JP6604258B2 - Thread shape measuring device for threaded tubes - Google Patents

Description

  The present invention relates to an apparatus for measuring the thread shape of a threaded pipe having an end formed with a screw, such as an oil well pipe. In particular, the present invention is not limited to the screw shape that can be measured by the conventional light projection method, but also the screw shape that is difficult to measure by the method using the light projection method or the contact probe (the angle of the flank surface, particularly the hook shape of the flank surface). The present invention relates to a thread shape measuring device for a threaded tube that can measure a flank angle, a radius of curvature of a thread bottom R portion, and the like on a threaded tube manufacturing line.

Conventionally, as a method of connecting the ends of pipes such as oil well pipes, a screw (male thread) is formed on the outer peripheral surface of the end of the pipe to form a threaded pipe, and each screw (male thread) of a pair of threaded pipes is used. A method is used in which the ends of the pipes are connected to each other by fastening them to a joint (box joint) in which a screw (female thread part) is formed on the inner peripheral surface.
If the dimensional accuracy of the screw formed at the end of the tube is low, the fastening state with the joint may be loosened, the connection between the tubes may be released, and the fluid flowing inside the tube may leak to the outside. In particular, in the case of oil well pipes, the demands on the dimensional accuracy and quality assurance level of screws are becoming stricter year by year as the oil well environment becomes severer in recent years.

FIG. 1 is an end view schematically showing an example of an end shape of an oil well pipe. FIG. 1A is an end view of one end in a radial direction of an end portion of an oil well pipe (an end view cut by a surface including a screw shaft), and FIG. 1B is surrounded by a symbol X shown in FIG. An enlarged end view of the region is shown.
As shown in FIG. 1, the end portion of the oil well pipe P includes a screw portion provided with a screw thread P1 and a screw groove P2, and a bevel portion provided adjacent to the screw portion and closer to the pipe end surface than the screw portion. And a lip portion provided adjacent to the bevel portion and closer to the tube end surface than the bevel portion.
As the oil well environment becomes severer in recent years, the oil well pipe P includes a pair of flank surfaces P3 (a top surface P11 of the screw thread P1 and a bottom surface P21 of the screw groove P2) that define each screw thread P1 of the screw portion. For example, the flank surface P3 located on the side opposite to the tube end surface side is inclined so as to approach the tube end surface side from the top surface P11 of the thread P1 toward the bottom surface P21 of the thread groove P2. Many are used. Conversely, the flank surface P3 located on the tube end surface side may be inclined so as to approach the side opposite to the tube end surface from the top surface P11 of the screw thread P1 toward the bottom surface P21 of the thread groove P2. Thus, the flank surface that approaches the side opposite to the side on which the flank surface P3 is located as it goes from the top surface P11 of the screw thread P1 to the bottom surface P21 of the screw groove P2 is appropriately referred to as a “hook-like flank surface P3h”. In the example shown in FIG. 1, the flank surface P3 located on the side opposite to the tube end surface side is a hook-shaped flank surface P3h.

Conventionally, the angle of the flank surface P3 (angle formed with the perpendicular N of the screw shaft A) β and the curvature radius of the screw bottom R portion (the portion where the flank surface P3 and the bottom surface P21 of the screw groove P2 intersect) P4 are known. It is evaluated off-line using a technique, and a pass / fail decision is made by comparison with an allowable range.
Since the evaluation as described above requires a lot of time and labor, it must be a sampling inspection such as inspecting the first and last oil well pipe P of the same production lot, and the total inspection is difficult.
Moreover, since the pass / fail determination is merely made by comparison with the allowable range, it is difficult to quantitatively evaluate the screw shape.

In order to solve such a problem, Patent Documents 1 to 3 disclose that a screw along the screw axis direction is detected by irradiating light along the bottom surface P21 of the screw groove P2 and detecting light passing through the screw portion. Proposed is a method (light projection method) for measuring the external shape (surface irregularities, screw profile). If the screw profile of the screw portion can be measured with high accuracy by this light projection method, the angle of the flank surface P3 and the radius of curvature of the screw bottom R portion P4 can be calculated with high accuracy from the screw profile.
However, since the screw profile draws a curve, in the light projection method for detecting transmitted light, the flank surface P3 may not be detected accurately because the flank surface P3 is hidden by the shadow of the ridge line of the screw thread P1. In particular, when the flank surface P3 is a hook-like flank surface P3h, it cannot be detected by the light projection method. The same applies to the thread bottom R portion P4 located at the portion where the flank surface P3 and the bottom surface P21 of the thread groove P2 intersect.

Therefore, as described in Patent Document 4, the present inventors have proposed a method of performing measurement related to the flank surface P3 of the threaded portion using a contact probe in addition to the measurement by the light projection method.
However, since the contact probe is sequentially moved and the spherical contact attached at the tip is brought into contact with the flank surface P3, the measurement time is inevitably increased. In order to measure in the production line of the oil well pipe P, it is necessary to shorten the measurement time to a certain value or less, so that a sufficient number of measurement points cannot be obtained. For this reason, if fine particles such as dust floating in the atmosphere in which the measuring device is installed adhere to any of the measurement points, a linear approximation with a small number of measurement points increases the error, and the angle of the flank surface P3 is accurate. May not be able to measure well. The same applies to the case where particles adhere to the contact. In order to suppress the adhesion of particles to the threaded portion of the oil well pipe P and the contact of the contact probe, it is necessary to purify the atmosphere in which the measuring device is installed, clean the threaded portion, clean the contactor, etc. Since it is necessary to exchange and calibrate the contact, there is a problem that it takes time and effort. Further, since the contact is worn by repeated use, there is a problem that the measurement accuracy is deteriorated due to wear.
In addition, since the diameter of the contact is 0.1 mm or more (paragraph 0067 of Patent Document 4), it is difficult to measure the radius of curvature of the thread bottom R portion P4 of about several hundred μm.

  In Patent Document 4 and Patent Document 5 described above, methods for detecting the position and direction of the screw shaft are proposed.

Japanese Patent No. 3552440 JP 63-212808 A JP 2010-38554 A Japanese Patent No. 4486700 Japanese Patent No. 4457370

  The present invention has been made to solve the above-mentioned problems of the prior art, and in addition to the screw shape that can be measured by the conventional light projection method, it is difficult to measure by the conventional method using the light projection method or the contact probe. It is an object of the present invention to provide a thread shape measuring device for a threaded tube that can measure the thread shape on a production line of the threaded tube.

In order to solve the above-mentioned problems, the present inventors have intensively studied, and as a result, applied a three-dimensional shape measurement method based on a so-called focusing method (Depth from Focus method), and arranged the illumination means and the imaging means. It has been found that if devised, it is possible to accurately measure flank surfaces and screw bottom R portions, which were difficult to measure in the past.
However, in general, in the three-dimensional shape measurement method based on the focusing method, the measurement area (imaging field of view of the imaging means) is reduced if the measurement time is shortened to such an extent that it can be measured on the threaded tube production line. I have to limit it. For this reason, it is difficult to measure all screw shapes using a three-dimensional shape measurement method that uses the focusing method as a measurement principle.
Therefore, the screw shape that can be measured by the conventional light projection method is measured using the light projection method, and the screw shape that cannot be measured by the light projection method is applied to the three-dimensional shape measurement method that uses the focusing method as the measurement principle. The present invention has been completed by conceiving that the arrangement of the illumination means and the image pickup means should be devised.

  That is, in order to solve the above problem, the present invention is an apparatus for measuring the shape of a screw formed at an end of a threaded tube, and illuminates the end of the threaded tube and leaks from the screw. A first optical system for detecting and imaging light; a second optical system for illuminating an end of the threaded tube; and changing the focal position of the illuminated end for imaging a plurality of times; and the first And an arithmetic means for calculating a shape of a screw formed at an end of the threaded tube based on an image captured by the optical system and the second optical system, and the first optical system includes the threaded First illumination means for illuminating the end of the threaded tube from a direction substantially orthogonal to the first surface including the screw shaft as viewed from the direction of the screw shaft of the tube, and a first surface including the screw shaft Is opposed to the first illumination means, and detects light leaking from the screw. First imaging means for imaging, and the second optical system includes second illumination means for illuminating an end of the threaded tube, and an end of the threaded tube illuminated by the second illumination means. The second imaging means is disposed along a second surface including the screw shaft of the threaded tube, and is configured to both the screw shaft and the perpendicular of the screw shaft. The second illuminating means is located at a position away from the second surface including the screw shaft. And an optical axis in a direction inclined with respect to both the perpendicular of the screw shaft and the visual axis of the second imaging means, and the computing means displays an image on a captured image captured by the first imaging means. The first outer shape which is a partial outer shape of the screw along the screw axis direction by performing the processing Calculate and perform image processing on each of the plurality of captured images captured by the second imaging unit to determine the in-focus state of each captured image, and based on the determination result, the three-dimensional shape of the end of the threaded tube And calculating a second outer shape that is a partial outer shape of the screw along the screw axis direction based on the calculated three-dimensional shape, and calculating the screw based on the calculated first and second outer shapes. Provided is a thread shape measuring device for a threaded tube, wherein the thread shape of the threaded tube is calculated.

The 1st optical system with which the screw shape measuring device concerning the present invention is provided is an optical system for performing the same light projection method as the past, and the 2nd optical system is an optical system for performing the focusing method. is there.
If the first illumination means provided in the first optical system illuminates the end of the threaded tube, and the first imaging means disposed opposite the first illumination means detects and leaks light from the screw, In the obtained captured image, the pixel area blocked by the end of the threaded tube is darkened, and the pixel area not blocked is brightened. For this reason, it is possible to calculate the first outer shape, which is a partial outer shape of the screw along the screw axis direction, by performing image processing such as binarization on the captured image by the calculation means. The first outer shape includes the top surface of the thread and the bottom surface of the thread groove, but does not include the hook-shaped flank surface and the thread bottom R portion.

The 2nd imaging means with which a 2nd optical system is provided is arrange | positioned along the 2nd surface containing the screw axis | shaft of a threaded pipe | tube, and has a visual axis of the direction inclined with respect to both the screw axis | shaft and the perpendicular of a screw axis | shaft. Therefore, by appropriately adjusting the imaging field of view of the second imaging means, it is possible to image both the bottom surface of the thread groove substantially parallel to the screw shaft and the flank surface substantially parallel to the perpendicular of the screw shaft.
Note that the visual axis of the second imaging means provided in the second optical system does not necessarily have to be strictly positioned in the second surface including the screw shaft, and both the bottom surface of the screw groove and the flank surface (surface including the screw shaft). The bottom surface of the thread groove and the cross-sectional shape of the flank surface) may be along the second surface including the screw shaft.
Moreover, the 2nd imaging means with which a 2nd optical system is provided changes the focus position, and images the edge part of a threaded pipe | tube several times. This “changing the focal position” is a concept that includes both moving the second imaging means in the visual axis direction and changing the focal length of the lens provided in the second imaging means. May be.

Here, since the end surface of the threaded tube such as an oil well tube is a metal surface after cutting and is a highly glossy surface, the metal image surface of the illumination light is within the same imaging field of view of the second imaging means. If there is a region in which excessively strong specularly reflected light is incident and a region in which almost no reflected light is incident on the metallic glossy surface, the dynamic range of the image sensor provided in the second imaging means is limited. As a result, an appropriate captured image cannot be captured, and there is a risk of hindering the determination of the in-focus state of the captured image by the calculation means described later. The problem of the excessive or small incident light quantity of the reflected light as described above is that the visual axis of the second imaging means and the optical axis of the second illumination means are in the same plane (for example, in the second plane including the screw axis). In some cases, it will be particularly noticeable.
The second illumination unit included in the second optical system is disposed at a position away from the second surface including the screw shaft, and is an optical axis in a direction inclined with respect to both the perpendicular of the screw shaft and the visual axis of the second imaging unit. Have In other words, since the optical axis of the second illuminating means provided in the second optical system is not located in the same plane as the visual axis of the second imaging means, the incident light quantity of the reflected light on the end surface where the screw is formed is The problem of over / under size is reduced, and it is possible to obtain an appropriate captured image.

  The calculation means performs image processing on each of a plurality of captured images (captured images of the end of the threaded tube captured by the second imaging means at a plurality of times with the focal position changed) by the second imaging means. The in-focus state of the captured image is determined, the three-dimensional shape of the end of the threaded tube is calculated based on the determination result, and the partial outer shape of the screw along the screw axis direction is calculated based on the calculated three-dimensional shape. A second outer shape is calculated. The second outer shape can include a hook-like flank surface and a screw bottom R portion. According to the focusing method, since a three-dimensional shape can be calculated with high resolution, a wide range such as a flank surface can be measured at a time as compared with the measurement using a conventional contact probe. For this reason, since a large number of coordinate points can be detected as a three-dimensional shape of the flank surface, it is possible to perform processing such as detecting a particle as an abnormal point and removing the abnormal point. Processing such as interpolation using coordinate point information becomes possible. In addition, unlike the measurement using a conventional contact probe, the screw bottom R portion can be measured because the contact diameter is not limited.

  The computing means computes the thread shape of the threaded tube based on the calculated first and second contours. For example, the calculation means can detect the screw shaft based on the first outer shape, and also the phase of the screw thread corresponding to the position of the screw thread in the screw shaft direction, and the outer diameter of the screw thread at a predetermined position in the screw shaft direction from the pipe end surface. It is possible to calculate a screw diameter, a taper that is a change in the diameter of the bottom surface of the screw groove along the screw axis direction, and the like. Further, for example, the calculation means can calculate the angle of the flank surface and the radius of curvature of the screw bottom R portion based on the second outer shape.

  As described above, according to the screw shape measuring apparatus according to the present invention, the screw shape that can be measured by the conventional optical projection method using the first optical system, and the conventional optical projection method or the contact probe using the second optical system. Thus, it is possible to measure the thread shape, which is difficult to measure, on the production line of the threaded tube.

  Preferably, the calculation means detects the screw shaft based on the first outer shape, calculates an angle formed by the screw shaft and a bottom surface of the screw groove, and calculates the angle of the screw groove based on the second outer shape. An angle formed between the bottom surface and the flank surface is calculated, and based on the calculated angle formed between the screw shaft and the bottom surface of the screw groove and the calculated angle formed between the bottom surface of the screw groove and the flank surface, the flank surface and the screw Calculate the angle formed by the axis perpendicular.

Originally, the angle of the flank surface is not the angle formed by the bottom surface of the thread groove and the flank surface that can be calculated based on the second external shape, because the angle of the bottom surface of the thread groove with respect to the screw shaft includes a machining error. The quality is controlled as an angle formed by the vertical axis of the screw shaft (see FIG. 1). Even if the position and direction of the screw shaft can be assumed in advance, the screw shaft bottom surface of the screw groove changes slightly depending on the misalignment of the threaded tube and the threaded tube, the bending of the threaded tube, etc. The angle formed between the flank surface and the perpendicular of the screw shaft cannot be accurately calculated only by the angle formed between the flank surface and the flank surface. Similarly, in the case of a taper screw where the diameter of the bottom surface of the thread groove changes along the screw axis direction, the angle formed by the bottom surface of the thread groove and the flank surface can be used to accurately determine the angle between the flank surface and the screw shaft perpendicular line. Can not be calculated.
According to the above preferred configuration, since the screw shaft is actually detected based on the first outer shape, the screw shaft of the threaded tube to be measured is accurately determined even if the threaded tube is misaligned or bent. It can be detected. Then, by combining the angle formed between the screw shaft calculated based on the first outer shape and the bottom surface of the screw groove and the angle formed between the bottom surface of the screw groove calculated based on the second outer shape and the flank surface, The angle between the flank surface to be managed and the perpendicular of the screw shaft can be calculated accurately.

  Preferably, the calculation means calculates a combined outer shape obtained by combining the first outer shape and the second outer shape by fitting a common portion of the first outer shape and the second outer shape, and calculates the calculated outer shape. The thread width and the thread valley width are calculated based on the synthesized outer shape.

In order to calculate the thread width and the thread valley width, the outer shapes of both the flank surface located on the side opposite to the pipe end face side and the flank face located on the pipe end face side are required (see FIG. 1). When one flank surface is a hook-like flank surface, the first outer shape calculated using the first optical system can include the other non-hook-like flank surface, but the one hook No flank surface can be included. On the other hand, it is possible to include the one hook-shaped flank surface in the second outer shape calculated using the second optical system.
According to the preferable configuration described above, by fitting the common parts of the first outer shape and the second outer shape (for example, the bottom surface of the thread groove, the top surface of the thread, and the thread R portion (see FIG. 1)), In order to calculate a combined outer shape in which the first outer shape and the second outer shape are combined, this combined waveform includes both flank surfaces. For this reason, it is possible to calculate the thread width and the thread valley width based on this composite outer shape.

  Further preferably, the calculation means calculates a thread phase based on the first outer shape, and determines a position of the second optical system in the screw axis direction based on the calculated thread phase. To do.

As described above, since the second optical system is an optical system for executing the focusing method, the imaging field of view of the second imaging unit must be limited to a certain extent. For this reason, when the flank surface and the screw bottom R portion are measured using the second optical system, the second optical system is accurately set so that the flank surface and the screw bottom R portion enter the imaging field of the second imaging means. Need to be positioned.
According to the above preferred configuration, since the phase of the screw thread is calculated based on the first outer shape calculated using the first optical system, even if the first optical system and the second optical system are threaded tubes, The second optical system can be positioned at a position where the flank surface and the screw bottom R portion can be measured even if they are arranged at positions spaced apart in the circumferential direction.

  According to the present invention, in addition to a screw shape that can be measured by a conventional light projection method, a screw shape that is difficult to measure by a conventional light projection method or a method using a contact probe can be measured on a production line of a threaded tube. is there.

It is an end view which shows typically an example of the edge part shape of an oil well pipe. It is a mimetic diagram showing a schematic structure of a screw shape measuring device concerning one embodiment of the present invention. It is a schematic diagram which shows the relationship between the 1st surface Q shown in FIG. 2, the 2nd surface M, and a lead angle. It is a figure which shows typically an example of the 1st external shape which the calculating means shown in FIG. 2 calculates. It is explanatory drawing explaining the principle of the focusing method which the calculating means shown in FIG. 2 performs. It is explanatory drawing explaining the calculation method of the 2nd external shape which the calculating means shown in FIG. 2 performs. It is explanatory drawing explaining the calculation method of the synthetic | combination waveform which the calculating means shown in FIG. 2 performs. It is explanatory drawing explaining the influence of the imaging visual field of the 2nd optical system shown in FIG. It is explanatory drawing explaining the positioning method of the 2nd optical system shown in FIG. It is a figure which shows an example of the relationship between the angle of the visual axis of the 2nd imaging means shown in FIG. 2, and the imaging resolution of the bottom face of a thread groove, and a flank surface. It is a figure which shows an example of the result of having evaluated the defect | deletion rate when changing the angle (theta) and (phi) of the optical axis of the 2nd illumination means shown in FIG. 2 into various values. An example of the result of having calculated the screw shape by the screw shape measuring apparatus which concerns on one Embodiment of this invention is shown.

Hereinafter, a thread shape measuring device for a threaded tube according to an embodiment of the present invention (hereinafter, simply referred to as “screw shape measuring device” as appropriate) will be described with reference to the accompanying drawings as appropriate.
FIG. 2 is a schematic diagram showing a schematic configuration of a screw shape measuring apparatus according to an embodiment of the present invention. 2A is a side view seen from a direction perpendicular to the second surface M including the screw shaft A, and FIG. 2B is a front view seen from the direction of the screw shaft A. FIG. For convenience of explanation, the second illuminating means 1 and the second imaging means 2 shown in FIG. 2 are illustrated at positions separated from the threaded tube P, but in actuality, positions closer to the threaded tube P. Is arranged. In the present embodiment, the case where the flank surface P3 located on the side opposite to the tube end surface side of the threaded tube P is a hook-shaped flank surface P3h will be described as an example.
As shown in FIG. 2, the screw shape measuring apparatus 100 according to the present embodiment includes a first optical system 10, a second optical system 20, and a calculation means 3, and is formed at the end of the threaded tube P. This is a device for measuring the shape of a screw.
In FIG. 2, the illustration of the screw is omitted for convenience, but the portion of the threaded tube P that is not hatched is the end of the threaded tube P, and has been described above with reference to FIG. 1. Similarly to this, a threaded portion, a beveled portion and a lip portion are formed at this end portion. The threaded tube P is fixed by a chuck (not shown) or the like when the thread shape is measured by the thread shape measuring apparatus 100 according to the present embodiment. Further, as will be described later, the position and direction of the screw axis A of the threaded tube P is detected using the first optical system 10.
Hereinafter, the components of the screw shape measuring apparatus 100 will be sequentially described.

<First optical system 10>
The first optical system 10 is an optical system for illuminating the end of the threaded tube P and detecting and leaking light leaking from the screw. That is, the first optical system 10 is an optical system for executing the light projection method.
Specifically, the first optical system 10 includes a first illumination unit 4 and a first imaging unit 5. In the present embodiment, the first optical system 10 includes two sets of the first illumination means 4 (4a, 4b) and the first in order to illuminate and image a portion facing the screw axis A of the threaded tube P. An imaging means 5 (5a, 5b) is provided.

  The first illuminating means 4 is seen from the direction of the screw axis A of the threaded tube P (see FIG. 2B), and the threaded tube P from the direction substantially orthogonal to the first surface Q including the threaded axis A. It is a means to illuminate the edge part. As the 1st illumination means 4, LED illumination, a halogen lamp, a laser, etc. are used, for example. The 1st illumination means 4 of this embodiment is attached to drive mechanisms, such as a linear stage (not shown) and a gonio stage, The position and the direction of an optical axis can be set variously.

The first imaging means 5 is a means that is arranged opposite to the first illumination means 4 with respect to the first surface Q including the screw axis A, and detects and images the light leaking from the screw. The first image pickup means 5 includes a two-dimensionally arranged image pickup device such as a CCD or a CMOS, and preferably a telecentric lens, whereby the parallel light component can be easily received by the image pickup device. is there. The first imaging means 5 of this embodiment is also attached to a driving mechanism such as a linear stage (not shown), and its vertical position can be set in various ways.
The vertical position of the first imaging unit 5 is adjusted so that the focal point of the first imaging unit 5 is aligned with the outer edge of the screw of the threaded tube P. As a result, it is possible to obtain a captured image in which the difference in brightness between the pixel area blocked by the end of the threaded tube P and the pixel area not blocked is clear.

FIG. 3 is a schematic diagram showing the relationship between the first surface Q, the second surface M, and the lead angle shown in FIG. FIG. 3A is a plan view of the threaded tube P viewed from the direction along the second surface M, and shows that the thread P1 has a lead angle γ. Actually, when the locus of the height center position of the hook-shaped flank surface P3h is viewed from the direction along the second surface M (projected onto the first surface Q), a straight line as shown in FIG. Although it does not become a sine wave shape, it is simplified in FIG. In FIG. 3A, for the sake of convenience, the screw is exaggerated, and the flank surface P3 is simplified so as to be parallel to the perpendicular of the screw shaft. FIG. 3B is a front view of the threaded tube P as viewed from the direction of the screw axis A. The first optical system 10 (the position of the imaging field of the first imaging means 5) and the second optical system 20 are shown in FIG. (Position of the imaging visual field of the second imaging means 2) is shifted in the circumferential direction of the threaded tube P by an angle δ.
As shown in FIG. 3A, the screw thread P1 is provided in a spiral shape on the outer periphery of the threaded tube P, and is perpendicular to the surface perpendicular to the screw axis (surface perpendicular to the second surface M). And has a constant inclination angle (lead angle γ).

<Second optical system 20>
The second optical system 20 is an optical system for illuminating the end of the threaded tube P and imaging the illuminated end a plurality of times by changing the focal position. That is, the second optical system 20 is an optical system for executing the focusing method. Specifically, the second optical system 20 includes a second illumination unit 1 and a second imaging unit 2.
In this embodiment, the second optical system 20 (the position of the imaging field of the second imaging unit 2) is a threaded tube with respect to the first optical system 10 (the position of the imaging field of the first imaging unit 5). They are arranged so as to be shifted by an angle δ in the circumferential direction of P (see FIG. 3B). The angle δ is preferably about 90 ° from the viewpoint of the degree of freedom of arrangement of the first optical system 10 and the second optical system, but can be freely set without being limited thereto.

  The 2nd illumination means 1 is a means to illuminate the edge part of the threaded pipe | tube P, for example, LED illumination with a condensing lens is used suitably. The 2nd illumination means 1 of this embodiment is attached to drive mechanisms, such as a linear stage and a gonio stage (not shown), The position and the direction of an optical axis can be set variously.

The second illuminating means 1 is disposed at a position away from the second surface M (in this embodiment, a surface that is shifted by an angle δ from the first surface Q) including the screw axis A of the threaded tube P. The optical axis 11 is set so as to be inclined with respect to both the perpendicular N of the screw axis A included in the second surface M and the visual axis 21 of the second imaging means 2 described later. In other words, since the optical axis 11 of the second illuminating unit 1 is not located in the same plane as the visual axis 21 of the second imaging unit 2, the incident light amount of reflected light on the end surface where the screw is formed is excessively large. It is possible to reduce the problem of excessiveness and obtain a proper captured image.
In FIG. 2, the single second illumination unit 1 is illustrated, but the present invention is not limited to the single second illumination unit 1, and a configuration including a plurality of second illumination units 1. It is also possible to do.

The second imaging unit 2 is a unit that images the end of the threaded tube P illuminated by the second illumination unit 1 and includes an imaging element such as a CCD or CMOS that is two-dimensionally arranged. The second imaging means 2 of the present embodiment is also attached to a drive mechanism such as a linear stage or a gonio stage (not shown), and the position and direction of the visual axis can be set in various ways.
The second imaging means 2 is disposed along the second surface M including the screw axis A of the threaded tube P, and has a visual axis 21 in a direction inclined with respect to both the screw axis A and the perpendicular N of the screw axis A. (In the example shown in FIG. 2, the visual axis 21 is located in the second surface M including the screw axis A). For this reason, by appropriately adjusting the imaging field of view of the second imaging means 2, both the bottom surface P21 of the thread groove substantially parallel to the screw axis A and the flank surface P3 substantially parallel to the perpendicular N of the screw axis A are obtained. Imaging is possible. However, it is difficult to simultaneously image the pair of flank surfaces P3 that divide each screw thread P1. In the example shown in FIG. 2A, the visual axis 21 of the imaging means 2 is inclined to the opposite side to the tube end surface side with respect to the perpendicular N of the screw shaft A, and thus is located on the opposite side to the tube end surface side. Only one flank surface (hook-like flank surface P3h in this embodiment) can be imaged. For this reason, when calculating the angle of both flank surfaces using only the second optical system 20, the second imaging means 2 for imaging one flank surface as shown in FIG. What is necessary is just to arrange | position both the 2nd imaging means 2 for the other flank surface imaging inclined to the end surface side. Alternatively, after the second imaging means 2 images one flank surface, the position of the second imaging means 2 and the direction of the visual axis 21 may be changed so that the other flank surface can be imaged.
The second imaging means 2 changes the focal position and images the end of the threaded tube P a plurality of times. In the present embodiment, the focal position is changed by moving the second imaging unit 2 in the direction of the visual axis 21.

<Calculation means 3>
The computing means 3 is connected to the first optical system 10 (first imaging means 5) and the second optical system 20 (second imaging means 2) (connection lines to the first imaging means 5 are not shown). Based on the captured images captured by the first optical system 10 and the second optical system 20, it is a means for calculating the shape of the screw formed at the end of the threaded tube P. For example, it executes a calculation process described later. It is comprised from the personal computer in which the program for this was installed.
The computing means 3 may be composed of a plurality of personal computers. In this case, image processing of the captured image captured by the first optical system 10, image processing of the captured image captured by the second optical system 20, the measurement order of the first optical system 10 and the second optical system 20, What is necessary is just to comprise so that each personal computer may share a role for every operation | movement, such as control of a measurement position, and may have a function to communicate mutually.

  The computing unit 3 performs image processing on the captured image captured by the first imaging unit 5 included in the first optical system 10, so that a first outer shape that is a partial outer shape of the screw along the direction of the screw axis A is obtained. Is calculated. If the end of the threaded tube P is illuminated by the first illumination means 4 included in the first optical system 10 and the light leaking from the screw is detected and imaged by the first imaging means 5, an obtained captured image is obtained. The pixel area blocked at the end of the threaded tube P becomes dark, and the pixel area not blocked is brightened. For this reason, it is possible to calculate the first outer shape, which is a partial outer shape of the screw along the screw axis A direction, by performing image processing such as binarization on the captured image by the calculation means 3.

  FIG. 4 is a diagram schematically showing an example of the first outer shape C1 calculated by the calculation means 3. As shown in FIG. The first outer shape C1 includes a first outer shape C1a and a first outer shape C1b. The first outer shape C1a is an outer shape calculated based on a captured image captured by a combination of the first illumination unit 4a and the first imaging unit 5a. The first outer shape C1b is an outer shape calculated based on a captured image captured by a combination of the first illumination unit 4b and the first imaging unit 5b. In the first outline C1, the portion indicated by the solid line is the calculated outline, and the portion indicated by the broken line is an outline that actually exists but is not calculated. The first outer shape C1 includes the top surface P11 of the screw thread P1 and the bottom surface P21 of the thread groove, but does not include the hook-shaped flank surface P3h and the screw bottom R portion P4.

The calculating means 3 calculates the thread shape of the threaded tube P based on the calculated first outer shape C1. For example, the calculation means 3 can detect the screw axis A based on the first outer shape C1, and also includes a thread phase corresponding to the position of the screw thread P1 in the screw axis A direction, and a predetermined position in the screw axis A direction from the pipe end surface The thread diameter that is the outer diameter of the screw thread P1 and the taper that is the diameter change of the bottom surface P21 of the thread groove along the direction of the screw axis A can be calculated.
Further, the calculation means 3 can calculate the outer diameter of the screw thread P and the diameter of the bottom surface P21 of the screw groove based on the calculated first outer shape C1, and can calculate the height of the screw thread P which is the difference between the two radii. It is.

  For the screw shaft A, for example, an approximate straight line L21a is calculated based on the point group data constituting the bottom surface P21 of the thread groove of the first outer shape C1a, and based on the point group data constituting the bottom surface P21 of the screw groove of the first outer shape C1b. An approximate straight line L21b can be calculated and detected as a bisector of the angle formed by both approximate straight lines L21a and L21b.

  In addition, the calculation unit 3 performs image processing on each of the plurality of captured images captured by the second imaging unit 2 to determine the in-focus state of each captured image, and based on the determination result, the end of the threaded tube P Is calculated, and a second outer shape that is a partial outer shape of the screw along the direction of the screw axis A is calculated based on the calculated three-dimensional shape. That is, the calculation means 3 calculates the three-dimensional shape of the end portion of the threaded tube P by the focusing method, and calculates the second outer shape based on the calculated three-dimensional shape.

FIG. 5 is an explanatory diagram for explaining the principle of the focusing method executed by the calculation means 3.
As shown in FIG. 5, the second imaging unit 2 captures an image every time it moves a certain amount in the direction of the visual axis 21. In the state shown in FIG. 5, the focal point is at a point E on the flank surface P3 (hook-like flank surface P3h) of the threaded tube P, and the point E is on the image sensor e (pixel e) of the second image pickup means 2. An image is formed. If the local spatial frequency of the captured image captured in this state is extracted by image processing, the local spatial frequency in the image region around the pixel e increases. On the other hand, since the point F on the bottom surface P21 of the thread groove is not in focus, if it is in focus, in the image region around the image sensor f (pixel f) at the position where the point F is imaged. The local spatial frequency is reduced.
Then, if the second imaging means 2 moves in the direction of the visual axis 21 from the state shown in FIG. 5 and comes close to the threaded tube P by the distance H shown in FIG. In the captured image, the local spatial frequency in the image region around the pixel f increases, and conversely, the local spatial frequency in the image region around the pixel e decreases.
Accordingly, image processing for extracting a local spatial frequency is performed on each of the plurality of captured images captured each time the second imaging unit 2 is moved by a certain amount, and each pixel constituting each captured image is determined according to the size of the local spatial frequency. If the in-focus state is determined, it is possible to calculate the coordinates in the direction of the visual axis 21 of the end point of the threaded tube P corresponding to each pixel. That is, the three-dimensional shape of the end portion of the threaded tube P can be calculated based on the determination result of the focused state. As the image processing for extracting the local spatial frequency, various known image processing algorithms such as two-dimensional Fourier transform can be applied.
In addition, as an apparatus for calculating the three-dimensional shape of a subject by the focusing method, an apparatus having an imaging field of view of about 4 mm × 4 mm and a movement span of about 25 mm is commercially available (for example, “Optical non-contact three-dimensional manufactured by Aricona Co., Ltd.). Therefore, it is also possible to apply a commercially available device as a part of the second imaging means 2 and the calculation means 3 of the present embodiment.

FIG. 6 is an explanatory diagram for explaining a method of calculating the second outer shape C <b> 2 executed by the calculation means 3.
As shown in FIG. 6A, the calculation means 3 first calculates the three-dimensional shape of the end of the threaded tube P by the focusing method as described above. Note that the X axis shown in FIG. 6 is a direction substantially along the screw axis A of the threaded tube P. The Y axis is a direction orthogonal to the X axis and substantially along the tube circumferential direction. The Z axis is orthogonal to the X axis and the Y axis, and is generally along the tube diameter direction. The three-dimensional shape calculated by the calculation means 3 is represented as point group data that is a combination of X-axis coordinates, Y-axis coordinates, and Z-axis coordinates.

Next, as shown in FIG. 6B, the calculation means 3 extracts point cloud data in the vicinity of the second surface M. Specifically, among the point group data constituting the above three-dimensional shape, Y-axis coordinates having some X-axis coordinates (10 points in the example shown in FIG. 6B, X = X1 to X10). And a combination of Z-axis coordinates. In other words, the sectional shape of the YZ plane passing through each X-axis coordinate is extracted. This cross-sectional shape is approximated by a quadratic function (Z = aY ² + bY + c) or a circle (Z = (R ² − (Y−a) ² ) ^1/2 + b) (a, b, c, and R are constants) To do. In this approximation, X = Xn (n is an integer) point cloud data having a large approximation error is data including a thread R portion, a screw bottom R portion, and the like, and therefore needs to be excluded from the approximation calculation. . Then, for the cross-sectional shape of each YZ plane (a combination of the Y-axis coordinate and the Z-axis coordinate having each X-axis coordinate), a point where the Z-axis coordinate in the approximated quadratic function or approximate circle is maximum is extracted, and each maximum An approximate straight line B (Y = Yc, Yc is a constant) that minimizes the sum of squares of the difference between the point and the Y-axis coordinate is calculated.

  Since the approximate straight line B may be considered as a straight line included in the second surface M including the screw axis A, by extracting the Z-axis coordinates on the approximate straight line B, it is shown in FIG. As described above, it is possible to calculate the second outer shape C2 which is a partial outer shape of the screw along the direction of the screw axis A cut by the second surface M. In the second outline C2 shown in FIG. 6C, the part indicated by a solid line is a calculated outline, and the part indicated by a broken line is an outline that actually exists but is not calculated. The second outer shape C2 can include a hook-shaped flank surface P3h and a screw bottom R portion P4. It is also possible to include a thread top surface P11.

  As described above, the calculation means 3 calculates the three-dimensional shape of the end of the threaded tube P by the focusing method, and calculates the second outer shape C2 based on the calculated three-dimensional shape. According to the focusing method, a three-dimensional shape can be calculated with high resolution. Therefore, unlike a measurement using a conventional contact probe, a hook-like flank can be used even when measuring on a production line for a threaded tube P. A large number of three-dimensional coordinate points in a certain range such as the surface P3h can be detected at a time. For this reason, the influence of particle adhesion is suppressed and stable measurement is possible. In addition, unlike the measurement using the conventional contact probe, the screw bottom R portion P4 can be measured because the contact diameter is not limited.

  The calculating means 3 calculates the thread shape of the threaded tube P based on the calculated second outer shape C2. For example, the calculation means 3 linearly approximates the point cloud data corresponding to the hook-shaped flank surface P3h based on the second outer shape C2, and calculates the inclination of the approximate straight line, thereby calculating the angle of the hook-shaped flank surface P3h. It is possible to calculate. The angle of the hook-shaped flank surface P3h that can be directly calculated from the second outer shape C2 shown in FIG. 6C is an angle formed by the hook-shaped flank surface P3h and the bottom surface P21 of the thread groove. However, in the present embodiment, as described above, since the screw shaft A can be detected from the first outer shape C1, the angle β formed by the hook-shaped flank surface P3h and the perpendicular N of the screw shaft A (see FIG. 1). It is also possible to calculate the angle of the hook-shaped flank surface P3h. That is, the angle formed between the screw shaft A and the bottom surface P21 of the screw groove is calculated based on the first outer shape C1, and the angle formed between the bottom surface P21 of the screw groove and the hook-shaped flank surface P3h is calculated based on the second outer shape C2. The angle formed by the hook-like flank surface P3h and the perpendicular N of the screw shaft A can be calculated by calculating the combination of both calculation results.

  Further, the calculation means 3 calculates the radius of curvature of the screw bottom R portion P4 by circularly approximating point group data corresponding to the screw bottom R portion P4 in the second outer shape C2 and calculating the radius of the approximate circle. Is possible.

  Furthermore, the calculation means 3 can also calculate a combined outer shape obtained by combining the first outer shape C1 and the second outer shape C2 by fitting a common part of the first outer shape C1 and the second outer shape C2.

FIG. 7 is an explanatory diagram for explaining a method of calculating a composite waveform executed by the calculation means 3.
As shown in FIG. 7, the common parts of the first outer shape C1 and the second outer shape C2 may include a thread top surface P11, a thread groove bottom surface P21, and a thread R portion P5. Examples of these fitting methods include the following procedures.
(1) The approximate straight line L11 is calculated by linearly approximating the point cloud data corresponding to the top face P11 of the thread of the first outer shape C1. Similarly, an approximate straight line L21 is calculated by linearly approximating point cloud data corresponding to the bottom surface P21 of the thread groove of the first outer shape C1.
(2) The sum of squares of the difference between the approximate straight line L11 and the point cloud data corresponding to the top surface P11 of the thread of the second outer shape C2, and the bottom surface P21 of the thread groove of the approximate straight line L21 and the second outer shape C2. The second outline C2 is rotated and translated with respect to the first outline C1 so that the sum total of the sum of squares of differences from the point cloud data is minimized.
(3) A point circle data corresponding to the thread R portion P5 of the second outer shape C2 is circularly approximated to calculate an approximate circle.
(4) Rotation / translation in (2) so that the sum of squares of the difference between the approximate circle in (3) and the point cloud data corresponding to the thread R portion P5 of the first outer shape C1 is minimized. The second outer shape C <b> 2 after being moved is translated along the approximate straight line 21.

  By the procedures (1) to (4), it is possible to calculate a combined outer shape in which the first outer shape C1 and the second outer shape C2 are combined. This composite waveform includes both flank surfaces P3. For this reason, the calculating means 3 can also calculate, for example, the thread width and the thread valley width based on the calculated composite outer shape.

  The calculating means 3 preferably calculates the phase of the screw thread based on the first outer shape C1, and determines the position of the second optical system 20 in the direction of the screw axis A based on the calculated phase of the screw thread. . Then, the drive mechanism to which the second illumination unit 1 and the second imaging unit 2 are attached may be driven so that the optical system 20 is at the determined position. Thereby, even if the 1st optical system 10 and the 2nd optical system 20 are arrange | positioned in the position spaced apart in the circumferential direction of the threaded pipe P like this embodiment, hook-like flank surface P3h and screw The second optical system 20 can be positioned at a position where the bottom R portion P4 can be measured. Hereinafter, the positioning of the second optical system 20 will be described in more detail with reference to FIGS. 8 and 9.

FIG. 8 is an explanatory diagram for explaining the influence of the imaging field of view of the second optical system 20 (second imaging means 2). FIG. 8A shows an example of an imaging field when an appropriate captured image is obtained, and FIG. 8B shows an example of an imaging field when an inappropriate captured image is obtained. In FIG. 8, the part indicated by the solid line is the part to be imaged, and the part indicated by the broken line is the part that is not imaged.
In the example shown in FIG. 8A, the center of the imaging field is substantially located at the center position in the height direction of the hook-shaped flank P3h, whereby the bottom surface P21 of the thread groove, the hook-shaped flank P3h, and the screw The top surface P11 of the mountain can be imaged at the same time. On the other hand, in the example shown in FIG. 8B, the captured image is discontinuous and only a part of the hook-shaped flank surface P3h can be captured. Therefore, it is preferable to position the second optical system 20 (second imaging means 2) so that an imaging field of view as shown in FIG.

FIG. 9 is an explanatory diagram for explaining a positioning method of the second optical system 20 (second imaging means 2).
As described above, the calculating means 3 calculates the thread phase based on the first outer shape C1. Specifically, as shown in FIG. 9, a hook located on the tube end face side from the center A1 of the imaging field of view of the first imaging unit 5b based on the first outer shape C1a obtained from the captured image of the first imaging unit 5b. A distance FS in the direction of the screw axis A to the flank surface P3 that is not shaped is calculated. In the present embodiment, this distance FS is used as a parameter corresponding to the thread phase.
Here, PP represents the thread width as a preset set value. Further, let R be the outer radius of the threaded tube P. Moreover, let the pitch of a screw be PT. Furthermore, when the center position in the height direction of the hook-shaped flank surface P3h is shifted by an angle δ (see FIG. 3) in the pipe circumferential direction, it is assumed that it is shifted by S in the screw shaft A direction. In this case, the second imaging means 2 obtains an appropriate imaging field as shown in FIG. 8A (as shown in FIG. 9, the center A2 of the imaging field is the center position of the hook-shaped flank surface P3h in the height direction). The position of the center A2 of the imaging field of the second imaging unit with respect to the position of the center A1 of the imaging field of the first imaging unit 5b is expressed by the following equation in the direction of the screw axis A. Just shift it.
L = FS + PP-S
= FS + PP-R · tanγ
= FS + PP-R. (1-cos.delta.). PT / (2.R)
The computing unit 3 computes L based on the above formula, whereby a suitable position of the second optical system 20 (second imaging unit 2) in the direction of the screw axis A can be determined.

  According to the screw shape measuring apparatus 100 according to the present embodiment, a screw shape that can be measured by the conventional optical projection method by the first optical system 10 is used, and a conventional optical projection method or a contact probe that is used by the second optical system 20 is used. A thread shape that is difficult to measure can be measured on the production line of the threaded tube P.

  Hereinafter, a preferable setting example of the angle of the visual axis 21 of the second imaging unit 2 and the angle of the optical axis 11 of the second illumination unit 1 constituting the screw shape measuring apparatus 100 according to the present embodiment will be described.

<An angle of the visual axis 21 of the second imaging unit 2>
FIG. 10 is a diagram illustrating an example of the relationship between the angle of the visual axis 21 of the second imaging unit 2 and the imaging resolution of the bottom surface P21 and the flank surface P3 of the thread groove. As shown in FIG. 2A, the abscissa of FIG. 10 shows the visual axis 21 of the second image pickup means 2 and the screw axis A when viewed from the direction orthogonal to the second surface M including the screw axis A. An angle α formed with the perpendicular N is shown. FIG. 10 shows the visual axis 21 when it is assumed that the bottom surface P21 of the thread groove is parallel to the screw axis A and the bottom surface P21 of the thread groove and the flank surface P3 form an angle of 90 °. This is the relationship between the angle α and the imaging resolution of each of the surfaces P21 and P3.
As shown in FIG. 10, when α = 45 °, the imaging resolution of the bottom surface P21 of the thread groove is equal to the imaging resolution of the flank surface P3 (in FIG. 10, the imaging resolution at this time is 1). As it deviates from this angle, the imaging resolution of either one increases. In order to prevent any one of the imaging resolutions from deteriorating (not increasing) more than twice, it is necessary to set the range of 20 ° ≦ α ≦ 70 °.

However, in a threaded tube P such as an actual oil well tube, when the flank surface P3 is a hook-shaped flank surface P3h, the angle of the hook-shaped flank surface P3h with respect to the bottom surface P21 of the thread groove is about 85 to 87 °. . Further, the bottom surface P21 of the thread groove is a tapered screw inclined (about 1.8 °) with respect to the screw axis A, or the screw axis A fluctuates (± 3 °) during actual measurement. In view of the above, it is necessary to set a range of about 25 ° ≦ α ≦ 65 ° so that one of the imaging resolutions does not deteriorate (not increase) by more than twice.
Further, when the focusing method is applied, generally, the second imaging means 2 and the threaded tube P are separated by a short distance of about several tens of millimeters in the direction of the visual axis 21, so that the second imaging means 2 is screwed. In order to avoid the possibility of colliding with the attached tube P, α is preferably as small as possible. For this reason, when there is no priority between the imaging resolution of the bottom surface P21 of the thread groove and the imaging resolution of the flank surface P3, it is preferable to set 25 ° ≦ α ≦ 45 °.

<Angle of the optical axis 11 of the 2nd illumination means 1>
As shown in FIG. 2A, the optical axis 11 of the second illuminating means 1 is first relative to the perpendicular N of the screw axis A when viewed from a direction orthogonal to the second surface M including the screw axis A. 2 Located on the same side as the visual axis 21 of the imaging means 2. In the example shown in FIG. 2A, since the second imaging means 2 images the hook-shaped flank surface located on the side opposite to the tube end face, the visual axis 21 of the second imaging means 2 is perpendicular to the screw axis A. It is inclined to the side opposite to the tube end surface side with respect to N (inclined counterclockwise in FIG. 2A). For this reason, the optical axis 11 of the second illumination means 1 is also inclined to the opposite side to the tube end face side with respect to the perpendicular N of the screw axis A (inclined counterclockwise in FIG. 2A). .
Here, when viewed from a direction orthogonal to the second surface M including the screw axis A, an angle formed by the optical axis 11 of the second illumination unit 1 and the perpendicular N of the screw axis A is defined as θ. Further, as shown in FIG. 2B, the angle formed by the optical axis 11 of the second illumination unit 1 and the perpendicular N of the screw shaft A when viewed from the direction of the screw shaft A is φ.

  FIG. 11 shows an example of the result of evaluating the defect rate when the angle α of the second imaging unit 2 is 30 ° and the angles θ and φ of the optical axis 11 of the second illumination unit 1 are changed to various values. FIG. FIG. 11A shows the result when the optical axis 11 of the second illumination unit 1 shown in FIG. 2B is tilted counterclockwise with respect to the perpendicular N of the screw axis A. FIG. FIG. 11B shows the results when the optical axis 11 of the second illumination means 1 shown in FIG. 2B is tilted clockwise with respect to the normal N of the screw axis A. FIG. In FIG. 11, in order to distinguish clockwise and counterclockwise, for convenience, the counterclockwise angle φ is set to a positive value (FIG. 11A), and the clockwise angle φ is set to a negative value (FIG. 11). (B)). In addition, the defect rate means that the in-focus state cannot be determined due to the problem of the incident light quantity of reflected light being too large or too small in the imaging device (approximately 4 million pixels) provided in the second imaging means 2 to have a three-dimensional shape. The ratio of pixels that could not be calculated is shown.

As can be seen from FIG. 11, when 40 ° ≦ θ ≦ 65 °, the defect rate is 2.0% or less regardless of the angle φ.
Therefore, it is preferable to set 40 ° ≦ θ ≦ 65 °.
As can be seen from FIG. 11A, when 45 ° ≦ θ ≦ 60 ° and 55 ° ≦ φ ≦ 60 °, the defect rate is 0.2% or less. Similarly, as can be seen from FIG. 11B, even when 45 ° ≦ θ ≦ 60 ° and −60 ° ≦ φ ≦ −55 °, the defect rate is 0.2% or less. Yes.
Therefore, in addition to the condition of 45 ° ≦ θ ≦ 60 °, it is more preferable to set the angle φ (absolute value) to 55 ° ≦ φ ≦ 60 ° without distinction between clockwise and counterclockwise.

FIG. 12 shows a screw shape measuring apparatus 100 according to the present embodiment. As a screw shape, in addition to the angle of the flank surface P3 (hook-like flank surface P3h) and the radius of curvature of the screw bottom R portion P4, An example of the result of calculating the curvature radius of the R part is shown. In FIG. 12, the measurement result by the screw shape measuring apparatus 100 according to the present embodiment was evaluated by the difference from the measured value by the needle type shape meter (Mitutoyo Contracer CV-1000N2: accuracy ± about 3.5 μm). The angle θ was set to 55 °, the angle φ was set to 60 °, and the angle α was set to 30 °.
As shown in FIG. 12, according to the screw shape measuring apparatus 100 according to the present embodiment, it has been found that any of the above screw shapes is within a range of accuracy to withstand practical use.

DESCRIPTION OF SYMBOLS 1 ... 2nd illumination means 2 ... 2nd imaging means 3 ... Calculation means 4 ... 1st illumination means 5 ... 1st imaging means 10 ... 1st optical system 11 ... Optical axis 20 ... second optical system 21 ... visual axis 100 ... screw shape measuring device P ... threaded tube

Claims (4)

A device for measuring the shape of a screw formed at the end of a threaded tube,
A first optical system that illuminates an end of the threaded tube and detects and images light leaking from the screw;
A second optical system that illuminates an end of the threaded tube and images the illuminated end a plurality of times by changing a focal position;
Computation means for computing the shape of the screw formed at the end of the threaded tube based on the captured image captured by the first optical system and the second optical system,
The first optical system illuminates the end of the threaded tube from a direction substantially orthogonal to the first surface including the threaded shaft as viewed from the direction of the threaded shaft of the threaded tube. And a first imaging means that is disposed opposite to the first illumination means with respect to the first surface including the screw shaft and detects and leaks light leaking from the screw,
The second optical system includes second illuminating means for illuminating the end of the threaded tube, and second imaging means for imaging the end of the threaded tube illuminated by the second illuminating means. ,
The second imaging means is disposed along a second surface including the screw shaft of the threaded tube, has a visual axis in a direction inclined with respect to both the screw shaft and a perpendicular to the screw shaft, Change the position and image the end of the threaded tube multiple times,
The second illumination means is disposed at a position away from the second surface including the screw shaft, and has an optical axis inclined with respect to both the perpendicular of the screw shaft and the visual axis of the second imaging means. And
The computing means is
By performing image processing on the captured image captured by the first imaging unit, a first external shape that is a partial external shape of the screw along the screw axis direction is calculated,
Each of the plurality of captured images captured by the second imaging means is subjected to image processing to determine the in-focus state of each captured image, and the three-dimensional shape of the end of the threaded tube is calculated based on the determination result. , Based on the calculated three-dimensional shape, to calculate a second outer shape that is a partial outer shape of the screw along the screw axis direction,
Based on the calculated first outer shape and second outer shape, the thread shape of the threaded tube is calculated.
An apparatus for measuring the thread shape of a threaded tube. The computing means is
Based on the first outer shape, the screw shaft is detected, and an angle formed by the screw shaft and the bottom surface of the screw groove is calculated.
Based on the second outer shape, the angle formed by the bottom surface of the thread groove and the flank surface is calculated,
Based on the calculated angle formed between the screw shaft and the bottom surface of the screw groove and the calculated angle formed between the bottom surface of the screw groove and the flank surface, the angle formed between the flank surface and the perpendicular of the screw shaft is calculated. The thread shape measuring apparatus for a threaded tube according to claim 1, wherein The computing means is
By fitting a common part of the first outer shape and the second outer shape, a combined outer shape obtained by combining the first outer shape and the second outer shape is calculated,
3. The thread shape measuring device for a threaded tube according to claim 1, wherein a thread width and a thread valley width are calculated based on the calculated composite outer shape. The computing means is
Based on the first outer shape, the thread phase is calculated,
4. The thread shape measuring device for a threaded tube according to claim 1, wherein the position of the second optical system in the screw shaft direction is determined based on the calculated phase of the screw thread. 5. .

Images