JPH065797B2 - Power supply for pulse laser - Google Patents

Description

TECHNICAL FIELD The present invention relates to a power supply circuit for a pulse laser using a flash lamp, and in particular, has been devised so as to protect or extend the life of the flash lamp.

(Prior Art) Solid-state lasers such as YAG (yttrium-aluminum-garnet) lasers and glass lasers, which are often used for laser processing, irradiate a laser medium such as a YAG rod or glass rod with an excitation light source to cause laser oscillation. It is a photo-excited laser. To obtain pulsed laser light with such a solid-state laser, a xenon flash lamp or a krypton flash lamp is used as an excitation light source, and the flash lamp can be repeatedly pulsated to oscillate repeatedly at 50 to 200 Hz. Has become.

Generally, a flash lamp for excitation is lit by discharging the electric charge stored in a capacitor. Therefore, in a pulsed laser that repeatedly generates pulsed laser light, the capacitor is repeatedly charged and the flash lamp is discharged, and the laser oscillation frequency increases as the repetition rate increases.

The pulsed laser is used for cutting, drilling, seam welding, spot welding, and other processes requiring a momentary high laser output.

(Problems to be Solved by the Invention) By the way, even if the charge stored in the capacitor is discharged, the flash lamp does not immediately enter the cut-off state and continues to conduct for a certain period of time. This is due to the inert material (Xe,
This is because Kr) is still in the ionized state.
The time from the end of discharge to the complete cut-off of the flash lamp is called the quench time. The quench time changes depending on conditions such as the magnitude of the lamp current, the repetition rate of light emission (lighting), and the temperature inside the lamp.

Such a quench time phenomenon is not a particular problem in a laser that oscillates only once such as continuous oscillation or a giant pulse, but a problem occurs in a pulse laser that repeats pulse oscillation.

In other words, if the oscillation frequency is increased while the quench time is long, charging for the next pulse oscillation will start before the quench time ends, and then the flash lamp is still in the conductive state, so the capacitor The electric charge to be charged flows through the flash lamp, resulting in a so-called DC discharge state. When this DC discharge state occurs, the flash lamp originally designed to emit light instantaneously continues to emit light regardless of the trigger, resulting in damage to the lamp or a drastic reduction in lamp life.

The present invention has been made in view of the above problems, and provides a power supply device for a pulse laser in which, even if direct current discharge occurs, it is immediately stopped to protect the flash lamp and extend its life. To aim.

(Means for Solving the Problems) The configuration of the present invention for achieving the above object is to provide a pulse laser power supply device in which a flash lamp for excitation is repeatedly pulsed so that a laser medium repeatedly causes pulsed laser oscillation, Means for detecting a predetermined voltage or current in a charging / discharging circuit including a flash lamp; and comparing the detected value of the voltage or current with a set value after a lapse of a predetermined time from the trigger of each pulse lighting. Means for determining whether or not direct current discharge is occurring in the flash lamp; and means for stopping charging to the charging / discharging circuit in response to this when the determining means determines that direct current discharge is occurring. It is characterized by having.

(Operation) When a trigger emits a pulse and the flash lamp lights up, the electric charge charged in the capacitor is discharged, and a pulsed current flows in the charge / discharge circuit, and eventually the discharge of the capacitor stops. However, the flash lamp does not enter the cutoff state there and continues to conduct for a while. If the conduction overtime, that is, the quench time is long or the pulse lighting interval is short, charging for the next pulse lighting may start while the flash lamp is still conducting. The electric charge to be charged flows through the flash lamp, resulting in a DC discharge state.

When such a DC discharge state is reached, in the charging / discharging circuit, for example, the charging voltage of the capacitor does not reach the normal level, and this is detected by the detection means and then compared with the set value by the determination means, so that the DC discharge The state is determined. Then, the charging stopping means operates to cut off the charging to the charging / discharging circuit, thereby stopping the DC discharge.

As described above, according to the present invention, when DC discharge is generated, it is immediately detected through a predetermined voltage or current in the charging / discharging circuit to forcibly stop the charging, thereby preventing the flash lamp from being destroyed or damaged. To be done.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

Structure FIG. 1 shows the main structure of a power supply device for a pulse YAG laser according to this embodiment.

A predetermined commercial AC voltage Eo supplied from the commercial power supply 10 is input to the charging circuit 14 via the step-up transformer 12.
The charging circuit 14 has a rectifier circuit that converts an AC voltage into a DC voltage, and outputs a constant charging voltage Vo in response to a charging start signal CS from a start button (not shown).

The output terminal of the charging circuit 14 is connected to one terminal of each of the capacitor 18 and the coil 20 via the resistor 16. The other terminal of the coil 20 is connected to one terminal of a xenon flash lamp or a krypton flash lamp 22, and the other terminal of the flash lamp 22 and the other terminal of the capacitor 18 are grounded. The resistor 16 is for giving a time constant to the charging speed of the condenser 18, and the coil 20 is for preventing a sudden discharge current to protect the flash lamp. Further, the flash lamp is provided with a trigger electrode 24, and a trigger pulse TP for starting each pulse oscillation of the flash lamp is applied from the trigger circuit 26 to the trigger electrode 24. Above, resistance 1
6, condenser 18, coil 20, flash lamp 2
The two trigger electrodes 24 and the trigger circuit 26 constitute the charge / discharge circuit of this embodiment. A YAG rod, a reflecting mirror, etc. (not shown) are arranged adjacent to the flash run 22.

Both terminals of the capacitor 18 are connected to the input terminals of the voltage detection circuit 28. The voltage detection circuit 28 detects or measures the voltage between the terminals of the condenser 18, that is, the charging voltage V, and supplies the detected voltage value MV to one input terminal of each of the error circuit 30 and the comparison circuit 32. A predetermined set voltage SV is applied from the charging voltage setting circuit 34 to the other input terminal of each of the error circuit 30 and the comparison circuit 32. The error circuit 30 generates an error voltage EV between the detected voltage value MV and the set voltage SV and supplies it to the charge control circuit 36, and the chargeability circuit 36 makes the error voltage EV zero, that is, the detected voltage EV. The output voltage Vo of the charging circuit 14 is controlled so that the value MV matches the set edge pressure SV. The comparator circuit 32 compares the detected voltage value MV with the set voltage SV, and when the former (MV) is lower than the latter (SV), the level is "0", and when not, that is, the former (MV) is the latter (SV).
When it is higher than or equal to, the comparison output voltage CO is set to the "1" level. This comparison output voltage CO is applied to the DC discharge determination circuit 38.

The DC discharge determination circuit 38 receives the determination timing signal TM from the timing circuit 40 and receives the comparison output signal C at that time.
It is determined whether the flash lamp 22 is in the DC discharge state according to the O level state, and the determination signal DE of "0" or "1" is given to the charge inhibition circuit 42. That is,
When the comparison output signal CO is "1", the decision circuit 38 decides that it is normal (cut state) and gives the decision signal DE of "0". When the comparison output signal CO is "0", the decision circuit 38 decides that there is an abnormality (DC discharge state) and gives the decision signal DE of "1". Then, the charge prohibition circuit 42 is set to "1".
When it receives the determination signal DE, the output of the charging voltage Vo to the charging circuit 14 is stopped.

The determination signal DE is also given to the start circuit 44,
When the start circuit 44 receives the determination signal DE of "1", it stops supplying the start signal ST to the timing circuit 40. The start signal ST is generated in each cycle of repetitive pulse oscillation, and in response to the signal ST, the timing circuit 40 sends the trigger instruction signal TR to the trigger circuit 26 and the charge timing signal CT to the charge control circuit 36. Therefore, when the supply of the start signal ST is cut off, the trigger instruction signal TR and the charging timing signal CT are also cut off.

In the above configuration, the voltage detection circuit 28 forms the detection means of this embodiment, and the comparison circuit 32 and the charging voltage setting circuit 3 are provided.
4. The DC discharge judging circuit 38 and the timing circuit 40 form the judging means of this embodiment, and the charge prohibiting circuit 42 forms the charge stopping means of this embodiment. Each element 28
˜44 may be an analog circuit or a digital circuit, or may be composed of a microcomputer.

Operation Next, the operation of this embodiment will be described with reference to FIG.

First, at time t ₁ , a start signal ST (FIG. 2C) of “1” is issued from the start circuit 44, and in response to this, the timing circuit 40 sends the trigger instruction signal TR to the trigger circuit 26 (see FIG. 2). (Not shown), trigger circuit 2
A trigger pulse TP (not shown in FIG. 2) is sent from 6 to the trigger electrode 24 to start the discharge of the flash lamp 22. Then, the electric charge charged in the capacitor 18 flows in a pulse shape through the flash lamp 22 (FIG. 2A). Due to this pulse discharge, the charging voltage V of the capacitor 18 drops, and eventually the discharge stops at time t ₂ (FIG. 2B).

However, the lamp current I is not cut at that time t ₂ and continues to flow until time t ₃ (FIG. 2A). This is the so-called quench time Q (t _{2 to} t ₃ ), which changes depending on the conditions such as the magnitude of the lamp current, the repetition rate of light emission (lighting), and the temperature in the lamp as described above.

In this example, the charge timing signal CT (FIG. 2D) is given at time t ₄ after a predetermined time To has passed from the discharge start time t ₁ . Therefore, if the quench time Q1 ends before time t ₄ as shown by the solid line in FIG. 2 (A), the capacitor 18 will be charged normally from time t ₄ as shown by the solid line in FIG. 2 (B). Be seen. In this case, the comparison output signal CO (FIG. 2F) is “1” when the determination timing signal TM (0 in FIG. 2) of “0” is given during the period from the time t _{5 to} t ₆ . Therefore, the determination signal DE (FIG. 2G) is "0", which indicates a normal state. As a result, at time t ₆ , the start signal ST
Is given, pulse discharge similar to the above is repeated.

However, as shown by the chain double-dashed line in FIG. 2 (A), when the quench time Q2 passes the time t4, the electric charge to be charged in the capacitor 18 flows to the flash lamp 22, and the charge is stored in the flash lamp 22.
As indicated by the dotted line in, the DC discharge state is established. In this case, Fig. 2
The capacitor charging voltage V is the set voltage V as shown by the dotted line in (B).
The judgment timing signal TM does not rise to 0 (Fig. 2E)
Is given, the comparison output signal CO (FIG. 2F) becomes "0", so the decision signal DE (FIG. 2G) becomes "1".
Indicates an abnormal state (DC discharge state). This allows
In FIG. 1, the charge inhibit circuit 42 stops the output of the charge voltage Vo to the charge circuit 14, and the start circuit 44 outputs the start signal ST to the timing circuit 40.
Stop the supply of. As a result, the capacitor charging voltage V drops as shown by the alternate long and short dash line in FIG.

As described above, when the DC discharge state occurs, the abnormal state is detected during the charging cycle at that time and the cutoff is forcibly performed by stopping the charging, so that the flash lamp 22 is effectively prevented from being broken or damaged. It

In the configuration of FIG. 1, the voltage across the terminals of the capacitor is monitored to detect the DC discharge state, but the lamp current I may be monitored using a current detection circuit. In addition, if a discharge circuit is connected in parallel with the capacitor, and if a DC discharge condition is detected, charging is stopped and the discharge circuit is activated to stop the charge stored in the capacitor from flowing to the flash lamp. It is also possible to promote lamp cut-off. Further, the charging / discharging circuit can have various configurations other than that shown in FIG. Furthermore, the present invention is applicable not only to pulsed YAG lasers, but also to other pulsed solid-state lasers, flash lamp pumped dye lasers, and the like.

(Effect of the Invention) As described above, according to the present invention, even if DC discharge occurs in a flash lamp, it is detected and stopped immediately, so that destruction of the flash lamp is prevented and its life is extended. can do. In addition, since the safety of the flash lamp is ensured in this way, the repetition frequency of pulse oscillation can be increased.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a power supply device for a pulse laser according to an embodiment of the present invention, and FIG. 2 is a timing chart for explaining the operation of the power supply device in FIG. 14 ... Charging circuit, 18 ... Capacitor, 20 ... Coil, 2
2 ... Flash lamp, 24 ... Trigger electrode, 26 ... Trigger circuit, 28 ... Voltage detection circuit, 30 ... Error circuit, 32 ...
Comparing circuit, 34 ... Charging voltage setting circuit, 36 ... Charging control circuit, 38 ... DC discharging circuit, 40 ... Timing circuit, 42
… Charge prohibition circuit, 44… Start circuit.

Claims (2)

[Claims] 1. A power supply device for a pulsed laser, wherein a flash lamp for excitation is repeatedly pulsed to cause a laser medium to repeatedly generate pulsed laser oscillation, wherein a predetermined voltage or current in a charge / discharge circuit including the flash lamp is supplied. Means for detecting, and means for determining whether or not DC discharge is occurring in the flash lamp by comparing the detected value of the voltage or current with a set value after a lapse of a predetermined time from the trigger of each pulse lighting. And a means for stopping the charging of the charging / discharging circuit in response to the determination by the monitoring means that the DC discharge is occurring. 2. The power supply device according to claim 1, wherein said detection means comprises voltage detection means for detecting a charging voltage of a capacitor of said charge / discharge circuit.