Thread profile measuring device and thread profile measuring method

Abstract

To provide a screw shape measurement device and the like of a pipe with a screw which can accurately specify a pipe end position of a pipe with a screw on the basis of a photographed image by means of the light projection method and accurately measure the screw shape by using the specified pipe end position.SOLUTION: A screw shape measurement device 100 comprises: an illumination unit 1; an imaging unit 2; and a calculation processing unit 3. The calculation processing unit can execute: a contour line detection method which calculates an approximation straight line L1 of a contour line formed by a tapered part of a pipe P with a screw and an approximation straight line L2 of a contour line formed by an end surface E of the pipe with a screw on the basis of the photographed image and detects an intersection point thereof as a first pipe end position candidate; and the inflection point detection method which detects an inflection point being a point starting to be apart from the end side of the end surface on the basis of the photographed image, calculates the approximation straight line of the tapered part and a straight line L3 passing through the inflection point and orthogonal to a pipe axis AX and detects an intersection point thereof as a second pipe end position candidate. One of the first pipe end position candidate and the second pipe end position candidate is specified as the pipe end position of the pipe with a screw.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a thread profile measuring device and a thread profile measuring method for measuring the thread profile of a threaded pipe having a thread formed at its end, such as an oil country tubular good, and in particular to a thread profile measuring device and a thread profile measuring method for a threaded pipe that can accurately identify the pipe end position of the threaded pipe based on an image generated by an optical projection method and accurately measure the thread profile using the identified pipe end position. [Background technology]

[0002] A conventional method for connecting the ends of pipes such as oil country tubular goods (OCTG) is to form a threaded pipe by forming a threaded portion (male threaded portion) on the outer peripheral surface of the end of the pipe, and then fastening each threaded portion (male threaded portion) of a pair of threaded pipes to a joint having a threaded portion (female threaded portion) formed on the inner peripheral surface, thereby connecting the ends of the threaded pipes. If the dimensional accuracy of the threaded portion formed at the end of a threaded pipe is low, the fastening state with the fitting may loosen, the threaded pipes may become disconnected and fall off, or the fluid flowing inside the threaded pipe may leak to the outside. In particular, in the case of oil country tubular goods, as the oil well environment has become more severe in recent years, requirements for the dimensional accuracy of the threaded portion and the level of quality assurance have become stricter every year.

[0003] For this reason, various devices have been proposed that use the so-called light projection method to automatically measure the thread shape of a threaded portion (see, for example, Patent Documents 1 to 3). The light projection method is a method of illuminating the end of a threaded pipe by emitting light from a direction perpendicular to the axis of the threaded pipe, and detecting the light that passes through the end of the threaded pipe without being obstructed by the end of the threaded pipe to generate an image of the end of the threaded pipe, and then measuring the thread shape of the threaded portion based on this image.

[0004] The thread profile to be measured includes the "thread diameter," which is the outer diameter of the thread at a position a predetermined distance from the pipe end in the pipe axial direction, and other measurements that must be made based on the pipe end position (the coordinate of the pipe end in the pipe axial direction of the threaded pipe). For this reason, it is necessary to measure the pipe end position with high accuracy. For many threaded pipes, the pipe end position can be easily measured by image processing of the captured image generated by the optical projection method. However, some threaded pipes used as oil country tubular goods have notches (also called grooves) formed on the end surface at a predetermined angular pitch (angular pitch around the axial direction of the pipe).

[0005] Figure 1 shows a schematic diagram of an example of the shape of the end of a threaded pipe with a notch formed in it. Figure 1(a) shows an end view of the end of the threaded pipe (an end view cut along a plane including the pipe axis AX), and Figure 1(b) shows a perspective view of the area surrounded by the dashed line indicated by the symbol A1 in Figure 1(a). In the following, as shown in Figure 1(a), in the direction along the pipe axis AX of the threaded pipe P, the side toward the back of the threaded pipe P, which is the side farther from the pipe end, will be referred to as the central side of the threaded pipe P, and the side toward the front of the threaded pipe P, which is the side closer to the pipe end, will be referred to as the end side of the threaded pipe P. As shown in FIG. 1(a), the outer peripheral surface of a threaded pipe P at its end includes, in order from the center, a threaded portion with threads Pa and thread grooves Pb, a bevel portion adjacent to the threaded portion, and a lip portion adjacent to the bevel portion where no threads are formed. The tip of the lip portion (the portion toward the end of the threaded pipe P) forms a tapered portion T that slopes toward the pipe axis AX as it approaches the end face E of the threaded pipe P. When viewed from a direction perpendicular to the pipe axis AX (direction Z), the end face E of the threaded pipe P slopes from the outer edge E1 of the end face E (the boundary with the tapered portion T) toward the pipe axis AX, moving away from the end of the threaded pipe P. In other words, the end face E has a cone-shaped recess starting from the outer edge E1. Also, as shown in FIG. 1(b), notches G are formed on the end face E (the area with dark hatching) at a predetermined angular pitch (specifically, 72° in the example shown in FIG. 1(b)).

[0006] In the case of a threaded pipe such as that shown in Figure 1, the image generated by capturing an image of the end using the optical projection method differs depending on the angle around the axial direction of the threaded pipe due to the presence of the notch, and simply processing the captured image may not be enough to accurately measure the pipe end position.

[0007] Although Patent Document 3 proposes a method for accurately measuring the tube end position using an image generated by an optical projection method, this method is constrained by the requirement that the image must be generated while the piece is in contact with the tube end. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2019-128203 [Patent Document 2] Patent No. 6849149 [Patent Document 3] Patent No. 6607227 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the problems of the prior art described above, and has as its object to provide an apparatus and method for measuring the thread shape of a threaded pipe that can accurately identify the pipe end position of a threaded pipe based on an image generated by an optical projection method, and that can accurately measure the thread shape using the identified pipe end position. [Means for solving the problem]

[0010] In order to solve the above problems, the inventors have conducted extensive research into methods for detecting the pipe end position (the coordinates of the pipe end in the pipe axis direction of a threaded pipe) based on images captured by the optical projection method. Specifically, they have conducted extensive research into the "contour line detection method" and "bending point detection method" described below. The "contour detection method" performs image processing on the captured image generated by the optical projection method to calculate an approximate straight line (approximate straight line of the pixel group that makes up the contour line of the tapered portion) of the contour (silhouette) of the tapered portion as seen from the measurement direction (the direction of the visual axis of the imaging unit that generates the captured image of the end portion in the optical projection method (direction perpendicular to the tube axis)), and an approximate straight line (approximate straight line of the pixel group that makes up the contour line of the end face) of the contour (silhouette) of the end face as seen from the measurement direction, and detects the intersection of these approximate straight lines as the tube end position (the coordinate in the tube axis direction of the intersection point is detected as the tube end position). The "bending point detection method" applies image processing to the captured image generated by the optical projection method to detect the bending point (corresponding to the outer edge E1 shown in Figure 1(a)), which is the point where the end face begins to move away from the end side when viewed from the measurement direction, and calculates an approximation line of the outline of the tapered section when viewed from the measurement direction and a line that passes through the bending point of the end face and is perpendicular to the tube axis (a line that passes through the pixel corresponding to the outer edge and is perpendicular to the tube axis), and detects the intersection of these approximation lines and the line as the tube end position (the coordinate of the intersection in the tube axis direction is detected as the tube end position).

[0011] After extensive research into the above-mentioned contour line detection method and bending point detection method, the inventor discovered that the pipe end position can be accurately determined by specifying either the pipe end position detected by the contour line detection method (first pipe end position candidate) or the pipe end position detected by the bending point detection method (second pipe end position candidate) as the final pipe end position, depending on the angle around the pipe axis of the threaded pipe when the end is illuminated by the light projection method (depending on the angle around the pipe axis of the threaded pipe reflected in the captured image).

[0012] The present invention has been completed based on the above findings of the inventors. That is, in order to solve the above-mentioned problems, the present invention provides a thread profile measuring device for measuring the thread profile of a threaded pipe having a threaded portion on the outer peripheral surface of an end portion thereof and a tapered portion on which no threads are formed, wherein the threaded pipe has an end face that, when viewed from a measurement direction perpendicular to the pipe axis of the threaded pipe, is inclined in the pipe axial direction so as to move away from the end of the threaded pipe as it approaches the pipe axis, and a notch is formed on the end face, and the thread profile measuring device comprises: an illumination unit that illuminates the end portion by emitting light in the measurement direction; an imaging unit that is arranged opposite the illumination unit across the end portion and that generates an image of the end portion by detecting light that passes through the end portion without being blocked by the end portion; and a calculation processing unit that calculates the thread profile of the threaded portion based on the image, and the calculation processing unit calculates the thread profile of the threaded portion based on the image a contour line detection method for calculating an approximation line of the contour line of the tapered portion as seen from the measurement direction and an approximation line of the contour line of the end face as seen from the measurement direction, and detecting the intersection of these approximation lines as a first pipe end position candidate; and a bending point detection method for detecting a bending point, which is a point at which the end face as seen from the measurement direction starts to move away from the end side, based on the captured image, calculating an approximation line of the contour line of the tapered portion as seen from the measurement direction and a straight line that passes through the bending point of the end face and is perpendicular to the pipe axis, and detecting the intersection of these approximation lines as a second pipe end position candidate, wherein the calculation processing unit identifies one of the first pipe end position candidate and the second pipe end position candidate as the pipe end position of the threaded pipe, and calculates the thread shape of the threaded portion using the identified pipe end position.

[0013] According to the present invention, the light projection method is performed by an illumination unit that illuminates the end of a threaded pipe by emitting light toward the end of the threaded pipe in a measurement direction (the direction of the visual axis of the imaging unit that generates an image of the end, which is perpendicular to the pipe axis), an imaging unit that is positioned opposite the illumination unit across the end of the threaded pipe and generates an image of the end of the threaded pipe by detecting light that passes through the end of the threaded pipe without being blocked by it, and a calculation processing unit that calculates the thread shape of the threaded portion based on the image.The calculation processing unit identifies either a first pipe end position candidate detected by the contour line detection method or a second pipe end position candidate detected by the inflection point detection method as the pipe end position of the threaded pipe based on the image generated by the light projection method.As the inventors have discovered, this makes it possible to accurately identify the pipe end position of a threaded pipe and to accurately measure the thread shape using the identified pipe end position.

[0014] Here, the inventors have conducted extensive research and found that when the contour line detection method does not accurately detect the first pipe end position candidate, the inclination angle of the approximation line of the contour line of the end face is not within a predetermined angle range. In other words, if the inclination angle of the approximation line of the contour line of the end face is within a predetermined angle range, the first pipe end position candidate can be accurately identified as the pipe end position. On the other hand, it was found that when the second pipe end position candidate is not detected accurately using the bending point detection method, the distance between the bending point of the end face and the approximate straight line of the contour line of the tapered portion is not within a predetermined distance range. In other words, it was found that if the distance between the bending point of the end face and the approximate straight line of the contour line of the tapered portion is within a predetermined distance range, the second pipe end position candidate can be accurately identified as the pipe end position. Furthermore, it was found that if the inclination angle of the approximate straight line of the contour line formed by the end face is within a predetermined angle range (i.e., the first pipe end position candidate can be accurately identified as the pipe end position), and the distance between the bend point of the end face and the approximate straight line of the contour line formed by the tapered portion is within a predetermined distance range (i.e., the second pipe end position candidate can be accurately identified as the pipe end position), the pipe end position can be identified with even greater accuracy by selecting the pipe end position candidate located on the end side of the threaded pipe from the first pipe end position candidate and the second pipe end position candidate.

[0015] Therefore, preferably, when the inclination angle of the approximation line of the contour line of the end face as seen from the measurement direction calculated by the contour line detection method is within a predetermined angle range, and the distance between the bend point of the end face as seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion as seen from the measurement direction is not within a predetermined distance range, the calculation processing unit specifies the first pipe end position candidate as the pipe end position of the threaded pipe, and when the inclination angle of the approximation line of the contour line of the end face as seen from the measurement direction calculated by the contour line detection method is not within a predetermined angle range, and the distance between the bend point of the end face as seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion as seen from the measurement direction is not within a predetermined distance range, the calculation processing unit specifies the first pipe end position candidate as the pipe end position of the threaded pipe, and when the inclination angle of the approximation line of the approximation line of the contour line of the end face as seen from the measurement direction calculated by the contour line detection method is not within a predetermined angle range, and the distance between the bend point of the end face as seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion as seen from the measurement direction is not within a predetermined distance range, the calculation processing unit specifies the first pipe end position candidate as the pipe end position of the threaded pipe If the distance between the approximate straight line of the contour of the tapered portion as viewed from the measurement direction and the second pipe end position candidate is within a predetermined distance range, the second pipe end position candidate is identified as the pipe end position of the threaded pipe.If the inclination angle of the approximate straight line of the contour of the end face as viewed from the measurement direction calculated by the contour line detection method is within a predetermined angle range, and the distance between the bend point of the end face as viewed from the measurement direction calculated by the bend point detection method and the approximate straight line of the contour of the tapered portion as viewed from the measurement direction is within a predetermined distance range, the pipe end position candidate located on the end side of the threaded pipe is identified as the pipe end position of the threaded pipe, out of the first pipe end position candidate and the second pipe end position candidate.

[0016] According to the above-described preferred configuration, the pipe end position of a threaded pipe can be accurately determined regardless of the angle around the pipe axis direction of the threaded pipe when the end is illuminated using the light projection method, and the thread shape can be accurately measured using the determined pipe end position.

[0017] In order to solve the above-mentioned problems, the present invention provides a thread shape measurement method for measuring the thread shape of a threaded pipe having a threaded portion on the outer peripheral surface of an end portion thereof and a tapered portion on which no threads are formed, wherein the threaded pipe has an end face that, when viewed from a measurement direction perpendicular to the pipe axis of the threaded pipe, is inclined in the pipe axial direction so as to move away from the end of the threaded pipe as it approaches the pipe axis, and a notch is formed on the end face, and the thread shape measurement method comprises: an illumination step of illuminating the end portion using an illumination unit that emits light in the measurement direction; an imaging step of generating an image of the end portion using an imaging unit that is positioned opposite the illumination unit across the end portion and that detects light that passes through the end portion without being blocked by the end portion; and a calculation processing step of calculating the thread shape of the threaded portion based on the image, wherein the calculation processing step The present invention also provides a thread shape measurement method that executes the following steps: a contour line detection method that calculates, based on the captured image, an approximate straight line of the contour line of the tapered portion as seen from the measurement direction and an approximate straight line of the contour line of the end face as seen from the measurement direction, and detects the intersection of these approximate straight lines as a first pipe end position candidate; and a bend point detection method that detects, based on the captured image, a bending point at which the end face as seen from the measurement direction starts to move away from the end side, calculates an approximate straight line of the contour line of the tapered portion as seen from the measurement direction and a straight line that passes through the bend point of the end face and is perpendicular to the pipe axis, and detects the intersection of these approximate straight lines as a second pipe end position candidate. In the calculation processing step, one of the first pipe end position candidate and the second pipe end position candidate is identified as the pipe end position of the threaded pipe, and the identified pipe end position is used to calculate the thread shape of the threaded portion.

[0018] Preferably, in the calculation step, if the inclination angle of the approximation line of the contour line of the end face as seen from the measurement direction calculated by the contour line detection method is within a predetermined angle range, and the distance between the bend point of the end face as seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion as seen from the measurement direction is not within a predetermined distance range, the first pipe end position candidate is specified as the pipe end position of the threaded pipe, and if the inclination angle of the approximation line of the contour line of the end face as seen from the measurement direction calculated by the contour line detection method is not within a predetermined angle range, and the distance between the bend point of the end face as seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion as seen from the measurement direction is not within a predetermined distance range, If the distance between the inclination angle of the approximation line of the contour line of the end face seen from the measurement direction calculated by the contour line detection method is within a predetermined angle range, and the distance between the inflection point of the end face seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion seen from the measurement direction is within a predetermined distance range, the pipe end position candidate located on the end side of the threaded pipe out of the first pipe end position candidate and the second pipe end position candidate is identified as the pipe end position of the threaded pipe. [Effects of the Invention]

[0019] According to the present invention, it is possible to accurately identify the pipe end position of a threaded pipe based on an image generated by the optical projection method without using pieces such as those described in Patent Document 3, and to accurately measure the thread shape using the identified pipe end position. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 10 is a diagram showing an example of the shape of the end of a threaded pipe on which a notch is formed. [Figure 2] 1 is a front view schematically showing an example of the general configuration of a thread profile measuring device according to an embodiment of the present invention; [Figure 3] 10A and 10B are diagrams illustrating an end face approximation line detection method using an example of a captured image. [Figure 4] 10A and 10B are diagrams illustrating an outer edge detection method using an example of a captured image. [Figure 5] 10A and 10B are diagrams for explaining a specific method for detecting an outer edge; [Figure 6] FIG. 10 is a diagram showing an example of a pipe end position (first pipe end position candidate) detected by the end face approximate line detection method and a pipe end position (second pipe end position candidate) detected by the outer edge detection method. [Figure 7] For the measurement results shown in FIG. 6, the inclination angle of the approximate line L2 and the distance between the outer edge and the approximate line L1 at each angle around the axial direction of the threaded pipe are calculated. [Figure 8] 10A and 10B are diagrams showing pipe end positions identified by a specific pipe end position identifying method. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an apparatus for measuring the thread profile of a threaded pipe according to one embodiment of the present invention will be described with reference to the accompanying drawings as appropriate.

[0022] FIG. 2 is a front view (viewed from the direction of the tube axis AX (X direction)) that schematically shows an example of the general configuration of a thread profile measuring device according to one embodiment of the present invention. As shown in Figure 2, the thread shape measuring device 100 of this embodiment is a device that measures the thread shape (thread diameter, etc.) of the threaded portion of a threaded pipe P as shown in Figure 1 above, and is equipped with an illumination unit 1, an imaging unit 2, and an arithmetic processing unit 3. The illumination unit 1 and imaging unit 2 of this embodiment are attached so as to be movable integrally in the vertical direction relative to the beam 4 that extends in the vertical direction (Z direction), which is the measurement direction, so that they face each other in the vertical direction. The thread profile measuring device 100 of this embodiment is equipped with two identical optical systems (illumination unit 1 and imaging unit 2) and the same beam 4 that illuminate and image opposing areas of the threaded pipe P on either side of the pipe axis AX in the Y direction (a direction perpendicular to the X direction, which is the direction of the pipe axis AX, and the Z direction, which is the measurement direction), so that the thread diameter, etc., can be calculated by measuring areas on both sides of the threaded pipe P. When measuring the thread profile using the thread profile measuring device 100 according to this embodiment, the position of the threaded pipe P is fixed by a chuck (not shown) or the like. The beam 4 is movable in the X direction according to the measurement portion of the threaded pipe P, and as the beam 4 moves in the X direction, the illumination unit 1 and imaging unit 2 attached to the beam 4 also move in the X direction. Therefore, by moving the beam 4 in the X direction, it is possible to measure portions on both sides of the threaded pipe P over the entire length in the direction of the pipe axis AX. Each of the components of the thread profile measuring device 100 will be described below in order.

[0023] <Lighting Section 1> The illumination unit 1 has an optical axis in a direction (Z direction) perpendicular to a cross section M including the tube axis AX of the threaded tube P, and emits parallel light L having a predetermined spread in the X and Y directions, thereby illuminating the end of the threaded tube P. The cross section perpendicular to the optical axis of the light beam of parallel light L emitted from the illumination unit 1 has an area sufficiently larger than the range detected and imaged by the imaging unit 2 (i.e., the imaging field of view). The illumination unit 1 is not particularly limited as long as it can emit parallel light L, and may be, for example, an LED illumination with a lens, a halogen lamp with a lens, or a laser.

[0024] <Imaging unit 2> The imaging unit 2 is a means for detecting and imaging the light that passes through the end of the threaded pipe P without being blocked, out of the parallel light L emitted from the illumination unit 1, and generating a captured image. 2, the imaging unit 2 of this embodiment includes an imaging unit main body 21 and a telecentric lens 22 attached to the imaging unit main body 21. The imaging unit main body 21 includes imaging elements such as CCDs and CMOSs ​​arranged two-dimensionally. By including the telecentric lens 22, the imaging unit 2 can easily receive parallel light components at the imaging elements of the imaging unit main body 21.

[0025] The imaging unit 2 has a visual axis (i.e., a visual axis in the Z direction) parallel to the optical axis of the illumination unit 1. The direction of the visual axis of the imaging unit 2 is referred to as the measurement direction in the thread profile measurement device 100. Because the imaging unit 2 is equipped with a telecentric lens 22, the angle of view near the object plane is 0° and the magnification is constant, making it suitable for dimensional measurement. The imaging unit 2 is adjusted so that its focal position coincides with a cross section M including the tube axis AX of the threaded pipe P. Specifically, as described above, the imaging unit 2 in this embodiment is movable in the vertical direction (Z direction) relative to the beam 4 (movable integrally with the illumination unit 1), and its vertical position is adjusted according to the position of the threaded pipe P so that the focal position of the imaging unit 2 coincides with the cross section M.

[0026] <Calculation processing unit 3> The calculation processing unit 3 is connected to the imaging unit 2 and is a means for calculating the thread shape of the threaded portion of the threaded pipe P based on the captured image generated by the imaging unit 2. The calculation processing unit 3 is composed of, for example, a personal computer installed with a program for executing the calculation processing described below (a contour line detection method and a bending point detection method for detecting pipe end position candidates, as well as a process for calculating the thread shape such as the thread diameter using the pipe end positions identified from the pipe end position candidates).

[0027] The contour line detection method and the bending point detection method executed by the calculation processing unit 3 for detecting the pipe end position candidate will be described below in order.

[0028] [Contour detection method] Figure 3 is a diagram illustrating the contour line detection method using an example of a captured image. The contour line detection method utilizes the property that pixel regions corresponding to the threaded pipe P appear dark and other pixel regions appear bright in a captured image. By performing image processing such as binarization on the captured image obtained by aligning the focal position with the cross section M, the boundary between the bright pixel region other than the threaded pipe P and the tapered portion T (the pixel group that constitutes the contour of the tapered portion T) and the boundary between the bright pixel region other than the threaded pipe P and the end face E (the pixel group that constitutes the contour of the end face E) are detected. The contour of the end face E is not limited to this, but may extend, for example, from the outer edge (bending point) E1 to approximately half the length of the end face E in the Y direction. Next, as shown in Figure 3, an approximation calculation method such as the least squares method is applied to the detected contour line of the tapered portion T (a group of pixels that make up the contour line of the tapered portion T) to calculate an approximate straight line L1 of the contour line of the tapered portion T. Similarly, an approximation calculation method such as the least squares method is applied to the detected contour line of the end face E (a group of pixels that make up the contour line of the end face E) to calculate an approximate straight line L2 of the contour line of the end face E. Then, an intersection point P1 of these approximate straight lines L1 and L2 is detected as a tube end position candidate (first tube end position candidate). That is, the coordinate of the intersection point P1 in the tube axis direction (X direction) is detected as the first tube end position candidate. The approximate positions of the pixel area in the captured image corresponding to the contour line of the tapered portion T and the pixel area corresponding to the contour line of the end face E can be estimated from the positional relationship (positional relationship in the Y direction) between the imaging unit 2 and the threaded pipe P, the imaging field of view of the imaging unit 2, etc., so the approximate straight lines L1 and L2 can be calculated using a group of pixels near the estimated positions. Also, in Figure 3, for the convenience of explaining the calculation of the approximate straight line L2 using the contour line of the end face E, the outer edge (bending point) E1 is shown, but the contour line detection method does not require actual detection of the outer edge E1 (coordinates of the outer edge E1).

[0029] [Flip-point detection method] FIG. 4 illustrates the inflection point detection method using an example of a captured image. FIG. 4(a) is a full view of the captured image, and FIG. 4(b) is an enlarged view of the area surrounded by the dashed line A2 in FIG. 4(a). In the inflection point detection method, similar to the contour line detection method, image processing such as binarization is performed on the captured image obtained by aligning the focal position with the cross section M to detect the boundary between the bright pixel area other than the threaded pipe P and the tapered portion T (the pixel group constituting the contour of the tapered portion T, a portion of which is indicated by the curve T' in FIG. 4(b)). Furthermore, the inflection point (outer edge E1) that begins to move away from the end of the end face E is detected. Hereinafter, the inflection point detected by image processing will be appropriately designated by the symbol E1, just like the outer edge E1 of the end face E of the actual threaded pipe P. When the outer edge E1 is captured in the captured image, a line E' corresponding to a portion of the end face that starts from the outer edge E1 and moves away from the end as it approaches the tube axis, and a contour line corresponding to the tube end, may be visible near the outer edge E1 in the captured image. Therefore, by setting an appropriate threshold value in advance when performing image processing such as binarization, it is possible to leave only the line E' corresponding to a portion of the end face that starts from the outer edge E1 and moves away from the end as it approaches the tube axis, and to erase the contour line of the tube end in the binarized image. Next, as shown in FIG. 4(a), an approximation calculation method such as the least squares method is applied to the detected contour line of the tapered portion T (a group of pixels constituting the contour line of the tapered portion T) to calculate an approximate straight line L1 of the contour line of the tapered portion T. Also, a straight line L3 that passes through the detected bending point E1 and is perpendicular to the tube axis AX (i.e., extends in the Y direction) is calculated. Then, an intersection P2 between these approximate straight lines L1 and L3 is detected as a tube end position candidate (second tube end position candidate). That is, the coordinate of the intersection P2 in the tube axis direction (X direction) is detected as the second tube end position candidate. In addition, when calculating the straight line L3, in order to precisely calculate the direction of the tube axis AX that is perpendicular to this straight line L3, for example, the average value of the slope of the approximated straight line L1 calculated using one of two sets of optical systems (the illumination unit 1 and the imaging unit 2 shown in Figure 2) and the slope of the approximated straight line L1 calculated using the other optical system may be calculated as the slope (direction) of the tube axis AX.

[0030] FIG. 5 is a diagram for explaining a specific method for detecting the bending point E1. As shown in Figure 5(a), image processing such as binarization is performed on the captured image to distinguish between dark pixel areas corresponding to the threaded pipe P and bright pixel areas other than the threaded pipe P, and as shown in Figure 5(b), a pixel group (a collection of pixels plotted with ●) corresponding to the boundary portion of the threaded pipe P is detected. Specifically, a pixel group corresponding to the outline of the tapered portion T and a pixel group corresponding to the outline of the end face E are detected.

[0031] As explained with reference to Figure 1, the end face E of the threaded pipe P to be measured starts at the outer edge E1 and slopes in the direction of the pipe axis AX, moving away from the end of the threaded pipe P as it approaches the pipe axis AX. For this reason, the boundary portion of the threaded pipe P is considered to be bent convexly toward the end of the threaded pipe P at the outer edge E1. Therefore, by taking a second-order derivative of the boundary portion of the threaded pipe P in the Y direction perpendicular to the pipe axis AX and calculating the extreme value of the convex bending toward the end of the threaded pipe P, it is considered possible to detect the bending point corresponding to the outer edge E1. The boundary of the threaded pipe P is actually considered to be curved. However, if we consider that the pixel group corresponding to the boundary of the threaded pipe P is arranged in order of coordinates in the pipe axis direction (X direction) as shown in Figure 5(c) (if we consider that the pixels connected by the line segments shown in Figure 5(c) are adjacent to each other), the three adjacent pixels used in the second differentiation will not follow the curve representing the boundary, and appropriate second differentiation will not be possible.

[0032] Therefore, a process is performed to link adjacent pixels so that the three adjacent pixels used in the second differentiation are along the curve representing the boundary portion. Specifically, as shown in FIG. 5(d), the pixel PX1 located farthest from the axis AX of the threaded pipe P (located at the bottom in FIG. 5(d)) is selected first, and the pixel PX2 located closest to this pixel PX1 is selected second. Next, excluding the pixel PX1 already selected, the pixel PX3 located closest to pixel PX2 is selected. After that, the last pixel PXn The same process is repeated until the selected This linking process links the pixels connected by the line segments shown in Figure 5(d) as being adjacent to each other, and the three adjacent pixels used for second-order differentiation are aligned along the curve representing the boundary.

[0033] As shown in FIG. 5(e), when the pixel group after the linking process is directly subjected to second-order differentiation to calculate the extreme values ​​that are convex toward the end of the threaded pipe P, multiple pixels may exhibit extreme values ​​due to variations in the positions of the pixel group. In the example shown in FIG. 5(e), multiple pixels PX8, PX 13 , P.X. 16 indicates an extreme value, and it is not possible to identify which pixel corresponds to the outer edge E1.

[0034] Therefore, as shown in FIG. 5(f), the positions of the pixel group are moved and averaged before the second differentiation, and the pixel group after the moving average is then second-order differentiated to calculate the extreme value that is convex toward the end of the threaded pipe P. As a result, if there is only one pixel that shows an extreme value, this pixel is identified as the bending point corresponding to the outer edge E1. In the example shown in FIG. 5(f), there are fewer pixels that show extreme values ​​than in the case shown in FIG. 5(e), but there are multiple pixels PX8, PX 13 indicates an extreme value, and it is not possible to identify which pixel corresponds to the outer edge E1. Therefore, in such a case, among the multiple pixels indicating extreme values, the pixel closest to the intersection of the approximation lines L1 and L2 (the position where the outer edge E1 is originally thought to exist) is identified as the bending point corresponding to the outer edge E1. In the example shown in FIG. 5(f), pixel PX 13 is identified as the bending point corresponding to the outer edge E1. In this manner, the inflection point E1 used in the inflection point detection method is detected.

[0035] The calculation processing unit 3 is capable of executing the contour line detection method and the bending point detection method described above, and identifies either the first pipe end position candidate (intersection point P1 shown in Figure 3) detected by the contour line detection method or the second pipe end position candidate (intersection point P2 shown in Figure 4) detected by the bending point detection method as the pipe end position of the threaded pipe P, and uses this identified pipe end position to calculate the thread shape of the threaded portion.

[0036] Fig. 6 shows an example of the pipe end position (first pipe end position candidate) detected by the contour line detection method and the pipe end position (second pipe end position candidate) detected by the bending point detection method. Specifically, Fig. 6 shows an example of the results of comparing the pipe end position (first pipe end position candidate) detected by the contour line detection method and the pipe end position (second pipe end position candidate) detected by the bending point detection method at each angle, which are measured using a contact-type shape measurement device (Mitutoyo Contracer, stylus tip angle 20°, tip radius 25 μm), by changing the angle around the pipe axis AX of a threaded pipe P (in the example shown in Fig. 6, a threaded pipe with notches G formed at 120° intervals on its end face E) at a predetermined angular interval within an angle range of 0° to 120° around a certain reference angle. Figure 6(a) shows an example of the measurement results of the pipe end position, and Figures 6(b) to (e) show examples of captured images generated when the threaded pipe P is at a specified angle. Note that the vertical axis in Figure 6(a) is a value indicating how far the pipe end position (including the pipe end position candidate) is from the center of the threaded pipe P, with a certain position as the reference (0 mm). Also, in Figure 6(a), the area marked "Contracer measurement not possible" indicates the angle range where the pipe end position could not be accurately measured because the contact point of the contracer contacted the notch G in the end face E.

[0037] As shown in Figure 6(a), in the area surrounded by the dashed line indicated by symbol A3, both the first pipe end position candidate detected by the contour line detection method and the second pipe end position candidate detected by the bending point detection method closely match the pipe end position measured by the contrast tracer. In this case, the captured image shown in Figure 6(b) is generated. In the captured image shown in Figure 6(b), it can be seen that the approximate line L2 used to detect the first pipe end position candidate is calculated with high accuracy, and the bending point E1 used to detect the second pipe end position candidate is also detected with high accuracy.

[0038] As shown in Figure 6(a), in the area surrounded by the dashed line A4, the first pipe end position candidate detected by the contour line detection method is smaller than the pipe end position measured by the contrast tracer. In other words, the first pipe end position candidate is detected as a coordinate located closer to the end of the threaded pipe P than the actual pipe end position measured by the contrast tracer. In this case, the captured image shown in Figure 6(c) is generated. In the captured image shown in Figure 6(c), the inclination angle θ (angle with the X direction) of the approximate line L2 used to detect the first pipe end position candidate is calculated to be larger than the inclination angle (θ ≒ 89°) of the approximate line L2 shown in Figure 6(b), which accurately detected the first pipe end position candidate due to the presence of the notch G. As a result, the first pipe end position candidate is smaller. Furthermore, as shown in Figure 6(a), in the area surrounded by the dashed line indicated by the symbol A5, the first pipe end position candidate detected by the contour line detection method has a larger value than the pipe end position measured by the contrast tracer. In other words, the first pipe end position candidate is detected as a coordinate located closer to the center of the threaded pipe P than the actual pipe end position measured by the contrast tracer. In this case, the captured image shown in Figure 6(d) is generated. In the captured image shown in Figure 6(d), the inclination angle θ of the approximate line L2 used to detect the first pipe end position candidate is calculated to be smaller than the inclination angle of the approximate line L2 shown in Figure 6(b), which accurately detected the first pipe end position candidate due to the presence of the notch G. As a result, the first pipe end position candidate has a larger value.

[0039] As shown in Figure 6(a), in the area surrounded by the dashed line A6 (an area where the contracer measurement is impossible due to the presence of the notch G), the second tube end position candidate detected by the bending point detection method changes discontinuously compared to other areas, and it is thought that it cannot be detected accurately. In this case, the captured image shown in Figure 6(e) is generated. In the captured image shown in Figure 6(e), the bending point E1 used to detect the second tube end position candidate cannot be detected accurately due to the presence of the notch G. It is detected at a position closer to the tube axis AX than the bending point E1 position shown in Figure 6(b), where the second tube end position candidate was detected accurately. This is thought to be the reason why the second tube end position candidate cannot be detected accurately.

[0040] Figure 7 shows the results of calculating the inclination angle θ of the approximate line L2 and the distance between the bending point E1 and the approximate line L1 at each angle around the axial direction of the threaded pipe P for the measurement results shown in Figure 6. Figure 7(a) shows the inclination angle θ of the approximate line L2, and Figure 7(b) shows the distance between the bending point E1 and the approximate line L1. As shown in Fig. 7(a), in the region where the first pipe end position candidate was detected with high accuracy (the region corresponding to region A3 in Fig. 6(a)), the tilt angle θ as viewed from the measurement direction is approximately 89°. Therefore, for example, when the tilt angle θ as viewed from the measurement direction is 90° or greater (the hatched region in Fig. 7(a)), it can be determined that the first pipe end position candidate was not detected with high accuracy, and the first pipe end position candidate in this case can be prevented from being selected as the final pipe end position. This makes it possible to eliminate the region where the first pipe end position candidate was not detected with high accuracy (region A4 in Fig. 6(a)). Furthermore, as shown in Fig. 7(b), in the region where the second pipe end position candidate was detected with high accuracy (the region corresponding to region A3 in Fig. 6(a)), the distance between bending point E1 and approximate line L1 as viewed from the measurement direction is just under 1 mm. Therefore, for example, if the distance between bending point E1 and approximate line L1 is 1 mm or more (the hatched region in Fig. 7(b)), it can be determined that the second pipe end position candidate was not detected with high accuracy, and the second pipe end position candidate in this case can be prevented from being selected as the final pipe end position. This makes it possible to eliminate the region where the second pipe end position candidate was not detected with high accuracy (region A6 in Fig. 6(a)).

[0041] [Pipe end position identification method] Based on the results described above, the calculation processing unit 3 of this embodiment identifies either the first pipe end position candidate or the second pipe end position candidate as the pipe end position of the threaded pipe P, specifically as described below. First, in this embodiment, if the inclination angle θ of the approximate straight line L2 of the contour line of the end face E calculated by the contour line detection method is within a predetermined angle range (for example, less than 90°) and the distance between the bend point E1 of the end face E calculated by the bend point detection method and the approximate straight line L1 of the contour line of the tapered portion T is not within a predetermined distance range (for example, less than 1 mm), the calculation processing unit 3 determines that the first pipe end position candidate has been detected accurately and that the second pipe end position candidate has not been detected accurately, and identifies the first pipe end position candidate as the pipe end position of the threaded pipe P. Furthermore, in the case where the inclination angle θ of the approximate straight line L2 of the contour line of the end face E calculated by the contour line detection method is not within a predetermined angle range (for example, less than 90°) and the distance between the bend point E1 of the end face E calculated by the bend point detection method and the approximate straight line L1 of the contour line of the tapered portion T is within a predetermined distance range (for example, less than 1 mm), the calculation processing unit 3 of this embodiment determines that the second pipe end position candidate has been detected accurately and that the first pipe end position candidate has not been detected accurately, and identifies the second pipe end position candidate as the pipe end position of the threaded pipe P. Furthermore, if the inclination angle θ of the approximation line L2 of the contour line of the end face E calculated using the contour line detection method is within a predetermined angle range, and the distance between the bend point E1 of the end face E calculated using the bend point detection method and the approximation line L1 of the contour line of the tapered portion T is within a predetermined distance range (e.g., less than 1 mm), the calculation processing unit 3 of this embodiment identifies the pipe end position candidate that is located closer to the end of the threaded pipe P (i.e., the pipe end position candidate with the smaller value on the vertical axis in Figure 6(a)) as the pipe end position of the threaded pipe P. This makes it possible to eliminate the area where the first pipe end position candidate could not be accurately detected (area A5 shown in Figure 6(a)). The distance between the bending point E1 of the end face E and the approximate straight line L1 of the contour line formed by the tapered portion T may be calculated as the length of a perpendicular line (a line segment that passes through the bending point and is perpendicular to the approximate straight line L1) drawn from the bending point E1 to the approximate straight line L1, or as the length from the bending point E1 to the intersection of the approximate straight line L1 with a line that passes through the bending point E1 and is perpendicular to the tube axis AX (extending in the Y direction).

[0042] Fig. 8 is a diagram showing the tube end positions identified by the specific tube end position identifying method described above. Specifically, Fig. 8 is a diagram showing the tube end positions identified by the above tube end position identifying method for the results shown in Fig. 6(a). As shown in Figure 8, in the entire angle range from 0° to 120°, the identified tube end positions agree well with the actual tube end positions measured by the contracer, and it can be seen that there is a smooth continuity even for tube end positions that cannot be measured by the contracer.

[0043] Furthermore, since the pipe end position of the threaded pipe P can be determined using each of the two sets of optical systems (illumination unit 1 and imaging unit 2 shown in Figure 2), it is also possible to use the average value of the pipe end position determined using one optical system and the pipe end position determined using the other optical system as the final pipe end position. The calculation processing unit 3 calculates the thread shape, such as the thread diameter, using the pipe end position identified as described above. However, since the method for calculating the thread shape can be appropriately selected from conventionally known methods such as those described in Patent Document 2, a detailed description thereof will be omitted here.

[0044] According to the thread shape measuring device 100 of this embodiment, the pipe end position of the threaded pipe P can be accurately determined regardless of the angle around the pipe axis direction of the threaded pipe P when illuminating the end E using the light projection method, and the thread shape can be accurately measured using the determined pipe end position. [Explanation of symbols]

[0045] 1. Lighting section 2. Imaging unit 3. Processing unit 4 beams 21. Imaging unit body 22 Telecentric Lens 100...Thread shape measuring device AX...tube axis E...End face E1: Outer edge (bending point) P···Threaded pipe T···Tapered section

Claims

1. 1. A thread profile measuring device for measuring the thread profile of a threaded portion of a threaded pipe having a threaded portion with a thread formed thereon and a tapered portion without a thread formed on the outer peripheral surface of an end portion thereof, The threaded pipe is When viewed from a measurement direction perpendicular to the pipe axis of the threaded pipe, the threaded pipe has an end face that is inclined in the pipe axis direction so as to move away from the end side of the threaded pipe as it approaches the pipe axis, and a notch is formed in the end face, The thread shape measuring device is an illumination unit that illuminates the end portion by emitting light in the measurement direction; an imaging unit that is disposed opposite the illumination unit across the end portion and detects light that passes through the end portion without being blocked by the end portion, thereby generating a captured image of the end portion; a calculation processing unit that calculates a thread shape of the thread portion based on the captured image; Equipped with the calculation processing unit is capable of executing a contour line detection method in which, based on the captured image, an approximation line of the contour line of the tapered portion seen from the measurement direction and an approximation line of the contour line of the end face seen from the measurement direction are calculated, and an intersection of these approximation lines is detected as a first tube end position candidate; and a bending point detection method in which, based on the captured image, a bending point is detected, which is a point at which the end face seen from the measurement direction starts to move away from the end side, and an approximation line of the contour line of the tapered portion seen from the measurement direction and a straight line that passes through the bending point of the end face and is perpendicular to the tube axis are calculated, and an intersection of these approximation lines and the straight line is detected as a second tube end position candidate. The calculation processing unit identifies either the first pipe end position candidate or the second pipe end position candidate as the pipe end position of the threaded pipe, and calculates the thread shape of the threaded portion using the identified pipe end position.

2. The arithmetic processing unit If the inclination angle of the approximation line of the contour line of the end face as seen from the measurement direction calculated by the contour line detection method is within a predetermined angle range, and the distance between the bend point of the end face as seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion as seen from the measurement direction is not within a predetermined distance range, the first pipe end position candidate is identified as the pipe end position of the threaded pipe; If the inclination angle of the approximation line of the contour line of the end face as seen from the measurement direction calculated by the contour line detection method is not within a predetermined angle range, and the distance between the bend point of the end face as seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion as seen from the measurement direction is within a predetermined distance range, the second pipe end position candidate is identified as the pipe end position of the threaded pipe; 2. A thread profile measuring device according to claim 1, wherein, if the inclination angle of the approximation line of the contour line of the end face seen from the measurement direction calculated by the contour line detection method is within a predetermined angle range, and the distance between the bend point of the end face seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion seen from the measurement direction is within a predetermined distance range, the pipe end position candidate that is located closer to the end of the threaded pipe, of the first pipe end position candidate and the second pipe end position candidate, is identified as the pipe end position of the threaded pipe.

3. 1. A thread profile measuring method for measuring the thread profile of a threaded portion of a threaded pipe having a threaded portion with a thread formed thereon and a tapered portion without a thread formed on the outer peripheral surface of an end portion, comprising: The threaded pipe is When viewed from a measurement direction perpendicular to the pipe axis of the threaded pipe, the threaded pipe has an end face that is inclined in the pipe axis direction so as to move away from the end side of the threaded pipe as it approaches the pipe axis, and a notch is formed in the end face, The thread profile measuring method includes: an illumination step of illuminating the end portion using an illumination unit that emits light in the measurement direction; an imaging step of generating a captured image of the end portion using an imaging unit that is disposed opposite the illumination unit across the end portion and detects light that passes through the end portion without being blocked by the end portion; a calculation processing step of calculating a thread shape of the thread portion based on the captured image; and In the calculation processing step, a contour line detection method is executed in which, based on the captured image, an approximate straight line of the contour line of the tapered portion seen from the measurement direction and an approximate straight line of the contour line of the end face seen from the measurement direction are calculated, and an intersection of these approximate straight lines is detected as a first tube end position candidate; and a bending point detection method is executed in which, based on the captured image, a bending point is detected, which is a point at which the end face seen from the measurement direction starts to move away from the end side, and an approximate straight line of the contour line of the tapered portion seen from the measurement direction and a straight line that passes through the bending point of the end face and is perpendicular to the tube axis are calculated, and an intersection of these approximate straight lines is detected as a second tube end position candidate. In the calculation processing step, either the first pipe end position candidate or the second pipe end position candidate is identified as the pipe end position of the threaded pipe, and the thread shape of the threaded portion is calculated using the identified pipe end position.

4. In the calculation step, If the inclination angle of the approximation line of the contour line of the end face as seen from the measurement direction calculated by the contour line detection method is within a predetermined angle range, and the distance between the bend point of the end face as seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion as seen from the measurement direction is not within a predetermined distance range, the first pipe end position candidate is identified as the pipe end position of the threaded pipe; If the inclination angle of the approximation line of the contour line of the end face as seen from the measurement direction calculated by the contour line detection method is not within a predetermined angle range, and the distance between the bend point of the end face as seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion as seen from the measurement direction is within a predetermined distance range, the second pipe end position candidate is identified as the pipe end position of the threaded pipe; 4. A thread profile measurement method according to claim 3, wherein, if the inclination angle of the approximation line of the contour line of the end face seen from the measurement direction calculated by the contour line detection method is within a predetermined angle range, and the distance between the bend point of the end face seen from the measurement direction calculated by the bend point detection method and the approximation line of the contour line of the tapered portion seen from the measurement direction is within a predetermined distance range, the pipe end position candidate that is located closer to the end of the threaded pipe, of the first pipe end position candidate and the second pipe end position candidate, is identified as the pipe end position of the threaded pipe.

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