Method and device for measuring local deformation of plate after flexible forming

Abstract

The invention belongs to the field of plate deformation measurement, and particularly discloses a method and device for measuring local deformation of a plate after flexible forming, and the method comprises the following steps: array-shaped mark holes are processed in the upper surface and the lower surface of the plate respectively, the mark holes are non-through holes, and the positions of the mark holes in the upper surface and the lower surface correspond to each other; images of the upper surface and the lower surface of the plate before flexible forming are obtained; flexible forming is conducted on the plate, and images of the upper surface and the lower surface of the plate after flexible forming are obtained; according to the images of the upper surface and the lower surface of the plate before and after flexible forming, the distance change of the adjacent marking holes before and after flexible forming is obtained, and then the local shrinkage amount and the angular deformation amount of plate flexible forming are obtained. The device can be applied to processing scenes with high temperature and mechanical contact, realizes non-contact accurate measurement of local deformation of the plate, and has the characteristics of simple device, easiness in implementation and high working environment adaptability.

Description

Technical Field

[0001] The invention belongs to the field of plate deformation measurement, and more specifically, relates to a method and device for measuring local deformation of a plate after flexible forming. Background Art

[0002] Curved sheet metal is an important component widely used in industries such as ships, automobiles, aircraft and construction. Considering the cost of mold manufacturing and the complexity of the target curved surface shape caused by the personalized needs of products, flexible forming processes such as water and fire bending or hot and cold integrated forming (such as patent CN107234151A) have become the main development direction of curved sheet metal forming processing. The principle of these flexible forming processes is usually to drive the sheet metal to undergo local deformation by local heating or mechanical force or heating-mechanical force coupling load. Local deformation includes local shrinkage and angular deformation. Effective control of the local deformation of the processed sheet is the key to completing the curved surface shape. Due to the high nonlinearity of the forming process, it is difficult to rely entirely on theoretical methods to develop and improve the forming process. Therefore, the measurement of the local deformation of the processed sheet metal is a necessary means to study flexible processes.

[0003] Due to the characteristics of the flexible forming process (such as high temperature, strong magnetic field and mechanical contact), traditional contact measurement methods (such as strain gauge measurement) may not be applicable or the cost is too high. In order to effectively track the deformation of the area of ​​interest, existing non-contact measurement methods (such as 3D laser scanning measurement or digital image measurement) usually require additional marking materials (such as paint) to be attached to the surface of the sheet, but these marking materials are likely to disappear after high temperature or mechanical contact, resulting in measurement failure. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method and device for measuring the local deformation of a plate after flexible forming, the purpose of which is to achieve non-contact and accurate measurement of the local deformation of the plate after flexible forming.

[0005] To achieve the above object, according to one aspect of the present invention, a method for measuring local deformation of a sheet material after flexible forming is proposed, comprising the following steps:

[0006] Before flexible forming, array-shaped marking holes are processed on the upper and lower surfaces of the plate, and the marking holes are all non-through holes, and the positions of the marking holes on the upper and lower surfaces correspond;

[0007] Respectively acquiring images of the upper and lower surfaces of the plate before flexible forming and images of the upper and lower surfaces of the plate after flexible forming;

[0008] According to the images of the upper and lower surfaces of the sheet before and after flexible forming, the distance change between adjacent marking holes before and after flexible forming is obtained, and then the local shrinkage δ and angular deformation θ of the sheet during flexible forming are obtained.

[0009] As a further preferred embodiment, the calculation formula of the local shrinkage amount δ is:

[0010]

[0011] The calculation formula of the angular deformation θ is:

[0012]

[0013] Among them, L b L is the distance between the centers of adjacent marking holes on the upper or lower surface of the sheet before flexible forming. ta L is the distance between the centers of adjacent marking holes on the upper surface of the sheet after flexible forming. ba is the distance between the centers of adjacent marking holes on the lower surface of the sheet after flexible forming, and h is the thickness of the sheet.

[0014] As a further preference, the diameter of the marking hole is 2 mm to 3 mm, and the depth of the marking hole is 0.5% to 1% of the thickness of the plate.

[0015] As a further preference, the maximum spacing between the centers of adjacent marking holes does not exceed 30 mm.

[0016] As a further preferred embodiment, local images of the plate are captured multiple times by a single camera, and then the local images are spliced ​​to obtain images of the upper and lower surfaces of the plate; each time the image is captured, it is ensured that there are no less than 2 marked holes in the picture.

[0017] As a further preferred embodiment, local images of the plate are captured simultaneously by multiple cameras, and then the local images are spliced ​​to obtain images of the upper and lower surfaces of the plate; each time the image is captured, it is ensured that there are no less than 2 marked holes in the picture.

[0018] As a further preferred embodiment, before shooting, the camera is calibrated by Zhang Zhengyou calibration method to obtain the conversion relationship between the world coordinate system and the camera pixel coordinate system; then, based on the images of the upper and lower surfaces of the plate before and after flexible forming, the distance between adjacent marking holes before and after flexible forming is obtained through this conversion relationship.

[0019] As a further preferred embodiment, after array-shaped marking holes are processed on the upper and lower surfaces of the plate, the surface of the plate around each marking hole is polished until an obvious bright surface appears.

[0020] According to another aspect of the present invention, there is provided a device for implementing the above-mentioned method for measuring the local deformation of the plate after flexible forming, comprising a punching module, a camera module, a lighting module and a computer, wherein:

[0021] The punching module is used to process array-shaped marking holes on the upper and lower surfaces of the plate;

[0022] The camera module is mounted on the surface of the plate through a camera fixture, and the illumination module is mounted on the surface of the plate through an illumination module fixture; the camera module is used to capture images of the upper and lower surfaces of the plate before and after flexible forming, and the illumination module is used to increase the brightness of the captured area of ​​the plate;

[0023] The computer is used to determine the local shrinkage and angular deformation of the sheet material during flexible forming according to the images of the upper and lower surfaces of the sheet material before and after flexible forming.

[0024] As a further preference, a surface cleaning module is also included, and the surface cleaning module is used to grind the surface of the plate around the marking hole.

[0025] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0026] 1. The present invention aims at the processing scenarios of high temperature and mechanical contact during flexible forming. By setting corresponding marking holes on the upper and lower surfaces of the plate, the present invention combines the images before and after flexible forming to realize non-contact accurate measurement of the local deformation of the plate. It is not affected by the processing environment and has the advantages of being simple, easy to implement, and having strong adaptability to the working environment.

[0027] 2. The method proposed in the present invention belongs to non-contact measurement. The measurement process does not require the installation of expensive high-temperature resistant or wear-resistant strain gauges. The tools or equipment used in the measurement process can be reused, and the cost is low. The measurement process does not require additional attachment of marking materials, avoiding measurement failure due to the disappearance of the attached materials. The measurement method is highly versatile and can adapt to the result measurement of different forming methods.

[0028] 3. The local deformation magnitude of the plate is usually in the range of 10 to 100 μm, which cannot be measured by general measurement methods. However, local photographic measurement can achieve high-precision measurement by using a lens with sufficiently high resolution, and the results are stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of a device for measuring local deformation of a plate after flexible forming according to an embodiment of the present invention.

[0030] In all the drawings, the same figure numbers are used to represent the same elements or structures, among which: 1-plate, 2-surface cleaning module, 3-punching module, 4-photographic module, 5-illumination module, 6-camera fixture, 7-illumination module fixture, 8-calibration module, 9-computer, 10-marking hole. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] An embodiment of the present invention provides a method for measuring local deformation of a plate after flexible forming, comprising the following steps:

[0033] S1. Array-shaped marking holes are processed on the upper and lower surfaces of the plate, respectively. The marking holes are all non-through holes, and the positions of the marking holes on the upper and lower surfaces correspond to each other; then the material near each marking hole on the upper and lower surfaces of the plate is polished.

[0034] Specifically, the process of machining the marking holes is as follows: using analytical or numerical calculation methods to estimate the local deformation distribution area of ​​the plate after forming processing; placing the plate on the ground or a special platform, and machining m×n matrix-distributed marking holes in the local deformation distribution area; after turning the plate over, machining m×n matrix-distributed marking holes at the same position; and numbering each marking hole.

[0035] Furthermore, the diameter of the marking hole does not exceed 3 mm, preferably 2 mm to 3 mm; the depth of the marking hole does not exceed 1% of the thickness of the plate, preferably 0.5% to 1%; the design of the diameter and depth of the marking hole can ensure that the impact of material damage on the forming process is minimized, and at the same time can ensure that it can be completed using common camera lenses without the need for special lenses.

[0036] Furthermore, the maximum spacing between the centers of adjacent marking holes does not exceed 30 mm, preferably 30 mm; the design of the spacing between the centers of adjacent marking holes can reduce the difference in object distance between each marking hole and the lens caused by the bending of the plate, thereby ensuring measurement accuracy.

[0037] Furthermore, the process of polishing the marking holes is as follows: polish the material within a radius of at least 10mm near each marking hole until an obvious bright surface is observed by the naked eye; during the polishing process, sandpaper or special tools are used, and industrial gauze or industrial wipe paper can be dipped in a small amount of solution (such as acetone) and wiped clean in the same direction. In this way, dirt and rust on the surface of the plate are cleaned, and the light and dark distinction between the area to be measured and the remaining area is strengthened.

[0038] S2, respectively obtaining images of the upper and lower surfaces of the plate before flexible forming; performing flexible forming on the plate, and after the forming process is completed, polishing the material near each marked hole on the upper and lower surfaces of the plate again to obtain images of the upper and lower surfaces of the plate after flexible forming.

[0039] Furthermore, when obtaining images through the camera before and after flexible forming, they are first calibrated according to the Zhang Zhengyou calibration method to obtain the conversion relationship between the world coordinate system and the camera pixel coordinate system. When shooting images, ensure that the camera lens and the surface to be shot are basically vertical, adjust the focal length of the lens to ensure a clear picture; and adjust the lens shooting picture amplitude to ensure that there are at least two adjacent marking holes in one shooting picture. The shooting of marking holes in a large area to be tested can be achieved by a single camera shooting locally in sequence and then stitching. It is also possible to shoot the marking holes in a large area to be tested by multiple cameras shooting different parts at the same time and then stitching.

[0040] S3. According to the images of the upper and lower surfaces of the sheet before and after the flexible forming, the distance change between adjacent marking holes before and after the flexible forming is obtained, and then the local deformation of the sheet during the flexible forming is obtained, including the local shrinkage and angular deformation.

[0041] Furthermore, the marked holes in the digital image are automatically identified on the computer based on artificial intelligence technologies such as neural networks to obtain the pixel positions of the marked holes; then, the pixel positions of the marked holes are converted into coordinates in the physical world according to the coordinate transformation relationship obtained by calibration; then, the distance change between the centers of adjacent marked holes before and after the forming process is calculated on the computer; finally, the distance change is converted into local deformation.

[0042] Furthermore, the calculation formula of the local shrinkage δ is:

[0043]

[0044] The calculation formula for the angular deformation θ is:

[0045]

[0046] Among them, L b L is the distance between the centers of adjacent marking holes on the upper or lower surface of the sheet before flexible forming. ta L is the distance between the centers of adjacent marking holes on the upper surface of the sheet after flexible forming. ba is the distance between the centers of adjacent marking holes on the lower surface of the sheet after flexible forming, and h is the thickness of the sheet.

[0047] An embodiment of the present invention provides a device for measuring local deformation of a plate after flexible forming, such as Figure 1 As shown, it includes a surface cleaning module 2, a punching module 3, a camera module 4, an illumination module 5, a camera fixture 6, an illumination module fixture 7, a calibration module 8, and a computer 9, wherein:

[0048] The surface cleaning module 2 is used to clean dirt and rust on the surface of the plate 1 before measurement;

[0049] The punching module 3 is used to process a marking hole 10 in the area to be measured on the plate;

[0050] The camera module 4 is used to photograph each marking hole 10 before and after the forming process, and includes a single camera or multiple cameras;

[0051] The illumination module 5 is used to illuminate the surface of the plate, compensate for the natural light, and enhance the distinction between light and dark between the plate surface and the marking hole;

[0052] The camera fixture 6 is used to clamp the camera module 4, and the camera fixture 6 has a total of 6 degrees of freedom of translation and rotation;

[0053] The illumination module fixture 7 is used to clamp the illumination module 5, and the illumination module fixture 7 has a total of 6 degrees of freedom in translation and rotation;

[0054] The calibration module 8 is used to calibrate the camera module 4 to achieve the conversion between the digital image coordinate system and the physical world coordinate system; as long as the camera module and the area to be measured on the board move relative to each other, the calibration module needs to be used for recalibration;

[0055] The computer 9 is used to receive the digital image generated by the camera module 4, and then convert the pixel position of the marking hole into the coordinates of the physical world according to the information provided by the calibration module 8; and further calculate the local deformation according to the change in the distance between adjacent marking holes before and after the forming process.

[0056] Furthermore, the surface cleaning module 2, the punching module 3, the camera module 4, the illumination module 5, the camera fixture 6, the illumination module fixture 7, and the calibration module 8 can be mounted on an industrial robot arm, and the full automatic control of the measurement process can be achieved with the help of communication technology and automation technology.

[0057] Before the forming process, the punching module 3 is used to process the marking hole 10 at the same position on the upper and lower surfaces of the plate 1; after the marking hole is processed, the surface cleaning module 2 is used to grind the area around the marking hole 10. After the grinding is completed, the camera module 4 and the camera fixture 6 are assembled and installed on the surface of the plate 1, and the illumination module 5 and the illumination module fixture 7 are assembled and installed on the surface of the plate 1; the camera fixture 6 is adjusted to ensure that the lens of the camera module 5 and the photographed surface of the plate are basically vertical; the illumination module fixture 7 is adjusted to ensure that the shooting area is well illuminated. The calibration module 8 is placed in the camera module screen, the camera module 5 is adjusted until the picture is clear, and then the calibration is performed according to the Zhang Zhengyou calibration method. After the calibration is completed, the camera module 5 is used to photograph the marking holes 10 in sequence. The digital image is transmitted to the computer 9 to calculate the local deformation of the plate.

[0058] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring local deformation of a sheet material after flexible forming, characterized in that: The steps include: Before flexible forming, array-shaped marking holes are processed on the upper and lower surfaces of the plate, and the marking holes are all non-through holes, and the positions of the marking holes on the upper and lower surfaces correspond; Respectively acquiring images of the upper and lower surfaces of the plate before flexible forming and images of the upper and lower surfaces of the plate after flexible forming; According to the images of the upper and lower surfaces of the sheet before and after flexible forming, the distance change between adjacent marking holes before and after flexible forming is obtained, and then the local shrinkage δ and angular deformation θ of the sheet during flexible forming are obtained.

2. The method for measuring local deformation of a sheet material after flexible forming as claimed in claim 1, characterized in that: The calculation formula of the local shrinkage amount δ is: The calculation formula of the angular deformation θ is: Among them, L b L is the distance between the centers of adjacent marking holes on the upper or lower surface of the sheet before flexible forming. ta L is the distance between the centers of adjacent marking holes on the upper surface of the sheet after flexible forming. ba is the distance between the centers of adjacent marking holes on the lower surface of the sheet after flexible forming, and h is the thickness of the sheet.

3. The method for measuring local deformation of a sheet material after flexible forming as claimed in claim 1, characterized in that: The diameter of the marking hole is 2 mm to 3 mm, and the depth of the marking hole is 0.5% to 1% of the thickness of the plate.

4. The method for measuring local deformation of a sheet material after flexible forming as claimed in claim 1, characterized in that: The maximum distance between the centers of adjacent marking holes shall not exceed 30 mm.

5. The method for measuring local deformation of a sheet material after flexible forming as claimed in claim 1, characterized in that: Use a single camera to take multiple local images of the plate, and then stitch the local images to obtain images of the upper and lower surfaces of the plate; ensure that there are no less than 2 marked holes in the picture each time you take a picture.

6. The method for measuring local deformation of a sheet material after flexible forming as claimed in claim 1, characterized in that: Multiple cameras are used to simultaneously capture local images of the plate, which are then stitched together to obtain images of the upper and lower surfaces of the plate; each shot ensures that there are no less than two marked holes in the image.

7. The method for measuring local deformation of a sheet material after flexible forming according to claim 5 or 6, characterized in that: Before shooting, the camera was calibrated using the Zhang Zhengyou calibration method to obtain the conversion relationship between the world coordinate system and the camera pixel coordinate system; then, based on the images of the upper and lower surfaces of the sheet before and after flexible forming, the distance between adjacent marking holes before and after flexible forming was obtained through this conversion relationship.

8. The method for measuring local deformation of a sheet material after flexible forming according to any one of claims 1 to 6, characterized in that: After machining array-shaped marking holes on the upper and lower surfaces of the plate, the surface of the plate around each marking hole is polished until an obvious bright surface appears.

9. A device for implementing the method for measuring local deformation of a sheet material after flexible forming as claimed in any one of claims 1 to 8, characterized in that: It comprises a punching module (3), a camera module (4), a lighting module (5) and a computer (9), wherein: The punching module (3) is used to process array-shaped marking holes (10) on the upper and lower surfaces of the plate (1); The camera module (4) is mounted on the surface of the plate (1) via a camera fixture (6), and the illumination module (5) is mounted on the surface of the plate (1) via an illumination module fixture (7); the camera module (4) is used to capture images of the upper and lower surfaces of the plate before and after flexible forming, and the illumination module (5) is used to increase the brightness of the captured area of ​​the plate; The computer (9) is used to determine the local shrinkage and angular deformation of the sheet material during flexible forming according to the images of the upper and lower surfaces of the sheet material before and after flexible forming.

10. The device for measuring local deformation of a sheet material after flexible forming as claimed in claim 9, characterized in that: It also comprises a surface cleaning module (2), which is used to grind the surface of the plate around the marking hole.

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