JP4705479B2 - Bead shape detection method and apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for detecting a bead shape in a weld bead.

  For example, the UO steel pipe is one of welded steel pipes and is manufactured as shown in FIG. After cutting the end in the width direction of the thick steel plate that will be the groove in the subsequent welding process, the end is bent with the C press, bent into the U shape with the U press, and then the end with the O press. After the butting, welding is performed in the order of tack welding, inner surface welding, and outer surface welding, and finally formed into a round pipe through a pipe expanding process of expanding the steel pipe from the inside of the steel pipe.

  The rise of a welded portion such as a UO steel pipe is called a weld bead (hereinafter referred to as “bead”) or extra build. The width and height of the bead and the way the bead rises around the bead periphery are related to the strength of the weld, and it is important for quality control of the UO steel pipe to quantitatively grasp the bead shape in each process.

  Traditionally, bead shape measurement has been performed manually using instruments and special jigs. FIG. 13 shows a peaking measurement method using a dial gauge. Using a jig with a dial gauge needle centered on a leg with a constant width of 2 W, the depth with respect to the straight line connecting the jig leg as the reference line with the dial gauge needle applied to the toe is peaking measure.

  However, manual methods such as peaking measurement using a dial gauge are time-consuming and time-consuming, so the measurement location is limited and intermittent measurement, and it is easy to overlook subtle shape changes in the tube axis direction. Alternatively, there is a problem that even if the individual differences among the inspectors and the inspectors are the same, the measurement results have no variation reproducibility because they are largely dependent on the inspector's subjectivity at the time of work.

  For this reason, various methods and apparatuses for automatically detecting the bead shape have been proposed. Among them, the optical method is useful in that measurement can be performed without contact. In the method disclosed in Patent Document 1, a weld bead is imaged from the top and side surfaces, an analog signal is converted into a digital signal representing the shade of the image, and then digital image processing such as differentiation processing for one line of the shade image. Thus, the point where the shading of the image changes abruptly is used as the boundary (toe end) between the bead portion and the base material portion, and no light source is required and only camera imaging is used, so that the apparatus configuration is simple.

  However, because it assumes the difference in brightness between the bead part and the base material part, or the difference in brightness due to shadows or foreign matter adhering to the boundary, etc., the surface of the bead part or base material part has nothing to do with the original shape. There was a possibility that the bead could not be detected due to the difference in properties.

  On the other hand, as a method of capturing a light source image irradiated on the part to be inspected and measuring the cross-sectional profile of the steel pipe from the pixel position of the captured light source image, an optical cutting method or a laser distance meter as shown in Patent Document 2 is used. A method is mentioned. If the light source image irradiated on the part to be inspected is bright enough to be reflected on the imaging unit, the cross-sectional shape itself can be measured with high accuracy.

  When detecting a bead part from the cross-sectional profile of a steel pipe measured by a light cutting method or a laser distance meter, it is assumed that there is a sudden change in the profile at the toe, which is the boundary between the bead part and the surrounding base metal part. It is conceivable to detect the toe portion by differentiating the profile. However, in the case of UO steel pipes, especially for pipes with large outer diameters or pipes that have not been expanded, it is difficult to distinguish the toe portion because the rise of the bead with respect to the surrounding base metal part is small. The surrounding area may be mistaken for the toe. In addition, if a long digital filter for differentiation is set in consideration of the influence of foreign matter, there is a problem in that the toe is detected inside the bead from the actual position.

JP-A-60-135705 Japanese Patent Laid-Open No. 2-1510

  The present invention was invented to solve the above-described problems of the prior art, and optical means such as an optical cutting method and a laser distance meter even when the bead rises gently and the bead height is low. An object of the present invention is to detect the bead shape with higher accuracy than the conventional one from the cross-sectional profile of the steel pipe obtained in the above.

In the bead shape detection method according to the present invention, the beam on the surface of the object to be inspected is scanned by irradiating the welded part with linear light or spot light so as to cross the welded part of the object to be inspected. wherein by an optical method based on the locus to obtain a cross-sectional profile of the object to be inspected, a bead shape detecting method for detecting the bead shape from the cross section profile, from the cross-sectional profile, by approximating the the cross section profile arc The center of curvature of the arc and the radius of curvature R are obtained, and a peak search is performed for a point where the value RD obtained by subtracting the distance D connecting the center of curvature and each point of the cross section of the inspection object from the radius of curvature R is maximum. calculating the coordinates of the bead apex of the provisional Te, the range of the first predetermined width including the beads apex of the temporary, a step of approximating a circular arc which is a first function which defines the cross-sectional profile in advance, in front A second function that predetermines the cross-sectional profile at a second predetermined width outside with a position separated by a predetermined distance from the temporary bead vertex as a starting point, and the left and right sides of the temporary bead vertex. , A step of calculating an intersection point of the first function and the second function as a toe point of the bead, a coordinate of the toe point, the first function, and the second function And a step of calculating a bead shape on the basis thereof.
The bead shape detection device according to the present invention scans the welded portion by irradiating the welded portion with linear light or spot light so as to cross the welded portion of the subject to be inspected. wherein the optical technique based on the locus to obtain a cross-sectional profile of the object to be inspected, a bead shape detection device for detecting the bead shape from the cross section profile, from the cross-sectional profile, by approximating the the cross section profile arc The center of curvature of the arc and the radius of curvature R are obtained, and a peak search is performed for a point where the value RD obtained by subtracting the distance D connecting the center of curvature and each point of the cross section of the inspection object from the radius of curvature R is maximum. means for calculating the coordinates of the bead apex of the provisional Te, the range of the first predetermined width including the beads apex of the temporary, means for approximating a circular arc which is a first function which defines the cross-sectional profile in advance, The temporary bead A second function that predetermines the cross-sectional profile in a second predetermined width outside starting from a position separated by a predetermined distance with respect to the point, for each of the left and right sides of the temporary bead vertex Based on the means for approximating, the means for calculating the intersection of the first function and the second function as the toe point of the bead, the coordinates of the toe point, the first function and the second function, And a means for calculating a bead shape.

  According to the present invention, it is possible to automatically measure a gentle bead shape, which has been difficult until now. And, for example, in welded steel pipes, it is possible to measure subtle changes in the shape of the pipe axis, which are often overlooked by manual measurement, and reflect this in the manufacturing and quality control of the bead shape in each manufacturing process. Quality assurance over the entire length can be realized.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a schematic view showing a configuration of a first embodiment of a bead shape detection device according to the present invention, taking a welded steel pipe as an example. Reference numeral 1 denotes a welded steel pipe to be measured (only a part is shown). Further, 2 is a light projecting means such as a laser light source, 5 is an image capturing means such as a camera, and 6 is a signal processing control device. The light projecting means 2 and the image capturing means 5 are placed inside the welded steel pipe 1 and the bead 10 on the inner surface. The state in the case of detecting the shape of is shown. The signal processing control device functions as each means in the present invention.

  In the present embodiment, the shape of the welded steel pipe to be measured is measured on a horizontal measurement table so that the bead is at the bottom. On the measurement table, the direction orthogonal to the bead direction, that is, the direction crossing the bead is defined as the x-axis, and the direction orthogonal to the measurement table is defined as the y-axis. In addition, when the bead is not the bottom at the time of measurement, it is clear that it can be handled as a reference plane (horizontal plane) assuming a tangential plane of the bead.

  As the light projecting means 1, for example, a linear light source that converges light emitted from a laser or a lamp linearly at an irradiation position on a measurement object using a cylindrical lens, a prism, or the like, or a point at the irradiation position is used. A scanning point light source is used that scans a point beam that converges in a line shape in the width direction of the bead with a polygon mirror that is rotationally controlled. When a linear light source is used as the light projecting means, reference numeral 4 in FIG. 1 shows a fan-shaped linear beam. When the welded steel pipe 1 including a bead to be measured is irradiated, a light cut image is taken along the surface shape. 3 is formed. When a scanning point light source is used as the light projecting means, 4 in FIG. 1 indicates a locus of a point beam scanned in the width direction, and 3 indicates a locus of a point image at an irradiation position on the welded steel pipe 1. Irradiation is performed so that the linear trajectory of the irradiation light traverses the bead, but it is desirable in terms of measurement accuracy to be in a plane orthogonal to the direction of the bead.

  For example, a CCD camera is used as the imaging unit 5 to capture the trajectory of the light section image or the point image. In the signal processing control device 6, the trajectory of the light section image or the point image captured from the image capturing means 5 is taken, and thinning processing or the like is performed by the image processing means to obtain the pixel position where the image appears. Then, the contour shape of the steel pipe surface including the bead is obtained as a cross-sectional profile from the constant determined by the optical arrangement of the light projecting means 2, the imaging means 5, and the measurement object and the pixel position where the image appears.

  The signal processing control device 6 controls the irradiation time of the light projecting means 1, the exposure time of the imaging means 5, etc., in addition to the calculation of image capturing from the imaging means 5, image processing, and bead shape detection described later. .

  FIG. 2 is a schematic view showing the configuration of the second embodiment of the bead shape detection apparatus according to the present invention by taking a welded steel pipe as an example. 2 ′ in FIG. 2 is a distance measuring means such as a laser distance meter in which a scanning point light source and a PSD (position detector) are integrated, and the welded steel pipe 1 to be measured by the triangulation method from the distance measuring means itself. You can directly measure the distance to the surface. In FIG. 2, 4 indicates a locus of a point beam emitted from a scanning point light source of the distance measuring means 5 ′ scanned in the width direction of the bead, and 3 indicates a locus of a point image at an irradiation position on the welded steel pipe 1. . Since the distance to the surface of the welded steel pipe 1 has already been calculated by the distance measuring means 5 ′, the signal processing control device 6 does not require image processing for calculating the cross-sectional profile. That is, in the case of the present embodiment, the signal processing control device 6 takes in the distance data from the distance measuring means 5 ′, calculates the cross-sectional profile based on the distance data, the calculation for the bead shape detection described later, and the distance measuring means 5 Control '.

  Below, the calculation procedure and calculation method which detect a bead shape from the cross-sectional profile of the welded steel pipe 1 are demonstrated. The horizontal axis (x axis) in FIG. 3A indicates the measurement position in the bead width direction, and is also referred to as the horizontal direction. Further, the vertical axis (y-axis) indicates irregularities. ○ schematically represents the measurement points of the cross-sectional profile obtained as discrete data, and the solid line represents an approximate function of the cross-sectional profile obtained from the discrete data.

  FIG. 3B shows a calculation procedure for detecting the bead shape from the cross-sectional profile of the welded steel pipe 1. As shown in FIG. 1, 10 is a bead portion, 11 is a toe portion, and 12 is a bead peripheral portion. First, temporary bead vertices are obtained by searching for local maximum points, which will be described later, for discrete data representing a cross-sectional profile (step S101). Next, the bead portion of the range WC narrower than the bead width is approximated by the first function with the temporary bead apex as a reference (step S102). The peripheral portions of the bead outer range WL (left side) and WR (right side) are approximated by the second function with reference to the temporary bead vertex (step S103). An intersection point of the first function and the second function is obtained as a stop point (step S104). A bead shape such as a bead width, a bead height, a toe angle, peaking, and an offset is calculated from the toe point coordinates, the first function, and the second approximate function (step S105). FIG. 15 illustrates these parameters representing the bead shape. The peaking is precisely the shape near the bead, but is included in one of the bead shapes for simplicity.

  The temporary bead vertex searching method in step S101 will be described. As shown in FIG. 4A, when a point at the center of the window is larger than any data in the search window with respect to the cross-sectional profile data in the search window having a constant width, this point is set as a maximum point and The height of the maximum point with respect to the surrounding points is also obtained at the same time. While moving the search window in the width direction, several local maximum points that are candidates for temporary bead vertices are obtained. Among the maximum points, a point having the maximum height of the maximum point with respect to surrounding points in the window is set as a temporary bead vertex. When a plurality of temporary bead vertex candidates are found near the top of the bead and are flattened, the center of gravity of the positions in the horizontal direction is set as the temporary bead vertex.

  As shown in FIG. 4B, when the beads are arranged obliquely, the maximum value in the vertical direction may not be found. In this case, first, the cross-sectional profile of the steel pipe is approximated to an arc by the least square method to obtain the center of curvature and the radius of curvature R, and the value RD obtained by subtracting the distance D connecting the center of curvature of the steel pipe and each point of the cross section of the steel pipe is obtained. As shown in FIG. Next, a peak search is performed for a point where the radial deviation RD is maximized to find a temporary bead apex. The method of approximating the arc by the least square method is the same as the calculation method appearing in the arc approximation method of the bead portion described below.

An approximation method using the first function and the second function performed in steps S102 and S103 will be described. The x-axis and y-axis are the steel pipe width direction and height direction, respectively, and the coordinates of the discrete data representing the cross-sectional profile are (x _i , y _i ). According to the least squares method, assuming a n-th order polynomial as in the form for example the following approximation function f (x), the coefficient to minimize the squared residuals E of the following formula _{(1) [a m] (} m = 0, 1,..., N), an approximate function can be obtained by solving the simultaneous equations of the following expression (2).

  When an arc is assumed as the approximate function, the approximate function can be obtained by solving the simultaneous equations of the following expression (4) regarding the coefficient [a, b, c] that minimizes the square residual E of the following expression (3).

  The first approximate function and the second approximate function determine the order in consideration of the cross-sectional profiles of the bead portion and the peripheral portion. A simple method using an arc and a straight line (first order polynomial) or a parabola (second order polynomial) as the first approximation function and the second approximation function will be described later. In addition, since the average bead size and the peripheral curvature vary depending on the type of steel pipe (outer diameter, thickness, and material), the data range WC (bead portion) that approximates the least squares using the first function and the second function. ), WL (bead left side), and WR (bead right side) are set for each type of steel pipe while accumulating the bead-shaped result data.

  The intersection of the first function f (x) and the second function g (x) in step S104 is obtained by solving f (x) = g (x). Depending on the order, an algebraic solution or a numerical solution such as Newton's method is used. Solve the equations for the left and right sides to find the coordinates of the toes.

  A method for calculating a bead shape such as a bead width, a bead height, a toe angle, peaking, and an offset from the toe point coordinates, the first approximate function, and the second approximate function in step S105 will be described.

As shown in FIG. 5 and the following equation (5), the bead width is determined by the left and right toe point coordinates (x _L , y _L ) and (x _R , y _R ) that are the intersections of the first function and the second function. Calculate as the distance between.

  The bead height h is a point giving the maximum value among the distances from the straight line ax + by + c = 0 connecting the left and right toe point coordinates to the point (x, y) on the first function, as shown in the following formula (6). I.e., the distance to the true bead apex.

  Since the slope of the tangent line on the true bead apex is equal to the slope of the straight line connecting the left and right toe point coordinates, the coordinates can be calculated by solving the following equation (7).

FIG. 6 shows a method for calculating the toe angle. The left toe angle θ _L is the tangent slope angle α _L of the first function f (x) and the tangent slope angle β of the second function g _L (x) at the left toe point as shown in the following equation (8). _Calculated from _L.

The right toe angle θ _R is the tangent slope angle α _R of the first function f (x) and the tangent slope angle β of the second function g _R (x) at the right toe point as shown in the following equation (9). _Calculated from _R.

FIG. 7A shows an offset calculation method. The intersection of the normal at the true bead vertex on the first function and the tangent of the second function at the left toe is O _L, and the intersection of the second function tangent at the right toe is O _R , it obtains the offset as the length of the line segment O _L O _R. Since the slope of the normal line at the true bead vertex on the first function is close to 90 °, as shown in FIG. 7B, the vertical line dropped from the true or temporary bead vertex and the second at the left toe point. the intersection between the tangent line of the function and O _L, the intersection of the tangent line of the second function in the right stop end point as O _R, may be determined offset as the length of the line segment O _L O _R.

FIG. 8 shows an approximate peaking calculation method. The left and right points on the cross-sectional profile at a distance in the width direction W around the toe point are A and B, and the midpoint of the straight line AB is C. The distance from the middle point C to the toe point is obtained as an approximate peaking Δy ₀ . When the straight line AB is inclined with respect to the horizontal line (x axis) at an angle α, Δy may be calculated by the following equation (10) as approximate peaking.

(Example)
A case where an arc is used as the first approximation function and a straight line is used as the second approximation function will be specifically described including the actual approximation result. The coordinates of the toe point can be easily obtained as a solution of the quadratic equation as a result of solving the equation of the arc and the line with respect to (x, y) as shown in the following equation (11).

  FIG. 9 shows a method for calculating the bead height. After obtaining the distance d from the center of curvature of the arc approximating the bead portion to the midpoint of the left and right toe points, the bead height h can be calculated by subtracting the distance d from the radius of curvature r of the arc and h = rd.

FIG. 10 shows a method for calculating the toe angle. Since the inclination angles α _L and α _R of the arc tangent at the toe point are equal to the angle formed by the straight line connecting the toe point and the center of curvature of the arc (x ₀ , y ₀ ) with the vertical direction, the following equation (12) is used. Can be calculated.

  FIG. 11 shows the result of approximating the cross-sectional profile of the UO steel pipe with an arc and a straight line, and FIG. 12 shows the measurement results of the bead height, toe angle and peaking calculated by the above method.

  Next, the case where an arc is used as the first approximation function and a parabola (second-order polynomial) is used as the second approximation function will be specifically described including the actual approximation results. Since the coordinates of the toe point may be solved by combining the arc and straight line equations with respect to (x, y) as in the following equation (13), it can be relatively easily obtained as a solution of the quaternary equation. .

  Quaternary equations can be solved by numerical methods such as Newton's method, but they can also be solved using the Ferrari and Euler solution formulas. 16 and 17 show the results of approximating the cross-sectional profile of a UO steel pipe with an arc and a straight line or a parabola. FIGS. 16A and 16B are examples of approximation results when the outside approximate range of the bead is wide, and FIGS. 17A and 17B are examples of approximation results when the periphery of the bead outside is bent. As described above, when the approximate range outside the bead is wide, or when the bend of the peripheral portion is large, the approximation by the parabola is effective.

  According to the present method, the bead shape can be calculated easily and at high speed, so that a subtle change in the tube axis direction that cannot be captured by intermittent manual measurement can be measured at fine intervals over the entire length. By measuring the bead shape that affects the welding strength in each manufacturing process and accumulating data, it is possible to determine the control value of the bead shape that can guarantee the welding strength. Quality assurance over the entire length is possible.

It is a figure which shows the whole structure by the light cutting method using the linear light source or the point light source which is the 1st Embodiment of this invention. It is a figure which shows the whole structure at the time of using the ranging means which is the 2nd Embodiment of this invention. It is a figure for demonstrating the method and procedure of a bead shape detection and calculation in the bead shape detection method to which this invention is applied. FIG. 6 is a diagram for explaining a method for searching for bead vertices; (a) is a diagram for explaining a method for searching for bead vertices; (b) is a diagram for explaining a method for calculating a radial displacement when beads are arranged obliquely; (C) is a figure explaining the search method of a bead vertex in case a bead is arrange | positioned diagonally. It is a figure explaining the calculation method of bead width and bead height. It is a figure explaining the calculation method of a toe angle. It is a figure explaining the calculation method of offset. It is a figure explaining the calculation method of peaking. It is a figure explaining the calculation method of bead height in the case of carrying out circular arc approximation of a bead part. It is a figure explaining the calculation method of the toe angle in the case of carrying out circular arc approximation of a bead part. It is the figure which showed the calculation result at the time of approximating the bead part in the cross-sectional profile of an actual UO steel pipe with a circular arc, and the peripheral part of a bead outer side with a straight line with a cross-sectional profile. It is a figure explaining the result obtained by applying the detection and calculation method of the bead shape to which the present invention is applied to an actual UO steel pipe, (a) is a diagram showing the measurement result of the bead height, (b) Is a diagram showing the measurement results of the toe angle, and (c) is a diagram showing the measurement results of peaking. It is a figure explaining the measuring method of the peaking using the dial gauge which is a prior art. It is a figure explaining the manufacturing process of a UO steel pipe. It is a figure explaining the bead shape of a UO steel pipe, (a) is a figure showing bead width, bead height, and toe angle, and (b) is a figure showing offset. It is the figure which showed the calculation result at the time of approximating the bead part in the cross-sectional profile of an actual UO steel pipe with a circular arc, and the peripheral part of a bead outer side with a parabola with a cross-sectional profile. It is the figure which showed the calculation result at the time of approximating the bead part in the cross-sectional profile of an actual UO steel pipe with a circular arc, and the peripheral part of a bead outer side with a parabola with a cross-sectional profile.

Explanation of symbols

1: welded steel pipe 2: linear laser light source or scanning point laser light source 3: light cut image 4: locus of linear laser beam or scanning point beam 5: camera 5 ′: laser rangefinder 6: signal processing control apparatus

Claims (14)

The welded portion is irradiated with linear light or spot light so as to traverse the welded portion of the object to be inspected, and is scanned by an optical method based on the ray trajectory on the surface of the object to be inspected. A bead shape detection method for obtaining a cross-sectional profile of an object to be inspected and detecting a bead shape from the cross-sectional profile,
From the cross-sectional profile, the cross-sectional profile is approximated to an arc to obtain a center of curvature and a radius of curvature R of the arc, and a distance D connecting the center of curvature and each point of the cross section of the inspection object is subtracted from the radius of curvature R. A peak search for a point where the obtained value RD is maximized to calculate the coordinates of a temporary bead vertex;
Approximating the cross-sectional profile with an arc that is a predetermined first function in a first predetermined width range including the temporary bead vertex;
A second function that predetermines the cross-sectional profile at a second predetermined outer width starting from a position separated by a predetermined distance with respect to the temporary bead apex, and a left side of the temporary bead apex. Approximating for each of the right side;
Calculating an intersection of the first function and the second function as a toe point of the bead;
A bead shape detecting method, comprising: calculating a bead shape based on the coordinates of the toe point and the first function and the second function.   The bead shape detection method according to claim 1, wherein the optical method is a light cutting method.   The bead shape detection method according to claim 1, wherein the optical method is a triangulation method.   The bead shape detection method according to any one of claims 1 to 3, wherein the bead shape includes a bead width, a bead height, a toe angle, peaking, and an offset.   The distance between the toe points is calculated as a bead width from the coordinates of the toe points on both sides of the bead calculated as an intersection of the first function and the second function. The bead shape detection method according to claim 1.   From the straight line connecting the toe points on both sides of the bead calculated as the intersection of the first function and the second function to the point on the first function that approximates the bead portion including the temporary bead vertex. The bead shape detection method according to any one of claims 1 to 5, wherein a maximum value of the distance is calculated as a bead height.   An inclination angle between the first tangent line and the second tangent line is obtained by differentiation of the first function and the second function at the toe point calculated as an intersection of the first function and the second function, The bead shape detection method according to claim 1, wherein a toe angle is calculated based on the inclination angle.   Find the midpoint of two points on the cross-sectional profile that are equidistant in the horizontal direction on both sides of the bead around the toe point calculated as the intersection of the first function and the second function, and from the midpoint to the toe point The bead shape detection method according to claim 1, wherein a predetermined approximate peaking is calculated based on the distance. From the straight line connecting the toe points on both sides of the bead calculated as the intersection of the first function and the second function to the point on the first function that approximates the bead portion including the temporary bead vertex. The point that gives the maximum value of the distance is obtained as a true bead vertex, and the tangent line of the second function at the toe point on the left side in the horizontal direction around the bead vertex on the normal line of the first function at the true bead vertex claims intersection, and obtain the intersection between the tangent line of the second function in the horizontal direction right stop end points around a bead apex, the distance between two intersection points, and calculates as the offset between The bead shape detection method according to any one of 1 to 8. From the straight line connecting the toe points on both sides of the bead calculated as the intersection of the first function and the second function to the point on the first function that approximates the bead portion including the temporary bead vertex. The point that gives the maximum value of the distance is obtained as a true bead vertex, the perpendicular passing through the position in the width direction near the true bead vertex or the temporary bead vertex, and the toe point at the left end in the horizontal direction centering on the bead vertex. An intersection with the tangent of the second function and an intersection with the tangent of the second function at the toe point on the right in the horizontal direction with the bead vertex as the center are obtained, and the distance between the two intersections is defined as a predetermined approximate offset . bead shape detecting method according to any one of claims 1-8, characterized in that calculated. The inspection object is a welded steel pipe;
The bead shape detection method according to claim 1, wherein the bead shape is calculated using an arc as the first function and a straight line or a parabola as the second function. The inspection object is a welded steel pipe;
The center of curvature and radius of curvature are obtained by approximating the cross-sectional profile of a welded steel pipe to a circular arc by the least square method, and the peak at the point where the value obtained by subtracting the distance connecting the center of curvature of the pipe and each point of the pipe cross section from the radius of curvature is the peak. The bead shape detection method according to claim 1, wherein a temporary bead vertex is calculated by searching. Scanning by irradiating the welded part with linear light or spot light so as to cross the welded part of the object to be inspected, and applying the optical method based on the ray trajectory of the surface of the object to be inspected A bead shape detection device for obtaining a cross-sectional profile of an object to be inspected and detecting a bead shape from the cross-sectional profile,
From the cross-sectional profile, the cross-sectional profile is approximated to an arc to obtain a center of curvature and a radius of curvature R of the arc, and a distance D connecting the center of curvature and each point of the cross section of the inspection object is subtracted from the radius of curvature R. A peak search for a point where the obtained value RD becomes the maximum and calculating the coordinates of the temporary bead vertex;
Means for approximating the cross-sectional profile with an arc that is a predetermined first function within a range of a first predetermined width including the provisional bead apex;
A second function that predetermines the cross-sectional profile at a second predetermined outer width starting from a position separated by a predetermined distance with respect to the temporary bead apex, and a left side of the temporary bead apex. Means for approximating each of the right side;
Means for calculating an intersection of the first function and the second function as a toe point of the bead;
A bead shape detection device comprising: means for calculating a bead shape based on the coordinates of the toe point and the first function and the second function.   The bead shape detection device according to claim 13, wherein the object to be inspected is a welded steel pipe.

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