Electrical generator or motor structure – Dynamoelectric – Reciprocating
Reexamination Certificate
1999-11-23
2001-05-01
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Reciprocating
C310S012060, C310S013000, C360S100100
Reexamination Certificate
active
06225712
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a voice coil motor used in positioning a magnetic head of a magnetic disk device.
BACKGROUND OF THE INVENTION
In a magnetic disk device, a voice coil motor has been conventionally used to position a magnetic head at a predetermined track. Recently, with the progress of a small and high-performance computer, there has been an increasing demand for a smaller magnetic disk device of a larger capacity and higher access. To satisfy the demand, the technology of high density track, and high-speed and high precision positioning is required, and requirements of the voice coil motor have become higher.
FIG. 25
shows a conventional voice coil motor.
The conventional voice coil motor includes a pair of yokes
1
arranged opposite to each other, a permanent magnet
2
fixed to at least one of the yokes
1
, a fan-shaped movable coil
3
formed in a magnetic space defined between the yoke
1
and the permanent magnet
2
and being rotatable around a bearing
5
, and a head carriage
4
coupled to the movable coil
3
.
When a predetermined driving current flows through the fan-shaped movable coil
3
, driving force is generated in the movable coil
3
according to the Fleming's left-hand rule, and the movable coil
3
rotates along an arrow A around the bearing
5
, thereby rotating the head carriage
4
around the bearing
5
along an arrow B. As a result, a magnetic head
6
provided at the end of the head carriage
4
is moved opposite the rotation of the movable coil, thus being positioned.
However, the conventional voice coil motor has the problem that the positioning precision is lowered by the vibration of the head carriage
4
when the magnetic head is positioned by high-speed drive, thereby interfering with the high-density recording process on the magnetic disk device.
This problem will be described below in detail by referring to FIG.
26
.
When an electric current flows through the fan-shaped movable coil
3
, the driving force F is generated in the radial sections of the movable coil
3
by the magnetic field of the magnetic circuit formed by the permanent magnet
2
and the yoke
1
. The resultant force generates a torque T around the bearing
5
, and the electric current of the movable coil
3
can be controlled, thereby positioning the magnetic head
6
.
At this time, a radial load of about 2F is applied to the bearing
5
with the torque T. When the flow of the current becomes opposite quickly in the movable coil
3
for high-speed drive, the direction of the radial load applied to the bearing
5
changes correspondingly, and therefore, the head carriage
4
vibrates along the arrow D.
Since the direction of the radial load applied to the bearing
5
is almost parallel to the direction C of the movement when the magnetic head
6
is positioned, the vibration of the head carriage
4
generated by the radial load deteriorates the positioning precision of the magnetic head
6
. This lowers the tracking precision in a shorter track, thereby interfering with the improvement in recording density.
In a magnetic disk device, it is necessary to quickly position the magnetic head
6
with high precision. However, when the conventional voice coil motor is used, the vibration of the head carriage
4
lowers the positioning precision when the magnetic head
6
is positioned in high-speed drive. This interferes with a higher-density record on the magnetic disk device.
This phenomenon will be described below in detail by referring to FIG.
25
. When an electric current flows through the movable coil
3
, the magnetic field of the magnetic circuit formed by the permanent magnet
2
and the yoke
1
generates the driving force F in the radial sections of the movable coil
3
. The resultant force generates the torque T around the bearing
5
, and the electric current in the movable coil
3
is appropriately controlled, thereby positioning the magnetic head
6
. At this time, the radial load of about 2F is applied to the bearing
5
with the torque T. When the direction of the flow of the electric current through the movable coil
3
is quickly switched for high-speed drive, the direction of the radial load applied to the bearing
5
changes correspondingly. As a result, the head carriage
4
vibrates along the arrow D. Since the direction of the radial load 2F applied to the bearing
5
is almost parallel to the movement direction C when the magnetic head
6
is positioned, the vibration of the head carriage
4
generated by the radial load 2F lowers the positioning precision of the magnetic head
6
.
The present invention has been developed to solve the above-described problems, and aims at providing a swing-type voice coil motor capable of quickly positioning a rotating member with high precision without applying a radial load to a unit such as a bearing supporting a freely rotating member or the like when moving a rotating member such as a head carriage supporting a magnetic head or the like.
SUMMARY OF THE INVENTION
To attain the above-described object, the voice coil motor according to the present invention has a configuration in which there are a plurality of coils whose radial sections extend at angles different in direction, and the resultant force generated in the coils is only a couple along the rotation without generating a radial load causing the vibration.
Furthermore, the plurality of coils are different in size, and the device can be small and thin with the thickness along the axis of the coil smaller by arranging a smaller coil in a larger hollow coil.
In addition, the voice coil motor according to the present invention has a configuration in which there are a plurality of coils whose radial sections extend in different directions, and includes a switch for selectively switching the combination of directions in which current flows, thereby allowing a quicker movement of a head carriage.
Furthermore, in the voice coil motor of the present invention, the plurality of layered coils are of a same shape, and the sides of coil layers from which leader line elements are led face the same direction.
According to the configuration, the layered coils are of a same shape, including the configuration of leader line elements. That is, since there is only one specification of the coil, the productivity can be improved and cost reduction can be achieved.
The voice coil motor according to the present invention also includes first and second hollow coils whose radial sections extend in different directions. The shortest distance from the rotation center to the second hollow coil is set shorter than the shortest distance from the rotation center to the first hollow coil. Thus, although the first and the second hollow coils are not of a same shape, their performance can be improved.
In the voice coil motor according to the present invention, the first and the second hollow coils differ in thickness, have substantially a same shape since the first and the second hollow coils are concentrically formed at least in part, and improve the performance.
Furthermore, in the voice coil motor according to the present invention, a predetermined area of at least one of the first and the second layered coils is compressed along the axis for plasticization, or the material of a coil is appropriately selected to make the total thickness of the layers thinner or to improve processability.
DISCLOSURE OF THE INVENTION
The voice coil motor according to the present invention comprises a pair of yokes opposite to each other having a predetermined space defined between the yokes; a permanent magnet fixed to at least one of the yokes in the space between the yokes; and a plurality of coils mounted on a rotating member which is rotatable around a predetermined rotating axis, and provided in a magnetic space formed by the permanent magnet and the yokes, said plurality of coils having radial sections contributing to generating a torque. With this configuration, the voice coil motor has the plurality of coils layered one on top of the other along the central r
Kita Hiromi
Kuwajima Hideki
Matsuoka Kaoru
Miyamoto Makoto
Sakamoto Ken'ichi
Lam Thanh
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Ramirez Nestor
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