JP2821764B2 - Gas laser oscillator - Google Patents

Description

The present invention relates to a high-power gas laser oscillation device for processing,
In particular, the present invention relates to a gas laser oscillation device having a laser gas pressure control device that prevents a change in laser gas pressure during processing.

[Conventional technology]

Recent gas laser oscillating devices provide high output and good laser beam quality, and have been widely used for laser processing such as cutting of metal or nonmetal material and solution of metal material. In particular, as a CNC laser processing machine combined with a CNC (numerical control device), it is rapidly developing in the field of cutting complicated shapes at high speed and with high accuracy.

Hereinafter, a conventional gas laser oscillation device will be described with reference to the drawings.

FIG. 3 is a diagram showing the entire configuration of a conventional gas laser oscillation device. An appropriate amount of laser gas is sealed in the discharge tube 1. At both ends of the discharge tube 1, an optically resonating product constituted by optical components of a total reflection mirror 5 and an output coupling mirror 6 is installed. Metal electrodes 2 and 3 are mounted on the outer circumference of the discharge tube 1. The metal electrode 3 is grounded, and the metal electrode 2 is connected to a high frequency power supply 4. Metal electrode 2
A high-frequency voltage is applied from a high-frequency power supply 4 between the first and third power supplies. As a result, a high-frequency glow discharge occurs in the discharge tube 1 and laser excitation is performed.

In a high-power laser oscillation device such as such a gas (CO ₂ ) laser oscillation device, a laser gas is forcibly circulated by a blower 9 to cool the laser gas. Because, in a gas gas laser, about 20% of the injected electric energy is converted into laser light, and the other is consumed for gas heating. However, according to the theory, since the laser oscillation gain is proportional to the absolute temperature T raised to the power of-(3/2), it is necessary to forcibly cool the laser gas in order to increase the oscillation efficiency.

In this device, the laser gas flows at a flow rate of about 200 m / sec.
And flows in the direction indicated by the arrow, and flows through the heat exchanger 7 for cooling.
It is led to. The heat exchanger 7 mainly removes heating energy due to discharge from the laser gas. Then, the blower 9 compresses the cooled laser gas. The compressed laser gas is led to the discharge tube 1 via the heat exchanger 8. this is,
This is for removing the heat of compression generated in the blower 9 by the heat exchanger 8 before being guided again to the discharge tube 1. Since these heat exchangers 7 and 8 are well known, detailed description is omitted.

When the gas laser oscillation device is started, first, the entire gas inside the device is exhausted by the vacuum pump 10.
Next, a needle valve with an appropriate conductance
Laser gas of a predetermined flow rate through the laser gas cylinder 14
The gas pressure in the apparatus reaches a specified value. Thereafter, evacuation by the vacuum pump 10 and introduction of replenishment gas by the needle valve 13 continue, and a part of the laser gas is continuously replaced with fresh gas while the gas pressure in the apparatus is kept at a specified value. This also prevents gas contamination in the device.

The numerical controller 20 controls output of the gas laser oscillator, table movement of the laser processing machine, and the like.
In this drawing, a table, a servo amplifier, a servomotor, and the like on the laser processing machine side are omitted.

The pressure control of the laser gas in the discharge tube 1 by the numerical controller (CNC device) 20 is performed as follows. Pressure sensor 12
Detects the gas pressure in the discharge tube 1, converts it into a voltage signal, and outputs it to the A / D converter 21 in the numerical controller 20.

The A / D converter 21 converts the analog voltage from the pressure sensor 12 into a digital signal and outputs the digital signal to the gas pressure control means 22. The gas pressure control means 22 compares the set value of the gas pressure setting means 25 with the digital signal of the A / D converter 21 and sends a digital control signal such that the deviation becomes zero to the D / A converter 23. Output. In the gas pressure setting means 25, an appropriate pressure value of the discharge tube 1 is stored in a nonvolatile memory or the like in advance.

The D / A converter 23 converts the control signal from the gas pressure control means into an analog value and outputs the analog value to the driver 24 of the variable leak valve 11. The driver 24 drives the variable leak valve 11 according to the output of the D / A converter 23, and controls the conductance.

[Problems to be solved by the invention]

The conventional gas laser oscillation device shown in FIG. 3 has the following problems.

The control system of the laser gas pressure by the numerical controller 20 as described above can provide sufficient control characteristics when the laser oscillation operation of the laser oscillation device is in a steady state. However, when actually performing laser processing, the discharge of the laser oscillation device is frequently turned on and off, or the discharge current value is changed. Therefore, there is a certain transient response immediately after the change in the discharge state during such laser processing. This is because the conductance of the laser gas in the discharge tube 1 with respect to the flow of the laser gas flowing in the discharge tube 1 changes as a function of the gas temperature in the discharge tube 1 due to the decrease in viscosity when the gas temperature rises.

This relationship will be described with reference to FIG. FIG. 4 is a diagram showing the relationship between the compression ratio and the gas flow rate at the entrance and exit of the blower 9 when the discharge input is 0% and 100%. Since the discharge tube 1 is designed to have the maximum gas flow resistance in the gas circulation path of the ordinary gas laser oscillation device, the compression ratio in FIG. 4 may be considered as the compression ratio for the discharge tube 1. .
This figure shows the characteristics when a Roots blower is used for the blower 9, so that the gas flow rate is actually unchanged, and only the compression ratio changes depending on the presence or absence of discharge (0% or 100% discharge). Since this change depends on the gas temperature, it occurs with a very small time constant of about several milliseconds. Therefore, when the discharge state is controlled during the control of the laser output, the compression ratio also changes between the point A and the point B as shown in FIG.

For simplicity, it is assumed that the discharge has simply turned on and off. FIG. 5 shows how the pressure sensor 12 changes at that time. FIG. 5 shows a pressure sensor based on a change in the discharge state.
FIG. 12 is a diagram illustrating an output of Twelve. In the figure, the horizontal axis represents time, and the vertical axis represents laser gas pressure, which is the output of the pressure sensor 12.
In the present specification, the term “discharge off” refers to a preliminary discharge state,
That is, it means a discharge within a range in which laser oscillation does not occur, and is used in a sense different from the 0% discharge in FIG.

As is apparent from FIG. 5, pressure spikes are generated in the positive and negative directions at the moment of on and off of the discharge, respectively. That is, the laser gas pressure is at a constant value during no discharge (discharge off), and the compression ratio at both ends of the discharge tube 1 increases at the same time when the discharge is turned on. Therefore, since the gas pressure in the pressure sensor 12 is on the low pressure side, the gas pressure decreases. When the measured value of the pressure sensor 12 deviates from the specified value, the numerical controller
By the operation of the gas pressure control means 22, the gas pressure in the discharge tube 1 eventually reaches a predetermined value. Therefore, a spike in the negative direction occurs at the moment when the discharge changes from discharge-off to discharge-on. Due to the opposite phenomenon, a spike in the positive direction is generated at the moment when the discharge changes from on to off.

Since the spikes in the positive and negative directions depend on the magnitude of the discharge, at the time of a strong discharge as shown in FIG.
Significant spikes occur.

The spike in the positive direction (spike generated when the discharge changes from discharge on to discharge off) has a problem that the preliminary discharge is erased. Further, a spike in the negative direction (a spike generated when the discharge changes from discharge-off to discharge-on) appears directly in the laser output, and thus has a problem in that the accuracy of laser processing is affected. That is, the time constant for decreasing the spike is a value (1) determined by the characteristics of the gas pressure control means 22.
~ 10 seconds), laser cutting of laser processing machine is 6m / m
If performed in, it will be affected by spikes over an area of about 10 cm.

The present invention has been made in view of such a point,
It is an object of the present invention to provide a gas laser oscillation device that prevents spikes due to a transient response of a gas pressure control unit that occurs immediately after a discharge is turned on or off, and has no transient fluctuation in laser oscillation characteristics.

[Means for solving the problem]

In order to solve the above problems, the present invention provides a discharge tube that is laser-excited by a gas discharge, a power supply that supplies power for generating the gas discharge, an optical resonator that performs laser oscillation, a blower, and a heat source. A gas circulation device that forcibly cools the laser gas by an exchanger,
A laser device configured to detect a gas pressure in the discharge tube and control the gas pressure in the discharge tube to a predetermined value, wherein the control device performs gas pressure control in a closed loop by the detected gas pressure during a preliminary discharge state. Further, a gas laser oscillation device is provided which is fixed at a control constant immediately before laser discharge occurs during a laser discharge state.

[Action]

During the pre-discharge state, gas pressure control by a normal closed loop is executed, and the gas pressure is fixed while laser discharge is occurring (when discharge is on). Therefore, the gas pressure during the laser discharge (when the discharge is on) shows a different decrease in the gas pressure depending on the intensity of the discharge, but the gas pressure is constant and constant for a constant discharge current. Therefore, high-precision laser processing can be performed without any precision error during laser processing. In addition, since no spike occurs in the gas pressure, the disadvantage that the preliminary discharge is cut off does not occur.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration diagram of an embodiment of the laser oscillation device of the present invention. The same components as those in FIG. 3 are denoted by the same reference numerals, and a description thereof will not be repeated.

This embodiment is essentially different from the conventional one in that a command from the high-frequency power supply 4 is sent to the gas pressure control means of the numerical controller 20.
At the same time as the discharge is turned on, the gas pressure control means 22 stops the normal pressure control operation, fixes the control constant immediately before the discharge is turned on, and sets the gas pressure determined by the control constant during the discharge on. is there.

Therefore, when the discharge is changed from the discharge on to the discharge off, the gas pressure control means 22 resumes the normal pressure control operation. Disturbance that disturbs the gas pressure is an extremely slow phenomenon such as a change in the conductance of a valve.In general, during laser processing, the discharge on time is generally shorter than the discharge off time. Even if the pressure control constant is fixed to a predetermined value during the discharge ON as in the present embodiment, the possibility that the gas pressure fluctuates is extremely small.

FIG. 2 is a diagram showing the output of the pressure sensor 12 due to a change in the discharge state when this embodiment is employed. This figure corresponds to FIG. 5 showing a conventional state. As is apparent from this figure, during the discharge-off, the gas pressure in the discharge tube 1 is controlled by the gas pressure control system of the numerical controller 20 so as to be at the discharge-off pressure level. On the other hand, during discharge-on, the pressure control target value remains fixed at the control constant immediately before discharge-on, and pressure control is not performed.
The gas pressure inside is fixed to a pressure level lower than the pressure level at the time of discharge off and according to the strength of discharge.

As described above, this embodiment uses the pressure sensor while the discharge is off.
Pressure control is performed in a closed loop that feeds back the output of 12, and during discharge on, pressure control is performed in an open loop fixed to the control constant immediately before discharge on, and execution and non-execution of the pressure control are switched by the high-frequency power supply 4. The control is performed based on the above command.

According to the present embodiment, the gas pressure when the discharge is on shows a different decrease in the gas pressure depending on the intensity of the discharge, but the gas pressure is constant and does not change for a constant discharge current. High-precision laser processing can be performed without any precision error during processing. In addition, since no spike occurs in the gas pressure, the disadvantage that the preliminary discharge is cut off does not occur.

〔The invention's effect〕

According to the present invention as described above, it is possible to prevent a gas pressure spike generated immediately after discharge on or off,
It is possible to provide a gas laser oscillation device having no transient fluctuation in laser oscillation characteristics.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a laser oscillation device of the present invention, FIG. 2 is a diagram showing an output waveform of a pressure sensor according to a change in a discharge state in the present invention, and FIG. FIG. 4 is a diagram showing the relationship between the compression ratio and the gas flow rate at the inlet and outlet of the blower when the discharge input is 0% and 100%, and FIG. 5 is a diagram showing the change in the discharge state in the prior art. FIG. 3 is a diagram illustrating an output waveform of a pressure sensor. DESCRIPTION OF SYMBOLS 1 ... Discharge tube 2, 3 ... Electrode 4 ... High frequency power supply 5 ... Total reflection mirror 6 ... Output coupling mirror 7, 8 ... Heat exchanger 9 ... Blower 10 ... Vacuum pump 11 ... Variable leak Valve 12 Pressure sensor 13 Needle valve 14 Gas cylinder 20 Numerical control device 21 A / D converter 22 Gas pressure control means 23 D / A converter 24 Driver 25 ... Gas pressure setting means

Claims (3)

(57) [Claims] 1. A discharge tube for exciting a laser by a gas discharge, a power supply for supplying electric power for generating the gas discharge, an optical resonator for performing laser oscillation, and a blower and a heat exchanger for forcing a laser gas. In a laser oscillating device comprising a gas circulating device for cooling to a predetermined temperature and a control device for detecting the gas pressure in the discharge tube and controlling the gas pressure in the discharge tube to a predetermined value, the control device uses the detected gas pressure during a preliminary discharge state. A gas laser oscillation device that performs gas pressure control in a closed loop and fixes the control constant immediately before laser discharge occurs during a laser discharge state. 2. The gas laser oscillation device according to claim 1, wherein the control device executes the gas pressure control and fixes a control constant based on an output of the power supply. 3. The gas laser oscillation device according to claim 1, wherein said discharge is performed by a high-frequency gas discharge.