JPH0456375A - Method and apparatus for controlling carbon dioxide gas laser - Google Patents

Abstract

PURPOSE:To obtain a stable laser output even in a pulse mode without ripple and hunting by rectifying and smoothing a primary power source voltage, then controlling to feed back it so as to become a DC constant voltage, inputting the constant voltage to an inverter, and controlling discharge current or high frequency power of each discharge tube. CONSTITUTION:A DC voltage made constant is supplied to an inverter 24 to drive a high voltage transformer 25. A smoothed DC high voltage is applied to a discharge tube 28, and a discharge current is detected by a discharge current detector 29. On the other hand, an output of a laser power setter 30 and an output of a laser power detector 31 for detecting the amplitude of a laser power are input to a second error amplifier 32, and its output is input together with the output from the detector 29 to a third error amplifier 33. The output of the amplifier 33 is input to a frequency controller 34 to so drive a power MOS-FET of the inverter 24 that the laser power becomes constant and a discharge current becomes constant through a driver 35.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for controlling a carbon dioxide laser, and more particularly to a feedback control method and apparatus for direct current excitation type and high frequency excitation type carbon dioxide lasers.

BACKGROUND OF THE INVENTION FIG. 3 shows the structure of a conventional high-speed axial-flow DC-excited carbon dioxide laser oscillator. In FIG. 2, a discharge electrode 3.4 is provided in a discharge region 1.2 made of a dielectric material such as glass.

The discharge electrodes 3 and 4 are supplied with the output of a DC high voltage power supply 5.6, for example, a voltage of about DC16kV, 80n+A. In the discharge space within discharge etc. 1.2, discharge occurs in the directions of arrows A and B.

A rear mirror (total reflection mirror) 7 and an output mirror (partial reflection mirror) 8 are fixedly arranged in the discharge space within the discharge tube 1.2.
These constitute an optical resonator. Laser output 9 is taken out from output mirror 8 .

The laser gas in the discharge tube 1.2 is circulated through the air pipe 10, and the gas whose temperature has risen through the blower 11 that circulates the discharge and laser gas is cooled by a heat exchanger 12.13. Ru.

FIG. 4 shows a control block of the control device in the carbon dioxide laser oscillator shown in FIG.

In FIG. 4, a three-phase 200V AC voltage from a commercial power source 21 is rectified by a rectifier 22 and then smoothed by a smoothing circuit 23, and the smoothed DC voltage is transferred to an inverter circuit 24.
supplied to The inverter circuit 24 includes a high voltage transformer 2
5, and the secondary voltage of the high voltage transformer 25 is connected to the rectifier 2.
6 and then smoothed by a high voltage capacitor 27.

The smoothed DC high voltage is applied to the discharge tube 28, and the discharge current flowing through the discharge tube 28 is detected by the discharge current detection circuit 2.

On the other hand, the output of the laser power setting circuit 30 and the output of the laser power detection circuit 31 that detects the magnitude of the laser power are input to the laser power error amplifier circuit 32.

The output of the laser power error amplifier circuit 32 is input to the discharge current error amplifier circuit 33 together with the output from the discharge current detection circuit 29. The output of the discharge current error amplifier circuit 33 is input to the frequency control circuit (PWM (fM)) 34, and the output of the frequency control circuit 34 is input to the driver circuit 35, and the power MO3-FET of the inverter circuit 24 is input.
to drive. Reference numeral 36 is a control block for controlling the discharge tube 28, and reference numeral 37 is a control block for other discharge tubes (not shown).

In this way, the feedback control of the conventional DC pumped carbon dioxide laser control device uses the output of the laser power setting circuit 30 that sets the laser output and the magnitude of the laser power, and the laser power detection circuit that detects the magnitude of the laser power. 31 is input to a laser power error amplifier circuit 32, and the output of this laser power error amplifier circuit 32 and the output of a discharge current detection circuit 29 that detects the magnitude of the discharge current are input to a discharge current error amplifier circuit 33. I was doing it.

Further, feedback control of the high frequency excitation type carbon dioxide laser control device is performed by providing a high frequency power detection circuit in place of the discharge current detection circuit and by providing a high frequency power error amplifier circuit in place of the discharge current error amplifier circuit.

Problems to be Solved by the Invention Discharge current ripple or high frequency power ripple and laser output ripple are in a proportional relationship. In the conventional control method for reducing ripple using the discharge current error amplifier circuit 33 or the high frequency power error amplifier circuit, in order to speed up the response and improve control accuracy, when the gain is increased, rapid discharge occurs. There were problems in that load fluctuations occurred, large ripples occurred, and hunting occurred. In addition, the frequency becomes higher in pulse mode, and the pulse intensity becomes 2
There is a problem in that feedback control cannot be performed when the time is about 00 to 300 uSec. Furthermore, large ripples occur due to rapid fluctuations in the primary power supply voltage, causing hunting. Especially in this case, the ripple may be larger than when no feedback control is performed.

The present invention solves these conventional problems. It is free from ripples and hunting, provides stable laser output even in pulse mode, and is not affected by fluctuations in the primary power supply voltage. It is an object of the present invention to provide a direct current excitation type or high frequency excitation type carbon dioxide gas laser control method and apparatus.

Means for Solving the Problems In order to achieve the above object, the present invention rectifies and smoothes the primary power supply voltage, then performs feedback control so that it becomes a constant DC voltage, and inputs this constant DC voltage to an inverter circuit. The discharge current or high frequency power of each discharge tube is controlled by

The present invention also provides a first error amplifier circuit that performs feedback control so that the DC voltage obtained by rectifying and smoothing the primary power supply voltage becomes a constant voltage, and a second error amplifier circuit that performs feedback control so that the laser power is constant. and a third error amplifier circuit that performs feedback control so that the discharge current or high frequency power of each discharge tube is constant, and the response time in each feedback control is appropriately determined.

Effect of the Invention According to the above configuration, the rectified and smoothed voltage is made constant after rectifying and smoothing the primary power supply voltage, so that the response of the discharge current error amplifier circuit or the high frequency power error amplifier circuit is made gentle or slow. In addition, since the gain can be set low, it is possible to prevent ripples and hunting from occurring in feedback control due to rapid fluctuations in discharge load. Further, even in the pulse mode, it is possible to prevent adverse effects in feedback control with high response and high gain, that is, overshoot and undershoot at the rise of the pulse. Furthermore,
Even if there is a sudden change in the primary power supply voltage, since the rectified and smoothed voltage after smoothing is made constant, it is possible to prevent ripples from occurring.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, unlike the conventional example shown in FIG. 4, a constant voltage feedback circuit is provided between the smoothing circuit on the primary power supply side and the inverter circuit. Since the only difference is that they are inserted, the same elements as in the conventional example will be described with the same reference numerals.

FIG. 1 shows a control block of a DC excitation type carbon dioxide laser control device in one embodiment of the present invention. In Fig. 1, 21 is a three-phase 200V commercial power supply, 22 is a rectifier, 23 is a smoothing circuit, and 38 is a power MO3-FET.
39 is a high-speed chopper circuit using a flywheel diode, 40 is a constant voltage setting circuit, 4
1 is the first error amplifier circuit, 42 is the frequency control circuit (P
WM (fM)), 43 is the driver circuit, 24 is the power M
25 is a high-voltage transformer, 26 is a rectifier, 27 is a high-voltage capacitor, 28 is a discharge tube of a carbon dioxide laser oscillator,
29 is a discharge current detection circuit such as a CT (current transformer or shunt resistor).

Further, 30 is a laser power setting circuit, 31 is a laser power detection circuit, 32 is a second error amplifier circuit, and 33 is a third error amplifier circuit.
34 is a frequency control circuit (PWM (f
M)), 35 is a driver circuit. 36 is the discharge tube 28
37 is a control block for other discharge tubes. The output of the smoothing circuit 39 is input to the inverter circuit 24 of the control block 36 and also to an inverter circuit (not shown) of another control block 37.

Next, the operation of the above embodiment will be explained. In FIG. 1, a three-phase 200V AC voltage from a commercial power supply 21 is rectified by a rectifier 22 and then smoothed by a smoothing circuit 23, and the smoothed DC voltage is supplied to a chopper circuit 38 and converted into a high-frequency voltage. converted. The output of the chopper circuit 38 is input to three smoothing circuits and smoothed, and the output of the smoothing circuit 39 is input to the first error amplifier circuit 41 together with the output of the constant voltage setting circuit 40. In the first error amplifier circuit 41, the difference between the input output voltage from the smoothing circuit 39 and the output voltage from the constant voltage setting circuit 40 is converted into a frequency control circuit 42.
is input, and the frequency control circuit 42 drives the power of the chopper circuit 38 ~40SFET through the driver circuit 43 so that the difference becomes zero.

The DC voltage regulated in this manner is supplied to the inverter circuit 24, and the output of the inverter circuit 24 drives the high voltage transformer 25. After the secondary voltage of the high voltage transformer 25 is rectified by the rectifier 26, the high voltage capacitor 27
smoothed. The smoothed DC high voltage of the second discharge tube 2
The discharge current applied to the discharge tube 8 and flowing through the discharge tube 28 is detected by a discharge current detection circuit 29.

On the other hand, the output of the laser power setting circuit 30 and the output of the laser power detection circuit 31 that detects the magnitude of the laser power are input to the second error amplifier circuit 32. The output of the second error amplifier circuit 32 is input to the third error amplifier circuit 33 together with the output from the discharge current detection circuit 29 described above.

The output of the third error amplifier circuit 33 is the frequency control circuit 3
4, and the frequency control circuit 34 is input to the driver circuit 3.
5, the power MOS-FET of the inverter circuit 24 is driven so that the laser power is constant and the discharge current is constant.

Although FIG. 1 shows the case where there are two discharge tubes, in the case of four discharge tubes, in addition to the control block 36 containing the discharge tube 28, three control blocks 37 for other discharge tubes are required. This results in a total of 4 blocks. Similarly, six discharge tubes may be used.

The switching frequency of the chopper circuit 38 is, for example, 30
kHz to 50kHz is selected, and the inverter circuit 24
The switching frequency is, for example, 10kHz to 4QkHz.
z is selected.

The response of the laser power detection circuit 31 is about 100 Hz.

The response of the discharge current detection circuit 29 is 1QkHz to 20kHz.
It is about Hz.

The responsiveness of the discharge current flowing through the discharge tube 28 varies depending on the discharge state, but is approximately 5 kHz to 20 kHz.

In the case of the conventional configuration without the chopper circuit TS38, a ripple of 360H2 occurs in the smoothed voltage of the smoothing circuit 23, and this ripple appears in the discharge current even without feedback control by the third error amplifier circuit 33. . As a result, the discharge current ripple and the laser output ripple are in a proportional relationship, which adversely affects laser processing. Conventionally, attempts have been made to solve this problem by increasing the gain in order to improve the response of the third error amplifier circuit 33 and increase the control accuracy.However, as mentioned above, since the load is a discharge load, performing feedback control Large ripples and hunting will occur in the current. Also, depending on the winding specifications of the high voltage transformer 25, in order to obtain high voltage, 2
Increasing the number of turns in the next winding increases inductance, which also makes it difficult to maintain stability in feedback control.

In contrast, according to this embodiment, the constant voltage feedback circuit including the chopper circuit 38 is provided in a completely different location from the discharge current feedback circuit, so that stable feedback control can be performed. In addition, since it is possible to supply a ripple-free voltage to the inverter circuit 24 and eliminate the instability of feedback control caused by the instability of the discharge load, the third error amplifier circuit 3
It is possible to slow down the response of 3 and set the gain to a level low enough to cause no practical problems.

Furthermore, because of the slow response and low gain of the third error amplifier circuit 33, overshoot and undershoot at the rise of the pulse can be prevented even in the pulse mode.

Furthermore, due to the slow response and low gain of the third error amplifier circuit 33, no problem arises with respect to wear and tear on the electrodes of the discharge tube.

On the other hand, the feedback control response time of the first error amplifier circuit 41 is t1, and that of the second error amplifier circuit 32 is t1.
1. When that of the third error amplifier circuit 33 is set to t3, priority is given to constant voltage feedback control so that tl<tl<
By setting the relationship of ja or j+<ja<tl, stable feedback control of the discharge current can be realized. In other words, it is not affected by fluctuations in the power supply voltage, and even if there is a fluctuation in the discharge load, the discharge current does not fluctuate more than that fluctuation.Furthermore, the fluctuation in the discharge load is as fast as 5kHz to 20kHz, so the laser There is no practical effect on processing, because ripples of about 2.5 kHz or less affect laser processing.

As described above, according to the embodiment, by performing high-speed constant voltage feedback control and controlling the entire device with low-speed current feedback, it is possible to reliably obtain stable discharge current and laser output. As a result, as shown in FIG. 2, the discharge power supply waveform of this embodiment becomes as shown in (b) in contrast to the conventional discharge current waveform (a).

The above embodiment is an example in which the present invention is applied to a direct current excitation type carbon dioxide laser control device. However, the present invention also involves injecting high frequency output into a discharge tube and generating laser light from a gas medium excited by the high frequency discharge. The present invention can be similarly applied to a high-frequency excitation type carbon dioxide laser control method and apparatus having a plurality of discharge tubes, and similar effects can be obtained. In this case, the "discharge current" of the discharge tube in the above embodiment shall be read as "high frequency power", and the "discharge current detection circuit" shall be read as "high frequency power detection circuit".

Effects of the Invention As described above, according to the present invention, the single-blow type B voltage is rectified and smoothed, and then feedback control is performed so that it becomes a constant DC voltage, and this constant DC voltage is input to the inverter circuit to power each discharge tube. Since the discharge current or high frequency power of the discharge current error amplifier circuit or the high frequency power error amplifier circuit can be controlled, the response of the discharge current error amplifier circuit or the high frequency power error amplifier circuit can be made gradual or slow, and the gain can be set low. This makes it possible to prevent ripples and hunting from occurring in feedback control due to fluctuations in discharge load. Further, even in the pulse mode, it is possible to prevent adverse effects caused by feedback control with high response and high gain, that is, overshoot and undershoot at the rise of the pulse. Furthermore, even if there is a sudden change in the primary power supply voltage, since the rectified and smoothed voltage after smoothing is made constant, it is possible to prevent ripples from occurring.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram of a DC excitation type carbon dioxide laser control device according to an embodiment of the present invention, and FIG. 2 is a discharge current waveform diagram showing the effects of the device shown in FIG. 1 in comparison with a conventional example.
FIG. 3 is a schematic perspective view showing the configuration of a conventional DC pumped carbon dioxide laser oscillator, and FIG. 4 is a control block diagram of a control device for the carbon dioxide laser oscillator shown in FIG. 21... Commercial power supply, 22... Rectifier, 23... Smoothing capacitor, 24... Inverter circuit, 25...
High voltage transformer, 26... Rectifier, 27... High voltage capacitor, 28... Discharge tube, 29... Discharge current detection circuit, 3o... Laser power setting circuit, 31... Laser power setting circuit, 32... second error amplifier circuit,
33...Third error amplifier circuit, 34...Frequency control circuit, 35...Driver circuit, 36.37...Control block for discharge tube, 38...Chopper circuit, 3
9... Smoothing circuit, 40... Constant voltage setting circuit, 41.
. . . first error amplifier circuit, 42 . . . frequency control circuit, 43 . . . driver circuit. Name of agent Patent attorney Masahiro Kura Figure 2 f = effect = 360Hz

Claims (4)

[Claims] (1) In a DC-excited carbon dioxide laser control method equipped with a plurality of discharge tubes that applies a high DC voltage to the discharge tube and generates laser light from a gas medium excited by DC glow discharge, the primary power supply voltage is rectified. 1. A carbon dioxide laser control method, which comprises smoothing, then feedback control to obtain a constant DC voltage, and inputting this constant DC voltage to an inverter circuit to control the discharge current of each discharge tube. (2) In a method for controlling a high-frequency excited carbon dioxide gas laser equipped with a plurality of discharge tubes that injects high-frequency output into the discharge tube and generates laser light from a gas medium excited by the high-frequency discharge, the primary power supply voltage is rectified and smoothed. , then feedback control is performed to obtain a constant DC voltage, and this constant DC voltage is input to an inverter circuit to control high frequency power injected into each discharge tube. (3) In a DC-excited carbon dioxide laser control device equipped with multiple discharge tubes that applies a high DC voltage to the discharge tube and generates laser light from a gas medium excited by DC glow discharge, the primary power supply voltage is rectified. a first error amplifier circuit that performs feedback control to smooth the rectified and smoothed voltage so that it becomes a constant voltage; and a second error amplifier circuit that performs feedback control so that the laser power is constant;
and a third error amplifier circuit that performs feedback control to keep the discharge current flowing through each discharge tube constant, and the feedback control response time of the first error amplifier circuit is t.
_1, when the feedback control response time of the second error amplifier circuit is t_2 and the feedback control response time of the third error amplifier circuit is t_3, these times t_1, t_2, and t_3 are t_1<t_2<t_3
Or, a carbon dioxide laser control device characterized in that it is set so that t_1<t_3<t_2. (4) In a high-frequency excitation type carbon dioxide laser control device equipped with a plurality of discharge tubes that inject high-frequency output into the discharge tube and generate laser light from a gas medium excited by the high-frequency discharge, the primary power supply voltage is rectified and smoothed. , a first error amplifier circuit that feedback-controls the rectified and smoothed voltage so that it becomes a constant voltage, a second error amplifier circuit that feedback-controls the laser power so that it becomes constant, and injects it into each discharge tube. and a third error amplifier circuit that performs feedback control to keep the high frequency power constant, the feedback control response time of the first error amplifier circuit is t_1, and the feedback control response time of the second error amplifier circuit is t_2. , when the feedback control response time of the third error amplifier circuit is t_3, these times t_1, t_2, and t_3 satisfy t_1<t_2<t_
3 or t_1<t_3<t_2.