JPS62221Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulsed laser waveform control device that generates a pulsed waveform suitable for, for example, welding, drilling, etc., and that does not cause damage to an excitation lamp.

The normal pulse laser of conventional pulse laser processing equipment applies a trigger pulse to the excitation flash lamp, causes a large current discharge at the rising edge of this pulse to obtain strong excitation light, and irradiates the laser medium with this. I got it by doing that. The laser output thus obtained has a large peak value, ie, beam energy, at the rising edge of the pulse.
By irradiating this large beam energy onto the metal surface of the workpiece, the light absorption rate of this metal surface is improved, and the beam energy of the subsequent pulse waveform is efficiently absorbed by the metal surface. There is. In order to obtain a laser output having a large beam energy at the rising edge of the pulse, the laser output must rise sharply.

However, even if a large current is suddenly passed through the flash lamp, the laser output does not rise immediately accordingly, so in order to obtain a laser output with a sudden rise, it is necessary to It is necessary to pass a current through the flash lamp. However, when a flash lamp starts discharging, its discharge impedance is high, so a high voltage must be applied to flow a large current having an extremely steep rise as described above.

However, if the discharge current of the flash lamp is suddenly increased, a large current will instantly flow into the cathode of the lamp, resulting in a shortened life span of the cathode. Furthermore, there is a fear that thermal stress and shock waves are suddenly generated in the tube wall of the lamp due to the heat generated by the large current, damaging the tube wall and causing the lamp to explode. Sudden rise of the discharge current of the flash lamp in this manner has the disadvantage of impairing the reliability of the device.

Generally, drilling with a normal pulse laser is performed by irradiating the workpiece with a pulse laser with a pulse width of about 1 ms. If machining is insufficient with one pulsed laser beam, the workpiece is irradiated with several to several dozen pulsed laser beams per second to perform the machining. In the drilling process performed in this manner, fine particles of the workpiece that are evaporated and scattered by the pulsed laser irradiation cross the incident beam optical path of the pulsed laser. Therefore, when a pulsed laser with a long pulse width is used, fine particles of the workpiece scattered by the energy of the front part of this pulse scatter the subsequent incident laser beam corresponding to the rear part of the pulse.
Since the vicinity of the machined part of the workpiece is heated by this scattered laser beam, there is a drawback that the hole shape of the machined part becomes droopy.

In addition, when the pulse width of the pulsed laser is shortened, if the interval between the pulsed lasers is not appropriate, the heat of the workpiece heated by the preceding pulsed laser irradiation will be re-irradiated by the subsequent pulsed laser. This has the disadvantage that by the time the process is completed, it is dispersed into the surrounding area, reducing machining efficiency.

The present invention has been made to eliminate the above-mentioned drawbacks, and provides a pulsed laser waveform control device that generates a pulsed waveform suitable for welding, drilling, etc., and that does not cause damage to the excitation lamp. The purpose is to

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of the present invention. A smoothing capacitor 2 is connected to both ends of a DC power supply 1, and the positive end of this capacitor 2 is connected to an anode of a thyristor 3 as a semiconductor switch. The cathode of this thyristor 3 is
It is connected to the anode of a flash lamp 7 which emits excitation light via a coil 4, a diode 5 whose anode is connected to the coil 4, and a coil 6 which is connected to the cathode of the diode 5. The cathode of this flash lamp 7 is connected to the negative end of the smoothing capacitor 2. An auxiliary DC power source 9 is connected to both ends of the flash lamp 7 via a resistor 8 to cause the flash lamp 7 to discharge a minute DC discharge in advance. The lamp 7 is discharged by a trigger pulse emitted from a trigger circuit 10. Note that the strong excitation light emitted from the flash lamp 7 is transmitted to the condenser 11.
The light is focused on the laser rod 12 by the laser beam. A laser beam is emitted from this laser rod 12, and this laser beam is reflected by reflecting mirrors 13A and 13B.
It oscillates by going back and forth between the two many times. Due to this oscillation, the laser beam with increased amplitude is transmitted through the transparent reflecting mirror 13B and projected onto the lens 14. This lens 14 converges the laser beam to form a very small spot with high energy density, thereby drilling a hole 15A in the workpiece 15. Further, the positive end of the smoothing capacitor 2 is connected to a resonant electric coil 16, and this coil 16 is connected to the coil 1.
The resonant charging capacitor 18 is connected to the positive end of the resonant charging capacitor 18 via a thyristor 17, which is a semiconductor switch whose anode is connected to the resonant charging capacitor 18, thereby forming a first resonant charging circuit. Further, the positive end of the resonant charging capacitor 18 is connected to a diode 1 whose anode is connected to the positive end of the capacitor 18.
9 to the positive end of the resonant charging capacitor 20, forming a second resonant charging circuit. Further, the positive end of the resonant charging capacitor 20 is connected to the positive end of the resonant charging capacitor 22 via a diode 21 whose anode is connected to the positive end of the capacitor 20,
A third resonant charging circuit is formed. Note that the negative ends of the capacitors 18, 20, and 22 are all connected to the negative end of the smoothing capacitor 2.

The positive ends of the resonant charging capacitors 18, 20, 22 of the first, second, and third resonant charging circuits are connected to the anodes of thyristors 23, 24, 25 as semiconductor switches, respectively,
Among the thyristors 22, 24, 25, the cathodes of the thyristors 23, 24 are connected to each other and to the anode of the flash lamp 7 via the coil 6. On the other hand, the cathode of the thyristor 25 is connected to the coil 26 and the anode side is connected to the coil 26.
6 is connected to one end of a switch 28, and the other end of this switch 28 is connected to the positive end of the smoothing capacitor 2. Note that a common portion of the coil 26 and the diode 27 is connected to the cathode side of the thyristor 3. The control circuit 29 includes the thyristors 3, 17,
Gate pulses are sent to gate ends 23, 24, and 25 at predetermined times.

Note that the capacitance of the resonance charging capacitors 18 and 20 is as follows when discharged through the thyristors 23 and 24, the coil 6, and the flash lamp 7.
The discharge time obtained in relation to the inductance of the coil 6 is set to be shorter than the turn-off time required to cut off the thyristor 3 by the reverse bias voltage. Further, the capacitance of the resonance charging capacitor 22 is, when discharged via the thyristor 25, the coils 26, 4, the diode 5, the coil 6, and the flash lamp 7,
The discharge time obtained in relation to the inductance of the coils 26, 4, and 6 is set to be longer than the turn-off time of the thyristor 3.
Further, the inductance of the resonant charging coil 16 is equal to the inductance of the resonant charging capacitors 18, 20, 2.
It is set so that it resonates with the capacitance of the DC power supply 1 and obtains a voltage larger than the supply voltage of the DC power supply 1. The inductance of the coil 4 is set to a value that can sufficiently maintain the current from the thyristor 3 even when a reverse bias voltage is applied to the cathode of the thyristor 3 for a time shorter than the turn-off time. The voltage applied to the flash lamp 7 by the auxiliary DC power supply 9 is applied to the trigger circuit 1.
0 to a value that causes a DC minute discharge when a trigger pulse is applied to the lamp 7.

The operation of this embodiment having such a configuration will be explained.
In the initial state, it is assumed that the switch 28 is open and no gate pulse is applied to the gate terminals of the thyristors 3, 17, 23, 24, and 25. First, connect the auxiliary DC power supply 9 to the flash lamp 7.
After applying a voltage, the trigger circuit 10 applies a trigger pulse. Then, the lamp 7 performs a continuous DC micro discharge. However, in this DC microdischarge, it is not possible to irradiate the laser rod with sufficiently strong excitation light from the lamp 7, so that no laser oscillation occurs. In this state, when a gate pulse is sent from the control circuit 29 to the gate terminal of the thyristor 17 at time t ₁ in FIG. Resonant charging capacitor 1
DC current is supplied to 8, 20, and 22 to perform charging. Then, the resonant charging coil 16
Due to the resonance of the resonant charging capacitors 18, 20, 22, a resonant voltage larger than the supply voltage of the DC power supply 1 is obtained, and each capacitor 18, 20, 2
2 is charged as shown in FIGS. 2a, b, and c. At time t ₂ in the figure, the capacitor 1
The charging voltages of 8, 20, and 22 are each voltage level.
The increase is stopped at V ₁₈ , V ₂₀ , and V ₂₂ and the voltage is kept constant thereafter. At time _t3 in the figure, when a gate pulse is sent from the control circuit 29 to the gate terminal of the thyristor 3, the thyristor 3 becomes conductive, and the DC power source 1 connects the thyristor 3, coil 4, diode 5, and coil. A current is supplied to the anode of the flash lamp 7 via 6. As a result, the discharge current of the lamp 7 gradually increases as shown in FIG. 7(e), stops increasing at the discharge current level of I _S1 , and maintains that level. Then, the current density flowing through the cathode of the lamp 7 becomes uniform, and the laser rod 12 is sufficiently excited by the excitation light from the lamp, resulting in a large gain. Time when the discharge current of the flash lamp 7 reaches I _S1
At _T4 , when a gate pulse is sent from the control circuit 29 to the gate terminal of the thyristor 23, the thyristor 23 becomes conductive, and the resonant charging voltage V18 of the resonant charging capacitor ₁₈ increases between the thyristor 23 and the coil 6. Start discharging through. At this point, the flash lamp 7 is in a discharging state at the discharging current level I _S1 as described above, so that the discharging current due to the large resonant charging voltage _V18 described above is superimposed, as shown in e of the figure. As shown, the current increases rapidly to the current level I _S2 at time _t4 . At this time, the resonance charging capacitor 18
A large resonant voltage V ₁₈ is applied to the cathode of the thyristor 3 via the conductive diode 5 and coil 4. However, the discharge time determined by the capacitor 18 and the coil 6 is set shorter than the turn-off time cut off by the reverse bias voltage of the thyristor 3, and the flash lamp 7 during discharge has an impedance. Since the voltage is small, discharging is easy, and the charging voltage of the capacitor 18 decreases to the supply voltage _V1 of the DC power supply 1 before the thyristor 3 is cut off. Therefore, the thyristor 3 is never cut off, and the current in the thyristor 3 continues to flow even during reverse bias due to the inductance of the coil 4.

When the charging voltage of the resonant charging capacitor 18 decreases to the supply voltage _V1 of the DC power supply 1 as a result of discharging, the discharge is mainly caused by the power supplied through the thyristor 3, and the discharge current becomes I _S1 . .

When a gate pulse is sent from the control circuit 29 to the thyristor 24 at time _t5 in the figure, this thyristor 24 becomes conductive, and the resonant charging voltage V ₂₀ of the resonant charging capacitor 20 increases
4. Start discharging via the coil 6. As a result, the discharge current due to the large resonant charging voltage V ₂₀ described above is superimposed on the discharge current I _S1 of the flash lamp 7, and the discharge current exceeds the current level I _S2 at time t ₅ as shown in e of the figure. rapidly increases to the level. At this time, a large resonant voltage V ₂₀ from the resonant charging capacitor 20 is applied to the cathode of the thyristor 3 via the conductive diode 5 and coil 4, but the operation of the resonant charging capacitor 18 As explained in the explanation, the thyristor 3 does not enter the cut-off state and continues to flow the discharge current I _S1 to the flash lamp 7.

When the charging voltage of the resonant charging capacitor 20 decreases to the supply voltage _V1 of the DC power supply 1 as a result of discharging, the discharge is mainly caused by the power supplied through the thyristor 3, and the discharge current becomes I _S1 . .

When the signal is sent from the control circuit 29 to the gate terminal of the thyristor 25 at time t ₆ in the figure, the thyristor 25 becomes conductive, and the resonance charging voltage V ₂₂ of the resonance capacitor 22 is applied to the thyristor 25, the coil 26, Discharge is started via the coil 4, diode 5, and coil 6. As a result, the discharge current due to the large resonant charging voltage V ₂₂ is superimposed on the discharge current I _S1 of the flash lamp 7, and the discharge current suddenly reaches the current level I _S3 at time t ₆ as shown in e of the figure. increases to

At this time, a large resonant voltage V ₂₂ from the resonant charging capacitor 22 is applied to the cathode of the thyristor 3 which is conducting.
It remains conductive during the reverse bias time that is less than the turn-off time of . However, since the discharging time determined by the resonant charging capacitor 22 and the coils 26, 4, and 6 is set larger than the turn-off time of the thyristor 3, even if the discharging time reaches this turn-off time, the thyristor 3 is still reverse biased, so that at time _t7 the thyristor 3 is cut off. As a result, this thyristor 3
The discharge current I _S1 that had been supplied through the resonant charging capacitor 22 stops flowing, and only the discharge current due to the charging voltage of the resonant charging capacitor 22 flows to the flash lamp 7. Then, the charging voltage of the capacitor 22 changes to the supply voltage of the DC power supply 1 due to discharge.
When the voltage drops to V ₁ , the diodes 19 and 21 are biased in the forward direction, so that the residual charging voltage V ₁ of the resonant charging capacitors 18 and 20 also causes a discharge current to flow through the thyristor 25 to the flash lamp 7 . Then, at time _t8 , the charging voltages of the capacitors 18, 20, and 22 drop to approximately zero level voltage, and the series of pulse generation operations is completed. Thereafter, the same operations as those at times t ₁ to _{t 8} described above are repeated.

In this way, in this embodiment, the flash lamp 7
discharge current from DC microdischarge state to current level I
After _the current I _S1 flows uniformly to the cathode surface of the lamp 7 by increasing it slowly to S1,
The _resonant charging capacitor 18,
The short pulse discharge currents obtained by the discharges 20 and 22 are superimposed. Therefore,
Since a large current does not flow through the cathode of the lamp 7 from the beginning, the electrode material of the cathode is not scattered, and the life of the cathode can be extended. In addition, thermal stress and shock waves generated on the tube wall of the lamp 7 due to large current can be suppressed, eliminating the risk of damage to the lamp 7.

In laser oscillation, different laser output waveforms can be obtained as shown in FIG. FIG. 2f shows the laser output waveform when the oscillation flash hold level is set to I _S4 , and FIG. 2g shows the laser output waveform when the discharge current level is set to I _S1 . As shown in FIG. 2 f and g, steeply rising pulses are output at predetermined time intervals. Therefore, the preceding pulse is irradiated to the workpiece, the removed material is scattered, and when the scattered particles are no longer in the laser beam optical path, the subsequent pulse is irradiated to the same workpiece again, so that the removed material is scattered. The laser beam is no longer scattered by flying particles, and the area around the processing area is no longer heated. Therefore, the waveforms shown in FIGS. 2(f) and 2(g) are suitable for drilling operations in which conventionally the scattered laser beam has caused drooping in the hole shape of the processed portion.

In addition, as shown in Figure 2 f and g, since laser pulses are automatically output continuously at predetermined time intervals, subsequent pulses can be output before the residual heat of the preceding pulse has dissipated. Since the beam is irradiated onto the workpiece, drilling is performed efficiently.

Further, when the switch 28 is closed and the above-described operation is performed, the operation from time _t1 to _t5 is the same as the above-described operation, but a different operation is performed at time _t6 . That is, the resonance charging capacitor 2
When a large resonant charging voltage of 2 is applied to the anode of the diode 27 through the coil 26, the diode 27 is forward biased and conducts, and the positive terminal of the smoothing capacitor 2 is connected to the positive terminal of the smoothing capacitor 2 through the closed switch 28. A discharge current flows to. Therefore, the discharge current I supplied via the thyristor 3
The discharge current from the resonance charging capacitor 22 is not superimposed on _S1 . FIG. 2h is a diagram showing the waveform of the discharge current of the flash lamp 7 when the switch 27 is closed as described above.
At time _t6 , no current pulse is superimposed on the discharge current I _S1 , and the current level I _S1 is maintained. Then,
It starts to decrease at time _t7 and reaches almost zero level at time _t8 . Figure 2i shows the laser output waveform when the laser oscillation threshold level is set to I _S4 . As is clear from FIG. 2i, the waveform has a high peak output at the beginning of the pulse and a gradual fall at the end. The waveform shown in Fig. 2i is suitable for welding in which the processed parts are melted and then joined. That is, the large energy at the front of the pulse can melt the processed portion, and the less large energy at the rear of the pulse can preheat the joint.

Note that the present invention is not limited to the one embodiment described above. For example, in the above embodiment, three resonant charging capacitors are provided to output two or three pulsed lasers, but two capacitors are provided to output one or three pulsed lasers. Two capacitors may be provided, or three or more capacitors may be provided to obtain three or more pulsed laser outputs. Further, in the embodiment described above, a thyristor was used as the semiconductor switch, but any other semiconductor element may be used as long as it becomes conductive in response to a gate pulse. Of course, various other modifications can be made without departing from the gist of the present invention.

In this way, the present invention gradually increases the discharge current of the excitation lamp that irradiates the laser medium with excitation light to a level at which the laser medium is sufficiently excited, so that the current density at the cathode of the lamp becomes uniform. When the temperature rises, one or more pulsed discharge currents with steep rises from the resonant charging circuit are
superimposed on the discharge current already flowing through the lamp,
The laser medium, which is already sufficiently excited and has a large gain, is irradiated with strong excitation light to obtain a pulsed laser with a steep rise. Therefore, according to the present invention, a large current does not suddenly flow through the excitation lamp, and the resulting laser pulse light is output continuously at predetermined time intervals, so there is no risk of damaging the excitation lamp. It is possible to provide a pulsed laser control device that can generate a pulse waveform suitable for welding, drilling, etc. without any problems.

[Brief explanation of drawings]

Fig. 1 and Fig. 2 relate to an embodiment of the present invention, Fig. 1 is a circuit diagram, Fig. 2 a, b, and c are waveform charts of the charging voltage of each resonant charging capacitor, and Fig. 2 d is a DC Waveform diagrams of the supply voltage of the power supply, e and h in the same figure are waveform diagrams of the discharge current of the flash lamp, f, g in the same figure,
i is a laser output waveform diagram. 1...DC power supply, 2...Smoothing capacitor, 3...
...Thyristor, 4...Coil, 5...Diode, 6...Coil, 7...Flash lamp, 9
...Auxiliary DC power supply, 10...Trigger circuit, 12...
...Laser rod, 16... Resonance charging coil, 1
7... Thyristor, 18, 19, 20... Resonance charging capacitor, 23, 24, 25... Thyristor, 26... Coil, 28... Switch, 29...
...control circuit.

Claims (1)

[Scope of utility model registration request] A pulsed laser waveform control device comprising a laser oscillation unit having a laser medium and an excitation lamp, and driving the excitation lamp to emit light to excite the laser medium to emit laser light. On the other hand, there is an auxiliary DC power supply circuit that supplies a DC minute current to perform continuous DC minute discharge, a main power supply circuit different from this auxiliary power supply circuit, and a plurality of resonant charging circuits that resonantly charge the output voltage of this main power supply circuit, respectively. and a step of gradually supplying a predetermined discharge current from the main DC power supply circuit to the excitation lamp to obtain a discharge state in which the current density on the cathode surface of the lamp is uniform, prior to discharging the circuit and the resonant charging circuit. 1 semiconductor switch circuit and each of the resonant charging circuits is selectively discharged at a predetermined timing, and each of the pulsed currents is superimposed on the discharge current from the main DC power supply circuit to the excitation lamp. a plurality of second semiconductor switch circuits that supply pulsed light to the excitation lamp to cause the excitation lamp to emit pulsed light with a steep rise; and control that controls the operation timing of these second semiconductor switch circuits and the first semiconductor switch circuit. A pulsed laser waveform control device characterized by comprising a circuit.