JP5920870B2 - Laser power supply - Google Patents

Description

  The present invention relates to a laser power supply apparatus that supplies power to an excitation lamp for laser oscillation.

  A solid-state laser device such as a YAG laser used for laser processing turns on an excitation lamp and excites a solid-state laser medium such as a YAG rod by the light energy to cause laser oscillation.

  In general, a power supply device used in such a laser device includes a rectifier circuit that rectifies commercial frequency alternating current and converts it into direct current, a capacitor that stores direct current power from the rectifier circuit, and electrical energy stored in the capacitor. And a lamp driving circuit for supplying a lamp current, that is, a driving current to the excitation lamp.

FIG. 10 shows a circuit configuration of a conventional simple laser power supply device used in a solid-state laser device. In this laser power supply device, the output terminals [OUT _a , OUT _b ] are connected to both electrode terminals of an excitation lamp (not shown) of the laser oscillation unit.

  The three-phase rectifier circuit 100 on the input side rectifies commercial frequency three-phase alternating current from the three-phase alternating current power supply terminals [S, T, U] and converts it into direct current. A coil 104, a resistor 106 and a first switch 108 are connected in series between the three-phase rectifier circuit 100 and the capacitor 102, and a second switch 110 is connected in parallel with the resistor 106 and the first switch 108. Is connected.

A switching element 112 for driving the lamp and the choke coil 114 are connected in series between the capacitor 102 and the output terminals [OUT _a , OUT _b ], and a flywheel diode in parallel with the choke coil 114 and the excitation lamp. 116 is connected. When the switching element 112 is turned on, capacitor 102 is discharged and the capacitor 102 the discharge current as the lamp current i _d, the switching element 112, flows through the closed circuit of the choke coil 114 and the excitation lamp. When the switching element 112 is turned off, discharge of the capacitor 102 is interrupted is, return current in the closed circuit of the choke coil 114, the excitation lamp and the flywheel diode 116 flows as the lamp current i _d. Accordingly, the lamp current _id is continuously supplied without interruption, the excitation lamp is continuously turned on, and continuous oscillation laser light can be obtained from the laser oscillation unit. The switching element 112 is turned on / off at a constant high frequency, for example, 20 kHz, by switching control of the switching control circuit 118.

The control unit 120 monitors the charging voltage V _c of the capacitor 102 through the charging voltage measuring circuit 122, and turns on / off each part in the device, particularly the switches 108 and 110, and the switching operation of the switching control unit (112, 118). To control.

In this laser power supply device, when charging the capacitor 102 from the non-charged state to the set voltage, the second switch 110 is kept off and the first switch 108 is turned on while the switching operation of the switching element 112 is stopped. To. Then, the three-phase rectifier coil 104 from the output terminal of the circuit 100, the charging current i _c of the DC through a resistor 106 and a first switch 108 flows to the capacitor 102, the voltage between the terminals, that the charge voltage V _c of the capacitor 102 rises To do. At this time, the resistor 106 functions as a current limiting resistor that prevents inrush current from flowing from the coil 104 to the capacitor 102. The control unit 120 monitors the charging voltage V _c of the capacitor 102 through the charging voltage measurement circuit 122, and turns on the second switch 110 when the charging voltage V _c reaches a value close to the set value V _S. As a result, the coil 104 and the capacitor 102 are short-circuited via the second switch 110. Thereafter, the charging current i _d from three-phase rectifier circuit 100 to the coil 104 is supplied to the capacitor 102 through the second switch 110. The first switch 108 may be switched to the off state at this time, but may be held in the on state as it is.

When the control unit 120 receives a start signal ST from an external device such as a manual start switch or a work transfer device after the charging voltage V _c of the capacitor 102 reaches the set value V _S , the control unit 120 performs switching control in response thereto. Circuit 118 is activated. The switching control circuit 118, a switching element 112 for switching control to flow lamp current i _d to the excitation lamp a predetermined current value. Thus, while the capacitor 102 supplies the lamp current i _d to the excitation lamp side, the coil 104 and the second phase are supplied from the three-phase rectifier circuit 100 side so as to supplement the electric energy released from the capacitor 102 by the supply of the lamp current i _d . The charging current _ic is supplied to the capacitor 102 via the two switch 110.

JP-A-11-26844

The simplified laser power supply device has an advantage that it is inexpensive and highly efficient because it has a minimum circuit configuration and has low power loss. On the other hand, it is vulnerable to load fluctuations. In particular, when the lamp current i _d increases rapidly, the charging voltage V _C of the capacitor 102 decreases rapidly, and the charging current i _c flowing from the coil 104 to the capacitor 102 increases rapidly. Change to inrush current. Such an inrush current causes problems that the coil 104, the switch 110, and the capacitor 102 are easily damaged, and that the fuse 124 on the AC circuit is frequently blown.

In order to solve this problem, the inductance of the coil 104 and the capacitance of the capacitor 102 are increased. However, even if the AC power supply voltage fluctuates, the charging voltage V _C of the capacitor 102 may fluctuate greatly during laser oscillation, and an inrush current may flow from the coil 104 to the capacitor 102. As a result, the coil 104 and the capacitor 102 are enlarged. This is not only a fundamental solution, but rather the degree of loss of component damage. For this reason, this type of simple laser power supply apparatus is currently specialized for low-power lasers by setting the laser output dynamic range low.

As another solution, the function of monitoring the charging voltage V _c of the capacitor 102 through the charging voltage measuring circuit 122 is used, and the switch 108 is turned on when the charging voltage V _c drops below a predetermined monitoring value during laser oscillation. , 110 may be turned off. However, when the fluctuation of the load or the fluctuation of the AC power supply voltage is relatively moderate, the inrush current will not be reached even if the charging voltage V _c of the capacitor 102 becomes lower than the monitored value. not good. On the other hand, when the AC power supply voltage fluctuates, an inrush current may flow through the capacitor 102 due to the rapid recovery of the voltage after the charging voltage V _c of the capacitor 102 has once decreased to a level that does not reach the monitored value. As described above, the method of monitoring the capacitor charging voltage has problems such as causing unnecessary stoppage of the device and preventing inrush current reliably.

Further, as another solution, it is conceivable to monitor the current value of the charging current _ic and turn off the switches 108 and 110 when the current value exceeds a predetermined monitored value. However, in this method, the switches 108 and 110 are turned off when a large charging current _ic flows through the coil 104. Therefore, the electromagnetic switch accumulated in the coil 104 loses its place and is turned off. There is a possibility that a spark (arc discharge) is generated in 110 and the switch 110 is damaged.

  Further, the method of directly monitoring the fluctuation of the AC power supply voltage and controlling the on / off of the switches 108 and 110 cannot cope with the fluctuation of the load or the fluctuation of the AC power supply voltage that does not develop into an inrush current. There is a risk of excessive response, and control accuracy and reliability are poor.

  Conventionally, by providing a charging circuit with a PFC (power factor correction) circuit, the influence of load fluctuations and AC power supply voltage fluctuations has been mitigated. However, the device configuration including the PFC circuit has the disadvantages that the efficiency is reduced due to the switching loss of the PFC circuit, and that the complexity of hardware and switching control and the device cost are increased.

  The present invention solves the above-described problems of the prior art, and prevents an abnormal increase in charging current (occurrence of inrush current) in response to load fluctuations and AC power supply voltage fluctuations. And a laser power supply device for improving reliability.

The laser power supply apparatus of the present invention is a laser power supply apparatus for supplying power to an excitation lamp that irradiates a solid-state laser medium with excitation light for laser oscillation, and rectifies a commercial frequency alternating current to convert it into a direct current. A circuit, a capacitor for storing DC power output from the rectifier circuit, a coil and a resistor connected in series between the rectifier circuit and the capacitor, and the AC circuit, or the rectifier circuit, A first switch connected in series with the resistor between the capacitor, a second switch connected in parallel with the resistor, and electric energy stored in the capacitor to the excitation lamp side A lamp driving circuit for discharging and supplying a lamp current to the excitation lamp, and a voltage drop generated by the coil and the resistor, or a voltage drop generated by the coil and the second switch Having a monitoring unit for monitoring the pressure drop, and a control unit for controlling said first and second switches on and off based on the monitoring result output from the monitoring unit.

In the above device configuration, when charging the capacitor from a substantially non-charged state to the set voltage, when the capacitor charge voltage approaches the set voltage, the voltage drop of the coil and resistance approaches zero, so the monitoring unit This situation can be detected easily and accurately. Further, when the lamp current rapidly increases while the excitation lamp is lit, or when the AC voltage increases rapidly, the charging current flowing from the rectifier circuit to the capacitor starts to increase rapidly. When the charging current starts to increase suddenly in this way, the voltage drop of the coil and the second switch rises from a low value up to the value corresponding to the increasing rate of change of the charging current. And it can detect correctly. In addition, since the control unit controls on / off of the first and second switches based on the accurate and highly accurate monitoring result from the monitoring unit, an abnormal increase in charging current, that is, inrush current is generated in advance. The capacitor charging operation can be successfully completed without being affected by the voltage level of the current AC power supply voltage.

  In a preferred aspect of the present invention, the controller monitors the monitoring result that the voltage drop of the coil and the resistor has divided the second reference value when charging the capacitor from a substantially non-charged state to a predetermined voltage. The second switch is turned on when it is output from the unit.

  In another preferred embodiment, the control unit may monitor that the voltage drop of the coil and the second switch is smaller than the first reference value after charging the capacitor from a substantially non-charged state to a predetermined voltage. While being output from the monitoring unit, the first and second switches are kept on, and a monitoring result that the voltage drop of the coil and the second switch has exceeded the first reference value is output from the monitoring unit. When at least one of the first and second switches is turned off. In this case, the control unit preferably outputs the first and second monitoring results when a monitoring result indicating that the voltage drop of the coil and the second switch exceeds the first reference value is output from the monitoring unit for a predetermined time. At least one of the second switches is turned off.

  According to the laser power supply device of the present invention, the above-described configuration and operation can prevent a charging current from increasing abnormally (occurrence of an inrush current) in response to load fluctuations and AC power supply voltage fluctuations. And reliability can be improved. Further, the capacitor charging operation can be successfully completed without being affected by the voltage level of the current AC power supply voltage.

It is a circuit diagram which shows the structure of the laser power supply apparatus in 1st Embodiment. In the laser power supply device of FIG. 1, it is a wave form diagram of each part for demonstrating an effect | action when a capacitor | condenser is charged from a substantially no-charge state to a setting voltage. In the laser power supply device of FIG. 1, it is a wave form diagram of each part for demonstrating an effect | action when the charging voltage of a capacitor | condenser is going to fall rapidly by the fluctuation | variation of load during laser processing. In the laser power supply device of FIG. 1, it is a wave form diagram of each part for demonstrating an effect | action when the charging voltage of a capacitor | condenser falls gradually gently by the fluctuation | variation of load during laser processing. It is a circuit diagram which shows the structure of the laser power supply apparatus in 2nd Embodiment. FIG. 6 is a waveform diagram of each part for explaining an operation when the capacitor is charged from a substantially non-charged state to a set voltage in the laser power supply device of FIG. 5. It is a circuit diagram which shows the structure of the laser power supply apparatus in 3rd Embodiment. It is a circuit diagram which shows the structure of the laser power supply device in one modification. FIG. 9 is a circuit diagram illustrating a configuration of a switching transformer circuit included in the laser power supply device of FIG. 8. It is a circuit diagram which shows the structure of the conventional simple type laser power supply device.

Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS.
[Embodiment 1]

  FIG. 1 shows a configuration of a laser power supply apparatus according to the first embodiment of the present invention. This laser power supply apparatus can be suitably applied to a solid-state laser apparatus such as a YAG laser processing apparatus, and can cope with high-power laser processing.

As a basic configuration, this laser power supply apparatus has a three-phase rectifier circuit 10 that rectifies a commercial frequency three-phase alternating current to convert it into a direct current, a capacitor 12 that stores electric power or electric energy from the rectifier circuit 10, and a rectifier circuit 10. A charging circuit 14 for sending a charging current I _c to the capacitor 12, a lamp driving circuit 18 for discharging the electrical energy stored in the capacitor 12 to supply a lamp current, that is, a driving current I _d to the excitation lamp 16, and And a control unit 20 that controls the operation of each unit.

  The three-phase rectifier circuit 10 is composed of, for example, a three-phase bridge circuit of a diode, and rectifies a commercial frequency three-phase alternating current from a three-phase alternating current power supply terminal [S, T, U] to convert it into direct current. Between the three-phase AC power supply terminal [S, T, U] and the three-phase rectifier circuit 10, a fuse 22 and an electromagnetic first switch 24 are inserted (connected) in series.

  A coil 26 and a current limiting resistor 28 are connected in series as a charging circuit 14 between the three-phase rectifier circuit 10 and the capacitor 12, and an electromagnetic second switch 30 is connected in parallel with the resistor 28. Has been.

The output terminals [OUT _A , OUT _B ] are connected to both terminals of the excitation lamp 16. Between the capacitor 12 and the output terminals [OUT _A , OUT _B ], a switching element 32 for driving the lamp and the choke coil 34 are connected in series, and the flywheel and the choke coil 34 and the excitation lamp 16 are connected in parallel. A diode 36 is connected. When the switching element 32 is turned on, the capacitor 12 is discharged and the capacitor 12, the switching element 32, flows through the closed circuit of the choke coil 34 and the excitation lamp 16 that discharge current as the lamp current I _d. When the switching element 32 is turned off, the discharge of the capacitor 12 is interrupted, but the return current flows as the lamp current I _{d in} the closed circuit of the choke coil 34, the excitation lamp 16 and the flywheel diode 36. As a result, the lamp current I _d is continuously supplied without interruption, the excitation lamp 16 is continuously turned on, and the continuous oscillation laser beam LB can be obtained from the laser oscillation unit 38.

The switching element 32 is made of, for example, IGBT or FET, and is turned on / off at a constant high frequency, for example, 20 kHz, by switching control of the switching control circuit 40. In this embodiment, for example, the current value of the lamp driving current I _d is measured by the current sensor 42 formed of a Hall element and the current measurement circuit 44, and the current measurement value MI _d is fed back to the switching control circuit 40. Reference numeral 40 denotes a PWM (pulse width modulation) type switching control.

  The laser oscillation unit 38 includes an excitation lamp 16 and a YAG rod 48 disposed in the chamber 46 and a pair of optical resonator mirrors 50 and 52 disposed on the optical axis of the YAG rod 48 outside the chamber 46. doing. Inside the chamber 46, the temperature of the excitation lamp 16 and the YAG rod 48 are controlled by a cooling medium, for example, cooling water, which is circulated and supplied from a cooling unit (not shown) outside the chamber.

  When the excitation lamp 16 is turned on to emit excitation light, the YAG rod 48 is excited by the energy of the excitation light, and light emitted from both end faces of the YAG rod 48 on the optical axis is between the optical resonator mirrors 50 and 52. After the reflection is repeated and amplified, the laser beam LB exits the output mirror 52. The laser beam LB that has escaped from the output mirror 52 is sent to the incident unit 56 of the laser optical system 54.

  The laser optical system 54 transmits the laser beam LB received from the laser oscillation unit 38 to the incident unit 56 to the emission unit 60 via the optical fiber 58, and is condensed from the emission unit 60 onto the workpiece W on the processing table 62. Irradiate.

  An electromagnetic third switch 64 and a current limiting resistor 66 are connected in parallel with the capacitor 12. When this laser power supply device is stopped, the control unit 20 turns on the third switch 64 to release electric energy from the capacitor 12 once for security reasons.

The control unit 20 includes a microcomputer and a required interface circuit, and is also connected to peripheral devices (not shown) such as a keyboard and a display on the operation panel and external devices (not shown) such as a work transfer device. While monitoring the voltage drop V _LR generated in the coil 26 and the resistor 28 of the charging circuit 14 or the voltage drop V _LS generated in the coil 26 and the second switch 30 through the monitoring circuit 70 described later, The on / off of the first and second switches 24, 30 and the switching operation of the switching controller (32, 40) are controlled.

The monitoring circuit 70 in this embodiment includes an isolation amplifier 74 for detecting the voltage drop V _LR of the coil 26 and the resistor 28 or the voltage drop V _LS of the coil 26 and the second switch 30, and for stopping in an abnormal state. A monitoring value generation circuit 76 for generating two kinds of monitoring values MV _M1 and MV _M2 for charging completion, a switch 78 for selecting one of the monitoring values MV _M1 and MV _M2 , and an isolation amplifier 74 A comparator 80 for comparing the output or (coil + resistance) voltage drop measurement value MV _LR or (coil + second switch) voltage drop measurement value MV _LS with the monitoring value MV _M1 (MV _M2 ) selected by the switch 78; Have Here, one (positive polarity) input terminal of the isolation amplifier 74 is connected to a node point N _A between the output terminal of the three-phase rectifier circuit 10 and the coil 26 via the voltage sense line 72A, and the other ( input terminal of the negative polarity) is connected via a voltage sense line 72C to the node N _C between the resistor 28 and the second switch 30 and a capacitor 12. The output of the comparator 80 is given to the control unit 20.

In the monitoring circuit 70, the monitoring value MV _M1 for stopping when abnormal is a positive set value. In the steady operation mode, the comparator 80 generates an L level output signal (comparison result signal) CO when MV _LS <MV _M1 , and generates an H level output signal CO when MV _LS > MV _M1. It has become. On the other hand, the monitoring value MV _M2 for completion of charging is also a positive set value. In the charging operation mode, the comparator 80 generates an L level output signal (comparison result signal) CO when MV _LR <MV _M2 , and generates an H level output signal CO when MV _LR > MV _M2. It has become.

This laser power supply apparatus has the above-described apparatus configuration, and in particular, by the monitoring function of the monitoring circuit 70 and the control function of the control unit 20, a rapid change in the load (lamp current I _d ) or the AC power supply voltage during laser processing. Even if a sudden fluctuation occurs, the charging circuit 14 does not cause an inrush current, and the coil 26, the second switch 30 and the capacitor 12 are protected from the inrush current. For this reason, the inductance of the coil 26 and the electrostatic capacity of the capacitor 12 are sufficiently increased so as to be able to cope with high-capacity and high-power laser processing. The capacitor 12 is preferably an electrolytic capacitor, and an array type capacitor in which a plurality of capacitors are connected in series, in parallel, or in series and in parallel is preferably used.

  Next, with reference to FIG. 2, the operation of charging the capacitor 12 from a substantially non-charged state to a set voltage in this laser power supply device will be described.

Control unit 20 in order to charge the capacitor 12, while stopping the switching operation of the switching element 32, the second switch 30 maintains the off state, to turn on the first switch 24 at time t _0. Then, a DC charging current I _C flows into the capacitor 12 from the output terminal of the three-phase rectifier circuit 10 via the coil 26 and the current limiting resistor 28, and the voltage between terminals of the capacitor 12, that is, the charging voltage V _C increases. In this case, when the charging current I _C starts to flow, since the rate of change with time is the largest, a voltage drop V _L of a large value V _LO corresponding to the output voltage of the three-phase rectifier circuit 10 occurs in the coil 26. . Thereafter, as the current value of the charging current I _C increases, the charging voltage V _C of the capacitor 12 and the voltage drop R · I _C of the resistor 28 (where R is the resistance value of the resistor 28) increase while the charging current increases. The rate of change of I _C decreases and the voltage drop V _L of the coil 26 decreases. If the inductance of the coil 26 is L, the voltage drop V _L is V _L = L · dI _C / dt.

Then, after reaching the charging current I _C is the maximum value I _CP at time t _1, along with a decrease in the charging current I _C, while the rate of increase in the charging voltage V _C of the capacitor 12 is reduced, the coil 26 As the voltage drop V _L changes to a negative polarity, the voltage drop R · I _{C of the} resistor 28 starts to decrease, and the voltage drop of the coil 26 and the resistor 28, that is, the (coil + resistance) voltage drop V _LR further decreases.

In the capacitor charging operation, the control unit 20 selects the monitoring value MV _M2 for completion of charging from the monitoring value generation circuit 76 through the switch 78 and supplies it to the comparator 80. The comparator 80 compares the (coil + resistance) voltage drop measurement value MV _LR from the isolation amplifier 74 with the monitoring value MV _M2 and continues to output the H level comparison result signal CO immediately after the start of charging.

When at time t ₂ is (coil + resistor) voltage drop V _LR dividing monitoring value V _M2, the output signal (comparison result signal) CO of the comparator 80 changes from H level to it L level. The control unit 20 turns on the second switch 30 immediately at this timing (time t ₂ ) or (more preferably) at time t ₃ after a certain delay time has elapsed.

When the second switch 30 is turned on, the coil 26 and the capacitor 12 are short-circuited via the second switch 30, and the electromagnetic energy remaining in the coil 26 is quickly released to the capacitor 12. As a result, the charging current I _C increases momentarily, and the charging voltage V _C of the capacitor 12 immediately reaches the set voltage V _S , whereupon the charging operation is completed (time t ₄ ).

The set voltage V _S in this embodiment is not a fixed value in advance, but is the maximum charge voltage possible under the current commercial AC power supply voltage, that is, a target value. Therefore, for example, if the current commercial AC power supply voltage is an effective value of 400 volts, the set voltage V _S is about 400√2 volts, and if the current commercial AC power supply voltage is 380 V, the set voltage V _S is 380√. Near 2 volts. In any case, in this embodiment, the voltage drop V _LR of the coil 26 and the resistor 28 divides the monitored value MV _M2, that is, the timing when the charging voltage V _{C of the} capacitor 12 approaches the set voltage V _S. The second switch 30 can be reliably switched from the off state to the on state.

In this regard, the conventional laser power supply device (FIG. 10) is a method for monitoring the charging voltage V _C of the capacitor 12. Therefore, for example, when the set voltage V _S is set to 400√2 volts and the monitored value is set to 390√2 volts, if the current commercial AC power supply voltage is 380 volts in terms of effective value, the second time will pass. The switch 110 cannot be switched from the off state to the on state. In that case, if the laser processing is performed by operating the switching control circuit 118 (that is, the excitation lamp emits light), the charging current continues to flow through the resistor 108, resulting in a large amount of power loss.

Next, with reference to FIG. 3, an explanation will be given of the operation of the laser power supply apparatus when the charging voltage V _{C of the} capacitor 12 is about to drop rapidly due to load fluctuation during laser processing.

During laser processing, the isolation amplifier 74 detects (measures) the voltage drop of the coil 26 and the second switch 30 (ie, the (coil + second switch)) voltage drop V _LS through the voltage sense lines 72A and 72C. The control unit 20 selects the monitoring value MV _M1 for stopping at the time of abnormality from the monitoring value generation circuit 76 through the switch 78 and supplies it to the comparator 80. The comparator 80 compares the (coil + second switch) voltage drop measurement value MV _LS from the isolation amplifier 74 with the monitoring value MV _M1, and when normal, since MV _LS <MV _{M1, the} L level comparison result signal CO Will continue to be output. The control unit 20 keeps the switches 24 and 30 on while the output signal CO of the comparator 80 is at the L level.

In FIG. 3, for example, it is assumed that the load (lamp current I _d ) suddenly increases at time t ₁₀ . Then, from this time point t ₁₀ , the charging voltage V _C of the capacitor 12 starts to rapidly decrease from the stable value V _CO until then, and the charging current I _C rapidly increases from the substantially constant value I _CO until then. Start to increase.

When the charging current I _C rapidly increases in this way, the (coil + second switch) voltage drop V _LS rises rapidly from the previous value near zero. When the increase fluctuation rate of the charging current I _C is considerably large, the (coil + second switch) voltage drop V _LS rises to a level exceeding the monitoring value V _M1 for stopping when abnormal. Then, the output (comparison result signal) CO of the comparator 80 changes from the previous L level to the H level. The controller 20 immediately or at this time (time t ₁₀ ) or (preferably) confirms that the output CO of the comparator 80 has continued for a predetermined time T _S , and at time t ₁₁ , the switches 24, 30. And the switching operation of the switching element 32 is stopped through the switching control circuit 40.

When the switches 24 and 30 are turned off, the electromagnetic energy accumulated in the coil 26 is released to the capacitor 12 through the current limiting resistor 28, and the charging current I _C is rapidly reduced and stopped. The timing for turning off the switches 24 and 30 and the timing for stopping the switching operation of the switching element 32 may be the same or may be slightly different.

As described above, when the charging voltage V _C of the capacitor 12 rapidly decreases during the laser oscillation or the laser processing and the charging current I _C tends to increase rapidly, the coil 26 and the second switch 30 are at the tip of the charging current I _C. Since the voltage drop V _LS exceeds the monitoring value V _M1 for stopping in the event of an abnormality, the control unit 20 operates the switch before the charging current I _C increases abnormally and before a large amount of electromagnetic energy accumulates in the coil 26. 24 and 30 can be turned off. As a result, inrush current can be prevented from occurring in the charging circuit 14, and spark can be prevented from occurring in the switch 30.

Next, with reference to FIG. 4, the operation of the laser power supply apparatus when the charging voltage V _{C of the} capacitor 12 is temporarily lowered gradually due to load fluctuations during laser processing will be described.

In FIG. 4, for example, it is assumed that the load (lamp current I _d ) increases relatively slowly at time t ₂₀ . Then, from this time t ₂₀ , the charging voltage V _C of the capacitor 12 starts to decrease from the stable value V _CO until then at the same gentleness, whereby the charging current I _C becomes the substantially constant value I _CO until then. It starts to increase with the same gentleness. In this case, since the temporal change rate of the charging current I _C is not so large, the voltage drop V _LS of the coil 26 and the second switch 30 does not rise to a level exceeding the monitoring value V _M1 for stopping at the time of abnormality. Therefore, the output (comparison result signal) CO of the comparator 80 remains at the L level, and the control unit 20 keeps the switches 24 and 30 on. In this way, even if a load change (especially an increase in load) occurs, if the inrush current does not occur in the charging circuit 14, it is not necessary to stop the apparatus unnecessarily, and laser processing is continued stably. can do.

The same applies when the commercial AC power supply voltage fluctuates. Also in this case, the charging current I _C changes with time according to the fluctuation of the commercial AC power supply voltage. In particular, when the commercial AC power supply voltage rises, the charging current I _C changes in an increasing direction, and when the current change rate and change amount are very large, the charging current I _C becomes an inrush current. However, in this embodiment, the switches 24 and 30 are surely turned off before the charging current I _C abnormally increases by the functions of the monitoring unit 70 and the control unit 20, thereby preventing inrush current from occurring. Can do.

Even if the commercial AC power supply voltage fluctuates and the output voltage of the three-phase rectifier circuit 10 becomes lower than the charging voltage V _{C of the} capacitor 12, the three-phase rectifier circuit 10 has a rectifying function, so that the capacitor 12 Current flows from the first switch 30 and the coil 26 to the three-phase rectifier circuit 10. That is, the charging current I _C does not flow in the reverse direction.

[Embodiment 2]

  FIG. 5 shows a configuration of a laser power supply apparatus according to the second embodiment of the present invention. In the drawing, parts having the same configuration or function as those of the first embodiment (FIG. 1) are denoted by the same reference numerals.

The monitoring circuit 70 in the second embodiment includes an isolation amplifier 74 for detecting the voltage drop V _L of the coil 26, and two types of monitoring values MV _M1 and -MV for stopping at the time of abnormality and for completing charging. A monitoring value generation circuit 76 for generating _M2 , a switch 78 for selecting one of the monitoring values MV _M1 and -MV _M2 , an output of the isolation amplifier 74, that is, a measured value of coil voltage drop MV _L and a switch 78 And a comparator 80 that compares the monitored value MV _M1 (−MV _M2 ) selected by. Here, one (positive polarity) input terminal of the isolation amplifier 74 is connected to a node point N _A between the output terminal of the three-phase rectifier circuit 10 and the coil 26 via the voltage sense line 72A, and the other ( input terminal of the negative polarity) is connected via a voltage sense line 72B to the node N _B between the resistor 28 and the second switch 30 and the coil 26. The output of the comparator 80 is given to the control unit 20.

Here, the monitoring value MV _M1 for stopping at the time of abnormality is a positive polarity set value. In the steady operation mode, the comparator 80 generates an L level output signal (comparison result signal) CO when MV _L <MV _M1 , and generates an H level output signal CO when MV _L > MV _M1. It has become. On the other hand, the monitoring value −MV _M2 for completion of charging is a negative polarity set value. In the charging operation mode, the comparator 80 generates an L level output signal (comparison result signal) CO when MV _L <−MV _M2 , and generates an H level output signal CO when MV _L > −MV _M2. It is supposed to be.

  With reference to FIG. 6, the operation when charging the capacitor 12 from a substantially non-charged state to a set voltage in the laser power source device of the second embodiment will be described.

Control unit 20 in order to charge the capacitor 12, while stopping the switching operation of the switching element 32, the second switch 30 maintains the off state, to turn on the first switch 24 at time t _0. Then, a DC charging current I _C flows into the capacitor 12 from the output terminal of the three-phase rectifier circuit 10 via the coil 26 and the current limiting resistor 28, and the voltage between terminals of the capacitor 12, that is, the charging voltage V _C increases. Similarly to the above, when the charging current I _C starts to flow, since the rate of change over time is the largest, the voltage drop V _L of the large value V _LO corresponding to the output voltage of the three-phase rectifier circuit 10 is applied to the coil 26. Occur. Thereafter, as the current value of the charging current I _C increases, the charging voltage V _C of the capacitor 12 and the voltage drop R · I _C of the resistor 28 (where R is the resistance value of the resistor 28) increase while the charging current increases. The rate of change of I _C decreases and the voltage drop V _L of the coil 26 decreases.

Then, after the charging current I _C at the time t ₁ has reached the maximum value I _CP is with a decrease of the charging current I _C, with increasing speed of the charging voltage V _C of the capacitor 12 decreases, the voltage of the resistor 28 The drop R · I _C begins to decrease, and the voltage drop V _L of the coil 26 changes to negative polarity.

In the capacitor charging operation, the control unit 20 selects the monitoring value −MV _M2 for charging completion from the monitoring value generation circuit 76 through the switch 78 and supplies it to the comparator 80. The comparator 80 compares the coil voltage drop measurement value MV _L from the isolation amplifier 74 with the monitoring value −MV _M2 and continues to output the H-level comparison result signal CO immediately after the start of charging. When the voltage drop V _L of the coil 26 changes to the negative polarity and becomes lower than the monitored value −V _M2 , the comparison result signal CO changes from the previous H level to the L level. The control unit 20 maintains the OFF state of the second switch 30 and the switching element 32 not only during the period in which the output signal CO of the comparator 80 is at the H level but also from the H level to the L level.

Thus, as the charging voltage V _C of the capacitor 12 approaches the set voltage V _S , the current value of the charging current I _C approaches zero, and the voltage drop V _L of the coil 26 decreases in the negative polarity direction. Then, at time t _2, when the changes from <-V _M2 V _L> V _L voltage drop V _L of the coil 26 is increased to -V _M2 (when the positive direction greater than -V _M2), the output of the comparator 80 The signal CO changes from the previous L level to the H level. The control unit 20 turns on the second switch 30 immediately at this timing (time t ₂ ) or (more preferably) at time t ₃ after a certain delay time has elapsed.

When the second switch 30 is turned on, the coil 26 and the capacitor 12 are short-circuited via the second switch 30, and the electromagnetic energy remaining in the coil 26 is quickly released to the capacitor 12. As a result, the charging current I _C increases momentarily, and the charging voltage V _C of the capacitor 12 immediately reaches the set voltage V _S , whereupon the charging operation is completed (time t ₄ ).

In the second embodiment, the action when the charging voltage V _{C of the} capacitor 12 is suddenly lowered due to the fluctuation of the load during laser processing and the charging voltage V _C of the capacitor 12 is temporarily lowered gradually. The operation of is exactly the same as in the first embodiment.

Therefore, also in the second embodiment, no inrush current flows in the charging circuit 14, and the coil 26, the second switch 30 and the capacitor 12 are protected from the inrush current. For this reason, the inductance of the coil 26 and the electrostatic capacitance of the capacitor 12 can be made sufficiently large to cope with large-capacity and high-power laser processing.

[Other Embodiments or Modifications]

  Although the preferred embodiments of the present invention have been described above, the first and second embodiments described above do not limit the present invention. Those skilled in the art can add other embodiments or various modifications and changes to specific embodiments without departing from the technical idea and technical scope of the present invention.

For example, as a third embodiment, as shown in FIG. 7, instead of monitoring the voltage drop V _L of the coil 26 in the monitoring unit 70, the temporal change rate of the current flowing through the coil 26, that is, the charging current I _C. It is also possible to monitor dI _C / dt (hereinafter referred to as ∇I _C ). In this embodiment, when the current sensor 82 attached to the electric circuit of the charging circuit 14 detects the current value (instantaneous value) of the charging current I _C as, for example, a Hall element, the output signal of the current sensor 82 is differentiated. providing a current differential value measuring circuit 84 for generating a current change rate measurements M∇I _C. When the current sensor 82 outputs a differential value ∇I _C of the charging current I _C like, for example, a toroidal coil, the current differential value measurement circuit 84 may be replaced with an amplifier. The monitoring value generation circuit 76 generates a monitoring value M∇V _M1 for stopping at the time of abnormality and a monitoring value −M∇V _M2 for completion of charging corresponding to the differential value of the charging current I _C.

Further, as shown in FIG. 7, the laser driving circuit 18 can drive the excitation lamp 16 by power feedback control. In the illustrated configuration example, the power (laser output) P _LB of the laser beam _LB is measured by the half mirror 86, the photo sensor 88, and the laser output measurement circuit 90, and the laser output measurement value MP _LB is fed back to the switching control circuit 40. The switching control circuit 40 performs PWM (pulse width modulation) type switching control.

  As a modification, as shown in FIGS. 8 and 9, a switching transformer circuit 92 is provided between the first capacitor 12 and the second capacitor 15 for accumulating laser electric energy for lamp excitation. The present invention can also be applied to a laser power supply apparatus. The switching transformer circuit 92 is configured by cascading an inverter circuit 94, a step-up transformer 95, a rectifier circuit 96, and a choke coil 98. A control circuit (not shown) for switching control of the switching elements constituting the inverter circuit 94 is also provided.

Although not shown, a configuration in which the first switch 24 is provided in the electric circuit in the charging circuit 14 is also possible. For example, first closing the coil 26 in series between the output terminal and the node N _B of the resistor 28 in series with the second switch 30 and configured to connect the first switch 24 in parallel, or a three-phase rectifier circuit 10 A configuration in which the device 24 is connected is also possible.

  Various modifications can be made to the configuration of the monitoring unit 70 and the control unit 20. For example, a configuration in which the control unit 20 has the functions of the monitoring value generation circuit 76 and the comparator 80 is also possible.

  Moreover, although the laser power supply apparatus of the embodiment described above inputs three-phase alternating current from a three-phase alternating current power supply, the present invention can also be applied to a laser power supply apparatus of a type that inputs single-phase alternating current from a single-phase alternating current power supply.

DESCRIPTION OF SYMBOLS 10 Three-phase rectifier circuit 12 Capacitor 14 Charging circuit 16 Excitation lamp 18 Lamp drive circuit 20 Control part 24 1st switch 26 Coil 28 Current limiting resistor 30 2nd switch 32 Switching element 38 Laser oscillation part 40 Switching control part 70 Monitoring 72A, 72B, 72C Voltage sense line 74 Isolation amplifier 76 Monitor value generation circuit 78 Switch 80 Comparator 82 Current sensor 84 Current differential value measurement circuit

Claims (6)

A laser power supply device for supplying power to an excitation lamp that irradiates a solid-state laser medium with excitation light for laser oscillation,
A rectifier circuit that rectifies commercial frequency alternating current and converts it to direct current;
A capacitor for storing DC power output from the rectifier circuit;
A coil and a resistor connected in series between the rectifier circuit and the capacitor;
A first switch provided in the AC circuit, or connected in series with the resistor between the rectifier circuit and the capacitor;
A second switch connected in parallel with the resistor;
A lamp driving circuit for discharging the electric energy stored in the capacitor to the excitation lamp side and causing a lamp current to flow to the excitation lamp;
A monitoring unit for monitoring a voltage drop caused by the coil and the resistor or a voltage drop caused by the coil and the second switch;
And a controller that controls on / off of the first and second switches based on a monitoring result output from the monitoring unit.   When the controller charges the capacitor from a substantially non-charged state to a predetermined voltage, a monitoring result that the voltage drop of the coil and the resistor has divided a second reference value is output from the monitoring unit. 2. The laser power supply device according to claim 1, wherein when the first switch is turned on, the second switch is turned on.   The control unit monitors a monitoring result that the voltage drop of the coil and the second switch is smaller than a first reference value after charging the capacitor from a substantially non-charged state to a predetermined voltage. The first and second switches are kept on during the output, and the monitoring result that the voltage drop of the coil and the second switch exceeds the first reference value is the monitoring unit. 3. The laser power supply device according to claim 1, wherein at least one of the first switch and the second switch is turned off when the power is further output.   When the monitoring result that the voltage drop of the coil and the second switch exceeds the first reference value is output from the monitoring unit for a predetermined time, the control unit outputs the first The laser power supply device according to claim 3, wherein at least one of the second switch and the second switch is turned off. The lamp driving circuit is
A switching element connected between the capacitor and the excitation lamp;
And a switching control unit for switching control of the switching element at a fixed frequency higher than the commercial frequency, laser power supply device according to any one of claims 1-4. The lamp driving circuit performs a switching operation of the switching element in a state where both the first and second switches are in an on state, and one of the first and second switches is in an off state from an on state. The laser power supply device according to any one of claims 1 to 5 , wherein when switching to, the switching operation of the switching element is stopped in conjunction with the switching.

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