Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism
Reexamination Certificate
2001-05-01
2004-02-17
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
C360S075000
Reexamination Certificate
active
06693757
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an apparatus for adjusting balance, a method for adjusting balance, and a method for assembling a disk, which are used to achieve the rotating balance of a disk in a hard disk drive or the like.
2. Description of the Related Art
A disk drive, such as a hard disk drive, has a circular plate-like disk for recording data. The disk is held on a spindle and driven to rotate by a spindle motor. A read/write head accesses an area on the disk surface to read the recorded data and write data onto the disk. In such a disk drive, if the disk is eccentric with respect to the spindle, deflection of rotation is caused when the disk rotates, and as a result, an access error or the like due to the read/write head may occur to reduce the accuracy of reading and writing data. Such eccentricity is caused by displacement of the disk in the radial direction thereof with respect to the center of rotation of the spindle in the range of the clearance formed between the inner peripheral surface of the disk's center hole and the outer periphery of the spindle.
The rotating balance of a disk is classified into two types, static balance and dynamic balance. The static balance is a balance against the vibration component comprising a translational force caused in the disk rotation, and it is influenced by the radial eccentricity of the disk with respect to the center of rotation. The dynamic balance is a balance against the vibration component by the torque (torsional moment) caused when an object rotates, and it is influenced not only by the radial eccentricity of the disk with respect to the center of rotation, but also by displacement of the center of gravity of the disk in the axial direction of the spindle.
If the spindle is provided with only one disk, the thickness of the disk (size in the axial direction of the spindle) is small as compared with the disk diameter, and thus the influence of the dynamic balance is negligibly small as compared with the influence of the static balance. Even if the spindle is provided with a plurality of disks, the influence of the dynamic balance can also be ignored, provided that the setting range of the disks provided on the spindle (setting distance between the disk at one end and the disk at the other end) is short and the spindle is also short. However, as the number of disks provided on the spindle becomes large and the setting range of the disks provided on the spindle becomes large, the effect of the dynamic balance becomes so large that it cannot be ignored. In particular, as the storage capacity demanded in the hard disk drive or the like has recently been larger and larger, the number of disks provided on the spindle tends to increase. Further, since the number of revolutions of the disk also tends to increase to accelerate the access speed, it is needed to accurately adjust dynamic balance as well as static balance.
There has been a technique for adjusting static balance and dynamic balance by attaching a weight to a system comprised of disks and a spindle. For instance, to provide dynamic balance, as shown in
FIG. 6
, the balance of a spindle
2
provided with a predetermined number of disks
1
is measured, and a weight
3
is attached to both ends of the spindle
2
as needed. However, in this approach, the attaching of the weight
3
is time-consuming, and the balance must be adjusted before the disks
1
and the spindle
2
can be assembled on a base
4
. Thus, limitations are imposed on the manufacturing process, and it is not an efficient approach.
The present invention is based on such a technical problem, and its object is to provide an apparatus for adjusting balance, a method for adjusting balance, and a method for assembling a disk, which can adjust dynamic balance reliably and efficiently.
In connection with the foregoing, as a technique for enabling the modification of balance with the disk and the spindle being assembled on the base, the applicant has already proposed the technique disclosed in Japanese Published Unexamined Patent Application No. 9-161394.
In this technique, the spindle is inserted into the center hole of the disk, and after temporarily fixing the disk to the spindle, an acceleration is provided to the spindle in the radial direction of the disk. Then, the disk stands still because of the inertial force by its own weight, and only the spindle skids in the radial direction thereof, by which the eccentricity of the disk is adjusted. And, after the rotating balance of the disk falls within a predetermined accuracy, the disk is permanently fixed to the spindle. By this, static balance can be provided efficiently and reliably.
Further, to adjust dynamic balance with this technique, as shown in
FIG. 7
, with an arrangement in which a spindle
2
having a predetermined number of disks
1
is set on a base
4
, acceleration is given to the base
4
in the radial direction of the disks
1
by actuators
5
A and
5
B. In this case, the base
4
supports one end (lower end) of the spindle
2
at its bottom
4
a
. And, to the side wall
4
b
of the base
4
which is provided so as to surround the outer periphery of the predetermined number of disks
1
, acceleration is provided at both the lower and upper ends thereof by the actuators
5
A and
5
B, thereby to provide acceleration to the two ends of the spindle
2
, respectively. Allowing for the overall unbalance of the predetermined number of disks
1
provided on the spindle
2
, dynamic balance is adjusted by making the accelerations acting on one end and the other end of the spindle
2
differ from each other.
For instance, to adjust the position of the disks
1
with respect to the center of rotation thereof only on the top end
2
a
side of the spindle
2
, a force is applied to the base
4
only by the actuator
5
A.
FIG. 8A
shows a dynamical model for this. If, in this model, it is assumed that the distance from the center of gravity G of a system comprising the disks
1
, spindle
2
, and base
4
to the upper end of the spindle
2
is h, and a force F is applied by the actuator
5
A at a position at a distance L from a line passing through the center of gravity G and perpendicular to the axis of the spindle
2
, then a distributed acceleration a(x) is observed on the axis of the spindle
2
. This acceleration a(x) is obtained as follows. The overall translational acceleration a
G
is expressed by:
a
G
=F/M
The rotating angular acceleration (around the center of gravity is G) is expressed by the following equation, where M is the overall mass, and I is the rotation moment with respect to the center of gravity G:
a−LF/I
Thus, the composite acceleration a(x) is expressed by the following equation, whose distribution is as shown in FIG.
8
B:
a
(
x
)=
a
G
+ax=F
(1/
M+Lx/I
)
As obvious from this figure, if only the upper actuator
5
A is operated, a large acceleration is applied to the disk
1
on the upper end side of the spindle
2
, and the disk
1
on the upper end side can be selectively skidded. Further, if the distance L is selected so as to fulfill the following expression, it is possible to zero the acceleration provided to the disk
1
on the lower end side of the spindle
2
, as shown in FIG.
8
C:
(1/
M−Lx/I
)=0
However, the careful examination of the above technique by the present inventors shows that the effect as desired cannot be obtained as a matter of fact. The reasons for that are as follows.
1) Since the system comprising the base
4
and the spindle
2
has a very high rigidity, the acceleration provided by the actuator
5
A to the upper portion of the spindle
2
is also applied to the lower portion of the spindle
2
.
2) If acceleration is provided on a jig
6
only by the upper actuator
5
A, it is also applied to the lower end of the side wall
4
b
of the base
4
by a plate
7
provided between the actuators
5
A and
5
B and the side wall
4
b
of the base
4
.
3) As shown in
FIG. 8D
, since the base
4
is set
Hayakawa Tatsuo
Hirano Toshiki
Tamura Hitoshi
Bracewell & Patterson L.L.P.
Hitachi Global Storage Technologies - Netherlands B.V.
Hudspeth David
Martin Robert B.
Slavitt Mitchell
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