Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-05-12
2001-07-31
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S261100
Reexamination Certificate
active
06268674
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to a magnetic bearing apparatus and more particularly to a magnetic bearing apparatus capable of being used under a clean atmosphere, for example, a semiconductor fabrication process, and capable of reducing in size in the rotational axis thereof.
2. Description of the Related Art
At present, a ball bearing is mainly employed as a bearing member for supporting a rotor in a rotational manner, such as a chemical vapor deposition (CVD) apparatus for growing a thin film of a predetermined component over a semiconductor substrate or a wafer.
Such chemical vapor deposition apparatus needs to be run in an evacuated clean atmosphere. In the current apparatus that uses the ball bearing as its component, however, a lubricating oil of the ball bearing will diffuse to contaminate the thin film to be formed on the wafer, thereby lowering the production yield. Further, rust on the ball bearing causes not only contamination in the clean atmosphere, but also results in imperfections on the outer surface of the ball bearing itself, thereby making the stable rotation thereof impossible. In this case, the ball bearing has to be replaced with a new one. However, this replacement adds time and cost in the fabrication process.
Therefore, investigations have been made to employ a magnetic bearing as a component in place of the ball bearing. The magnetic bearing has been developed in various researches and applications in numerous aspects due to non-contact, no lubrication requirements, and long lifetime characteristics.
A current magnetic bearing apparatus is constituted, for example, as shown in FIG.
1
. This magnetic bearing apparatus
90
includes: a cylindrical rotor
93
accommodated in a casing
91
and equipped with a thrust disk
93
a
at the lower end side of a rotational axis
92
, and electromagnets
94
a
and
94
b
constituting a thrust magnetic bearing
94
for supporting the rotor
93
in a non-contact manner in the thrust direction by making their magnetic poles face (or confront) each other through gaps in the upper and lower surfaces of the thrust disk
93
a
. The rotor
93
is supported in a non-contact manner in the radial direction by radial magnetic bearings
95
and
96
which are disposed at the upper portion and the lower portion of the rotational axis
92
, and is rotationally driven on the rotational axis
92
by an electric motor
97
.
The radial magnetic bearings
95
and
96
include: cylindrical laminated yoke portions
93
b
and
93
c
fixed on the rotor
93
such that they are laminated in the direction of the rotational axis
92
, and upper electromagnets
95
a
,
95
b
,
95
c
and
95
d
(the electromagnets
95
b
and
95
d
are not shown) and lower electromagnets
96
a
,
96
b
,
96
c
and
96
d
(the electromagnets
96
b
and
96
d
are not shown) fixed on the casing
91
at positions to face (or confront) the yoke portions
93
b
and
93
c
and are proportionally divided into four segments (quadri-divided) in the circumferential direction.
Moreover, displacement sensors (not shown) for detecting the axial and radial displacements of the rotor
93
is disposed in the casing
91
so that the thrust magnetic bearing
94
and the radial magnetic bearings
95
and
96
are controlled by the control signals produced in a control unit (not shown) in accordance with the detected displacements.
In the magnetic bearing apparatus as constituted above, the thrust magnetic bearing
94
, the radial magnetic bearings
95
and
96
, the displacement sensors (not shown) and the electric motor
97
are disposed along the direction of the rotating axis
92
. This construction elongates the magnetic bearing apparatus in the direction of the rotational axis
92
. Because the laminated yoke portions
93
b
and
93
c
in the rotor
93
are exposed at their laminated end surfaces to the inside of the evacuated casing
91
, rust, if allowed to grow due to environmental circumstances, will be scattered by the rotations of the rotor
93
to contaminate the inside of the casing
91
. In the CVD apparatus, especially, the thin film to be formed over the wafer may be contaminated, resulting in a lower production yield.
The magnetic bearing apparatus thus described is elongated in the direction of the rotational axis because the radial magnetic bearings are disposed at a plurality of positions along the axial direction. Further, rust on the end surfaces exposed to the inside of the casing of the laminated yokes may contaminate the inside of the casing.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned circumstances and is intended to solve the above-mentioned problems. In particular, an object of the present invention is to provide a magnetic bearing apparatus which can be reduced in size in the rotational axis and which can avoid contamination in the inside thereof. Additional objects and advantages of the invention may be apparent from the following description or may be learned by practice of the invention.
The present invention provides a magnetic bearing apparatus capable of supporting a rotatable rotor in a non-contact manner, including a plurality of electromagnets disposed around the rotor for supporting the rotor in a non-contact manner in the axial direction of the rotor and the radial direction thereof by a magnetic attraction force, and a conductivity adjusting unit disposed at positions to face the electromagnets of the rotor for making the conductivity discontinuous with respect to the rotational direction of the rotor.
The conductivity adjustment unit may include a slit formed in the rotor. The conductivity adjustment unit may also include an anisotropic conductive material applied on the rotor.
The slit may be formed in a planes containing the axis direction of the rotor and the radial direction thereof. The electromagnets may include a first magnetic bearing that supports the rotor in the axial direction, and a second magnetic bearing that supports the rotor in the radial direction.
The rotor may include a disk around the surface of the rotor, and the slit may be formed in the disk. At least one of the electromagnets may face this disk.
The rotor may be cylindrically shaped. At least one of the electromagnets may be disposed so as to face the outer surface of the rotor, and at least one of the electromagnets may be disposed so as to face the inner surface of the rotor.
The present invention may further include a motor that rotates the rotor. The motor may be disposed so as to face the outer surface of the rotor, and may be disposed so as to face the inner surface of the rotor.
The present invention may further include a plurality of displacement sensors that detect the displacement of the rotor in the axial direction and the radial direction thereof. The displacement sensors may include a first sensor that detects the displacement of the rotor in the axial direction, and a second displacement sensor that detects the displacement of the rotor in the radial direction. At least one of the displacement sensors may be faced so as to detect the displacement of the disk.
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patent: 11325073A (19
Foley & Lardner
Kabushiki Kaisha Toshiba
Waks Joseph
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