JP4543272B2 - Laser oscillation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser oscillation method, and more particularly to a laser oscillation method for pulsing a laser beam.
[0002]
[Prior art]
Conventionally, in a CO ₂ laser oscillator, a laser beam is pulse-oscillated by exciting a CO ₂ gas as a laser medium in a resonator by pulse discharge. Further, a Q switch device is provided in a laser oscillator to cause Q switch pulse oscillation. Examples of the Q switch device include a method using a chopper disk having a slit, a method using an electro-optic element, a method incorporating an ultrasonic modulator, and the like.
By the way, when a via hole processing is performed on a printed circuit board or the like, a method using a chopper disk capable of high peak and short pulse oscillation, sharpening the via hole shape and preventing carbonization is preferable. In such via hole processing, since the energy value of the irradiated laser beam is related to the shape of the via hole, the control of the energy value is very important.
For this reason, in a Q switch device using a chopper disk, the start or end of pulse discharge excitation is synchronized with the passage timing of the slit of the chopper disk, and the energy value of the laser beam oscillated by the Q switch pulse is controlled by the discharge excitation time width. Has been proposed (Japanese Patent Laid-Open No. 7-30179).
[0003]
[Problems to be solved by the invention]
However, in the above-described conventional example, if the time width of the immediately preceding pulse discharge is different, the internal gain remaining in the resonator after the Q switch pulse oscillation is also different, and the pulse discharge is excited again before the internal gain disappears. Therefore, it is difficult to accurately control the energy value of the oscillated laser beam even if the excitation time width is accurately controlled. In addition, the temperature, pressure, flow rate, and the like of the gas in the resonator constantly fluctuate, and there is a problem that the energy value for the set excitation time width varies.
Therefore, the present invention provides a laser oscillation method capable of accurately controlling the total energy value of the laser beam oscillated by the pulse excitation with a simple configuration regardless of the time width of the previous pulse excitation and the state of the laser medium. Is to provide.
[0004]
[Means for Solving the Problems]
In other words, the invention of claim 1 includes a laser oscillator that oscillates a laser beam by pulse-exciting the laser medium in the resonator, and a measurement unit that measures the energy value of the laser beam. In the laser oscillation method of controlling the laser beam so that the energy value of the laser beam becomes a predetermined value based on the measured value,
Among the laser beams that are oscillated a plurality of times during one pulse excitation, the energy values of a predetermined number of laser beams are extracted and measured by the measuring means, and each measured value is added to obtain an initial energy value, The expected total energy value of the laser beam oscillated by the pulse excitation is predicted from the initial energy value, and the energy values of all the laser beams actually measured by the measuring means based on the obtained expected total energy value. The excitation time is controlled so that the total energy value obtained by adding the values becomes a preset target energy value.
[0005]
According to the above-described invention, in one pulse excitation, when the expected total energy value predicted from the initial energy value obtained by adding the measurement values measured a plurality of times during the excitation is larger than the target energy value, the excitation time If the expected total energy value is shorter than the target energy value, the excitation time can be lengthened to accurately control the actually obtained total energy value.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The illustrated embodiment will be described below. In FIG. 1, reference numeral 1 denotes a CO ₂ laser oscillator that oscillates a laser beam L, and CO ₂ gas is circulated in the laser tube 2 as a laser medium.
The laser oscillator 1 is provided on the left side of the laser tube 2, reflects a laser beam L oscillated by discharge excitation (hereinafter referred to as excitation) in the laser tube 2, and the right side of the laser tube 2. An output mirror 4 that partially reflects the laser beam L excited in the laser tube 2 and allows the laser beam L to pass therethrough, and is disposed between the reflecting mirror 3 and the output mirror 4. 4 includes a Q switch device 5 that intermittently oscillates a laser beam L with a predetermined oscillation period and oscillation time, and in the laser oscillator 1, the reflecting mirror 3 and the output mirror 4 include a resonator. Is configured.
The Q switch device 5 is disposed between the laser tube 2 and the reflecting mirror 3 and is fixedly mounted on a telescope lens 7 for condensing the laser beam L in front of the reflecting mirror 3 and a frame (not shown). A spindle motor 8 as drive means and a disk-like chopper disk 11 which is integrally attached to the rotating shaft 9 of the spindle motor 8 and is inserted near the focal position of the laser beam L are provided. A plurality of penetrating portions (not shown) through which the laser beam L passes when the laser beam L is crossed at equal intervals on the circumference centered on the rotation center 11 are formed.
Further, on the left side of the reflecting mirror 3, a power monitor 14 is provided as a measuring means for detecting a slight laser beam L 'that has passed through the reflecting mirror 3, and the measured values from the power monitor 14 will be described in detail later. By inputting to the control device 13, the energy value of the laser beam L oscillated from the output mirror 4 is measured.
[0007]
In the control device 13, a different target oscillation cycle is set for each type of workpiece, and the rotational speed with respect to the spindle motor 8 is stored in advance so as to obtain this target oscillation cycle. Controls the spindle motor 8 according to this rotational speed. Further, the control device 13 is set with a different target energy value for each type of workpiece, and discharge current, discharge voltage, excitation for the laser gas in the laser tube 2 in advance so as to obtain this target energy value. Basic data of time and gas pressure are stored. And in the conventional control apparatus 13, the laser oscillator 1 was controlled according to the basic data mentioned above.
[0008]
Therefore, in this embodiment, the excitation time is controlled by the control device 13 so that the deviation from the target energy value becomes small according to the energy value of the laser beam L.
For this reason, the control device 13 monitors the measurement value input from the power monitor 14 simultaneously with the start of excitation, and is expected from the initial energy value obtained by adding the energy values of the laser beam L pulsated by the Q switch device 5. In addition to predicting the total energy value, predictive control is performed so that the excitation time excluding the discharge current, discharge voltage, and gas pressure is increased or decreased based on the prediction result so as to approach the target energy value. The control device 13 compares the total energy value actually obtained by the predictive control with the target energy value, and simultaneously performs feedback control for correcting the next excitation time based on the result.
[0009]
The above-described prediction control and feedback control processing will be specifically described based on the flowchart of FIG.
First, when an operator selects a workpiece to be processed, the control device 13 extracts corresponding basic data from the storage unit for the selected workpiece, and performs laser processing based on the extracted basic data. Initial setting of the oscillator 1 and the Q switch device 5 is performed. When the initial setting is completed, the process proceeds to predictive control. First, it is determined whether or not a trigger signal is input in the trigger signal detection process.
When a trigger signal is input during the trigger signal detection process, the control device 13 that has detected the trigger signal outputs a reset signal to the power monitor 14 and performs a reset process for correcting the value to zero. .
After completing the reset process, the control device 13 then proceeds to the excitation process, where the discharge voltage, discharge current, and excitation time commands based on the basic data are output to the laser oscillator 1 to start via hole processing. To do.
[0010]
Here, the control device 13 controls the discharge current, the discharge voltage, and the gas pressure in the laser tube 2 of the laser oscillator 1 based on the basic data, while the laser beam L pulsated by the Q switch device 5 at the start of excitation. The process of adding the measurement values input from the power monitor 14 for the energy output of the current is started. In this addition process, a pulse is oscillated a plurality of times during one pulse excitation, and the total energy value of the laser beam L ′ measured by the power monitor 14 after passing through the reflecting mirror 3 is added to obtain a total energy value. On the other hand, the energy value is stored individually for each number of times. This addition process is performed in parallel with other processes until it is read by a subsequent total energy value reading process.
The control device 13 performs a pulse number counting process that counts the number of times of input every time the addition process proceeds once. In this pulse number counting process, if the count number is less than 5, the addition process is performed again. However, when the count reaches 5, the process proceeds to the next initial energy value calculation process.
In the initial energy value calculation process, the second to fifth measurement values stored in the addition process are extracted and added to obtain the initial energy value . That is, the initial energy value is a value obtained by extracting the initial energy value from the total energy value obtained by adding all the energy outputs. When the initial energy value is obtained, it is stored, and the process proceeds to the next excitation time correction calculation process.
[0011]
In this excitation time correction calculation process, the excitation time X is determined by the following calculation formula to obtain a target energy value.
First, in order to collect data, the total energy value at each excitation time was measured by setting the excitation time between 200 to 600 μSec every 100 μSec, and a graph as shown in FIG. 3 was created. From this result, the relational expression between the excitation time X and the total energy value Y is
Y = 0.31X + 18.56 (1-1)
It becomes.
From the above approximate expression (1-1), the total energy value up to 300 μSec set as a standard is 111.56 mJ. When this value is a standard value, for example, when the initial energy value obtained by adding the actually obtained second to fifth measurement values is 100 mJ, the total energy value predicted from the actual initial energy value is obtained. . Here, from the past experimental results, the approximate expression when the discharge current is changed under the condition where the gas pressure is constant has a substantially constant slope, and a result of shifting in parallel is obtained. Therefore, if the approximate expression is Y = aX + b, a is constant and b changes.
Thus, when a is constant and b is obtained,
b = 100− (0.31 × 300 μSec) = 7
Therefore, the approximate expression is
Y = 0.31X + 7 (1-2)
It becomes.
Thereby, for example, when the target energy value is 150 mJ, when the excitation end time at 150 mJ is obtained from the approximate expression (1-2),
X = (150-7) /0.31=461
It becomes.
Therefore, it can be found that the excitation time is 461 μSec.
When the excitation time is found in this way, the process proceeds to the next excitation time resetting process, and 461 μSec is reset as the excitation time instead of the 300 μSec that has been temporarily set.
[0012]
By the way, the experiment of FIG. 3 was conducted under the following conditions.
In the present embodiment, as shown in FIG. 4, the pulse width of the Q switch device 5 is set to 5 μSec, the oscillation cycle is set to 50 μSec (20 kHz), and the timing (oscillation cycle) at which the slit of the Q switch device 5 passes is set. In contrast, the laser oscillator 1 is excited under the asynchronous condition.
By making the excitation timing of the laser oscillator 1 asynchronous in this way, the excitation can be started almost simultaneously with the detection of the trigger signal transmitted from the processing machine side. There is no wasted time from the trigger signal detection to the excitation start timing as when synchronized with the passage timing of the slit. Further, by continuing the oscillation with the internal gain remaining in the resonator after the excitation is completed, the residual internal gain can be effectively used and the efficiency is high. This is apparent from the experimental results of FIG. 4, and in this experiment, the time required to obtain a total energy value of 150 mJ was only 800 μSec from the detection of the trigger signal.
[0013]
Then, the control device 13 repeatedly determines whether or not the total time from the start of excitation has reached the above-mentioned 461 μSec in the excitation end processing, and outputs a command to the laser oscillator 1 when the total time reaches the excitation time 461 μSec. Then, excitation is terminated.
The process so far is the predictive control, and the pulse oscillation is continuously performed by the internal gain remaining in the laser tube 2 even after the excitation is finished based on the predictive control. It becomes settled around the target value of 150 mJ (see FIG. 4).
[0014]
And the control apparatus 13 which completed the above excitation completion | finish process transfers to feedback control in preparation for the next via hole process following predictive control.
In this feedback control, first, a total energy value reading process is performed. At this timing, the total energy value actually output by the current predictive control is read from the addition process continuously performed from the start of excitation to the end of pulse oscillation.
The timing for performing the feedback control may be based on the time from the end of the excitation end processing, or may be based on the absence of pulse oscillation even when 50 μSec or more has elapsed since the previous pulse oscillation.
The control device 13 that has read the total energy value in the total energy value reading process compares the total energy value with the target energy value 150 mJ in the next excitation time correction process, and the total energy value exceeds the target energy value 150 mJ. If so, the excitation time is increased or decreased by an amount proportional to the difference in energy value. For example, when the current total energy value is 153 mJ, the next excitation time is 452 μSec by subtracting 9 μSec corresponding to 3 mJ from the current excitation time 461 μSec.
In the next excitation time setting rewriting process, the control device 13 changes the excitation time from 300 μSec to 452 μSec. In the next via hole processing, the via hole processing is performed with reference to 452 μSec, and it is predicted for some reason. When the control is not in time, control is performed according to 452 μSec.
When this excitation time rewriting process is completed, feedback control, that is, via hole machining by the first pulse excitation is completed, and the control device 13 returns to the trigger determination process and prepares for a new via hole machining.
[0015]
As understood from the above description, in this embodiment, even if the energy output of the laser beam L fluctuates, a total energy value close to the target energy value can be obtained by laser oscillation by predictive control. In addition, since the control of the control device 13 makes it possible to increase the oscillation period and shorten the pulse excitation time without having to consider the synchronization of the oscillation period of the Q switch device 5 and the pulse excitation of the laser oscillator 1. Compared to the above, the time required for via hole processing can be shortened, and the configuration can be simplified because the synchronization signal generator and the delay circuit generator can be omitted.
[0016]
In the above embodiment, the present invention is applied to a gas laser oscillator, but the present invention is not limited to this, and a solid-state laser oscillation apparatus may be used.
[0017]
In the above embodiment, the Q switch device 5 includes the chopper disk 11, but is not limited thereto, and may be a Q switch device including an electro-optical element and a rotating mirror.
[0018]
Further, in the above embodiment, the present invention is applied to the laser oscillator 1 provided with the Q switch device 5, but the present invention is not limited to this, and the present invention may be applied to a laser oscillator that simply performs pulse excitation and pulse oscillation. .
[0019]
Further, in the above embodiment, the measurement values from the second time to the fifth time are added in order to obtain the initial energy value. However, the present invention is not limited to this, and the measurement is performed as early as possible in the pulse excitation. do it. The first pulse oscillation slightly varies depending on the deviation of the excitation start with respect to the passage of the Q switch device 5 through the slit. However, since the variation is very small, there is no problem with adding the first measurement value.
[0020]
【The invention's effect】
According to the present invention, the total energy value close to the target energy value can be obtained by laser oscillation by predictive control compared to the conventional laser oscillation method, and the processing time can be increased by using asynchronous control. Can be shortened, and the configuration of the laser oscillator itself can be simplified.
[Brief description of the drawings]
FIG. 1 is a layout view of a laser oscillator 1 showing a first embodiment of the present invention.
FIG. 2 is a flowchart showing prediction control and feedback control of the control device 13;
FIG. 3 is a graph showing experimental results obtained by measuring characteristics of energy output when the discharge voltage, the discharge current, and the gas pressure are fixed and the excitation time is changed.
FIG. 4 is a graph obtained by measuring the energy output of a laser beam obtained by predictive control according to an embodiment of the present invention and the time behavior of various signals related thereto.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Laser oscillator 2 ... Laser tube 13 ... Control apparatus 14 ... Power monitor L ... Laser beam

Claims (4)

A laser oscillator that oscillates a laser beam by exciting the laser medium in the resonator; and a measuring unit that measures the energy value of the laser beam. Based on the measured value obtained from the measuring unit, the laser beam In a laser oscillation method of performing laser oscillation by controlling the energy value to be a predetermined value ,
Among the laser beams that are oscillated a plurality of times during one pulse excitation, the energy values of a predetermined number of laser beams are extracted and measured by the measuring means, and each measured value is added to obtain an initial energy value, The expected total energy value of the laser beam oscillated by the pulse excitation is predicted from the initial energy value, and the energy values of all the laser beams actually measured by the measuring means based on the obtained expected total energy value. A laser oscillation method characterized in that the excitation time is controlled so that a total energy value obtained by adding up to a target energy value set in advance. 2. The laser oscillation method according to claim 1, wherein the next excitation time is set based on an actual total energy value obtained by one pulse excitation by the measuring means. 3. The laser oscillation method according to claim 1, wherein a Q switch device is arranged in the resonator to cause pulse oscillation, and an energy value of each pulse laser beam is measured and added. 4. The laser oscillation method according to claim 3, wherein the Q switch device is asynchronous with the excitation of the laser medium.

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