Method for Measuring the Length of Steel Pipe

Abstract

The present invention belongs to the technical field of length measurement, and particularly relates to a method for measuring the length of a steel pipe. The equipment required for measurement is conveniently arranged and has a wide range of applications. A light source and a camera are respectively arranged on both sides of the transfer track. The outgoing light of the light source will form a bright spot at the end face of the steel pipe, so that the end of the steel pipe can be marked in real time and clearly on the conveying path of the steel pipe. In the picture taken by the camera, the bright spot is the area where the steel pipe is marked by the light source, which greatly reduces the difficulty of identifying the end face of the steel pipe, can greatly improve the speed and reliability of image analysis, and thus ensure the accuracy of steel pipe length measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field of length measurement, and particularly relates to a method for measuring the length of steel pipes. Background Art

[0002] In the field of automated production and processing of steel pipes, such as in scenarios like the steel pipe loading platform before furnace charging, cooling beds, and the arrival inspection and shipment inspection of pipes and bars, it is necessary to obtain the length information of multiple steel pipes in real time. Currently, the measurement of steel pipe length can be divided into contact measurement and non-contact measurement according to the measurement method. Among them, contact measurement has the characteristics of low measurement efficiency and limited measurement scenarios, and non-contact measurement is mostly used at present.

[0003] The following is an explanation of the prior art and its advantages and disadvantages:

[0004] 1. Chinese Patent CN115112024A discloses an algorithm for texture positioning in the process of measuring the length of wire. This method requires texture labels to be pasted at both ends of the wire to be measured, and then a handheld terminal takes one or more photos of the wire to be measured. Then, the length of the wire is calculated based on the wire photos. This method identifies the two ends of the wire based on texture labels and then calculates the length of the wire. The calculation accuracy of the wire length is greatly affected by the pasting position of the texture labels, and the accuracy of manual pasting of texture labels cannot be guaranteed, resulting in low accuracy of wire length identification.

[0005] 2. Chinese Patent CN217331047U discloses a vision-based cable length measurement system. This system uses a high-speed dot spraying system to spray color marking points on the cable. When the color marking points pass through the sensor, it triggers the image acquisition and processing system. The image acquisition and processing system calculates the length of the cable between two color marking points based on the color marking points. Then, the cable passes through a marking point wiping device to erase the ink. This method uses a high-speed dot spraying system to spray color marking points to mark the measurement endpoints of the cable length, and can only measure single cables sequentially, with slow measurement speed, and the use and maintenance costs of the high-speed dot spraying system, wiping device, and spraying ink are high.

[0006] 3. Chinese Patent CN205175355U discloses a device for measuring the specified length of round steel. When this device is in use, the round steel to be measured needs to be transported to the alignment roller table. After that, the alignment roller table rotates to drive one end of the round steel to align at the alignment baffle. Then, under the oblique illumination of the light source, the other end is photographed. The collected image is segmented and fitted to obtain the minimum circumscribed rectangle of the round steel object. Then, the rectangle angle is calculated and the coordinates of the midpoint of the measured side width are measured. These coordinates are used as the vertex coordinates of the round steel, and the distance between the vertex coordinates and the aligned end of the round steel is calculated to obtain the length of the round steel to be measured. This method requires transporting the round steel to a specific measurement station and driving the round steel to abut against the alignment baffle. The devices required for measurement are complex and time-consuming, which affects production efficiency. In addition, the accuracy of this method highly depends on the accuracy of image segmentation. However, the processing site has complex conditions and many interference factors, making it difficult to ensure the reliability of image segmentation. Further, this device cannot measure shorter round steel because the alignment baffle cannot be close to the acquisition end. After one end of the round steel with a small length abuts against the alignment baffle, if the end near the acquisition end is outside the acquisition range, it cannot be measured. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for measuring the length of steel pipes, which can perform fast on-line measurement on the transportation path of steel pipes with high measurement accuracy.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A method for measuring the length of steel pipes, on one side of the transportation track, there are a first light source and a first camera, and on the other side, there are a second light source and a second camera corresponding to them. The first light source and the second light source are line light sources or surface light sources. The light emission directions of the first light source and the second light source are coplanar. The lens of the first camera points to the illumination area of the first light source, and the lens of the second camera points to the illumination area of the second light source;

[0010] In the debugging stage, the first camera and the second camera establish a world coordinate system with the length and width directions of the transportation track as axes,

[0011] In the on-line detection stage, the first camera collects an image of one end of the steel pipe to be measured, and the second camera collects an image of the other end of the steel pipe to be measured. The light spot formed by the irradiation of the first light source / second light source on the end face of the single steel pipe to be measured in the image is recognized to obtain the end face coordinates of the steel pipe to be measured. Based on the conversion relationship between the first camera / second camera and the world coordinate system, the world coordinates of the corresponding end of the steel pipe to be measured are obtained. The length of the steel pipe to be measured is calculated based on the world coordinates of both ends of the same steel pipe to be measured photographed by the first camera and the second camera at the same moment.

[0012] Compared with the prior art, the present invention has the following technical effects: The equipment layout required for measurement is convenient, and it can be arranged on both sides of any conveying path of the steel pipe, with a wide range of applications, and the installation and layout are convenient. The emitted light of the light source will form a bright spot at the end face of the steel pipe, so that the end of the steel pipe can be marked in real time and clearly on the conveying path of the steel pipe. In the camera shooting image, the bright spot is the area where the steel pipe is marked by the light source, which greatly reduces the difficulty of identifying the end face of the steel pipe, and can greatly improve the speed and reliability of the analysis of the image, thus ensuring the accuracy of the steel pipe length measurement. After the steel pipe continues to move away from the light source irradiation area, the mark is eliminated, and the mark on the end face of the steel pipe is traceless, reliable and convenient. Description of the Drawings

[0013] The following briefly describes the content expressed in each drawing of this specification and the marks in the drawings:

[0014] Figure 1 is a three-dimensional schematic diagram of Embodiment 1;

[0015] Figure 2 is a top view schematic diagram of Embodiment 2;

[0016] Figure 3 is a schematic diagram of the steel pipe detection area on the image of Embodiment 1;

[0017] Figure 4 is a schematic diagram of calibrating the direction vector in the steel pipe detection area in the debugging stage of Embodiment 1;

[0018] Figure 5 is a schematic diagram of identifying the steel pipe image area in the on-line detection stage of Embodiment 1.

[0019] In the figure: A. Steel pipe to be measured, B. Bright spot, 11. First light source, 12. First camera, 21. Second light source, 22. Second camera, 30. Transfer track. Detailed Description of the Invention

[0020] The following further details the specific embodiments of the present invention in conjunction with the drawings and through the description of the embodiments.

[0021] A method for measuring the length of a steel pipe, a first light source 11 and a first camera 12 are arranged on one side of the transfer track 30, and a second light source 21 and a second camera 22 are arranged correspondingly on the other side. The first light source 11 and the second light source 21 are linear light sources or surface light sources, and the light emission directions of the two light sources are coplanar. The lens of the first camera 12 points to the irradiation area of the first light source 11, and the lens of the second camera 22 points to the irradiation area of the second light source 21, so as to be able to capture the end image of the steel pipe A to be measured.

[0022] In this embodiment, the first light source 11 and the second light source 21 are laser light sources. The laser spots formed on the end face of the steel pipe A are obvious and easy to identify, and are applicable to both high-temperature red steel and low-temperature cold steel.

[0023] The first camera 12 and the second camera 22 can be cameras with a single lens and a photosensitive element. However, the image acquisition area of such cameras is relatively single. In actual production, although the steel pipes A on the transfer track 30 are arranged in parallel, the lengths of the steel pipes A are different, or the positions of the ends of the steel pipes A will shift. To ensure the length measurement of each steel pipe A on the transfer track 30, the first camera 12 or the second camera 22 or both the first camera 12 and the second camera 22 can use a camera with multiple lenses or lens groups, or can also be a multi-functional camera composed of multiple unit cameras, with the criterion that there are multiple image acquisition areas and the acquisition areas can cover the areas on the transfer track 30 that need to be detected. In this way, the image acquisition areas of each lens or unit camera are different, and can cover multiple areas in the width direction of the transfer track 30, thus meeting the measurement requirements of the steel pipe A.

[0024] In this embodiment, the first camera 12 includes three lenses with different focal lengths, and a photosensitive element is provided corresponding to each lens. The image acquisition areas of the lenses are arranged in sequence in the width direction of the transfer track 30.

[0025] After the light source and the camera are installed, in the debugging stage, the first camera 12 and the second camera 22 establish a world coordinate system with the length and width directions of the transfer track 30 as axes, that is, obtain the conversion relationship between the coordinates of each pixel in the images collected by the first camera 12 and the second camera 22 and the world coordinates.

[0026] In the on-line detection stage, the first camera 12 collects an image of one end of the steel pipe A to be measured, and the second camera 22 collects an image of the other end of the steel pipe A to be measured. Taking the first light source 11 and the first camera 12 as an example, identify the spot formed by the irradiation of the first light source 11 on the end face of the single steel pipe A to be measured in the image, obtain the end face coordinates of the steel pipe A to be measured, and then, based on the conversion relationship between the first camera 12 and the world coordinate system, obtain the world coordinates of the end of the steel pipe A to be measured adjacent to the first light source 11 and the first camera 12. Similarly, the world coordinates of the end of the steel pipe A to be measured adjacent to the second light source 21 and the second camera 22 can also be obtained. Then, based on the world coordinates of both ends of the same steel pipe A to be measured taken by the first camera 12 and the second camera 22 at the same moment, the length of the steel pipe A to be measured can be calculated.

[0027] As shown in the appendix Figure 4In the illustrated embodiment, the emitted light of the first light source 11 forms a light spot at the end face of the steel pipe A and forms light rays on the pipe body of the steel pipe A, and the light spot is connected to the light rays. In order to identify the light spots formed at the end face adjacent to the light source side on the same measured steel pipe A, the following image processing method is adopted in this embodiment: identify the image regions of each steel pipe A in the image collected by the identification camera. As shown in the attached Figure 5 Two steel pipes A are identified in the image shown. Identify the image region of the bright spot B irradiated by the light source in the image. As shown in the attached Figure 4 In the image shown, there are 4 bright spots B. Find the pixel points of all the bright spots B within the image region of a single steel pipe A, and average a number of pixels at the leftmost end of the pixel point set, then the end face coordinates of the steel pipe A can be obtained. It should be noted that as can be seen from the attached Figure 4 In the image shown, the left end of the bright spot B is located at the end face of the steel pipe A. Therefore, a number of pixels at the leftmost end of the pixel point set are selected for analysis to obtain the coordinates of the steel pipe A adjacent to the end face. In other embodiments, the pixel points used for analyzing and obtaining the coordinates can be selected in other ways.

[0028] In order to further optimize the steel pipe length measurement method in this embodiment, a light source, a camera and a processing system are arranged on the downstream conveying path of the existing shaping mechanism on the steel pipe A processing production line, so that the measurement of the length of the steel pipe A can be more conveniently realized.

[0029] As shown in the attached Figure 1 、 2 Shown, there is a shaping mechanism upstream of the first light source 11 and the second light source 21 on the transfer track 30. After the shaping mechanism shapes the steel pipe A, each steel pipe A is arranged in parallel on the material bearing surface of the transfer track 30. That is to say, the steel pipes A to be measured are arranged in parallel. Further, in this embodiment, the length direction of each steel pipe A is parallel to the width direction of the transfer track 30. The following will be described by taking the first light source 11 and the first camera 12 as examples:

[0030] After the first light source 11 and the first camera 12 are fixedly installed, it enters the debugging stage. The debugging stage includes at least the following two steps.

[0031] Step 1: Place a marker in the irradiation area of the first light source 11, and the first camera 12 collects an image including the marker and the transfer track 30, and obtains the conversion matrix from the coordinates of each pixel in the image collected by the first camera 12 to the world coordinate system , where the track length direction is the x-axis and the width direction is the y-axis. The marker can be a strip-shaped rod placed along the length direction of the transfer track 30 and a strip-shaped rod placed along the width direction of the transfer track 30, or a plate or block whose outer contour conforms to the length direction and width direction of the track 30, etc.;

[0032] Step 2: After being shaped, steel pipe A is conveyed by the transfer track 30 to the irradiation area of the first light source 11. The first camera 12 captures an image including the end part and partial pipe body image of steel pipe A, and an operator calibrates the direction vector Dir of the measured steel pipe A in this image. As shown in the appendix Figure 1 In this embodiment, as shown, the camera lens obliquely points downward to the irradiation areas of the first light source 11 and the second light source 21 at the transfer track 30 to obtain the required image. In other embodiments, the camera lens can also be arranged below the light source, and the camera lens obliquely points upward to the irradiation areas of the first light source 11 and the second light source 21 at the transfer track 30. As shown in the appendix Figure 4 As shown, the direction vector Dir can show which end of the bright spot B is adjacent to the light source, thus providing a basis for the analysis of the detection image in the online detection stage.

[0033] After entering the online detection stage, the first camera 12 captures the end image of the measured steel pipe A. Identify the image area of each steel pipe A in the image , where is the set of polygon vertices of the outer contour of the nth steel pipe A in the image, and N is the number of interesting objects segmented. Identify the image area of the bright spot B irradiated by the light source in the image , where is the set of polygon vertices of the mth laser contour, and M is the number of interesting regions extracted. Find all the pixel points located within the image area of the same steel pipe A in the image area of the bright spot B irradiated by the light source. Based on the direction vector Dir, select V pixel sets Dimg = in the proximal region closest to the light source in this pixel point set, where V is a constant and V is valued according to requirements. In this embodiment, V = 50. Average these V pixels to obtain the image coordinate , which represents the position of the proximal end face of the nth steel pipe A in the image in the image. Based on the transformation matrix obtain the world coordinate of the end face of the nth steel pipe A close to the first camera 12 .

[0034] The second light source 21 and the second camera 22 use the same debugging method and online detection method to obtain the world coordinate of the end face of the nth steel pipe A close to the second camera 22. Since the x coordinate in the world coordinate is the coordinate in the length direction of the transfer track 30 and the y coordinate is the coordinate in the width direction of the transfer track 30, the length of the nth steel pipe is .

[0035] Furthermore, in order to avoid the posture of the measured steel pipe A changing due to external forces during the conveying process, a verification step is added, that is, the nth steel pipe obtains the verification length according to the following calculation formula , and compare with If the difference between the two is within the specified range, it is determined that the detection value of the steel pipe is valid; if the difference between the two exceeds the specified range, it is determined that the detection value of the steel pipe is invalid.

[0036] As shown in the appendix Figure 4 As shown, the first light source 11 and the second light source 21 are coplanar, which can avoid bright spots B formed by the irradiation of two different light sources on the pipe body of the steel pipe A to be measured in the image collected by the camera, thereby affecting the recognition of the end face of the steel pipe A. To ensure that the outgoing light of the light source can irradiate on the end face of the steel pipe A to be measured, in the preferred solution, the plane where the outgoing light of the two light sources is located is parallel to the material carrying surface of the transfer track 30, and the distance between the plane where the outgoing light of the two light sources is located and the material carrying surface is less than the outer diameter of the steel pipe A to be measured.

[0037] As shown in the appendix of this embodiment Figure 2 As shown, the first light source 11 and the second light source 21 are arranged oppositely, and the connection line of their outgoing directions is arranged at an angle with the width direction of the transfer track 30. In this way, the light source can irradiate on the end faces of more steel pipes A, that is, one light source can mark multiple steel pipes A. By collecting the images of all the marked steel pipes A, the length of multiple steel pipes A can be measured at the same time, thereby further improving the length measurement efficiency of the steel pipe A. The lens axes of the first camera 12 and the second camera 22 are arranged at an acute angle with the width direction of the transfer track 30, and the collected image is as shown in the appendix Figure 5 As shown, in this way, oblique shooting can collect more images of the steel pipe A, and at the same time, it is also convenient to identify the adjacent endpoints of the bright spot B irradiated by the light source.

[0038] To eliminate the interference of the image in the non-detection area and reduce the calculation amount, during the debugging stage, after the first camera 12 collects an image containing the end part and a partial pipe body image of the steel pipe A, as shown in the appendix Figure 3 As shown, manually calibrate the steel pipe detection area t on the image, and the collected image is as shown in the appendix Figure 4 As shown, mask processing is performed on the image area outside the steel pipe detection area t.

Claims

1. A method for measuring the length of a steel pipe, characterized in that: On one side of the transfer track (30), a first light source (11) and a first camera (12) are provided. On the other side, a second light source (21) and a second camera (22) are correspondingly provided. The first light source (11) and the second light source (21) are linear light sources or surface light sources. The light-emitting directions of the first light source (11) and the second light source (21) are coplanar. The lens of the first camera (12) points to the irradiation area of the first light source (11), and the lens of the second camera (22) points to the irradiation area of the second light source (21). In the debugging stage, the first camera (12) and the second camera (22) establish a world coordinate system with the length and width directions of the transfer track (30) as axes. In the online detection stage, the first camera (12) acquires an image of one end of the steel pipe (A) to be measured, and the second camera (22) acquires an image of the other end of the steel pipe (A) to be measured. Identify the light spots formed by the irradiation of the first light source (11) / second light source (21) at the end face of a single steel pipe (A) to be measured in the image, obtain the end face coordinates of the steel pipe (A) to be measured, and based on the conversion relationship between the first camera (12) / second camera (22) and the world coordinate system, obtain the world coordinates of the corresponding end of the steel pipe (A) to be measured. Based on the world coordinates of both ends of the same steel pipe (A) to be measured taken by the first camera (12) and the second camera (22) at the same moment, calculate the length of the steel pipe (A) to be measured. In the online detection stage, the first camera (12) / second camera (22) acquires an end image of the steel pipe (A) to be measured, identifies the image areas of each steel pipe (A) and the image area of the light spot (B) irradiated by the light source in the image, finds the pixel points of all light spots (B) located within the image area of a single steel pipe (A), and selects several pixel points close to the first light source (11) / second light source (21) side for analysis, then the end face coordinates of the single steel pipe (A) can be obtained. An shaping mechanism is provided upstream of the first light source (11) and the second light source (21) on the transfer track (30). After the shaping mechanism shapes the steel pipes (A), the steel pipes (A) are arranged in parallel on the material bearing surface of the transfer track (30). After the first light source (11) and the first camera (12) are fixedly installed, the debugging stage is entered. Place a marker in the illumination area of the first light source (11). The first camera (12) acquires an image including the marker and the transfer track (30), and obtains a conversion matrix from the pixel coordinates of each pixel in the image acquired by the first camera (12) to the world coordinate system , where the length direction of the track is the x-axis and the width direction is the y-axis After being shaped, the steel pipe (A) is conveyed by the transfer track (30) to the irradiation area of the first light source (11). The first camera (12) acquires an image including the end and partial body image of the steel pipe (A), and manually calibrates the direction vector Dir of the steel pipe (A) to be measured in this image. Entering the online detection stage, the first camera (12) acquires an end image of the steel pipe (A) to be measured. Identify the image regions of each steel pipe (A) , where is the set of polygon vertices of the outer contour of the nth steel pipe (A) in the image, and N is the number of objects of interest segmented Identify the image area of the bright spot (B) illuminated by the light source , where is the set of polygon vertices of the m-th laser profile, and M is the number of regions of interest extracted Find all the pixel points located within the image region of the same steel pipe (A) in the image region of the bright spot (B) irradiated by the light source. Based on the direction vector Dir, select V pixel sets Dimg that are closest to the proximal region, where V is a constant. Average these V pixels to obtain the image coordinates , and these image coordinates represent the position of the proximal end face of the nth steel pipe (A) in the image. Based on the transformation matrix , obtain the world coordinates of the end face of the nth steel pipe (A) close to the first camera (12) = = ; The second light source (21) and the second camera (22) use the same debugging and on-line detection method to obtain the world coordinates of the end face of the nth steel pipe (A) close to the second camera (22). , then the length of the nth steel pipe is .

2. The method for measuring the length of a steel pipe according to claim 1, characterized in that: The first camera (12) or the second camera (22) has two or more image acquisition areas, and the image acquisition areas are arranged in sequence in the width direction of the transfer track (30).

3. The method for measuring the length of a steel pipe according to claim 1, characterized in that: The plane where the outgoing light rays of the first light source (11) and the second light source (21) are located is parallel to the material bearing surface of the transfer track (30), and the distance between the plane where the outgoing light rays of the first light source (11) and the second light source (21) are located and the material bearing surface is less than the outer diameter of the steel pipe (A) to be measured.

4. The method for measuring the length of a steel pipe according to claim 1, wherein: The camera lens points obliquely downward or obliquely upward to the irradiation areas of the first light source (11) and the second light source (21) at the transfer track (30).

5. The method for measuring the length of a steel pipe according to claim 4, characterized in that: The lens axes of the first camera (12) and the second camera (22) are arranged at an acute angle with the width direction of the transfer track (30).

6. The method for measuring the length of a steel pipe according to claim 1, characterized in that: In the debugging stage, after the first camera (12) acquires an image containing the end part and a partial pipe body image of the steel pipe (A), the steel pipe detection area t is manually calibrated on the image, and the image area outside the steel pipe detection area t is masked.

7. The method for measuring the length of a steel pipe according to claim 1, characterized in that: The verification length of the nth steel pipe is obtained according to the following calculation formula , compare with . If the difference between the two is within the specified range, the inspection value of the steel pipe is determined to be valid; if the difference between the two exceeds the specified range, the inspection value of the steel pipe is determined to be invalid.

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