Patent Description:
As described in Patent Literatures <NUM> and <NUM>, a laser welding monitoring device monitors whether or not laser welding is normally performed when the welding is performed on a material to be welded by a laser welding machine. Patent Literature <NUM> discloses a method and apparatus for judging welding performance and root gap accuracy in laser butt welding. Patent Literature <NUM> discloses all features in the preamble of claims <NUM> and <NUM>. Patent Literature <NUM> discloses a laser processing apparatus and a processing method capable of performing laser processing with good controllability even if the thickness of a layer to be processed varies.

It is desirable that the laser welding monitoring device starts monitoring at a timing at which the laser welding machine starts welding of the material to be welded. For example, the laser welding monitoring device may start the monitoring in accordance with a timing at which a laser oscillator starts emission of a laser beam. However, some laser oscillators do not output a signal indicating the start of the emission of the laser beam at the timing of starting the emission of the laser beam. Therefore, a configuration is required in which the laser welding monitoring device starts the monitoring by accurately detecting the timing at which the laser welding machine starts the welding of the material to be welded.

An object of one or more embodiments is to provide a laser welding monitoring device and a laser welding monitoring method capable of starting monitoring of laser welding by accurately detecting a timing at which a laser welding machine starts welding of a material to be welded.

According to a first aspect of the present invention, a laser welding monitoring device is defined in claim <NUM>, which includes a beam receiving unit configured to receive, when a material to be welded is irradiated with a laser beam emitted by a processing head provided to a laser welding machine, a radiated beam generated at an irradiation position of the laser beam and including a reflected beam of the laser beam and a monitoring beam, the monitoring beam being caused by thermal radiation and having a wavelength different from a wavelength of the reflected beam, a spectrometer unit configured to spectrally separate the reflected beam and the monitoring beam included in the radiated beam and convert the spectrally separated monitoring beam into a first electric signal, a trigger unit configured to convert the reflected beam into a second electric signal and output a trigger signal when a level of the second electric signal is a predetermined threshold value or higher, and a laser welding monitor configured to start a determination of whether or not laser welding of the material to be welded is normally performed based on the first electric signal when the trigger signal is input.

According to a second aspect of the present invention, a laser welding monitoring method is defined in claim <NUM>, which includes receiving, when a material to be welded is irradiated with a laser beam emitted by a processing head provided to a laser welding machine, by a beam receiving unit, a radiated beam generated at an irradiation position of the laser beam and including a reflected beam of the laser beam and a monitoring beam, the monitoring beam being caused by thermal radiation and having a wavelength different from a wavelength of the reflected beam, spectrally separating the reflected beam and the monitoring beam included in the radiated beam, converting the spectrally separated monitoring beam into a first electric signal, converting the reflected beam into a second electric signal, generating a trigger signal when a level of the second electric signal is a predetermined threshold value or higher, and starting a determination of whether or not laser welding of the material to be welded is normally performed based on the first electric signal by using an input of the trigger signal as a trigger.

Further embodiments of the first and second aspects of the present invention are defined in the dependent claims.

According to the laser welding monitoring device and the laser welding monitoring method of the one or more embodiments, it is possible to start the monitoring of the laser welding by accurately detecting the timing at which the laser welding machine starts the welding of the material to be welded.

Hereinafter, a laser welding monitoring device and the laser welding monitoring method of one or more embodiments will be described with reference to the attached drawings. In <FIG>, a laser welding machine <NUM> is provided with an NC device <NUM>, a laser oscillator <NUM>, and a processing head <NUM>. The laser oscillator <NUM> is, for example, a fiber laser oscillator that emits a laser beam having a wavelength of <NUM> to <NUM>. The laser beam emitted by the laser oscillator <NUM> is transmitted to the processing head <NUM> by a process fiber <NUM>.

As shown in <FIG>, the processing head <NUM> is provided with a galvano scanner <NUM> and an fθ lens <NUM>. The galvano scanner <NUM> is provided with galvano mirrors <NUM> and <NUM>, and drive units <NUM> and <NUM> that rotate the galvano mirrors <NUM> and <NUM> so as to have a predetermined angle, respectively. The laser beam emitted from the process fiber <NUM> and made incident on the galvano mirror <NUM> is reflected by the galvano mirror <NUM> and made incident on the galvano mirror <NUM>, and then is reflected by the galvano mirror <NUM> and made incident on the fθ lens <NUM>. The fθ lens <NUM> focuses the incident laser beam to irradiate a material to be welded with the laser beam.

By changing the respective angles of the galvano mirrors <NUM> and <NUM>, the laser beam with which the material to be welded is irradiated can be displaced. By continuously moving the galvano mirrors <NUM> and <NUM>, the laser beam can be vibrated or rotated. The fθ lens <NUM> can also focus the laser beam on one plane of the material to be welded when the galvano scanner <NUM> is operated.

Returning to <FIG>, the NC device <NUM> controls the laser oscillator <NUM> and the drive units <NUM> and <NUM> of the galvano scanner <NUM>. The NC device <NUM> also controls the movement of the processing head <NUM>. The laser beam emitted from the processing head <NUM> is applied on an abutting surface <NUM> of sheet metals W1 and W2, which are examples of the materials to be welded, so that the sheet metal W1 and the sheet metal W2 are welded.

It is not essential that the processing head <NUM> is provided with the galvano scanner <NUM>, but it is preferable that the processing head <NUM> is provided with the galvano scanner <NUM>. If the processing head <NUM> is not provided with the galvano scanner <NUM>, the processing head <NUM> may be provided with a bend mirror that reflects the laser beam toward the sheet metal W1 and the sheet metal W2 and a normal focusing lens instead of the fθ lens <NUM>.

In <FIG>, a laser welding monitoring device <NUM> is provided with four beam receiving units that are beam receiving units 30a to 30c, and an unillustrated beam receiving unit located at a position facing the beam receiving unit 30b with the processing head <NUM> interposed therebetween. The beam receiving unit at an arbitrary position is referred to as a beam receiving unit <NUM>. In a configuration in which the processing head <NUM> is provided with the galvano scanner <NUM>, the number of the beam receiving units <NUM> is preferably two or more, and a plurality of beam receiving units <NUM> are preferably arranged on the periphery of the fθ lens <NUM> at equal intervals. When the processing head <NUM> is not provided with the galvano scanner <NUM>, the number of the beam receiving unit <NUM> may be one. Even in the configuration in which the processing head <NUM> is not provided with the galvano scanner <NUM>, the number of the beam receiving units <NUM> may be two or more.

Further, the laser welding monitoring device <NUM> is provided with a spectrometer unit <NUM>, a trigger unit <NUM>, and a laser welding monitor <NUM>.

When the abutting surface <NUM> of the sheet metals W1 and W2 is irradiated with the laser beam, a radiated beam including a reflected beam of the laser beam and a near-infrared beam caused by thermal radiation is generated from the irradiation position of the laser beam. The four beam receiving units <NUM> receive the radiated beam, and the radiated beam received by the four beam receiving units <NUM> is made incident on the spectrometer unit <NUM> by a bundle fiber <NUM>. In <FIG>, the solid arrow line travelling from the abutting surface <NUM> to the beam receiving unit <NUM> indicates the reflected beam of the laser beam, and the alternate long and short dash arrow line indicates the near-infrared beam. The wavelength of the near-infrared beam is <NUM> to <NUM>. The near-infrared beam is a preferable example of a monitoring beam that is caused by thermal radiation and has a wavelength different from a wavelength of the reflected beam of the laser beam.

The beam receiving unit <NUM> is configured to include a protective glass on an incident surface of the radiated beam so that the radiated beam is made incident on the end surface of a core of an optical fiber. The beam receiving unit <NUM> may be configured to receive the radiated beam including the reflected beam of the laser beam and the near-infrared beam caused by thermal radiation, and the configuration thereof is not limited.

As shown in <FIG>, the spectrometer unit <NUM> is provided with a dichroic mirror <NUM> that transmits a beam having a wavelength of <NUM> or more and reflects a beam having a wavelength of less than <NUM>, and a photosensor <NUM>. The reflected beam of the laser beam indicated by the solid arrow line is reflected by the dichroic mirror <NUM>, and the near-infrared beam indicated by the alternate long and short dash arrow line passes through the dichroic mirror <NUM> and is made incident on the photosensor <NUM>. The photosensor <NUM> converts the incident near-infrared beam into an electric signal (a near-infrared monitor signal) and outputs the signal. The near-infrared monitor signal is an example of a first electric signal. The first electric signal is preferably a digital signal.

In <FIG>, the reflected beam of the laser beam emitted from the spectrometer unit <NUM> is transmitted via the reflected beam transmission fiber <NUM> and made incident on the trigger unit <NUM>. The near-infrared monitor signal output from the spectrometer unit <NUM> is transmitted via a monitor signal transmission cable <NUM> and input to the laser welding monitor <NUM>.

As shown in <FIG>, the trigger unit <NUM> is provided with a photosensor <NUM>, a level determination unit <NUM>, and a trigger signal generation unit <NUM>. The photosensor <NUM> converts the reflected beam of the incident laser beam into an electric signal (a second electric signal). The level determination unit <NUM> determines whether or not the level of the input electric signal is a predetermined threshold value or higher. The trigger signal generation unit <NUM> generates and outputs a trigger signal if the electric signal input to the level determination unit <NUM> is a predetermined threshold value or higher. The level determination unit <NUM> and the trigger signal generation unit <NUM> can be configured by a circuit. The level determination unit <NUM> and the trigger signal generation unit <NUM> may be configured by a processor. The second electric signal may be an analog signal or a digital signal. The trigger signal is preferably a digital signal.

In <FIG>, the trigger signal is transmitted via a trigger signal transmission cable <NUM> and is input to the laser welding monitor <NUM>. When the trigger signal is input, the laser welding monitor <NUM> starts monitoring of whether or not laser welding is normally performed based on the near-infrared monitor signal by using the input of the trigger signal as a trigger. As an example, the laser welding monitor <NUM> integrates the input near-infrared monitor signals for a predetermined period of time, and if the integrated value is between the upper limit value and the lower limit value that are preset, the laser welding is determined to be normally performed. If the integrated value is not between the upper limit value and the lower limit value, the laser welding monitor <NUM> determines that the laser welding is not performed normally and that an abnormality has occurred. How the laser welding monitor <NUM> determines whether or not the laser welding is normally performed is not limited.

The laser welding monitor <NUM> is provided with light emitting diodes L1 to L4 on the front surface of a housing thereof. When the laser welding monitor <NUM> determines that the laser welding is normally performed, the light emitting diode L4 of green color is turned on, for example, and when the laser welding monitor <NUM> determines that an abnormality has occurred in the laser welding, the light emitting diode L3 of red color is turned on, for example. For example, the light emitting diode L1 of green color is turned on when the power of the laser welding monitor <NUM> is applied. For example, the light emitting diode L2 of green color is turned on when a trigger signal is input.

The timing at which the laser welding monitor <NUM> starts the monitoring of the laser welding will be described with reference to the characteristic diagram shown in <FIG>. In <FIG>, it is assumed that the processing head <NUM> starts irradiation of the laser beam to the abutting surface <NUM> between the sheet metals W1 and W2 at time t0 and ends the irradiation of the laser beam at time t1. The radiated light intensity of the near-infrared beam indicated by the alternate long and short dash line increases gradually after the start of the irradiation of the laser beam. On the other hand, the radiated light intensity of the reflected beam of the laser beam shown by the solid line increases sharply immediately after the start of the irradiation of the laser beam, decreases sharply, and then becomes a substantially constant value.

Assuming that the threshold value set to the level determination unit <NUM> of the trigger unit <NUM> is the level of the electric signal corresponding to the radiated light intensity of a threshold value TH1 shown in <FIG>, the trigger unit <NUM> outputs the trigger signal immediately after the time t0. Therefore, the laser welding monitoring device <NUM> can accurately detects the timing at which the laser welding machine <NUM> starts welding of the sheet metals W1 and W2, and start monitoring of the laser welding with almost no time delay from the timing at which the welding is started.

In <FIG>, if the trigger unit <NUM> is configured to output the trigger signal at the timing at which the radiated light intensity of the near-infrared beam increases to a predetermined intensity, the radiated light intensity of the near-infrared beam increases only gradually. Therefore, when the processing is repeated under the same laser welding conditions, the timing at which the threshold value TH1 is exceeded varies. Therefore, it is not possible to output the trigger signal immediately after the time t0, and the timing of outputting the trigger signal may be delayed or vary. In comparison to this, since the reflected beam increases sharply immediately after the start of the processing, it is possible to suppress variations in the timing at which the threshold value TH1 is exceeded even when the processing is repeated, which enables the monitoring of the laser welding to be started with high repeatability.

The laser welding monitoring method executed by the laser welding monitoring device <NUM> will be described with reference to the flowchart shown in <FIG> also includes processing executed by the laser welding machine <NUM>. In step S1 of <FIG>, the NC device <NUM> determines whether or not an instruction to start welding has been given. If the instruction to start welding is not given (NO), the NC device <NUM> repeats the process of step S1. If the instruction to start welding is given (YES), the NC device <NUM> starts the laser welding in step S2 by starting laser oscillation in the laser oscillator <NUM>.

In step S3, the four beam receiving units <NUM> receive the radiated beams from the irradiation position of the laser beam, and the bundle fiber <NUM> transmits the received radiated beams to the spectrometer unit <NUM>. In step S4, the spectrometer unit <NUM> spectrally separates the reflected beam of the laser beam and the near-infrared beam that are included in the radiated beam. In step S5, the photosensor <NUM> of the spectrometer unit <NUM> converts the near-infrared beam into the electric signal and supplies the electric signal to the laser welding monitor <NUM>.

In parallel to step S5, in step S6, the trigger unit <NUM> converts the reflected beam transmitted via the reflected beam transmission fiber <NUM> into the electric signal, and outputs the trigger signal when the level of the electric signal exceeds the threshold value.

In step S7, the laser welding monitor <NUM> determines whether or not the trigger signal has been received from the trigger unit <NUM>. If the trigger signal is not received (NO), the laser welding monitor <NUM> repeats the process of step S7. If the trigger signal is received (YES), the laser welding monitor <NUM> starts monitoring of the laser welding in step S8.

In step S9, the laser welding monitor <NUM> determines whether or not a preset measurement time has elapsed. If the measurement time does not elapse (NO), the laser welding monitor <NUM> repeats the process of step S9. The monitoring of the laser welding is continued while the process of step S9 is repeated. If the measurement time has elapsed (YES), the laser welding monitor <NUM> ends the monitoring of the laser welding.

Even when the laser welding monitor <NUM> has ended the monitoring of the laser welding, the welding by the laser welding machine <NUM> may not be ended. The welding by the laser welding machine <NUM> may be ended before the laser welding monitor <NUM> ends the monitoring of the laser welding. Note that even if the trigger signal is input to the laser welding monitor <NUM> again within the measurement time, the trigger signal within the measurement time is ignored.

The timing at which the laser welding monitor <NUM> ends the monitoring of the laser welding is not limited to the point of time at which the measurement time has elapsed. The laser welding monitor <NUM> may end the monitoring of the laser welding at the point of time at which the welding by the laser welding machine <NUM> is completed.

As described above, according to the laser welding monitoring device and the laser welding monitoring method of the one or more embodiments, it is possible to start the monitoring of the laser welding by accurately detecting the timing at which the laser welding machine <NUM> starts the welding of the material to be welded.

The present invention is not limited to the one or more embodiments described above, and various modifications can be made without departing from the summary of the present invention. In the one or more embodiments, the laser welding monitor <NUM> uses the near-infrared monitor signal obtained by converting the near-infrared beam into the electric signal so as to determine whether or not the laser welding is normally performed. However, a plasma beam or a visible beam may be converted into an electric signal. A beam having a wavelength different from the wavelength of the laser beam emitted by the laser oscillator <NUM> may be converted into an electric signal.

As the laser oscillator <NUM>, a direct diode laser oscillator (a DDL oscillator) may be used instead of the fiber laser oscillator. The DDL oscillator emits a laser beam having a wavelength of <NUM> to <NUM>. The wavelength of the laser beam emitted from the laser oscillator <NUM> is preferably in the <NUM> band having a wavelength of <NUM> to <NUM>.

Although the laser welding monitoring device <NUM> shown in <FIG> is provided with a separate housing for each of the spectrometer unit <NUM>, the trigger unit <NUM>, and the laser welding monitor <NUM>, the trigger unit <NUM> may be provided in the housing of the laser welding monitor <NUM>. The spectrometer unit <NUM> and the trigger unit <NUM> may be provided in one housing. The spectrometer unit <NUM> and the trigger unit <NUM> may be provided in the housing of the laser welding monitor <NUM>. The position at which the spectrometer unit <NUM> or the trigger unit <NUM> is provided is not limited.

Claim 1:
A laser welding monitoring device (<NUM>), comprising:
a beam receiving unit (30a, 30b, 30c) configured to receive, when a material to be welded is irradiated with a laser beam emitted by a processing head (<NUM>) provided to a laser welding machine (<NUM>), a radiated beam generated at an irradiation position of the laser beam and including a reflected beam of the laser beam and a monitoring beam, the monitoring beam being caused by thermal radiation and having a wavelength different from a wavelength of the reflected beam; and
a spectrometer unit (<NUM>) configured to spectrally separate the reflected beam and the monitoring beam included in the radiated beam and convert the spectrally separated monitoring beam into a first electric signal,
characterized by
a trigger unit (<NUM>) configured to convert the reflected beam into a second electric signal, to determine whether or not a level of the second electric signal is a predetermined threshold value or higher, and to output a trigger signal indicating a timing at which the laser welding machine (<NUM>) starts welding of the material to be welded when the level of the second electric signal is the predetermined threshold value or higher; and
a laser welding monitor (<NUM>) configured to start a determination of whether or not laser welding of the material to be welded is normally performed based on the first electric signal when the trigger signal is input.