Coherent light generators – Particular active media – Gas
Reexamination Certificate
2000-10-02
2002-06-11
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular active media
Gas
C372S037000, C372S058000, C372S098000, C372S065000
Reexamination Certificate
active
06404794
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to an excimer laser apparatus having a circulating fan for producing a high-speed laser gas stream, and more particularly to an excimer laser apparatus having a feature in a motor for rotating a shaft of a circulating fan and a magnetic bearing for supporting the shaft of the circulating fan.
2. Description of the Related Art
FIG. 5
is a schematic view showing a structure of a conventional excimer laser apparatus. As shown in
FIG. 5
, the conventional excimer laser apparatus comprises a container
41
sealing a laser gas including a halogen gas such as a fluorine gas therein, ionization electrodes (not shown) disposed in the container
41
for ionizing the laser gas, and discharge electrodes
42
,
42
disposed in the container
41
for inducing an electric discharge capable of oscillating a laser light. A circulating fan
43
for producing a high-speed laser gas stream between a pair of the discharge electrodes
42
and
42
is disposed in the container
41
.
The circulating fan
43
has a shaft
44
penetrating therethrough and protruding from both ends thereof. The shaft
44
is supported in a non-contact manner by radial magnetic bearings
51
,
52
provided at both ends of the container
41
, and by an axial magnetic bearing
53
provided at one end of the container
41
. A motor
54
is provided at a shaft end side of the radial magnetic bearing
52
.
Displacement sensor targets
51
c
,
51
c
and electromagnet targets
53
d
,
52
d
of the radial magnetic bearings
51
,
52
, and a displacement sensor target
53
d
and an electromagnet target
53
e of the axial magnetic bearing
53
are secured to the shaft
44
. Further, a rotor
54
b
of the motor
54
is secured the shaft
44
. Displacement sensors
51
a
,
52
a
,
53
a
, electromagnets
51
b
,
52
b
,
53
b
,
53
c
, and a stator
54
a
of the motor
54
are disposed at positions opposed to the displacement sensor targets
51
c
,
52
c
,
53
d
, the electromagnet targets
51
d
,
52
d
,
53
e
, and the rotor
54
b.
Thin cylindrical bulkheads
55
,
56
are provided on inner peripheral surfaces of the displacement sensors
51
a
,
52
a
and the electromagnets
51
b
,
52
b
of the radial magnetic bearings
51
,
52
, and the stator
54
a
of the motor
54
. The bulkheads
55
,
56
are formed of a material having corrosion resistance to the halogen gas included in the laser gas, e.g., austenitic stainless steel such as SUS316L. The bulkheads
55
,
56
prevent the displacement sensors
51
a
,
52
a
, the electromagnets
51
b
,
52
b
, and the stator
54
a
from contacting the laser gas.
Like the radial magnetic bearings
51
,
52
, a bulkhead
57
is provided on the inner peripheral surface of the displacement sensor
53
a
of the axial magnetic bearing
53
to prevent the displacement sensor
53
a
from contacting the laser gas. The electromagnets
53
b
,
53
c
comprise cores formed of a ferromagnetic material having corrosion resistance to the halogen gas included in the laser gas, e.g., permalloy, and have bulkheads
58
provided only on the coils thereof.
The displacement sensor targets
51
c
,
52
c
,
53
d
and the electromagnet targets
51
d
,
52
d
,
53
e
of the radial magnetic bearings
51
,
52
and the axial magnetic bearing
53
secured to the shaft
44
are disposed in airtight spaces communicating with the container
41
. Therefore, the displacement sensor targets
51
c
,
52
c
,
53
d
and the electromagnet targets
53
d
,
52
d
,
53
e
are formed of a ferromagnetic material having corrosion resistance to the halogen gas, e.g., permalloy. The rotor
54
b
of the motor
54
is composed of a composite of a silicon steel plate and an aluminum alloy, and a permanent magnet. Therefore, a thin cylindrical bulkhead
59
is provided on the outer peripheral surface of the rotor
54
b
. The bulkhead
59
forms a sealed structure to prevent the rotor
54
b
from contacting the laser gas.
As described above, the conventional excimer laser apparatus requires the displacement sensors
51
a
,
52
a
,
53
a
and the electromagnets
51
b
,
52
b
,
53
b
,
53
c
of the radial magnetic bearings
51
,
52
and the axial magnetic bearing
53
, which are sequentially arranged in the axial direction. Therefore, the axial length of the shaft
44
is long, and the critical speed of the shaft
44
is decreased. Particularly, high-power laser light with continuous oscillation has been demanded in recent excimer laser apparatus. In order to perform continuous oscillation, it is necessary to replace the laser gas between the discharge electrodes
42
and
42
in a shorter time. Thus, it is necessary that the speed of the laser gas stream produced by the circulating fan
43
should be increased. Accordingly, the circulating fan
43
needs to be rotated at a high speed. However, when the axial length of the shaft
44
increases, the critical rotational speed decreases, so that it is difficult to rotate the circulating fan
43
at a high speed.
If the power of the motor
54
is increased to rotate the circulating fan
43
at a high speed, the motor
54
increases in rotational driving force and also increases in magnetic attraction force in the radial direction. This radial magnetic attraction force causes vibrations to the shaft
44
. In order to cancel out the vibrations, the electromagnets
51
b
,
52
b
of the radial magnetic bearings
51
,
52
need to be increased in magnetic force. Consequently, it is necessary to simultaneously achieve the increase in the power of the motor
54
, and the enhancement of the magnetic force of the electromagnets
51
b
,
52
b
of the radial magnetic bearings
51
,
52
. This causes both of the radial magnetic bearings
51
,
52
and the motor
54
, and their installation spaces to be larger.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide an excimer laser apparatus which can solve the above drawbacks with a conventional excimer laser apparatus, and can facilitate high-speed rotation of a circulating fan, and requires reduced installation spaces for a bearing portion and a motor portion.
According to an aspect of the present invention, there is provided an excimer laser apparatus having a container sealing a laser gas including a halogen gas therein, a pair of discharge electrodes disposed in the container for inducing an electric discharge capable of oscillating a laser light, and a circulating fan with a shaft for producing a high-speed laser gas stream between a pair of the discharge electrodes, the excimer laser apparatus characterized in that: both ends of the shaft are rotatably supported by rotor-stator mechanisms, or one end of the shaft is rotatably supported by a rotor-stator mechanism, and the other end of the shaft is supported by a magnetic bearing; and the rotor-stator mechanism comprises a rotor formed of a magnetic material and attached to the shaft of the circulating fan, a stator provided at a position opposed to the rotor, an electric motor winding provided in the stator for applying torque to the rotor, and a position control winding provided in the stator for producing a magnetic force to levitate and support the rotor.
As described above, the rotor-stator mechanism comprises the rotor formed of a magnetic material and attached to the shaft of the circulating fan, the stator provided at a position opposed to the rotor, the electric motor winding provided in the stator for applying torque to the rotor, and the position control winding provided in the stator for producing a magnetic force to levitate and support the rotor. The end of the shaft is rotatably supported by the rotor-stator mechanism. This arrangement can eliminate the need to provide cores for electromagnets of the magnetic bearing and the motor. Therefore, the shaft length of the shaft can be shortened, and the installation spaces for the magnetic bearing and the motor can be reduced. Accordingly, since the crit
Mori Satoshi
Nakazawa Toshiharu
Osawa Masaru
Sato Tadashi
Sekiguchi Shinichi
Armstrong Westerman & Hattori, LLP
Ebara Corporation
Jr. Leon Scott
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