JP2003298160A - Solid laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize a laser device capable of obtaining a stable output immediately after an emission of laser beams starts, thereby providing a laser processing device capable of attaining the processing quality which is always stable. <P>SOLUTION: A solid laser device outputs solid laser beams 7 from a solid laser unit by excitation by a laser diode LD. The solid laser device is provided with an energization control part for energizing excitation currents I(t), I(n) offsetting a temporal fluctuation change in an output of the solid laser beams to the laser diode LD, and a desired laser output value can be obtained in the output of the solid laser beams immediately after the output of the solid laser beams 7 starts by this energization control part. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly composed of a solid-state laser unit excited by a laser diode (hereinafter referred to as "LD"), and the stability of the solid-state laser output immediately after starting is greatly improved. The solid-state laser device.

[0002]

2. Description of the Related Art In recent years, high output of solid-state laser units,
Advances in high-brightness technology and the realization of a solid-state laser device that satisfies both performances at the same time have made it possible to perform precision welding and fine removal processing at high speed and precision that could not be achieved with conventional processing equipment. Came. For this reason, high-power / high-brightness solid-state laser units have come to be used for spot welding and seam welding of electric / electronic parts, and are actively applied to scribing and cutting of metals, semiconductors, ceramics, etc. .

As a typical example of the conventional solid-state laser device, the most popular laser active medium in the market is a rod type Nd: Y.
LD excitation pulse type Nd: Y with AG crystal and average output of 300W class
The configuration of the AG laser unit is shown in FIG.

Here, N is the core of the solid-state laser unit.
The d: YAG crystal 1 is the LD light 3 emitted from the LD 2 which is the excitation source.
And a total reflection mirror 5 which is excited by
1.06 emitted from the Nd: YAG crystal 1 between the output coupling mirror 6 and the output coupling mirror 6.
The μm light is selectively amplified, and is output from the output coupling mirror 6 to Nd: YAG.
It becomes the laser light 7 and is emitted. In addition, Nd: YAG according to the application
The laser output is controlled by the stabilized DC power supply 16 electrically coupled to the LD 2, and a constant LD excitation current corresponding to the desired solid state laser output is supplied to the LD. Further, in order to continuously maintain a constant Nd: YAG laser output, the Nd: YAG crystal 1 and the LD 2 are cooled by the cooling medium supply device 8 so that the Nd: YAG crystal 1 and the LD 2 have a constant temperature directly or in the peripheral portion thereof. The temperature is controlled through the medium.

The Nd: YAG laser light 7 is condensed by the incident condensing optical system 13 so as to satisfy the transmission condition of the transmission optical fiber 14 having a core diameter of 0.3 mm. In addition, the optical fiber 14
The laser beam emitted from the laser beam is shaped or focused by the emission focusing optical system 19 so as to have a beam shape suitable for processing on the workpiece 18 placed on the CNC table 17, and desired laser processing is performed. .

In the figure, reference numeral 9 indicates a beam splitter, reference numeral 10 indicates monitor light extracted by being reflected by the beam splitter, reference numeral 1
Reference numeral 1 indicates a thermoelectric conversion type monitor light output measuring instrument for output measurement, reference numeral 12 indicates a safety shutter which is activated when machining is not necessary, and reference numeral 15 indicates a beam damper to be irradiated at that time. Is.

[0007]

However, in the conventional configuration, since the output of the Nd: YAG laser beam 7 has two main output fluctuation factors, it is possible that Even when a constant excitation current is passed as in 3 (a), there is an unstable output period τ that is not seen in the steady state as shown in FIGS.

The first output fluctuation factor is that the LD2 itself is heated by self-heating when the LD2 starts to be supplied with an excitation current, and the temperature of the active layer rises, causing a wavelength shift of about +0.3 nm / ° C. . In addition, since the absorptance of the Nd: YAG crystal 1 with respect to the LD excitation light 3 has a strong wavelength dependence, the wavelength shift of the LD excitation light 3 causes a change in the output of the Nd: YAG laser light 7. Become.

More specifically, when the LD 2 is forcibly cooled at 20 ° C., even if the LD active layer temperature before energization is 20 ° C., it becomes 25 ° C.-35 ° C. in the energized state. Excitation light 3 is 1.
Increase by 5 to 4.5 nm. In this steady state of energization, Nd: YAG crystal 1
LD to emit light at a wavelength of 808 nm that maximizes absorption
2 is designed, the absorption rate is about 30% lower than that of 808 nm at the wavelength 803-806 nm immediately after the start of the excitation current to LD2. The output of: YAG laser light 7 is about 30% compared to the steady value.
The output is low, and the Nd: YAG laser light output tends to increase in a stepwise manner as the temperature of LD2 rises.

The second output fluctuation factor is that the absorption of the LD excitation light 3 raises the internal temperature of the Nd: YAG crystal 1 and the outer peripheral portion of the crystal 1 is cooled to a constant temperature. This is the generation of a thermal lens due to the generation of a temperature gradient to. In this case, the thermal lens is generated inside the crystal as a convex lens, so that the stability of laser oscillation increases in the steady state. Generally, since the laser oscillator is configured by taking into consideration the thermal lens inside the crystal generated in this steady state, it is unstable as compared with the stability in the steady state immediately after the start of emission of the Nd: YAG laser light output. This is a simple laser oscillator configuration. Therefore, the Nd: YAG laser light output is output low immediately after the LD is energized, and the Nd: YAG laser light output tends to increase in proportion to the increase in the internal temperature of the crystal.

As described above, since there is an unstable output period that cannot be seen in a steady state for a few seconds to a few minutes immediately after the emission of the Nd: YAG laser light, for example, in the laser bonding processing using the same laser light, Immediately after the start, there was a problem that the bonding strength became insufficient and processing defects occurred.

Further, in order to solve the above-mentioned problems, as is generally known, the Nd: YAG laser light output which is the controlled object amount is measured, and the result is fed back to the control command system to output the same. There is a feedback control method that controls the LD excitation current to increase or decrease so that the deviation from the target setting value of
This method is not applicable to commercial machines.

The reason for this is that an output sensor that can measure the Nd: YAG laser light output, which is the controlled object amount, at high speed and with high accuracy cannot be obtained at low cost.

There is also a technique in which the LD and the laser crystal are kept in a stable steady state by performing the warm-up operation under the conditions used in actual processing before performing the laser processing, and the actual processing is started. However, this has a drawback in that unnecessary energy is consumed without performing processing, which wastes energy and unnecessarily warms the surrounding environment.

The present invention solves the problem of instability immediately after the start of the emission of a solid-state laser light output, which is a problem in the above-mentioned LD-pumped solid-state laser device, by the following method.
The present invention provides a laser processing apparatus that can always obtain stable processing quality by realizing a laser apparatus that can obtain stable output immediately after the start of laser light emission.

[0016]

In order to solve the above-mentioned problems, the present invention corrects the deviation amount from the steady laser output value generated immediately after the start of laser light output, so that the deviation amount is equal to or more than a specified value. LD that is energized in steady state in
By passing the current increased or decreased from the excitation current,
It is intended to provide a technique capable of stably obtaining a desired laser output value immediately after the output of solid-state laser light is started.

In this case, such correction is not based on an instantaneous feedback control but is based on an open control based on a correction function such as a correction function or a table set in advance based on the characteristics of the solid-state laser. Therefore, there is no need to measure the solid-state laser output at high speed, and there is no need for warm-up operation.

By applying the laser output stabilization technique according to the present invention, high precision and high speed processing can be achieved at the same time, and the laser processing efficiency can be greatly improved. As a result, the processing time and the operating cost of the laser processing apparatus can be significantly reduced, and the problem of global warming can be solved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG.
Will be described with reference to. Since the mechanical structure is the same as that of the conventional example described based on FIG. 2, the description thereof is omitted, and only the control part of the LD excitation current having a structure different from that of the conventional example will be mainly described.

In the present embodiment, the temporal behavior of the pulse output type Nd: YAG laser device which reaches a steady state immediately after the start of the laser output injection can be linearly approximated by a linear function. Therefore, during the same period, by energizing while changing the relationship between the LD excitation current value and the elapsed time by approximating and changing it as a linear function, a stable laser output in which the laser output matches the steady state immediately after the start of injection is obtained. A description will be given of an application example of the above.

When the initial LD excitation current value at the start of the emission of the laser beam energized for correction is represented by αIs which is α times the steady LD excitation current value Is, continuous laser output operation is performed in the correction period 0 ≦ t <τ. The LD excitation current for making the equation becomes I (t) = ((1-α) ・ Is) ・ (t / τ) + α ・ Is ... by the linear function approximation, and it is necessary to perform the correction operation by this formula. is there. Here, the correction control magnification is α and the correction control time is τ.

To this end, a storage unit for providing a program area for storing a program for executing the calculation of the equation and a data area for storing the values of the parameters α, Is and τ is provided inside the LD excitation power supply control device. The storage unit includes an arithmetic unit that calls programs and data from the storage unit to sequentially perform necessary arithmetic operations, and an output unit that outputs a control signal to obtain an LD excitation current I (t) obtained as a result of the arithmetic operations. Is provided. The storage unit, arithmetic unit, and output unit can be configured using a general-purpose computer unit including a CPU, a memory, an interface, or the like, or can be configured as a dedicated machine. t
For example, the clock oscillated by the computer unit may be picked up and used.

However, in this embodiment, the repetition frequency f
Since pulse oscillation is performed with, it is necessary to correct each pulse according to the formula. In this case, the correction formula for the nth pulse is I (n) = (((1-α) · Is) · (n−1)) / (f · τ) + α · Is ... LD is the LD excitation current with the pulse corrected according to the formula
It was decided to carry out each pulsed LD excitation current by sequentially calculating it in the calculation unit inside the excitation power supply control device. Here, since the energization time of each pulse is 1 msec at the maximum and it is not necessary to correct the fluctuation of the laser output, the correction is not performed within the energization time. For this reason, the storage unit also stores a program necessary for executing the expression.
Whether the laser output is continuous operation or pulse operation,
It can be arbitrarily switched.

In each of the above programs, τ≤t
In the time domain of, the excitation current I (t) is switched to a constant value of I (t) = Is.

Here, in the conventional pulse output type Nd: YAG laser device, the pulse peak current is 70 A and the pulse width is 500.
In the operating state of μsec and repetition frequency f = 200Hz, the output value immediately after the start of laser output injection was 15% lower than the steady value, and it took 0.8 seconds to reach the steady output value. , Α = 1.1, τ = 0.5 sec, the laser output can be obtained with the desired stability (within ± 2%) from the first pulse immediately after the start of the laser output injection. FIGS. 1A and 1B show the relationship between the LD excitation current corrected according to the present embodiment and the laser output identification improved thereby.

By adjusting α and τ under other operating conditions, the initial rise characteristics of the laser output could be greatly improved.

In this embodiment, the correction function for the elapsed time of the LD excitation current was linearly approximated by a linear function. However, in order to improve the rising characteristics, a linear function of a quadratic or higher order or an exponential function is used. Then, a correction function may be created.

Further, in the above embodiment, the laser active medium forming the core of the solid laser unit is Nd: YAG of Nd: YAG crystal.
Although the case of the laser has been described, the laser active medium is the same as the present embodiment even if the solid crystal composed of a single solid crystal such as Yb: YAG, Nd: YVO4 or a combination thereof, or a ceramic crystal. The effect of can be expected.

Other configurations can be variously modified without departing from the spirit of the present invention.

[0030]

Since the present invention has the above-described structure, not only the accuracy and speed of laser processing can be greatly improved, but also warming-up operation is not required, which contributes to further resource saving. A device can be provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing laser output characteristics with respect to an LD excitation current according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a laser processing apparatus according to a conventional example.

FIG. 3 is a schematic diagram showing laser output characteristics with respect to an LD excitation current in the configuration of the conventional example.

[Explanation of symbols]

2 ... Laser diode (LD) 7 ... Solid-state laser light I (t), I (n) ... Excitation current

Claims (6)

[Claims] 1. In a solid-state laser device for outputting a solid-state laser light from a solid-state laser unit by excitation by a laser diode (LD), an excitation current for canceling a temporal increase / decrease change in the output of the solid-state laser light is applied to the laser diode. A solid-state laser device comprising an energization control unit, and the energization control unit is configured to obtain a desired laser output value in the solid-state laser light output immediately after the output of the solid-state laser light is started. 2. An LD excitation current I applied to the laser device.
The laser device according to claim 1, wherein (t) is approximated and corrected by the following equation using a linear function. Time of 0 ≦ t <τ: I (t) = ((1-α) · Is) · (t / τ) + α · Is ... Time of τ ≦ t: I (t) = Is (where Is Is the LD excitation current value at which the desired solid-state laser light output is obtained in a steady state, α is the ratio of the LD excitation current value that is conducted at the start of laser light emission to Is, and τ is the solid-state laser light output start when the LD excitation current is constant. From α to 1, the formula is a correction line that decreases with time when α <1, and when α> 1, the formula is a correction line that increases with time. Become.) 3. A desired solid-state laser in which the LD excitation current I (t) to be supplied is approximated and corrected by using a higher-order function or an exponential function of second order or more during the time 0 ≦ t <τ of the laser device. The laser device according to claim 1, wherein an optical output is obtained. 4. The laser device I (n) = according to claim 1, wherein, when the laser device is operating to output a pulse laser, the current value is changed for each pulse based on the following equation. (((1-α) · Is) · (n−1)) / (f · τ) + α · Is Equation (where f is the pulse repetition frequency and n is the nth pulse It represents.) 5. The laser device according to claim 2, wherein when the laser device is in continuous laser output operation, correction control of the LD excitation current can be performed according to an equation at regular time intervals. 6. The laser active medium of the solid-state laser unit is
6. The laser device according to claim 1, wherein the laser device is a single solid crystal such as Nd: YAG, Yb: YAG, or Nd: YVO4, a solid crystal composed of a combination thereof, or a ceramic crystal.