JP2016059932A - Laser processing apparatus and output method of pulse laser beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing apparatus capable of changing pulse energy by adjusting laser power for each laser pulse.SOLUTION: A laser power source applies a high frequency voltage to a discharge electrode of a laser oscillator according to a duty cycle of an input excitation command signal. An excitation pattern command signal including duty cycle information is input to a laser control apparatus. The laser control apparatus gives the excitation command signal to the laser power source on the basis of the duty cycle information included in the excitation pattern command signal. A machine control apparatus gives a pulse output timing signal, which commands output timing of a pulse laser beam, and the excitation pattern command signal to the laser control apparatus. A stage holds a workpiece. An optical system guides the pulse laser beam output from the laser oscillator to the workpiece held on the stage.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laser processing apparatus that performs processing by causing a pulse laser beam to enter a processing object, and a pulse laser beam output method that is applied to the laser processing apparatus.

  Patent Documents 1 to 3 disclose power supply devices that control laser output by applying a high-frequency voltage supplied to a discharge electrode of a carbon dioxide laser.

  In the power supply device disclosed in Patent Document 1, on / off control of the inverter is performed based on a command pulse that has been pulse frequency modulated in accordance with the machining conditions of the workpiece. A voltage pulse whose pulse frequency is modulated is output from the inverter and applied to the discharge electrode. Thereby, improvement of processing quality can be aimed at.

  In the power supply device disclosed in Patent Document 2, the pulse width of the output voltage of the inverter is controlled so that the detected value of the discharge current matches the set value. The switching frequency of the inverter is increased according to the decrease of the discharge current so that the rise of the output current of the inverter is delayed from the rise of the output voltage of the inverter. Thereby, high efficiency and low noise of the laser power source can be achieved.

  In the power supply device disclosed in Patent Document 3, pulse width modulation is employed to control the output of the RF power supply of the gas discharge laser. The average power of the digital pulse train is selectively changed by incrementally varying the duration of the digital pulses in the digital pulse train applied to the RF power supply.

JP 2013-089788 A Japanese Patent No. 0436369 Special table 2013-507790 gazette

  In order to improve the laser processing quality, it is required to control the pulse energy of the pulse laser beam. The pulse energy is obtained by time-integrating the instantaneous value of the laser power from the rising point to the falling point. In order to increase the pulse energy, a method of increasing the pulse width and a method of increasing the laser power can be considered. When a carbon dioxide laser is used as the laser light source, conventionally, the pulse energy is changed by changing the pulse width of the laser pulse. This is because it was difficult to change the laser power for each laser pulse, and it was easy to change the pulse width.

  However, it has been found that even if the pulse energy is the same, the processing quality is different if the pulse width and laser power are different. Only the method of changing the pulse energy by adjusting the pulse width is insufficient for high-quality processing, and a technique for adjusting the laser power and changing the pulse energy is desired.

An object of the present invention is to provide a laser processing apparatus capable of changing pulse energy by adjusting laser power for each laser pulse. Another object of the present invention is to provide a pulse laser beam output method applied to a laser processing apparatus.

According to one aspect of the invention,
A laser oscillator including a pair of discharge electrodes and outputting a pulsed laser beam;
A laser power source for applying a high-frequency voltage to the discharge electrode according to a duty cycle of an input excitation command signal;
When an excitation pattern command signal including duty cycle information and a pulse output timing signal for commanding the output timing of a pulsed laser beam are input, the laser power supply is supplied to the laser power source based on the duty cycle information included in the excitation pattern command signal. A laser control device for providing the excitation command signal;
A processing machine control device for supplying the pulse output timing signal and the excitation pattern command signal to the laser control device, and a stage for holding a workpiece;
There is provided a laser processing apparatus having an optical system for guiding the pulsed laser beam output from the laser oscillator to an object to be processed held on the stage.

According to another aspect of the invention,
A laser oscillator including a pair of discharge electrodes and outputting a pulsed laser beam;
A laser power source for applying a high-frequency voltage to the discharge electrode according to a duty cycle of an input excitation command signal;
When duty cycle information is input, a control device that provides the excitation command signal to the laser power source based on the input duty cycle information;
An input device for inputting the duty cycle information to the control device;
A stage for holding the workpiece,
There is provided a laser processing apparatus having an optical system for guiding the pulsed laser beam output from the laser oscillator to an object to be processed held on the stage.

According to yet another aspect of the invention,
A method of exciting a plasma and outputting a pulsed laser beam by applying a high frequency voltage in a pulsed manner to a discharge electrode of a gas laser oscillator through an H bridge circuit,
By changing the duty cycle of the conduction time of the H-bridge circuit for each laser pulse, there is provided a pulse laser beam output method for changing the average power within the pulse width of the laser pulse.

  By applying a high frequency voltage to the discharge electrode according to the duty cycle of the excitation command signal, the average power within the pulse width of the pulse laser beam can be changed. By changing the duty cycle of the excitation command signal for each laser pulse, the average power within the pulse width can be changed for each laser pulse.

FIG. 1 is a schematic diagram of an optical system and a block diagram of a control system of a laser processing apparatus according to an embodiment. FIG. 2 is a cross-sectional view of the laser oscillator. FIG. 3 is an equivalent circuit diagram of the high-frequency power source. FIG. 4 is a timing chart of an excitation pattern command signal, a pulse output timing signal, an excitation command signal, a high frequency voltage, a discharge current, and a pulse laser beam. FIG. 5A is a graph showing an example of the waveform of the excitation pattern command signal, the excitation command signal, and the pulse laser beam, and FIG. 5B is another example of the waveform of the excitation pattern command signal, the excitation command signal, and the pulse laser beam. It is a graph which shows. FIG. 6 is a graph showing an example of the relationship between the switching frequency and the average power within the pulse width of the pulse laser beam.

  FIG. 1 shows a schematic diagram of an optical system and a block diagram of a control system of a laser processing apparatus according to an embodiment. The laser power source 11 applies the high frequency voltage Ve to the discharge electrode 12 of the laser oscillator 10 in a pulse manner. The laser power source 11 includes a DC power source 13 and a high frequency power source 14. For example, a carbon dioxide laser oscillator is used as the laser oscillator 10. Based on a command from the processing machine control device 35, the laser control device 15 gives a control value Cv to the DC power supply 13 and gives an excitation command signal Ec to the high frequency power supply 14.

  The DC power supply 13 controls the DC voltage applied to the high frequency power supply 14 based on the control value Cv. The high frequency power supply 14 applies a high frequency voltage Ve to the discharge electrode 12 based on the excitation command signal Ec. Specifically, the average output within the pulse width of the pulse laser beam is controlled by the control value Cv. Here, the “average output within the pulse width” means a value obtained by averaging the laser output during the period in which the laser pulse is output, and is equal to a value obtained by dividing the pulse energy by the pulse width. On the other hand, “average output of pulse laser” generally used means a value obtained by averaging the laser output over a unit time including the time when the laser pulse is not output. The average output of the pulse laser is smaller than the average output within the pulse width.

  For example, when drilling a printed circuit board or the like, the average output within the pulse width, the pulse width, the pulse repetition frequency, and the like are controlled to match the target value.

  The high frequency power supply 14 includes a plurality of switching elements 14a, and switches the direct current supplied from the direct current power supply 13 to convert it into alternating current. The switching element 14 a is on / off controlled by an excitation command signal Ec input from the laser control device 15. The detailed configuration of the high frequency power supply 14 will be described later with reference to FIG.

  As the laser medium gas of the laser oscillator 10, for example, a mixed gas of carbon dioxide gas and nitrogen gas is used. When a high frequency voltage Ve is applied from the laser power source 11 to the discharge electrode 12, plasma is excited between the discharge electrodes, and a pulsed laser beam Lp is output from the laser oscillator 10.

  The pulsed laser beam Lp output from the laser oscillator 10 is branched into a transmitted beam and a reflected beam by the partial reflection mirror 21. The reflected beam enters the photodetector 20. When the light detector 20 detects light, it sends a detection value Dv corresponding to the light intensity to the laser control device 15. The photodetector 20 includes, for example, a mercury cadmium tellurium (MCT) photoconductive element having sensitivity in the wavelength region of a carbon dioxide laser.

  The transmitted beam that travels straight through the partial reflecting mirror 21 enters the workpiece 31 through the light guide optical system. The light guide optical system includes a spot position stabilizing optical system 22, an aspherical lens 23, a collimating lens 24, a mask 25, a field lens 26, a folding mirror 27, a beam scanner 28, and an fθ lens 29. The workpiece 31 is held on the stage 30.

The pulsed laser beam Lp that has passed through the spot position stabilizing optical system 22 enters the aspherical lens 23. The spot position stabilizing optical system 22 includes a plurality of convex lenses, and the position of the beam spot at the position where the aspherical lens 23 is disposed even when the pulse laser beam Lp output from the laser oscillator 10 is shaken in the traveling direction. To stabilize. The aspheric lens 23 changes the beam profile of the pulsed laser beam Lp. For example, a Gaussian beam profile is changed to a top flat beam profile.

  The pulse laser beam Lp transmitted through the aspheric lens 23 is collimated by the collimator lens 24 and then enters the mask 25. The mask 25 includes a transmission window and a light shielding part, and shapes the beam cross section of the pulse laser beam Lp. The pulse laser beam Lp transmitted through the transmission window of the mask 25 is incident on the beam scanner 28 via the field lens 26 and the folding mirror 27. The beam scanner 28 scans the laser beam in a two-dimensional direction according to a command from the processing machine control device 35. As the beam scanner 28, for example, a galvano scanner is used.

  The pulsed laser beam Lp scanned by the beam scanner 28 is condensed by the fθ lens 29 and enters the workpiece 31. The field lens 26 and the fθ lens 29 image the transmission window of the mask 25 on the surface of the workpiece 31. The stage 30 can move the workpiece 31 in a direction parallel to the surface thereof according to a command from the processing machine control device 35. At least one of the beam scanner 28 and the stage 30 functions as a moving mechanism for moving the incident position of the pulse laser beam Lp on the surface of the workpiece 31.

  The processing machine control device 35 gives the pulse output timing signal Pt and the excitation pattern command signal Ep to the laser control device 15. The laser control device 15 gives the excitation command signal Ec to the laser oscillator 10 during the period when the pulse output timing signal Pt is input. The duty cycle of the excitation command signal Ec and the pulse repetition frequency are specified by the excitation pattern command signal Ep. The repetition frequency of the pulses of the excitation command signal Ec matches the switching frequency of the high frequency power supply 14.

  FIG. 2 shows a cross-sectional view of the laser oscillator 10. A blower 40, a pair of discharge electrodes 12, a heat exchanger 46, and a laser medium gas are accommodated in the laser chamber 50. A discharge space 42 is defined between the pair of discharge electrodes 12. The discharge of the discharge space 42 excites the laser medium gas. In FIG. 2, a cross section orthogonal to the length direction of the discharge electrode 12 is shown. Each of the discharge electrodes 12 includes a conductive member 43 and a ceramic member 44. The ceramic member 44 isolates the conductive member 43 and the discharge space 42.

  A circulation path from the blower 40 to the blower 40 via the discharge space 42 and the heat exchanger 46 is formed in the laser chamber 50. The heat exchanger 46 cools the laser medium gas that has become hot due to the discharge.

  A pair of terminals 51 are attached to the wall surface of the laser chamber 50. The conductive member 43 of the discharge electrode 12 is connected to the terminal 51 by an in-chamber current path 52, respectively. The terminal 51 is connected to the laser power source 11 by an out-chamber current path 55.

  FIG. 3 shows an equivalent circuit diagram of the high-frequency power source 14. The high frequency power supply 14 includes an H bridge circuit having two bridge arms 14A and 14B. Each of the bridge arms 14A and 14B includes two switching elements 14a connected in series with each other. The discharge electrode 12 is connected to an intermediate point between the two bridge arms 14A and 14B via the transformer 14C. A DC power supply 13 applies a DC voltage to the H bridge circuit. On / off control of the switching element 14a is performed by the excitation command signal Ec from the laser control device 15.

After all the switching elements 14a are turned off, the switching element 14a on the high potential side of one bridge arm 14A and the switching element 14a on the low potential side of the other bridge arm 14B are switched on and then turned off. Then, after switching the switching element 14a on the low potential side of one bridge arm 14A and the switching element 14a on the high potential side of the other bridge arm 14B to the ON state, the procedure of returning to the OFF state is repeated. Thus, a high frequency voltage is applied to the discharge electrode 12.

  FIG. 4 shows an example of a timing chart of the excitation pattern command signal Ep, the pulse output timing signal Pt, the excitation command signal Ec, the high frequency voltage Ve, the discharge current Ie, and the pulse laser beam Lp. Excitation pattern command signal Ep includes duty cycle information and switching frequency information. As an example, the excitation pattern command signal Ep is transmitted from the processing machine control device 35 (FIG. 1) to the laser control device 15 (FIG. 1) by general serial communication or parallel communication. After transmitting the excitation pattern command signal Ep, the processing machine control device 35 raises the pulse output timing signal Pt. When it is desired to change the duty cycle or switching frequency within one laser pulse, the excitation pattern command signal Ep may include a plurality of duty cycle information and switching frequency information and information for instructing switching timing. .

  The pulse output timing signal Pt commands the start and stop of the output of the excitation command signal Ec by its rise and fall. When the pulse output timing signal Pt rises at time t1, the laser control device 15 starts outputting the excitation command signal Ec to the high frequency power source 14. When the pulse output timing signal Pt falls at time t <b> 3, the laser control device 15 stops outputting the excitation command signal Ec to the high frequency power supply 14.

  In FIG. 4, when the excitation command signal Ec is in the state Ec0, it indicates that all the switching elements 14a of the high-frequency power source 14 (FIG. 3) are in the OFF state. When the excitation command signal Ec is in the state Ec1, it indicates that the switching element 14a on the high potential side of one bridge arm 14A and the switching element 14a on the low potential side of the other bridge arm 14B are in the ON state. When Ec is in the state Ec2, it indicates that the switching element 14a on the low potential side of one bridge arm 14A and the switching element 14a on the high potential side of the other bridge arm 14B are in the ON state.

  When the excitation command signal Ec is given to the high frequency power supply 14, the high frequency power supply 14 applies the high frequency voltage Ve to the discharge electrode 12 in accordance with the duty cycle and switching frequency of the excitation command signal Ec. When the high-frequency voltage Ve is applied to the discharge electrode 12, plasma is excited between the discharge electrodes 12, and a discharge current Ie flows. Slightly behind the rising time t1 of the pulse output timing signal Pt, the output of the pulse laser beam Lp is started at time t2.

  When the excitation command signal Ec stops at time t3, the application of the high frequency voltage Ve to the discharge electrode 12 is also stopped, and the discharge current Ie starts to decrease. As a result, the output power of the pulse laser beam Lp also starts to decrease.

  Next, the relationship among the duty cycle information of the excitation pattern command signal Ep, the excitation command signal Ec, and the pulsed laser beam Lp will be described with reference to FIGS. 5A and 5B.

FIG. 5A shows an example of the waveforms of the excitation command signal Ec and the pulse laser beam Lp. States Ec1, Ec0, Ec2, and Ec0 appear in this order within one cycle of the excitation command signal Ec. The time T1 of each of the state Ec1 and the state Ec2 and the period T2 of the excitation command signal Ec are commanded by the excitation pattern command signal Ep (FIG. 4). The switching frequency fs of the high frequency power supply 14 is 1 / T2. The duty cycle Dcc of the excitation command signal Ec, that is, the duty cycle of the conduction time of the H bridge circuit constituting the high frequency power supply 14 (FIG. 3) is 2 ×
It is represented by T1 / T2.

  When the duty cycle Dcc and the switching frequency fs of the excitation command signal Ec are the conditions shown in FIG. 5A, the average power within the pulse width of the pulse laser beam Lp is Wa1. The pulse energy is obtained by multiplying the pulse width average power Wa1 by the pulse width.

  FIG. 5B shows another example of the waveforms of the excitation command signal Ec and the pulse laser beam Lp. Each time T1 of the state Ec1 and state Ec2 of the excitation command signal Ec shown in FIG. 5 is shorter than the time T1 of the excitation command signal Ec shown in FIG. 5A. The cycle T2 of the excitation command signal Ec is equal to the cycle T2 of the excitation command signal Ec shown in FIG. 5A. For this reason, the duty cycle Dcc of the excitation command signal Ec shown in FIG. 5B is smaller than the duty cycle Dcc of the excitation command signal Ec shown in FIG. 5A. The switching frequency fs of the excitation command signal Ec shown in FIG. 5B is equal to the switching frequency fs of the excitation command signal Ec shown in FIG. 5A. When the duty cycle Dcc of the excitation command signal Ec decreases, the high frequency power supplied to the discharge electrode 12 (FIG. 3) decreases, and the average power within the pulse width of the pulse laser beam Lp decreases. Therefore, the average power Wa2 within the pulse width of the pulse laser beam Lp when the duty cycle Dcc of the excitation command signal Ec and the switching frequency fs are the conditions shown in FIG. 5B is within the pulse width of the pulse laser beam Lp shown in FIG. 5A. Less than average power Wa1.

  As shown in FIGS. 5A and 5B, the average power within the pulse width of the pulse laser beam Lp can be changed by changing the duty cycle information commanded to the laser controller 15 by the excitation pattern command signal Ep. .

  Also by changing the output voltage of the DC power supply 13 (FIG. 1), the high frequency power supplied to the discharge electrode 12 can be changed, and the average power within the pulse width of the pulse laser beam Lp can be controlled. However, the output voltage of the DC power supply 13 is smoothed by a smoothing capacitor or the like. For this reason, it is difficult to change the output voltage of the DC power supply 13 with a time constant as short as the pulse interval of the pulse laser beam.

  In the above embodiment, the average power within the pulse width of the pulse laser beam is changed by changing the duty cycle Dcc of the excitation command signal Ec while keeping the DC voltage applied to the high frequency power supply 14 (FIG. 1) constant. I am letting. The duty cycle Dcc of the excitation command signal Ec can be changed every time the pulse output timing signal Pt is output. For this reason, it is possible to control the average power within the pulse width for each laser pulse.

  In FIGS. 5A to 5B, the switching frequency fs of the excitation command signal Ec is made constant and the duty cycle Dcc is changed to change the average power within the pulse width. On the other hand, even if the duty cycle Dcc is made constant and the switching frequency fs is changed, the average power within the pulse width can be changed.

  The switching frequency fs of the excitation command signal Ec is set in the vicinity of the resonance frequency fr of the resonance circuit including the transformer 14C and the discharge electrode 12 shown in FIG. Thereby, the high frequency power can be efficiently supplied to the laser oscillator 10. When the switching frequency fs deviates from the resonance frequency fr, the high frequency power supplied to the laser oscillator 10 decreases.

FIG. 6 shows an example of the relationship between the switching frequency fs and the average power Wa within the pulse width of the pulse laser beam Lp. When the switching frequency fs is equal to the resonance frequency fr, high-frequency power is efficiently supplied to the laser oscillator 10, so that the average power Wa within the pulse width shows the maximum value. When the switching frequency fs deviates from the resonance frequency fr, the high frequency power supplied to the laser oscillator 10 decreases, and the average power Wa within the pulse width decreases. Therefore, the average power Wa within the pulse width can also be changed by changing the switching frequency fs.

  In order to change the average power Wa within the pulse width, both the duty cycle Dcc and the switching frequency fs of the excitation command signal Ec may be changed. The duty cycle Dcc and the switching frequency fs of the excitation command signal Ec are commanded by an excitation pattern command signal Ep transmitted from the processing machine control device 35 to the laser control device 15.

  When the laser processing apparatus according to the embodiment is used for drilling a printed circuit board, the processing quality can be improved by controlling the average power within the pulse width for each laser pulse. The duty cycle information and the switching frequency information are input to the processing machine control device 35 through the input device 36.

  In the above embodiment, the carbon dioxide laser oscillator is used as the laser oscillator 10 (FIG. 1), but other gas laser oscillations can also be used.

  In the above embodiment, the laser control device 15 and the processing machine control device 35 are realized by different devices. However, the laser control device 15 and the processing machine control device 35 may be integrated and realized as one device. Good. In this case, the integrated control device provides the excitation command signal Ec to the laser power source 11 based on the duty cycle information input through the input device 36.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

DESCRIPTION OF SYMBOLS 10 Laser oscillator 11 Laser power supply 12 Discharge electrode 13 DC power supply 14 High frequency power supply 14a Switching element 14A, 14B Bridge arm 14C Transformer 15 Laser control apparatus 20 Photodetector 21 Partial reflection mirror 22 Spot position stabilization optical system 23 Aspherical lens 24 Collimating lens 25 Mask 26 Field lens 27 Folding mirror 28 Beam scanner 29 fθ lens 30 Stage 31 Processing object 35 Processing machine controller 36 Input device 40 Blower 42 Discharge space 43 Conductive member 44 Ceramic member 46 Heat exchanger 50 Laser chamber 51 Terminal 52 Current path in chamber 55 Current path Cv outside chamber Cv Control value Dcc Duty cycle Dv Detected value Ec Excitation command signal Ep Excitation pattern command signal Ie Discharge current Lp Pulse laser beam Pt Pulse output timing Average power in the grayed signal Ve frequency voltage Wa pulse width fr resonant frequency fs the switching frequency

Claims (9)

A laser oscillator including a pair of discharge electrodes and outputting a pulsed laser beam;
A laser power source for applying a high-frequency voltage to the discharge electrode according to a duty cycle of an input excitation command signal;
When an excitation pattern command signal including duty cycle information and a pulse output timing signal for commanding the output timing of a pulsed laser beam are input, the laser power supply is supplied to the laser power source based on the duty cycle information included in the excitation pattern command signal. A laser control device for providing the excitation command signal;
A processing machine control device for supplying the pulse output timing signal and the excitation pattern command signal to the laser control device, and a stage for holding a workpiece;
A laser processing apparatus comprising: an optical system that guides the pulsed laser beam output from the laser oscillator to an object to be processed held on the stage. further,
An input device for inputting the duty cycle information to the processing machine control device;
The laser processing apparatus according to claim 1, wherein the processing machine control device provides the excitation pattern command signal to the laser power source based on the duty cycle information input through the input device.   The laser processing apparatus according to claim 1, wherein the processing machine control device changes the excitation pattern command signal for each output of the pulse output timing signal.   The laser processing apparatus according to claim 1, wherein the laser oscillator is a carbon dioxide laser oscillator. The laser power supply is
An H-bridge circuit including two bridge arms;
A DC power supply for applying a DC voltage to the H-bridge circuit,
Each of the bridge arms includes two switching elements connected in series with each other,
Each of the pair of discharge electrodes is connected to an intermediate point between the two bridge arms,
The laser processing apparatus according to claim 1, wherein the excitation command signal performs on / off control of the switching element of the H bridge circuit. The excitation pattern command signal further includes switching frequency information for switching the H bridge circuit,
The laser processing device according to claim 5, wherein the laser control device gives the excitation command signal to the laser power source based on the duty cycle information and the switching frequency information included in the excitation pattern command signal. A laser oscillator including a pair of discharge electrodes and outputting a pulsed laser beam;
A laser power source for applying a high-frequency voltage to the discharge electrode according to a duty cycle of an input excitation command signal;
When duty cycle information is input, a control device that provides the excitation command signal to the laser power source based on the input duty cycle information;
An input device for inputting the duty cycle information to the control device;
A stage for holding the workpiece,
A laser processing apparatus comprising: an optical system that guides the pulsed laser beam output from the laser oscillator to an object to be processed held on the stage. A method of exciting a plasma and outputting a pulsed laser beam by applying a high frequency voltage in a pulsed manner to a discharge electrode of a gas laser oscillator through an H bridge circuit,
A pulse laser beam output method for changing the average power within the pulse width of the laser pulse by changing the duty cycle of the conduction time of the H-bridge circuit for each laser pulse.   The pulse laser beam output method according to claim 8, further comprising changing an average power within a pulse width of the laser pulse by changing a switching frequency of the H bridge circuit for each laser pulse.

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