JP7770982B2 - Measurement device, measurement method, and computer program - Google Patents

Description

Embodiments of the present invention relate to a measurement device, a measurement method, and a computer program.

In laser welding, AE waves generated by acoustic emission (AE) at the welding point during welding are detected by an AE sensor, and the AE signals obtained from the detected AE waves are used for quality assessment, such as identifying abnormalities in the weld and predicting penetration depth. The AE waves generated during welding are a type of elastic wave. However, since the detected AE signal strength (AE signal level) fluctuates depending on the change in distance between the laser welding position and the AE sensor installation position, the AE signal strength constantly fluctuates when the laser welding position moves as welding progresses. Furthermore, if the distance between the laser welding position and the AE sensor installation position changes due to reasons such as unintentional displacement of the AE sensor installation position, the AE signal strength also fluctuates. These variations in AE signal strength affect the quality assessment of the weld.

Japanese Patent Application Laid-Open No. 2020-266404 Japanese Patent Application Laid-Open No. 2007-111745 Japanese Patent Application Laid-Open No. 2004-038448

Embodiments of the present invention provide a measurement device, measurement method, and computer program that enable calculation of penetration depth while correcting for the effects of movement of the welding point.

The measuring device according to this embodiment includes a sensor that detects elastic waves generated from the welded portion during laser welding. The device further includes a position information acquisition unit that acquires sensor position information indicating fluctuations in the position of the sensor over time during the laser welding, and welding position information indicating fluctuations in the position of the welded portion over time during the laser welding. The device further includes a processing unit that performs calculations for the laser welding, and that calculates distance information indicating fluctuations in the distance between the sensor and the welded portion over time based on the sensor position information and the welding position information, corrects elastic wave data indicating fluctuations in the elastic waves detected by the sensor over time during the laser welding based on the distance information, and calculates penetration depth information indicating fluctuations in the penetration depth of the laser weld over time based on the corrected elastic wave data.

FIG. 1 is a block diagram of a measurement system according to a first embodiment. FIG. 3 is a top view illustrating an example of a laser welding process according to the first embodiment. FIG. 10 is a top view illustrating another example of the laser welding process according to the first embodiment. FIG. 10 is a top view illustrating another example of the laser welding process according to the first embodiment. FIG. 4 is a diagram showing detected AE data. FIG. 10 is a diagram showing corrected AE data. FIG. 10 is a diagram showing the measurement results of penetration depth. 4 is a flowchart showing an example of processing performed by a CPU according to the first embodiment. FIG. 10 is a block diagram of a measurement system according to a second embodiment. FIG. 10 is a block diagram of a measurement system according to a third embodiment.

Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
1 is a block diagram of a measurement system 1 according to the first embodiment. The measurement system 1 includes a laser welding apparatus 100 and a measurement apparatus 200. The laser welding apparatus 100 and the measurement apparatus 200 may be integrated, or the measurement apparatus 200 may be installed outside the laser welding apparatus 100. The measurement system 1 will be described below with reference to FIG. 1, and in the description, FIGS. 2 to 7 will also be referenced.

The laser welding device 100 includes a laser control device 10, a laser oscillator 11, an optical fiber 12, and a welding head 13.

The laser control device 10 controls the laser oscillator 11. For example, it controls the power of the laser output by the laser oscillator 11 and the timing at which the laser oscillator 11 starts, pauses, or ends laser irradiation. When the laser control device 10 starts, pauses, or ends laser output, it notifies the CPU 19, described below.

The laser oscillator 11 outputs laser light L for use in laser welding by laser oscillation.

The optical fiber 12 transmits the laser light L output by the laser oscillator 11 to the welding head 13.

The welding head 13 irradiates the transmitted laser light L onto a predetermined welding position (welding point) on the workpiece W, which is the object to be laser welded. This welds the workpiece W. The welding head 13, for example, focuses the laser light L using a focusing lens and irradiates it onto the workpiece W.

Laser welding may be performed by fixing the absolute position of the workpiece W and scanning the welding head 13 along a predetermined weld line on the workpiece W. Alternatively, the absolute position of the welding head 13 may be fixed and laser welding may be performed by moving the workpiece W. Alternatively, laser welding may be performed by moving both the welding head 13 and the workpiece W.

The workpiece W is made of a thermoplastic material such as metal. The absolute position of the workpiece W may be fixed using a jig or the like, or it may be attached to a workpiece manipulation device (not shown) such as an articulated robot or an NC processing machine. The workpiece manipulation device is a device that moves the workpiece W so that the welding head 13 follows a predetermined weld line on the workpiece W in order to weld the workpiece W.

The welding head 13 may have its absolute position fixed by a jig or the like, or may be attached to a welding head operating device (not shown), such as an articulated robot or NC processing machine. The welding head operating device is a device that scans the welding head 13 along a predetermined weld line on the workpiece W in order to weld the workpiece W.

The measuring device 200 includes an AE sensor 14, a preamplifier 15, a filter 16, a main amplifier 17, an A/D converter 18, a CPU (Central Processing Unit) 19, and a position information acquisition unit 20.

The AE sensor 14 detects AE waves, which are elastic waves generated from the weld area by AE during laser welding, and outputs an electrical signal (AE signal) that indicates the temporal variation of the detected AE waves. For example, the voltage level of the AE signal corresponds to the level of the detected AE waves. The data represented by the AE signal is called AE data. AE data is, for example, time-series data of the AE waves detected by the AE sensor 14. AE data is an example of elastic wave data.

In laser welding, the greater the penetration depth, the greater the AE generated, and the larger the AE waves generated. Therefore, the greater the penetration depth, the larger the detected AE waves and the larger the output AE signal. Furthermore, the AE waves originate at the welded point on the workpiece W and propagate through the interior of the workpiece W and the air, attenuating as they do so. Therefore, the greater the distance between the AE sensor 14 and the welded point, the smaller the detected AE waves and the smaller the output AE signal.

In the first embodiment, the AE sensor 14 includes, for example, a piezoelectric element (piezo element). When the AE sensor 14 includes a piezoelectric element, the AE sensor 14 is fixed in contact with the workpiece W. Here, "fixing the AE sensor 14 to the workpiece W" means that the relative position of the AE sensor 14 with respect to the workpiece W is constant. In this case, to eliminate any gaps (air layers) between the AE sensor 14 and the workpiece W, a contact medium may be applied to the AE sensor 14, and the AE sensor 14 may be tightly attached to the workpiece W. By applying a contact medium to the AE sensor 14 and tightly attaching it to the workpiece W, AE waves can be detected with higher sensitivity.

The AE sensor 14 transmits its own position information to the position information acquisition unit 20, which will be described later. Alternatively, the position information acquisition unit 20 acquires the position information of the AE sensor 14.

When the AE signal transmitted from the AE sensor 14 is weak, the preamplifier 15 amplifies the AE signal according to predetermined amplification conditions.

The filter 16 passes AE signals transmitted from the preamplifier 15 in a frequency band related to the penetration depth in laser welding, and attenuates signals in frequency bands other than this frequency band. The filter 16 can remove AE signals that are not related to the quality evaluation of the welded area, for example, when the laser light L initially collides with the workpiece W, when spatter occurs, or when foreign matter adheres.

The main amplifier 17 amplifies the AE signal transmitted from the filter 16 under specified amplification conditions.

The A/D converter 18 converts the AE signal transmitted from the main amplifier 17 from an analog signal to a digital signal.

At least one of elements 15-18 may be installed externally to the AE sensor 14, or may be built into the AE sensor 14. In particular, if the preamplifier 15 is built into the AE sensor 14, a highly sensitive, low-noise AE signal can be obtained.

Here, an example of the laser welding process in the first embodiment will be described.

Figures 2, 3, and 4 are top views illustrating an example of the laser welding process. Here, we will explain the case where two workpieces W1, W2 are butted together and laser welded. The weld line WL represents the line (surface) where the two workpieces W1, W2 meet. As the welding head 13 moves along the weld line WL, laser light L is irradiated onto the weld line WL, performing welding. The AE sensor 14 is fixed at a sufficient distance from the weld line WL so as not to directly affect the welding. The weld line WL can take any shape depending on the application of the laser welding. Here, the weld line WL is assumed to be a line segment, and the AE sensor 14 is installed approximately in the center of the weld line WL.

Figure 2 is a top view showing the state immediately after welding begins. As shown in Figure 2, immediately after welding begins, the welding head 13 (weld location) is at one end of the weld line WL, and the distance D between the weld location and the AE sensor 14 is large. As a result, the amount of attenuation of the AE wave increases, and the output AE signal becomes smaller.

Figure 3 is a top view of the welding head as it moves to approximately the center of the weld line WL. As shown in Figure 3, as time passes after the start of welding and the welding head 13 moves closer to the center of the weld line WL, the distance D between the weld point and the AE sensor 14 decreases. As a result, the amount of attenuation of the AE wave decreases, and the output AE signal increases.

Figure 4 is a top view showing the state immediately before the end of welding. As shown in Figure 4, immediately before the end of welding, the welding head is at one end of the weld line WL, and the distance D between the weld point and the AE sensor 14 increases again. As a result, the output AE signal decreases again.

As described above, the fluctuation over time of the AE signal output during laser welding will include the influence of the fluctuation over time of the distance D. In other words, the AE data (measurement data) obtained during laser welding will include the influence of the fluctuation over time of the distance D.

The position information acquisition unit 20 acquires information indicating the fluctuation over time of the position of the AE sensor 14 during laser welding (sensor position information) and information indicating the fluctuation over time of the position of the welded area during laser welding (welding position information). The position of the welded area may be determined by directly observing the position of the welded area, or may be calculated from the position of the welding head 13 and the optical path of the laser light L. The sensor position information is, for example, time-series data on the position of the AE sensor 14, and the welding position information is, for example, time-series data on the position of the welded area.

The position information acquisition unit 20 may be, for example, a device such as a camera that observes the welding point on the workpiece W and/or the welding head 13 and the AE sensor 14 within its field of view. Alternatively, the position information acquisition unit 20 may be a device such as a computer that acquires the mechanical coordinates of the welding head 13 from a welding head operating device to which the welding head is attached and determines the welding position information. In this case, the processing by the position information acquisition unit 20 (computer) may be performed by an electrical circuit or a program.

The position information acquisition unit 20 may acquire the welding position information during laser welding, or after laser welding is completed.

For example, the position information acquisition unit 20 may acquire welding position information from the trajectory history of the welding head operating device after laser welding is completed. Alternatively, if the position information acquisition unit 20 is equipped with a camera, it may observe the welding marks remaining on the workpiece W after laser welding is completed, and calculate the welding position information backward based on the welding marks and the period from the start of laser welding to the end of laser welding.

The CPU 19 receives the digitalized AE signal transmitted from the A/D converter 18. The CPU 19 then performs waveform processing and/or complex wave removal on the digitalized AE signal to extract the AE data required for measuring the penetration depth of the laser weld. The AE data includes the acquisition time of the AE signal and fluctuations in amplitude over time. Waveform processing can be any process, such as peak separation or smoothing.

Generally, AE waves are complex waves consisting of longitudinal waves (compression waves) and shear waves. Here, complex wave removal refers to removing at least one of the longitudinal wave and shear wave components of the acquired AE signal. For example, AE data may be extracted from only the longitudinal wave component of the AE signal, which is considered to have higher intensity.

The information processing performed by CPU 19 is realized, for example, by having CPU 19 execute a computer program installed in a storage device within measurement device 200. The storage device within measurement device 200 is, for example, an HDD (Hard Disc Drive). The computer program can be installed in the storage device of measurement device 200 by storing the computer program recorded on a recording medium such as semiconductor memory in this storage device, or by downloading the computer program from a network to this storage device.

Figure 5 shows AE data obtained by applying the waveform processing and/or complex wave removal described above to the time-varying data of the AE signal obtained through the laser welding process of Figures 2 to 4. The left end of Figure 5 represents the start of AE signal acquisition (start of laser welding), and the right end represents the end of AE signal acquisition (end of laser welding). As mentioned above, the AE data exhibits a mountain-like variation over time, with small values at the start and end of laser welding and relatively large values at other times.

The CPU 19 then imports the sensor position information and welding position information acquired by the position information acquisition unit 20. It then calculates information (distance information) that indicates the time-dependent variation in the distance D between the AE sensor 14 and the welding point during laser welding, and corrects the AE data based on the distance information. The distance information is, for example, time-series data on the distance D between the AE sensor 14 and the welding point.

For example, if the position information acquisition unit 20 is equipped with a camera, the position information acquisition unit 20 acquires an image that captures the welding head 13 (welding point) and the welding point on one page, and the CPU 19 calculates the distance D based on the distance between the camera and the workpiece W and the distance (e.g., the number of pixels) between the AE sensor 14 and the welding point on the image.

The relationship (relational equation) between the intensity of the output AE signal and the penetration depth of the welded portion, and the relationship (relational equation) between the distance between the AE sensor 14 and the welded portion and the intensity of the detected AE signal, which are used in calculating the penetration depth of the welded portion, are stored in advance in memory (not shown) within the CPU 19. The captured AE signal and sensor/welding position information are processed by the CPU 19 to measure the penetration depth. Based on the corrected AE data, the CPU 19 calculates information (penetration depth information) that indicates changes in the penetration depth of the welded portion over time. The penetration depth information is, for example, time-series data on the penetration depth of the welded portion.

Figure 6 shows the AE data after the AE data shown in Figure 5 has been corrected based on distance information. As a result of the correction, the AE signal near the start and end of welding is emphasized, and the AE signal during welding is attenuated. Therefore, the peak-shaped change seen in Figure 5 is mitigated in Figure 6.

Figure 7 shows penetration depth information (penetration depth measurement results) calculated from the corrected AE data shown in Figure 6. In Figure 7, the penetration depth is almost uniform throughout the entire welded portion of the workpiece W. This indicates that welding was performed normally.

The CPU 19 outputs the penetration depth measurement results to communicate the obtained penetration depth measurement results to the user of the laser welding device 100. For example, the CPU 19 may display the penetration depth measurement results shown in FIG. 7 on a user interface (not shown) such as a display. The penetration depth measurement results are displayed, for example, as numerical values or graphs on the display.

The horizontal axis in Figure 7 may represent the time from the start to the end of laser welding (measurement time), or may be converted into weld length based on the movement speed of the welding head 13 and/or the workpiece W.

If the CPU 19 detects an abnormality from the penetration depth measurement results, it may notify the user of the laser welding device 100. For example, a predetermined upper and/or lower threshold may be set, and if the measured penetration depth exceeds the upper and/or lower threshold, the user may be notified of the abnormality. This allows the user to know that an abnormality has occurred and the areas that were not properly welded if an abnormality is detected. The user may be notified, for example, by displaying notification information on a display, by turning on a warning lamp or outputting a warning sound, or by outputting to another user interface.

The CPU 19 may also instruct the laser control device 10 to reduce or stop the laser output when the depth exceeds the upper threshold, or to increase or stop the laser output when the depth is below the lower threshold. This prevents welding from proceeding without proper welding and reduces the area where welding is not performed properly.

Figure 8 is a flowchart showing an example of processing performed by the CPU 19 according to the first embodiment. Below, an example of a series of processing performed by the CPU 19 will be explained with reference to this flowchart.

First, the CPU 19 receives a notification from the laser control device 10 that welding has started (step S101).

Next, the CPU 19 acquires the digitalized AE signal from the A/D converter 18 (step S102).

Next, the CPU 19 acquires the sensor position information and welding position information acquired by the position information acquisition unit 20 (step S103). Note that steps S102 and S103 may be performed in any order or simultaneously.

Next, the CPU 19 performs waveform processing and/or complex wave removal on the AE signal to extract the AE data necessary for measuring the penetration depth of the laser welded area (step S104).

Next, distance information is calculated from the acquired sensor position information and welding position information (step S105). Note that steps S104 and S105 may be performed in any order, or may be performed simultaneously.

Next, the extracted AE data is corrected based on the distance information (step S106).

Finally, penetration depth information is calculated from the corrected AE data and output as the measurement result (step S107).

The above series of processes may be performed after laser welding, or may be performed simultaneously with laser welding. If the above processes are performed simultaneously with laser welding, the user can know the penetration depth in real time during laser welding, allowing for quick quality assessment.

As described above, according to the first embodiment, it is possible to measure the laser weld penetration depth while taking into account fluctuations over time in the distance between the AE sensor 14 and the welded area. Furthermore, according to the first embodiment, it is possible to measure the laser weld penetration depth correctly even if the position of the AE sensor 14 is unintentionally shifted from the predetermined position.

Second Embodiment
Figure 9 is a block diagram of a measurement system 2 according to the second embodiment. Elements with the same names or functions as those in Figure 1 of the first embodiment described above are assigned the same reference numerals. In the first embodiment, the AE sensor 14 that detects AE waves is of a contact type, but in the second embodiment, the AE sensor 21 is of a non-contact type. Hereinafter, explanations will be omitted except for changes or additions.

As shown in Figure 9, the AE sensor 21 is a non-contact sensor and does not need to be in contact with the workpiece W. The AE sensor 21 is, for example, an optical sensor. The optical sensor irradiates laser light onto the workpiece W and detects the AE waves propagated to the workpiece W during laser welding due to interference between the incident light and reflected light, thereby acquiring an AE signal.

The AE sensor 21 is fixed so that its relative position to the workpiece W remains constant.

If the AE sensor 21 is a non-contact sensor such as an optical sensor, the AE sensor 21 does not need to be in contact with the workpiece W, and there is no need to use a contact medium. This allows for greater freedom in where the AE sensor 21 is fixed, making measurements easier.

(Third embodiment)
In the third embodiment, another embodiment of the laser welding penetration depth measuring device will be described.

Figure 10 is a block diagram of a measurement system 3 according to the third embodiment. Elements with the same names or functions as those in Figure 1 of the first embodiment and/or Figure 9 of the second embodiment described above are denoted by the same reference numerals. Hereafter, explanations will be omitted except for changes or additions.

In the first embodiment, the AE sensor 14 and in the second embodiment, the AE sensor 21 were fixed to the workpiece W, but in the third embodiment, the AE sensor 22 is fixed to the welding head 13. The AE sensor 22 is a non-contact sensor, and is, for example, an optical sensor.

It is assumed that during laser welding, the welding head 13 and the workpiece W are always maintained at a constant distance. Welding may be performed by fixing the absolute position of the workpiece W and scanning the welding head 13 along a predetermined weld line on the workpiece W. Alternatively, welding may be performed by fixing the absolute position of the welding head 13 and moving the workpiece W. Alternatively, welding may be performed by moving both the welding head 13 and the workpiece W.

Here, the AE sensor 22 being fixed to the welding head 13 means that the relative positional relationship of the AE sensor 22 to the welding head 13 is constant. For example, in Figure 10, the AE sensor 22 and the welding head 13 are integrated, but the AE sensor 22 and the welding head 13 do not have to be integrated.

As a result, the AE sensor 22 follows the same trajectory as the welding head 13 and outputs an AE signal. Because the distance between the welding head 13 and the workpiece W is always constant, the distance between the welding point and the AE sensor 22 is also always constant.

Then, distance correction is performed at a fixed distance, and the penetration depth is calculated using the penetration depth conversion formula.

As described above, according to the third embodiment, the distance between the AE sensor 22 and the welding point is always constant, eliminating the need for correction to take into account fluctuations in distance over time, allowing for simpler measurements.

The present invention is not limited to the above-described embodiment and each embodiment as it is, and in the implementation stage, the components can be modified and embodied without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, configurations in which some components are omitted from all of the components shown in the embodiments may also be considered. Furthermore, components described in different embodiments may be combined as appropriate.

1: Measurement system 2: Measurement system 3: Measurement system
10: Laser control device 11: Laser oscillator 12: Optical fiber
13: Welding head 14, 21, 22: AE sensor 15: Preamplifier
16: Filter 17: Main amplifier 18: A/D converter
20: Position information acquisition unit 100: Laser welding device 200: Measuring device
D: Distance L: Laser beam W, W1, W2: Workpiece WL: Weld line

Claims (11)

a sensor for detecting elastic waves generated from a welding point during laser welding;
a position information acquiring unit that acquires sensor position information indicating a change in the position of the sensor over time during the laser welding and welding position information indicating a change in the position of the welded portion over time during the laser welding;
A processing device that performs calculations regarding the laser welding,
calculating distance information indicating a time-dependent change in the distance between the sensor and the welding point during the laser welding based on the sensor position information and the welding position information;
correcting elastic wave data indicating a time-dependent variation of the elastic waves detected by the sensor during the laser welding based on the distance information;
a processing device that calculates penetration depth information that indicates a time-dependent change in the penetration depth of the laser welding based on the corrected elastic wave data; and
A measuring device comprising: The location information acquisition unit
The measuring device according to claim 1 , further comprising a camera for observing the sensor and a welding head that irradiates the laser beam used for the laser welding onto the object to be laser-welded or the welding location. The measuring device according to claim 1 or 2, wherein the arithmetic processing device calculates and outputs the penetration depth information in parallel with the laser welding. The measurement device described in claim 1, wherein the arithmetic processing device outputs the penetration depth information or information obtained from the penetration depth information to a user interface, or controls the laser welding based on the penetration depth information. The measurement device according to claim 1 , wherein the arithmetic processing unit corrects at least one of a longitudinal wave component and a transverse wave component contained in the elastic wave detected by the sensor based on the distance information. a sensor that detects elastic waves generated from a welding point during laser welding in a non-contact state with respect to an object to be laser welded, the sensor being fixed to a welding head used for the laser welding;
A processing device that performs calculations regarding the laser welding,
correcting elastic wave data indicating a time-dependent variation of the elastic waves detected by the sensor during the laser welding based on a distance between the sensor and the welding point;
a processing device that calculates penetration depth information that indicates a time-dependent change in the penetration depth of the laser welding based on the corrected elastic wave data; and
A measuring device comprising: The measurement device according to claim 6 , wherein the arithmetic processing device calculates and outputs the penetration depth information in parallel with the laser welding. The measuring device according to claim 6 or 7, wherein the arithmetic processing device corrects at least one of a longitudinal wave component and a transverse wave component contained in the elastic wave detected by the sensor based on a distance between the sensor and the welding point. During laser welding, the sensor detects elastic waves generated from the welding point,
acquiring sensor position information indicating a change in the position of the sensor over time during the laser welding, and welding position information indicating a change in the position of the welded portion over time during the laser welding;
calculating distance information indicating a time-dependent change in the distance between the sensor and the welding point during the laser welding based on the sensor position information and the welding position information;
correcting elastic wave data indicating a time-dependent variation of the elastic waves detected by the sensor during the laser welding based on the distance information;
calculating penetration depth information indicating a time-dependent change in the penetration depth of the laser welding based on the corrected elastic wave data. During laser welding, an elastic wave generated from a welding point is detected by a sensor that is in a non-contact state with respect to an object to be laser welded and is fixed to a welding head used for the laser welding;
correcting elastic wave data indicating a time-dependent variation of the elastic waves detected by the sensor during the laser welding based on a distance between the sensor and the welding point;
calculating penetration depth information indicating a time-dependent change in the penetration depth of the laser welding based on the corrected elastic wave data. During laser welding, when an elastic wave generated from a welding point is detected by a sensor, the sensor position information and the welding position information are acquired from a position information acquisition unit that has acquired sensor position information indicating a change in the position of the sensor over time during the laser welding and welding position information indicating a change in the position of the welding point over time during the laser welding,
calculating distance information indicating a time-dependent change in the distance between the sensor and the welding point during the laser welding based on the sensor position information and the welding position information;
correcting elastic wave data indicating a time-dependent variation of the elastic waves detected by the sensor during the laser welding based on the distance information;
and calculating penetration information indicating a time-dependent change in the penetration depth of the laser welding based on the corrected elastic wave data.