Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-08-05
2003-06-17
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06700R, C310S156430, C310S156450, C310S156820, C310S216055, C310S261100, C310S090000
Reexamination Certificate
active
06580190
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circumferential confronting type motor, in which an armature core and a drive magnet are positioned opposite each other in the radial direction. More specifically, it relates to a thrust bearing mechanism that relatively regulates through magnetic action the movement in the axial direction of a rotor assembly and a stator assembly of the circumferential confronting type motor.
2. Description of Related Art
A variety of motors have been proposed that employ a thrust magnetic bearing mechanism in order to stabilize support in the thrust direction of a rotor assembly in a circumferential confronting type motor.
FIG. 12
is a cross-sectional view of a prior art that employs a thrust magnetic bearing mechanism in a circumferential confronting type pneumatic dynamic pressure bearing motor used in deflection scanning devices that use polygon mirrors.
The pneumatic dynamic pressure bearing motor shown in
FIG. 12
comprises primarily of a rotor assembly
1
and a stator assembly
2
. The rotor assembly
1
is equipped with a generally cylindrical-shaped rotor
10
with a shaft hole
13
, and a drive magnet
11
mounted on an outer circumference side of the rotor
10
via a magnet yoke
12
. In the meantime, the stator assembly
2
is equipped with a fixed shaft
20
, whose one end section is fixed to a motor frame
21
and which is inserted in the shaft hole
13
of the rotor
10
, and an armature core
22
, which is indirectly supported by the motor frame
21
and has a drive coil
23
wound around it; where an outer circumference surface of the armature core
22
and an inner circumference surface of the drive magnet
11
oppose each other in the radial direction across a predetermined gap.
A dynamic pressure bearing mechanism
4
is formed between an outer circumference surface of the fixed shaft
20
and an inner circumference surface of the shaft hole
13
formed in the rotor
10
, and two blocks of radial dynamic pressure bearing sections
41
and
42
that comprise the dynamic pressure bearing mechanism
4
are formed on at least one of the outer circumference surface of the fixed shaft
20
or the inner circumference surface of the shaft hole
13
. When a predetermined amount of current is supplied to the drive coil
23
, electromagnetic action between the armature core
22
and the drive magnet
11
causes an optical deflecting polygon mirror
6
mounted on the rotor
10
to rotate, and an incoming laser beam is reflected off of the polygon mirror
6
and is deflection-scanned in a predetermined direction.
In the pneumatic dynamic pressure bearing motor having such a structure, a concave section
24
is formed at the tip section of the fixed shaft
20
, and a ring-shaped fixed-side thrust magnet
31
is provided in the concave section
24
. A rotation-side thrust magnet
32
is provided more interior in the radial direction than the fixed-side thrust magnet
31
in a manner confronted with the fixed-side thrust magnet
31
. The fixed-side thrust magnet
31
and the rotation-side thrust magnet
32
are positioned so that their respective poles are placed opposite to the opposing poles of the other thrust magnet, and together they make up a thrust magnetic bearing mechanism
3
. The magnetic attractive force or the magnetic repulsive force that is generated between the two thrust magnets
31
and
32
restrains the oscillation of the rotor
10
in the thrust direction.
However, in such a pneumatic dynamic pressure bearing motor, dust such as magnetic particles and/or dust generated by abrasion is sometimes attached, although in extremely minuscule amounts, to the surfaces of the thrust magnets
31
and
32
, due to the fact that the fixed-side thrust magnet
31
and the rotation-side thrust magnet
32
are formed by mixing and kneading magnetic particles and a binder and by using such methods as compress molding or sintering. The dust is then carried by the air current inside the motor and moves into the dynamic pressure bearing mechanism
4
, which is formed between the outer circumference surface of the fixed shaft
20
and the inner circumference surface of the shaft hole
13
. Since the dynamic pressure bearing mechanism
4
normally has a bearing gap of several micrometers, once dust enters the bearing gap, so-called bums occur in the dynamic pressure bearing mechanism
4
, which can lead to problems in the bearing life and cause major problems such as the motor failing to rotate.
This problem is not limited to motors that use pneumatic dynamic pressure bearings, and can equally occur in motors that use bearings in which the bearing and the shaft are supported in a relatively rotatable manner across a minuscule gap, such as oil dynamic pressure bearings and oil-impregnated sintered bearings.
In this type of motor, the thrust bearing mechanism
3
is provided to restrain the oscillation of the rotor
10
in the thrust direction, and rare earth magnets are normally used as the thrust magnets
31
and
32
, since they require large magnetic attractive force in spite of their relatively small volumes. This can consequently lead to escalating parts cost, which then makes the entire motor expensive.
SUMMARY OF THE INVENTION
In view of the problems described above, the present invention provides an inexpensive circumferential confronting type motor that can reduce both the parts cost and the motor price by improving the structure of the thrust bearing mechanism such that an independent thrust bearing mechanism that supports the rotor can be eliminated. The present invention also provides a circumferential confronting type motor that can reduce the occurrence of bearing failures by preventing the dust that is generated in the thrust bearing mechanism from entering the bearing section.
In order to solve the above problems, a circumferential confronting type motor in accordance with an embodiment of the present invention comprises an armature core that has drive coils wound around its plurality of poles, and a drive magnet positioned opposite to the armature core in the radial direction, wherein the drive magnet has a plurality of divided magnetized sections, each with a magnetic center and formed separated from each other in the axial direction by a non-magnetized section. In one aspect, the magnetic centers of the respective plurality of divided magnetized sections are provided in symmetrical positions to a magnetic center in the axial direction of the armature core. Further, electromagnetic action between the drive magnet and the armature core causes the two to rotate relatively, while magnetic action between the plurality of divided magnetized sections and the armature core regulates their relative movements in the axial direction.
According to the present invention, due to the fact that the electromagnetic action to rotatively drive the rotor is generated by having the drive magnet and the armature core positioned opposite to each other, and to the fact that the oscillation of the rotor in the thrust direction is restrained by the magnetic action between the plurality of divided magnetized sections, which are formed separated in the axial direction, and the armature core, it is possible to eliminate an independent thrust bearing mechanism that independently supports the rotor in the thrust direction, and thereby reduce the parts cost and the motor price.
In the circumferential confronting type motor described above, it is preferable for the plurality of divided magnetized sections to be formed symmetrically to the magnetic center in the axial direction of the armature core.
With such a structure, since the divided magnetized sections are symmetrically shaped there is no change in the magnetic actions and effects, even when the posture of the drive magnet is inverted vertically. As a result, motor components can be shared, which can reduce the motor price even further.
Additionally, the drive magnet may comprise a first divided magnetized section and a second divided magnetized section tha
Hogan & Hartson LLP
Lam Thanh
Sankyo Seiki Mfg. Co. Ltd.
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