Dynamic information storage or retrieval – Dynamic mechanism subsystem – Specific detail of storage medium support or motion production
Reexamination Certificate
1998-06-23
2001-03-20
Ometz, David L. (Department: 2754)
Dynamic information storage or retrieval
Dynamic mechanism subsystem
Specific detail of storage medium support or motion production
C360S099080
Reexamination Certificate
active
06205110
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a disk drive motor for driving recording disks and, more particularly, to a disk drive motor which is required to operate at high speed with high stability.
2. Description of the Related Art
Various types of recording disks have been proposed and used for the purpose of recording and reproduction of data, such as compact disks (CD), floppy disks (FD), magneto-optical disks (MO), mini-disks (MD), digital video disks (DVD), hard disks (HD), and so forth. Different types of recording disks employ different recording/reproduction methods and have different specifications in regard to the size or capacity of stored data, disk driving speed, recording density, and so on, as well as disk materials and prices. Consequently, drive motors of different specifications are used for driving different types of recording disks.
Nowadays, there is a trend towards a higher degree of sophistication and a greater size of electronic data, as image data are handled more than text data. This has given rise to the demand for inexpensive recording disks and disk drives which are capable of performing quick storage and reproduction of large volumes of information.
For instance, CDs were initially used as music recording/playback media but are nowadays applied for spreading use as CD-ROMs which are major storage disks for computers, by virtue of their advantages over other types of media. This type of storage media offers greater storage capacity and shorter operation time, i.e., reduced seek time, permitting much higher speed of rotation by means of high-speed disk drive motors, thus affording disk rotation speeds 20 times as high as that of music CDs.
FIG. 1
shows the construction of a conventional disk drive motor.
The conventional disk drive motor shown in
FIG. 1
has a substantially cylindrical sleeve
3
which at its lower end fits in an opening
2
formed on a base member
1
as a part of a chassis of a disk drive device. The lower opening of the sleeve
3
is closed by a tabular member
4
which carries a thrust bearing member
5
. A sleeve bearing
6
made of an oil-impregnated metal or a wear-resistant resin is received in the sleeve
3
.
A stator
8
includes a stator core
8
a
which is secured to the outer surface of the sleeve
3
and stator coils
8
b
wound therearound. A shaft
9
is rotatably supported by the sleeve bearing
6
such that it is in contact at its lower end, with the thrust bearing member
5
while its upper end projects beyond the upper end of the sleeve
3
. A rotor hub
10
made of non-magnetic material such as aluminum is fixed to the upper end of the shaft
9
. A yoke
11
made of magnetic material such as iron is fixed to the rotor hub
10
.
The yoke
11
has a disk-shaped base portion and a cylindrical skirt portion which is integrally formed with the base portion and extends downward from the radially outer end of the base portion. The sleeve
3
is received in a central opening formed at the center of the base portion of the yoke
11
. The inner peripheral edge of the base portion defining the central opening is fixed to a lower end portion of the rotor hub
10
. An annular rotor magnet
12
is fixed to the inner peripheral surface of the cylindrical skirt portion of the yoke
11
, so as to radially face the stator
8
.
A turntable
14
which is secured to the outer peripheral surface of the rotor hub
10
carries a recording disk D, through an intermediary buffer member
15
. A clamp magnet
16
is provided in a recess formed on the top of the rotor hub
10
, such that the upper surface of the clamp magnet
16
is flush with the top surface of the rotor hub
10
. The clamp magnet
16
magnetically attracts a disk pressing means (not shown) on the disk drive unit, thereby fixing the recording disk D.
In operation, electrical current supplied to the coils
8
b
of the stator
8
serves to generate magnetic force which acts between the stator
8
and the rotor magnet
12
so as to induce a torque for rotation. As a consequence, the rotor magnet
12
, the yoke
11
, the rotor hub
10
and the shaft
9
rotate as a unit, relative to the stator
8
which is stationary, whereby the turntable
14
and, hence, the recording disk D thereon rotate in a predetermined direction.
When such a conventional motor is driven at high speed, there occurs a problem which is not serious when the conventional motor is driven at low speed. Namely, high speed driving of the motor makes is difficult to control and regulate motor performance such as run-out of the rotary part, vibration and noise of the motor. In particular, when the run-out of the rotary part increases, storage and reproduction of data become less reliable.
Run-out, vibration and noise are considered to be attributable to slight local dimensional errors which produce only negligibly small effect in low speed driving but shows serious effect on high speed driving as described above, resulting in imbalance of motor parts under rotation.
It is true that rotational performance of the conventional motor structure shown in
FIG. 1
can be improved to some extent when, for example, the shaft
9
and the sleeve bearing
6
are machined, finished and mounted with higher degree of precision. This solution, however, is still unsatisfactory from the viewpoint of production costs.
Rotational performance is also affected by any dimensional error of the recording disk, particularly when the rotation speed is high. When production costs of disks are considered, however, it is difficult and impractical to achieve a higher dimensional precision of recording disks.
It is materially impossible to completely eliminate any dimensional error and mass imbalance of the rotary system including the motor and the disk. Under this circumstance, a demand exists for a measure which improves the rotational performance while allowing dimensional error and mass imbalance to some extent.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a disk drive motor of which impairment of rotational performance, in particular run-out of the rotary part of the motor, is suppressed at high speed operation of the motor.
Another object of the present invention is to provide a disk drive motor that offers high rotational performance while accommodating dimensional errors of the motor and disk.
It is still another object of the present invention to provide a disk drive motor which can be fabricated at reduced costs but yet is capable of operating with high rotational performance.
To attain those objects, a disk drive motor according to the present invention comprises a rotor having an annular space formed therein coaxially with the axis of rotation, and balancing members accommodated in the annular space and capable of changing its mass distribution circumferentially along the circle of the annular space.
When the motor speed is low, the balancing members assume random positions within the annular space. As the motor is driven at speed beyond a predetermined value, the balancing members distribute at equal spaces along the radially outer circumferential surface of the annular space, due to effect of centrifugal force. In case of any imbalance occurring during the rotation, the balancing members temporarily gather to a portion of the annular space where the mass imbalance is taking place. However, when the motor speed exceeds the value at which resonance takes place due to coincidence between the frequency of the vibration of the balancing members and the natural frequency of the motor, the balancing members move to a position symmetrical with the point of mass imbalance to eliminate the mass imbalance, thereby suppressing the run-out.
The drive motor may have means for urging the balancing members radially inward so as to prevent the random movement of the balancing members during low-speed operation of the motor. Such urging means effectively urges the balancing members towards the radially inner end of the annular space, thereby reducing vibra
Chuta Masanobu
Miyamoto Eiji
Osawa Harushige
Castro Angel
McCormick Paulding & Huber LLP
Nidec Corporation
Ometz David L.
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