JP2019195814A - Device and method for detecting contamination on protective glass - Google Patents

Abstract

To realize a device for detecting contamination on protective glass and a method for detecting contamination on protective glass with respect to protective glass that protects a laser head from being contaminated by scattering deposit, such as spatter and fume from a weldment, in a laser welding machine.SOLUTION: A device for detecting contamination on protective glass includes: a band-pass filter which transmits light of a specific wavelength from scattered light emitted from a side face of protective glass of a laser welding machine; and a photosensor which detects the transmitted light transmitted through the band-pass filter. Further, preferably, the device for detecting contamination on protective glass additionally includes a first plano-convex lens between the band-pass filter and the side face of the protective glass.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a protective glass contamination detection device and a protective glass contamination detection method for protective glass that protects a laser head from contamination by scattered deposits such as spatter and fumes from a welded material in a laser welding machine.

  At the time of laser processing, the surface of the protective glass disposed on the front surface of the lens of the processing head is contaminated by fumes and spatters from the welding material. If the contamination of the protective glass accumulates, the laser output decreases, the focus shifts, and the like occur, affecting the processing state. Therefore, the user cleans or replaces the protective glass every time.

  However, in many cases, the protective glass employs a high-priced product in order to obtain a certain transmittance with a high-power laser, and it is necessary to continue to use it to the limit of the allowable range in order to reduce the cost. At present, protection glass cleaning and replacement are often reliant on the user's feeling, the processing state changes before and after the replacement of the protective glass, or it is replaced at an earlier stage than necessary. There are cases where production costs are increasing. In order to solve this problem, development of a product that can numerically determine the replacement time of the protective glass is required.

  Here, the following patent document 1 states that “the protective glass applied during the laser machining process becomes increasingly dirty due to particles removed from the workpiece, so that the laser beam passing through the glass is severely affected and also machined. The process is also significantly affected: some of the incident laser beam is absorbed and scattered by dirt, dust and smoke particles collected on the glass surface, and some of the scattered light is collected by the protective glass wall and directed outwards. "The more dirt and dust particles on the glass surface, the more the incident laser beam scatters. The absorbed part of the light beam will cause an increase in temperature."

  Further, in US Pat. No. 6,089,089, since the incident laser beam is also a working machining beam, such absorption and scattering of the beam is a problem because the power density of the focused beam is reduced. This is a welding capability. Is particularly disadvantageous in laser welding systems, and it is also disadvantageous in laser engraving systems of the type shown in Swedish patent 9403349-5 in which small complex engraving patterns are produced by a laser beam. If the beam is not sharp due to scattering effects, the good quality of the pattern or script produced by the laser beam cannot be maintained.

JP-T-2002-515341

  Patent Document 1 discloses that a heat detector 10 and a light detector 8 are set on a sensor card 11 disposed on an end mounting portion of a protective glass to detect a rise in glass temperature or scattered light. Has been. However, when the scattered light is detected by the light detector 8, a lot of noise light is mixed in the scattered light. Therefore, only the scattered light that is truly useful for detecting dirt on the protective glass is extracted. In the past, it was difficult to detect.

  Therefore, the present invention realizes a protective glass contamination detection device and a protective glass contamination detection method for the protective glass that protects the laser head from contamination due to scattered deposits such as spatter and fume from the welded material in a laser welding machine. The purpose is to do.

  In order to solve the above problems, in the present invention, a bandpass filter that transmits light of a specific wavelength from scattered light emitted from the side surface of a protective glass of a laser welding machine, and transmitted light that has passed through the bandpass filter are detected. And a protective sensor for detecting contamination of a protective glass. Preferably, the protective glass contamination detector further includes a first plano-convex lens between the bandpass filter and the side surface of the protective glass.

  Further, in the present invention, in a method for detecting contamination of a protective glass attached to a laser welder that performs welding with a laser beam having a wavelength of 1075 nm, light having a specific wavelength is obtained from scattered light emitted from the side surface of the protective glass of the laser welder. A step of transmitting only light in the 1050 nm to 1150 nm band scattered by dirt adhering to the protective glass, and a step of detecting the transmitted light transmitted through the bandpass filter with a photo sensor. It is set as the dirt detection method of the protective glass which has.

  According to the present invention, in the laser welding machine, it is possible to realize a protective glass contamination detection device and a protective glass contamination detection method for the protective glass that protects the laser head from contamination due to scattered deposits such as spatter and fumes from the welded material.

It is a figure explaining the structure which attaches a photodiode to the side part (periphery end surface) of protective glass, and measures the laser beam which propagates to a glass side surface. It is a figure explaining the side light measurement verification result of the protective glass which performed detection performance verification with the prototype photosensor. (A) is a figure explaining the detection light waveform of the protective glass end surface at the time of irradiating the 500 W laser pulse of 1 second of pulse width in the state which does not set the welding material as a welding workpiece, (b) is a welding material. It is a figure explaining the detection light waveform of the protective glass end surface at the time of irradiating the 500 W laser pulse with a pulse width of 1 second in the set state. (A) is a figure explaining the detection model of a scattered light in case a welding material is not set with the new glass in the state without the dirt of protection glass, (b) is a figure of the laser beam resulting from dirt of protection glass. (C) is a diagram showing a simple model of how scattered light enters the sensor, and (c) shows the scattered light of the laser light caused by dirt on the protective glass when the welding material is set. It is a figure which shows what modeled the mode of light simply. It is a figure which shows the emission spectrum measured when SUS304 which is a general welding steel material is irradiated with a laser. It is a figure explaining the outline | summary of the optical system block diagram for extracting only the scattered light of the laser beam itself which propagates the inside of the protective glass concerning 2nd Embodiment to an end surface. It is a figure explaining the relative comparison of the detection capability with the presence or absence of a band pass filter.

  According to the present invention, it is possible to reliably and accurately detect and detect the contamination of the protective glass for protecting the laser head of the laser welding machine from spatter scattering from the welding object and contamination due to evaporation of fumed fumes. It is possible to have a protective glass contamination detection device and structure. The protective glass is disposed between the laser head and the object to be welded, and prevents spatter and fumes inevitably generated by the laser welding process and the laser processing process from adhering to the laser head.

  As a result, the laser head is protected from contamination, while the protective glass is exposed to spatter and fumes, and the protective glass is gradually contaminated with the progress of the process such as laser welding and the elapsed time. Laser light that provides processing energy passes through (transmits) the protective glass and is applied to the object to be processed. Therefore, if dirt adheres to the protective glass, the transmittance is reduced and the desired energy is processed. Can no longer be given to objects. Sputter grains and fume particles adhering to the surface of the protective glass scatter laser light that should be transmitted.

  For this reason, it is possible to grasp | ascertain the dirt adhesion degree of the surface of protective glass by monitoring the scattered light of a laser beam by the end surface (side surface) of protective glass. However, the light that reaches the end face of the protective glass includes laser light scattered by sputtering, etc., as well as light reflected from the welding object, plasma light generated from the welding object, and thermal radiation. Return light from the welding object including various light such as light and Raman scattered light is also included. From such return light, information for grasping the degree of contamination of the protective glass cannot be obtained.

  In the present invention, the scattered light emitted from the end face of the protective glass is guided to a desired location with an optical fiber, and the return light is discarded from the scattered light through a band pass filter, and only the scattered light of the laser light itself is obtained. We propose a protective glass contamination detection device that can accurately and accurately grasp the degree of contamination of the protective glass by extracting and monitoring this strength. If the detected light intensity is increased above a predetermined threshold by the protective glass contamination detection device of the present invention, the operator is notified that the protective glass is contaminated more than a predetermined value and that maintenance work such as replacement is performed. be able to.

  Conventionally, with only laser processing work time as a guide, for example, after 500 hours of laser processing, maintenance such as replacement of protective glass is performed. However, since the degree of contamination progresses greatly depending on various conditions such as laser processing conditions and workpieces, there are not a few cases when the elapsed time alone is far from the actual protection glass contamination. It was. According to the present invention, in addition to the notification of the maintenance time according to the conventional time, it is possible to monitor the real time dirt of the protective glass, so by using both of them, the maintenance time such as replacement of the protective glass can be more accurately and accurately. It is possible to grasp and notify.

  In addition, the sensor is not directly mounted on the edge of the protective glass, but after the scattered light is guided to a desired measurement location with an optical fiber, it is to be detected by a photo sensor or the like through a bandpass filter. It can also contribute to space saving and weight reduction of the laser head periphery. As a result, the bandpass filter, the photosensor, and the housing for housing them are not contaminated by spatter, fume, etc. The degree of freedom of adoption of sheath, weight, shape, etc. will be greatly improved. Therefore, further detailed description will be given below based on the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration in which a photosensor (for example, a photodiode) 1050 is attached to a side surface portion (peripheral end surface) of a protective glass 1030 and laser light propagating to the glass side surface is measured. As shown in FIG. 1, a plano-convex lens 1040 for adjusting laser light is provided near the tip of the laser processing head 1010, and a protective glass 1030 held by a protective glass holder 1020 is provided on the tip side. Yes.

  A photo sensor 1050 is mounted on the protective glass holder 1020 so as to detect scattered light emitted from the side surface of the protective glass 1030. The detection signal of the photosensor 1050 is amplified by the amplifier circuit 1060 and transmitted to the determination / processing circuit 1070. In the determination / processing circuit 1070, when the detection signal is large due to the increase in the magnitude of the detection signal with time, comparison with a predetermined threshold value, etc., it is possible to notify the protection glass replacement time or maintenance time. . As the photosensor 1050 shown in FIG. 1, a so-called ring sensor arranged around the protective glass 1030 can be used.

  In this configuration, when the laser beam is irradiated to the foreign matter attached to the glass surface, the laser beam is scattered, reflected inside the protective glass, propagated in the side surface direction, and reaches the photosensor 1050 on the side surface. For this reason, since the detection value of the photosensor 1050 becomes higher when the dirt on the protective glass 1030 becomes severe, it becomes possible to grasp the degree of dirt on the protective glass 1050 by monitoring this.

  FIG. 2 is a diagram for explaining the side light measurement verification result of the protective glass in which the detection performance is verified with the prototype photosensor. In the experimental schematic diagram (a) and the experimental schematic diagram (b) shown in FIG. 2, a protective glass holder 2020 is provided on the front end side of the laser processing head 2010 of f100-200, and the protective glass holder 2020 was prototyped. A protective glass 2030 is mounted. In addition, in the experimental schematic diagram (a), a reflector 2080 that reflects laser light to the space at a substantially right angle is used, and in the experimental schematic diagram (b), a laser welding material 2090 is set and this is set at a speed of 20 mm / s. The actual welding process was simulated and reproduced by moving it.

  The detected values of the photosensors in the experimental schematic diagram (a) and the experimental schematic diagram (b) shown in FIG. 2 are “(c) detection value without welding material” and “(d) detection value with welding material, respectively. Is a graph. A new product (no spatter adhesion) and a sputtered protective glass 2030 were prepared in advance, and the scattered light intensity from the side surface of the protective glass 2030 was measured for each laser output, depending on the presence or absence of a welding material.

  From the verification results shown in FIG. 2, since any sensor detection value increases due to spattering or the like adhering to the protective glass, spatter adhesion itself can be detected, but the experimental schematic diagram (b) in which a welding material exists is shown. If it is in the state, as shown in “(d) Detection value with welding material”, the detection value ratio between spatter adhesion (upper three dots) and new product (lower three dots) decreases (difference between the two) Therefore, the detection accuracy of spatter adhesion tends to decrease. That is, as shown in the experimental schematic diagram (b), when the measurement was performed during the laser welding, it was found that the detection capability was reduced to about ½ due to the influence of the reflected light from the laser welding material 2090.

  This is obvious by referring to “(c) Detection value without welding material” which is the detection result in the state of the experimental schematic diagram (a) where no reflected light exists. In this case, each laser output (0 ... (50 kw, 0.75 kw, 1.00 kw) The photosensor detection values at the time of sputter adhesion are plotted above the new dots (no spatter adhesion) at a large distance. In other words, in “(d) detection value with welding material” which is the detection result in the state of the experimental schematic diagram (b), the return light from the laser welding material 2090 becomes noise, and the laser beam itself is sputtered, etc. Since it is superimposed on the scattered light caused by the glass surface contamination, the S / N ratio decreases, resulting in a lack of clarity in determining the degree of contamination on the protective glass surface. It is thought that.

  As described above, by monitoring the scattered light intensity from the end face of the protective glass, it can be understood that the presence or absence of spatter adhesion to the protective glass can be detected according to the degree of increase in the intensity. However, when such a measurement is performed during welding, the S / N ratio is lowered and the detection ability is lowered due to the presence of return light reflected from the welding workpiece or the welding object as noise.

  FIG. 3A is a diagram for explaining a detection light waveform of the end face of the protective glass when a 500 W laser pulse having a pulse width of 1 second is irradiated without setting a welding material as a welding work, and FIG. These are the figures explaining the detection light waveform of the protective glass end surface at the time of irradiating the 500 W laser pulse of 1 second of pulse width in the state which set the welding material. If based on FIG. 3, the influence of the reflected light (return light) from a welding material can be considered as a cause that a detection capability falls.

  That is, as can be understood from FIG. 3 (a), when there is no welding material, a clean rectangular wave having a constant irradiation output corresponding to the output waveform of the laser is obtained, but the welding material shown in FIG. 3 (b). In the case of being present, a waveform having a fine amplitude is obtained, and the detection value is raised by noise as a whole and becomes high. This is thought to be because the welded material is melted violently, so that the return light from the molten part (molten pool) behaving in a complicated manner is captured. As can be understood from FIG. 3B, the fluctuation width of the finely oscillated detection signal in the case of including the return light from the molten pool is much larger than the increase width of the detection signal caused by the laser irradiation on / off. The size of is not negligible.

  FIG. 4A is a diagram for explaining a detection model of scattered light when a welding material is not set with a new glass in a state where the protective glass 3030 is not dirty, and FIG. FIG. 4C is a diagram showing a simple model of how the scattered light of the laser beam caused by 100 enters the sensor, and FIG. 4C shows the dirt 100 on the protective glass 3030 in a state where the welding material is set. It is a figure which shows what modeled the mode that the scattered light of the laser beam resulting from incidents on a sensor. In FIG. 4, reference numeral 3050 denotes a photosensor (for example, a photodiode).

  As shown in FIG. 4A, when the glass is not contaminated, the laser light is slightly scattered from the glass interface, so that minute light enters the photodiode 3050. In addition, when dirt 100 such as spatter adheres to the interface outside the protective glass 3030 (welding material side) as shown in FIG. 4B, the detection value increases because reflection from the deposit 100 also enters the photodiode. . However, when there is return light due to reflection from the welding material as shown in FIG. 4C, the return light enters the photodiode 3050 due to scattering from the interface of the protective glass 3030, but the return light from the deposit 100 The reflection hardly enters the protective glass 3030. For this reason, it is considered that only noise light not related to the deposit 100 becomes large, and a difference in the ability to detect dirt appears.

(Second Embodiment)
From the viewpoint of detecting dirt in real time during welding, it is essential to detect dirt simultaneously with welding. Further, in order to detect a smaller degree of dirt or a lower degree of dirt, it seems necessary to increase the S / N ratio as close as possible to the detection capability without welding material. Therefore, the present inventor has created the device described below as the second embodiment.

  That is, in the second embodiment, a band-pass filter that transmits only the scattered light of the laser light itself is disposed in front of the photosensor to remove excess return light from the welding material. Return light from the welding material includes plasma light, heat radiation light, and Raman scattered light that is generated when the laser light is absorbed by the material, and such return light. Is propagated through the inside of the protective glass and reaches its end face regardless of the presence or absence of dirt adhering to the outer surface of the protective glass.

  First, in order to investigate how components are actually contained in the light during welding, the emission spectrum of the welding material was measured with a spectrometer. FIG. 5 is a diagram showing an emission spectrum measured when SUS304, which is a general welded steel material, is irradiated with laser. As can be understood from FIG. 5, light emission is detected in the 500 to 800 nm band, which is considered to be caused by plasma light, thermal radiation light, Raman scattered light, and the like, in addition to the reflected light of the laser light around 1070 nm itself. The light in this band is shown as “welding light” in FIG.

  The light in the 500 nm to 800 nm band does not contribute to the detection of dirt on the protective glass, but is a return light from the welding material and the peak value is not so high, but spreads broadly. Has light intensity. By removing the light in this band and reducing the return light from the welding material, it is considered that the S / N ratio is improved and the dirt detection capability is improved.

  FIG. 6 is a diagram for explaining the outline of an optical system configuration diagram for extracting only the scattered light of the laser light itself propagating through the protective glass 4030 according to the second embodiment to the end face. In order to extract the laser light, a band pass filter 200 that matches the wavelength (1070 nm to 1075 nm) of the laser light is used. However, due to its size, the end face of the protective glass 4030 passes through the optical fiber 300 once the emitted light from the end face. Then, a configuration is adopted in which light is transmitted to the photosensor 4050 through the band pass filter 200 after being transmitted to a desired position of the photosensor 4050.

  As shown in FIG. 6, a protective glass holder 4020 is provided on the laser processing head 4010, and a protective glass 4030 is mounted on the protective glass holder 4020. Further, an optical fiber 300 is provided on the end face of the protective glass 4030, and scattered light guided to the end face in the protective glass 4030 is taken out from the end face and guided into the optical fiber 300. Here, since the end face of the protective glass 4030 and the light incident portion of the optical fiber 300 are brought into close contact with each other without having a space, the light inside the protective glass 4030 can be smoothly taken out to the optical fiber 300. preferable. In addition, various adhesives (for example, optical path coupling adhesives) whose refractive index during curing is appropriate as a waveguide may be used between the end face of the protective glass 4030 and the light incident part of the optical fiber 300. Is possible.

  The scattered light guided in the optical fiber 300 passes through the band-pass filter 200 having a 1075 nm transmission band via the first plano-convex lens 4040 (a) and passes through the second plano-convex lens 4040 (b) to the photosensor 4050. The light intensity is detected at. As shown in FIG. 6, the first plano-convex lens 4040 (a) and the second plano-convex lens 4040 (b) are both arranged so that the band-pass filter 200 side is convex. The light intensity detection signal detected by the photosensor 4050 is input to a determination / processing circuit (not shown), and is compared with a predetermined threshold value, or the degree of contamination of the protective glass 4030 is determined based on the change over time of the signal increase. It is judged or / and notification of replacement / maintenance time of the protective glass 4030 is made. In addition, the detection signal of the photosensor 4050 may be transmitted to the determination / processing circuit via an amplification circuit (not shown).

  Further, in the present embodiment, by using the optical fiber 300, even if the size size of the protective glass holder 4020 and the size size of the band pass filter 200 are not matched, it is possible to conduct photoconduction between the two. Is. For example, even when the bandpass filter 200 is larger than the thickness of the protective glass holder 4020 and cannot be accommodated therein, the optical fiber 300 is not spaced between the protective glass 4030 and the optical fiber 300 provided separately. The fiber 300 can be optically connected. However, when the bandpass filter 200 is small enough to be housed in the protective glass holder 4020, the bandpass filter 200 is arranged directly in the protective glass holder 4020 without using the optical fiber 300. Also good. As a result, the device is lighter and more compact and easier to handle and store.

  In addition, regarding the bandpass filter 200, only the scattered laser reflected light band may be transmitted through the filter to detect the intensity, or the intensity of the residual light obtained by removing only the welding light band returned from the welding material with the filter. It is good also as a structure which detects. If the latter configuration is adopted, even if the laser light wavelength used for processing uses a band that is different from the band of 1070 nm to 1075 nm, it becomes possible to detect the contamination of the protective glass appropriately.

  FIG. 7 is a diagram for explaining a relative comparison of detection capability with and without a band-pass filter. A new protective glass such as the photograph shown in FIGS. 7 (a) and 7 (b) and a protective glass with sputtered particles are prepared in advance, and the bandpass filter is attached and detached to SUS304, which is a welding object. Laser irradiation was performed, and scattered light was detected by the configuration shown in FIG. From the experimental results shown in FIG. 7 (c), it was found that the numerical value increased by about 5.7 times when the dirt was adhered without the filter, but the numerical value increased by about 10.7 times through the filter. Thus, it can be understood that the use of a bandpass filter that transmits only the wavelength of the laser light improves the S / N ratio and increases the detection capability by about twice.

  A protective glass contamination detector according to the present invention includes an optical fiber having one end mounted on an end of the protective glass so as to propagate scattered light emitted from the side surface of the protective glass of the laser welding machine, and an optical fiber. A bandpass filter mounted at the other end of the optical fiber so as to transmit light of a specific wavelength from the scattered light that has propagated, and a photosensor that detects transmitted light that has passed through the bandpass filter, To do. As a result, the scattered light emitted from the side surface (end surface) of the protective glass propagates to the photosensor through the optical fiber, and only the scattered light having a desired wavelength that has passed through the bandpass filter is detected by the photosensor. Therefore, it becomes possible to extract and detect only the light caused by the dirt on the protective glass from the various lights included in the scattered light. Therefore, it is possible to realize a protective glass contamination detection device capable of reliably detecting and reporting the contamination of the protective glass.

  The protective glass contamination detection apparatus according to the present invention preferably further includes a first plano-convex lens between the bandpass filter and the other end of the optical fiber. Thereby, the scattered light guided by the optical fiber can be surely transmitted through the band-pass filter without being diffused at the other end of the optical fiber. In this case, the first plano-convex lens is preferably arranged so that the band-pass filter side is convex.

  In addition, the protective glass contamination detection device according to the present invention is more preferably characterized by further including a second plano-convex lens between the bandpass filter and the photosensor. This makes it possible to reliably guide the scattered light transmitted through the bandpass filter to the photosensor without being scattered on the light emission surface side of the bandpass filter. In this case, the second plano-convex lens is preferably arranged so that the bandpass filter side is convex.

  The protective glass contamination detection apparatus according to the present invention is more preferably characterized in that the laser welding machine performs welding with a laser beam having a wavelength of 1075 nm. Currently, it is known that near infrared fiber lasers of around 1075 nm are often used for laser welding and the like.

  In the protective glass contamination detection apparatus according to the present invention, more preferably, the band-pass filter has a transmission band of 1075 nm. Therefore, the wavelength of the light that is scattered as it is due to dirt or the like adhering to the surface of the protective glass is 1075 nm. For example, plasma light, thermal radiation from a symmetric workpiece, or 500 nm to 800 nm due to Raman scattered light. The light is preferably blocked by a band pass filter. Accordingly, it is possible to detect scattered light with higher reliability that is not affected by optical noise.

  In the protective glass contamination detection apparatus according to the present invention, more preferably, the band-pass filter blocks return light from the object to be welded. Most of the return light from the welding object is plasma light radiated from plasma generated around the welding object, or heat radiation light radiated from around the welding spot that has become hot. For this reason, since most of them are not laser wavelengths of 1075 nm, it is preferable to exclude detection from the viewpoint of improving detection accuracy and reliability.

  In the protective glass contamination detection apparatus according to the present invention, more preferably, the scattered light is laser light scattered by the contamination attached to the protective glass, and the bandpass filter transmits only the scattered laser light. It is characterized by that. Thereby, it becomes possible to detect the contamination of the protective glass accurately.

  The protective glass contamination detection device and the structure thereof according to the present invention are not limited to the shape and structure shown in the above description and drawings, and can be appropriately understood by those skilled in the art within the scope of the present invention. It may be modified, arranged and modified using a known or well-known technique.

  1010... Laser processing head, 1020... Protective glass holder, 1030... Protective glass, 1040... Plano-convex lens, 1050.

Claims (11)

A bandpass filter that transmits light of a specific wavelength from scattered light emitted from the side surface of the protective glass of the laser welder;
And a photosensor for detecting transmitted light that has passed through the band-pass filter. In the protective glass dirt detector according to claim 1,
A protective glass stain detector, further comprising a first plano-convex lens between the bandpass filter and the side surface of the protective glass. In the protection glass dirt detection device according to claim 1 or 2,
A protective glass stain detection device further comprising a second plano-convex lens between the bandpass filter and the photosensor. In the protective glass dirt detector according to any one of claims 1 to 3,
The said laser welding machine welds with the laser beam of a wavelength of 1075 nm. The dirt detection apparatus of the protective glass characterized by the above-mentioned. In the protection glass dirt detector according to any one of claims 1 to 4,
The bandpass filter has a transmission band of 1075 nm. In the protection glass dirt detector according to any one of claims 1 to 5,
The bandpass filter blocks a return light from an object to be welded. In the protective glass dirt detector according to claim 6,
The return light has a wavelength range of 500 nm to 800 nm. In the protection glass dirt detector according to any one of claims 1 to 7,
The scattered light is laser light scattered by dirt adhered to the protective glass, and the band-pass filter transmits only the scattered laser light. In the protection glass dirt detector according to any one of claims 1 to 8,
One end of the protective glass is mounted so as to propagate the scattered light emitted from the side surface of the protective glass, and the bandpass filter is mounted on the other end, further comprising an optical fiber. Protective glass stain detection device. In a method for detecting contamination of protective glass attached to a laser welding machine that performs welding with a laser beam having a wavelength of 1075 nm,
A step of transmitting only light in a band of 1050 nm to 1150 nm scattered by dirt attached to the protective glass with a bandpass filter that transmits light of a specific wavelength from scattered light emitted from the side surface of the protective glass of the laser welding machine; ,
And a step of detecting, with a photo sensor, transmitted light that has passed through the band-pass filter. In the method for detecting the contamination of the protective glass attached to the laser welding machine for welding,
A step of removing return light from the welding material in the 500 nm to 800 nm band with a bandpass filter that blocks light of a specific wavelength from scattered light emitted from the side surface of the protective glass of the laser welding machine;
And a step of detecting, with a photo sensor, transmitted light that has passed through the band-pass filter.