JPH0410682A - Method and apparatus for controlling laser oscillator - Google Patents

Abstract

PURPOSE:To control an output in a wider range without increasing a discharge- current ripple by a method wherein the switching frequency and the switching-on time of a switching element are controlled properly. CONSTITUTION:A signal of an output-instruction setting circuit 27 is input to a frequency setting circuit 28 and to a continuity-time setting circuit 29. When, inside the continuity-time setting circuit 29, the signal from the output- instruction setting circuit 27 is at a low output of a reference voltage V1 or lower and its output is to be lowered furthermore, the continuity time of a switching element 23 is limited. When the signal is at a high output exceeding the reference voltage V1, it is fixed to the reference continuity time. On the other hand, when, inside the frequency-setting circuit 28, the signal from the output-instruction setting circuit 27 is at a high output exceeding the reference voltage V1 and its output is to be increased furthermore, a switching frequency is increased. When the signal is at a low voltage of the reference voltage V1 or lower, the switching frequency is fixed to a minimum switching frequency. When the switching frequency is controlled so as not to be lowered to 5kHz or lower, it is possible to restrain a discharge-current ripple from being increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for controlling a laser oscillator for generating laser light used for cutting, welding, heat treatment, etc.

2. Description of the Related Art The structure of a conventional general laser oscillator will be explained with reference to FIG. One or more discharge tubes 1a and 1
A laser resonator 1 consisting of a laser resonator 1 is provided with a set of discharge electrodes consisting of an anode 2 and a cathode 3 for each discharge tube la, lb. In Fig. 6, two sets of discharge tubes la, lb
are arranged symmetrically to form a discharge section, and a current is supplied from a switching high-voltage power supply 4 to each discharge electrode 2.3. Further, an output mirror 5 and a termination mirror 6 are arranged at both ends of the laser resonator 1, and a substantially E-shaped circulation tube body 7 is located near the cathode 3 at both ends and near the anode 2 at the center. are connected to form a circulation path for the gaseous laser medium. This circulation pipe body 7 is provided with a blower 8 for circulating the gas laser medium and a heat exchanger 9 for cooling the gas laser medium. The laser resonator 1 also includes an anode 2 and a cathode 3 of each discharge tube la, lb.
A discharge starting auxiliary ring 10 electrically connected to the anode 2 or the cathode 3 is disposed on the outer circumferential portion between the anode 2 and the cathode 3.

FIG. 7 shows the configuration of the switching high voltage power supply 4 in the laser oscillator. After receiving and rectifying the three-phase 200V by the primary rectifier 11, the primary smoothing capacitor 12 reduces voltage ripples, the switching element 13 switches to convert it into a pulse train, and sends power to the high frequency transformer 14. The high-frequency transformer 14 sends power to the secondary side and generates a high voltage on the secondary side, which is rectified by a high-speed high-voltage secondary rectifier 15 and then smoothed by a high-voltage secondary capacitor 16. A voltage is applied to the anode 2 and cathode 3 of the laser resonator 1, respectively.

Inside the laser resonator 1, a glow discharge occurs between the anode 2 and the cathode 3 to excite the internal gas laser medium and generate laser light.

On the other hand, the drive circuit 2Q (Drive circuit) includes an output setting circuit 18 (PWM circuit) that determines the switching-on time based on a command from the output command setting circuit 17, and a switching frequency setting circuit 19 that sets the reference switching frequency. The switching on time and switching frequency are determined based on the signal, and the drive signal is generated. This drive signal is applied to the gate of the switching element 13 to generate a pulse signal.

In a laser oscillator configured in this way, the gas flow direction, the discharge direction, and the laser beam oscillation axis are coaxial, so the discharge and the gain distribution formed by the discharge are concentric when viewed from the optical axis direction. It is said that the symmetry is good, and the performance of processing such as cutting using the output laser light is good.

Problems to be Solved by the Invention However, in such conventional laser oscillators, the output power is controlled by keeping the conduction time of the switching element 13 constant and changing its switching frequency, so that the control range of the output power is limited. There was a problem that the laser output was narrow and the range of variable output of the laser was also narrow. Furthermore, if the laser output is lowered by lowering only the switching frequency of the switching element 13, there is a problem in that the discharge current ripple becomes large in the region where the switching frequency is low, and the laser output fluctuates.

The present invention solves these conventional problems, and by appropriately controlling the switching frequency and switching on time of the switching element, it is possible to control the output over a wider range without increasing the discharge current ripple. An object of the present invention is to provide an oscillator control method and device.

Means for Solving the Problems In order to achieve the above object, the present invention controls the output power by changing the switching frequency when the output is high, and when a specific switching frequency of, for example, 5 kHz or more is reached when the output is low. The switching frequency is fixed, and the conduction time of the switching element is varied to control the output power.

The present invention also controls the output power by changing the switching on time at high output, fixes the switching on time when a specific switching on time is reached at low output, and changes the switching frequency to 5
The output power is controlled by changing it in a range of kHz or more.

The present invention also controls the output power by simultaneously changing both the conduction time and the switching frequency of the switching element.

Effect of the present invention is that the switching frequency is 5k due to the above configuration.
A wide range of output power control can be performed without increasing the discharge current ripple in the region of Hz or higher, and stable laser light output can be obtained.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a control device for carrying out the laser oscillator control method of the present invention, in which 21 is a primary rectifier, 22 is a primary smoothing capacitor, 23 is a switching element, and 24 is a primary side smoothing capacitor. High frequency transformer, 25 is secondary rectifier,
26 is a secondary smoothing capacitor, both ends of which are connected to the discharge electrodes 2 and 3 of the laser resonator 1.

27 is an output command setting circuit, 28 is a frequency setting circuit (FM
29 is a conduction time setting circuit (PWM circuit). The output of the output command setting circuit 27 is transmitted to the frequency setting circuit 28.
and conduction time setting circuit 29.

30 is a frequency setting circuit 28 and a conduction time setting circuit 29
This is a drive circuit that drives the switching element 23 by receiving a signal from the switching element 23.

Next, the operation of the above embodiment will be explained. When AC 200V from the commercial power supply is input to the rectifier 21, first the rectifier 2
1 and smoothed by a smoothing capacitor 22 to become direct current, which is converted into a pulse train by a switching element 23. The switching frequency and switching-on time at this time are controlled by the drive circuit 30.

The pulse output output from the switching element 23 is boosted by the high frequency transformer 24 and then sent to the secondary rectifier 2 again.
5 and smoothed by the secondary smoothing capacitor 26 to become a high voltage direct current, which is applied to the discharge electrodes 2 and 3 of the laser resonator 1. Inside the laser resonator 1, the glow discharge between the discharge electrodes 2 and 3 excites the internal gas laser medium and oscillates a laser beam.

If such a laser oscillator control device is used, various control methods such as those shown in the following embodiments can be implemented simply by changing the program.

Example 1 Next, a first example of the laser oscillator control method of the present invention will be described. The signal from the output command setting circuit 27 is input to a frequency setting circuit 28 and a conduction time setting circuit 29. In the conduction time setting circuit 29, when the signal from the output command setting circuit 27 is low output below a certain reference voltage v1, the conduction time of the switching element 23 is narrowed down to further lower the output, and when the signal is high output exceeding the reference voltage v1, the output is reduced. Fixed to standard conduction time. On the other hand, in the frequency setting circuit 28, the switching frequency is increased to further increase the output when the signal from the output command setting circuit 27 is high output exceeding the reference voltage v1, and the switching frequency is set to the lowest switching frequency when the output is low below the reference voltage V1. Fixed to frequency.

FIG. 2 shows the relationship between discharge current ripple and switching frequency. As is clear from Figure 2, 5kH
When the switching frequency becomes lower than or equal to z, the discharge current ripple increases rapidly, and the laser output fluctuation also increases accordingly. Therefore, by controlling the switching frequency so as not to lower it below 5 kHz, it is possible to suppress the increase in discharge current ripple.

FIG. 3 shows the discharge current characteristics when using the conventional method of controlling the output power by keeping the conduction time of the switching element constant and changing the switching frequency, and the control method according to the present embodiment.

As is clear from this figure, when the discharge current is high and the output power is high, the switching frequency is changed to control the output power, and when the discharge current is low and the output power is low, the switching frequency is controlled at 5kHz.
When the above specific switching frequency fo is reached, the switching element 23
By narrowing the conduction time, the discharge current is lowered and the output power is lowered.

In this way, in the first embodiment, when the output power is high, the switching frequency is changed to control the output power, and when the output power is low, when a certain switching frequency of 5 kHz or more is reached, the switching frequency is fixed.
By narrowing down the conduction time of the switching element 23, a wider range of output control becomes possible without increasing the discharge current ripple.

Example 2 A second example of the laser oscillator control method of the present invention is based on the first example.
The same device as in the first embodiment is used to perform control different from that in the first embodiment. That is, in the conduction time setting circuit 29, when the signal from the output command setting circuit 27 is a high output exceeding a certain reference voltage v2, the conduction time of the switching element is controlled to be extended, and when the signal is low output below the reference voltage v2, the basic conduction time is increased. Fixed to. On the other hand, within the frequency setting circuit 28, the reference voltage v with the signal from the output command setting circuit 27 is
When the output is low (2 or less), the switching frequency is lowered, and when the output is high (over the reference voltage V2), the switching frequency is fixed at the maximum switching frequency fmaX.

That is, as shown in FIG. 4, when the output power is high exceeding the reference voltage V2, the switching frequency is fixed at fmaX and the switching on time is varied to control the output power.
At the time of low output below the reference voltage v2, when a specific switching on time is reached, the switching on time is fixed, and the switching frequency is lowered from f max to control the output power.

In this second embodiment as well, as shown in FIG. 2, it is necessary to control the output power so as not to lower the switching frequency below 5kHz.
By changing in the above range, the output can be controlled over a wider range without increasing the discharge current ripple.

Embodiment 3 In a third embodiment of the laser oscillator control method of the present invention, the same apparatus as in the first embodiment is used to perform control different from that in the first embodiment. In other words, the output command setting circuit 2
7 is input to the frequency setting circuit 28 and the conduction time setting circuit 29 to lower the output power, as shown in FIG. By lowering the switching frequency of the switching element 23 and narrowing the conduction time at the same time, and conversely, when increasing the output power, by increasing the switching frequency of the switching element 23 and at the same time widening the conduction time,
A wider range of output control can be performed without increasing discharge current ripple.

Effects of the Invention As is clear from the above explanation, according to the laser oscillator control method of the present invention, without increasing discharge current ripple,
It is possible to perform wide-range output control, obtain stable laser output, and significantly improve the reliability of laser processing. Further, according to the laser oscillator control device of the present invention, by preparing a plurality of control programs, various control methods can be performed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the laser oscillator control device of the present invention, Fig. 2 is a graph showing the relationship between discharge current ripple and switching frequency in the laser oscillator, and Fig. 3 is the laser oscillator control according to the present invention. Graph showing the output characteristics in the first embodiment of the method together with the conventional example, the fourth
The figure is a graph showing the output characteristics in the second embodiment of the laser oscillator control method according to the present invention, FIG. 5 is a graph showing the output characteristics in the third embodiment of the laser oscillator control method according to the present invention, and FIG. A schematic configuration diagram showing an example of a conventional laser oscillator, and FIG. 7 is a block diagram of a switching high voltage power supply in the conventional example. ■... Laser resonator, 2, 3... Discharge electrode, 4...
・Switching high voltage power supply, 5... Output mirror, 6...
・Terminal mirror, 7... Circulation pipe body, 8... Blower, 9
...Heat exchanger, 10...Discharge start auxiliary ring, 21
...Primary side rectifier, 22...Primary side smoothing capacitor, 23...Switching element, 24...High frequency transformer, 25...Secondary side rectifier, 26...Secondary side capacitor, 27... Output command setting circuit, 28... Frequency setting circuit (FM circuit), 29... Continuation time setting circuit (PWM circuit), 30... Drive circuit. Name of agent Patent attorney Masahiro Kura Go Figure 2 Switch jig frequency (kHz) Figure 3 5 f. Switch puffer frequency (kHz)

Claims (7)

[Claims] (1) In a laser oscillator that generates laser light by exciting a gas laser medium in a laser resonator by discharging a discharge electrode connected to a switching high-voltage power supply, when the output of the laser light is high, the switching frequency of the switching high-voltage power supply is changed. A laser characterized in that the output power is controlled by changing the output power, and when the switching frequency reaches a certain switching frequency when the output is low, the switching frequency is fixed, and the output power is controlled by changing the conduction time of the switching element. Oscillator control method. (2) The laser oscillator control method according to claim (1), wherein the specific switching frequency exists in a region of 5 kHz or more. (3) In a laser oscillator that generates laser light by exciting a gas laser medium in a laser resonator by discharging a discharge electrode connected to a switching high-voltage power supply, when the output of the laser light is high, the switching element in the switching high-voltage power supply It is characterized by controlling the output power by changing the switching on time, fixing the switching on time when a certain switching on time is reached at low output, and controlling the output power by changing the switching frequency. Laser oscillator control method. (4) Switching frequency at minimum output power is 5kHz
The laser oscillator control method according to claim (3), which is the above. (5) In a laser oscillator that generates laser light by exciting a gas laser medium in a laser resonator by discharging a discharge electrode connected to a switching high-voltage power supply, the conduction time and switching frequency of the switching element of the switching high-voltage power supply are controlled. A laser oscillator control method characterized by controlling output power by changing both simultaneously. (6) The laser oscillator control method according to claim (5), wherein the switching frequency is 5 kHz or more. (7) In a laser oscillator that generates laser light by exciting a gas laser medium in a laser resonator by discharging a discharge electrode connected to a switching high-voltage power supply, the switching high-voltage power supply has an output command setting circuit and the output A frequency setting circuit and a conduction time setting circuit that receive an output signal from the command setting circuit, and a drive circuit that drives a switching element of the switching high voltage power supply using the output signal from the frequency setting circuit and the conduction time setting circuit. Laser oscillator control device.