Measurement device, measurement method, and computer program

Abstract

To provide a measurement device, a method of measurement, and a computer program that can calculate a welding penetration depth in which an impact from movement of a welding part is corrected.SOLUTION: A measurement device includes: a sensor for detecting an elastic wave generated from a welding part during laser welding; a position information acquisition part for acquiring sensor position information indicating temporal variation of a position of the sensor during laser welding and welding position information indicating temporal variation of a welding position during laser welding; and an arithmetic processing unit for calculating distance information indicating temporal variation of a distance between the sensor and the welding position during laser welding on the basis of the sensor position information and the welding position information, correcting elastic wave data indicating temporal variation of the elastic wave detected by the sensor during laser welding on the basis of the distance information, and calculating welding penetration depth information indicating temporal variation of the welding penetration depth of laser welding on the basis of the corrected elastic wave data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a measurement apparatus, a measurement method, and a computer program. [Background technology]

[0002] In laser welding, acoustic emission (AE) waves generated at the welding point during welding are detected by an AE sensor. 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, the detected AE signal strength (AE signal level) fluctuates depending on the change in the distance between the laser welding position and the AE sensor installation position. Therefore, when the laser welding position moves as the welding progresses, the AE signal strength constantly fluctuates. Furthermore, if the distance between the laser welding position and the AE sensor installation position changes due to unintentional displacement of the AE sensor, the AE signal strength also fluctuates. These fluctuations in AE signal strength affect the quality assessment of the weld. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-266404 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-111745 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-038448 Summary of the Invention [Problem to be solved by the invention]

[0004] The embodiments of the present invention provide a measurement device, a measurement method, and a computer program that enable calculation of a penetration depth that is corrected for the influence of movement of a welding point. [Means for solving the problem]

[0005] The measuring device according to this embodiment includes a sensor that detects elastic waves generated from a welded portion during laser welding. The device further includes a position information acquisition unit that acquires sensor position information indicating a temporal change in the position of the sensor during the laser welding and welding position information indicating a temporal change in the position of the welded portion during the laser welding. The device further includes a calculation processing device that performs calculations for the laser welding, the calculation processing device calculating distance information indicating a temporal change in the distance between the sensor and the welded portion based on the sensor position information and the welding position information, correcting elastic wave data indicating a temporal change in the elastic waves detected by the sensor during the laser welding based on the distance information, and calculating penetration depth information indicating a temporal change in the penetration depth of the laser weld based on the corrected elastic wave data. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a block diagram of a measurement system according to a first embodiment. [Figure 2] FIG. 3 is a top view illustrating an example of a laser welding process according to the first embodiment. [Figure 3] 5A to 5C are top views illustrating another example of the laser welding process according to the first embodiment. [Figure 4] 5A to 5C are top views illustrating another example of the laser welding process according to the first embodiment. [Figure 5] FIG. 10 is a diagram showing detected AE data. [Figure 6] FIG. 10 shows corrected AE data. [Figure 7] FIG. 10 is a diagram showing the measurement results of penetration depth. [Figure 8] 4 is a flowchart showing an example of processing performed by a CPU according to the first embodiment. [Figure 9] FIG. 10 is a block diagram of a measurement system according to a second embodiment. [Figure 10] FIG. 10 is a block diagram of a measurement system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0008] (First embodiment) Fig. 1 is a block diagram of a measurement system 1 according to a 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 Figs. 2 to 7 will also be referenced in the description.

[0009] The laser welding apparatus 100 includes a laser control device 10, a laser oscillator 11, an optical fiber 12, and a welding head 13.

[0010] 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, interrupts, or ends laser irradiation. When starting, interrupting, or ending laser output, the laser control device 10 notifies a CPU 19 (described later) of that effect.

[0011] The laser oscillator 11 outputs laser light L for use in laser welding by laser oscillation.

[0012] The optical fiber 12 transmits the laser light L outputted by the laser oscillator 11 to the welding head 13 .

[0013] The welding head 13 irradiates the transmitted laser light L onto a predetermined welding position (welding spot) of the workpiece W, which is an object to be laser welded, thereby welding the workpiece W. The welding head 13, for example, focuses the laser light L using a focusing lens and irradiates the workpiece W with the focused laser light.

[0014] 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, laser welding may be performed by fixing the absolute position of the welding head 13 and moving the workpiece W. Alternatively, laser welding may be performed by moving both the welding head 13 and the workpiece W.

[0015] The workpiece W is made of a thermoplastic material such as metal. The absolute position of the workpiece W may be fixed by a jig or the like, or the workpiece W 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.

[0016] The absolute position of the welding head 13 may be fixed by a jig or the like, or it may be attached to a welding head operating device (not shown) such as an articulated robot or an 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.

[0017] 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 .

[0018] The AE sensor 14 detects AE waves, which are elastic waves generated from the welding point 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. Data represented by the AE signal is called AE data. The AE data is, for example, time-series data of the AE waves detected by the AE sensor 14. The AE data is an example of elastic wave data.

[0019] 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 greater the detected AE waves and the larger the output AE signal. Furthermore, the AE waves propagate from the welded portion of the workpiece W as they originate inside the workpiece W and through the air while attenuating. Therefore, the greater the distance between the AE sensor 14 and the welded portion, the smaller the detected AE waves and the smaller the output AE signal.

[0020] In the first embodiment, the AE sensor 14 includes, for example, a piezoelectric 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, in order to eliminate a gap (air layer) 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.

[0021] 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.

[0022] When the AE signal transmitted from the AE sensor 14 is weak, the preamplifier 15 amplifies the AE signal under predetermined amplification conditions.

[0023] Of the AE signals transmitted from preamplifier 15, filter 16 passes signals in a frequency band related to the penetration depth in laser welding and attenuates signals in frequency bands other than the said frequency band. Filter 16 can remove AE signals that are not related to the quality evaluation of the welded portion, for example, when laser light L initially collides with the workpiece W, when spatter occurs, or when foreign matter adheres.

[0024] The main amplifier 17 amplifies the AE signal transmitted from the filter 16 under predetermined amplification conditions.

[0025] The A / D converter 18 converts the AE signal transmitted from the main amplifier 17 from an analog signal to a digital signal.

[0026] At least one of the elements 15 to 18 may be installed outside the AE sensor 14, or may be built into the AE sensor 14. In particular, when the preamplifier 15 is built into the AE sensor 14, a highly sensitive and low-noise AE signal can be obtained.

[0027] Here, an example of the laser welding process in the first embodiment will be described.

[0028] 2, 3, and 4 are top views illustrating an example of the laser welding process. Here, the case where two workpieces W1 and W2 are butted together and laser-welded will be described. The weld line WL represents the line (surface) where the two workpieces W1 and W2 are in contact. As the welding head 13 moves along the weld line WL, laser light L is irradiated onto the weld line WL, and welding is performed. 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.

[0029] Fig. 2 is a top view showing the state immediately after welding has started. As shown in Fig. 2, immediately after welding has started, the welding head 13 (welding point) is at one end of the weld line WL, and the distance D between the welding point and the AE sensor 14 is large. Therefore, the amount of attenuation of the AE wave increases, and the output AE signal becomes small.

[0030] Fig. 3 is a top view of the welding head when it has moved to approximately the center of the weld line WL. As shown in Fig. 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 welding 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.

[0031] Fig. 4 is a top view showing the state immediately before the end of welding. As shown in Fig. 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 welded portion and the AE sensor 14 increases again. As a result, the output AE signal decreases again.

[0032] As described above, the fluctuation over time of the AE signal output during laser welding includes the influence of the fluctuation over time of the distance D. In other words, the AE data (measurement data) obtained during laser welding includes the influence of the fluctuation over time of the distance D.

[0033] Position information acquisition unit 20 acquires information indicating fluctuations over time in the position of AE sensor 14 during laser welding (sensor position information) and information indicating fluctuations over time in the position of the welded point during laser welding (welding position information). The position of the welded point may be determined by directly observing the position of the welded point, or may be calculated from the position of welding head 13 and the optical path of laser light L. The sensor position information is, for example, time-series data on the position of AE sensor 14, and the welding position information is, for example, time-series data on the position of the welded point.

[0034] Position information acquisition unit 20 may be, for example, a device such as a camera that observes the welding point on workpiece W and / or welding head 13 and AE sensor 14 within its field of view. Alternatively, position information acquisition unit 20 may be a device such as a computer that acquires the mechanical coordinates of welding head 13 from a welding head operating device to which the welding head is attached and determines welding position information. In this case, the processing by position information acquisition unit 20 (computer) may be performed by an electric circuit or a program.

[0035] The position information acquisition unit 20 may acquire the welding position information during laser welding, or may acquire the welding position information after laser welding is completed.

[0036] For example, the position information acquiring unit 20 may acquire the welding position information from the trajectory history of the welding head operating device after the laser welding is completed. Alternatively, if the position information acquiring unit 20 is equipped with a camera, the position information acquiring unit 20 may observe the welding marks remaining on the workpiece W after the laser welding is completed, and calculate the welding position information backward based on the welding marks and the period from the start of the laser welding to the end of the laser welding.

[0037] 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. The waveform processing may be any process such as peak separation or smoothing.

[0038] 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 component and shear wave component 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 a higher intensity.

[0039] The information processing performed by the CPU 19 is realized, for example, by having the CPU 19 execute a computer program installed in a storage device within the measuring device 200. The storage device within the measuring device 200 is, for example, an HDD (Hard Disc Drive). The computer program may be installed in the storage device of the measuring device 200 by storing the computer program recorded on a recording medium such as a semiconductor memory into this storage device, or by downloading the computer program from a network to this storage device.

[0040] 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 described above, the AE data is small at the start and end of laser welding, and relatively large at other times, forming a mountain-like fluctuation over time.

[0041] The CPU 19 then acquires the sensor position information and welding position information acquired by the position information acquisition unit 20. Then, the CPU 19 calculates information (distance information) indicating 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 of the distance D between the AE sensor 14 and the welding point.

[0042] 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 on the image and the welding point.

[0043] The relationship (relational formula) between the intensity of the output AE signal and the penetration depth of the welded portion, and the relationship (relational formula) 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 a memory (not shown) within the CPU 19. The captured AE signal and sensor / welding position information are processed by the CPU 19, and the penetration depth is measured. 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 of the penetration depth of the welded portion.

[0044] 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 signals near the start and end of welding are emphasized, and the AE signals during welding are attenuated. Therefore, the peak-like changes seen in Figure 5 are mitigated in Figure 6.

[0045] Figure 7 shows penetration depth information (penetration depth measurement results) calculated from the corrected AE data shown in Figure 6. In the case of Figure 7, the penetration depth is almost uniform over the entire welded portion of the workpiece W. This indicates that welding was performed normally.

[0046] The CPU 19 outputs the penetration depth measurement result to notify the obtained penetration depth measurement result to a user of the laser welding apparatus 100. For example, the CPU 19 may display the penetration depth measurement result shown in Fig. 7 on a user interface (not shown) such as a display. The penetration depth measurement result is displayed, for example, as a numerical value or a graph on the display.

[0047] 7 may represent the time from the start to the end of laser welding (measurement time), or may be converted into the weld length based on the movement speed of welding head 13 and / or workpiece W.

[0048] When an abnormality is detected from the penetration depth measurement results, the CPU 19 may notify the user of the laser welding apparatus 100. For example, a predetermined upper threshold and / or lower threshold may be set, and when the measured penetration depth exceeds the upper threshold and / or falls below the lower threshold, the CPU 19 may notify the user of the abnormality. This allows the user to know that an abnormality has occurred and the location that was not properly welded when an abnormality is detected. The notification to the user may be, for example, displayed on a display, illuminated by a warning lamp or output of a warning sound, or output to another user interface.

[0049] Furthermore, CPU 19 may instruct laser control device 10 to reduce or stop the laser output when the depth exceeds the upper threshold, or may instruct laser control device 10 to increase or stop the laser output when the depth is below the lower threshold. This prevents welding from proceeding without being properly welded, and makes it possible to reduce the range of improper welding.

[0050] 8 is a flowchart showing an example of processing performed by the CPU 19 according to the first embodiment. An example of a series of processing performed by the CPU 19 will be described below with reference to this flowchart.

[0051] First, CPU 19 receives a notification of the start of welding from laser control device 10 (step S101).

[0052] Next, the CPU 19 receives the digitalized AE signal from the A / D converter 18 (step S102).

[0053] Next, the CPU 19 acquires the sensor position information and the 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 may be performed simultaneously.

[0054] Next, the CPU 19 performs waveform processing and / or complex wave removal on the AE signal, and extracts AE data required for measuring the penetration depth of the laser welded portion (step S104).

[0055] 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.

[0056] Next, the extracted AE data is corrected based on the distance information (step S106).

[0057] Finally, penetration depth information is calculated from the corrected AE data and output as the measurement result (step S107).

[0058] The above series of processes may be performed after laser welding or may be performed simultaneously with laser welding during the laser welding. When the above processes are performed simultaneously with laser welding, the user can know the penetration depth in real time during the laser welding and can quickly evaluate the quality.

[0059] As described above, according to the first embodiment, it is possible to measure the laser weld penetration depth taking into account the time-dependent fluctuation of the distance between the AE sensor 14 and the welded portion. 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.

[0060] (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.

[0061] 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, detects AE waves propagated to the workpiece W during laser welding due to interference between the incident light and reflected light, and acquires an AE signal.

[0062] The AE sensor 21 is fixed so that its relative position with respect to the workpiece W is constant.

[0063] If the AE sensor 21 is configured as 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 it possible to perform measurements more easily.

[0064] (Third embodiment) In the third embodiment, another embodiment of the laser welding penetration depth measuring device will be described.

[0065] Fig. 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 Fig. 1 of the first embodiment and / or Fig. 9 of the second embodiment described above are given the same reference numerals. Hereinafter, explanations will be omitted except for changes or additions.

[0066] While the AE sensor 14 in the first embodiment and the AE sensor 21 in the second embodiment are fixed to the workpiece W, 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.

[0067] During laser welding, the welding head 13 and the workpiece W are always kept 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.

[0068] Here, "AE sensor 22 is fixed to welding head 13" means that the relative positional relationship of AE sensor 22 to welding head 13 is constant. For example, although AE sensor 22 and welding head 13 are integrated in Fig. 10, AE sensor 22 and welding head 13 do not have to be integrated.

[0069] This causes AE sensor 22 to follow the same trajectory as welding head 13 and output an AE signal. Since the distance between welding head 13 and workpiece W is always constant, the distance between the welding point and AE sensor 22 is also always constant.

[0070] Then, distance correction is performed at a fixed distance, and the penetration depth is calculated using a penetration depth conversion formula.

[0071] As described above, according to the third embodiment, the distance between the AE sensor 22 and the welding point is always constant, so there is no need to make corrections taking into account fluctuations in the distance over time, and simpler measurements are possible.

[0072] The present invention is not limited to the above-described embodiment and each embodiment as it is, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiments. For example, a configuration in which some components are omitted from all the components shown in the embodiments can also be considered. Furthermore, components described in different embodiments can be appropriately combined. [Explanation of symbols]

[0073] 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

1. 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; Based on the corrected elastic wave data, penetration depth information indicating a time-dependent change in the penetration depth of the laser welding is calculated. a processing unit; A measuring device comprising:

2. The location information acquisition unit The laser welding head irradiates the laser beam used for the laser welding onto the object to be laser-welded, or the welding point, and a camera for observing the sensor are provided. The measurement device according to claim 1 .

3. The arithmetic processing device calculates and outputs the penetration depth information in parallel with the laser welding. The measuring device according to claim 1 or 2.

4. The measurement device according to 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.

5. The arithmetic processing unit corrects at least one of a longitudinal wave component and a transverse wave component included in the elastic wave detected by the sensor based on the distance information. The measurement device according to claim 1 .

6. 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; Based on the corrected elastic wave data, penetration depth information indicating a time-dependent change in the penetration depth of the laser welding is calculated. a processing unit; A measuring device comprising:

7. The arithmetic processing device calculates and outputs the penetration depth information in parallel with the laser welding. The measurement device according to claim 6.

8. 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 the distance between the sensor and the welding point. The measuring device according to claim 6 or 7.

9. 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; Based on the corrected elastic wave data, penetration depth information indicating a time-dependent change in the penetration depth of the laser welding is calculated. Measurement methods that include:

10. 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; Based on the corrected elastic wave data, penetration depth information indicating a time-dependent change in the penetration depth of the laser welding is calculated. Measurement methods that include:

11. 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; Based on the corrected elastic wave data, penetration information indicating a time-dependent change in the penetration depth of the laser welding is calculated. A computer program that causes a computer to execute a measurement method including the steps of:

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