Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2003-06-25
2004-11-02
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100, C360S098070, C360S099080, C360S099040
Reexamination Certificate
active
06812603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flat motor that is so called an axial gap type flat motor in which a driving magnet faces toward a driving coil in the plane, particularly, relates to a spindle motor for flexible disc drive (FDD) that is essential to be thinner.
2. Description of the Related Art
A so-called axial gap type flat motor in which a driving magnet and a driving coil is constituted to be faced toward with each other in the plane is utilized for various equipment such as an FDD.
With referring to FIGS.
9
(
a
),
9
(
b
) and
10
, a conventional flat motor for FDD is explained.
FIGS.
9
(
a
) and
9
(
b
) are cross-sectional views of a flat motor according to the prior art.
FIG. 10
is an enlarged fragmentary cross-sectional view of the flat motor shown in FIG.
9
(
a
).
In FIGS.
9
(
a
) and
10
, a flat motor is composed of a rotor
100
that is formed by a soft magnetic material and a stator
50
. The rotor
100
is further composed of a rotor yoke
20
and a ring-shaped driving magnet
30
that is adhered on the rotor yoke
20
. A lower surface of the ring-shaped driving magnet
30
is magnetized with multipolar driving magnetic poles.
On the other hand, the stator
50
that is disposed under the rotor
100
is constituted by a plurality of ring-shaped driving coils
40
, which is adhered in a ring shape on a plane stator yoke
60
that is to be a part of magnetic circuit and formed by a soft magnetic material.
Further, a shaft
80
to be an axis of revolution is installed in the rotor
100
. The shaft
80
is held in the center of the stator
50
by way of a bearing
70
to rotate freely.
A slight gap “d
1
” is provided between the ring-shaped driving coil
40
and the ring-shaped driving magnet
30
to eliminate interference between them while the rotor
100
is rotating.
The rotor
100
rotates by rotational driving force that is generated by interaction between a magnetic field caused by the multipolar driving magnetic poles and rotational magnetic field caused by applying predetermined electric current to the ring-shaped driving coil
40
.
Recently, a spindle motor for FDD is strongly required to be smaller in size and lighter in weight. Consequently, a rare-earth magnet having strong suction power is utilized for a ring-shaped driving magnet in order to increase operational efficiency while a thickness of motor is made thinner.
The stator yoke
60
is strongly drawn by the ring-shaped driving magnet
30
because of strong suction power, and resulted in deforming its shape such that the stator yoke
60
approaches to the ring-shaped driving magnet
30
. Consequently, the gap “d
1
” between the ring-shaped driving magnet
30
and the ring-shaped driving coil
40
is narrowing in accordance with being toward the outer circumference of the stator yoke
60
.
The Japanese Patent Application Laid-open Publications No. 6-11163/1994 discloses a structure of the stator yoke
60
. As shown in FIG.
9
(
b
), the structure is such that the stator yoke
60
is bent toward the opposite direction to the rotor
100
in accordance with being away from the axis of revolution when assembled.
The shape of the stator yoke
60
is, as shown in FIG.
9
(
a
), formed like a saucer to maintain the gape “d
1
” between the ring-shaped driving magnet
30
and the ring-shaped driving coil
40
to be proper distance when the stator
50
is assembled with the rotor
100
.
Generally, rotational torque increases in accordance with narrowing a gap between a driving magnet and a driving coil because magnetic flux generated by the driving magnet effectively links with the driving coil. Consequently, a motor is led to have higher efficiency, and the motor can be made thinner. However, in the case of the aforementioned stator yoke formed in a shape of saucer, deformation of the stator yoke caused by the strong suction power that acts between the driving magnet and the stator yoke is not uniform. Consequently, there existed a wider gap and a narrower gap between the driving coil and the stator yoke in the radial direction.
More specifically, the stator yoke approaches to the driving coil and the gap between them becomes narrower in accordance with the direction from the driving coil towards a spindle shaft. On the contrary, the stator yoke is deformed such that the gap between the driving magnet and the driving coil gradually increases in accordance with the direction towards the outer circumference.
Accordingly, there existed a restriction for the gap “d
1
” to be made narrower and resulted in a problem such that thinning the motor further more is hardly conducted.
Further, there existed another problem such that motor characteristics change in accordance with elapsed time and resulted in less reliability. Because, the stator yoke is always strained by the strong suction power and deformed gradually, and further, a creep phenomenon that changes drastically by external thermal load occurs in the stator yoke. By the creep phenomenon, the gap between the driving magnet and the driving coil is narrowed and resulted in a further problem. In the worst case, the driving magnet and the driving coil interferes with each other and are possibly damaged while revolving.
SUMMARY OF THE INVENTION
Accordingly, in consideration of the above-mentioned problems of the prior art, an object of the present invention is to provide a flat motor, which can be thinned more and has less change of characteristic by time elapsed and is high in reliability.
In order to achieve the above object, the present invention provides, according to an aspect thereof, a flat motor comprising a rotor composed of an axis and a driving magnet in a ring shape having multipolar driving magnetic poles; and a stator yoke composed of a plane section for mounting a bearing for holding the rotor to rotate freely with centering the axis and another plane section for mounting a plurality of driving coils disposed in a concentric circle with facing towards the driving magnet, wherein the other plane section is disposed in conjugating with the outer side of the plane section, the flat motor is further characterized in that the plane section is formed flat in a circular shape with centering the axis, and the other plane section is a part of surface of approximately a circular cone shape having a vertex on the axis and is in a shape of inclining towards a direction away from the rotor in accordance with being far away from the axis and formed with a pleat by bending the stator yoke in a conjugating section between the plane section and the other plane section.
Other object and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.
REFERENCES:
patent: 4594524 (1986-06-01), Sudo
patent: 5446325 (1995-08-01), Iwabuchi
patent: 5793135 (1998-08-01), Suzuki et al.
patent: 6-11163 (1994-02-01), None
Connolly Bove & Lodge & Hutz LLP
Nguyen Tran
Pham Leda T.
Victor Company of Japan Ltd.
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