WO2020179834A1 - Control device and control method for fiber laser - Google Patents

Abstract

This control device for a fiber laser is provided with a laser diode that irradiates the fiber laser with excitation light, and a current control circuit that controls the laser diode to perform quasi-continuous-wave operation excitation by controlling current supplied to the laser diode.

Description

Fiber laser control device and control method

The present invention relates to a fiber laser control device and a control method.
The present application claims priority with respect to Japanese Patent Application No. 2019-041789 filed in Japan on March 7, 2019, the contents of which are incorporated herein by reference.

Highly reflective materials such as copper, silver, and aluminum are mainly used for processed objects such as electronic parts. When processing such a high-reflection material using a CW (CW: Continuous Wave Oscillation (continuous wave)) laser device, a portion of the laser light is reflected, so a laser with a large power of several kW class. Light may be required.

Also, Patent Documents 1 and 2 disclose a technique in which a high output peak power is obtained by operating a laser beam with a QCW (Quasi Continuous Wave Oscillation).

Japanese Patent Laid-Open No. 2001-127366 Japan Special Table 2016-514055

Conventionally, when generating a large power laser beam of several kW class in CW operation, it is necessary to cool with water in order to process heat. In addition, it is necessary to disperse the thermal load by sparsely arranging heat-generating components, and the power supply capacity required tends to increase as the output power increases.

In Patent Document 1, a YAG laser is used. The YAG laser becomes difficult to cool, especially when the power is increased.

Patent Document 2 describes that a high output peak power can be obtained by operating in the QCW mode. However, in Patent Document 2, since the power source of the pump source is turned on/off to perform the QCW operation, the power source startup time is required, and it is difficult to control the drive timing of the laser device with high accuracy. In particular, if the capacity of the power supply is increased in order to output excitation light of a large power, the size of the device becomes large.

In view of the above problems, it is an object of the present invention to provide a fiber laser control device and control method capable of reducing the size of the device and suppressing heat generation to increase the peak power.

In order to solve the above-described problems, a fiber laser control device according to an aspect of the present invention is a laser diode that irradiates a fiber laser with excitation light, and a current supplied to the laser diode to control the laser. It includes a current control circuit that controls the diode to excite a pseudo-continuous wave (QCW) operation.

In the fiber laser control device according to one aspect of the present invention, the current control circuit may be configured to independently control continuous pulses to drive the laser diode.

In the fiber laser control device according to one aspect of the present invention, the continuous pulse includes a first pulse and a second pulse after the first pulse, and the current control circuit determines a pulse height. It may be configured to control the first pulse so as to change it stepwise.

In the fiber laser control device according to the aspect of the present invention, the continuous pulse may be configured to be QCW (Quasi Continuous Wave Oscillation).

The fiber laser control device according to one aspect of the present invention may further include a charging unit that stores energy while the light emission of the laser diode is stopped.

A method for controlling a fiber laser according to one aspect of the present invention is a method for controlling a fiber laser that emits laser light by excitation light from a laser diode, wherein the laser is controlled by controlling a current supplied to the laser diode. The diode is excited for pseudo continuous wave operation.

According to the above aspect of the present invention, the average energy is suppressed and the peak power is suppressed by operating the laser diode in a pseudo continuous wave (QCW) by controlling the current flowing through the laser diode that irradiates the fiber laser with excitation light. Can be raised. As a result, the device can be miniaturized, heat generation can be suppressed, and a highly reflective material can be processed. Further, according to the above aspect of the present invention, since the laser diode that irradiates the excitation light is driven by current control, the laser diode can be turned on/off at a high speed, and continuous pulses can be independently controlled, The light emission state of the fiber laser can be optimally controlled.

It is an explanatory view of the outline of a fiber laser system to which this embodiment can be applied. It is a block diagram which shows the outline of the control device of the fiber laser which concerns on 1st Embodiment. It is a connection diagram which shows the specific circuit structure of the control device of the fiber laser which concerns on 1st Embodiment. FIG. 6 is a waveform diagram for explaining the operation of the first embodiment. It is a graph which compared the temperature of a chip at the time of CW operation and the time of QCW operation. It is explanatory drawing of the pulse waveform in the control apparatus of the fiber laser which concerns on 1st Embodiment. It is a block diagram which shows the outline of the control apparatus of the fiber laser which concerns on 2nd Embodiment. It is a connection diagram which shows the specific circuit structure of the control device of the fiber laser which concerns on 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 is an explanatory diagram of an outline of a fiber laser system 1 to which this embodiment can be applied.
In FIG. 1, the core of the optical fiber 11 is doped with a rare earth element such as Yb (ytterbium) as a laser medium. Both ends of the optical fiber 11 are sandwiched between reflectors 12a and 12b to form a resonator. As the reflectors 12a and 12b, for example, FBG (Fiber Bragg Grating) is used.

The laser diodes 13-1 to 13-n (n is an arbitrary integer) are light sources for irradiating the optical fiber 11 with excitation light. The laser beams from the laser diodes 13-1 to 13-n are combined by the pump combiner 14 and are incident on the optical fiber 11. When the laser light from the laser diodes 13-1 to 13-n is incident on the optical fiber 11, the laser medium of the optical fiber 11 is excited, and the reflection is repeatedly amplified between the reflecting mirror 12a and the reflecting mirror 12b, and the laser is used. Light is stimulatedly emitted.

The laser light generated by the fiber laser system 1 is used for various purposes such as product processing, cutting, and patterning. In the present embodiment, the laser light generated by the fiber laser system 1 is used for processing a highly reflective material such as copper, silver and aluminum. Processing of highly reflective materials requires a large amount of power, for example, a power of 1 kW or more in output for CW operation.

The fiber laser system 1 of the present embodiment is used to operate the laser beam by QCW (Quasi Continuous Wave Oscillation (pseudo continuous wave)). In the QCW operation, after emitting the excitation laser light with a predetermined pulse width, the emission is paused for a predetermined time, and the excitation laser light is emitted again with a predetermined pulse width. In the QCW operation, the pumping laser light is intermittently driven while optically maintaining a steady state, so that the influence of heat on the pumping laser diode is reduced and the peak power can be increased. Then, in the present embodiment, the laser diode that generates the excitation light is driven by current control so that the laser diode can be turned on / off at high speed. By turning the laser diode on / off in this way, the laser beam can be operated by QCW.

FIG. 2 is a block diagram showing an outline of the fiber laser control device 100 according to the present embodiment. As shown in FIG. 2, the fiber laser control device 100 according to the first embodiment of the present invention includes a laser diode 13 (13-1 to 13-n) for excitation, a power supply unit 21, and a current control circuit 22. Composed of and.

The power supply unit 21 is a power supply for driving the laser diode 13 (13-1 to 13-n). The current control circuit 22 controls the current of the laser diode 13 (13-1 to 13-n). A control signal is supplied to the current control circuit 22 from the control terminal 43. By this control signal, the current flowing through the laser diode 13 (13-1 to 13-n) is controlled to turn on/off the laser diode 13 (13-1 to 13-n), thereby operating the laser light in the QCW mode. be able to.

FIG. 3 is a connection diagram showing a specific circuit configuration of the fiber laser control device 100 according to the present embodiment shown in FIG.

In FIG. 3, a MOSFET (Metal-Oxide-Semiconductor) is used.
The source of the Field-Effective Transistor) 41 is connected to the negative electrode of the power supply unit 21 via the resistor 42. The control terminal 43 is derived from the gate of the MOSFET 41. Further, a backflow prevention diode 44 is connected between the drain and the source of the MOSFET 41. The MOSFET 41 and the resistor 42 correspond to the current control circuit 22 in FIG.

The laser diodes 13-1 to 13-n are connected in series. The anodes of the laser diodes 13-1 to 13-n connected in series are connected to the positive electrode of the power supply unit 21. The cathodes of the laser diodes 13-1 to 13-n connected in series are connected to the drain of the MOSFET 41.

In such a configuration, the MOSFET 41 becomes a constant current circuit, and a current flows through the MOSFET 41 according to a control signal supplied from the control terminal 43 to the gate of the MOSFET 41. Further, the laser diodes 13-1 to 13-n and the MOSFET 41 are connected in series. Therefore, the current flowing through the laser diodes 13-1 to 13-n can be controlled by the control signal supplied to the control terminal 43.

In this embodiment, a control pulse is supplied to the control terminal 43 when the laser beam is operated by QCW. As a result, the currents flowing through the laser diodes 13-1 to 13-n are turned on/off, and the laser diodes 13-1 to 13-n are driven intermittently. The pulse width when the laser diodes 13-1 to 13-n are turned on is a length that can maintain the optical steady state of the fiber laser, and is, for example, 0.01 ms to 100 ms. This is a wider pulse width as compared with a pulse laser device having a pulse width of several ps to several ns. For example, by using a pulse width of 0.01 ms to 100 ms with a power of 1 kW or more, even highly reflective materials such as copper, silver, and aluminum can be sufficiently processed. In this embodiment, the QCW (pseudo continuous wave) is a continuous wave having a pulse width of 0.01 ms to 100 ms as described above.

FIG. 4 is a waveform diagram for explaining the operation of the present embodiment. Part (A) of FIG. 4 shows the QCW operation, and part (B) of FIG. 4 shows the CW operation.

As shown in Part (A) of FIG. 4, when the QCW operation of the laser light is performed, the operation of suspending the emission of the laser light is repeated after the emission of the laser light is performed for a predetermined time. In this example, the QCW operation is performed with the duty ratio of the control pulse set to 10%. That is, assuming that the time of one cycle is 10T, the operation of emitting the laser light for only 1T and then suspending the emission of the laser light for the remaining 9T is repeated. On the other hand, when the CW operation is performed, the laser light is continuously emitted as shown in Part (B) of FIG.

Also, in the QCW operation, the average energy can be suppressed and the peak power can be increased compared to the CW operation. In this example, assuming that the peak power during CW operation is P as shown in the part (B) of FIG. 4, the peak power during the QCW operation is raised to 3P as shown in the part (A) of FIG. ing. Here, comparing the average energy during QCW operation and the average energy during CW operation, in QCW operation, assuming that the duty ratio is 10% and the peak power is 3P, the average energy in one cycle (10T) is 3P. ×T=3PT(J). On the other hand, the average energy at the same time (10T) in the CW operation is P×10T=10PT(J).

In this way, when the QCW operation is performed, the peak power is increased up to 3 times that during the CW operation, while the average energy can be reduced from 10 PT (J) to 3 PT (J). The decrease in average energy brings about an improvement in the thermal environment around the laser diodes 13-1 to 13-n. When the thermal environment around the laser diodes 13-1 to 13-n is improved, the life of the chip on which the laser diodes 13-1 to 13-n are arranged is extended, and the chip can be downsized. Can increase the number of laser diodes arranged on the chip.

FIG. 5 is a graph comparing the temperature of the chip on which the laser diode for excitation is arranged during the CW operation and the QCW operation. In FIG. 5, the horizontal axis is the current value of the laser diode for excitation, and the vertical axis is the temperature of the chip on which the laser diode for excitation is arranged.

As shown in FIG. 5, when the laser light performs the QCW operation, the temperature rise of the chip is suppressed. Further, in the CW operation, the temperature rise rate increases in the region where the current value exceeds 15 A. This is a phenomenon in which the life of the chip is shortened at an accelerated rate, and is the upper limit of the designed current value of the laser diode in consideration of the life of the entire fiber laser device. However, in the QCW operation, no accelerating temperature rise is observed even in a large current region where the current value exceeds 15A. From this result, since there is still a margin in terms of heat, it can be considered that even if the laser diode is arranged more densely on the chip, the effect on the life is small, and the device can be miniaturized.

Further, in the present embodiment, the laser diodes 13-1 to 13-n are turned on / off by current control to perform the QCW operation. The advantage of controlling the current of the laser diodes 13-1 to 13-n is that the laser diodes 13-1 to 13-n can be turned on / off at high speed.
That is, the laser diodes 13-1 to 13-n require a rising time from when the power is turned on until the current reaches the threshold value and the stimulated emission of the laser light starts. In the case of controlling the current of the laser diodes 13-1 to 13-n, the rise time is not required, so that the laser diodes 13-1 to 13-n can be turned on/off at high speed.

Further, in the present embodiment, since the laser diodes 13-1 to 13-n are current-controlled, continuous pulses can be independently controlled to an arbitrary waveform. FIG. 6 is an explanatory diagram of a pulse waveform in the fiber laser control device according to the present embodiment. In Part (A) to Part (C) of FIG. 6, the horizontal axis represents time and the vertical axis represents pulse height. Part (A) of FIG. 6 is an example in which the first pulse and the second pulse are controlled so that the duty ratios are different. In this example, as shown in the part of FIG. 6A, the first pulse is controlled to have a duty ratio of 10%, and the second pulse is controlled to have a duty ratio of 20%. The pulse width is controlled by the current control circuit 22.

In general, in the case of welding, when high-power laser light is irradiated, spatter easily occurs and processing defects tend to occur. On the other hand, in the present embodiment, as shown in the part (A) of FIG. 6, the pulse energy is gradually increased by changing the pulse width from T to 2T. As a result, according to the pulse of Part (A) of FIG. 6, it is possible to obtain the effect of suppressing spatter generation by gradually increasing the pulse energy. In addition, in Part (A) of FIG. 6, an example in which the pulse width is changed in two steps is shown, but the pulse width may be changed in three steps or more.

In part (B) of FIG. 6, the first pulse and the second pulse are controlled so that the peak powers are different. In this example, as shown in Part (B) of FIG. 6, control is performed so that the peak power of the first pulse is 3P and the peak power of the second pulse is 2P. Of course, it is also possible to perform control such that the duty ratio and the peak power are different between the continuous first pulse and the second pulse. The current control circuit 22 controls the pulse height. Further, in the part (B) of FIG. 6, an example in which the pulse height is changed in two steps is shown, but the change in the pulse height may be in three steps or more.

Part (C) of FIG. 6 is an example in which the continuous first pulse and the second pulse are controlled so as to be a unique pulse. In part (C) of FIG. 6, reference numeral g11 indicates a first pulse, and reference numeral g12 indicates a second pulse. In this example, as shown in part (C) of FIG. 6, the first pulse g11 is a pulse in which the power changes in two stages such that the power is first increased to melt the metal and then the power is decreased after the metal is melted. .. Specifically, during the period from time t1 to t2, the pulse height is controlled to be gradually increased from 0 to 3P. During the period from time t2 to t3, the pulse height is controlled to be kept at 3P. At time t3, the pulse height is controlled to be lowered from 3P to 2P. Then, during the period from time t3 to r4, the pulse height is controlled to be kept at 3P. At time t4, the pulse height is controlled from 2P to 0. The second pulse g12 is a simple pulse. The current control circuit 22 controls the pulse height. In addition, in part (C) of FIG. 6, an example in which the height of the first pulse is changed in two steps is shown, but the change in pulse height may be in three steps or more.

By gradually reducing the power in one pulse, it is possible to suppress heat generation more than necessary for the workpiece compared to the case where the pulse power is constant. Further, when the pulse power does not change, the temperature of the workpiece suddenly drops, causing thermal distortion. However, according to the pulse shape of part (C) of FIG. 6, the temperature of the workpiece can be gradually lowered. Therefore, it is possible to reduce the thermal strain generated in the workpiece. The pulse shape of part (C) of FIG. 6 is suitable for laser welding where heat needs to be applied continuously. As a result, the welding quality can be improved even in the area of fine processing. That is, according to the pulse shape of the part (C) of FIG. 6, since the pulse rises slowly, it is possible to obtain the effect of suppressing the generation of spatter during welding.

As described above, the fiber laser control device 100 according to the first embodiment of the present invention includes a laser diode 13 (13a to 13-n) for irradiating the fiber laser with excitation light and a laser diode 13 (13a to 13). A power supply unit 21 that supplies power to −n) and a current control circuit 22 that controls to excite the QCW operation by controlling the current supplied to the laser diodes 13 (13a to 13—n) are provided. .. In the present embodiment, the laser diode 13 (13a to 13-n) is turned on / off with a pulse width of 0.01 ms to 100 ms, and the laser beam is operated by QCW to suppress the average energy and increase the peak power. Can be raised.

Further, in the fiber laser control device 100 according to the present embodiment, the laser diode 13 (13a to 13-n) for irradiating the fiber laser with the excitation light is controlled by the current. As a result, the laser diode 13 (13a to 13-n) can be turned on / off at high speed. Further, in the fiber laser control device 100 according to the first embodiment of the present invention, continuous pulses are independently controlled by controlling the laser diodes 13 (13a to 13-n) that irradiate the fiber laser with excitation light with an electric current. The laser diode 13 (13a to 13-n) can be driven by controlling the laser diode 13. With this, not only the pulse width and the repetition frequency but also the duty ratio and the peak power of the continuous first pulse and the second pulse are independently controlled, so that the emission state of the fiber laser can be optimally controlled.
Further, according to the present embodiment, by controlling the pulses independently, it is possible to oscillate under various conditions by operating each of the plurality of pulses independently, and to combine a plurality of materials (material/thickness). It is advantageous for processing parts made from For example, in an electric / electronic component made of a combination of copper and aluminum, when copper-copper processing and copper-aluminum processing are mixed, the processing speed can be increased by independently changing the pulse energy.
As a result, according to the present embodiment, even when the peak power is increased enough to process the highly reflective material, the device can be downsized as compared with the conventional device and the heat generation can be suppressed more than the conventional device.

<Second Embodiment>
Next, a second embodiment will be described. FIG. 7 is a block diagram showing a fiber laser control device 200 according to the present embodiment. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 7, the fiber laser control device 200 according to the present embodiment is further configured to include a laser diode 13 (13-1 to 13-n), a power supply unit 21, and a current control circuit 22. The charging unit 50 is added. In the QCW control, the laser diode 13 (13-1 to 13-n) is driven intermittently, and occurs while the light emission of the laser diode 13 (13-1 to 13-n) is stopped. Therefore, in this embodiment, the charging unit 50 is provided, and energy from the power supply unit 21 is accumulated in the charging unit 50 while the laser diode 13 (13-1 to 13-n) is not emitting light. When the diodes 13 (13-1 to 13-n) emit light, the energy stored in the charging unit 50 is used. As a result, the capacity of the power supply that supplies energy from outside the device can be reduced.

FIG. 8 is a connection diagram showing a specific circuit configuration of the fiber laser control device 200 according to the present embodiment. As shown in FIG. 8, the charging unit 50 includes a switching transistor 51, a coil 52, a diode 53, and a capacitor 54. One end of the coil 52 is connected to the positive electrode of the power supply unit 21. The other end of the coil 52 is connected to the anode of the diode 53 and to the collector of the switching transistor 51. The emitter of the switching transistor 51 is connected to the negative electrode of the power supply unit 21. The cathode of the diode 53 is connected to the anode of the laser diode 13-1, and the capacitor 54 is connected between the cathode of the diode 53 and the negative electrode of the power supply unit 21.

When the switching transistor 51 is on, a current flows from the positive electrode of the power supply unit 21 to the negative electrode of the power supply unit 21 via the coil 52 and the switching transistor 51. This current causes electromagnetic energy to be stored in the coil 52.

When the switching transistor 51 is turned off, the electromagnetic energy stored in the coil 52 is released through the diode 53 and the capacitor 54 is charged. By repeating the on / off of the switching transistor 51, electrostatic energy is accumulated in the capacitor 54. As the capacitance of the capacitor 54, for example, a capacitor of about (4700 μF × 8) is used.

In this embodiment, the external power supply can be reduced by preparing a capacitor 54 having a capacitance suitable for the energy to be oscillated by the QCW laser. For example, when the electro-light conversion efficiency is 50%, when laser oscillation is performed under the conditions of peak power 1500 W, pulse energy 15 J, duty ratio 10%, and repetition frequency 1 kHz, electrostatic energy of 30 J or more is stored in the charging unit 50. As a result, the capacity of the external power source is about 1500 W, which causes no problem. On the other hand, in CW laser oscillation, a power supply of 3000 W is required with the light conversion efficiency set to 50%.

As described above, the second embodiment includes the charging unit 50 that accumulates energy from the power supply unit 21 while the laser diode 13 (13-1 to 13-n) is not emitting light. As a result, the capacity of the power supply that supplies energy from the outside of the device can be reduced.
As a result, according to the present embodiment, as in the first embodiment, even when the peak power is sufficiently increased to process the highly reflective material, the device can be made smaller than before, and heat is generated more than the conventional device. Can be suppressed.

Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and various modifications can be made without departing from the gist of the present invention. .. Modifications include addition, replacement, omission, and other changes of components in each embodiment. It is also possible to appropriately combine the components used in the embodiments.

11... Optical fiber, 12a, 12b... Reflecting mirror, 13-1 to 13-n... Laser diode, 14... Pump combiner, 21... Power supply section, 22... Current control circuit, 50... Charging section

Claims (6)

1. A laser diode that irradiates a fiber laser with excitation light,
   A current control circuit that controls the laser diode to excite the pseudo continuous wave operation by controlling the current supplied to the laser diode.
   A fiber laser controller.
2. The fiber laser control device according to claim 1, wherein the current control circuit independently controls a continuous pulse to drive the laser diode.
3. The continuous pulse comprises a first pulse and a second pulse after the first pulse.
   The fiber laser control device according to claim 2, wherein the current control circuit controls the first pulse so as to change the height of the pulse stepwise.
4. The fiber laser control device according to claim 2 or claim 3, wherein the continuous pulse is QCW (Quasi Continuous Wave Oscillation).
5. The fiber laser control device according to any one of claims 2 to 4, further comprising a charging unit that stores energy while the laser diode stops emitting light.
6. It is a control method of a fiber laser that emits laser light by excitation light from a laser diode.
   A method for controlling a fiber laser that excites the laser diode in a pseudo continuous wave operation by controlling the current supplied to the laser diode.

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