JP4630220B2 - Apparatus and method for preventing contamination of laser optical element - Google Patents

Description

  The present invention relates to a device and method for preventing contamination of an optical element used in laser processing in a poor environment.

  Usually, in a laser processing machine, an optical system such as a mirror that transmits laser light and a lens that condenses laser light is housed in the housing separately from the laser body, and the inside of the housing is made positive with clean purge gas or the like. It prevents dust and the like from entering and avoids contamination of the optical system. However, in an inferior environment with many foreign objects such as dust and dirt on the floor and in the air, such as factory lines such as steelworks, it is difficult to completely prevent entry into the case. When the body is opened, a considerable amount of foreign matter such as dust and dirt enters and stays in the casing.

  Foreign matter such as dust or dust may float on the purge gas or the like and adhere to the lens or mirror. Until now, in order to remove this foreign matter, a purge gas was blown locally to the lens or mirror to cope with it.

  In the case of a carbon dioxide laser with a laser wavelength of 10.6 μm or a YAG laser with a laser wavelength of 1.06 μm, which is called multimode, and does not have a very high intensity distribution at the center, there was no problem. However, in a laser having a high output and a high intensity distribution at the center of a single mode, represented by a fiber laser having a laser wavelength near 1.08 μm, which has recently started to be used for laser processing, it is necessary to simply blow a purge gas. The present inventors have found that a phenomenon occurs in which the lens is clouded or clouded.

  One of the features of the fiber laser is that it can focus on a small spot of several tens of μm. However, in the case of microfabrication by microfocusing, the white turbidity of this lens deteriorates the focusing characteristics of the laser beam, resulting in processing quality. It will have a big influence on. For example, when this phenomenon occurs, the transmittance of the laser beam obtained by dividing the laser power after passing through the optical system by the laser power at the laser body exit port decreases, and the laser power necessary for processing cannot be obtained.

  Further, when the condenser lens becomes clouded, the focal length may be shorter than the design, or the laser irradiation diameter on the workpiece may be larger than the design, and desired processing may not be performed.

  In order to solve this problem, Patent Document 1 discloses a method for creating a clean room inside the housing. However, this method is very expensive and inconvenient for adjustment work and maintenance work of the optical system. There are some problems and it is difficult to realize.

JP-A-8-332586

  The object of the present invention is to provide stable laser processing by preventing the occurrence of clouding, dirt, etc. of optical elements in laser processing in a harsh environment where there are many foreign matters such as dust and dust such as factory lines of steelworks. Therefore, the present invention provides a technique for preventing contamination of a laser optical element that is simple, low-cost, and easy to maintain.

  The present inventor has studied in detail the phenomenon of clouding of optical elements, such as clouding and dirt, in laser processing under a poor environment that occurs even when blowing a normal clean purge gas. In view of the above, the present inventors have found an apparatus and a method for preventing the occurrence of white turbidity such as clouding and dirt of optical elements in laser processing in a poor environment. The gist of the present invention is shown below.

  The laser optical element contamination preventive apparatus according to the present invention is an optical element contamination preventive apparatus used in a laser processing apparatus for transmitting a laser beam to a workpiece using an optical element, and condensing and irradiating the workpiece. An electrostatic polarity determination sensor for detecting a charge polarity and a charge amount on the surface of the optical element, an ion generator for blowing a purge gas containing reverse ions on the surface of the optical element based on the detected value of the charge polarity and the charge amount, And a dust collection box for collecting dust blown away by the purge gas and facing the ion generator with the optical element interposed therebetween.

  The method for preventing contamination of a laser optical element according to the present invention is a method for preventing contamination of an optical element used in a laser processing apparatus for transmitting a laser beam to a workpiece using an optical element, and collecting and irradiating the laser beam. The electrostatic polarity determination sensor detects the charge polarity and charge amount on the surface of the optical element, and based on the detected value of the charge polarity and charge amount, purge gas containing reverse ions is detected using the ion generator. The dust and the dust blown by the purge gas are collected in a dust collection box facing the ion generator with the optical element interposed therebetween.

  Until now, in laser processing in a poor environment with a lot of foreign matters such as dust and dust, stable processing has been difficult due to the occurrence of cloudiness and dirt on the optical lens, and the maintenance load on the optical element has been high. According to the present invention, stable laser processing can be performed for a long period of time, and a maintenance cycle such as cleaning of the optical element is extended, and a maintenance load is reduced. Moreover, it can be realized simply and at low cost.

  The present inventor has studied in detail the phenomenon of clouding of optical elements, such as clouding and dirt, in laser processing under a poor environment that occurs even when blowing a normal clean purge gas. From the above, it has been considered that the generation mechanism of white fogging of the lens, which has a great influence on the light condensing characteristics, is the generation mechanism described below. Hereinafter, the examination results will be described.

  The purge gas causes friction between the pipe and the air passing therethrough and is charged with static electricity. When this purge gas charged with static electricity is blown onto the optical element, the optical element is also charged with static electricity. Then, foreign matters such as dust, dust, and dust floating in the atmosphere are attracted to the static electricity and adhere to the optical element. The adhering foreign matter is considered to be one in which organic matter or inorganic matter has been altered by irradiation and heating with a laser beam, evaporation of water or the like, or chemical reaction.

  However, there remains a question as to why only a local purge gas has not been a problem until now, and why a problem has occurred in the fiber laser. In order to verify this, the laser power of the fiber laser was changed under the condition that only the normal purge gas was blown, and the change in the minimum focused diameter after 10 days was investigated.

  FIG. 5 shows the laser irradiation apparatus used to measure the light collection characteristics in this study. The laser beam 9 emitted from the laser device 1 is condensed by the condenser lens 2, and the condensing characteristic is measured by the beam profiler 7. The purge gas 6 is jetted from the supply hose 3 to the condenser lens. The tip of the supply hose 3 for the purge gas 6 is equipped with an ion generator 4 and an electrostatic polarity determination sensor 5, which are not used in this survey. In addition, the ion generator 4 and the electrostatic polarity determination sensor 5 utilized the commercially available thing.

  Other than the beam profiler 7 is housed in the housing 10. The laser beam is a 200 W continuous wave fiber laser with a wavelength of 1.08 μm, the laser beam diameter is 6 mm, and the focal length of the condenser lens is 200 mm. As the purge gas, an inert gas such as nitrogen gas or argon gas, clean air, or the like was used. This time, clean air with dry air passed through a foreign matter removal filter was used.

  FIG. 4 shows the relationship between the laser power density incident on the lens and the minimum focused diameter. The laser power density Ip on the horizontal axis is defined by laser power / laser beam area, and the laser power was changed to change the laser power density Ip. The laser beam area is defined by calculating from a diameter that includes 86% of the laser power in the beam incident on the lens. The minimum condensing diameter on the vertical axis is defined as a diameter including 86% of the laser power in the beam condensed by the condensing lens.

From this figure, when the laser power density Ip is about 0.5 kW / cm ² or more, white turbidity occurs and the minimum condensing diameter increases. When the laser power density Ip is about 0.5 kW / cm ² or less, white turbidity does not occur even after 10 days, and is about the same as the minimum focused diameter of 50 μm immediately after irradiation. For comparison, in the case of a carbon dioxide laser used for cutting, etc. as an example, the laser power is 6000 W, the laser beam diameter is 40 mm, the laser power density Ip is 0.48 kW / cm ² , and the occurrence of cloudiness is observed. I can't.

  Thus, it is considered that until now, even in a high-power laser, the laser power density Ip has not been large, and thus no cloudiness has occurred.

Therefore, to prevent the laser optical element from becoming clouded, it is necessary that the laser power density Ip incident on the optical element be 0.5 kW / cm ² or less. However, in laser processing having a single mode such as a fiber laser, a high-power laser beam is often used for reasons such as increasing the processing speed. Therefore, it is often difficult to satisfy this condition.

  The present inventor believes that, based on the generation mechanism of the white clouding of the lens, which has a great influence on the light condensing characteristics, to prevent this, it is important to suppress static electricity, particularly static electricity of the optical element. It was. The use of an antistatic film can be considered so that the optical element is not charged with static electricity. However, depending on the characteristics of the antistatic film layer, the optical characteristics such as the reflectance of the optical lens change.

  In particular, when the absorption rate with respect to the laser increases, it causes thermal expansion of the lens, which significantly affects the optical characteristics of the focal length and the focused diameter. There is also a problem with the long-term stability of the antistatic film.

  In addition, the humidity can be controlled by increasing the humidity to prevent static electricity, but condensation tends to occur due to moisture in the air, and the components of the glass and moisture react on the lens surface to cloud the optical lens. , Will increase dirt.

  First, when the purge gas was blown, it was confirmed by a sensor that the optical element was positively charged. Therefore, when negative ions were supplied and neutralized by the negative ion generator, the adhesion of foreign matters such as dust and dust was suppressed at first, but the amount of adhesion increased with time. This is because the negative ions were supplied too much, so that the lens was charged negatively and attracted the positively charged foreign matter.

  Next, the charged polarity on the surface of the optical element was detected, and ions having the opposite polarity were supplied. This was a significant effect compared to the negative ion supply described above, but it also resulted in foreign matter adhering over time. The cause of this is that, by supplying ions to the optical element, foreign particles that are secondarily charged positively and negatively exist in the housing.

  Since the ion generator generates the positive and negative ions alternately in time to neutralize the optical element, the charged reverse polarity foreign matter is attracted. For this reason, foreign substances adhere to the optical element and the electrode needle for generating ions for a short time.

  When foreign matter adheres to the electrode needle, a reaction occurs during discharge to cover the electrode, and the ion supply capacity is reduced. For this reason, it is considered that the optical element is charged again by the static electricity of the purge gas, and the foreign matter adheres again.

  Therefore, in order not to allow the positively and negatively charged foreign matter to be present in the housing, the foreign matter removed by the ion generator and the purge gas is captured by a filter or a discharge dust collector and re-applied to the optical element and electrode needle. Inspired by a method to prevent adhesion.

  In the present invention, the dust collection box for capturing foreign substances has an opening that can sufficiently take in the purge gas blown to the lens, has a suction force by a fan, and has a filter or a discharge type dust collector inside.

  In this embodiment, the optical system is housed in the housing. However, when dust or dust is not significant, it is not necessary to house the optical system in the housing.

(Condensing characteristics)
FIG. 1 shows an example of a laser irradiation apparatus used in this embodiment for measuring the condensing characteristic of a laser beam incorporating a dirt prevention apparatus. As in FIG. 5, the laser beam 9 emitted from the laser device 1 is condensed by the condenser lens 2, and the condensing characteristic is measured by the beam profiler 7.

  The purge gas 6 is jetted from the supply hose 3 to the condenser lens 2. The tip of the supply hose 3 for the purge gas 6 is equipped with an ion generator 4 using a commercially available static eliminator and an electrostatic polarity determination sensor 5, and the dust removed by the purge gas 6 across the condenser lens 2. A dust collection box 8 for collecting foreign matters such as dust is disposed. In this example, a commercially available air cleaning filter 12 was mounted in a dust collection box 8 having an opening 11 and a fan 13.

  Other than the beam profiler 7 is housed in the housing 10. The size of the housing 10 is 1 m (W) × 1 m (L) × 0.5 m (H). As measurement conditions, a 200 W continuous-wave fiber laser with a wavelength of 1.08 μm is used, the laser beam diameter is 6 mm, and the focal length of the condenser lens is 200 mm.

  Table 1 shows device configurations of the present invention and comparative examples. Immediately after the start of laser irradiation, and in the case of using the present invention, only the purge gas (Comparative Example 1), and only the purge gas and the ion generator (Comparative Example 2), the condensed light of the condensed diameter after 10 days. The characteristics are shown in FIG. The focus position is a position where the condensing diameter is the smallest immediately after the start of irradiation, and the larger the minus, the farther the condensing lens side is, and the farther the distance is from the condensing lens.

  In the present invention, the light condensing characteristic substantially the same as that immediately after the start of irradiation is maintained. On the other hand, with only the purge gas of Comparative Example 1, the minimum condensing diameter is increased from 50 μm to 100 μm, and the position is also shifted by 5 mm toward the side closer to the lens. With only the purge gas and the ion generator of Comparative Example 2, the minimum condensing diameter is increased from 50 μm to 70 μm, and the position is also shifted by 1 mm toward the side closer to the lens.

  When the appearance of the condensing lens of Comparative Example 1 was observed, a white cloud was clearly seen around the center of the lens surface where the laser beam was incident. The condensing lens of Comparative Example 2 was also very thin but white cloudy was observed.

  From this, it is considered that the reason why the condensing diameter was increased was that aberrations were generated by this white cloud. Further, the transmission efficiency of the laser beam power was reduced by about 10%. From this, the laser beam power is absorbed by this white cloud, and it becomes heat, which causes the thermal lens effect. Therefore, it is considered that the focal position has shifted.

  As a result, as shown in FIG. 3, in Comparative Example 1 using only the purge gas, a white cloud was generated in which the condensed light diameter was about twice in about 4 days. Further, in Comparative Example 2 in which a commercially available static eliminator is used as the ion generator 4, a white clouding in which the condensed light diameter is approximately doubled in about 15 days was generated. It was possible to prevent the occurrence until 30 days.

  According to the present invention, stable laser processing can be performed for a long period of time, and a maintenance cycle such as cleaning of the optical element is extended, and a maintenance load is reduced.

  After 30 days, when the appearance of the electrode needle of the static eliminator of the present invention was inspected, foreign matter was adhered. The filter was also dirty. As a result, the ability to capture foreign matter has been reduced, so that charged floating foreign matter has increased and adhered to the optical element and the electrode needle, and it is considered that white clouding has occurred due to the reduced ion supply ability. The main factor is influenced by the cleanliness of the purge gas itself. Therefore, if purge gas with a higher cleanliness can be supplied, a long-term effect can be expected.

It is a figure which shows the outline of the pollution prevention apparatus of the optical element for lasers in the inferior environment of this invention. It is a figure which shows the relationship between the condensing characteristic in the Example and comparative example of this invention, a focus position, and a condensing diameter. It is a figure which shows the relationship between the irradiation days in the Example and comparative example of this invention, and a condensing diameter. It is a figure which shows the relationship between a laser power density and the minimum condensing diameter. It is a figure which shows the outline of the laser irradiation apparatus used in order to measure the condensing characteristic of the fiber laser beam at the time of purge gas blowing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Condensing lens or f (theta) lens 3 Purge gas piping 4 Ion generator 5 Electrostatic sensor 6 Purge gas 7 Beam profiler 8 Dust collection box 9 Laser beam 10 Apparatus housing 11 Opening part 12 Filter 13 Fan

Claims (2)

A device for preventing contamination of an optical element used in a laser processing apparatus that transmits a laser beam to a workpiece using an optical element, collects and irradiates the workpiece,
An electrostatic polarity determination sensor for detecting the charge polarity and charge amount of the optical element surface;
An ion generator that blows a purge gas containing reverse ions on the surface of the optical element based on the detected value of the charge polarity and charge amount; and
An apparatus for preventing contamination of an optical element for a laser, comprising a dust collection box for collecting dust blown away by the purge gas and facing the ion generator with the optical element interposed therebetween. A method for preventing contamination of an optical element used in a laser processing apparatus for transmitting a laser beam to a workpiece using an optical element, and condensing and irradiating the workpiece.
The electrostatic polarity determination sensor detects the charge polarity and charge amount of the optical element surface,
Based on the detected value of the charging polarity and charge amount, a purge gas containing reverse ions is blown onto the optical element surface using an ion generator,
A method for preventing contamination of a laser optical element, wherein dust or dust blown off by the purge gas is collected in a dust collection box facing the ion generator with the optical element interposed therebetween.

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