JP2012187591A - Laser processing head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing head used in laser welding or the like which can exactly determine a thermal lens phenomenon of an optical component during laser processing by an extremely simple constitution.SOLUTION: A temperature of the laser light permeation center o of protection glass 5 attached in a head housing 10 as the laser processing head 1A is measured, and a monitoring mechanism capturing the thermal lens phenomenon of the protection glass 5 is added on the basis of the measurement value.

Description

  The present invention relates to a laser processing head with high brightness and high convergence such as a fiber laser or a disk laser used for laser welding or the like.

  Laser welding irradiates the surface of the workpiece with a high-power laser beam focused by the condenser lens of the machining head, and moves the irradiation position along the welding site, thereby allowing the workpiece at the irradiated site to move. The material is continuously melted and solidified, and high-density energy can be concentrated in a very narrow range, so that deep penetration can be achieved with a narrow weld bead width and high efficiency welding with a small heat input. There is an advantage that can be performed. Thus, optical components of laser processing heads for a laser wavelength band of 1 μm, such as fiber lasers and disk lasers frequently used for laser welding, are usually used to prevent reflection of the applied laser wavelength on the surface of a quartz base material. Non-reflective coating is applied.

  However, in laser welding, it is generally recognized that the weld quality tends to decrease with increasing distance from the welding start position. This is because, as a thermal lens phenomenon, an optical component such as a condensing lens or protective glass interposed in the laser beam path in the processing head absorbs the laser beam and rises in temperature, causing thermal expansion and a change in refractive index. This is because the focal length changes (usually the focal length is shortened by the convex lens effect). Absorption of laser light leading to such a thermal lens phenomenon occurs to some extent in the base material itself of the optical component, but is largely absorbed by the non-reflective coating and surface deposits on the surface of the optical component. In particular, the protective glass placed on the laser beam emission side of the processing head is exposed to the outside so as to face the welded part, so that spatter of the melt generated from the welded part, metal vapor, plasma fumes, etc., adhere to it. If the adhesion contamination increases, the absorption rate of the laser beam is remarkably increased, and a large thermal lens action is caused as the temperature rises. Therefore, it is important to monitor the thermal lens phenomenon of the optical components of the laser processing head in order to avoid the deterioration of the welding quality in laser welding. Especially, the thermal lens action due to the contamination of the protective glass has an acceptable level. It must be exchanged for a new one before it exceeds.

  Conventionally, as a means for dealing with a thermal lens phenomenon in a laser processing head, an automatic rotary stage having two sets of temperature sensors attached above the condenser lens is provided, and the upper surface on the laser beam incident side of the condenser lens is provided by both temperature sensors. By scanning the whole, calculating the focal length change amount of the condenser lens from the obtained temperature data, and moving the condenser lens up and down by the focal length automatic adjustment device based on the calculated value, the focus is always covered. There has been proposed a method of controlling so as to be tied onto a workpiece (Patent Document 1). On the other hand, with respect to the protective glass arranged on the laser beam emitting side of the laser processing head, the intensity of the scattered light of the laser beam due to the particles adhering to the outer surface side is measured by a photodetector provided on the inner periphery of the head, and additionally In addition, the temperature of the side surface of the protective glass and the temperature of the peripheral wall of the head are measured with a temperature detector, and the measured values of the scattered light intensity and temperature are compared with a set reference value to determine dirt in two stages (Patent Document 2) A method of measuring the temperature of the outer peripheral portion of the inner surface of the protective glass with a heat detector and determining that there is a fear of breakage when the time differential value of the temperature rise exceeds a set threshold value (Patent Document 3) has been proposed. ing.

Japanese Patent No. 2612311 JP 2002-361252 A JP 2006-55879 A

  However, in the method in which the entire upper surface of the condenser lens is scanned by two sets of temperature sensors as in Patent Document 1, two sets of temperature sensors, a rotary automatic stage and its drive mechanism, a vertical movement mechanism of the focus lens and its control mechanism The cost of the laser processing head and incidental equipment is extremely high, and the construction of a thermal analysis means that calculates the temperature measurement value → temperature distribution of the entire condenser lens → thermal deformation → focal length change in order In addition, a large amount of labor is required, and in the case of a laser processing head equipped with a protective glass, there is a problem in that it cannot cope with the thermal lens phenomenon accompanying the contamination of the protective glass.

  On the other hand, in the dirt determination method for protective glass as in Patent Document 2, dirt particles do not uniformly adhere to the surface of the protective glass, and the scattered light intensity measured by the photodetector varies depending on the distribution state of the adhered particles. In addition, the temperature rise due to dirt is small on the side of the protective glass and the peripheral wall of the head, and the temperature detector can detect only when the dirt becomes extremely severe. Even if it is possible to determine a state where the entire surface is made into a film and the workability is deteriorated due to a decrease in the amount of transmitted light, it is difficult to accurately determine the degree of contamination corresponding to the thermal lens phenomenon. Further, in the method for predicting damage to the protective glass as in Patent Document 3, since the temperature rise at the outer peripheral portion on the inner surface of the protective glass due to dirt is small, the protective glass is on the verge of being damaged based on the measured value by the heat detector. Even if the use limit can be determined, it is difficult to accurately determine the degree of contamination corresponding to the thermal lens phenomenon.

  In view of the above-described circumstances, the present invention provides a laser processing head used for laser welding or the like that can accurately determine the degree of the thermal lens phenomenon of an optical component during laser processing with a very simple configuration. It is aimed.

  If means for achieving the above object is shown with reference numerals in the drawings, the laser processing head 1A according to the invention of claim 1 is a laser of an optical component (protective glass 5) mounted in the head housing 10. A monitoring mechanism for measuring the temperature of the light transmission center o and capturing the thermal lens phenomenon of the optical component based on the measured value is attached.

  According to a second aspect of the present invention, in the laser processing head 1A of the first aspect, the temperature of the laser light transmission center portion o of the optical component is measured by a single infrared sensor 7 that receives radiant infrared rays and converts them into electrical signals. It is configured to do.

  According to a third aspect of the invention, in the laser processing head 1A of the first aspect, the infrared sensor 7 has a sensitivity band between infrared wavelengths of 8 to 14 μm.

  According to a fourth aspect of the present invention, in the laser processing head 1A according to any one of the first to third aspects, the infrared sensor 7 is attached facing the inside of the head housing 10.

  The laser processing head 1A according to the invention of claim 5 includes the temperature of the laser light transmitting central portion o of the optical component (protective glass 5) mounted in the head housing 10, and the peripheral portion s or the support portion 10a of the optical component. And a monitoring mechanism for capturing the thermal lens phenomenon of the optical component based on the difference between the measured temperatures.

  The invention of claim 6 is the laser processing head 1 </ b> A according to any one of claims 1 to 5, wherein the optical component is the protective glass 5 mounted on the front end side of the head housing 10.

  According to a seventh aspect of the present invention, in the laser processing head 1A of any one of the first to sixth aspects, an allowable limit value of the focus shift Δf due to the thermal lens phenomenon is set, and a reference temperature and a measurement temperature corresponding to the allowable limit value are set. And a replacement notification function for notifying that replacement of optical components is required when the measured temperature exceeds the reference temperature.

  According to the laser processing head 1A according to the first aspect of the present invention, the temperature of the laser light transmitting central portion o is measured as a mechanism for monitoring the thermal lens phenomenon of the optical component (protective glass 5) mounted in the head housing 1. Based on this measurement value, it is possible to accurately grasp the degree of the thermal lens phenomenon accompanying the contamination of the optical component. That is, the relationship between the temperature measurement data of the central portion o when using a new optical component without contamination and the focus shift Δf is obtained in advance, and this central portion obtained at the time of actual processing is used as basic reference data. By comparing the temperature measurement data of o, it is possible to accurately determine whether or not the thermal lens phenomenon is within an allowable range, and thus whether or not the optical component can be continuously used.

  According to the invention of claim 2, since one infrared sensor 7 is used for temperature measurement of the laser light transmission center portion o of the optical component, the entire laser processing head 1A has a simple and compact configuration, and temperature measurement is performed. There is an advantage that can be continuously performed with a simple operation.

  According to the invention of claim 3, since the infrared sensor 7 used for the above temperature measurement has a sensitivity band between infrared wavelengths of 8 to 14 μm, it is raised from a general quartz glass and an antireflection film material as an optical component material. There is an advantage that infrared rays emitted with temperature can be reliably measured.

  According to the fourth aspect of the present invention, since the infrared sensor 7 used for the temperature measurement is mounted facing the inside of the head housing 10, the light receiving portion is hardly contaminated, and the infrared sensor 7 itself has a long life. Turn into.

  According to the invention of claim 5, the temperature of the laser light transmitting central portion o of the optical component (protective glass 5) mounted in the head housing 10, and the average temperature of the peripheral portion s of the optical component or the support portion 10 a Since the thermal lens phenomenon of the optical component is captured based on the difference between the two measured temperatures, the temperature of the central portion o and the peripheral portion s or the support portion 10a when a new optical component that is not soiled in advance is used. Whether the thermal lens phenomenon is within the allowable range by comparing the actual measurement data with this as basic reference data and whether the optical components can be used continuously. It is possible to accurately determine whether or not.

  In the invention of claim 6, the optical component is the protective glass 5 mounted on the tip side of the processing head 1A, and the necessity of replacement with a new one can be determined by accurately grasping the degree of the thermal lens phenomenon caused by the dirt. Therefore, high laser processing quality can be secured while eliminating waste due to premature replacement.

  The invention of claim 7 sets the reference temperature corresponding to the allowable limit value of the focal displacement Δf due to the thermal lens phenomenon, and notifies that the optical component needs to be replaced when the measured temperature exceeds the reference temperature. It is possible to prevent a situation in which the quality of laser processing deteriorates without noticing the replacement timing of the optical component.

It is a model longitudinal cross-sectional view of the laser processing head of the fiber laser for laser welding used for the preliminary test of thermal lens phenomenon monitoring. The measurement data by the said preliminary test are shown, (a) is a correlation characteristic figure of laser output-focus shift, (b) is a correlation characteristic figure of laser output-center part temperature of an optical component. The temperature distribution along the diameter direction of the protective glass in the preliminary test is shown, (a) is a characteristic diagram when using an existing protective glass with dirt, (b) is a characteristic diagram when using a new protective glass without dirt. It is. It is a model longitudinal cross-sectional view of the laser processing head which concerns on one Embodiment of this invention. It is a correlation characteristic figure of protection glass center part temperature used for setting of one evaluation index of thermal lens phenomenon monitoring in the embodiment. It is a correlation characteristic figure of the temperature difference-focus shift of the center part of a protective glass used for setting of one evaluation index of thermal lens phenomenon monitoring in other embodiments of the present invention, and a peripheral part.

  A laser processing head 1B shown in FIG. 1 constitutes a fiber laser welding head for laser welding, and a vertical cylindrical housing 10 in which a fiber emitting end 2 (core diameter 0.2 mm) is arranged facing the center of the upper end. The collimator lens 3 (focal length 100 mm) for converting the laser light L emitted from the fiber emitting end 2 into parallel light sequentially from the upper side converges the parallel light to the workpiece (not shown). A condensing lens 4 (focal length 200 mm) for converging the focal point F near the surface, a flat protective glass 5 made of quartz glass and having an antireflection film on the surface and having a thickness of 2 mm are held, and the peripheral wall of the housing 10 Inside, cooling water passages 11 and 12 are provided at positions where the collimator lens 3 and the condenser lens 4 are respectively arranged. Therefore, the laser processing head 1B includes a power meter 6 that receives the laser light L at a position immediately below the processing head 1B and measures the output for a preliminary test, and a laser light transmission central portion o of the protective glass 5. The infrared sensor 7 that receives the radiant infrared light and converts it into an electrical signal to measure the temperature, the infrared viewer 8 that captures the temperature distribution of the front surface of the protective glass 5 from the diagonally lower side, and the temperature value based on the measurement signal of the infrared sensor 7 A personal computer PC for displaying the monitoring status is attached.

  The thermal lens phenomenon in the laser processing head 1B having the above configuration was analyzed by the following preliminary tests 1 to 3. In these preliminary tests, a commercially available head (imaging magnification: 2) is used as the laser processing head 1B, and SC620 manufactured by FILR Systems is used as the infrared viewer 8, and the cooling water temperature of the cooling water passages 11 and 12 is set to 30. Set to ° C. Although not shown in the figure, a focus monitor manufactured by Primus Co., Ltd. was used for measuring the position of the focal point F of the laser light L.

[Preliminary test 1]
Using the power meter 6 and the focus monitor, the focus shift Δf after 3 minutes and 10 minutes from the start of emission of the laser beams L with outputs of 6 kW, 8 kW, and 10 kW in the state where the protective glass 5 is not present, and dirt The focus shift Δf after 3 minutes and 10 minutes after the start of the emission of the laser light L with an output of 10 kW was examined using each of the new protective glass 5 having no dirt and the existing protective glass 5 having dirt. The result is shown in FIG.

[Preliminary test 2]
Using the power meter 6 and the infrared sensor 7, the laser beam transmitted through the condenser lens 4 3 minutes and 10 minutes after the start of emission of the laser beams L of 6 kW, 8 kW, and 10 kW with no protective glass 5 While measuring the temperature of the central part and using each of the new protective glass 5 without dirt and the existing protective glass 5 with dirt, 3 minutes and 10 minutes after the start of emission of the laser light L with an output of 10 kW The temperature of the laser light transmission center part o of the protective glass 5 after that was measured. The result is shown in FIG.

[Preliminary test 3]
Minutes from the start of emission at laser outputs of 2 kW, 4 kW, 5 kW, and 6 kW, respectively, using the infrared viewer 8 and using the existing protective glass 5 with dirt and the new protective glass 5 without dirt. The temperature distribution along the radial direction of the protective glass was examined. The results are shown in FIG. 3A for the existing protective glass 5 and in FIG. 3B for the new protective glass 5, respectively.

  As shown in FIG. 2A, in the state without the protective glass 5, the focal shift Δf increases as the output of the laser light L increases and as the time from the start of emission increases. Further, the focus shift Δf is further increased by providing the protective glass 5. For example, the focus shift Δf after 10 minutes from the start of emission at the output of 10 kW of the laser light L is about 12% in the new protective glass 5 without dirt. In contrast to the increase, the existing protective glass 5 with dirt is remarkably increased to about 56%. Further, as shown in FIG. 2 (b), the temperature of the laser light transmission central portion o of the protective glass 5 after 10 minutes from the start of emission at an output of 10 kW of the laser light L is the protection of a new product without contamination. While the glass 5 has a temperature of about 90 to 100 ° C., the existing protective glass 5 with dirt reaches a high temperature of 280 to 300 ° C. On the other hand, as shown in FIGS. 3 (a) and 3 (b), the temperature of the protective glass 5 during use of the laser processing head 1B depends on the central portion (laser light transmission central portion o) regardless of the difference in laser output and the presence or absence of dirt. ), And a large temperature difference appears between the central part and the peripheral part. However, in the existing protective glass, which is particularly dirty, there is a considerable temperature difference between the peripheral parts (both ends in the radial direction in the figure). Yes.

  In other words, the laser beam has an intensity distribution that attenuates in the radial direction with the center of the optical component as the center of the optical axis. When the laser beam passes through the optical component, internal heat generation occurs due to light absorption. The heat is exhausted by heat conduction toward the peripheral part cooled by the cooling water of the optical component. Therefore, optical components during laser processing show a temperature distribution where the central portion is always the highest if the optical absorption increases due to surface contamination, but is not dirty enough to damage itself. Since there is a difference in the amount of heat generated between the part with dirt and the part without dirt, there are many cases where a significant difference occurs in the temperature of the peripheral part as shown in FIG.

  From the results of these preliminary tests 1 to 3, the existing protective glass 5 is heated to a large temperature toward the center side due to the absorption of the laser light L caused by the dirt, and the remarkable heat that deforms into a convex lens shape due to the thermal expansion associated therewith. Although a lens phenomenon occurs, there is a high correlation between the magnitude of the focal shift Δf due to the thermal lens phenomenon and the temperature of the protective glass 5, so the thermal lens phenomenon is accurately measured using the measured temperature of the laser light transmission center o as an index. It turns out that it can monitor well. However, since the temperature rise due to dirt is small in the peripheral portion of the protective glass 5 and temperature variation is likely to occur due to a difference in local stain degree, the measured temperature in the peripheral portion is poor as an indicator of the monitoring. Therefore, the relationship between the temperature measurement data of the laser light transmission center o when using a new protective glass 5 without dirt and the focus shift Δf is obtained in advance and obtained as basic reference data during actual processing. By comparing the temperature measurement data of the central portion o, it is possible to accurately determine whether or not the thermal lens phenomenon is within an allowable range, and thus whether or not the optical component can be used continuously.

  Here, the temperature measuring means of the laser light transmission center portion o of the protective glass 5 is not particularly limited, but an infrared sensor 7 similar to that used in the preliminary test is suitable. That is, the infrared sensor 7 receives radiant infrared light and converts it into an electrical signal, but using only one of them, the temperature measurement can be continuously performed with a simple operation, and the structure is simple. In addition, it is easy to assemble in the head housing due to its small size, which makes it possible to set the entire laser processing head in a simple and compact configuration, and makes its own light receiving part difficult to get dirty, reducing sensitivity and shortening the service life. And the overall equipment cost can be reduced.

  Such an infrared sensor 7 is not particularly limited, but a sensor having a sensitivity band between infrared wavelengths of 8 to 14 μm is recommended. This is because an infrared wavelength of 8 to 14 μm is a wavelength region of infrared rays emitted from quartz glass and an antireflection film material that are generally used as optical component materials as the temperature rises, so that the infrared radiation can be reliably measured. . It should be noted that the sensitivity band of the infrared sensor 7 only needs to include the above-mentioned wavelength range, and it goes without saying that it may extend over a wide wavelength range over one or both of the longer wavelength side and the shorter wavelength side than the wavelength range. Yes.

  FIG. 4 shows a laser processing head 1A according to an embodiment of the present invention using an infrared sensor 7 as the temperature measuring means. Since the basic structure of the laser processing head 1A is substantially the same as that of the laser processing head 1B (see FIG. 1) used in the preliminary test, the constituent parts of the laser processing head 1A are denoted by the same reference numerals as the laser processing head 1B. However, a sensor mounting hole 13 is provided on the lower side of the head housing 10 between the holding portions of the condenser lens 4 and the protective glass 5, and the infrared sensor 7 is provided in the sensor mounting hole 13. It is loaded in such a manner that the detection direction is directed to the central portion o on the inner surface side of the protective glass 5, and the signal cable 7a of the infrared sensor 7 is connected to an external personal computer PC. W in the figure indicates a workpiece to be laser welded.

  In order to monitor the thermal lens phenomenon during processing by the laser processing head 1A, laser processing is performed in advance under the corresponding processing conditions using the new protective glass 5 as a preliminary test as described above, and the accumulation of dirt is performed. From the relationship between the temperature measurement data until the processing quality reaches the allowable limit and the focus shift Δf, the temperature T2 of the laser light transmission central portion o of the protective glass 5 corresponding to the focus shift amount F2 that is the allowable limit in processing quality is obtained. I ask for it. Then, using the temperature T2 as a reference temperature, during processing by the laser processing head 1A, in the personal computer PC, the temperature Tx continuously monitored by the infrared sensor 7 using the temperature T2 as a reference temperature is equal to or lower than the reference temperature T2. The protective glass 5 can be used continuously for a certain period of time, and when the monitor temperature Tx exceeds the reference temperature T2, it is necessary to replace the protective glass 5, and the arrival of the replacement time is indicated on the display screen, an alarm lamp, an alarm buzzer. It may be set so as to be notified by, for example. Thereby, since the end of the life of the protective glass 5 can be recognized before the processed quality exceeds the allowable limit, high processed quality can be stably secured by replacing the protective glass 5 with a new one.

  FIG. 5 shows the temperature of the laser light transmission center portion o of the protective glass 5 when laser processing is performed with the laser output set to 10 kW using the new protective glass 5 in the preliminary test described above. It is an example of data which shows the relationship with focus shift (DELTA) f. In this data, the temperature T1 of the central portion o of the protective glass 5 at the start of use was 100 ° C., and the focus shift amount F1 at that time was 1.25 mm. The focus shift amount F2 when the focus shift became large and the processing quality reached the limit was 3.75 mm, and the temperature T2 of the central portion o was 200 ° C. That is, the focus shift Δf from the start of use of the new protective glass 5 to the allowable limit is 2.5 mm, and the temperature rise ΔT of the laser light transmission center portion o corresponding to the focus shift Δf is 100 ° C.

  Therefore, when performing predetermined processing such as laser welding with a set output of 10 kW with the same type of laser processing head, the thermal temperature phenomenon is monitored by setting the reference temperature T2 to 200 ° C., and monitoring by the infrared sensor 7 The protective glass 5 may be continuously used while the temperature Tx is 200 ° C. or lower, and the protective glass 5 may be replaced when the monitor temperature Tx exceeds 200 ° C.

  In the monitoring of the thermal lens phenomenon in the above-described embodiment, the optical component to be measured is the protective glass 5. However, the thermal lens phenomenon can be similarly monitored for other optical components such as the condensing lens 4 in the laser optical path. . In the illustrated embodiment, the temperature of the laser light transmission center portion of the optical component (protective glass 5) is measured, and the temperature of the laser light transmission center portion o and the peripheral portion s (see FIG. 1) or the head. The temperature of the support portion 10a (see FIG. 1) on the housing 10 side may be measured, and the thermal lens phenomenon of the optical component may be captured based on the difference between the two measured temperatures.

  FIG. 6 shows a laser light transmission center portion o and a peripheral portion s of the protective glass 5 measured using the infrared viewer 8 when a new product and an existing product are used as the protective glass 5 in the same preliminary test as described above. The correlation between the temperature difference Δt and the focus shift Δf measured using the focus monitor is shown. As is apparent from FIG. 6, there is a large difference between the temperature difference Δt and the focus shift Δf depending on whether the protective glass 5 is dirty. For example, at a laser output of 6 kW, the difference between the temperature differences Δt is 32 ° C. and the focus shift Δf. The difference is 0.5 mm, and it is suggested that the degree of the thermal lens phenomenon can be determined from the difference in the temperature difference Δt. In this case, from the relationship between the temperature difference Δt obtained using the new protective glass 5 in the preliminary test and the focus shift Δf, the focal position F1 of the laser light L serving as a reference under the processing conditions, Further, the focus position F2 is shifted from the focus position F1 to set a focus position F2 that is an allowable limit in terms of machining quality, and the temperature difference Δt corresponding to the focus position F2 of the allowable limit is used as a reference to measure the protection measured during actual processing. The temperature difference Δt of the glass 5 is compared, and the glass 5 can be used continuously while it is below the reference standard, and should be set as replacement when the reference standard is exceeded.

  When the thermal lens phenomenon is monitored by using the temperature difference between the laser light transmission center portion of the optical component and the peripheral portion or the support portion as an index, the degree of contamination of the peripheral portion and the support portion is not as described above. It is desirable to calculate the average temperature from the measurement values at the entire circumference or at a plurality of locations, because the temperature becomes uniform and temperature variations are likely to occur. In this regard, if the infrared viewer 8 is used as the temperature measuring means, only one of them is used, and the average temperature of the peripheral part or the support part is calculated from the obtained temperature distribution data in addition to the temperature of the central part of the optical component. However, it is expensive compared to the infrared sensor 7 and has a disadvantage that it is large and takes up space and becomes complicated in terms of operation.

  The laser processing head of the present invention has a detailed configuration such as the structure of the head housing 10, the arrangement of lens systems such as the collimator lens 3 and the condenser lens 4, and the additional structure of the monitoring mechanism such as the infrared sensor 7. Various design changes are possible. In addition, as the protective glass 5, the thing of thickness 1-5mm is suitable.

  The reference data used for monitoring the thermal lens phenomenon is obtained by the preliminary test described above. The preliminary test is performed by the laser processing head manufacturer, and the obtained reference data is provided to the laser processing user. do it. Therefore, various expensive measuring instruments used for the preliminary test are not necessary on the user side. For example, a simple laser processing head having only one infrared sensor as shown in FIG. It is possible to easily and reliably monitor the thermal lens phenomenon by using the reference data, and to ensure a stable high processing quality.

DESCRIPTION OF SYMBOLS 1A, 1B Laser processing head 10 Head housing 10a Support part 2 Fiber exit end 3 Collimator lens 4 Condensing lens 5 Protective glass 7 Infrared sensor o Laser light transmission center part s Peripheral part

Claims (7)

  A laser processing head comprising a monitoring mechanism for measuring the temperature of a laser beam transmission center of an optical component mounted in the head housing and capturing a thermal lens phenomenon of the optical component based on the measured value.   2. The laser processing head according to claim 1, wherein the temperature of the laser beam transmission center portion of the optical component is measured by a single infrared sensor that receives radiant infrared rays and converts them into an electrical signal.   The laser processing head according to claim 2, wherein the infrared sensor has a sensitivity band between infrared wavelengths of 8 to 14 μm.   The laser processing head according to claim 1, wherein the infrared sensor is attached facing the inside of the head housing.   The temperature of the laser light transmission center part of the optical component mounted in the head housing and the temperature of the peripheral part or the support part of the optical component are measured, and the thermal lens phenomenon of the optical component is based on the difference between the measured temperatures. A laser processing head that comes with a monitoring mechanism to capture.   The laser processing head according to any one of claims 1 to 5, wherein the optical component is a protective glass mounted on a front end side of a head housing.   Set the tolerance limit value for focal displacement due to thermal lens phenomenon, compare the reference temperature corresponding to this tolerance limit value and the measured temperature, and announce that the optical component needs to be replaced when the measured temperature exceeds the reference temperature. The laser processing head according to claim 1, further comprising an exchange notification function.

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