Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
1999-02-18
2001-10-16
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
C363S058000, C363S098000
Reexamination Certificate
active
06304475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser power supply apparatus for supplying an AC voltage to a laser device for use in, for example, laser beam machining so as to cause the laser device to discharge and radiate laser light.
2. Description of the Prior Art
Referring now to
FIG. 26
, there is illustrated a diagram showing the structure of a laser device., As shown in the figure, the laser device is provided with a pair of electrodes
1
, a pair of dielectric layers
2
on the pair of electrodes
1
, respectively, a high-frequency AC power supply
3
, and a partial reflection mirror
4
for causing the laser device to generate laser radiation
6
in cooperation with a total reflection mirror
5
.
FIG. 27
shows an equivalent circuit of the pair of dielectric layers
2
and a discharge area or space in which a discharge occurs to excite a gas contained in the discharge space to start laser action. In
FIG. 27
, reference numeral
7
denotes a dielectric capacitance caused by the pair of dielectric layers
2
, and
8
denotes an equivalent resistance caused by the discharge area. Further,
FIG. 28
is a schematic circuit diagram showing the detailed structure of the high-frequency power supply
3
. As shown in the figure, the high-frequency power supply
3
is provided with a plurality of high-speed semiconductor switches
9
-
1
to
9
-
4
, a DC power supply
10
, a high-frequency transformer
11
, and a pair of output reactors
12
.
As shown in
FIG. 28
, the plurality of high-speed semiconductor switches
9
-
1
to
9
-
4
form a full-bridge inverter. The full-bridge inverter is driven by four control signals S
1
to S
4
as shown in
FIG. 29
, for example. The full-bridge inverter generates a rectangular high-frequency voltage Vout. The high-frequency transformer
11
increases and furnishes the rectangular high-frequency voltage Vout to the load by way of the pair of output reactors
12
. The pair of output reactors
12
and the dielectric capacitor
7
eliminate high-frequency components in the output current flowing from the high-frequency transformer
11
to the load. An approximately sinusoidal current I
d
thus flows through the load and forms a discharge. The discharge generated excites a gas contained in the discharge space to start laser action. The combination of the partial reflection mirror
4
and the total reflection mirror
5
forces the excited gas to radiate in phase. The laser light
6
generated by the laser radiation can be used for laser beam machining, for example. In most cases, the leakage inductance of the high-frequency transformer
11
can be utilized as the pair of output reactors
12
.
Although the required intensity and pulse width the laser beam
6
depends on objects to be machined, when a high degree of accuracy is required, the laser beam
6
should have a higher intensity and a shorter pulse width in most cases, as shown in FIG.
30
. In order to increase the intensity of the laser light
6
, a larger amount of current needs to be passed through the discharge space in the laser device.
Since the impedance of the discharge load is capacitive, when causing a larger amount of current to be passed through the discharge space, the higher the frequency of the AC voltage applied to the load, the lower the voltage Vc across the dielectric capacitor
7
, as shown in FIGS.
31
(
a
) to
31
(
d
). As can be seen from FIGS.
31
(
a
) to
31
(
d
), the voltage Vc required to generate the same amount of current I
d
decreases with an increase in the frequency of the AC voltage applied to the load. When the thickness of each of the pair of dielectric layers
2
is restricted to a certain value, there is no other choice but to increase the frequency of the AC voltage in order to cause a larger amount of current to be passed through the load, because the voltage across each of the pair of dielectric layers
2
has to be less than its withstand voltage. On the other hand, when the frequency of the AC voltage applied to the load is increased, the amount of current flowing through the load is limited by the electrical size of the pair of output reactors
12
, other than the discharge resistance
8
. When the electrical size of the pair of output reactors
12
is relatively large, the voltage Vc across the dielectric capacitor
7
drops before the current Id rises up to an adequate value, and hence a large amount of current cannot be passed through the load. The leakage inductance of the high-frequency transformer
11
is utilized as the pair of output reactors
12
in most cases, as previously mentioned. Further, the leakage inductance of the high-frequency transformer
11
cannot be reduced to zero because of its structural limits. Thus the minimum of the total inductance of the pair of output reactors
12
is inevitably determined and the largest amount of current resulting from the minimum inductance is therefore limited. In general, since the leakage inductance of a transformer is proportional to the square of the winding ratio of the secondary winding to the primary winding, the electrical size of the pair of output reactors
12
is increased when the secondary winding is higher than the primary winding in voltage. As a result, the frequency of the AC voltage applied to the load has an upper limit and hence the intensity of the laser light
6
has an upper limit because of the withstand voltage of the dielectric capacitor
7
. Accordingly, the prior art laser power supply apparatus using the high-frequency transformer
11
cannot cause gas laser devices to generate laser radiation having a sufficient intensity suitable for close tolerance machining.
SUMMARY OF THE INVENTION
The present invention is made to overcome the above problem. It is therefore an object of the present invention to provide a laser power supply apparatus suitable for close tolerance machining, reducing the electrical size of a pair of power supply reactors connected in series to a discharge load, and determining the maximum discharge power, so as to increase the laser intensity.
In accordance with the present invention, there is provided a laser power supply apparatus for supplying AC power to a gas contained in a laser device by way of a pair of dielectrics so as to form a high-frequency discharge in the gas to excite the gas, thereby causing the laser device to radiate, the laser power supply apparatus comprising: a DC power supply; and an inverter comprised of a plurality of arms each including a plurality of high-speed semiconductor switches in series, for directly converting a DC high voltage from the DC power supply to a series of AC output pulses having a much higher AC voltage to be supplied to the laser device by simultaneously turning on or off those high-speed semiconductor switches in series disposed in each of the plurality of arms, and for furnishing the series of AC output pulses to the laser device by way of a pair of output terminals thereof.
In accordance with a preferred embodiment of the present invention, the inverter includes a plurality of gate circuits respectively corresponding to the plurality of arms, each including a plurality of drive circuits for respectively driving the plurality of high-speed semiconductor switches in series disposed in each of the plurality of arms, the plurality of drive circuits respectively receiving a plurality of AC voltages from a plurality of secondary windings of at least a transformer. Further, one drive circuit for driving a corresponding one of the plurality of high-speed semiconductor switches that is electrically farther from an output of the inverter is the one that receives an AC voltage from one secondary winding that is nearer to a core of the transformer.
Preferably, the inverter further includes a plurality of voltage-dividing capacitors electrically connected in parallel with the plurality of high-speed semiconductor switches in series disposed in each of the plurality of arms, respectively. Further, one voltage-dividing capacitor connected in parallel to a cor
Iwata Akihiko
Kumagai Takashi
Matsubara Masato
Nishimae Jun-ichi
Tanaka Masaaki
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Vu Bao Q.
Wong Peter S.
LandOfFree
Switching power supply for gas laser does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switching power supply for gas laser, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switching power supply for gas laser will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2580426