Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-08-22
2004-11-02
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S216006, C310S193000
Reexamination Certificate
active
06812600
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a thin type inner rotor motor for driving rotation of a medium that can be used in a magnetic disk driving apparatus.
2. Description of the Related Art
Disk apparatuses are widely used in, for example, office computers and word processors including personal computers. One type of disk apparatus is shown in FIG.
14
.
In
FIG. 14
, element
101
represents a chassis having a spindle center
102
as a disk rotation center, which is installed in a housing (not shown) of, for example, a personal computer. A slot is formed by a box with a bottom which is opened forward and upward and has a housing space to which a disk cartridge
103
approaches.
At a rear end of the chassis
101
are disposed a stepping motor
124
for forwarding a head carriage and a head carriage which is configured to be movable in a cross direction by the stepping motor
124
. At the tip of the head carriage is held a first head
130
which reads recorded information on a disk. At a rear upper end part thereof, a head arm
132
having a second head
131
which corresponds to the first head
130
through an elastic body is mounted such that it can oscillate. This head arm
132
is biased in such a direction that the second head
131
approaches the first head
130
. In the disk apparatus of this example are disposed a cartridge holder
136
which holds the disk cartridge
103
removably and a mechanism which opens and closes a shatter of the disk cartridge
103
.
To reduce the thickness of this type of disk apparatus, an inner rotor motor as shown in
FIG. 15
has been used as a motor for rotating a disk. The disk comprises a stator
164
having a circular yoke
161
extending in the circumferential direction and a plurality of cores
163
which are disposed on an inner peripheral surface of the yoke
161
in a radial pattern and on which coils
162
are wound. A rotor
166
is rotatably disposed in an inner peripheral part of the stator
164
. A circular magnet
165
lies opposite the cores
163
. In the figure, a holding part
170
that houses a bearing
169
is mounted on a circuit board
168
. A rotation shaft
171
fixes the rotor which is rotatably supported by the holding part
170
on the circuit board
168
through the bearing
169
and has an axis line extending upward and downward. In addition, the rotor
166
of this inner rotor motor functions as a turntable which has a magnet (not shown) and a turning lever (not shown) for chucking a disk.
In this kind of stator for use in the inner rotor motor, the yoke
161
and cores
163
are disposed to surround nearly the entire circumference of the round shaped rotor
166
except for a movement zone of the heads
130
and
131
, and are made for example, of silicon steel which is expensive compared to galvanized sheet iron which forms the chassis
101
.
Presently, there exists a demand to reduce manufacturing cost and a strong demand to reduce the size and weight of disk apparatuses. Therefore, there is a demand to reduce the areas of the yoke
161
and cores
163
, which are made of expensive silicon steel, in the stator used in the inner rotor motor.
However, if the yoke
161
and the cores
163
are reduced, the magnetic interaction with the rotor
166
becomes uneven along a circumferential direction so cogging torque was often generated. Cogging torque triggers defects such as a reduction in the torque of the rotor
166
, rotational irregularity of the rotor
166
, and increase of control currents for compensating the rotational irregularity. Thus, the cogging torque has to be reduced as much as possible.
Cogging torque will be described with reference to a schematic diagram of a motor shown in FIG.
16
. In
FIG. 16
,
501
represents a circular magnet rotor magnetized with multipoles and
502
represents a stator core having three magnetic teeth
502
a
to
502
c
. Coils
502
d
are wound on the respective magnetic teeth
502
a
to
502
c.
In
FIG. 16
, magnetic fluxes pass from an N pole near the magnetic teeth
502
a
toward an S pole near the magnetic teeth
502
b
. Magnetic fluxes pass from an N pole near the magnetic teeth
502
c
toward an S pole near the magnetic teeth
502
a
and
502
b
, respectively. When the total number of magnetic fluxes of N poles and S poles in the stator core
502
are made equal, cogging torque is reduced.
However, in an actual motor, due to, for example, magnetization irregularity of a magnet, dimensional accuracy of respective components and influence of a magnetic body disposed around the magnet, the total number of magnetic fluxes of N poles and S poles are not equal so cogging torque was often generated.
SUMMARY OF THE INVENTION
The present invention provides a motor that can reduce cogging torque and maintain rotation stability.
The invention employs the following structure.
A motor of the invention comprises a rotor having a plurality of magnetic poles disposed in an arch or circular shape, and a stator in which coils are disposed on respective magnetic teeth of a stator core having a plurality of the magnetic teeth disposed outside or inside of the circumference and opposite the rotor, wherein a magnetic pole part for cancelling cogging torque is disposed around the rotor.
Since the magnetic pole part for cancelling cogging torque is disposed around the rotor, the cogging torque of the motor can be canceled because of the magnetic interaction between the magnetic pole part and the rotor.
Further, the stator is disposed at an outer peripheral side of the rotor covering a range of within about 180° relative to a center angle of the rotor. The magnetic pole part is disposed at an opposite side to the stator by sandwiching a center of the rotor.
According to such a motor, since the magnetic pole part is disposed at the opposite side to the stator by sandwiching the center of the rotor, the magnetic pole part doe not interfere with the magnetic interaction between the rotor and the stator. Thus, it becomes possible to configure a motor which reduces rotation irregularity.
Furthermore, the rotor is supported rotatably on a surface of a base made of a ferromagnetic material through a rotation axis. A tip of the magnetic teeth of the stator is disposed at a position from which is viewed a cutting portion disposed on the surface of the base and which is opposite the outer peripheral surface of the rotor. A tip of the magnetic pole part is disposed at a position from which is viewed another cutting portion disposed on the surface of the base and which is opposite the outer peripheral surface of the rotor.
According to such a motor, since the tip of the magnetic teeth and the tip of the magnetic pole part are disposed at a position from which is viewed the cutting portion of the base, at a portion where the magnetic teeth and the magnetic pole part are located, magnetic fluxes from the rotor affect only the magnetic teeth and the magnetic pole part and do not affect the base. Therefore, the generation of cogging torque due to the operation of the base and the rotor can be reduced.
Moreover, in the motor of the invention, the magnetic pole part is plate-shaped. An end face which is located at the tip of the magnetic pole part is made to be a curved surface along the outer peripheral surface of the rotor.
According to such a motor, since the end face of the platy magnetic pole part is made to be a curved surface along the outer peripheral surface of the rotor, magnetic fluxes from the rotor can be effectively applied to the magnetic pole part so cogging torque can be reduced.
Further, in the motor of the invention, a center position in a thickness direction of the tip of the magnetic teeth and a center position in a thickness direction of the end face of the magnetic pole are disposed at an identical position along the rotor's rotation axis.
According to such a motor, since the magnetic teeth and the magnetic pole part are disposed at an identical position along the rotor's rotation axis, the rotor is not inclined to the rotation a
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Le Dang
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