Disk device

Details Disk device Disk device

2002-09-03

2004-12-21

Cao, Allen (Department: 2652)

Dynamic optical information storage or retrieval

Dynamic mechanism optical subsystem

Optical storage medium support

C369S263100

Reexamination Certificate

active

06834393

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a disk drive for use to write and/or read information on/from a disk storage medium (which will be herein simply referred to as a “disk”), and more particularly relates to a disk drive that generates a minimized degree of vibration even when a disk is rotated at a high velocity.
BACKGROUND ART
In recent years, to increase the data transfer rates of various types of disk drives such as a CD-ROM drive, it has become more and more necessary to further increase the rotational velocity of the disk. However, the disk normally has unbalanced mass due to a variation in its thickness, for example, and has a center of mass at a position that has shifted from its real center (i.e., has an eccentric center of mass). When such a disk is rotated at a high velocity, an unbalanced centrifugal force (unbalanced force) is applied onto the center of rotation of the disk, thus generating some vibration in the disk drive. The magnitude of this unbalanced force increases proportionally to the square of the rotational frequency. Accordingly, as the rotational frequency of the disk is increased, the amplitude of the vibration increases steeply. That is to say, when the disk is rotated at a high velocity, the disk drive vibrates significantly, and cannot perform its write or read operation with good stability. Furthermore, the vibration generated is also transmitted to external units outside of the disk drive. Thus, when such a disk drive is built in a computer, for example, other peripheral units are affected as well by the vibration that has been transmitted thereto. In view of these considerations, to increase the data transfer rate by increasing the rotational velocity of the disk, the vibration of the disk drive needs to be minimized.
To overcome the problems described above, according to a known technique, the vibration of a disk drive is minimized by getting the mass eccentricity of a disk corrected automatically by an auto-balancer, which includes balancing members such as balls. This technique is disclosed in Japanese Patent Publication No. 2824250, for example. Hereinafter, the configuration and operation of a conventional disk drive including the auto-balancer will be described with reference to
FIGS. 18 and 19
.
FIG. 18
is a cross-sectional view illustrating a configuration for the conventional disk drive. This disk drive includes a spindle motor
2
with a turntable
18
, and an auto-balancer
16
. A disk
1
is sandwiched between the turntable
18
and the auto-balancer
16
. By driving the spindle motor
2
, the disk
1
rotates along with the turntable
18
around a rotation axis P
0
.
As shown in
FIG. 19
, the auto-balancer
16
includes a hollow ring portion
23
that is concentric with the rotation axis P
0
. Inside the hollow ring portion
23
, multiple balancing members
17
are stored. The balancing members
17
may be a number of iron balls, for example, and can move inside the hollow ring portion
23
.
Referring back to
FIG. 18
, the spindle motor
2
is secured to a sub-base
6
, which in turn is fixed to a main base
8
by way of insulators (first elastic members)
7
that serve as elastic members. The vibration and impact that are externally applied to the sub-base
6
by way of the main base
8
are dammed by the insulators
7
.
The vibration system that is made up of the main base
8
, sub-base
6
and insulators
7
has a natural frequency (i.e., resonance frequency) at which vibration is transmitted from the main base
8
to the sub-base
6
at the maximum transmissibility. In this disk drive, the natural frequency f
1
in a mode in which the sub-base
6
vibrates parallelly to the recording surface of the disk
1
is defined to be lower than the rotational frequency fm of the disk
1
by selecting an appropriate material for the insulators
7
or by any other suitable technique. For example, when the rotational frequency fm is 100 Hz, the natural frequency f
1
may be set to 60 Hz.
Hereinafter, it will be described how the conventional disk drive having such a configuration operates to rotate a disk having an eccentric center of mass. As shown in
FIG. 19
, the center of mass G
1
of the disk
1
is located at a position that has shifted from the rotation axis P
0
. Accordingly, when the disk
1
is rotated, a centrifugal force F is generated and oriented from the rotation axis P
0
toward the center of mass G
1
. The specific direction in which this centrifugal force F is applied changes as the disk rotates. It should be noted that this centrifugal force F is generated due to the unbalanced mass of the disk
1
and will be herein sometimes referred to as an “unbalanced force”. When such an unbalanced force F is applied, the disk
1
and the sub-base
6
make a whirling motion with respect to the main base
8
.
In this case, the whirling motion changes in accordance with the relationship between the rotational frequency fm of the disk
1
and the natural frequency f
1
. Specifically, if the rotational frequency fm of the disk
1
is sufficiently lower than the natural frequency f
1
, then no phase delay is created and the direction in which the unbalanced force F is applied (from the rotation axis P
0
toward the center of mass G
1
) is the same as the direction in which the sub-base
6
is displaced (see FIG.
20
(
a
)). On the other hand, if the rotational frequency fm is sufficiently higher than the natural frequency f
1
as described above, then a phase delay is created. Accordingly, the direction in which the unbalanced force F is applied becomes substantially opposite to the direction in which the sub-base
6
is displaced (see FIG.
20
(
b
)). In this case, the whirling center axis P
1
is located between the center of mass G
1
of the disk and the rotation axis P
0
.
Hereinafter, it will be described how the auto-balancer
16
operates when the whirling center axis P
1
is located between the center of mass G
1
of the disk and the rotation axis P
0
. While the whirling motion is being made, a centrifugal force q is applied from the whirling center axis P
1
toward the balancing members
17
that are stored inside the hollow ring portion
23
. On the other hand, a drag force N is also applied from the outer sidewall
25
of the hollow ring portion
23
toward the balancing members
17
. This drag force N is applied toward the rotation axis (i.e., the center of rotation) P
0
that is also the center of the auto-balancer
16
and the center of the outer sidewall
25
. Consequently, a moving force R is applied as a resultant force of the centrifugal force q and the drag force N to the balancing members
17
in a tangential direction of the hollow ring portion
23
. This moving force R moves the balancing members
17
along the outer sidewall
25
. As a result, the balancing members
17
gather toward a position that is substantially opposite to the center of mass G
1
of the disk
1
with the whirling center axis P
1
interposed between them. That is to say, while the disk
1
is being rotated, the auto-balancer
16
operates in such a manner as to have its center of mass located on an extension of the line that connects together the center of mass G
1
of the disk
1
and the whirling center axis P
1
. Thus, a centrifugal force Q is applied to the auto-balancer
16
in the direction opposite to the direction in which the unbalanced force F is applied. That is to say, the unbalanced force F is canceled by this centrifugal force Q, thus decreasing the magnitude of the force being applied to the sub-base
6
. Consequently, the vibration of the sub-base
6
can be reduced.
In this disk drive, however, if the unbalanced force F being canceled decreases, then the moving force R applied to the balancing members
17
also decreases. In such a situation, the balancing members sometimes cannot reach their ideal positions because the balancing members receive a frictional resistance from the hollow ring portion
23
, for example. Then, the desired vibration damping effects are not achievable and a residual vibration is ge

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