
26
is positioned along an inner radial portion or “landing region” of the disc
22
not used for data storage. Regardless of whether the impact occurs in the data region or the landing region of the disc
22
, the impact typically generates debris particles that can migrate across the surface of the disc
22
and interfere with the air bearing surface of the slider
26
, thereby causing damage to more vital regions of the disc
22
during disc operation and possibly leading to a disc “crash.”
Previous efforts to minimize the above described “head slap” phenomenon have focused on either increasing the preload force applied by the bend region
40
or reducing the mass of the suspension
32
between the bend region
40
and the head or slider
26
. Due to the resiliency of the bend region
40
of the load beam
34
, it is primarily the mass of the end portion of the suspension
32
distal to the bend region
40
that determines the lifting force applied to the slider
26
during a shock event. That is, if the force tending to pull the head or slider
26
off the disc surface—as measured by the acceleration of the shock event (the number of Gs) multiplied by the combined mass of the slider
26
and the portion of the suspension
32
distal to the bend region
40
—is greater than the preload force applied by the load beam
34
, then the slider
26
will separate from the disc surface resulting in a “head slap” as described above. Therefore, a reduction in the mass of the suspension
32
distal to the bend region
40
leads to a reduction in the force applied to the slider
26
during a shock event and thus to improved shock performance for the disc drive
20
.
However, reducing the mass of the suspension
32
typically leads to further problems and design compromises. For example, the typical method for reducing the mass of the suspension
32
entails shortening the portion of the suspension between the bend region
40
and the slider
26
. However, shortening the suspension tends to increase the variation in t

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