Patent Description:
A laser processing head used for a laser processing system includes a collecting lens that collects laser light of a high power oscillated from a laser oscillation device. The collecting lens further increases the energy density of the laser light, and radiates the laser light to a work material to process the work material (welding, fusing, or punching). At this time, the sputters or fumes (for example, evaporated zinc metal particles) generated from the work material can scatter into a surrounding embodiment, and can contaminate the surface of the collecting lens. When the sputters or fumes adhere to the collecting lens to contaminate the lens, the optical characteristic (light transmittance or the like) of the collecting lens reduces, and the intensity of the laser light to be radiated to the work material decreases. Therefore, the laser processing head includes a protective glass for protecting the collecting lens from contaminants such as the sputters or fumes.

For example, Patent Literature <NUM> describes a laser processing head that includes a protective glass for protecting the collecting lens from contaminants (dust) such as sputters or fumes. The laser processing head further includes a dirt detecting means for detecting the dirt adhering to the protective glass. Furthermore, in the description, the laser processing head of Patent Literature <NUM> suppresses the adhesion of the contaminants to the protective glass of an air downstream side (rim), by blowing off the contaminants with the air ejected from an air ejecting means.

Patent Literature <NUM> describes a dirt detecting means (optical fiber connected to an optical sensor) disposed at the rim of the protective glass. The protective glass with contaminants diffusely reflects the detection light which has been radiated diagonally upward from a plurality of point light sources toward the protective glass. The dirt detecting means detects the diffusely reflected detection light. Patent Literature <NUM> describes that, when the detection value of the diffusely reflected detection light becomes higher than a previously set reference value, the protective glass is replaced.

PTL <NUM> discloses a laser processing head reflecting the preamble of present claim <NUM>.

However, a dirt detecting means described in Patent Literature <NUM> is disposed on the rim (substantially the same height level as the protective glass) of the protective glass. Therefore, the intensity of the diffusely reflected light coming from contaminants adhering to the protective glass is low and its detection value also low, and hence the contaminants adhering to the protective glass cannot be accurately detected. Due to the described arrangement of the dirt detecting means, the following phenomena occur: the dirt detecting means easily and directly detects illumination light from a plurality of point light sources or reflected light; and the dirt detecting means is apt to be adversely affected by the light (disturbance light) scattered by the contaminants such as sputters or fumes floating under the protective glass.

The present disclosure is provided for solving the above-mentioned problems. The present disclosure provides a laser processing head for detecting the degree of the adhesion of the contaminants in a method different from the conventional method, and provides a laser processing system using this head.

A first aspect in accordance with the present disclosure relates to a laser processing head as defined in claim <NUM>.

The laser processing head includes a housing, a transparent protector that is detachably fixed to the housing, and a temperature sensor that detects the temperature of the transparent protector. The housing includes an optical path of processing laser light. The transparent protector passes the processing laser light, and suppresses dust, which is generated from the work material irradiated with the processing laser light, entering into the housing.

A second aspect in accordance with the present disclosure relates to a laser processing system as defined in claim <NUM>.

The laser processing system includes a processing laser light source, a laser processing head according to claim <NUM> and a controller coupled to the processing laser light source and the temperature sensor.

The transparent protector having the contaminants (dust) is heated by the irradiated processing laser light. In the laser processing head and laser processing system related to one aspect of the present disclosure, the degree of the contaminants adhering to the transparent protector can be detected by using the temperature of the transparent protector. In other words, by using the laser processing head and laser processing system related to one aspect of the present disclosure, the degree of the contaminants adhering to the transparent protector can be detected in a method different from the conventional method.

First, a schematic configuration of laser processing system <NUM> related to one aspect of the present disclosure is described. Laser processing system <NUM> related to one aspect of the present disclosure includes processing laser light source (simply referred to also as "laser light source") <NUM>; housing <NUM>; transparent protector <NUM> that is detachably fixed to housing <NUM>; temperature sensor <NUM> that detects the temperature of transparent protector <NUM>; and controller <NUM> connected to processing laser light source <NUM> and temperature sensor <NUM>. Housing <NUM> includes an optical path of processing laser light (simply referred to also as "laser light") LB from the processing laser light source <NUM>. Transparent protector <NUM> passes processing laser light LB, and suppresses dust, which is generated from work material W irradiated with processing laser light LB, entering into housing <NUM>. For example, when the temperature of transparent protector <NUM> detected by temperature sensor <NUM> exceeds an allowable temperature, controller <NUM> can determine that the temperature of transparent protector <NUM> exceeds the allowable temperature (or the allowable dirt degree of glass plate <NUM>). Therefore, controller <NUM> can urge a user to perform the replacement of transparent protector <NUM>.

Processing laser light LB is near-infrared light. Transparent protector <NUM> has glass plate <NUM> having a portion for passing processing laser light LB. Temperature sensor <NUM> may include an infrared radiation thermometer. The thermometer optically detects the temperature of glass plate <NUM> by detecting the peak wavelength of far-infrared light generated by black-body radiation from the dust adhering to glass plate <NUM>. Even when processing laser light LB is reflected on work material W adhering to glass plate <NUM>, temperature sensor <NUM> can clearly distinguish between the reflected light (near-infrared light) and the far-infrared light (black-body radiation light) to be detected. Therefore, controller <NUM> can further certainly detect the degree of the contaminants adhering to transparent protector <NUM> at a higher reliability. In other words, controller <NUM> can accurately detect that the temperature of transparent protector <NUM> exceeds an allowable temperature, (or an allowable dirt degree of glass plate <NUM>), furthermore the time for replacement of transparent protector <NUM>.

Furthermore, glass plate <NUM> may include: exposure region <NUM> for passing processing laser light LB; and non-exposure region <NUM> that does not pass processing laser light LB. Temperature sensor <NUM> may optically detect the temperature of glass plate <NUM> in non-exposure region <NUM>. Even when processing laser light LB is radiated to the dust adhering to glass plate <NUM>, and a part of glass plate <NUM> is heated locally the temperature of glass plate <NUM> in non-exposure region <NUM> that is apt to have a further uniform temperature can be optically detected. Thus, the detection error of the temperature due to variation (non-uniformity) of the dust adhering to glass plate <NUM> can be suppressed as much as possible.

Housing <NUM> may include shade <NUM> that blocks the light coming into temperature sensor <NUM> from glass plate <NUM> in exposure region <NUM>. Thus, the components of temperature sensor <NUM> can be protected from the reflected light of processing laser light LB of a high power, and the long-term reliability of temperature sensor <NUM> can be secured.

Transparent protector <NUM> includes: glass plate <NUM> including a portion for passing processing laser light LB; and frame <NUM> for holding glass plate <NUM>.

In an example not covered by the present invention,the temperature sensor may detect the temperature of glass plate <NUM> by electrically detecting the temperature of frame <NUM>. Similarly to temperature sensor <NUM> for optically detecting the temperature of transparent protector <NUM>, - on the basis of the temperature of transparent protector <NUM> that is indirectly detected by electrically detecting the temperature of frame <NUM> -, controller <NUM> can determine the dirt degree and/or the time for replacement of transparent protector <NUM>.

Furthermore, laser processing system <NUM> further includes a display connected to controller <NUM>. Controller <NUM> may cause the display to display the temperature of transparent protector <NUM> detected by temperature sensor <NUM>. Alternatively, controller <NUM> may cause the display to display the output reduction rate representing the output reduction of processing laser light LB radiated to work material W. Here, the output reduction is caused by the dust adhering to transparent protector <NUM>. Thus, the user can know the relative value (output reduction rate indicating the degree of decrease in output) between the following values: the intensity of processing laser light LB absorbed by the dust adhering to glass plate <NUM>; and the output intensity of processing laser light LB.

Furthermore, laser processing system <NUM> further includes an input unit connected to controller <NUM>. Controller <NUM> may receive, via the input unit, a set value of the output reduction rate representing the output reduction of processing laser light LB radiated to work material W. Here, the output reduction is caused by the dust adhering to transparent protector <NUM>. Thus, the user can be informed of the time for replacement of transparent protector <NUM> according to the cost-effectiveness demanded by the user. Here, the time for replacement is obtained, by comparing the detected output reduction rate of processing laser light LB radiated to work material W with the set value of a previously set output reduction rate.

Hereinafter, the exemplary embodiments of a laser processing head related to the present disclosure and a laser processing system using this are described with reference to the accompanying drawings. In the description of the exemplary embodiments, the terms (for example, "longitudinal" and "lateral") showing the directions are appropriately used for facilitating the understanding. These terms are used for description, and do not limit the present disclosure. In each drawing, these sizes are relatively shown in order to clarify the shapes or features of the components of the laser processing head, and they are not necessarily shown in the same scale ratio.

Laser processing system <NUM> related to the first exemplary embodiment is described with reference to <FIG>. <FIG> is a block diagram showing a schematic configuration of laser processing system <NUM> in accordance with the first exemplary embodiment. Laser processing system <NUM> schematically includes: laser oscillation device <NUM>; and laser processing head <NUM> connected to laser oscillation device <NUM> via a process fiber (not shown). Laser oscillation device <NUM> includes: controller <NUM>; laser light source <NUM> electrically connected to controller <NUM>; and display input unit <NUM> (user interface device). Laser processing head <NUM> includes temperature sensor <NUM> described later in detail, and electrically connected to controller <NUM> of laser oscillation device <NUM>.

Laser light source <NUM> radiates laser light (processing laser light) LB to work material (work) W, and welds, fuses, and punches work material W. Hereinafter, as one example, laser light source <NUM> is a direct diode laser (DDL) light source for outputting laser light LB of a high power (<NUM> kW or more). The laser light LB from laser light source <NUM> is near-infrared light as one example, and its peak wavelength is <NUM> (<NUM>).

Infrared light is categorized into three regions according to the wavelength, and is typically categorized into near-infrared light (<NUM> to <NUM>), mid-infrared light (<NUM> to <NUM>), and far-infrared light (<NUM> to <NUM>). The wavelength regions of these laser lights may be used as the wavelengths of laser light LB. Temperature sensor <NUM> described later may be an infrared radiation thermometer for optically detecting the temperature by detecting infrared light within a detection wavelength region. The wavelength region of laser light LB coming from laser light source <NUM> is preferably different from the detection wavelength region of temperature sensor <NUM>.

Display input unit <NUM> includes: an inputting means (input unit) allowing the user to adjust the intensity of laser light LB coming from laser light source <NUM>; and a displaying means (display) for showing the temperature data from temperature sensor <NUM> to the user. For example, display input unit <NUM> is a general-purpose touch panel. Display input unit <NUM> related to one aspect of the present disclosure is not limited to the general-purpose touch panel. Display input unit <NUM> may be any user interface device. In the user interface device, the user inputs an intensity into the user interface device in order to adjust the intensity of laser light LB, and the user is informed of the temperature data from temperature sensor <NUM>. The display input unit may separately include the display and the input unit (for example, keyboard).

<FIG> is a schematic diagram showing a configuration of laser processing head <NUM> in accordance with the first exemplary embodiment. Laser processing head <NUM> is connected to an incident connector (not shown) of the process fiber (not shown) for transmitting laser light LB coming from laser light source <NUM>. Laser processing head <NUM> includes housing <NUM> having: incident end <NUM> for receiving laser light LB; and outgoing end <NUM> for outputting (radiating) laser light LB. In other words, housing <NUM> includes the optical path of laser light LB from laser light source <NUM> between incident end <NUM> and outgoing end <NUM>.

In housing <NUM>, laser processing head <NUM> includes collimator lens <NUM>, collecting lens <NUM>, and transparent protector <NUM>. Collimator lens <NUM> converts laser light LB coming from incident end <NUM> into parallel light. Collecting lens <NUM> collects the parallel light Transparent protector <NUM> suppresses dust, which is generated from work material W irradiated with the laser light LB, entering into housing <NUM>. In other words, transparent protector <NUM> protects the components (especially, collecting lens <NUM>) in housing <NUM> from the dust of work material W.

Furthermore, housing <NUM> of laser processing head <NUM>, which is not shown in detail, has a (detachably fixable) slit into which transparent protector <NUM> can be detachably fitted. As discussed above, transparent protector <NUM> protects the components in housing <NUM> from the dust of work material W. Therefore, it is preferable that transparent protector <NUM> has a shape and size so as to prevent a gap from being formed between transparent protector <NUM> and housing <NUM> when transparent protector <NUM> is fitted into the slit.

<FIG> is a plan view showing transparent protector <NUM> in accordance with the first exemplary embodiment. Transparent protector <NUM> includes: glass plate <NUM> made of quartz glass or the like; and frame <NUM> for fixing the periphery of glass plate <NUM>. Frame <NUM> may be made of any material having a heat resistance, but it is preferable that this material is a metal (steel such as SUS) having a high strength and an electric conductivity. Transparent protector <NUM> is inserted into the slit of housing <NUM> in the direction shown by arrow A. For convenience of description, in <FIG>, frame <NUM> includes front end <NUM>, rear end <NUM>, right side portion <NUM>, and left side portion <NUM>. Glass plate <NUM> includes: exposure region <NUM> for passing processing laser light LB; and non-exposure region <NUM> that does not pass processing laser light LB.

Laser light source <NUM> provides laser light LB of a high power such as, for example, 1kW or more to process work material W. Work material W irradiated with laser light LB of a high power generates evaporated composition or dust (for example, zinc vapor) of work material W. The evaporated composition or dust adheres to transparent protector <NUM> attached to housing <NUM> of laser processing head <NUM>. The dust adhering to transparent protector <NUM> is opaque. The dust adhering to exposure region <NUM> absorbs laser light LB coming from laser light source <NUM>. As a result, transparent protector <NUM> in exposure region <NUM> is heated, and the intensity of laser light LB radiated to work material W is reduced.

For example, when laser light LB of an intensity corresponding to <NUM> W is output from laser light source <NUM>, and when the dust of work material W absorbs laser light LB of the intensity corresponding to <NUM> W, laser light LB of the intensity corresponding to <NUM> W is radiated to work material W (output reduction rate becomes <NUM>%). Therefore, a desired processing rate or processing accuracy cannot be obtained. Furthermore, transparent protector <NUM> is extremely degraded, and the components in housing <NUM> are exposed to a high temperature of an allowable temperature or more.

Incidentally, when the mass of glass plate <NUM> is about <NUM> and its specific heat is about <NUM> J/gK, the heat capacity required for increasing the temperature of glass plate <NUM> by <NUM> is about <NUM> J. Glass plate <NUM> is heated to about <NUM> (room temperature is <NUM>), when the following assumptions are established: laser light LB corresponding to <NUM> W (<NUM>% of the initial laser output intensity) is absorbed by the dust of work material W; and only glass plate <NUM> of transparent protector <NUM> is heated.

Laser processing head <NUM> in accordance with the first exemplary embodiment includes temperature sensor <NUM> attached to housing <NUM> as shown in <FIG>. Laser light LB from laser light source <NUM> is partially absorbed by the dust adhering to transparent protector <NUM>. The absorbed laser light LB is not radiated to work material W. Temperature sensor <NUM> detects the intensity (or output reduction rate of laser light LB) of the absorbed laser light LB.

Next, temperature sensor <NUM> in accordance with the first exemplary embodiment is described in detail. Temperature sensor <NUM> is an infrared radiation thermometer. The thermometer optically detects the temperature of glass plate 50by detecting the far-infrared light (peak wavelength) generated by black-body radiation from the dust adhering to glass plate <NUM> of transparent protector <NUM>. Temperature sensor <NUM> (infrared radiation thermometer), which is not shown in detail, may include the following components, for example:
any photodetector (photodetector, photodiode, or photo-multiplier) for converting light into electricity; and a bandpass filter for passing the light of a specific wavelength band. Furthermore, temperature sensor <NUM> may be a thermography that optically measures the temperature of glass plate <NUM> and displays the measured temperature as a color image.

Hereinafter, temperature sensor <NUM> is described as one example. Temperature sensor <NUM> includes a photodetector (PD). Temperature sensor <NUM> receives the far-infrared light generated by black-body radiation from the dust via a bandpass filter for passing light of a wavelength band of <NUM> to <NUM>, for example. In other words, temperature sensor <NUM> outputs an electric signal corresponding to the intensity of the light of a wavelength band of <NUM> to <NUM> having passed through the bandpass filter.

When the dust of work material W is not adhering to glass plate <NUM> of transparent protector <NUM>, most of laser light LB transmits (passes) through glass plate <NUM>, and is radiated to work material W. Therefore, the temperature of glass plate <NUM> is equivalent to room temperature (for example, <NUM>). However, when laser light LB is continued to be radiated to work material W, the dust of work material W is accumulated on the glass plate <NUM> of transparent protector <NUM>. The dust is accumulated in a larger area of glass plate <NUM> (the dirt gets worse), the loss of laser light LB passing through glass plate <NUM> increases and the temperature of glass plate <NUM> increases.

While, according to Wien's displacement law, peak wavelength (λ) of far-infrared light generated by black-body radiation is expressed by the following equation using absolute temperature (T). Here, the Wien's displacement law shows that the peak wavelength of the black-body radiation (radiation from the black-body) is inversely proportional to the temperature.

Here, the unit of peak wavelength (λ) is micron (µm), and the unit of absolute temperature T is Kelvin (K).

Temperature sensor <NUM> has the characteristic in which the electric signal output from temperature sensor <NUM> extremely increases in the following cases: the far-infrared light generated by black-body radiation from the dust of work material W has a peak wavelength at which the intensity of the light becomes maximum in the wavelength band of about <NUM> to about <NUM>; namely the temperature of glass plate <NUM> is about <NUM> to about <NUM> (room temperature is <NUM> (<NUM>)).

In other words, when new transparent protector <NUM> is mounted to laser processing head <NUM> and then laser light LB is radiated to work material W; adhesion degree (contamination degree) of the dust to glass plate <NUM> increases, and the electric signal output from temperature sensor <NUM> to controller <NUM> increases.

Therefore, when the peak wavelength becomes lower than a predetermined value and temperature sensor <NUM> detects the peak wavelength of the wavelength band of about <NUM> to about <NUM>; controller <NUM> can determine that the temperature of glass plate <NUM> arrives at about <NUM> to about <NUM>. Then, controller <NUM> cause display input unit <NUM> to display the temperature (about <NUM> to about <NUM>) of glass plate <NUM>.

The wavelength band for passing the light of a bandpass filter - which is not limited to the above-mentioned one -, may be a wavelength band corresponding to the temperature of about <NUM>±<NUM> of glass plate <NUM>, for example. At this time, controller <NUM> can more finely (more accurately) detect the temperature range of the temperature increase of glass plate <NUM>. Temperature sensor <NUM> includes a bandpass filter of a wavelength band corresponding to each of a plurality of temperatures to be detected. Controller <NUM> may more elaborately monitor the temporal change of the temperature of glass plate <NUM> after the radiation of laser light LB. Thus, controller <NUM> may show, to the user, the temperature of glass plate <NUM> as needed via display input unit <NUM>. Controller <NUM> may also show, to the user, the dirt degree of glass plate <NUM>, and the time for replacement of transparent protector <NUM> or the sign of the time for replacement.

Furthermore, when temperature sensor <NUM> has detected a peak wavelength lower than the peak wavelength of the wavelength band of about <NUM> to about <NUM> for example, as a predetermined value: controller <NUM> can determine that glass plate <NUM> of transparent protector <NUM> absorbs laser light LB of an intensity exceeding <NUM>% of initial laser light LB, for example, (output reduction rate exceeds <NUM>%). Then, controller <NUM> causes display input unit <NUM> to display this output reduction rate (for example, <NUM>%, or exceeding <NUM>%). At this time, controller <NUM> may inform, via display input unit <NUM>, the user of the requirement of replacement of transparent protector <NUM> or the approach to the time for replacement.

Furthermore, the following method is allowed. The user inputs, as a set value, the relative value (output reduction rate, for example <NUM>%) between the following values: the intensity of laser light LB absorbed by the dust adhering to glass plate <NUM>; and the output intensity of laser light LB. When the relative value arrives at the input output reduction rate, controller <NUM> may inform the user of the arrival via display input unit <NUM>. Thus, by comparing the detected output reduction rate of processing laser light LB radiated to work material W with the set value of a previously set output reduction rate; the user is informed of the time for replacement of transparent protector <NUM> according to the cost-effectiveness demanded by the user. Here, when the user can input any output reduction rate, a bandpass filter of a wavelength band corresponding to each output reduction rate must be disposed in temperature sensor <NUM>.

In the above-mentioned example, display input unit <NUM> visually shows the time for replacement to the user, but is not limited to this. The time for replacement may be shown to the user using an acoustic means such as a buzzer.

As discussed above, laser light LB from laser light source <NUM> is near-infrared light having a peak wavelength of <NUM> (<NUM>), for one example. While, the black-body radiation light coming from the dust adhering to glass plate <NUM> is far-infrared light having a wavelength band of about <NUM> to about <NUM>, for example. In Patent Literature <NUM>, the wavelengths of the detected reflected light and the disturbance light (both are near-infrared light) are the same, so that detection error is apt to be caused. However, in the present disclosure, even when laser light LB is reflected on work material W adhering to glass plate <NUM>, the reflected light (near-infrared light) can be clearly distinguished from far-infrared light (black-body radiation light) to be detected. Therefore, the temperature of transparent protector <NUM>, namely, the dirt degree of glass plate <NUM> (further, the time for replacement of transparent protector <NUM>) can be accurately detected.

Furthermore, the dust of work material W does not always uniformly adhere to glass plate <NUM>, but adheres to a part of glass plate <NUM>. Therefore, a part of exposure region <NUM> of glass plate <NUM> is sometimes heated by laser light LB of a high power, and glass plate <NUM> locally has high temperature. Furthermore, glass plate <NUM> has a low thermal conductivity and exposure region <NUM> is connected to non-exposure region <NUM> in glass plate <NUM>. Therefore, the heat generated in exposure region <NUM> is conducted to non-exposure region <NUM>, and glass plate <NUM> in non-exposure region <NUM> is apt to have more uniform temperature. Therefore, preferably, temperature sensor <NUM> is configured to optically detect the temperature of glass plate <NUM> in non-exposure region <NUM>. Specifically, temperature sensor <NUM> may be disposed so that the optical axis of the far-infrared light coming into temperature sensor <NUM> points to non-exposure region <NUM>. Thus, the detection error of the temperature due to variation (non-uniformity) of the dust adhering to glass plate <NUM> can be suppressed as much as possible.

Incidentally, as discussed above, temperature sensor <NUM> (infrared radiation thermometer) related to the present disclosure does not detect the reflected light by the dust adhering to glass plate <NUM>. However, the intensity (optical energy) of the reflected light of laser light LB of a high power is extremely higher than that of the far-infrared light (black-body radiation light). Therefore, when the bandpass filter constituting temperature sensor <NUM> is exposed to the reflected light having a high optical energy for a long time, the bandpass filter is heated to be deteriorated and can damage the desired optical characteristic. Then, as shown in <FIG>, laser processing head <NUM> of the present disclosure may include shade <NUM>, which extends from the inner wall of housing <NUM>, between temperature sensor <NUM> and exposure region <NUM> of glass plate <NUM>. Here, shade <NUM> is used for blocking the direct reflected light of laser light LB coming into temperature sensor <NUM> from glass plate <NUM> in exposure region <NUM>. Thus, the components of temperature sensor <NUM> are protected from the reflected light of laser light LB of a high power, and the long-term reliability of temperature sensor <NUM> can be secured.

In the description of the first exemplary embodiment and the modified example, laser light source <NUM> is a direct diode laser (DDL) light source, laser light LB from laser light source <NUM> is near-infrared light, and its peak wavelength is <NUM>. However, laser light source <NUM> is not limited to this. In other words, laser light source <NUM> may radiate the light of another wavelength of the DDL light source, or may be a light source other than the DDL light source. Laser light LB from laser light source <NUM> may be the light of a wavelength capable of being clearly distinguished from the far-infrared light generated by black-body radiation from the dust adhering to glass plate <NUM> of transparent protector <NUM>. In other words, it is preferable - in order to prevent a detection error - that the wavelength region of the laser light LB from laser light source <NUM> is different from the detection wavelength of the infrared light used for optically detecting the temperature with temperature sensor <NUM>.

Claim 1:
A laser processing head (<NUM>) comprising:
a housing (<NUM>) including an optical path of a processing laser light (LB);
a transparent protector (<NUM>) configured to be detachably fixed to the housing (<NUM>), to pass the processing laser light (LB), and to suppress dust entering into the housing (<NUM>), the dust being generated from the processed material (W) irradiated with the processing laser light (LB); and
a temperature sensor (<NUM>) configured to detect a temperature of the transparent protector (<NUM>),
wherein
the transparent protector (<NUM>) has a glass plate (<NUM>) having a portion configured to pass the processing laser light (LB), and
the temperature sensor (<NUM>) includes an infrared radiation thermometer, the infrared radiation thermometer being configured to optically detect a temperature of the glass plate (<NUM>) by detecting a peak wavelength of a far-infrared light generated by a black-body radiation from the dust adhering to the glass plate (<NUM>),
characterized in that
the glass plate (<NUM>) includes:
an exposure region (<NUM>) configured to pass the processing laser light (LB); and
a non-exposure region (<NUM>) configured not to pass the processing laser light (LB), and
the exposure region (<NUM>) is connected to the non-exposure region (<NUM>), and
the temperature sensor (<NUM>) optically detects a temperature of the glass plate (<NUM>) in the non-exposure region (<NUM>).