Root gap measuring device, welding device, root gap measuring method, and welding method

Abstract

In measuring the root gap, measurement anomalies are appropriately detected. [Solution] The root gap measuring device 10 includes a shape measuring machine 3 that acquires a measurement shape showing the cross-sectional shape of the groove using a predetermined light source, a reference position identification unit 811 that identifies a reference position in the width direction of the measurement shape by detecting the portions of both groove sides or the ends of both groove sides on the base material surface side of the measurement shape, a candidate range identification unit 812 that identifies a candidate range of the root gap in the width direction of the measurement shape using a gap detection height set to a position deeper than the bottom ends of both groove sides, an abnormality determination unit 813 that determines whether or not there is an abnormality in the candidate range by comparing the candidate range with the reference position, and a root gap acquisition unit 814 that acquires the candidate range as the root gap range when there is no abnormality in the candidate range, and detects a measurement abnormality of the root gap when there is an abnormality in the candidate range.

Description

Technical Field

[0001] The present invention relates to a technique for measuring a root gap of a groove provided between base materials, and a technique for welding the groove.

Background Art

[0002] Conventionally, a welding apparatus having a function (automatic tracing function) of measuring the shape of a groove of a base material using a laser beam and adjusting the aiming position of a welding torch based on the measurement result has been put into practical use. In the measurement of the groove shape, the laser beam emitted from the shape measuring machine is reflected on the surface of the groove and its vicinity, and the reflected light is received by the shape measuring machine, whereby a light cutting image of the groove is acquired as point cloud data. Then, welding line tracing or the like is performed based on the shape indicated by the point cloud data.

[0003] In addition, in a welding apparatus, when a root gap is provided in a groove, the welding conditions such as the set current may be adjusted according to the width of the root gap or the like. In Patent Document 1, a method of detecting a root gap using a slit sensor is disclosed. In Patent Document 2, a method of obtaining the root gap width from image information obtained by performing integral processing and differential processing on a groove image is disclosed. In this method, when the peak values corresponding to the two root gap ends in the above image information are not less than a predetermined value, the positions of the two root gap ends are obtained by the peak values and the root gap width is determined. When the peak value is less than the predetermined value, the width between the two root gap ends is indirectly determined by calculation from the positions of the two shoulders of the groove.

[0004] Furthermore, Patent Document 3 discloses a method for suppressing the occurrence of welding defects caused by abnormalities in the cross-sectional measurement of the groove. In this method, the position of characteristic points in the cross-sectional shape of the groove measured at each position in the welding direction is detected as a first detection position by a first detection method, and as a second detection position by a second detection method different from the first detection method. Then, an abnormality in the measurement result is detected based on the comparison result between the first detection position and the second detection position. Patent Document 4 discloses a method in which a slit-shaped light is irradiated onto the welding groove and the welding groove is detected from an image of the welding groove taken in the width direction. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-47932 [Patent Document 2] Patent No. 2515143 [Patent Document 3] Japanese Patent Publication No. 2024-104666 [Patent Document 4] Patent No. 3449917 [Overview of the initiative] [Problems that the invention aims to solve]

[0006] However, when measuring groove shape using the shape measuring machine described above, if the groove side surface (groove wall surface) is close to a mirror finish, if the measurement conditions are inappropriate, or if there is an obstacle between the shape measuring machine and the groove, it becomes impossible to accurately measure the groove shape, resulting in measurement errors. When measuring the root gap based on the measurement shape obtained by the shape measuring machine and adjusting the welding conditions according to the measurement results, if welding is performed with a root gap measurement error, welding defects will occur, requiring complicated repair work. Therefore, a method for appropriately detecting measurement errors in root gap measurement is required.

[0007] This invention has been made in view of the above problems, and aims to appropriately detect measurement anomalies in the measurement of the root gap. [Means for solving the problem]

[0008] One aspect of the present invention is a root gap measuring device for measuring the root gap of a groove provided between base materials, comprising: a shape measuring machine that acquires a measurement shape showing the cross-sectional shape of the groove using a predetermined light source; a reference position identification unit that identifies a reference position in the width direction of the measurement shape by detecting portions of both groove sides or the ends of the both groove sides on the base material surface side of the measurement shape; a candidate range identification unit that identifies a candidate range of the root gap in the width direction of the measurement shape using a gap detection height set to a position deeper than the bottom ends of both groove sides; an abnormality determination unit that determines whether or not there is an abnormality in the candidate range by comparing the candidate range with the reference position; and a root gap acquisition unit that acquires the candidate range as the root gap range when there is no abnormality in the candidate range, and detects a measurement abnormality in the root gap when there is an abnormality in the candidate range.

[0009] Aspect 2 of the present invention is a root gap measuring device according to aspect 1, wherein the reference position identification unit identifies the position in the width direction of any of the following as the reference position: a point at a predetermined position between the ends on the base material surface side of both groove sides in the measurement shape, a point at a predetermined position between positions of the same height on both groove sides, or the intersection of lines representing both groove sides.

[0010] A third aspect of the present invention is a root gap measuring device according to aspect 1 (or aspect 1 or 2), wherein the reference position identification unit determines whether or not there is an abnormality in the reference position by comparing a point at a predetermined position between the ends on the base material surface side of both groove sides in the measurement shape, a point at a predetermined position between positions of the same height on both groove sides, or the intersection of lines indicating both groove sides, with respect to the position in the width direction.

[0011] Aspect 4 of the present invention is a welding apparatus for welding a groove provided between base materials, comprising: a welding torch for welding a groove extending in a predetermined welding direction; a moving mechanism for moving the welding torch relative to the base material on which the groove is provided in the welding direction; a root gap measuring device of any one of aspects 1 to 3, which measures the root gap of the groove at each position of the groove in the welding direction using a shape measuring machine positioned in front of the welding torch in the welding direction; and a control unit that adjusts the welding conditions of the welding torch for each position according to the measurement results from the root gap measuring device.

[0012] Aspect 5 of the present invention is a welding apparatus according to aspect 4, wherein the control unit stops welding by the welding torch when the root gap measuring device detects an abnormality in the root gap measurement at a predetermined number of positions in the groove in the welding direction.

[0013] Aspect 6 of the present invention is a welding apparatus according to aspect 4 (or aspect 4 or 5), wherein when the root gap measuring device detects an abnormality in the root gap measurement at a position in the groove in the welding direction, the control unit adjusts the welding conditions based on the measurement results for positions immediately before and / or immediately after the position.

[0014] Aspect 7 of the present invention is a root gap measurement method for measuring the root gap of a groove provided between base materials, comprising: a) acquiring a measurement shape showing the cross-sectional shape of the groove using a shape measuring machine that utilizes a predetermined light source; b) identifying a reference position in the width direction of the measurement shape by detecting portions of both groove sides or the ends of the both groove sides on the base material surface side in the measurement shape; c) identifying a candidate range of the root gap in the width direction of the measurement shape using a gap detection height set to a position deeper than the bottom ends of the both groove sides; d) determining whether or not there is an abnormality in the candidate range by comparing the candidate range with the reference position; and e) acquiring the candidate range as the root gap range if there is no abnormality in the candidate range, and detecting a measurement abnormality in the root gap if there is an abnormality in the candidate range.

[0015] Aspect 8 of the present invention is a welding method for welding grooves provided between base materials, comprising: f) moving a welding torch relative to a base material having a groove extending in a predetermined welding direction in the welding direction; g) measuring the root gap at each position of the groove in the welding direction by performing the root gap measurement method of Aspect 7 at each position of the groove in the welding direction using a shape measuring machine positioned in front of the welding torch in the welding direction; and h) performing welding with the welding torch at each position while adjusting the welding conditions of the welding torch according to the measurement results of the root gap in step g). [Effects of the Invention]

[0016] According to the present invention, measurement abnormalities can be appropriately detected when measuring the root gap. [Brief explanation of the drawing]

[0017] [Figure 1] This is a front view of the welding apparatus. [Figure 2] This is a cross-sectional view of the bevel. [Figure 3]It is a block diagram showing the functional configuration of the control unit. [Figure 4A] It is a diagram showing the welding process. [Figure 4B] It is a diagram showing the welding process. [Figure 5A] It is a diagram showing an example of the measured shape. [Figure 5B] It is a diagram showing another example of the measured shape. [Figure 6] It is a diagram showing another example of the measured shape. [Figure 7] It is a cross-sectional view of the groove. [Figure 8] It is a diagram showing another example of the welding apparatus. [Figure 9] It is a diagram showing another example of the welding apparatus.

Embodiments for Carrying Out the Invention

[0018] FIG. 1 is a front view of a welding apparatus 1 according to an embodiment of the present invention. The welding apparatus 1 is an apparatus (automatic welding apparatus) that automatically performs welding on a groove 93 provided between base materials 91 and 92. In FIG. 1, three mutually perpendicular directions are indicated by arrows as the X direction, the Y direction, and the Z direction (the same applies to FIG. 2 and the like described later). In the example of FIG. 1, the X direction and the Y direction are substantially horizontal directions, and the Z direction is a substantially vertical direction. In the following description, terms such as "upper side" and "lower side" are used in accordance with the vertical direction of FIG. 1, but the vertical direction in this specification is for convenience and is not limited to the vertical direction.

[0019] FIG. 2 is a cross-sectional view of the groove 93 and shows a cross-section in a plane perpendicular to the welding direction described later. As shown in FIG. 2, the groove 93 is a groove-shaped depression provided between the base materials 91 and 92. In the present embodiment, the base materials 91 and 92 are flat plates substantially perpendicular to the Z direction and are arranged in the X direction. The groove 93 extends, for example, substantially parallel to the Y direction and in a substantially straight line. The groove 93 does not necessarily have to be straight and may extend while curving. In the following description, the direction in which the groove 93 extends is also referred to as the "welding direction".

[0020] In the example shown in Figure 2, the cross-sectional shape of the groove 93 is V-shaped. The width of the groove 93 (width in the X direction in Figure 2) gradually decreases inward from the (+Z) oriented surfaces 911 and 921 of the base materials 91 and 92 (hereinafter also referred to as "base material surfaces 911 and 921"). More specifically, each side surface 931 and 932 within the groove 93 (hereinafter referred to as "groove side surfaces 931 and 932") is inclined along the welding direction and inclined with respect to the YZ plane, and the distance between the two groove side surfaces 931 and 932 gradually decreases as it moves away from the base material surfaces 911 and 921. Groove side surface 931 is part or all of the end face of the base material 91, and groove side surface 932 is part or all of the end face of the base material 92.

[0021] In the cross-sections of the base materials 91 and 92 perpendicular to the welding direction, the angle between the groove side surface 931 and the base material surface 911 is obtuse, and the angle between the groove side surface 932 and the base material surface 921 is similar. In the following explanation, the corners 961 and 962 formed by the groove side surfaces 931 and 932 and the base material surfaces 911 and 921 are referred to as the upper ends 961 and 962 of the groove side surfaces 931 and 932. The upper end 961 of the groove side surface 931 on the (-X) side is the boundary with the base material surface 911 of the base material 91 on the (-X) side. The upper end 962 of the groove side surface 932 on the (+X) side is the boundary with the base material surface 921 of the base material 92 on the (+X) side. In the example in Figure 2, the vertical (Z-direction) positions of the upper ends 961 and 962 of both groove side surfaces 931 and 932 are approximately the same.

[0022] A root gap 94 (root spacing) is provided between the base materials 91 and 92 on the bottom side ((-Z) side) of the groove 93. In Figure 2, the root gap is indicated by an arrow labeled 94. Typically, the root gap 94 is the smallest gap between the base materials 91 and 92. In the example in Figure 2, the root gap 94 is the gap between the ends 971 and 972 (hereinafter referred to as "lower ends 971 and 972") of both groove sides 931 and 932 that are opposite to the base material surfaces 911 and 921. In the example in Figure 2, the vertical positions of the lower ends 971 and 972 of both groove sides 931 and 932 are approximately the same. The root gap 94 may also be formed between mutually parallel surfaces (root surfaces) of the base materials 91 and 92 (see Figure 7 below).

[0023] The welding apparatus 1 in Figure 1 performs welding on the groove 93 between the base materials 91 and 92, moving from right to left in Figure 1 (i.e., from the (-Y) side to the (+Y) side). The welding apparatus 1 may perform either multi-layer welding, which involves repeating welding multiple times over approximately the entire length of the groove 93, or single-layer welding, which involves performing the welding only once. By welding the groove 93, the base materials 91 and 92 are joined together.

[0024] The welding apparatus 1 comprises a welding torch 21, a wire guide unit 22, a welding power supply 23, a wire supply unit 24, a shape measuring machine 3, a position adjustment unit 4, a moving mechanism 5, and a control unit 8. The welding torch 21 and the wire guide unit 22 are supported by a support plate 11 above the groove 93 of the base materials 91, 92 (i.e., on the (+Z) side). In the example shown in Figure 1, the welding torch 21 extends vertically, with its lower (i.e., (-Z) side) tip positioned near the groove 93. The wire guide unit 22 is supplied with filler wire from the wire supply unit 24. The wire supply unit 24 is provided on a support arm 12, which will be described later. The wire is guided below the tip of the welding torch 21 via the wire guide unit 22.

[0025] The welding torch 21 and the base materials 91 and 92 are electrically connected to the welding power supply 23. The welding power supply 23 is mounted on a trolley 51, which will be described later. The welding power supply 23 supplies power to the welding torch 21, and welding is performed near the tip of the welding torch 21. As will be described later, the support plate 11 moves in the welding direction (Y direction) by the moving mechanism 5, so that welding is performed by the welding torch 21 over almost the entire length of the groove 93. Depending on the design of the welding torch 21, the wire may be supplied into the welding torch 21.

[0026] The shape measuring device 3 is positioned in front of the welding torch 21 in the welding direction (i.e., on the (+Y) side). The front in the welding direction is the direction in which the welding torch 21 moves when welding is performed on the groove 93. In the example shown in Figure 1, the shape measuring device 3 is supported by a support plate 11 above the groove 93 of the base materials 91 and 92. The position of the shape measuring device 3 is fixed relative to the welding torch 21. The shape measuring device 3 measures the shape of the cross section of the groove 93 perpendicular to the welding direction (i.e., the cross section parallel to the XZ plane). The shape measuring device 3 is moved in the welding direction together with the welding torch 21 by the moving mechanism 5, and measures the cross-sectional shape of the groove 93 at each position in the welding direction. The cross-sectional shape of the groove 93 also includes the cross-sectional shape of the parts of the base materials 91 and 92 near the groove 93. The cross-sectional shape of the groove 93 obtained by the shape measuring device 3 is hereinafter referred to as the "measured shape".

[0027] An example of the shape measuring machine 3 is equipped with an optical sectioning sensor. The optical sectioning sensor irradiates the surface of the base materials 91 and 92 with a band-shaped laser beam extending in the X direction, and receives the reflected light diffusely reflected from the surface with an image sensor to acquire the cross-sectional shape of the groove 93. In the shape measuring machine 3, the cross-sectional shape of the groove 93 is acquired as a set of multiple points corresponding to multiple measurement positions arranged in the X direction. These multiple measurement positions are, for example, arranged at approximately equal intervals with respect to the X direction. As previously described, the X direction is the direction corresponding to the width of the groove 93, and will hereinafter also be referred to as the "width direction". The shape measuring machine 3 may be a measuring machine other than the optical sectioning type, as long as it can measure the cross-sectional shape of the groove 93. For example, a laser displacement meter that measures the distance in the Z direction to the surface of the base materials 91 and 92 at multiple measurement positions arranged in the X direction may be used as the shape measuring machine 3. Alternatively, the shape measuring machine 3 may irradiate the surface of the base materials 91 and 92 with a band-shaped light such as white light. In other words, the shape measuring machine 3 only needs to acquire the measured shape of the groove 93 using a predetermined light source, such as a laser light source or a white light source.

[0028] The position adjustment unit 4 is, for example, a two-axis slider having a ball screw mechanism and an electric motor, and is capable of moving the support plate 11 in the width direction and the vertical direction (X direction and Z direction). In the welding apparatus 1, the positions of the welding torch 21 and the shape measuring machine 3 in the width direction and the vertical direction can be adjusted integrally by the position adjustment unit 4. A drive mechanism such as a linear motor may be used in the position adjustment unit 4.

[0029] The moving mechanism 5 comprises a trolley 51 and a rail 52. The rail 52 extends substantially parallel to the Y direction. The trolley 51 is self-propelled, equipped with an electric motor or the like, and moves along the rail 52 in the Y direction. A support arm 12 is attached to the trolley 51. The support arm 12 supports the position adjustment unit 4 at a position offset in the (-X) direction relative to the rail 52. As the trolley 51 moves in the Y direction, the position adjustment unit 4 and the support plate 11 move together with the trolley 51 in the Y direction. As a result, the welding torch 21 and the shape measuring machine 3 move in the welding direction relative to the base materials 91 and 92. The structure of the moving mechanism 5 is not limited to the above example and can be modified in various ways. The welding apparatus 1 may be provided with a moving mechanism that moves the members supporting the base materials 91 and 92 in the welding direction.

[0030] Figure 3 is a block diagram showing the functional configuration of the control unit 8, and other components of the welding apparatus 1 are also shown as blocks. The control unit 8 comprises a calculation unit 81 and a control unit 82. The calculation unit 81 comprises a storage unit 810, a reference position identification unit 811, a candidate range identification unit 812, an abnormality determination unit 813, and a root gap acquisition unit 814. The storage unit 810 stores the measured shape acquired by the shape measuring machine 3. The reference position identification unit 811 identifies the reference position described later in the measured shape. The candidate range identification unit 812 identifies the candidate range of the root gap 94. The abnormality determination unit 813 compares the candidate range with the reference position to determine whether there is an abnormality in the candidate range. The root gap acquisition unit 814 acquires the candidate range as the range of the root gap 94 if there is no abnormality in the candidate range, and detects a measurement abnormality of the root gap 94 if there is an abnormality in the candidate range. In the welding process described later, a root gap measuring device 10 is realized, which measures the root gap 94 of the groove 93 using a shape measuring machine 3 and a calculation unit 81, which are enclosed by dashed lines in Figure 3.

[0031] The control unit 82 controls the welding power supply 23, wire supply unit 24, position adjustment unit 4, and moving mechanism 5, etc., according to the measurement results from the root gap measuring device 10. The control unit 82 is also responsible for the overall control of the welding apparatus 1. The control unit 8 is implemented by, for example, a computer having a CPU and memory, or a programmable logic controller (PLC). All or part of the functions of the control unit 8 may be implemented by a dedicated electrical circuit. In Figure 1, the control unit 8 is mounted on the trolley 51, but all or part of the control unit 8 may be mounted in a location different from the configuration shown in Figure 1.

[0032] Next, the welding process using welding apparatus 1 will be explained with reference to Figures 4A and 4B. When welding the base materials 91 and 92 is performed using welding apparatus 1 in Figure 1, first, the welding torch 21 and shape measuring machine 3 are moved in the Y direction by the moving mechanism 5, and the shape measuring machine 3 is positioned above the (-Y) end (i.e., the starting end) of the groove 93. Subsequently, the movement of the welding torch 21 and shape measuring machine 3 in the (+Y) direction is started (step S11). As the shape measuring machine 3 moves in the (+Y) direction by the moving mechanism 5, it acquires a measurement shape that shows the cross-sectional shape of the groove 93 at each position in the Y direction (i.e., the welding direction) (step S12). Steps S12 in Figures 4A and 4B, and the following step S22, show processing that focuses on one position in the welding direction of the groove 93 (hereinafter referred to as the "position of interest"). In reality, all or part of the processing in steps S12 to S22 is performed in parallel with each other for multiple positions of the groove 93.

[0033] When the shape measuring machine 3 reaches above the point of interest, the shape measuring machine 3 acquires a measurement shape that shows the cross-sectional shape of the groove 93 at the point of interest. Figure 5A is a diagram showing an example of the measurement shape, and Figure 5B is a diagram showing another example of the measurement shape. As shown in Figures 5A and 5B, the shape measuring machine 3 acquires the approximately V-shaped measurement shape of the groove 93 as a set of multiple points 90 (hereinafter referred to as "point set 90") that are spaced approximately at regular intervals in the width direction (X direction). The point set 90 acquired by the shape measuring machine 3 is output from the shape measuring machine 3 to the storage unit 810 (see Figure 3) and stored in the storage unit 810.

[0034] As explained with reference to Figure 2, the cross-sectional shape of the groove 93 has inflection points at the upper end 961 and lower end 971 of the groove side surface 931 on the (-X) side, and at the upper end 962 and lower end 972 of the groove side surface 932 on the (+X) side. In the following explanation, the parts indicating the groove sides 931 and 932 in the measured shape acquired by the shape measuring machine 3 (see Figures 5A and 5B) will also be referred to as groove sides 931 and 932. The same applies to the upper end 961 and 962, the lower end 971 and 972, and the base material surface 911 and 921. In this processing example, the shape measuring machine 3 assigns a constant (farthest) Z coordinate sufficiently far from the shape measuring machine 3 to positions where the reflected laser light does not return, as shown in the root gap 94 in Figure 2 (see Figures 5A and 5B). The same applies when the reflected laser light does not return to the shape measuring machine 3 due to the groove surfaces 931 and 932 being mirror-like, etc.

[0035] Next, the reference position identification unit 811 detects the upper ends 961 and 962 of the groove sides 931 and 932 in the measured shape. In Figures 5A and 5B, the upper ends 961 and 962 are shown by circles larger than the points constituting the point set 90. The detection of the upper ends 961 and 962 may be performed by any method. In one method, the position of the upper ends 961 and 962 is detected based on the inclination with respect to the width direction in the shape shown by the point set 90. For example, for each point in the point set 90 in Figures 5A and 5B, the inclination with respect to the width direction of the line from that point to the next point (for example, a point adjacent to the (+X) side) (i.e., dZ / dX) is determined. Two points are extracted from the point set 90 where dZ / dX changes abruptly within a predetermined range. In this processing example, points where dZ / dX is outside that range are excluded from these two points as singular points. This prevents points that constitute the candidate for the root gap 94 described later, or points adjacent to such points, from being included in the two points. In extracting these two points, (dZ / dX) 2 The following may be used.

[0036] Of the two points, the point located on the (-X) side is identified as the upper end 961 of the groove surface 931 on the (-X) side, and the point located on the (+X) side is identified as the upper end 962 of the groove surface 932 on the (+X) side. In the following process, only the X coordinate of each point is used, so in detecting the upper ends 961 and 962, only the X coordinates of the upper ends 961 and 962 may be obtained (the same applies hereafter). The changes in the point set 90 may be smoothed by calculating a moving average of the Z coordinates of each point in the point set 90, and the above process may be performed on the smoothed point set 90. The detection of the upper ends 961 and 962 may also be performed by other methods, for example, the upper ends 961 and 962 may be detected using a learning model created in advance by machine learning.

[0037] When the upper ends 961 and 962 of both groove sides 931 and 932 are detected, for example, the X-coordinate of the midpoint C1 of the line segment connecting the two upper ends 961 and 962 is identified as the reference position in the measurement shape (step S13). The reference position is a position in the width direction that is compared with the candidate range of the root gap 94 described later, and is a reference position in the cross-sectional shape of the groove 93 indicated by the measurement shape. In this way, the reference position identification unit 811 identifies the reference position in the width direction (the X-coordinate of the midpoint C1) by detecting the upper ends 961 and 962 of both groove sides 931 and 932 in the measurement shape. In this example, the reference position is the central position of the groove 93 in the width direction, and is the position in the width direction (target position) where the welding torch 21 should be placed when welding to the position of interest. As will be described later, the reference position is not limited to the X coordinate of the midpoint C1 of the line segment between the upper ends 961 and 962, but may be a position at a predetermined ratio (for example, 1:2) on the line segment.

[0038] In the reference position identification unit 811, the reference position may be identified based on the shapes of both groove sides 931 and 932. In one example, a first approximate line is obtained by least squares or the like from a point group representing the groove side 931 on the (-X) side, that is, a predetermined number of points continuous in the (+X) direction from the upper end 961 (excluding the singularity mentioned above). Similarly, a second approximate line is obtained by least squares or the like from a point group representing the groove side 932 on the (+X) side. The X coordinate of the intersection of the two approximate lines is then identified as the reference position in the width direction. The point group used to calculate the first approximate line may be a point group included in a predetermined range in the width direction set with respect to the upper end 961 (it does not have to include the upper end 961). The same applies to the second approximate line. In another example, two points that are the same in the vertical direction (Z direction) are extracted from the first and second approximate lines representing the two groove sides 931 and 932, and the X coordinate of the point at a predetermined position on the line segment between these two points is identified as the reference position in the width direction.

[0039] As described above, the reference position identification unit 811 can identify the reference position in the width direction by detecting the portion of both groove side surfaces 931, 932 in the measurement shape, or the upper end portions 961, 962 on the base material surface 911, 921 side of both groove side surfaces 931, 932. Preferably, the reference position is identified as one of the following locations in the width direction: a point at a predetermined position between the upper end portions 961, 962 of both groove side surfaces 931, 932 in the measurement shape, a point at a predetermined position between positions of the same height on both groove side surfaces 931, 932, or the intersection of the first and second approximate lines representing both groove side surfaces 931, 932.

[0040] Once the reference position is identified, the candidate range identification unit 812 sets the gap detection height in the measurement shape. In this example, the gap detection height (shown as a dashed line H1 in Figures 5A and 5B) is set at a position a set distance D1 in the (-Z) direction from the upper end 961 of the groove side surface 931 on the (-X) side. The set distance D1 is greater than the design value of the vertical distance between the upper ends 961, 962 and the lower ends 971, 972 of the groove 93 in Figure 2. Therefore, as a general rule, the gap detection height H1 is set at a position deeper than the lower ends 971, 972 on the bottom side of the groove side surfaces 931, 932 in the measurement shape.

[0041] Of the set of points 90, each point 901 located on the (-Z) side from the gap detection height H1 is identified as a candidate point 901 indicating the root gap 94. The widthwise range between the candidate point 901 located furthest to (-X) and the candidate point 901 located furthest to (+X) is identified as the candidate range R1 of the root gap 94 (indicated by arrow R1 in Figures 5A and 5B) (step S14). The gap detection height H1 may be set based on the upper end 962 of the groove surface 932 on the (+X) side, or it may be set based on the height obtained from both upper ends 961, 962 (for example, the average height of both). Typically, the gap detection height H1 is set based on at least one of the upper ends 961, 962. If no point located on the (-Z) side from the gap detection height H1 is identified, it is determined that there is no root gap 94, and steps S15 and S16 described below are omitted.

[0042] In the abnormality determination unit 813, the candidate range R1 of the root gap 94 is compared with the reference position. For example, the X coordinate of the midpoint C2 of the candidate range R1 is identified, and the distance D2 in the width direction between the midpoint C2 and the reference position is determined. The distance D2 can be considered as the amount of deviation of the candidate range R1 with respect to the reference position. As shown in Figure 5A, if the distance D2 is relatively small and below a predetermined determination threshold, the candidate range R1 of the root gap 94 is determined to be normal (step S15). In this case, the root gap acquisition unit 814 acquires the candidate range R1 of the root gap 94 as is, as the range of the root gap 94 at the position of interest (step S16). The range of the root gap 94 is output to the control unit 82 as the measurement result by the root gap measuring device 10 at the position of interest. The range of the root gap 94 includes, for example, the position and size in the width direction, and in one example, is represented by the X coordinates of both ends of the range.

[0043] As the welding torch 21 and shape measuring machine 3 move, when the point of interest moves from below the shape measuring machine 3 to below the welding torch 21, the control unit 82 adjusts the welding conditions of the welding torch 21 according to the measurement results from the root gap measuring device 10. Therefore, welding is performed on the point of interest by the welding torch 21 with welding conditions that match the measurement results (step S17). The welding conditions of the welding torch 21 include, for example, a set target position, a set current, a set welding speed, a set wire feeding speed, or a set oscillation width. The set target position is the position in the width direction where the welding torch 21 should be positioned, and in this example, it is the reference position which is the center position of the groove 93. By controlling the position adjustment unit 4, the control unit 82 adjusts the position of the welding torch 21 in the width direction at the point of interest to match the center position of the groove 93.

[0044] The set target position may include a vertical position, in which case the set target position may be changed according to the width of the root gap 94. For example, if the width of the root gap 94 is greater than the set width which is the design value, the position adjustment unit 4 may move the welding torch 21 downward to reduce the distance between the welding torch 21 and the groove 93. Also, unlike the example in Figure 1, when the base materials 91 and 92 are aligned vertically (when performing horizontal welding, etc.), the position adjustment unit 4 may move the welding torch 21 in that vertical direction according to the width of the root gap 94 to bring the welding torch 21 closer to the base material 91 or base material 92 (upper plate or lower plate).

[0045] The welding power supply 23, wire supply unit 24, or moving mechanism 5 may be controlled to match the width of the root gap 94 at the point of interest. For example, if the width of the root gap 94 is greater than the set width, the current supplied to the welding torch 21 by the welding power supply 23 is reduced to less than the set current, and if the width of the root gap 94 is smaller than the set width, the supply current is increased to more than the set current. If the width of the root gap 94 is greater than the set width, the moving speed of the welding torch 21 by the moving mechanism 5 may be reduced to less than the set welding speed, and the wire supply speed by the wire supply unit 24 may be increased to more than the set wire feeding speed. If the width of the root gap 94 is smaller than the set width, the moving speed may be increased to more than the set welding speed, and the wire supply speed may be reduced to less than the set wire feeding speed.

[0046] Weaving (oscillating) welding may be performed in welding apparatus 1. In weaving welding, welding is performed by moving the welding torch 21 in the welding direction using the movement mechanism 5 while vibrating the welding torch 21 in the welding direction, vertical direction, or width direction using the position adjustment unit 4. If the width of the root gap 94 is greater than the set width, the oscillation width of the welding torch 21 by the position adjustment unit 4 is made greater than the set oscillation width, and if the width of the root gap 94 is smaller than the set width, the oscillation width is made smaller than the set oscillation width. In addition, the weaving pattern may be changed to match the width of the root gap 94. As described above, the welding conditions of the welding torch 21 are adjusted according to the measurement results from the root gap measuring device 10.

[0047] If the abnormality determination unit 813 determines that the candidate range R1 of the root gap 94 is normal for each position in the welding direction (Y direction) of the groove 93 (step S15), then steps S12 to S17 described above are repeated in parallel with each other for multiple positions aligned in the welding direction (step S18), and welding to the groove 93 proceeds in the welding direction.

[0048] On the other hand, in the comparison between the candidate range R1 of the root gap 94 and the reference position by the abnormality determination unit 813, as shown in Figure 5B, if the widthwise distance D2 between the midpoint C2 of the candidate range R1 and the reference position is relatively large and greater than the determination threshold, the candidate range R1 of the root gap 94 is determined to be abnormal (step S15). In this case, the root gap acquisition unit 814 detects the measurement abnormality of the root gap 94 (step S19), and a signal indicating the measurement abnormality is output to the control unit 82 as the measurement result for the position of interest by the root gap measuring device 10. Measurement abnormalities of the root gap 94 can occur due to various causes, such as the influence of secondary reflected light of the laser beam irradiated from the shape measuring machine 3, unsuitability of the measurement conditions in the shape measuring machine 3, unintended sudden operation of the welding device 1, foreign matter present between the shape measuring machine 3 and the base materials 91, 92, and foreign matter such as burrs present on the inner surface of the groove 93. Furthermore, if an abnormality in the root gap measurement is detected, a warning message may be displayed on the screen or a warning light may be illuminated to notify the operator of the detection of the abnormality in the root gap measurement.

[0049] The control unit 82 checks whether a predetermined stop condition is met. In this example, the stop condition is determined to be met if a measurement abnormality of the root gap 94 is detected at a predetermined number of positions in a continuous sequence in the welding direction in the groove 93. Here, it is assumed that the measurement abnormality of the root gap 94 has not been detected continuously, and therefore the stop condition is not met (step S20). The stop condition may be other conditions, such as when a measurement abnormality of the root gap 94 is detected at a predetermined number of positions continuously or intermittently within a set distance range. Next, the control unit 82 estimates the range of the root gap 94 with respect to the position of interest (step S21). In estimating the range of the root gap 94, the range of the root gap 94 at positions adjacent to the (-Y) side and the (+Y) side of the position of interest, that is, positions immediately before and immediately after the position of interest in the welding direction, is used.

[0050] For example, the X-coordinate of the position furthest to the (-X) side of the root gap 94 range is determined for each position immediately before and immediately after the position of interest. The arithmetic mean of these X-coordinates is then taken as the position furthest to the (-X) side of the root gap 94 range relative to the position of interest. The same applies to the position furthest to the (+X) side of the root gap 94 range. The root gap 94 range relative to the position of interest may be the same as the root gap 94 range at the position immediately before or immediately after the position of interest. Alternatively, the root gap 94 range relative to the position of interest may be determined from multiple positions, including the position immediately before or immediately after the position of interest. Thus, in the process of step S21, the root gap 94 range relative to the position of interest is estimated based on the measurement results of the root gap measuring device 10 at the positions immediately before and / or immediately after the position of interest.

[0051] When the point of interest reaches below the welding torch 21, the control unit 82 adjusts the welding conditions of the welding torch 21 to match the estimated range of the root gap 94 relative to the point of interest, and welding is performed at the point of interest (step S17). In effect, when the root gap measuring device 10 detects an abnormality in the measurement of the root gap 94 at the point of interest, the control unit 82 adjusts the welding conditions of the welding torch 21 based on the measurement results for the position immediately before and / or immediately after the point of interest.

[0052] If the stopping condition is not met during the process in step S20, steps S12 to S17 or steps S12 to S15, S19 to S21 are performed on multiple positions of the groove 93. When the welding torch 21 reaches the (+Y) side end (i.e., the terminal) of the groove 93 (step S18), the movement of the welding torch 21 and the shape measuring machine 3 by the moving mechanism 5 is stopped, and the welding process is completed (step S23). Of course, welding to the groove 93 may be repeated in the welding apparatus 1, and multi-layer welding may be performed.

[0053] On the other hand, in the process of step S20, if the control unit 82 determines that the stop condition is met (in this case, abnormal measurement of the root gap 94 is detected at a predetermined number of positions consecutive in the welding direction), the welding power supply 23 and the moving mechanism 5 are controlled, and welding to the groove 93 is emergency stopped (step S22). As a result, welding is not continued based on the abnormal measurement result (range of the root gap 94), and widespread welding defects are suppressed. In other words, welding is not continued in a state of welding defects. As a result, it is possible to reduce welding repairs (i.e., rework) in subsequent processes.

[0054] In the control unit 82, when the range of the root gap 94 is input as a measurement result for the position of interest (i.e., when the candidate range R1 of the root gap 94 is determined to be normal), the range of the root gap 94 at the position of interest may be corrected using the ranges of the root gap 94 at the positions immediately before and / or immediately after the position of interest. For example, an average range (for example, a range represented by the average of the X coordinates of the position on the (-X) side and the average of the X coordinates of the position on the (+X) side) is obtained from the ranges of the root gap 94 at multiple positions including the position of interest. Then, the welding conditions of the welding torch 21 are adjusted using this average range.

[0055] As described above, the root gap measuring device 10 comprises a shape measuring machine 3, a reference position identification unit 811, a candidate range identification unit 812, an abnormality determination unit 813, and a root gap acquisition unit 814. The shape measuring machine 3 acquires a measurement shape showing the cross-sectional shape of the groove 93 using a predetermined light source. The reference position identification unit 811 identifies the reference position in the width direction of the measurement shape by detecting the portions of both groove sides 931, 932, or the ends of both groove sides 931, 932 on the base material surface 911, 921 side (upper ends 961, 962 in the above example) in the measurement shape. The candidate range identification unit 812 identifies the candidate range R1 of the root gap 94 in the width direction of the measurement shape using a gap detection height H1 set to a position deeper than the bottom ends of both groove sides 931, 932 (lower ends 971, 972 in the above example). The abnormality determination unit 813 determines whether or not there is an abnormality in the candidate range R1 by comparing the candidate range R1 with the reference position. The root gap acquisition unit 814 acquires the candidate range R1 as the range of the root gap 94 if there is no abnormality in the candidate range R1, and detects a measurement abnormality in the root gap 94 if there is an abnormality in the candidate range R1. The root gap measuring device 10 can appropriately detect measurement abnormalities when measuring the root gap 94.

[0056] The welding apparatus 1 comprises a welding torch 21, a moving mechanism 5, the root gap measuring device 10, and a control unit 82. The welding torch 21 performs welding on a groove 93 extending in a predetermined welding direction. The moving mechanism 5 moves the welding torch 21 relative to the base materials 91 and 92 on which the groove 93 is provided, in the welding direction. The root gap measuring device 10 uses a shape measuring machine 3 positioned in front of the welding torch 21 in the welding direction to measure the root gap 94 of the groove 93 at each position of the groove 93 in the welding direction. The control unit 82 adjusts the welding conditions of the welding torch 21 according to the measurement results from the root gap measuring device 10 for each position of the groove 93. The welding apparatus 1 can appropriately perform welding on the groove 93 according to the range of the root gap 94.

[0057] Here, we will describe the processing of the comparative example for detecting abnormal root gap 94 measurements. In the comparative example's processing, if the X-coordinate of the midpoint of the candidate range R1 of the root gap 94 at the position of interest deviates by a predetermined value or more from the X-coordinate of the midpoint at the position immediately preceding the position of interest, the candidate range R1 at the position of interest is determined to be abnormal. In the comparative example's processing, if an abnormality in root gap 94 measurement occurs from the start of the welding process, welding based on the abnormal root gap 94 range may continue. In this case, welding defects will occur over a wide area of ​​the groove 93, requiring significant repairs in subsequent processes.

[0058] In contrast, in the welding apparatus 1 equipped with the root gap measuring device 10, even if a measurement abnormality of the root gap 94 occurs from the start of the welding process, the abnormality can be detected early by comparing the candidate range R1 with the reference position. This makes it possible to suppress welding defects from occurring over a wide area of ​​the groove 93 and to reduce the need for welding repairs in subsequent processes. In addition to the above processing by the root gap measuring device 10, the welding apparatus 1 may also perform the processing of the comparative example (comparison with the X coordinate of the midpoint at the immediately preceding position). Furthermore, if the width of the candidate range R1 of the root gap 94 at the position of interest falls outside a predetermined range derived from the design value, processing may be performed to determine that the candidate range R1 is abnormal.

[0059] Preferably, when the root gap measuring device 10 detects an abnormality in the measurement of the root gap 94 at a position in the welding direction of the groove 93, the control unit 82 adjusts the welding conditions based on the measurement results of the root gap 94 at the positions immediately before and / or immediately after that position. This allows for the appropriate continuation of adjustment of the welding conditions even when an abnormality in the measurement of the root gap 94 occurs, thereby suppressing the occurrence of welding defects caused by the abnormality.

[0060] Preferably, when the root gap measuring device 10 detects an abnormality in the root gap 94 at a predetermined number of positions in the groove 93 in the welding direction, the control unit 82 stops welding with the welding torch 21. This prevents welding from continuing in a defective state, allowing for early repair or reducing the need for welding repairs.

[0061] In the root gap measuring device 10 described above, the presence or absence of abnormalities in the candidate range R1 of the root gap 94 is determined based on the reference position; therefore, it is undesirable for there to be an abnormality at the reference position. Next, a method for checking for abnormalities at the reference position will be described. The following process is typically performed when identifying the reference position in step S13.

[0062] Figure 6 shows an example of the measurement shape. In this processing example, the white dots labeled 961 and 962a in Figure 6 are detected by the reference position identification unit 811 as the upper ends of both groove surfaces 931 and 932. Originally, the upper end of the groove surface 932 on the (+X) side is the point labeled 962, but due to some abnormality, point 962a is detected as the upper end. The reference position identification unit 811 identifies the X coordinate of the midpoint C3 of the line segment connecting the two upper ends 961 and 962a as the reference position. In addition, a first approximate straight line is obtained from the point group representing the groove surface 931 on the (-X) side using the least squares method, and a second approximate straight line is obtained from the point group representing the groove surface 932 on the (+X) side using the least squares method. Two points with the same vertical (Z-direction) position are extracted from the first and second approximation lines, and the X-coordinate of the midpoint C4 of the line segment between these two points is identified as the detected position.

[0063] Then, the widthwise distance D3 between the reference position and the detected position is determined, and if the distance D3 is greater than a predetermined judgment threshold, the reference position (or the position detected as the upper end) is determined to be abnormal. In this case, for example, the identification of the candidate range R1 of the root gap 94 in step S14 is omitted, and the measurement of the root gap 94 is considered abnormal, similar to when the candidate range R1 is abnormal (steps S15, S19). On the other hand, if the distance D3 is less than or equal to the judgment threshold, the reference position is determined to be normal. In this case, the reference position is used as is and compared with the candidate range R1 of the root gap 94 identified in step S14.

[0064] As previously described, the reference position is not limited to the X-coordinate of the midpoint C3 of the line segment between the upper ends 961 and 962a, but may also be the X-coordinate of a position at a predetermined ratio (e.g., 1:2) on the line segment. The same applies to the detection position. Furthermore, the X-coordinate of the intersection of the two approximate lines may be specified as the detection position. Moreover, the reference position may be the detection position, and the detection position may be the reference position.

[0065] As described above, the reference position identification unit 811 determines whether or not there is an abnormality in the reference position by comparing a predetermined point between the ends of both groove sides 931 and 932 on the base material surface 911 and 921 side in the measurement shape with a predetermined point between positions at the same height on both groove sides 931 and 932, or the intersection of the first and second approximate lines representing both groove sides 931 and 932, with respect to the position in the width direction. By determining whether or not there is an abnormality in the reference position in this way, it becomes possible to accurately detect measurement abnormalities in the root gap 94.

[0066] Various modifications are possible for the root gap measuring device 10, welding device 1, root gap measuring method, and welding method described above.

[0067] The shape of the groove 93 is not limited to V-shape; it may be X-shape, L-shape, K-shape, J-shape, U-shape, H-shape, etc. Figure 7 is a cross-sectional view of a roughly J-shaped groove 93. In the groove 93 of Figure 7, a bottom surface is provided that extends in the (-X) direction from the lower end 972 of the groove side surface 932 on the (+X) side. The (-X) side edge 973 of this bottom surface is located near the end face of the base material 91 on the (-X) side that faces the (+X) direction. On the end face of the base material 91, the position opposite to the edge 973 is the lower end 971 of the groove side surface 931 on the (-X) side. In the example of Figure 7, on the end face of the base material 91, the region from the lower end 971 of the groove side surface 931 on the (-Z) side becomes the root surface that forms the (-X) side boundary of the root gap 94. Furthermore, on the end face of the base material 92 on the (+X) side facing the (-X) direction, the region from the bottom edge 973 on the (-Z) side becomes the root surface that forms the (+X) side boundary of the root gap 94.

[0068] In the groove 93 shown in Figure 7, the midpoint between the two upper ends 961 and 962 and the midpoint of the root gap 94 are significantly misaligned in the X direction. Therefore, the amount of misalignment between the reference position, which is the X-coordinate of the midpoint between the upper ends 961 and 962 in the measured shape, and the X-coordinate of the midpoint of the candidate range of the root gap 94, is considered normal if it is sufficiently greater than 0. In the processing of the groove 93 in Figure 7 by the abnormality determination unit 813, for example, the presence or absence of an abnormality in the candidate range of the root gap 94 is determined by whether or not the amount of misalignment falls between the lower limit and upper limit values ​​derived from the design value of the groove 93. Also, in the example of Figure 7, if the reference position, which is the X-coordinate of the midpoint between the upper ends 961 and 962, falls within the candidate range of the root gap 94, the candidate range of the root gap 94 may be determined to be abnormal. The abnormality determination unit 813 may determine the presence or absence of an abnormality in the candidate range by various methods of comparing the candidate range of the root gap 94 with the reference position.

[0069] The welding apparatus 1 described above may be of various forms, for example, as shown in Figures 8 and 9, it may be a circumferential welding apparatus that performs welding on a groove 93 provided between cylindrical base materials 91 and 92 aligned in the direction of the central axis. In the welding apparatus 1 of Figure 8, the positions of the welding torch 21 and the shape measuring machine 3 are fixed, and the moving mechanism 5 includes a roller 53 that rotates the base materials 91 and 92 around the central axis J1. Due to the rotation of the base materials 91 and 92, the welding torch 21 and the shape measuring machine 3 move relative to the base materials 91 and 92 in the welding direction (circumferential direction). In the welding apparatus 1 of Figure 9, an annular rail 52 is provided inside the cylindrical base materials 91 and 92 along the inner circumferential surface of the base materials 91 and 92, and the welding torch 21 and the shape measuring machine 3 move in the welding direction along the rail 52. In the position adjustment section 4 of Figure 9, the welding torch 21 may be movable in the central axis direction, along the circumferential direction, and in the radial direction (i.e., it may move forward, backward, up, down, left, and right). In this case, the movement pattern and speed when oscillating in these directions may be changed according to the width of the root gap 94.

[0070] The above-described moving mechanism 5 is a mechanism that moves both the welding torch 21 and the shape measuring machine 3 relative to the base materials 91 and 92 in the welding direction. However, depending on the design of the welding apparatus 1, the welding torch 21 and the shape measuring machine 3 may move independently of each other relative to the base materials 91 and 92. In this case, for example, the measurement results of the root gap 94 for each position of the groove 93 may be obtained in advance by moving the shape measuring machine 3, and then the welding torch 21 may move and welding may be performed. When the welding torch 21 moves, the welding conditions of the welding torch 21 are adjusted according to the measurement results of the root gap 94 for each position of the groove 93, and welding is performed by the welding torch 21.

[0071] The configurations in the above embodiments and each modified example may be combined as appropriate, as long as they do not contradict each other. [Explanation of symbols]

[0072] 1. Welding equipment 3 Shape measuring machine 5 Moving mechanism 10. Root gap measuring device 21 Welding Torch 82 Control Unit 91,92 Base material 93 Bevel 94 Root Gap 811 Reference position identification part 812 Candidate Range Identification Unit 813 Abnormality determination section 814 Root Gap Acquisition Section 911,921 Base material surface 931,932 Bevel side view 961,962,962a Upper end 971,972 Lower end H1 Gap detection height R1 Candidate Range S11~S23 Step

Claims

1. A root gap measuring device for measuring the root gap of a groove provided between base materials, A shape measuring machine that acquires a measurement shape showing the cross-sectional shape of a groove using a predetermined light source, A reference position identification unit identifies a reference position in the width direction of the measurement shape by detecting the portion of the side surfaces of both grooves, or the end of the side surfaces of both grooves on the base material surface side, A candidate range identification unit identifies a candidate range of the root gap in the width direction in the measurement shape, using a gap detection height set to a position deeper than the bottom ends of both groove sides. An abnormality determination unit that determines whether or not there is an abnormality in the candidate range by comparing the candidate range with the reference position, A root gap acquisition unit that, when there is no abnormality in the candidate range, acquires the candidate range as the root gap range, and when there is an abnormality in the candidate range, detects an abnormality in the root gap measurement, A root gap measuring device equipped with the following features.

2. A root gap measuring device according to claim 1, A root gap measuring device in which the reference position identification unit identifies the position in the width direction of one of the following as the reference position: a point at a predetermined position between the ends on the base material surface side of both groove sides in the measurement shape, a point at a predetermined position between positions of the same height on both groove sides, or the intersection of the lines representing both groove sides.

3. A root gap measuring device according to claim 1, A root gap measuring device in which the reference position identification unit determines whether or not there is an abnormality in the reference position by comparing a point at a predetermined position between the ends on the base material surface side of both groove sides in the measurement shape, a point at a predetermined position between positions of the same height on both groove sides, or the intersection of lines representing both groove sides, with respect to the position in the width direction.

4. A welding apparatus that performs welding on grooves provided between base materials, A welding torch that performs welding on a groove extending in a predetermined welding direction, A moving mechanism that moves the welding torch relative to the base material having the groove in the welding direction, A root gap measuring device according to any one of claims 1 to 3, wherein a shape measuring machine positioned in front of the welding torch in the welding direction is used to measure the root gap of the groove at each position of the groove in the welding direction, A control unit that adjusts the welding conditions of the welding torch according to the measurement results from the root gap measuring device for each of the aforementioned positions, A welding apparatus equipped with the following features.

5. A welding apparatus according to claim 4, A welding apparatus in which, when the root gap measuring device detects an abnormality in the root gap measurement at a predetermined number of positions in the groove in the welding direction, the control unit stops welding with the welding torch.

6. A welding apparatus according to claim 4, A welding apparatus in which, when the root gap measuring device detects an abnormality in the root gap measurement at a position in the groove in the welding direction, the control unit adjusts the welding conditions based on the measurement results for positions immediately before and / or immediately after the position.

7. A root gap measurement method for measuring the root gap of a groove between base materials, a) A step of obtaining a measurement shape showing the cross-sectional shape of the groove using a shape measuring machine that utilizes a predetermined light source, b) A step of identifying a reference position in the width direction of the measurement shape by detecting the portion of the sides of both grooves, or the end of the sides of both grooves on the base material surface side, c) A step of identifying a candidate range of the root gap in the width direction in the measurement shape using a gap detection height set to a position deeper than the bottom end of both groove sides, d) A step of determining whether or not there is an abnormality in the candidate range by comparing the candidate range with the reference position, e) If there is no abnormality in the candidate range, the candidate range is acquired as the range of the root gap, and if there is an abnormality in the candidate range, the measurement abnormality of the root gap is detected. A method for measuring the root gap, comprising the following features.

8. A welding method that performs welding to a groove provided between base materials, f) A step of moving a welding torch relative to a base material having a groove extending in a predetermined welding direction in the welding direction, g) A step of measuring the root gap at each position of the groove in the welding direction by performing the root gap measurement method described in claim 7 for each position of the groove in the welding direction, using a shape measuring machine positioned in front of the welding torch in the welding direction, h) A step of performing welding with the welding torch at each of the above positions, while adjusting the welding conditions of the welding torch in accordance with the measurement results of the root gap in step g), A welding method comprising the following features.

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