JP7449836B2 - Laser oscillator, laser processing machine, and stimulated Raman scattering suppression method - Google Patents

Description

The present invention relates to a laser oscillator, a laser processing machine, and a method for suppressing stimulated Raman scattering.

In recent years, laser oscillators installed in laser processing machines have become higher in brightness and output, and laser processing machines equipped with laser oscillators with a laser output of 10 kW or more have been introduced into the market. In order to cut a thin sheet metal at high speed with a laser processing machine, it is necessary to irradiate the sheet metal with a high-intensity, well-focused laser beam. For this purpose, it is common to reduce the core diameter of the optical fiber included in the laser oscillator.

When the output of a laser oscillator increases, stimulated Raman scattering, which is one of the nonlinear phenomena of optical fibers, becomes more likely to occur. Hereinafter, stimulated Raman scattering may be abbreviated as SRS. Furthermore, if the core diameter of the optical fiber is made smaller, SRS is more likely to occur. The SRS generation threshold Psrs_th, which is the threshold of the laser power generated by SRS, is the effective core cross-sectional area of the optical fiber Aeff, the polarization factor which is a constant fp, the Raman gain which is a constant Gr, and the effective fiber length of the optical fiber Leff. Then, it is calculated using equation (1).
Psrs_th=16×(Aeff/(fp×Gr×Leff))…(1)

As can be seen from equation (1), when the core diameter of the optical fiber is small, the SRS occurrence threshold Psrs_th becomes small, making it easier for SRS to occur. If the core diameter is increased, the beam quality of the laser beam will deteriorate and the processing quality of the thin plate will be degraded, so the core diameter cannot be increased. If the effective fiber length Leff of the optical fiber is shortened, the SRS generation threshold Psrs_th will increase, but since the feeding fiber included in the laser oscillator has a length of 10 m to 20 m, it is difficult to shorten the effective fiber length Leff. .

JP2020-61512A

When a large amount of SRS occurs in a laser oscillator, the output of the laser beam emitted from the laser oscillator becomes unstable, and the beam quality deteriorates. This will reduce the processing speed or processing quality for cutting the sheet metal. A laser oscillator oscillates a laser beam by performing either a continuous wave (CW) oscillation operation or a pulse oscillation operation. SRS rarely occurs when a laser oscillator performs CW oscillation operation, but it often occurs when a laser oscillator performs pulse oscillation operation. It is required to suppress SRS that occurs when a laser oscillator performs a pulse oscillation operation to oscillate a laser beam.

The present invention provides a laser oscillator, a laser processing machine, and a method for suppressing stimulated Raman scattering that can effectively suppress stimulated Raman scattering that occurs when a laser oscillator performs a pulse oscillation operation to oscillate a laser beam. The purpose is to

The present invention provides a pulse generation section that generates a drive voltage signal consisting of a pulse signal that alternately repeats high and low based on an output command signal that consists of a pulse signal that alternately repeats high and low; a laser oscillation module that performs a pulse oscillation operation to oscillate a laser beam based on the output command signal; When the drive voltage signal has a high voltage value, the voltage value during the high period of the drive voltage signal is maintained in a high state for a preset time from the rise time of the high period of the drive voltage signal, and the voltage value is maintained in the drive voltage value. A sub-pulse is superimposed on the drive voltage signal by modulating it in a pulsed manner so as to alternately repeat a low state in which the voltage signal is lowered by a predetermined voltage value without lowering it to the voltage value in the low period of the voltage signal, and the voltage signal is outputted. When the command signal has a voltage command value corresponding to a laser output that is less than or equal to the predetermined laser output during the high period, the voltage value during the high period of the drive voltage signal is not modulated in a pulse form, and the drive voltage signal To provide a laser oscillator that does not superimpose sub-pulses on the oscillator.

The present invention provides a control device that generates an output command signal consisting of a pulse signal that alternately repeats high and low levels, and a control device that performs a pulse oscillation operation based on the output command signal to oscillate a laser beam and emit the laser beam. and a processing section that processes a sheet metal using a laser beam emitted by the laser oscillator, the laser oscillator comprising a pulse signal that alternately repeats high and low based on the output command signal. The pulse generation unit includes a pulse generation unit that generates a drive voltage signal, and a laser oscillation module that performs a pulse oscillation operation based on the drive voltage signal to oscillate a laser beam, and the pulse generation unit is configured to generate a high output command signal when the output command signal is high. When the voltage command value corresponds to a laser output exceeding a predetermined laser output for a period, the voltage value during the high period of the drive voltage signal is changed for a preset time from the rise time of the high period of the drive voltage signal. , modulated in a pulsed manner so as to alternately repeat a high state in which the voltage value is maintained and a low state in which the voltage value is reduced by a predetermined voltage value without reducing the voltage value to the voltage value during the low period of the drive voltage signal. and superimpose a sub-pulse on the drive voltage signal, and when the output command signal has a voltage command value corresponding to a laser output that is less than or equal to the predetermined laser output during the high period, the high period of the drive voltage signal Provided is a laser processing machine that does not modulate the voltage value of the drive voltage signal into a pulse shape and does not superimpose sub-pulses on the drive voltage signal.

In the present invention, in order to cause a laser oscillator to emit a laser beam, a control device generates an output command signal consisting of a pulse signal that alternately repeats high and low, and the voltage command value during the high period is set by the laser oscillator. Drive configured according to the laser output of the laser beam to be emitted, and in which a pulse generation unit included in the laser oscillator generates a pulse signal that alternately repeats high and low based on the output command signal supplied from the control device. A voltage signal is generated, a laser oscillation module included in the laser oscillator performs a pulse oscillation operation based on the drive voltage signal to oscillate a laser beam, and stimulated Raman scattering occurs during a period in which the output command signal is high. When the voltage command value corresponds to the laser output to be output, the voltage value during the high period of the drive voltage signal generated by the pulse generator is set for a preset time from the rise time of the high period of the drive voltage signal. , modulated in a pulsed manner so as to alternately repeat a high state in which the voltage value is maintained and a low state in which the voltage value is lowered to a voltage value corresponding to a voltage command value corresponding to a laser output that does not cause stimulated Raman scattering, A stimulated Raman scattering suppression method is provided in which a sub-pulse is superimposed on the drive voltage signal.

According to the laser oscillator, laser processing machine, and stimulated Raman scattering suppression method of the present invention, stimulated Raman scattering that occurs when the laser oscillator performs pulse oscillation operation to oscillate a laser beam can be effectively suppressed. .

1 is a diagram illustrating an embodiment of a laser processing machine including an embodiment of a laser oscillator; FIG. 2 is a waveform diagram showing a first example of an output command signal that the NC device 30 in FIG. 1 supplies to the pulse generator 11. FIG. 2A is a waveform diagram showing a drive voltage signal generated by the pulse generation unit 11 to which the output command signal shown in FIG. 2A is input. FIG. FIG. 3 is a waveform diagram showing a second example of an output command signal that the NC device 30 supplies to the pulse generator 11. FIG. 3A is a waveform diagram showing a drive voltage signal generated by the pulse generation section 11 to which the output command signal shown in FIG. 3A is input. FIG. FIG. 3 is a waveform diagram showing a third example of an output command signal that the NC device 30 supplies to the pulse generation section 11. FIG. 4A is a waveform diagram showing a drive voltage signal generated by the pulse generating section 11 to which the output command signal shown in FIG. 4A is input. FIG. FIG. 7 is a partially enlarged waveform diagram for explaining details of a sub-pulse superimposed on a high period of a drive voltage signal. 2 is a waveform diagram showing a laser output when the laser oscillation module 12 in FIG. 1 oscillates a laser beam based on a drive voltage signal that does not superimpose a sub-pulse during a high period, and an output of stimulated Raman scattering generated at that time. FIG. . 2 is a waveform diagram showing a laser output when the laser oscillation module 12 oscillates a laser beam based on a drive voltage signal on which a sub-pulse is superimposed in a high period, and an output of stimulated Raman scattering generated at that time. FIG. Laser output when the laser oscillation module 12 oscillates a laser beam based on a drive voltage signal whose voltage value is uniformly reduced for a predetermined time from the rise time of the high period without superimposing sub-pulses, and at that time FIG. 2 is a waveform diagram showing the output of stimulated Raman scattering generated in FIG. FIG. 6 is a characteristic diagram showing changes in the output ratio of stimulated Raman scattering when the frequency of the output command signal is changed. FIG. 6 is a characteristic diagram showing a change in the ratio of beam parameter products when the frequency of an output command signal is changed.

Hereinafter, a laser oscillator, a laser processing machine, and a method for suppressing stimulated Raman scattering according to one embodiment will be described with reference to the accompanying drawings.

FIG. 1 shows a laser processing machine 100 according to one embodiment. The laser processing machine 100 is a laser cutting machine that cuts a sheet metal W. The laser processing machine 100 may be a laser welding machine that welds the sheet metal W. As shown in FIG. 1, the laser processing machine 100 includes a fiber laser oscillator 10, a process fiber 15, a processing section 20, and an NC device 30. The fiber laser oscillator 10 is a laser oscillator of one embodiment. Process fiber 15 transmits the laser beam emitted by fiber laser oscillator 10 to processing section 20 . The NC device 30 controls the processing of the sheet metal W by the laser processing machine 100. The NC device 30 is an example of a control device that controls the laser processing machine 100. Laser oscillators are not limited to fiber laser oscillators.

The fiber laser oscillator 10 includes a pulse generator 11, a laser oscillation module 12, a feeding fiber 13, and a beam coupler 14. As will be described in detail later, the pulse generation unit 11 generates a drive voltage signal for driving the laser oscillation module 12 based on the output command signal supplied from the NC device 30 and supplies it to the laser oscillation module 12. .

The laser oscillation module 12 has a known configuration including a plurality of laser diodes, a combiner, a high reflection fiber Bragg grating, an active fiber, and a low reflection fiber Bragg grating. The combiner optically combines laser beams emitted from a plurality of laser diodes and transmitted by optical fibers. The core of the active fiber is doped with a rare earth element, typically Yb (ytterbium). A laser beam emitted from the combiner is incident on an active fiber provided between a high reflection fiber Bragg grating and a low reflection fiber Bragg grating.

The laser beam emitted from the active fiber repeatedly goes back and forth between the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating. The low reflection fiber Bragg grating emits a laser beam having a wavelength of 1060 nm to 1080 nm, for example, which is different from the wavelength of the laser beam emitted by the laser diode.

A laser beam emitted from the laser oscillation module 12 is incident on the core of the feeding fiber 13. Feeding fiber 13 transmits the laser beam to beam coupler 14 .

The beam coupler 14 includes a collimating lens 141, a total reflection mirror 142, and a focusing lens 143. The collimating lens 141 collimates the diverging laser beam emitted from the exit end of the feeding fiber 13 and converts it into collimated light. The total reflection mirror 142 totally reflects the incident collimated light and makes it enter the focusing lens 143 . The focusing lens 143 focuses the incident collimated laser beam, converts it into a convergent light, and makes the convergent light enter the core of the process fiber 15 . Process fiber 15 transmits the laser beam to processing section 20 .

The processing section 20 includes a processing head 21 and a drive section 22 that drives the processing head 21. The processing head 21 includes a collimating lens 211 and a focusing lens 212. The collimating lens 211 collimates the diverging laser beam emitted from the exit end of the process fiber 15 and converts it into collimated light. The focusing lens 212 focuses the incident collimated laser beam, converts it into convergent light, and irradiates the sheet metal W with the convergent light. The drive unit 22 moves the processing head 21 along the sheet metal W so that the laser beam irradiated onto the sheet metal W is moved to cut the sheet metal W. The drive unit 22 may have the processing head 21 fixed thereto and may move the sheet metal W. The drive unit 22 may move the processing head 21 relative to the sheet metal W so as to cut the sheet metal W.

Next, in the laser processing machine 100 configured as described above, the operation of the NC device 30 and the pulse generator 11 when the fiber laser oscillator 10 performs pulse oscillation operation to oscillate a laser beam will be described.

As shown in FIG. 2A, the NC device 30 supplies the pulse generator 11 with an output command signal consisting of a pulse signal that alternately repeats high and low levels. The output command signal is composed of a digital signal, and the height of each pulse during the high period indicates the voltage command value. The NC device 30 sets the voltage command value during the high period according to the desired laser output (laser power) of the laser beam emitted by the fiber laser oscillator 10 (laser oscillation module 12). FIG. 2A shows an output command signal having a voltage command value corresponding to 100% laser output (100% voltage command value).

When the period of the output command signal is T0 and the high period is H0, the duty ratio is expressed as (H0/T0)×100. The output command signal shown in FIG. 2A and the output command signal described below are based on an example in which the duty ratio is 50%. The duty ratio is not limited to 50%, and may be set to any duty ratio between 10% and 90%, for example. In the output command signal shown in FIG. 2A, the period H0 is, for example, 600 μs.

FIG. 2B shows a drive voltage signal generated by the pulse generation section 11 when the output command signal shown in FIG. 2A is supplied to the pulse generation section 11. The drive voltage signal generated by the pulse generator 11 is, for example, an analog signal. However, the drive voltage signal generated by the pulse generator 11 is not limited to an analog signal.

The pulse generator 11 generates a drive voltage signal consisting of a pulse signal that alternately repeats high and low levels based on the input output command signal. Since the voltage command value during the high period H0 of the output command signal is 100%, the pulse generation unit 11 generates a drive voltage signal having a voltage value of 100% during the high period. At this time, as shown in FIG. 2B, the pulse generation unit 11 modulates the voltage value in a pulse form for a preset time from the rise time of the high period. The pulse generation unit 11 maintains the voltage value of the drive voltage signal in a high state, and lowers the voltage value by a predetermined voltage value without reducing it to the voltage value (minimum voltage value) during the low period of the drive voltage signal. The voltage value is modulated in a pulsed manner so that the low state and low state are alternately repeated.

The pulse waveform superimposed on the drive voltage signal by modulating the voltage value will be referred to as a sub-pulse. The time for superimposing the sub-pulse on the high period is, for example, 400 μs from the rising time of the high period.

Since the period H0 of the output command signal shown in FIG. 2A is 600 μs, the high period of the drive voltage signal is also 600 μs, and a sub-pulse is superimposed on a portion of the 400 μs period. No sub-pulses are superimposed during a period exceeding 400 μs from the rise time of the high period.

FIG. 3A shows an output command signal having a voltage command value of 90% corresponding to 90% laser output and a period H0 of 400 μs. FIG. 3B shows the drive voltage signal generated by the pulse generator 11. Since the period H0 of the output command signal shown in FIG. 3A is 400 μs, as shown in FIG. 3B, the high period of the drive voltage signal is also 400 μs, and the sub-pulse is superimposed on the entire period of 400 μs. If the high period of the drive voltage signal is less than or equal to the preset time, the sub-pulse is superimposed on the entire high period of the drive voltage signal.

In this way, when the output command signal has a voltage command value corresponding to a laser output exceeding a predetermined laser output during a high period, the pulse generation unit 11 pulses the voltage value during the high period of the drive voltage signal. It is configured to modulate and superimpose sub-pulses on the drive voltage signal. On the other hand, when the output command signal has a voltage command value corresponding to a laser output equal to or less than a predetermined laser output during the high period, the pulse generator 11 modulates the voltage value during the high period of the drive voltage signal into a pulse shape. First, it is configured so that sub-pulses are not superimposed on the drive voltage signal. The predetermined laser output is a predetermined percentage of the laser output of 100%, and the predetermined percentage is, for example, 80%.

FIG. 4A shows an output command signal having a voltage command value of 70%, which corresponds to 70% laser output. When the output command signal shown in FIG. 4A is input, the pulse generation unit 11 generates a sub-pulse during the high period as shown in FIG. 4B because the output command signal has a voltage command value of 80% or less. Generate non-overlapping drive voltage signals.

The sub-pulses will be explained in detail using an enlarged view of one pulse of the drive voltage signal shown in FIG. The range from the 0% voltage value (minimum voltage value) corresponding to the 0% voltage command value to the voltage value during the period in which the sub-pulse is low will be referred to as the output restriction rate PLR. Note that the minimum voltage value is a predetermined small voltage value that is not a voltage value of 0.

When the laser oscillation module 12 performs a pulse oscillation operation to oscillate a laser beam, stimulated Raman scattering (SRS) occurs if the laser output is high, and no SRS occurs if the laser output is low. The output limiting rate PLR is set to a voltage value corresponding to a laser output at which SRS does not occur. The output limiting rate PLR is preferably set to a voltage value corresponding to a laser output as high as possible without causing SRS. If SRS does not occur when the voltage command value is 80%, the pulse generation unit 11 does not superimpose a sub-pulse at a voltage command value of 80% or less, as described above. The output restriction rate PLR at this time may be set to a voltage value of 80% corresponding to the voltage command value of 80%.

Assuming that the voltage value during the high period of the drive voltage signal is 100% as shown in FIG. Modulate to repeat alternately. As a result, the pulse generator 11 superimposes a sub-pulse with a voltage value of 100% during the high period of the sub-pulse and 80% of the voltage value during the low period of the sub-pulse during the high period of the drive voltage signal.

The sub-pulse period T1 is, for example, 20 μs. The duty ratio of the sub-pulses is, for example, 50%. In FIGS. 2B, 3B, and 5, the period T1 is expanded in the time direction for convenience of illustration. During the period when the sub-pulses are superimposed, the average value of the laser output per unit time of the laser beam emitted by the laser oscillation module 12 is lower than when the sub-pulses are not superimposed. However, even during the period in which the sub-pulses are superimposed, the maximum value commanded by the voltage command value of the laser output is maintained. The period during which the sub-pulses are superimposed will be referred to as output limit time PLT. As mentioned above, the output limit time PLT is, for example, 400 μs.

The voltage value of the drive voltage signal at which SRS begins to occur in the laser oscillation module 12 varies depending on individual differences in the laser oscillation module 12. Therefore, the output limiting rate PLR may be set by each individual laser oscillation module 12. The period T1 and duty ratio of the sub-pulses are not particularly limited.

The effects obtained when the pulse generation unit 11 superimposes sub-pulses on the drive voltage signal will be described with reference to FIGS. 6 and 7. FIG. 6 shows the laser output when the laser oscillation module 12 oscillates a laser beam based on a drive voltage signal without superimposing sub-pulses, and the SRS output generated at that time. The SRS output is laser power that indicates the amount of SRS generated. The example shown in FIG. 6 shows the laser output and SRS output when the high period of the drive voltage signal is 500 μs, the duty ratio is 50%, and the frequency is 1 kHz.

As shown in FIG. 6, the laser output indicated by the solid line sharply increases from the minimum value as the drive voltage signal rises at time 0, and then gradually increases to reach the maximum value and maintain the maximum value. The laser output sharply decreases from the maximum value as the drive voltage signal falls after 500 μs, and then gradually decreases to the minimum value. The SRS output shown by the broken line gradually increases from the minimum value to the maximum value as the laser output rises, and then gradually decreases to the minimum value after about 300 μs. For example, SRS is generated with a center wavelength of 1110 nm to 1130 nm. The minimum value is a very small value of approximately zero. In addition, in FIGS. 6 and 7, the laser output and the SRS output indicate the temporal timing at which each output value occurs, and each output value in the vertical axis direction does not indicate the relationship between the absolute values of the two. do not have.

As can be seen from FIG. 6, the inventor's verification has confirmed that SRS occurs only in a period of about 300 μs from time 0 even if the high period of the drive voltage signal is longer than 300 μs, such as 500 μs. ing. SRS occurs only in a period of 400 μs from time 0 at the longest.

FIG. 7 shows the laser output when the laser oscillation module 12 oscillates a laser beam based on the drive voltage signal on which sub-pulses are superimposed, and the SRS output generated at that time. FIG. 7 also shows the laser output and SRS output when the high period of the drive voltage signal is 500 μs, the duty ratio is 50%, and the frequency is 1 kHz. In FIG. 7, the output limit time PLT is set to 300 μs.

As shown in Figure 7, when a subpulse is superimposed on the output limit time PLT of 300 μs from time 0 when SRS occurs, SRS slightly occurs during the high period of the subpulse, but no SRS occurs during the low period of the subpulse. . Therefore, although the SRS output increases once during the high period of the sub-pulse, it decreases during the low period of the sub-pulse, so it does not become a large mountain-like value as shown in Figure 6, but repeats increases and decreases at small values. . By superimposing sub-pulses on the drive voltage signal by the laser oscillation module 12, the SRS output can be significantly reduced. In the above example, the output limit time PLT is set to 400 μs because SRS occurs only from time 0 to 400 μs at the longest.

As described above, the stimulated Raman scattering suppression method of the present embodiment suppresses SRS in the following manner when the output command signal has a voltage command value corresponding to the laser output at which SRS occurs during the high period. The pulse generation unit 11 pulse-modulates the voltage value during the high period of the generated drive voltage signal for a preset time from the rise time of the high period of the drive voltage signal, and generates sub-pulses in the drive voltage signal. Superimpose. The sub-pulses superimposed by the pulse generator 11 alternate between a high state in which the voltage value of the drive voltage signal is maintained and a low state in which the voltage value is lowered to a voltage value corresponding to a voltage command value corresponding to a laser output that does not generate SRS. Repeat.

As described above, according to the fiber laser oscillator 10 including the laser oscillation module 12, which is the laser oscillator of this embodiment, and the stimulated Raman scattering suppression method of this embodiment, SRS can be effectively suppressed. According to the laser processing machine 100, which is the laser processing machine of this embodiment, the beam quality is hardly deteriorated by suppressing SRS, so that the sheet metal W can be processed with good processing quality.

As described above, even if sub-pulses are superimposed on the drive voltage signal, the maximum value commanded by the voltage command value of the laser output is maintained, so the laser processing machine 100 uses a high-intensity laser beam to process sheet metal. W can be processed.

FIG. 8 is a comparative example, showing the laser output when the laser oscillation module 12 oscillates a laser beam by uniformly reducing the voltage value to 80% from time 0 to 200 μs instead of superimposing sub-pulses. , shows the SRS output generated at that time. FIG. 8 also shows the laser output and SRS output when the high period of the drive voltage signal is 500 μs, the duty ratio is 50%, and the frequency is 1 kHz.

As shown in FIG. 8, when the voltage value is reduced to 80% in the time period from time 0 to 200 μs, no SRS occurs in the time period from time 0 to 200 μs. However, if the voltage value is increased to 100% at 200 μs, a mountain-like SRS with a relatively large value similar to that shown in FIG. 6 occurs after 200 μs. On the other hand, as shown in FIG. 7, when sub-pulses are superimposed on the drive voltage signal, the mountain-like SRS does not occur after the output limit time PLT has elapsed.

The effect obtained by the pulse generation unit 11 superimposing sub-pulses on the drive voltage signal will be further explained using FIGS. 9 and 10. FIG. 9 shows the change in the SRS output ratio when the frequency of the output command signal (drive voltage signal) is changed. The SRS output ratio here is a value obtained by dividing the SRS output by the sum of the laser output and the SRS output. That is, the SRS output ratio is the ratio of the laser power of 1110 nm to 1130 nm to the total laser power including 1060 nm to 1080 nm and 1110 nm to 1130 nm. In FIGS. 9 and 10, the polygonal line connecting triangles shows the SRS output ratio when the drive voltage signal is not modulated with sub-pulses, and the polygonal line connecting circles shows the SRS output ratio when the drive voltage signal is modulated with sub-pulses. The minimum value of frequency is 100Hz.

As shown in FIG. 9, it can be seen that by modulating the drive voltage signal with sub-pulses, only a small amount of SRS occurs in the entire frequency range of 100 Hz to 10 kHz. If the drive voltage signal is not modulated with sub-pulses, the SRS output ratio reaches a maximum of 25% at a frequency of 2 kHz, indicating that a large amount of SRS occurs over the entire frequency range.

FIG. 10 shows the change in the BPP ratio when the frequency of the output command signal is changed. BPP stands for Beam Parameter Products, and is an index representing beam quality defined as the product of the beam waist radius and the half-width at half maximum of the beam divergence angle. The BPP ratio here means the BPP when the laser oscillation module 12 operates in pulse oscillation with a laser output of 100% and a duty ratio of 50%, and the BPP when the laser oscillation module 12 operates in CW oscillation with a laser output of 50%. This is the divided value.

Note that if the NC device 30 supplies an output command signal of a constant value to the pulse generation section 11 instead of a pulse signal, the pulse generation section 11 supplies a drive voltage signal of a constant value to the laser oscillation module 12, and the laser oscillation module 12 performs CW oscillation operation.

The average output when pulse oscillation is performed with a laser output of 100% and a duty ratio of 50%, and the average output when CW oscillation is performed with a laser output of 50% are both 50%. Since the average output is the same, the heat load per unit time applied to the fiber laser oscillator 10 and the measurement optical system is equivalent. If the heat load increases, thermal lensing will occur and BPP will worsen. Since the heat loads are the same, the BPPs of both can be appropriately compared.

As described above, when the laser oscillation module 12 performs the CW oscillation operation, SRS hardly occurs. Therefore, when the laser oscillation module 12 performs pulse oscillation operation with a laser output of 100% and a duty ratio of 50%, the BPP ratio approaches 100% as the SRS decreases. Conversely, in FIG. 10, the closer the BPP ratio is to 100%, the less SRS will occur when the laser oscillation module 12 performs pulse oscillation at 100% laser output.

As shown in FIG. 10, it can be seen that by modulating the drive voltage signal with sub-pulses, only a small amount of SRS occurs in the entire frequency range of 100 Hz to 10 kHz. When the drive voltage signal is not modulated with sub-pulses, the BPP ratio reaches nearly 150% of its maximum at a frequency of 3 kHz, indicating that BPP is worsened by the occurrence of SRS over the entire frequency range.

The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the gist of the present invention.

10 Fiber laser oscillator 11 Pulse generation unit 12 Laser oscillation module 13 Feeding fiber 14 Beam coupler 15 Process fiber 20 Processing unit 21 Processing head 22 Drive unit 30 NC device (control device)
100 Laser processing machine W Sheet metal

Claims (5)

a pulse generation unit that generates a drive voltage signal consisting of a pulse signal that alternately repeats high and low based on an output command signal that consists of a pulse signal that alternately repeats high and low;
a laser oscillation module that performs a pulse oscillation operation based on the drive voltage signal to oscillate a laser beam;
Equipped with
The pulse generation section includes:
When the output command signal has a voltage command value corresponding to a laser output exceeding a predetermined laser output during the high period, the voltage value during the high period of the drive voltage signal is set to the voltage value during the high period of the drive voltage signal. For a preset time from the rise time, a high state in which the voltage value is maintained and a low state in which the voltage value is reduced by a predetermined voltage value without reducing it to the voltage value during the low period of the drive voltage signal are alternated. modulating the drive voltage signal in a pulsed manner so as to repeat the sub-pulses on the drive voltage signal;
When the output command signal has a voltage command value corresponding to a laser output equal to or less than the predetermined laser output during the high period, the voltage value during the high period of the drive voltage signal is not modulated in a pulse form, and the drive A laser oscillator that does not superimpose subpulses on the voltage signal. The pulse generation unit modulates the voltage value during the high period of the driving voltage signal so that the voltage value during the low period of the sub-pulse becomes a voltage value corresponding to a voltage command value corresponding to the predetermined laser output. The laser oscillator according to claim 1. The pulse generation section includes:
When the high period of the drive voltage signal is longer than the preset time, the sub-pulse is superimposed for the preset time from the rise time of the high period of the drive voltage signal, and the high period of the drive voltage signal is The sub-pulse is not superimposed during a period exceeding the preset time of
The laser oscillator according to claim 1 or 2, wherein when the high period of the drive voltage signal is less than or equal to the preset time, the sub-pulse is superimposed during the entire high period of the drive voltage signal. a control device that generates an output command signal consisting of a pulse signal that alternately repeats high and low;
a laser oscillator that performs a pulse oscillation operation based on the output command signal to oscillate a laser beam and emit the laser beam;
a processing section that processes sheet metal using a laser beam emitted by the laser oscillator;
Equipped with
The laser oscillator is
a pulse generation unit that generates a drive voltage signal consisting of a pulse signal that alternately repeats high and low levels based on the output command signal;
a laser oscillation module that performs a pulse oscillation operation based on the drive voltage signal to oscillate a laser beam;
Equipped with
The pulse generation section includes:
When the output command signal has a voltage command value corresponding to a laser output exceeding a predetermined laser output during the high period, the voltage value during the high period of the drive voltage signal is set to the voltage value during the high period of the drive voltage signal. For a preset time from the rise time, a high state in which the voltage value is maintained and a low state in which the voltage value is reduced by a predetermined voltage value without reducing it to the voltage value during the low period of the drive voltage signal are alternated. modulating the drive voltage signal in a pulsed manner so as to repeat the sub-pulses on the drive voltage signal;
When the output command signal has a voltage command value corresponding to a laser output equal to or less than the predetermined laser output during the high period, the voltage value during the high period of the drive voltage signal is not modulated in a pulse form, and the drive A laser processing machine that does not superimpose subpulses on voltage signals. In order to cause the laser oscillator to emit a laser beam, a control device generates an output command signal consisting of a pulse signal that alternately repeats high and low, and outputs a voltage command value during the high period to cause the laser oscillator to emit a laser beam. Set according to the laser output of
A pulse generation unit included in the laser oscillator generates a drive voltage signal consisting of a pulse signal that alternately repeats high and low based on the output command signal supplied from the control device,
A laser oscillation module included in the laser oscillator performs a pulse oscillation operation based on the drive voltage signal to oscillate a laser beam,
When the output command signal has a voltage command value corresponding to a laser output at which stimulated Raman scattering occurs during the high period, the voltage value during the high period of the drive voltage signal generated by the pulse generation unit is set to the voltage value during the high period of the drive voltage signal. A high state in which the voltage value is maintained for a preset time from the rise time of the high period of the voltage signal, and a low state in which the voltage value is lowered to a voltage value corresponding to the voltage command value corresponding to the laser output that does not cause stimulated Raman scattering. A method for suppressing stimulated Raman scattering, which modulates the drive voltage signal in a pulsed manner so as to alternately repeat the states and superimposes sub-pulses on the drive voltage signal.

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