JP2006055879A - Method and device for detecting breakage of protective glass of laser beam emission aperture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for detecting breakage of a protective glass 9 at a laser beam emission aperture of an optical system housing of a laser beam machining head 1. <P>SOLUTION: The temperature of a protective glass 9a is measured by a heat detector 16, and it is judged that breakage of the protective glass 9a will occur in near future when the time differential of the temperature is not less than the predetermined threshold. Breakage of the protective glass 9a can be more correctly predicted by removing the period of temperature rise of the protective glass 9a due to the radiant heat from a weld of a work 10a when starting the laser beam welding from the period of judgment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for automatically detecting breakage of a protective glass provided at a laser emission port of an optical system housing of a laser processing head for welding.

  Laser processing is applied to processing of metals, ceramics, etc., and concentrates high-density energy in a very narrow range, allowing deeper penetration than conventional arc heat sources and reducing heat input. Become. Therefore, high-efficiency and high-quality welding and cutting can be performed, and in recent years, it has spread to various industries. In particular, laser processing capable of transmitting an optical fiber such as a YAG laser is applied to processing a mass-produced product in combination with a robot or the like.

  The schematic structure of the laser processing head will be described with reference to FIG. FIG. 4 is a schematic view showing the structure of a laser processing head in which the protective glass is relatively far from the processing portion. The optical component of the laser processing head 1a includes an emission optical system that guides the laser light 11 and an observation optical system for observing a processing point of the workpiece 10a.

  The YAG laser light is guided to the laser processing head 1 a by the optical fiber 2 and emitted from the end of the optical fiber 2 at a wide angle. The optical fiber 2 is fixed to the housing 4 a by an optical fiber connector 3. The emission optical system includes a deflector 6 that reflects the laser beam 11 emitted from the optical fiber 2 downward, a collimator lens 7 that makes the spread of the laser beam 11 parallel light, and the laser beam 11 at a processing point of the workpiece 10a. It is composed of a condenser lens 8 and the like for focusing.

  As the collimating lens 7 and the condensing lens 8, lenses having a focal length of 100 to 200 mm are generally used. In many cases, the laser processing head 1a is provided with an observation optical system for observing a processing point of the workpiece 10a. In this case, a CCD camera 5 as an imaging device is attached to an upper portion of the housing 4a. In order to provide such an observation optical system, a deflector 6 that reflects YAG laser light and transmits visible light is used.

  In laser processing such as cutting and welding, the laser beam 11 of several kW is focused in a spot shape and applied to the workpiece 10a such as metal, so that the metal is instantaneously melted and evaporated, and the workpiece 10a is arranged. From the molten portion, metal vapor, plasma, spatter, fumes from metal surface deposits, and the like are generated. In order to protect the optical components from the products from these melting parts, the optical components are installed in a hermetically sealed housing 4a, and a protective glass 9a is installed at the laser emission port of the housing 4a containing the optical components.

  An assist gas nozzle 15 is provided in the vicinity of the housing 4a for blowing off plasma or metal vapor generated from the melted portion and injecting an assist gas for shielding the welded portion to the welded portion, and further to the protective glass 9a. In order to prevent the adhesion of spatter and fumes, an air curtain nozzle 14 that blows air at a high speed in a direction parallel to the plane of the protective glass 9 a is attached to the housing 4 a by a support 13.

  By these measures, most of the scattered matter from the melting part is removed, so that the protection glass 9a is less contaminated. However, when the laser processing head 1a is used for a long time, the protective glass 9a is gradually contaminated. In particular, depending on the target workpiece (workpiece 10a), the distance between the protective glass 9a and the molten part may approach, and in this case, the probability of contamination of the protective glass 9a becomes very high.

  FIG. 5 is a schematic diagram showing the structure of the laser processing head 10b in which the protective glass 9b is relatively close to the processed portion 10b. As shown in FIG. 5, when the workpiece 10 b that is the target workpiece is in a narrow portion, a mirror 17 is installed in the optical path of the focused laser beam 11, the laser beam 11 is bent, and the corner of the target workpiece Can be processed.

  When the protective glass 9b is contaminated with spatter and fumes from the melted part, the laser beam 11 is reflected or absorbed, so that the laser power irradiating the workpiece 10b is attenuated, so that the processing capability is reduced and processing defects are reduced. Cause it to happen. Further, since the contamination also causes damage to the protective glass 9b, it is necessary to replace the protective glass 9b when the contamination progresses.

  As an example of the breakage of the protective glass 9b, the adhered spatter absorbs the laser beam 11, the glass temperature of the sputtered portion increases, the protective glass 9b is cracked due to thermal strain, and the laser light is further emitted to the cracked portion. 11 may be irradiated to cause a rapid temperature rise, and the protective glass 9b may melt and burst.

  In addition, there are various possible causes of damage to the protective glass 9 (9a, 9b). When the protective glass 9 is melted and ruptured, the expensive optical system is contaminated by the molten rupture, and laser processing is continued in a contaminated state. If it does so, of course, processing is not performed normally, and there is a possibility that the optical system is damaged by the product from the melted part. That is, when the laser processing head 1 (1a, 1b) is mounted on a robot or the like and continuous welding is performed fully automatically, the function of detecting the contamination state of the protective glass 9 and a sign of breakage such as melting breakage of the protective glass 9 A detection function is required.

  In particular, when the distance between the protective glass 9 and the melted portion where the workpiece 10 is disposed is close, the protective glass 9 is easily contaminated, and the power density of the laser light 11 passing through the protective glass 9 is high. Since melting damage is likely to occur, a function of detecting a failure sign such as melting damage is desired.

  As a function for detecting the contamination state of the protective glass 9, JP-A-9-57479 discloses a method of photographing the protective glass with a CCD camera of an observation optical system and determining the contamination state with an image processing apparatus. However, since the CCD camera cannot shoot while the laser beam is irradiated, the contamination state of the protective glass cannot be detected in real time during the processing of the workpiece.

  As a method for detecting the contamination state of the protective glass in real time during the laser processing of the workpiece, Japanese Patent Publication No. 7-16795 discloses light reflected from the inner surface of the glass due to dirt adhering to the protective glass. A method is disclosed in which a dirt state is determined by detection with an optical sensor installed beside the door. Japanese Patent Application Publication No. 2002-515341 discloses a method in which a temperature sensor is installed on protective glass or a protective glass holder, the temperature of the protective glass is measured, and the contamination state is determined.

As a method for detecting breakage of the protective glass, Japanese Patent Application Laid-Open No. 9-122962 discloses that air is supplied from the outside to the space between the condenser lens and the protective glass, and the pressure in the space is detected by a pressure sensor. A method of detecting breakage of the protective glass by detecting air leakage when the protective glass is broken, and a method of detecting breakage of the protective glass by the presence / absence sensor of the protective glass are disclosed. However, this method cannot detect an abnormality until after the protective glass is broken, so if the protective glass melts and bursts, the optical system may be contaminated or damaged by melting and breaking of the glass and products generated from the molten part. there were.
JP-A-9-57479 Japanese Patent Publication No.7-16795 JP-T-2002-515341 Japanese Patent Laid-Open No. 9-122962

In the above prior art, the protection glass can be detected only after the protection glass is ruptured. Therefore, when the protection glass is melted and ruptured, the optical system is contaminated by the melting damage of the protection glass and the product generated from the molten part. Or there was a problem that it might be damaged.
An object of the present invention is to provide a detection method and apparatus for predicting breakage of a protective glass disposed at a laser emission port of an optical system housing of a laser processing head.

The above-described problems of the present invention are solved by the following solution means.
According to the first aspect of the present invention, the breakage of the protective glass provided at the laser emission port of the optical system housing of the laser processing head for welding and disposed at the position facing the workpiece to be welded by laser light is detected. In the method for detecting damage to the laser exit protective glass, the laser exit for measuring the temperature of the protective glass and determining that the protective glass is in the near future when the time differential value of the temperature rise is equal to or greater than a preset threshold value. This is a method for detecting breakage of protective glass.

  The invention according to claim 2 is the method for detecting breakage of the laser exit protective glass according to claim 1, wherein the temperature rise period of the protective glass due to radiant heat from the workpieces to be welded at the start of welding is excluded from the breakage determination period of the protective glass. is there.

  According to a third aspect of the present invention, the breakage of the protective glass provided at the laser emission port of the optical system housing of the laser processing head for welding and disposed at the position facing the workpiece to be welded by laser light is detected. In the laser exit opening protective glass breakage detection device, a protective glass for measuring the temperature of the protective glass, and the protective glass when the time differential value of the temperature rise of the protective glass measured by the thermal detector is equal to or greater than a preset threshold value. It is a damage detection apparatus of the laser emission port protection glass provided with the determination means which determines that there is a breakage of near future.

(Function)
FIG. 2 shows the protective glass when the protective glass provided at the laser emission port of the welded part of the workpiece and the optical system housing of the laser processing head for welding is relatively far away and is not affected by the radiant heat from the welded part. The temperature curve of is shown. Usually, the protective glass is coated with a multilayer antireflection coating for the laser light wavelength used (1064 nm in the case of YAG laser), so there is little loss of heat even when high energy laser light is transmitted, There is little temperature change, and there is no sudden temperature change.

  FIG. 3 shows a temperature curve of the protective glass when the welded portion of the workpiece and the protective glass are relatively close to each other and there is an influence of radiant heat from the welded portion. At the start of laser processing, the temperature of the protective glass rises rapidly due to the influence of the radiant heat of the weld. However, with such a welding device, the surroundings of the protective glass are cooled with water or air with dry air, so that after a few seconds, the rapid temperature rise of the protective glass is suppressed, the temperature change is small, and particularly rapid temperature changes are not caused. Absent.

  Next, FIG. 1 shows a temperature curve of the protective glass when the protective glass is broken. Fig. 1 shows the measured temperature of the protective glass when the distance between the weld and the protective glass is relatively close. At the start of processing, the protective glass is affected by the radiant heat from the melted part of the workpiece. The temperature is rising rapidly. A sudden temperature rise occurs immediately before the protective glass melts and bursts. This is because there is an abrupt temperature rise due to absorption of laser light before large contaminants adhere or cracks in the protective glass, and the protective glass melts and bursts due to this temperature rise.

  If a sudden temperature rise of the protective glass is detected and the irradiation of the laser beam is stopped, the protective glass can be exchanged without melting and bursting the protective glass. By exchanging the protective glass at an appropriate timing, the expensive optical system is not contaminated or damaged.

  According to the first and third aspects of the present invention, when the time differential value of the temperature rise of the protective glass provided at the laser emission port of the optical system housing of the welding laser processing head is equal to or higher than a preset threshold value, this rapid temperature rise It is determined that there is damage to the protective glass in the near future.

  Further, according to the invention described in claim 2, in addition to the action of the invention described in claim 1, in the case where the temperature of the protective glass rises due to radiant heat from the welded portion at the time of laser processing start, By removing from the determination period for detecting breakage of the protective glass, erroneous determination of breakage of the protective glass can be eliminated.

  According to the first to third aspects of the present invention, it is possible to detect a rapid temperature rise before the protective glass disposed at the laser emission port of the optical system housing of the laser processing head for welding is melted, burst, and damaged, and to irradiate the laser beam. Therefore, the protective glass can be exchanged without melting and rupturing the protective glass, and the expensive optical system is not contaminated or damaged. As a result, continuous laser processing can be performed automatically, so that productivity can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 4 is a schematic view showing the structure of the laser processing head in which the protective glass is separated from the processing portion.

In the laser processing head 1a of the present embodiment, an optical fiber 2 that guides laser light 11 generated by a laser oscillator (not shown) to the laser processing head 1a and optical components such as the optical fiber 2 are fixed and protected. A housing 4a; an optical fiber connector 3 for fixing optical components such as the optical fiber 2; a CCD camera 5 for monitoring and confirming the surface of the workpiece 10a; a laser emitted from the optical fiber 2; A deflector 6 that reflects light 11 downward and transmits visible light; a collimator lens 7 that collimates laser light 11 emitted from the optical fiber 2 at a wide angle; and laser light 11 that has been collimated by the collimator lens 7 The optical system is kept from the condensing lens 8 that focuses on the processing point of the workpiece 10a, the fume and spatter from the workpiece 10a, and the like. Housing the protective glass 9a for.
Although the protective glass 9a is provided at the laser emission port of the housing 4a, a workpiece 10a is disposed at a position where the laser beam 11 is focused below the protective glass 9a.

  A support 13 is provided in the housing 4 a, and the support 13 supports and fixes the air curtain nozzle 14 and the assist gas nozzle 15. High-speed air for blowing away fumes, spatters and the like from the welded portion of the workpiece 10a is jetted from the air curtain nozzle 14 between the protective glass 9a and the workpiece 10a, and from the welded portion of the workpiece 10a. The assist gas for blowing off the generated plasma and metal vapor and shielding the welded portion of the workpiece 10a is injected from the assist gas nozzle 15 toward the welded portion of the workpiece 10a.

  Further, a temperature detector 16 for measuring the temperature of the protective glass 9a during laser processing is attached to the tip of the support 13 so as to contact the protective glass 9a.

  FIG. 5 shows a schematic side view of the laser processing head 1b in which the welded portion of the protective glass 9b and the workpiece 10b are relatively close to each other. The laser processing head 1b shown in FIG. 5 is different from the laser processing head 1a shown in FIG. The laser processing head 1b of FIG. 5 is provided with a protective glass 9b at the laser emission port of the housing 4b, and a reflection mirror 17 for preventing the laser beam 11 emitted from the laser emission port from being attenuated is provided on the housing 4b near the laser emission port. Located inside. Also in this case, the temperature detector 16 for measuring the temperature of the protective glass 9b during laser processing is attached to the lower end portion of the reflection mirror 17 so as to contact the protective glass 9b.

  As already explained, FIG. 1 is a time-dependent change curve of the temperature of the protective glass 9 including when the protective glass 9 (9a, 9b) is broken. FIG. 2 is a diagram showing a time-dependent change curve of the temperature of the protective glass 9 when there is no influence of radiant heat from the welded portion of the workpiece 10 (10a, 10b). FIG. 3 is a diagram showing a time-dependent change curve of the temperature of the protective glass 9 when there is an influence of radiant heat from the welded portion.

  As shown in FIG. 2, when the welded part of the workpiece 10 and the protective glass 9 are relatively far apart and the influence of the radiant heat from the welded part does not reach the protective glass 9, the temperature of the protective glass 9 The change is small and shows a substantially constant temperature during welding. Usually, the surface of the protective glass 9 is coated with a multi-layered antireflection film for the used laser light wavelength (1064 nm for YAG laser), so that the protective glass 9 transmits the high-energy laser light 11. However, since the heat loss is small, the temperature change of the protective glass 9 is small, and a particularly rapid temperature change does not occur.

  As shown in FIG. 3, when the distance between the welded portion and the protective glass 9 is relatively close and there is an influence of radiant heat from the welded portion, the protective glass 9 is affected by the radiant heat of the welded portion at the start of processing. The temperature rises rapidly. However, in such an apparatus, since the periphery of the protective glass 9 is cooled with water or air with dry air, after a few seconds, the rapid temperature rise of the protective glass 9 is suppressed, the temperature change is small, and a particularly rapid temperature change occurs. There is nothing.

  Moreover, as shown in FIG. 1, at the start of laser processing, the temperature of the protective glass 9 is rapidly increased due to the influence of the radiant heat of the welded portion. When the protective glass 9 is melted and broken, a rapid temperature rise occurs. This is because, when cracks occur due to large contaminants adhering to the surface of the protective glass 9, a sudden temperature rise is caused by absorption of the laser light 11, and the protective glass 9 melts and bursts.

  If this rapid temperature rise is detected and the irradiation of the laser beam 11 is stopped, the protective glass 9 can be replaced without melting and rupturing the protective glass 9, and the expensive optical system is contaminated or damaged. There is nothing to let you. The method for detecting this rapid temperature rise is achieved by determining that the breakage of the protective glass 9 will occur in the near future when the time differential value of the temperature rise is not less than a preset threshold value. Further, when the temperature of the protective glass 9 rises due to radiant heat from the welded portion at the start of processing, it is possible to eliminate the erroneous determination of breakage of the protective glass 9 by removing the temperature rising period at the start from the determination period. The threshold value varies depending on the welding conditions such as the distance between the workpiece 10 and the protective glass 9 and / or the irradiation intensity of the laser beam 11, and is thus determined after the specific welding conditions are determined.

  The temperature detector 16 for measuring the temperature of the protective glass 9 is not attached to the fixture of the protective glass 9 in order to improve the detection sensitivity, but is preferably brought into direct contact with the protective glass 9 for temperature detection. In order to reduce the influence of radiant heat from the part, it is preferable to install in the housing 4 (4a, 4b).

  The present invention is a technique for enhancing the durability of optical components in the laser welding technique, and is highly applicable when performing HRSG header stub implantation welding with a laser welding robot.

It is a figure which shows the temperature curve of the protection glass at the time of protection glass failure. It is a figure which shows the temperature curve of the protective glass when there is no influence of the radiant heat from a welding part. It is a figure which shows the temperature curve of the protective glass in case there exists the influence of the radiant heat from a welding part. It is a schematic diagram which shows the structure of the laser processing head from which protective glass is comparatively separated from the welding part. It is a schematic diagram which shows the structure of the laser processing head in which protective glass is comparatively close to the welding part.

Explanation of symbols

1 (1a, 1b) Laser processing head 2 Optical fiber 3 Optical fiber connector 4 (4a, 4b) Housing 5 CCD camera 6 Deflector 7 Collimating lens 8 Condensing lens 9 (9a, 9b) Protective glass 10 (10a, 10b) Covered Workpiece 11 Laser beam 13 Support 14 Air curtain nozzle 15 Assist gas nozzle 16 Temperature detector 17 Mirror

Claims (3)

Damage detection of the protective glass of the laser emission port, which is provided at the laser emission port of the optical housing of the laser processing head for welding and detects the breakage of the protective glass arranged at the position facing the workpiece to be welded by laser light. In the method
Measuring the temperature of the protective glass, and determining that the protective glass is broken in the near future when the time differential value of the temperature rise is equal to or higher than a preset threshold value. .   The method for detecting breakage of protective glass for a laser emission port according to claim 1, wherein the temperature rise period of the protective glass due to radiant heat from the workpieces to be welded at the start of welding is excluded from the breakage determination period of the protective glass. Damage detection of the protective glass of the laser emission port, which is provided at the laser emission port of the optical housing of the laser processing head for welding and detects the breakage of the protective glass arranged at the position facing the workpiece to be welded by laser light. In the device
A heat detector that measures the temperature of the protective glass, and a determination that the protective glass breaks in the near future when the time differential value of the temperature rise of the protective glass measured by the heat detector is equal to or greater than a preset threshold value. An apparatus for detecting breakage of laser exit port protection glass, characterized by comprising means.

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