Coherent light generators – Particular active media – Gas
Reexamination Certificate
2001-06-08
2004-08-31
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
Gas
C372S069000, C372S057000, C372S058000
Reexamination Certificate
active
06785314
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an excimer laser or electric discharge gas laser comprising a magnetic bearing device which is adapted to support a shaft of a rotating fan provided in a laser housing to circulate a gas in the housing. Specifically, the present invention is directed to an excimer laser comprising a magnetic bearing device which insures easy replacement of a magnetic bearing mechanism body or a control device of the laser.
FIG. 1
shows an example of an arrangement of a conventional excimer laser. The excimer laser comprises a laser body
10
and a control device
20
. The laser body
10
comprises a laser housing
11
containing a gas used for generating a laser beam, a rotating fan
12
provided in the laser housing
11
to circulate the gas at a high velocity and at least a pair of discharge electrodes (not shown) for obtaining electric discharge for enabling oscillation of the laser beam. The rotating fan
12
has a rotating shaft
13
protruding from opposite ends thereof and the rotating shaft
13
is magnetically supported in a floating condition by two radial magnetic bearings
14
and one axial magnetic bearing
15
. An electric motor
16
for rotating the fan
12
is provided on a side opposite to the axial magnetic bearing
15
.
FIG. 2
shows examples of the radial magnetic bearings
14
for magnetically supporting the rotating shaft of the fan in a floating condition and the electric motor
16
for rotating the shaft
13
. Radial magnetic bearing targets
14
-
1
and
14
-
2
and displacement sensor targets
14
-
3
and
14
-
4
are fixed to the rotating shaft
13
of the rotating fan
12
. As stationary elements, at least one pair of radial electromagnets, namely radial electromagnets
14
-
5
a
and
14
-
5
b
, are provided so as to face each other and have the radial magnetic bearing target
14
-
1
located therebetween. Further, at least one pair of radial electromagnets, namely radial electromagnets
14
-
6
a
and
14
-
6
b
, are provided so as to face each other and have the radial magnetic bearing target
14
-
2
located therebetween. Also as stationary elements, at least one pair of displacement sensors, namely displacement sensors
14
-
7
a
and
14
-
7
b
, are provided so as to face each other and have the displacement sensor target
14
-
3
located therebetween. Further, at least one pair of displacement sensors, namely displacement sensors
14
-
8
a
and
14
-
8
b
, are provided so as to face each other and have the displacement sensor target
14
-
4
located therebetween. The electric motor
16
comprises an armature
16
-
1
fixed to the rotating shaft
13
and a stationary element or stator
16
-
2
.
Position indicating signals delivered from the displacement sensors
14
-
7
a
,
14
-
7
b
,
14
-
8
a
and
14
-
8
b
are processed in a signal processing circuit
21
and transmitted to an exciting electric power control
22
, which in turn controls exciting currents applied to the radial electromagnets
14
-
5
a
,
14
-
5
b
,
14
-
6
a
and
14
-
6
b
, to thereby control the rotating shaft
13
so that it is adjusted to a target position between the radial electromagnets
14
-
5
a
and
14
-
5
b
and a target position between the radial electromagnets
14
-
6
a
and
14
-
6
b
. The signal processing circuit
21
comprises a preamplifier
21
-
1
, an adding circuit
21
-
2
, an offset output unit
21
-
3
and a gain controllable circuit
21
-
4
. The exciting electric power control
22
comprises a phase compensating circuit
22
-
1
and an electromagnet driving circuit
22
-
2
. The signal processing circuit
21
and the exciting electric power control
22
provide the control device
20
for controlling the magnetic bearings for the excimer laser.
Thus, the displacement sensors
14
-
7
a
,
14
-
7
b
,
14
-
8
a
and
14
-
8
b
generate the signals indicating the positions of the displacement sensor targets
14
-
3
and
14
-
4
(the position of the rotating shaft
13
). The signals are processed in the signal processing circuit
21
of the control device
20
and by means of an electromagnet exciting current obtained by the exciting electric power control
22
, a magnetic attracting force or magnetic repulsive force generated in the radial electromagnets
14
-
5
a
and
14
-
5
b
and a magnetic attracting force or magnetic repulsive force generated in the radial electromagnets
14
-
6
a
and
14
-
6
b
are controlled, to thereby control non-contact magnetic floating support of the radial magnetic bearing targets
14
-
1
and
14
-
2
fixed to the rotating shaft
13
at respective target positions between the radial electromagnets
14
-
5
a
and
14
-
5
b
and between the radial electromagnets
14
-
6
a
and
14
-
6
b.
Although not shown, in the axial magnetic bearing
15
, a displacement sensor detects an axial displacement of the rotating shaft
13
and the signal is processed in the signal processing circuit
21
of the control device
20
, to thereby control an exciting current applied to an axial electromagnet.
As the displacement sensors
14
-
7
a
,
14
-
7
b
,
14
-
8
a
and
14
-
8
b
which are used in conventional magnetic bearings, use is generally made of a non-contact type displacement sensor which electromagnetically detects a displacement, such as a magnetic self-excited oscillation type sensor.
Thus, radial displacement of the rotating shaft
13
(the radial magnetic bearing targets
14
-
1
and
14
-
2
) between the stationary radial electromagnets is detected by the sensors. In order to output the signals from the sensors at a predetermined level of sensitivity, it is required to conduct adjustments in the signal processing circuit
21
during assembly of the magnetic bearings.
However, in the above-mentioned conventional technique, the signal processing circuit
21
, which processes the position indicating signals from the displacement sensors
14
-
7
a
,
14
-
7
b
,
14
-
8
a
and
14
-
8
b
for use in controlling magnetic floating support of the shaft
13
, is contained in the control device
20
. That is, a mechanism for adjustment of the sensitivity is located in the control device. Therefore, when replacement of either a magnetic bearing mechanism body or the control device is conducted, an operation for re-adjustment is necessary for enabling the signal processing circuit to have properties suitable for the bearing mechanism body.
In order to reduce such an operation for re-adjustment, there has been employed a technique in which variations in manufacturing tolerances or variations in material properties of the bearing mechanism bodies are minimized at the time of completion of assembly, so as to prevent variations in outputs of the displacement sensors
14
-
7
a
,
14
-
7
b
,
14
-
8
a
and
14
-
8
b
. In this technique, there is no apparent difference between individual bearing mechanism bodies.
However, a difference between individual bearing mechanism bodies cannot be completely eliminated by the above-mentioned technique. In practice, it is only possible to minimize such a difference by putting tolerances of individual parts under highly strict control and suppressing dimensional tolerances generated in the course of assembly to a level within a predetermined allowable range. In addition, a selection operation is necessary and assembled parts having tolerances exceeding beyond the allowable range are subjected to additional processing or disposal, thereby lowering a yield. This makes it difficult to achieve an appropriate level of cost reduction which should normally result from mass production.
SUMMARY OF THE INVENTION
In view of the above, the present invention has been made. It is an object of the present invention to provide an excimer laser or electric discharge gas laser in which a mechanism for adjusting displacement sensors is provided in a magnetic bearing mechanism body, which enables a difference between individual bearing mechanism bodies to be eliminated in design terms by means of the adjusting mechanism, and which insures easy replacement of either the magnetic bea
Barada Toshimitsu
Nakazawa Toshiharu
Ooyama Atushi
Sekiguchi Shinichi
Shinozaki Hiroyuki
Ebara Corporation
Wong Don
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