Image acquisition system and calibration method applied to a transparent tubular workpiece

Abstract

The application is suitable for the field of detection, and discloses an image acquisition system applied to a transparent tubular workpiece and a calibration method. The image acquisition system comprises an imaging unit, a triggering and motion control unit and an illumination unit. The triggering and motion control unit comprises a driving device and a controller. The driving device is used for carrying and driving the measured transparent tubular workpiece to move horizontally and rotate. The imaging unit comprises a double-telecentric lens, a zoom assembly, an image sensing acquisition element and a half-mirror. The driving device and the zoom assembly are connected with the controller respectively. The illumination unit comprises a telecentric light source. The telecentric light source is arranged directly below the double-telecentric lens and below the measured transparent tubular workpiece. Through cooperation of the telecentric light source and the double-telecentric lens, the definition of image acquisition can be improved.

Description

Technical Field

[0001] This invention relates to the field of detection, and in particular to an image acquisition system and calibration method for transparent tubular workpieces. Background Technology

[0002] In fields such as precision manufacturing, medical devices, and fiber optic communications (e.g., microstructured optical fibers), ultrafine hollow glass tubes are a critical fundamental component with extremely stringent quality requirements. For a glass tube with an outer diameter of 2.4 mm, an inner diameter of 1.6 mm, and a wall thickness of only 0.4 mm, any minute defects, such as scratches on the inner wall, surface cracks, uneven wall thickness, internal contamination, or air bubbles, can directly affect its mechanical strength, optical performance, or fluid permeability, leading to final product failure. Currently, visual inspection of such transparent or semi-transparent tubular workpieces faces significant challenges:

[0003] 1. Light Transmission and Reflection Interference: Glass material has high light transmission and high reflectivity. Traditional front lighting methods will cause the camera lens to receive strong surface reflections, forming flares or halos, thereby obscuring the defect information of the glass tube itself, resulting in the inability to clearly image defects on the inner wall.

[0004] 2. Difficulty in imaging the internal structure: Because the glass tube is hollow, light passes directly through the tube wall, making it difficult to form a high-contrast image of the internal contours and features in the camera. Tiny scratches or contaminants on the inner wall are easily missed due to their low contrast with the background.

[0005] 3. High requirements for illumination uniformity: For high-precision dimensional measurements (such as inner and outer diameters, concentricity) and defect detection, uniform illumination height is required throughout the entire field of view. Any non-uniformity will be misjudged as uneven wall thickness or shape distortion.

[0006] 4. Limitations of existing technologies: Commonly used backlighting is suitable for contour dimension measurement, but cannot effectively display inner wall defects; side lighting or coaxial lighting can enhance surface texture, but the enhancement effect on inner wall features is limited, and it is easily affected by reflections from the outer surface.

[0007] Therefore, existing technologies still need improvement and development. Summary of the Invention

[0008] The first objective of this invention is to provide an image acquisition system for transparent tubular workpieces, which aims to solve the technical problem of blurred imaging of double-walled tubular workpieces.

[0009] To achieve the above objectives, the solution provided by the present invention is as follows:

[0010] An image acquisition system for transparent tubular workpieces includes an imaging unit, a triggering and motion control unit, and an illumination unit. The triggering and motion control unit includes a drive device and a controller. The drive device carries and drives the transparent tubular workpiece under test in horizontal linear and rotational motion. The imaging unit includes dual telecentric lenses, a zoom assembly, an image sensing element, and a semi-reflective mirror. The drive device and the zoom assembly are respectively connected to the controller. The illumination unit includes a telecentric light source positioned directly below the dual telecentric lenses and below the transparent tubular workpiece under test. The telecentric light source emits... A parallel light source illuminates the transparent tubular workpiece under test perpendicularly. The parallel light source passes through the transparent tubular workpiece and, after three refractions, enters the dual telecentric lens. The refracted light is filtered and calibrated by the dual telecentric lens, then transmitted through the semi-reflective lens and enters the zoom assembly. The zoom assembly receives a trigger signal from the controller and successively adjusts the direction of the light to align with the imaging focal plane of the upper tube wall and the imaging focal plane of the lower tube wall of the transparent tubular workpiece under test. The light, after being directionally reflected by the zoom assembly, is reflected by the semi-reflective lens and projected along the adjusted optical path onto the image sensing element, which then converts it into a digital image signal.

[0011] Preferably, the zoom component is a micromirror array.

[0012] Preferably, the image sensing and acquisition element is a CMOS image sensor.

[0013] Preferably, the imaging unit further includes a polarizer and a quarter-wave plate. The polarizer is disposed between the dual telecentric lens and the semi-reflective mirror, and the quarter-wave plate is disposed between the semi-reflective mirror and the zoom assembly. The polarizer is used to filter the light after being filtered and calibrated by the dual telecentric lens into polarized light with only one polarization direction. The quarter-wave plate is used to adjust the polarization angle of the polarized light transmitted through the semi-reflective mirror, and to adjust the polarization angle of the light after being directionally reflected by the zoom assembly.

[0014] Preferably, the driving device includes a linear motion platform, a linear drive component, and a rotary drive component. The linear drive component is connected to the linear motion platform and is used to drive the linear motion platform to move the transparent tubular workpiece being tested in a linear motion along the horizontal direction. The rotary drive component is disposed on the linear motion platform and is used to drive the transparent tubular workpiece being tested to rotate.

[0015] Preferably, the lighting unit further includes a light source fixing bracket, and the telecentric light source is mounted on the light source fixing bracket.

[0016] The second objective of this invention is to provide a calibration method based on the image acquisition system for transparent tubular workpieces as described in claim 1. The driving device includes a linear motion platform, a linear drive component, and a rotary drive component. The linear drive component is connected to the linear motion platform and drives the linear motion platform to move the transparent tubular workpiece under test in a horizontal linear motion. The rotary drive component is disposed on the linear motion platform and drives the transparent tubular workpiece under test to rotate. The calibration method includes: placing a dot array calibration plate on the linear motion platform and driving the linear motion platform to move the dot array calibration plate to one side of the imaging unit's field of view; moving the linear motion platform at a fixed distance, acquiring one image of the dot array calibration plate through the imaging unit each time the platform moves, obtaining multiple images of the dot array calibration plate, each image including multiple dots; calculating the offset angle of each group of corresponding dots in two adjacent images of the dot array calibration plate; calculating the average value of all offset angles to obtain the mean offset angle, and completing the calibration.

[0017] Preferably, calculating the center offset angle of each group of corresponding dots in two adjacent dot array calibration board images includes: calculating the ratio of the center of the dots in the later dot array calibration board image to the center of the corresponding dots in the previous dot array calibration board image. Directional offset and Directional offset; based on Directional offset and The directional offset is calculated to obtain the offset angle of each dot center in the subsequent dot array calibration plate image compared to the corresponding dot center in the previous dot array calibration plate image; the average value of all offset angles is calculated to obtain the average offset angle, thus completing the calibration.

[0018] The image acquisition system for transparent tubular workpieces provided by this invention uses a telecentric light source and dual telecentric lenses to emit vertical parallel light, which is refracted three times by the transparent tubular workpiece under test to complete light filtering and calibration. Combined with a driving device, the workpiece achieves coordinated horizontal linear motion and rotational motion. With a zoom component that can receive controller trigger signals and accurately switch the imaging focal plane of the upper and lower tube walls, and an image sensing and acquisition element that converts light signals efficiently, the system effectively solves the core problem of blurred imaging of the double-layer tube walls of transparent tubular workpieces, and can improve the clarity, geometric accuracy and detection efficiency of image acquisition. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of an image acquisition system for transparent tubular workpieces provided in an embodiment of the present invention;

[0021] Figure 2 This is a flowchart of the calibration method provided in the embodiments of the present invention.

[0022] Explanation of icon numbers:

[0023] 10. Imaging unit; 11. Dual telecentric lens; 12. Zoom assembly; 13. Image sensing and acquisition element; 14. Semi-reflective mirror; 15. Polarizer; 16. Quarter wave plate; 20. Trigger and motion control unit; 21. Drive device; 211. Linear motion platform; 212. Linear drive; 213. Rotary drive; 22. Controller; 30. Illumination unit; 31. Telecentric light source; 32. Light source fixing bracket; 100. Transparent tubular workpiece under test. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0026] It should also be noted that when a component is described as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intervening component present. When a component is described as "connected to" another component, it can be directly connected to the other component or there may be an intervening component present.

[0027] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0028] like Figure 1 As shown, this is an embodiment of the image acquisition system applied to a transparent tubular workpiece according to the present invention.

[0029] Please see Figure 1 As shown, the image acquisition system for transparent tubular workpieces according to an embodiment of the present invention includes an imaging unit 10, a triggering and motion control unit 20, and an illumination unit 30. The triggering and motion control unit 20 includes a driving device 21 and a controller 22. The driving device 21 is used to carry and drive the transparent tubular workpiece 100 under test to perform horizontal linear motion and rotational motion. The imaging unit 10 includes a dual telecentric lens 11, a zoom assembly 12, an image sensing and acquisition element 13, and a semi-reflective lens 14. The driving device 21 and the zoom assembly 12 are respectively connected to the controller 22. The illumination unit 30 includes a telecentric light source 31, which is located directly below the dual telecentric lens 11 and at the transparent tubular workpiece under test. Below 100, the parallel light emitted by the telecentric light source 31 illuminates the transparent tubular workpiece 100 under test perpendicularly. The parallel light passes through the transparent tubular workpiece 100 under test, and after three refractions, it enters the double telecentric lens 11. After being filtered and calibrated by the double telecentric lens 11, the refracted light is transmitted through the semi-reflective lens 14 and enters the zoom assembly 12. The zoom assembly 12 receives the trigger signal from the controller 22 and adjusts the direction of the light to align with the imaging focal plane of the upper tube wall and the imaging focal plane of the lower tube wall of the transparent tubular workpiece 100 under test. The light after being directionally reflected by the zoom assembly 12 is reflected by the semi-reflective lens 14 to the image sensing and acquisition element 13, and is converted into a digital image signal by the image sensing and acquisition element 13.

[0030] In this embodiment, the controller 22 integrates the working logic of the imaging unit 10, the trigger and motion control unit 20, and the illumination unit 30 to ensure that each component operates accurately and synchronously according to the preset process, and finally realizes the automated and high-precision image acquisition of the transparent tubular workpiece 100 under test.

[0031] In this embodiment, the parallel light source emitted by the telecentric light source 31 illuminates the transparent tubular workpiece 100 being tested perpendicularly. After three refractions, the light enters the double telecentric lens 11, which refers to the three refractions of air-glass, glass-air, and air-glass.

[0032] In this embodiment, the zoom component 12 is a micromirror array, and the image sensing and acquisition element 13 is a CMOS image sensor. The micromirror array has a fast response speed and small size, and can quickly complete the focal plane switching, adapting to the real-time imaging requirements of workpiece movement; the CMOS image sensor has high frame rate and low power consumption characteristics, and can efficiently convert light signals into digital signals, taking into account both acquisition speed and energy consumption control.

[0033] In this embodiment, the imaging unit 10 further includes a polarizer 15 and a quarter-wave plate 16. The polarizer 15 is disposed between the double telecentric lens 11 and the semi-reflective mirror 14, and the quarter-wave plate 16 is disposed between the semi-reflective mirror 14 and the zoom assembly 12. The parallel light source passes through the transparent tubular workpiece 100 being measured, and after three refractions, enters the double telecentric lens 11. After being filtered and calibrated by the double telecentric lens 11, the refracted light is filtered by the polarizer into polarized light with only one polarization direction, and then enters the semi-reflective mirror 14. At this time, the semi-reflective mirror 14 only allows the polarizer 15 to transmit light. The quarter-wave plate 16 adjusts the angle of the incident polarized light before it enters the micromirror array. The zoom assembly 12 receives the trigger signal from the controller 22 and successively adjusts the direction of the light to align with the imaging focal planes of the upper and lower tube walls of the transparent tubular workpiece 100 being measured. After being directionally reflected by the zoom assembly 12, the light is re-polarized by the quarter-wave plate 16 and then enters the semi-reflective mirror 14. At this time, the semi-reflective mirror 14 only allows the polarized light to be reflected, so that the light is finally projected onto the image sensing and acquisition element 13 and converted into a digital image signal. The polarizer 15 can filter out the stray polarized light generated by the refraction / reflection of the transparent tubular workpiece (such as diffuse reflection light from the tube wall surface and internal multiple scattering light), retaining only the single polarized light propagating along the target direction, reducing the interference of stray light on imaging from the source. In conjunction with the adjustment of the polarization angle by the quarter-wave plate 16, it can further weaken the polarization disorder caused by the characteristics of transparent materials, avoiding halo, fog, or blurry details in the image.

[0034] In this embodiment, the driving device 21 includes a linear motion platform 211, a linear drive component 212, and a rotary drive component 213. The linear drive component 212 is connected to the linear motion platform 211 and is used to drive the linear motion platform 211 to move the transparent tubular workpiece 100 under test in a linear direction along the horizontal direction. The rotary drive component 213 is disposed on the linear motion platform 211 and is used to drive the transparent tubular workpiece 100 under test to rotate. The combined drive of linear motion and rotary motion can basically drive the transparent tubular workpiece 100 under test to achieve all-round imaging without blind spots, avoiding the omission of tube wall defects. Moreover, the driving device 21 has a clear division of labor, more precise motion control, and is suitable for the detection of transparent tubular workpieces of different lengths and specifications.

[0035] Understandably, in this embodiment, the linear drive 212 can be a linear motor, the rotary drive 213 can be a rotary motor, and a gripper (not shown) is installed at the end of the rotary motor shaft. The gripper holds the transparent tubular workpiece 100 to be tested. The gripper gripping position does not exceed 5mm, and the gripping force of the gripper will not damage the transparent tubular workpiece 100 to be tested.

[0036] In this embodiment, the illumination unit 30 further includes a light source fixing bracket 32, on which the telecentric light source 31 is mounted. The light source fixing bracket 32 ​​ensures the stability of the position of the telecentric light source 31, avoids imaging deviation caused by the offset of the illumination angle, and improves the stability and repeatability of the acquired images. The bracket design facilitates the installation, debugging and maintenance of the light source, reducing equipment operation and maintenance costs.

[0037] In this embodiment, the image acquisition system controller 22 issues commands to control the linear drive 212 to move linearly in a specified direction (e.g., forward) and at a speed (e.g., 5 mm / s), and to rotate in a specified direction (e.g., clockwise) and at a speed (e.g., 360° / s). Once both reach a stable, uniform motion state, the controller 22 sends trigger signals to the micromirror array at a fixed frequency. Each time the micromirror array receives a trigger signal, it completes two zoom operations, successively focusing on the upper and lower walls of the transparent tubular workpiece 100 being measured. Each zoom operation synchronously triggers the CMOS image sensor to acquire an image, achieving separate capture of images of the upper and lower walls. The controller 22 continuously monitors the stroke of the linear drive 212. When the linear drive 212 reaches a preset specified length, it stops sending trigger signals and simultaneously controls both the linear drive 212 and the rotation drive 213 to stop moving, completing the entire image acquisition process.

[0038] In this embodiment, the telecentric light source 31 and the dual telecentric lens 11 work together to emit vertical parallel light, which is refracted three times by the transparent tubular workpiece 100 under test to complete the light filtering and calibration. Combined with the driving device 21, the workpiece is driven to achieve coordinated horizontal linear motion and rotational motion. With the zoom component 12 that can receive the trigger signal of the controller 22 and accurately switch the imaging focal plane of the upper and lower tube walls, and the image sensing and acquisition element 13 that converts light signals efficiently, the core pain point of blurred imaging of the double-layer tube wall of the transparent tubular workpiece is effectively solved, which can improve the clarity, geometric accuracy and detection efficiency of image acquisition.

[0039] Please see Figure 2 As shown, in this embodiment, a calibration method is also provided. The calibration method is based on an image acquisition system applied to the transparent tubular workpiece described above. The driving device 21 includes a linear motion platform 211, a linear drive 212, and a rotary drive 213. The linear drive 212 is connected to the linear motion platform 211 and is used to drive the linear motion platform 211 to move the transparent tubular workpiece 100 under test in a horizontal linear motion. The rotary drive 213 is disposed on the linear motion platform 211 and is used to drive the transparent tubular workpiece 100 under test to rotate. The calibration method includes:

[0040] S101. Place the dot array calibration plate on the linear motion platform 211, and drive the linear motion platform 211 to move the dot array calibration plate to one side of the field of view of the imaging unit 10.

[0041] S102. The linear motion platform 211 is moved at a fixed distance. Each time it moves, the imaging unit 10 acquires an image of the dot array calibration plate, resulting in multiple images of the dot array calibration plate. Each image of the dot array calibration plate includes multiple dots.

[0042] S103. Calculate the offset angle of each group of corresponding dots in two adjacent dot array calibration board images;

[0043] S104. Calculate the average value of all offset angles, obtain the average offset angle, and complete the calibration.

[0044] It should be noted that since the image acquisition system uses a dual telecentric imaging lens, the calibration can be simplified to the calibration of the system's vertical rotation angle.

[0045] In this embodiment, calculating the center offset angle of each group of corresponding dots in two adjacent dot array calibration plate images includes: calculating the ratio of the center of the dots in the later dot array calibration plate image to the center of the corresponding dots in the previous dot array calibration plate image. Directional offset and Directional offset; based on Directional offset and The directional offset is calculated to obtain the offset angle of each dot center in the subsequent dot array calibration plate image compared to the corresponding dot center in the previous dot array calibration plate image; the average value of all offset angles is calculated to obtain the average offset angle, thus completing the calibration.

[0046] In this embodiment, it is assumed that The direction refers to the direction of motion of the linear motion platform 211. The direction refers to the direction perpendicular to the linear motion platform 211, and the pixel resolution of the image acquired by the imaging unit 10 is... The fixed distance is The total number of moves was 100. Then, a total of [number] shots were taken. Images of a dot array calibration board, each image containing dots. One, with the center of the dot as ,but:

[0047]

[0048]

[0049]

[0050]

[0051] In the formula, Indicates the first Image number 1 The offset of the center of each dot in the direction, Indicates the first Image number 1 The center of each dot is Offset in direction Indicates the first Image number 1 The center of each dot is Coordinates in direction Indicates the first Image number 1 The center of each dot is Coordinates in direction Indicates the first Image number 1 The center of the circle and its position on the 1st The offset angle is calculated from the center of the corresponding dot on the image. This represents the mean of the offset angles, which is the average of all offset angles to eliminate random errors.

[0052] Understandably, the above formula Used to calculate the direction of movement along the displacement stage ( The offset of a single dot (in pixels): Given a fixed distance movement of sum and an image resolution of uum, s / u gives the offset in pixels along the movement direction of the stage. (Direction) The offset of a single dot.

[0053] Understandably, the core principle of this calibration method is: to simplify the calibration dimensions by utilizing the characteristics of the dual telecentric lenses 11, to acquire multiple sets of images through the linear motion of the dot array calibration plate, to calculate the offset angle of corresponding dots in adjacent images and take the average value, thereby achieving accurate calibration of the system's vertical rotation angle. Specifically, this is manifested as follows:

[0054] In two adjacent images, the deviation in the center position of the same dot is caused by the system's vertical rotation angle. This is determined by calculating the position of the dot's center relative to the previous image in the later image. Direction (direction of platform movement) and The directional (vertical platform direction) offset is calculated by combining geometric relationships to determine the offset angle of a single dot, and then the random error is offset by averaging multiple sets of dot data.

[0055] The average of all calculated offset angles is used to obtain the calibration result of the vertical rotation angle of the image acquisition system. This average value can more accurately reflect the actual deviation of the system, ensure the geometric accuracy of image acquisition after calibration, and provide a calibration basis for the subsequent accurate imaging of the transparent tubular workpiece 100 under test.

[0056] In this embodiment, the calibration is simplified to vertical rotation angle calibration by utilizing the characteristics of the dual telecentric lens 11. Multiple images are acquired by moving the dot array calibration plate at a fixed distance with the linear motion platform 211, and the corresponding dots in adjacent images are calculated. , The directional offset angle is averaged, which simplifies the calibration process, reduces operational complexity, effectively offsets random errors, and ensures calibration accuracy.

[0057] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. An image acquisition system for transparent tubular workpieces, characterized in that, The system includes an imaging unit, a triggering and motion control unit, and an illumination unit. The triggering and motion control unit includes a drive device and a controller. The drive device carries and drives the transparent tubular workpiece under test to perform horizontal linear and rotational movements. The imaging unit includes dual telecentric lenses, a zoom assembly, an image sensing and acquisition element, and a semi-reflective mirror. The drive device and the zoom assembly are respectively connected to the controller. The illumination unit includes a telecentric light source, which is positioned directly below the dual telecentric lenses and below the transparent tubular workpiece under test. The parallel light emitted by the telecentric light source illuminates the workpiece perpendicularly. When measuring a transparent tubular workpiece, a parallel light source passes through the workpiece and, after three refractions, enters the dual telecentric lens. The refracted light is filtered and calibrated by the dual telecentric lens, then transmitted through the semi-reflective lens and enters the zoom assembly. The zoom assembly receives a trigger signal from the controller and successively adjusts the light direction to align with the imaging focal planes of the upper and lower walls of the workpiece. The light, after being directionally reflected by the zoom assembly, is reflected by the semi-reflective lens and projected along the adjusted light path onto the image sensing element, where it is converted into a digital image signal.

2. The image acquisition system for transparent tubular workpieces as described in claim 1, characterized in that, The zoom component is a micromirror array.

3. The image acquisition system for transparent tubular workpieces as described in claim 1, characterized in that, The image sensing and acquisition element is a CMOS image sensor.

4. The image acquisition system for transparent tubular workpieces as described in claim 1, characterized in that, The imaging unit further includes a polarizer and a quarter-wave plate. The polarizer is disposed between the dual telecentric lens and the semi-reflective mirror, and the quarter-wave plate is disposed between the semi-reflective mirror and the zoom assembly. The polarizer is used to filter the light after being filtered and calibrated by the dual telecentric lens into polarized light with only one polarization direction. The quarter-wave plate is used to adjust the polarization angle of the polarized light transmitted through the semi-reflective mirror, and to adjust the polarization angle of the light after being directionally reflected by the zoom assembly.

5. The image acquisition system for transparent tubular workpieces as described in claim 1, characterized in that, The driving device includes a linear motion platform, a linear drive component, and a rotary drive component. The linear drive component is connected to the linear motion platform and is used to drive the linear motion platform to move the transparent tubular workpiece being tested in a horizontal linear motion. The rotary drive component is disposed on the linear motion platform and is used to drive the transparent tubular workpiece being tested to rotate.

6. The image acquisition system for transparent tubular workpieces as described in claim 1, characterized in that, The lighting unit also includes a light source mounting bracket, on which the telecentric light source is mounted.

7. A calibration method, characterized in that, The calibration method is based on the image acquisition system for transparent tubular workpieces as described in claim 1. The driving device includes a linear motion platform, a linear drive component, and a rotary drive component. The linear drive component is connected to the linear motion platform and is used to drive the linear motion platform to move the transparent tubular workpiece under test in a horizontal linear motion. The rotary drive component is disposed on the linear motion platform and is used to drive the transparent tubular workpiece under test to rotate. The calibration method includes: Place the dot array calibration plate on the linear motion platform and drive the linear motion platform to move the dot array calibration plate to one side of the imaging unit's field of view; The linear motion platform moves at a fixed distance. Each time it moves, it acquires an image of the dot array calibration plate through the imaging unit, resulting in multiple images of the dot array calibration plate. Each image of the dot array calibration plate includes multiple dots. Calculate the offset angle of each group of corresponding dots in two adjacent dot array calibration board images; Calculate the average value of all offset angles, obtain the average offset angle, and complete the calibration.

8. The calibration method as described in claim 7, characterized in that, The calculation of the center offset angle of each group of corresponding dots in two adjacent dot array calibration plate images includes: calculating the center offset angle of the dots in the later dot array calibration plate image compared to the center offset of the corresponding dots in the previous dot array calibration plate image. Directional offset and Directional offset; based on Directional offset and The directional offset is calculated to obtain the offset angle of each dot center in the subsequent dot array calibration plate image compared to the corresponding dot center in the previous dot array calibration plate image; the average value of all offset angles is calculated to obtain the average offset angle, thus completing the calibration.

Images