Large-diameter part corner measurement device based on machine vision and its measurement method

Abstract

The present invention relates to the field of rotary angle measurement of large-diameter parts, and discloses a rotary angle measurement device and a measurement method for large-diameter parts based on machine vision, including a rotary angle measurement reference plate and a binocular vision measurement mechanism. The rotary angle measurement reference plate is fixedly connected to the large-diameter part and rotates with the large-diameter part; the binocular vision measurement mechanism is connected to the upper end of the main column of the machine body and is placed directly above the rotary angle measurement reference plate. By continuously collecting the calibration circle images in the rotary angle measurement reference plate through the binocular vision measurement mechanism, the relationship between the center of the camera's field of view and the physical coordinates of the center of the calibration circle in the rotary angle measurement reference plate is established, and the rotary angle of the large-diameter part is obtained through the angle turned by the line connecting the centers of the fields of view of the two cameras in the measurement physical coordinate system. It obtains the reinstallation of the large-diameter part with high precision and solves the problem of low measurement accuracy of the rotary angle of the large-diameter part.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-precision detection, and particularly relates to a large-diameter part corner measurement device and a measurement method based on machine vision. Background Art

[0002] Angle measurement is an important part of metrology science, and corner measurement has been widely applied in many fields such as aerospace, precision machining, and high-precision detection. At present, the research tasks of angle measurement mainly focus on improving measurement accuracy, resolution, and expanding the measurement range.

[0003] Patent Application No.: 200810013124.8, titled "In-machine Measuring Instrument for Measuring Deviations of Large Gears with Edge Rack Probes in Machine", uses a friction disk measurement method to obtain the rotation angle of a large gear. However, the method of obtaining the rotation angle of a large gear through a friction disk is prone to slipping, and the diameter of the friction disk is small, while the diameter of the large gear workbench that undergoes pure rolling with it is large. The rotation angle error of the friction disk is much smaller than the actual rotation angle error of the large gear, and it cannot reflect the true value of the rotation angle of the large gear. Both reasons will cause corner errors and cannot guarantee high-precision measurement.

[0004] Patent Application No.: 201110076643.0, titled "Method and Device for Measuring Small High-Precision Angles", uses the polarized light of the reference light beam obtained after collimation processing, divides it into reflected light and transmitted light with an intensity ratio of 1:1, the two beams of light are respectively incident on two prisms for reflection, and the reflected optical signals are received and processed by two detectors, finally realizing the measurement of small high-precision rotation angles, having the advantages of ultra-high precision and a large measurement range. However, the measurement process is relatively complex, with high requirements for measurement personnel, and there are certain limitations for large rotation angle measurement.

[0005] Patent Application No.: 201910580076.9, titled "A Vision-Based High-Precision Dynamic Rotation Angle Measurement System", uses a laser beam to extract and convert the tiny rotation angle feature into the straight-line fitting and slope solution of the laser beam, having the advantages of simple operation and good real-time performance. However, the measurement accuracy for the rotation angle of large-diameter parts needs to be improved.

[0006] In summary, it is necessary to develop a large-diameter part corner measurement device and adopt a new measurement method to quickly and accurately measure the rotation angle of large-diameter parts. Summary of the Invention

[0007] The present invention aims at the defects existing in the prior art and provides a large-diameter part corner measurement device and a measurement method based on machine vision.

[0008] To meet the requirement of a large field of view during the measurement of large-diameter parts, a "binocular" measurement method is adopted to solve the problem of large distances between measurement points. However, the positions of the two cameras are in their respective regional coordinate systems. To solve the problem of non-uniform regional coordinate systems, a high-precision rotation angle measurement reference plate is designed to establish the relationship between the center of the camera's field of view and the physical coordinates of the rotation angle measurement reference plate. The rotation angle measurement reference plate is fixedly connected to the large-diameter part and rotates with the large-diameter part. By measuring the angle rotated by the line connecting the center points of the two cameras' fields of view within the coordinate system of the reference plate, the rotation angle of the large-diameter part is obtained.

[0009] A high-precision rotation angle measurement device for large-diameter parts includes a rotation angle measurement reference plate and a binocular vision measurement mechanism. It is characterized in that the rotation angle measurement reference plate is placed on the large-diameter part and rotates with the large-diameter part; the binocular vision measurement mechanism is placed directly above the rotation angle measurement reference plate.

[0010] Furthermore, the rotation angle measurement reference plate includes a reference plate main frame, a parallel light source, a two-dimensional dot matrix calibration plate, a pressing strip, and a reference plate horizontal adjustment device; the parallel light source is placed below the reference plate main frame, the two-dimensional dot matrix calibration plate is placed above the reference plate main frame and is pressed tightly with a pressing strip, and the reference plate horizontal adjustment device is connected to the side of the reference plate main frame.

[0011] Furthermore, the reference plate horizontal adjustment device includes a magnetic suction seat, a double-headed stud, an adjusting block, and an L-shaped bent plate; the magnetic suction seat is placed on the large-diameter part, the double-headed stud is connected to the magnetic suction seat, the adjusting block is sleeved on the double-headed stud, one end of the L-shaped bent plate is fixed to the rotation angle measurement reference plate, and the other end is connected to the double-headed stud. After the reference plate is leveled, it is locked and fixed with a nut.

[0012] Furthermore, the binocular vision measurement mechanism includes a double telecentric lens, a camera, a channel steel, a lens fixture, and a lens horizontal adjustment device. One end of the channel steel is connected to the main column of the machine body, the camera is connected to the double telecentric lens, the lens fixture clamps the double telecentric lens and is placed above the lens horizontal adjustment device, and the lens horizontal adjustment device is placed inside the channel steel and is connected to it.

[0013] Furthermore, for the lens fixture and the lens horizontal adjustment device, for easy installation and adjustment, according to the characteristic that the middle diameter of the double telecentric lens is small, the lens fixture is divided into a left fixture and a right fixture. The left and right fixtures are connected by bolts and clamp the small-diameter part in the middle of the lens. The lower surface of the lens fixture presses a spherical washer and is connected to the base of the lens horizontal adjustment device with four adjustment bolts. The spherical washer and the base of the horizontal adjustment device are in line contact, and by rotating the four adjustment bolts respectively, the purpose of horizontal adjustment of the double telecentric lens is achieved.

[0014] A high-precision rotation angle measurement method for large-diameter parts includes the following steps:

[0015] (1) Use the reference plate horizontal adjustment device to level the corner measurement reference plate, and collect the calibration circle images on the calibration plate through the camera. Extract the center point coordinates of the calibration circle, and obtain the distance between the centers of the calibration circles. If the distances between the centers of the calibration circles are all equal, it indicates that the reference plate is horizontal; otherwise, adjust the reference plate according to the distribution of the distances between the centers of the calibration circles, and repeat the above process until the distances between the centers of the calibration circles are equal everywhere.

[0016] (2) Two cameras respectively collect the images of the corner measurement reference plate, and respectively determine the center coordinates of the 5×5 calibration circles in the center of the field of view, and then deduce the pixel coordinates A1(x1, y1), B1(u1, v1) of the calibration circle center closest to the center of the field of view in the two-dimensional dot matrix calibration plate.

[0017] (3) Taking the lower left corner of the corner measurement reference plate as the origin of the physical coordinate system, the coordinates C1(t1, s1), C2(t2, s2) of the calibration circle center in the center of the camera field of view on the two-dimensional dot matrix calibration plate can be obtained. Since the pixel coordinates (M, N) of the center of the two camera fields of view are fixed, the relationship between the center of the camera field of view and the physical coordinates of the calibration circle center closest to the center of the field of view in the two-dimensional dot matrix calibration plate can be established. The physical coordinates D1(t3, s3), E1(t4, s4) of the centers of the two camera fields of view can be solved by the following formula.

[0018]

[0019]

[0020] In the above formula, l is the pixel equivalent between the physical coordinate system and the image coordinate system, which can be determined by system calibration.

[0021] (4) The corner measurement reference plate rotates at an arbitrary angle together with the large-diameter part, and repeat steps 2) and 3) to obtain the physical coordinates D2(t5, s5), E2(t6, s6) of the center of the camera field of view after rotation.

[0022] (5) Calculate the rotation angle of the large-diameter part, and substitute the corresponding parameters into the following formula

[0023]

[0024] The beneficial effects of the present invention compared with the prior art.

[0025] (1) The present invention adopts the binocular measurement method, fixes the corner measurement reference plate on the large-diameter part and rotates with the large-diameter part. By measuring the angle turned by the connection line between the centers of the two camera fields of view in the reference plate coordinate system, the reinstallation of the large-diameter part is obtained with high precision, and the problem of low accuracy of the rotation angle measurement of the large-diameter part is solved.

[0026] (2) The present invention combines vision measurement technology, breaking through the limitations of expensive measurement equipment and cumbersome measurement processes in traditional measurement methods. Under the same measurement conditions, it can effectively improve the detection accuracy and measurement efficiency of the rotation angle of large-diameter parts, expanding the application of vision measurement technology in the field of large-diameter part measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the drawings and specific embodiments. The protection scope of the present invention is not limited to the description of the following content.

[0028] Figure 1 It is a schematic diagram of a high-precision measurement device for the rotation angle of large-diameter parts.

[0029] Figure 2 It is a schematic diagram of a rotation angle measurement reference plate.

[0030] Figure 3 It is a schematic diagram of a binocular vision measurement mechanism.

[0031] Figure 4 It is a diagram of a lens fixture and a lens horizontal adjustment device.

[0032] In the figure, 1 is the large-diameter part to be measured, 2 is the rotation angle measurement reference plate, 3 is the binocular vision measurement mechanism, 4 is the main frame of the reference plate, 5 is the calibration plate, 6 is the pressing strip, 7 is the reference plate horizontal adjustment device, 8 is the parallel light source, 9 is the L-shaped bent plate, 10 is the adjusting block, 11 is the magnetic suction seat, 12 is the stud, 13 is the camera, 14 is the lens fixture, 15 is the lens horizontal adjustment device, 16 is the main body column, 17 is the double telecentric lens, 18 is the channel steel, 19 is the left lens fixture, 20 is the lens fixture base, 21 is the adjusting bolt, 22 is the fixing bolt, 23 is the spherical washer, and 24 is the right lens fixture. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] As Figures 1-4 , parts with a diameter greater than 500 mm are called large-diameter parts. A high-precision measurement device for the rotation angle of large-diameter parts proposed by the present invention includes a rotation angle measurement reference plate and a binocular vision measurement mechanism; the rotation angle measurement reference plate is placed on the large-diameter part and rotates with the large-diameter part; the binocular vision measurement mechanism is connected to the upper end of the main body column of the machine and is placed directly above the rotation angle measurement reference plate.

[0034] Preferably, the rotation angle measurement reference plate includes a main frame of the reference plate, a parallel light source, a two-dimensional dot matrix calibration plate, a pressing strip, and a reference plate horizontal adjustment device; the parallel light source is placed below the main frame of the reference plate, the two-dimensional dot matrix calibration plate is placed above the main frame of the reference plate and is pressed tightly with the pressing strip, and the reference plate horizontal adjustment device is connected to the side of the main frame of the reference plate.

[0035] Preferably, the reference plate horizontal adjustment device includes a magnetic suction seat, a double-headed stud, an adjustment block, and an L-shaped bent plate; the magnetic suction seat is placed on the large-diameter part, the double-headed stud is connected to the magnetic suction seat, the adjustment block is sleeved on the double-headed stud, one end of the L-shaped bent plate is fixed to the corner measurement reference plate, and the other end is connected to the double-headed stud. After the reference plate is leveled, it is locked and fixed with a nut.

[0036] Preferably, the binocular vision measurement mechanism includes a double telecentric lens, a camera, a channel steel, a lens fixture, and a horizontal adjustment device. One end of the channel steel is connected to the main body column of the machine, the camera is connected to the double telecentric lens, the lens fixture clamps the double telecentric lens and is placed above the horizontal adjustment device, and the horizontal adjustment device is placed inside the channel steel and connected to it.

[0037] Preferably, the binocular vision measurement mechanism includes a double telecentric lens, a camera, a channel steel, a lens fixture, and a lens horizontal adjustment device. One end of the channel steel is connected to the main body column of the machine, the camera is connected to the double telecentric lens, the lens fixture clamps the double telecentric lens and is placed above the lens horizontal adjustment device, and the lens horizontal adjustment device is placed inside the channel steel and connected to it.

[0038] Preferably, for the lens fixture and the lens horizontal adjustment device, for the convenience of installation and adjustment, according to the characteristic that the middle diameter of the double telecentric lens is small, the lens fixture is divided into a left fixture and a right fixture. The left and right fixtures are connected by bolts and clamp the small-diameter part in the middle of the lens. The lower surface of the lens fixture presses the spherical washer and is connected to the base of the lens horizontal adjustment device with four adjustment bolts. The spherical washer and the base of the horizontal adjustment device are in line contact. By rotating the four adjustment bolts respectively, the purpose of horizontal adjustment of the double telecentric lens is achieved.

[0039] A high-precision measurement method for the corner of a large-diameter part includes the following steps:

[0040] (1) Use the reference plate horizontal adjustment device to level the corner measurement reference plate, use the lens horizontal adjustment device to level the lens, and collect the calibration circle images on the calibration plate through the camera. Extract the center coordinates of the calibration circles, and obtain the distances between the centers of the calibration circles. If the distances between the centers of the calibration circles are all equal, it means the reference plate is horizontal. Otherwise, adjust the reference plate according to the distribution of the distances between the centers of the calibration circles, and repeat the above process until the distances between the centers of the calibration circles are equal everywhere.

[0041] (2) Two cameras respectively collect the images of the corner measurement reference plate, and respectively determine the center coordinates of the 5×5 calibration circles in the center of the field of view, and then deduce the pixel coordinates A1(x1, y1), B1(u1, v1) of the calibration circle center closest to the center of the field of view in the two-dimensional dot matrix calibration plate.

[0042] (3) Taking the lower left corner of the corner measurement reference plate as the origin of the physical coordinate system, the coordinates C1(t1, s1) and C2(t2, s2) of the calibration circle center at the center of the camera's field of view on the two-dimensional lattice calibration plate in the physical coordinate system can be obtained. Since the pixel coordinates (M, N) of the two camera field of view centers remain fixed, the relationship between the camera field of view center and the physical coordinates of the calibration circle center closest to the center of the two-dimensional lattice calibration plate can be established, and the physical coordinates D1(t3, s3) and E1(t4, s4) of the two camera field of view centers can be solved by the following formula.

[0043]

[0044]

[0045] In the above formula, l is the pixel equivalent between the physical coordinate system and the image coordinate system, which can be determined by system calibration.

[0046] (4) The corner measurement reference plate rotates at an arbitrary angle together with the large-diameter part, and steps 2) and 3) are repeated to obtain the physical coordinates D2(t5, s5) and E2(t6, s6) of the camera field of view center after rotation.

[0047] (5) Calculate the rotation angle of the large-diameter part and substitute the corresponding parameters into the following formula

[0048]

[0049] The working principle and process of the present invention are as follows:

[0050] 1) Fix the corner measurement reference plate 2 to the measured large-diameter part 1 through the magnetic suction seat 11. Among them, the two magnetic suction seats 11 need to be close to the outer end of the large-diameter part. Rotate the adjustment blocks 10 in the reference plate horizontal adjustment device 7 at three positions respectively to horizontally adjust the corner measurement reference plate 2, and rotate the four adjustment bolts 21 of the lens horizontal adjustment device 15 to horizontally adjust the double telecentric lens 17.

[0051] 2) Collect the calibration circle image on the calibration plate 5 through the camera 13. Adopt the sub-pixel edge localization algorithm to extract the sub-pixel edge of the calibration circle, and determine the coordinates of the calibration circle center point by the least squares circle fitting, and calculate the distance between adjacent calibration circle centers. According to the distribution of the calibration circle center distances, finely adjust the reference plate horizontal adjustment device 7 to level the corner measurement reference plate 2 until the calibration circle center distances are equal everywhere. After the corner measurement reference plate 2 is leveled, through the horizontal adjustment device 15, ensure that the central fields of view of the two double telecentric lenses 20 are respectively near the center position of the calibration plate.

[0052] 3) Based on the mechanical structure of the corner measurement reference plate 2 designed, taking a certain corner point of the corner measurement reference plate 2 as the origin, a measurement physical coordinate system is established to determine the center coordinates C of each calibration plate i , i = 1, 2, 3..., n.

[0053] 4) The binocular vision measurement mechanism 3 is used to continuously take pictures of the corner measurement reference plate 2. The pictures collected by the two cameras 13 are processed to extract the sub-pixel edges of the 5×5 calibration circles in the center of the field of view in the image, and the center coordinates of the calibration circles in the image coordinate system are determined by least squares circle fitting. The center coordinates A of the calibration circle closest to the center of the field of view in the image are determined by weighting i , i = 1, 2, 3..., n, B i , i = 1, 2, 3..., n.

[0054] 5) Since the center coordinates (M, N) of the fields of view of the two cameras 13 are fixed, and the center coordinates of the camera 13 in the field of view and the calibration circle closest to the center of the field of view in the calibration plate 5 in the image coordinate system are known, the positional relationship between the two, including the angle and distance between the two, can be determined. And the center coordinates of each calibration circle in the calibration plate in the measurement physical coordinate system are known. Then, according to the positional relationship between the center of the camera 13 in the field of view and the calibration circle in the calibration plate 5 in the image coordinate system, the center coordinates D of the camera 13 in the field of view in the measurement physical coordinate system can be determined i , i = 1, 2, 3..., n, E i , i = 1, 2, 3..., n.

[0055] 6) A straight line can be determined according to the physical coordinates of the centers of the fields of view of the two cameras 13 obtained each time of taking pictures. The angle between any two adjacent straight lines is the corner of the large-diameter part to be measured.

[0056] It can be understood that the above specific description of the present invention is only for explaining the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced to achieve the same technical effects; as long as the use requirements are met, they are all within the protection scope of the present invention.

Claims

1. A method for measuring the rotation angle of large-diameter parts based on machine vision, comprising a rotation angle measurement reference plate, a binocular vision measurement mechanism, and motion control and signal processing software; characterized in that: The corner measurement reference plate is placed on the large-diameter part and rotates with the large-diameter part; the binocular vision measurement mechanism is connected to the upper end of the main column of the machine body and is placed directly above the corner measurement reference plate; Two cameras are used to collect images of the corner measurement reference plate respectively, extract the center coordinates of the calibration circle at the center of the field of view, and establish the physical coordinate relationship between the centers of the two camera fields of view according to the physical coordinates of the calibration circle center in the corner measurement reference plate. The rotation angle of the large-diameter part is measured by the angle turned by the line connecting the center points of the two camera fields of view in the physical coordinate system; The corner measurement reference plate includes a reference plate main frame, a parallel light source, a two-dimensional dot matrix calibration plate, a pressing strip, and a reference plate horizontal adjustment device; the parallel light source is placed below the reference plate main frame, the two-dimensional dot matrix calibration plate is placed above the reference plate main frame and is pressed tightly with a pressing strip, and the reference plate horizontal adjustment device is connected to the side of the reference plate main frame; Two cameras collect images of the corner measurement reference plate respectively, and determine the center pixel coordinates of the 5×5 calibration circle at the center of the field of view respectively. The weighted method is used to deduce the center pixel coordinates A1(x1, y1), B1(u1, v1) of the calibration circle closest to the center of the field of view in the two-dimensional dot matrix calibration plate; according to the positional relationship of each calibration circle in the corner measurement reference plate, the coordinates C1(t1, s1), C2(t2, s2) of the center of the calibration circle closest to the center of the field of view in the two-dimensional dot matrix calibration plate in the physical coordinate system can be obtained; the center pixel coordinates (M, N) of the two camera fields of view are fixed. Coordinate transformation is performed on the center pixel coordinates of the camera field of view to establish the relationship between the center of the camera field of view and the physical coordinates of the center of the calibration circle closest to the center of the field of view in the two-dimensional dot matrix calibration plate. The physical coordinates D1(t3, s3), E1(t4, s4) of the centers of the two camera fields of view can be solved by equations (1) and (2); where l is the pixel equivalent between the physical coordinate system and the image coordinate system, which can be determined by system calibration; after the corner measurement reference plate rotates at will with the large-diameter part, the physical coordinates D2(t5, s5), E2(t6, s6) of the center of the camera field of view after rotation can be obtained; according to the physical coordinates of the centers of the two camera fields of view obtained by each photograph, a straight line can be determined, and the included angle between the two straight lines is the rotation angle of the measured large-diameter part, which can be obtained by equation (3); 2. The method for measuring the rotation angle of large-diameter parts based on machine vision according to claim 1, characterized in that: The reference plate horizontal adjustment device includes a magnetic suction seat, a double-headed stud, an adjusting block, and an L-shaped bent plate; the magnetic suction seat is placed on the large-diameter part, the double-headed stud is connected to the magnetic suction seat, the adjusting block is sleeved on the double-headed stud, one end of the L-shaped bent plate is fixed to the corner measurement reference plate, and the other end is connected to the double-headed stud. After the reference plate is leveled, it is locked and fixed with a nut.

3. The method for measuring the rotation angle of large-diameter parts based on machine vision according to claim 1, characterized in that: The binocular vision measurement mechanism includes a double telecentric lens, a camera, a channel steel, a lens fixture, and a lens horizontal adjustment device. One end of the channel steel is connected to the main column of the machine body, the camera is connected to the double telecentric lens, the lens fixture clamps the double telecentric lens and is placed above the lens horizontal adjustment device, and the lens horizontal adjustment device is placed inside the channel steel and is connected to it.

Images