JPH07154020A - Laser output control method - Google Patents

Abstract

PURPOSE:To obtain a stabilized output having short rising and falling times by operating a current feedback control system having high response from the start of rising of pulse whereas feeding a micro discharge current under open loop control from the start of falling of pulse until the end of laser output thereby suppressing fluctuation in the waveform at the time of rising. CONSTITUTION:A comparator 13 compares a signal, obtained by averaging a reference pulse signal from a laser output reference signal generator 11 through an average value operating unit 12, with a feedback signal of laser output from an average value operating unit 10. The difference is amplified by an error amplifier 14 and a laser output feedback control loop is operated to sustain a constant average value of laser output. An electronic switch 19 is turned OFF from the start of falling of the output pulse signal from a multiplier 15 and the current feedback control loop is opened. Consequently, an open loop control system is operated by an output signal from a base current reference signal generator 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a laser output control method for feedback controlling the laser output of a carbon dioxide gas laser oscillator based on a pulsed laser output reference signal and the discharge current in a discharge tube.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram of a conventional laser output controller for a carbon dioxide gas laser oscillator. In the figure, a laser gas is supplied into a discharge tube 2 of a laser oscillator 1, and a high voltage is applied between an anode electrode 3 and a cathode electrode 4 from a high voltage DC power source 22 to discharge the laser gas and excite it by the discharge. The laser light 7 is output from the output mirror 5. Here, when the output of the laser light 7 is P and the discharge current flowing through the discharge tube 2 is I, this relationship is as shown in FIG. When the discharge current I exceeds the laser output start current I0, the laser output P monotonically increases as the discharge current I increases. Therefore, it is possible to control the laser output P by controlling the discharge current I. If the discharge current I is pulsed, the laser output P can also be pulsed.

A power monitor laser beam 8 for monitoring the laser beam 7 is output from the power monitor mirror 6 and input to a laser output detector 9. The signal output from the laser output detector 9 (FIG. 5B) is fed back to the comparator 13 and compared with the pulse signal (FIG. 5A) output from the laser output reference signal generator 11. Comparator 13
Is output to the comparator 17 through the error amplifier 14 and is compared with the output signal of the discharge current detector 23 that detects the discharge current I (FIG. 5D) flowing through the discharge tube 2. The output signal of the comparator 17 is amplified by the error amplifier 18 and input to the high voltage DC power supply 22, and the feedback signal from the laser output detector 9 is used as a reference for the output signal of the laser output reference signal generator 11. Feedback control is performed so as to match the output signal of the generator 11, and the output current of the high-voltage DC power supply 22, that is, the discharge current I
Is feedback-controlled so that the output signal of the error amplifier 14 coincides with the output signal (FIG. 5C).

A feedback control system for controlling the laser output P at a constant level is called a laser output feedback control system, and a feedback control system for controlling the discharge current I at a constant level is called a current feedback control system. As described above, the conventional laser output control device has the current feedback control system as a minor loop in the loop of the laser output feedback control system, and uses the pulse signal output from the laser output reference signal generator 11 as a reference. The laser output can be controlled by controlling the discharge current I in the discharge tube of the oscillator.

[0005]

The wavelength of the laser beam 7 output from the carbon dioxide gas laser oscillator is about 10 μm, and as a device for detecting the laser output P of this wavelength, there are two types.
Divided into two groups. One is a photoconductive detector using HgCdTe, which has a short detection time of the laser output P.
Since it is expensive, it is rarely used in laser output control devices. The other group is a thermal detector using a bolometer, a thermopile, etc., which is inexpensive, but the detection time of the laser output P is longer than several milliseconds. Generally, in the conventional apparatus, the latter thermal type detector, which is inexpensive, is used as the laser output detector 9. For this reason, in the laser output control device of the prior art in FIG. 3 having the laser output detector 9 having a long detection time of the laser output P, the response of the laser output feedback control system becomes longer than several milliseconds.

On the other hand, the responsivity of the current feedback control system having the discharge current detector 23 in which the discharge current I can be easily detected by a resistor and the discharge current detection time is short can be set to about 0.1 msec. Therefore, even if the voltage of the commercial power source input to the high-voltage DC power source 22 fluctuates, or if the discharge current I fluctuates due to changes in the gas temperature and the gas flow rate in the discharge tube 2, the laser output reference signal can be handled. The discharge current I is controlled to be constant. However, when controlling a laser output P having a pulse width of several milliseconds or less with a conventional device, the laser output feedback control system has a slow response, so the laser output P
The pulse waveform of 1 was blunted, and a pulse output of 1 kHz or higher could not be obtained at all.

Further, as shown in FIG. 5, when the discharge current I becomes zero and the discharge is interrupted, it passes through the unstable discharge region near the discharge start current at the rise of the next pulse, so the waveform of the discharge current I at the rise Is different for each pulse, and as a result, variations occur in the waveform of the laser output P at the rising edge of each pulse.

[0008]

In order to solve the above conventional problems, in the laser output control method of the present invention, the laser output of the carbon dioxide gas laser oscillator based on the pulsed laser output reference signal and the discharge current in the discharge tube are measured. Targeting a laser output control method that feeds back, the signal output by comparing the average value of the laser output reference signal with the average value of the laser output is multiplied by the laser output reference signal to output the laser output by the pulse signal output. Feedback control,
From the start of the rise of the pulse signal to the start of the fall, the pulse signal is compared with the discharge current by the signal output and the discharge current is feedback controlled with faster response than the feedback control of the laser output. From the start of the falling of the pulse signal to the start of the next pulse signal, the open loop control is performed so that a minute discharge current that does not interrupt the discharge flows.

[0009]

According to the laser output control method of the laser output control apparatus having the above-described structure, the laser output reference signal is a signal obtained by comparing and amplifying the average value of the pulsed laser output reference signal and the average value of the laser output P. The pulse signal obtained by multiplying the signals becomes a pulse signal with a short rise time and a short fall time, and the desired laser output P can be obtained by operating the laser output feedback control system with this pulse signal. Further, by operating the current feedback control system having a high responsiveness from the start of the rise of the pulse on the basis of this signal, it is possible to obtain the pulsed discharge current I having the short rise time. Further, from the start of the falling edge of this signal to the start of the rising edge of the next pulse signal at the end of the laser output zero, the operation of the current feedback control system is interrupted, and a minute discharge current is flown by open loop control. Since no undershoot occurs in the discharge current I when the pulse falls, the discharge is not interrupted. Therefore, the discharge current I with a short pulse fall time can be obtained, and the current feedback control system is operated again from the time when the next pulse starts to the time when the pulse starts to fall. Dispersion of the discharge current I can be reduced, and a constant and stable pulsed discharge current I can be passed. As described above, it is possible to suppress variations in the waveform of the laser output P at the time of rising, and to obtain a stable pulsed laser output P with a short rising time and falling time.

[0010]

1 is a block diagram of an apparatus for carrying out a laser output control method for a carbon dioxide laser oscillator according to the present invention.
FIG. 2 is a time chart showing the operation of each unit. In FIG. 1, a laser gas is supplied into a discharge tube 2 of a laser oscillator 1, and a high voltage is applied between an anode electrode 3 and a cathode electrode 4 from a high voltage DC power supply 22 to discharge the laser gas and excite it by the discharge. The laser light 7 is output from the output mirror 5.

The power monitor laser beam 8 is output from the power monitor mirror 6 and input to the laser output detector 9.
The signal output from the laser output detector 9 (Fig. 2 (c))
Are averaged by the average value calculator 10 and fed back to the comparator 13. In the comparator 13, the pulsed laser output reference signal (FIG. 2A) output from the laser output reference signal generator 11 is averaged by the average value calculator 12 (FIG. 2B), that is, The average value of the laser output reference signal and the output signal from the average value calculator 10 (see FIG. 2).
(D)) The feedback signal corresponding to the average value of the laser output P is compared, and the difference is amplified by the error amplifier 14 so that the average value of the laser output P becomes constant. Works. The signal output from the error amplifier 14 (FIG. 2E) becomes a DC signal with a small pulsation width by the average value calculators 10 and 12, and is input to the multiplier 15.

On the other hand, the pulsed laser output reference signal output from the laser output reference signal generator 11 is also input to the multiplier 15 and is multiplied by the signal output from the error amplifier 14. Therefore, the pulse signal (FIG. 2 (f)) output from the multiplier 15 has a pulse waveform with a short rise time and fall time similar to the laser output reference signal, and this signal is the output current of the high-voltage DC power supply 22. That is, it becomes a reference signal of the current feedback control system for controlling the discharge current I to be constant, and operates as follows.

The signal output from the multiplier 15 is the comparator 1
7 and is compared with the output signal (FIG. 2 (j)) of the discharge current detector 23 that detects the discharge current I flowing through the discharge tube 2. The output signal of the comparator 17 is amplified by the error amplifier 18 and input to the electronic switch 19. Electronic switch 1
9 has a function of sending or stopping the output signal of the error amplifier 18 (FIG. 2 (g)) to the adder 20 of the next stage by turning on and off. Turn on this electronic switch 19
The signal to turn off (FIG. 2 (h)) is controlled by the pulse rise / fall detector 16 as follows. The pulse rise / fall detector 16 detects the rise and fall of the pulse signal output from the multiplier 15, and turns on the electronic switch 19 from the start of the rise of the pulse signal to the start of the fall of the pulse signal. A signal for turning on the electronic signal is output to the electronic switch 19, and a signal for turning off (cutting off) the electronic switch 19 is output to the electronic switch 19 from the start of falling of the pulse signal to the start of rising of the next pulse signal. It

In the adder 20, the output signal of the error amplifier 18 output from the electronic switch 19 and having a short fall time and the signal output from the base current reference signal generator 21 are added to each other to generate a high voltage direct current. It is output to the power supply 22 as a control signal (FIG. 2 (i)). Here, the signal output from the base current reference signal generator 21 is a discharge current Ib (Fig. 2 (j)) that does not interrupt discharge when the laser output P (Fig. 2 (k)) shown in Fig. 2 is zero. ) Is a signal corresponding to
Here, Ib is referred to as a base current. This base current I
There is a relation of Is <Ib <I0 between b, the discharge start current Is and the laser output start current I0 at which the laser output P starts to output.

As shown in FIG. 2, from the start of the falling edge of the pulse signal output from the multiplier 15 to the start of the rising edge of the next pulse at the end of the laser output zero, the electronic switch 19 is turned off and the discharge is started. Since the loop of the current feedback control system for controlling the current I to be constant is broken at the electronic switch 19, the current feedback control system does not operate, and the open loop control system is controlled by the signal output from the base current reference signal generator 21. Works. Therefore, at the fall of the pulse signal, no undershoot occurs in the discharge current I, and the discharge current I immediately becomes the base current Ib without interruption.

By the way, since the discharge current detector 23 can use a resistor or the like and can detect the discharge current I in a short time, the response of the current feedback control system can be made a high-speed response of 0.1 msec or less. . In order to shorten the rise time of the pulsed laser output P, it is preferable to make the response of the current feedback control system as fast as possible. Multiplier 1
From the start of the rise of the pulse signal output from 5 to the start of the fall, the electronic switch 19 is turned on, a high-speed response is possible, and the loop of the current feedback control system for controlling the discharge current I at a constant level is the electronic switch 19. Since the parts are connected, the current feedback control system operates, and the discharge current I has a short rise time and a pulse waveform with a small waveform variation. Therefore, it is possible to reduce variations in the waveform of the laser output P at the time of rising, and to obtain a pulsed laser output P with a short rise time and a short fall time.

[0017]

As described above, in the laser control method for obtaining the pulsed laser output according to the present invention, the variation in the waveform at the rise of the laser output can be reduced, so that the laser processing using the carbon dioxide laser oscillator is performed. It is possible to suppress variations in processing quality such as drilling and cutting of wood and metal by the machine, and to minimize processing failures due to defective quality. In addition, since it is possible to obtain a pulse output with a short rise time and a short fall time of the laser output, it is possible to output a pulse output of 1 kHz or more and a short pulse width, which could not be achieved in the past, and a wide range of pulse processing conditions of the laser processing machine. Therefore, processing applications such as drilling and cutting can be expanded.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus for carrying out a laser output control method for a carbon dioxide laser oscillator according to the present invention.

FIG. 2 is a time chart showing the operation of each part of the laser output control device shown in FIG.

FIG. 3 is a block diagram of a conventional laser output control device for a carbon dioxide laser oscillator.

FIG. 4 is a characteristic diagram showing a relationship between a discharge current I and a laser output P.

5 is a time chart showing the operation of the laser output control device shown in FIG.

[Explanation of symbols]

 1 Laser Oscillator 2 Discharge Tube 3 Anode Electrode 4 Cathode Electrode 5 Output Mirror 6 Power Monitor Mirror 7 Laser Light 8 Power Monitor Laser Light 9 Laser Output Detector 10, 12 Average Value Calculator 11 Laser Output Reference Signal Generator 13, 17 Comparator 14, 18 Error amplifier 15 Multiplier 16 Pulse rising / falling detector 19 Electronic switch 20 Adder 21 Base current reference signal generator 22 High voltage DC power supply 23 Discharge current detector P Laser output I Discharge current Ib Base current I0 laser output start current

Claims (1)

[Claims] 1. A laser output control method for feeding back a laser output of a carbon dioxide gas laser oscillator based on a pulsed laser output reference signal and a discharge current in a discharge tube, wherein an average value of the laser output reference signal and an average of the laser output. The signal output is compared with the value, while the laser output is feedback-controlled by the pulse signal output by being multiplied by the laser output reference signal, the pulse signal from the rising start to the falling start of the pulse signal. A signal and the discharge current are compared and outputted, and the discharge current is feedback-controlled by making the response faster than the feedback control of the laser output, and the rising of the next pulse signal from the start of the falling of the pulse signal. Up to the start, open loop control is performed so that a minute discharge current that does not interrupt the discharge flows. Laser output control method.