Measuring tape verification system and method based on visual inspection

Abstract

The invention discloses a measuring tape verification system based on visual inspection, which comprises a verification platform, and a standard comparison mechanism and a visual inspection mechanism are arranged on the verification platform. After the measuring tape is unfolded, the visual detection mechanism shoots a scale image of the measuring tape, and the standard comparison mechanism is combined to carry out scale analysis on the scale image of the measuring tape; the tape surface of the measuring tape is a curved surface. A measuring tape flattening mechanism is further arranged on the verification table and can flatten the tape surface of the measuring tape, so that the visual inspection mechanism shoots a scale image of the measuring tape in the flattened state. The measuring tape which is concave and provided with scales is a front surface, and the measuring tape which is arched is a back surface; the measuring tape flattening mechanism comprises an upper fixed clamp and a lower movable clamp; the upper fixed clamp is used for limiting the front surface of the measuring tape, and a shooting opening is formed in the upper fixed clamp; the lower movable clamp can push the measuring tape to the upper fixed clamp, so that the measuring tape is flattened, and the front face of the flattened measuring tape is tightly attached to the shooting opening. According to the invention, the calibration error caused by the curved surface of the measuring tape can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of tape measure calibration, and in particular to a tape measure calibration system and a calibration method based on visual detection. Background Art

[0002] The tape measure is a widely used measuring tool. After the tape measure is manufactured, it needs to be calibrated. At present, when calibrating the tape measure, the tape measure is laid on the calibration table, the scale image of the tape measure is captured by a camera, and the pixel points in the image are analyzed by a computer to obtain the scale comparison result.

[0003] However, the calibration table is a flat surface, while the tape measure is a curved surface. When the camera shoots the curved surface, the tape measure has different widths and arc surfaces, so the distance between the tape measure and the camera cannot be guaranteed. There is no way to guarantee the focal length, and it is inevitable that there will be a certain degree of image distortion, resulting in shooting errors. Due to the existence of shooting errors, the pixel points corresponding to the scale lines on the tape measure surface image will deviate, which will eventually increase the error of the scale results analyzed by the computer. Summary of the invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a tape measure calibration system and a calibration method based on visual inspection, aiming to reduce the calibration error caused by the curved surface of the tape measure.

[0005] Technical solution: To achieve the above-mentioned purpose, the tape measure calibration system based on visual inspection of the present invention includes a calibration platform, on which are provided a standard measuring mechanism and a visual inspection mechanism; after the tape measure is unfolded, the visual inspection mechanism captures the scale image of the tape measure, and performs scale analysis on the scale image of the tape measure in combination with the standard measuring mechanism; the scale surface of the tape measure is a curved surface; a tape measure flattening mechanism is also provided on the calibration platform, which can flatten the scale surface of the tape measure, so that the visual inspection mechanism captures the scale image of the tape measure in the flattened state.

[0006] Furthermore, the concave part with scales on the tape measure is the front side, and the arched part of the tape measure is the back side; the tape measure flattening mechanism includes an upper fixed clamp and a lower movable clamp; the upper fixed clamp limits the front side of the tape measure, and a shooting port is provided on the upper fixed clamp; the lower movable clamp can push the tape measure toward the upper fixed clamp to flatten the tape measure, and the front side of the flattened tape measure is close to the shooting port.

[0007] Furthermore, a pre-tightening mechanism is provided on the calibration platform, and the pre-tightening mechanism can apply tension to the measuring tape to straighten the measuring tape.

[0008] Furthermore, a calibration plane is provided on the upper fixture, and the length direction of the calibration platform is parallel to the calibration plane; when the edge of the straightened tape measure is against the calibration plane, the length direction of the tape measure is consistent with the length direction of the calibration platform.

[0009] Furthermore, the lower movable clamp includes a flattening wheel that can translate; when the flattening wheel translates, it gradually moves along the arched contour on the back of the tape measure to the highest arch point, so that the flattening wheel flattens the tape measure and pushes the tape measure toward the correction plane.

[0010] Furthermore, in the process of the flattening wheel gradually moving along the back contour of the tape measure to the highest arch point, it successively experiences a sliding stage and a rolling stage; in the sliding stage, the flattening wheel is in sliding contact with the back of the tape measure in a non-rotating state; in the rolling stage, the flattening wheel is in rolling contact with the back of the tape measure in a rotating state.

[0011] Furthermore, the axial direction of the flattening wheel is parallel to the correction plane, the translation direction of the flattening wheel is perpendicular to the correction plane, and the tape measure flattening mechanism includes a displacement driving component that can drive the flattening wheel to translate.

[0012] Furthermore, the upper fixed clamp includes two clamping blocks with relative spacing, the shooting port is between the two clamping blocks, and step blocks are arranged on the opposite surfaces of the two clamping blocks, and the front side of the flattened tape measure is attached to the step blocks; the two clamping blocks are respectively a movable clamping block and a fixed clamping block; the movable clamping block can be movably displaced to change the spacing between the two clamping blocks; the fixed clamping block is fixedly installed on the tape measure flattening mechanism, and the side of the fixed clamping block facing the movable clamping block is the correction plane.

[0013] Furthermore, the standard measuring mechanism is a standard ruler or a grating ruler, and the length direction of the standard ruler or the grating ruler is consistent with the length direction of the calibration platform.

[0014] Furthermore, the tape measure calibration method based on visual inspection includes the following steps: Step S: inserting the tape measure between the upper fixed clamp and the lower movable clamp of each tape measure flattening mechanism; Step S: straightening the tape measure by the pre-tightening mechanism; Step S: the flattening wheel translates toward the correction plane, and the flattening wheel first slides along the arched contour on the back of the tape measure, pushing the tape measure toward the correction plane, so that the straightened tape measure is parallel to the standard ruler; then the flattening wheel gradually rolls along the arched contour on the back of the tape measure to the highest arch point, flattening the tape measure; Step S: the visual inspection mechanism captures the scale image of the tape measure in the flattened state, and performs scale analysis on the scale image of the tape measure in combination with the standard comparison mechanism.

[0015] Beneficial effects: The tape measure calibration system and calibration method based on visual detection of the present invention have the following beneficial effects:

[0016] 1) There is a tape flattening mechanism on the calibration table. Flattening the tape surface before taking a picture of the tape scale image can reduce the shooting error and improve the reliability of the calibration result;

[0017] 2) The tape measure flattening mechanism flattens the tape measure through the flattening wheel; during the flattening process, the flattening wheel gradually moves along the arched contour on the back of the tape measure to the highest arch point, so that the flattening wheel can apply vertical and horizontal forces to the tape measure, wherein the applied vertical force can flatten the tape measure, and the applied horizontal force can push the tape measure to the calibration plane, so that the length direction of the tape measure is consistent with the length direction of the calibration platform;

[0018] 3) The process of the flattening wheel moving along the back of the tape measure includes a sliding stage and a rolling stage. In the sliding stage, the flattening wheel is in sliding contact with the back of the tape measure. At this time, the friction force is relatively large, ensuring that the flattening wheel can push the tape measure onto the correction plane. In the rolling stage, the flattening wheel is in rolling contact with the back of the tape measure. At this time, the friction force is relatively small, allowing the flattening wheel to flatten the tape measure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Attached Figure 1 This is a schematic diagram of multiple cameras on the calibration platform;

[0020] Attached Figure 2 It is a three-dimensional structural diagram of the tape measure flattening mechanism;

[0021] Attached Figure 3 It is a side view of the flattening mechanism of the measuring tape;

[0022] Attached Figure 4 It is the front view of the tape measure flattening mechanism;

[0023] Attached Figure 5 is a schematic diagram of a standard measuring mechanism as a standard ruler;

[0024] Attached Figure 6 Schematic diagram of a single movable camera on the calibration platform. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings.

[0026] As attached Figures 1 to 6 The tape measure calibration system based on visual inspection comprises a calibration platform 1, on which a standard measuring mechanism and a visual inspection mechanism are provided. The tape measure 4 is in a reeled state when not in use. When the tape measure 4 is scaled, the tape measure 4 is unrolled from the reeled state, and the scale image of the tape measure 4 is photographed by the visual inspection mechanism, and the scale image of the tape measure 4 is scaled analyzed in combination with the standard measuring mechanism.

[0027] The surface of the tape measure 4 is a curved surface, that is, the cross section of the tape measure 4 is U-shaped, and the concave side of the tape measure 4 with scales is called the front side, and the arched side of the tape measure 4 is called the back side. When the camera shoots the curved surface, it is impossible to ensure the distance between the curved surface and the camera, and there is no way to ensure the focal length. It is inevitable that there will be a certain degree of image distortion, thereby causing shooting errors. Therefore, a tape measure flattening mechanism 3 is also provided on the calibration platform 1. The tape measure flattening mechanism 3 can flatten the surface of the tape measure 4, so that the visual detection mechanism can shoot the scale image of the tape measure 4 in the flattened state, thereby reducing the shooting error.

[0028] The visual inspection mechanism needs to take an image of the tape measure 4, and then use a computer to compare the pixel differences of the scale lines on the image, so as to analyze the calibration result of the tape measure 4. However, when photographing a curved surface, a shooting error will occur, so it is necessary to first flatten the tape measure 4 from a curved surface to a flat surface, and then take an image for scale comparison, thereby reducing the shooting error and improving the reliability of the calibration result.

[0029] The tape measure flattening mechanism 3 includes an upper fixed clamp 5 and a lower movable clamp 6. The upper fixed clamp 5 limits the front of the tape measure 4, and a shooting port 20 is provided on the upper fixed clamp 5, and the standard ruler 2 is adjacent to the shooting port 20. The lower movable clamp 6 can push the tape measure 4 toward the upper fixed clamp 5 to flatten the tape measure 4, and the front of the flattened tape measure 4 is closely attached to the shooting port 20. Since there are scale lines on the front of the tape measure 4, when the front of the tape measure 4 is closely attached to the shooting port 20, the camera can capture the scale image on the tape measure 4.

[0030] The calibration platform 1 is provided with a pre-tightening mechanism 8, which can apply tension to the measuring tape 4, so that the measuring tape 4 is straightened and then compared with the standard ruler 2. Figure 1 In one embodiment shown in , a fixed seat 17 is provided at one end of the calibration platform 1, and a hook is installed at the front end of the measuring tape 4, and the hook is hooked on the fixed seat 17. A pre-tensioning mechanism 8 is provided at the other end of the calibration platform 1, and the pre-tensioning mechanism 8 includes a counterweight block, and the counterweight block is connected to the rear end of the measuring tape 4, thereby applying tension to the measuring tape 4, so that the measuring tape 4 is straightened.

[0031] The upper fixture 5 is provided with a calibration plane 9, which is a vertical plane, and the length direction of the calibration platform 1 is parallel to the calibration plane 9. When the edge of the straightened tape measure 4 is against the calibration plane 9, the length direction of the tape measure 4 is consistent with the length direction of the calibration platform 1. The standard measuring mechanism is a standard ruler 2 or a grating ruler, and the length direction of the standard ruler 2 or the grating ruler is consistent with the length direction of the calibration platform 1. Only when the length directions of the tape measure 4 and the calibration platform 1 are ensured to be consistent, can the scale of the tape measure 4 be better compared and analyzed by the standard ruler 2 or the grating ruler.

[0032] Generally speaking, the flattening wheel 7 should be able to move up and down, that is, when the flattening wheel 7 needs to flatten the tape measure 4, the flattening wheel 7 is pressed against the back of the tape measure 4 from bottom to top, and pushes the tape measure 4 upward, thereby flattening the tape measure 4. However, if the flattening wheel 7 is able to move up and down, the versatility of the flattening wheel 7 is low, and it cannot adapt to tape measures 4 of different widths. In other words, when the width of the tape measure 4 to be calibrated changes, the flattening wheel 7 cannot be guaranteed to be pressed against the highest arch point on the back of the tape measure 4, and the flattening effect on the tape measure 4 is poor. In addition, it is also impossible to keep the edge of the tape measure 4 against the calibration plane 9, and it is difficult to ensure that the length direction of the tape measure 4 is consistent with that of the standard ruler 2 or the grating ruler.

[0033] Therefore, in the present invention, the lower movable clamp 6 includes a flattening wheel 7 that can be translated, that is, the flattening wheel 7 can be translated back and forth in the horizontal direction. Since the surface of the tape measure 4 is a curved surface, the back of the tape measure 4 has an arched profile, so when the flattening wheel 7 is translated, the tape measure 4 will gradually move to the highest arch point along the arched profile on the back of the tape measure 4, thereby, during the translation process, the flattening wheel 7 will not only apply a vertical force to the tape measure 4, but also apply a horizontal force to the tape measure 4, wherein the vertical force enables the flattening wheel 7 to flatten the tape measure 4, and the horizontal force enables the flattening wheel 7 to push the tape measure 4 to the correction plane 9, so that the tape measure 4 is close to the correction plane 9, thereby ensuring that the length direction of the tape measure 4 is consistent with that of the standard ruler 2 or the grating ruler.

[0034] If there is no horizontal thrust of the calibration plane 9 and the flattening wheel 7 on the tape measure 4, then even if the tape measure 4 is straightened by the pre-tensioning mechanism 8, the tape measure 4 may be skewed to a certain extent relative to the standard ruler 2, resulting in errors in the calibration results. To ensure the reliability of the calibration results, it is necessary to ensure that the length direction of the tape measure 4 is consistent with that of the standard ruler 2 or the grating ruler.

[0035] In addition, since the flattening wheel 7 moves horizontally instead of vertically, when the width of the tape measure 4 to be calibrated changes, the flattening wheel 7 can be adjusted adaptively to ensure that the flattening wheel 7 can still move to the highest arch point on the back of the tape measure 4.

[0036] The flattening wheel 7 gradually moves along the back contour of the tape measure 4 to the highest arch point, and experiences a sliding stage and a rolling stage in sequence. In the sliding stage, the flattening wheel 7 is in sliding contact with the back of the tape measure 4 in a non-rotating state, that is, the flattening wheel 7 does not rotate in the sliding stage. At this time, there is sliding friction between the flattening wheel 7 and the tape measure 4, and the friction between the two is large. Therefore, the flattening wheel 7 has a greater thrust effect on the tape measure 4, so that the flattening wheel 7 can ensure that the flattening wheel 7 pushes one side of the tape measure 4 to be close to the correction plane 9. In the rolling stage, the flattening wheel 7 is in rolling contact with the back of the tape measure 4 in a rotating state, that is, in the rolling stage, the flattening wheel 7 rotates. At this time, there is rolling friction between the flattening wheel 7 and the tape measure 4, and the friction between the two is small. Therefore, when the flattening wheel 7 rolls along the back of the tape measure 4, the tape measure 4 is flattened, and the extrusion effect on the back of the tape measure 4 is relatively weak. The two sides of the tape measure 4 are not easy to be twisted under the extrusion, so the flatness of the tape measure 4 after being flattened is better.

[0037] In one embodiment, the flattening wheel 7 is arranged on the rotating shaft, and by reasonably setting the friction between the flattening wheel 7 and the rotating shaft, the flattening wheel 7 can be in sliding contact when it first contacts the measuring tape 4. After the contact continues, the friction force increases, so that the flattening wheel 7 starts to rotate around the rotating shaft, and the flattening wheel 7 and the measuring tape 4 start to turn into rolling contact. In another embodiment, there is a wheel brake mechanism between the flattening wheel 7 and the rotating shaft, and the wheel brake mechanism can be used to control whether the flattening wheel 7 can rotate, so that the flattening wheel 7 is in a non-rotating state when it first contacts the measuring tape 4, and turns into a rotating state in the subsequent process.

[0038] As attached Figure 3 As shown in the figure, the rotation axis direction of the flattening wheel 7 is parallel to the correction plane 9, the translation direction of the flattening wheel 7 is perpendicular to the correction plane 9, and the tape measure flattening mechanism 3 has a displacement drive assembly 10 that can drive the flattening wheel 7 to translate. Figure 4 In one embodiment shown in the figure, the displacement drive assembly 10 includes a motor 15, which drives a screw 19 to rotate through a transmission belt 18. The screw 19 is threadedly matched with a screw hole on a sliding seat 16. When the screw 19 rotates, it drives the sliding seat 16 to slide on the slide rail. The flattening wheel 7 is installed on the sliding seat 16. When the sliding seat 16 slides, it drives the flattening wheel 7 to translate.

[0039] As attached Figure 2As shown in , the upper fixed clamp 5 includes two clamping blocks with relative spacing, the shooting port 20 is between the two clamping blocks, and step blocks 11 are arranged on the opposite surfaces of the two clamping blocks. The step blocks 11 are arranged close to the upper contour surface of the clamping blocks. The front side of the flattened measuring tape 4 is attached to the bottom of the step block 11, and the front side of the measuring tape 4 is limited by the step block 11. The two clamping blocks are respectively a movable clamping block 12 and a fixed clamping block 13. The movable clamping block 12 can be movably displaced to change the spacing between the two clamping blocks. The fixed clamping block 13 is fixedly mounted on the measuring tape flattening mechanism 3, and the side of the fixed clamping block 13 facing the movable clamping block 12 is the correction plane 9. In the process of the flattening wheel 7 flattening the measuring tape 4, the measuring tape 4 is pushed toward the fixed clamping block 13.

[0040] The visual detection mechanism can be a plurality of fixedly arranged cameras 14, as shown in the attached Figure 1 and 5 In one embodiment shown in the figure, a standard ruler 2 is provided on a calibration platform 1, and the length direction of the standard ruler 2 is consistent with that of the calibration platform 1. A plurality of tape measure flattening mechanisms 3 are spaced apart on the calibration platform 1 along the length direction of the standard ruler 2, and a plurality of cameras 14 are respectively located directly above a shooting port 20 of each tape measure flattening mechanism 3. Each camera 14 respectively captures an image of the flattened tape measure 4, and then compares the scale with the image of the standard ruler 2. The image is analyzed by a computer to finally obtain a calibration result.

[0041] The visual inspection mechanism may also be a single movable camera 14, the moving direction of the camera 14 being consistent with the length direction of the inspection platform 1, as shown in the attached Figure 6 In one embodiment shown in , there is a grating scale on the calibration platform 1, and the tape measure 4 is laid in the tape measure flattening mechanism 3 of the calibration platform 1, the tail end of the tape measure 4 is clamped on the hanging structure, and a corresponding force is applied as required, and then the camera 14 moves to the zero position, shoots the zero line and calculates the zero error, and then moves the camera to 0.5 meters to shoot the line and calculate the error, moves to 1 meter to shoot the line and calculate the error, moves to 2 meters to shoot the line and calculate the error, and keeps moving like this to finally obtain the calibration result of the tape measure 4.

[0042] The present invention also provides a tape measure calibration method based on visual detection, comprising the following steps:

[0043] Step S1: inserting the measuring tape 4 between the upper fixed clamp 5 and the lower movable clamp 6 of each measuring tape flattening mechanism 3;

[0044] Step S2: The hook at the front end of the measuring tape 4 is hooked on the fixing seat 17 at one end of the calibration platform 1, and a tension is applied to the rear end of the measuring tape 4 through the pre-tightening mechanism 8 at the other end of the calibration platform 1 to straighten the measuring tape 4;

[0045] Step S3: the flattening wheel 7 moves toward the calibration plane 9, and the flattening wheel 7 first slides along the arched contour on the back of the measuring tape 4, pushing the measuring tape 4 toward the calibration plane 9, so that the length direction of the straightened measuring tape 4 is consistent with the length direction of the standard ruler 2 or the grating ruler; then the flattening wheel 7 gradually rolls along the arched contour on the back of the measuring tape 4 to the highest arch point, flattening the measuring tape 4;

[0046] Step S4: the visual inspection mechanism captures the scale image of the measuring tape 4 in a flattened state, and performs scale analysis on the scale image of the measuring tape 4 in combination with the standard measuring mechanism and the computer, and finally obtains the calibration result of the measuring tape 4.

[0047] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. The tape measure calibration system based on visual inspection is characterized by: The apparatus comprises a calibration platform (1), on which a standard measuring mechanism and a visual inspection mechanism are provided; after the tape measure (4) is unfolded, the visual inspection mechanism photographs a scale image of the tape measure (4), and performs scale analysis on the scale image of the tape measure (4) in combination with the standard measuring mechanism; the scale surface of the tape measure (4) is a curved surface; and the calibration platform (1) is also provided with a tape measure flattening mechanism (3), which can flatten the scale surface of the tape measure (4), so that the visual inspection mechanism photographs the scale image of the tape measure (4) in a flattened state.

2. The tape measure calibration system based on visual inspection according to claim 1, characterized in that: The concave portion of the tape measure (4) with scales is the front side, and the arched portion of the tape measure (4) is the back side; the tape measure flattening mechanism (3) comprises an upper fixed clamp (5) and a lower movable clamp (6); the upper fixed clamp (5) limits the front side of the tape measure (4), and a photographing port (20) is provided on the upper fixed clamp (5); the lower movable clamp (6) can push the tape measure (4) toward the upper fixed clamp (5) to flatten the tape measure (4), and the front side of the flattened tape measure (4) is in close contact with the photographing port (20).

3. The tape measure calibration system based on visual inspection according to claim 2, characterized in that: The calibration platform (1) is provided with a pre-tightening mechanism (8), which can apply a tensile force to the measuring tape (4) to straighten the measuring tape (4).

4. The tape measure calibration system based on visual inspection according to claim 3, characterized in that: The upper fixture (5) is provided with a calibration plane (9), and the length direction of the calibration platform (1) is parallel to the calibration plane (9); when the edge of the straightened measuring tape (4) is abutted against the calibration plane (9), the length direction of the measuring tape (4) is consistent with the length direction of the calibration platform (1).

5. The tape measure calibration system based on visual inspection according to claim 4, characterized in that: The lower movable clamp (6) comprises a flattening wheel (7) which can be translated; when the flattening wheel (7) translates, it gradually moves along the arched contour on the back of the measuring tape (4) to the highest arch point, so that the flattening wheel (7) flattens the measuring tape (4) and pushes the measuring tape (4) toward the correction plane (9).

6. The tape measure calibration system based on visual inspection according to claim 5, characterized in that: The flattening wheel (7) gradually moves along the back contour of the measuring tape (4) to the highest arch point, and sequentially experiences a sliding stage and a rolling stage; in the sliding stage, the flattening wheel (7) is in sliding contact with the back of the measuring tape (4) in a non-rotating state; During the rolling stage, the flattening wheel (7) is in rolling contact with the back side of the measuring tape (4) in a rotating state.

7. The tape measure calibration system based on visual inspection according to claim 6, characterized in that: The axis direction of the flattening wheel (7) is parallel to the correction plane (9), the translation direction of the flattening wheel (7) is perpendicular to the correction plane (9), and the tape measure flattening mechanism (3) includes a displacement driving component (10) capable of driving the flattening wheel (7) to translate.

8. The tape measure calibration system based on visual inspection according to claim 6, characterized in that: The upper fixed clamp (5) comprises two clamping blocks with a relative spacing, the shooting port (20) is between the two clamping blocks, and step blocks (11) are arranged on the opposite surfaces of the two clamping blocks, and the front side of the flattened measuring tape (4) is attached to the step blocks (11); the two clamping blocks are respectively a movable clamping block (12) and a fixed clamping block (13); the movable clamping block (12) can be movably displaced to change the spacing between the two clamping blocks; the fixed clamping block (13) is fixedly mounted on the measuring tape flattening mechanism (3), and the side of the fixed clamping block (13) facing the movable clamping block (12) is the correction plane (9).

9. The tape measure calibration system based on visual inspection according to claim 6, characterized in that: The standard measuring mechanism is a standard ruler (2) or a grating ruler, and the length direction of the standard ruler (2) or the grating ruler is consistent with the length direction of the calibration platform (1).

10. The tape measure calibration method based on visual inspection according to claim 6, characterized in that: The following steps are involved: Step S1: inserting the measuring tape (4) between the upper fixed clamp (5) and the lower movable clamp (6) of each measuring tape flattening mechanism (3); Step S2: straightening the measuring tape (4) by means of the pre-tightening mechanism (8); Step S3: the flattening wheel (7) moves horizontally toward the calibration plane (9), and the flattening wheel (7) first slides along the arched contour on the back of the measuring tape (4), pushing the measuring tape (4) toward the calibration plane (9), so that the straightened measuring tape (4) and the standard ruler (2) are parallel to each other; then the flattening wheel (7) gradually rolls along the arched contour on the back of the measuring tape (4) to the highest arch point, flattening the measuring tape (4); Step S4: the visual inspection mechanism photographs the scale image of the measuring tape (4) in a flattened state, and performs scale analysis on the scale image of the measuring tape (4) in combination with the standard comparison mechanism.

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