Method and device for measuring local deformation of a sheet after flexible forming

Abstract

The present application belongs to the field of plate deformation measurement, and discloses a kind of plate local deformation measurement method and device after flexible forming, which includes the following steps: marking hole array is processed on the upper and lower surfaces of plate, marking hole is non-through hole, and the marking hole position of upper and lower surfaces corresponds;Respectively obtain the images of the upper and lower surfaces of plate before flexible forming;Plate is subjected to flexible forming, and the images of the upper and lower surfaces of plate after flexible forming are obtained respectively;According to the images of the upper and lower surfaces of plate before and after flexible forming, the distance change of adjacent marking holes before and after flexible forming is obtained, and then the local shrinkage and angular deformation of plate flexible forming are obtained.The present application can be applied to the processing scene with high temperature and mechanical contact, realize the non-contact accurate measurement of plate local deformation, with the characteristics of simple device, easy to implement, strong adaptability of working environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of plate deformation measurement, and more particularly, relates to a method and device for measuring local deformation of a plate after flexible forming. BACKGROUND

[0002] Curved plate is an important part widely used in the industries of shipbuilding, automobile, aircraft and construction. Considering the cost of mold manufacturing and the complexity of target curved shape caused by the demand of product individualization, flexible forming processes such as water fire bending or cold-hot integrated forming (such as patent CN107234151A) become the main development direction of curved plate forming processing. The principle of these flexible forming processes is usually to drive the local deformation of the plate by heating or mechanical force or heating-mechanical force coupling load in the local part of the plate, which includes local shrinkage and angular deformation. Effective control of the local deformation of the processed plate is the key to complete the curved shape. Due to the high nonlinearity of the forming process, it is difficult to develop and improve the forming process completely relying on theoretical methods. Therefore, the measurement of the local deformation of the processed plate is a necessary means to study the flexible process.

[0003] Due to the characteristics of flexible forming process (such as high temperature, strong magnetic field and mechanical contact), the traditional contact measurement method (such as strain gauge measurement) may not be applicable or too expensive. In order to effectively track the deformation of the concerned area, the existing non-contact measurement method (such as three-dimensional laser scanning measurement or digital image measurement) usually needs to attach additional marking materials (such as paint) on the surface of the plate, but these materials for marking may disappear after high temperature or mechanical contact, which leads to measurement failure. SUMMARY

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

[0005] To achieve the above-mentioned purpose, according to one aspect of the present application, a method for measuring local deformation of a plate after flexible forming is provided, comprising the following steps:

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

[0007] 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 are obtained respectively;

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

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

[0010]

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

[0012]

[0013] Wherein, L b is the distance between the centers of adjacent marking holes on the upper surface of the flexible forming front plate, L ta is the distance between the centers of adjacent marking holes on the upper surface of the flexible forming rear plate, L ba is the distance between the centers of adjacent marking holes on the lower surface of the flexible forming rear plate, and h is the thickness of the plate.

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

[0015] As a further preferred, the maximum distance between the centers of adjacent marking holes is not more than 30mm.

[0016] As a further preferred, the images of each local part of the plate are captured multiple times by a single camera, and the local images are spliced to obtain the images of the upper and lower surfaces of the plate; at least 2 marking holes are ensured in the frame during each shooting.

[0017] As a further preferred, the images of each local part of the plate are captured simultaneously by multiple cameras, and the local images are spliced to obtain the images of the upper and lower surfaces of the plate; at least 2 marking holes are ensured in the frame during each shooting.

[0018] As a further preferred, 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; and then according to the images of the upper and lower surfaces of the flexible forming front and rear plates, the distance between the adjacent marking holes of the flexible forming front and rear plates is obtained through the conversion relationship.

[0019] As a further preferred, after the 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 a clear bright surface appears.

[0020] According to another aspect of the present application, a device for realizing the local deformation measurement method of the plate after flexible forming is provided, which comprises a punching module, a photographing module, an illumination module and a computer, wherein:

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

[0022] The photographing module is installed on the surface of the plate through a camera clamp, and the light module is installed on the surface of the plate through a light module clamp; the photographing module photographs the images of the upper and lower surfaces of the plate before and after flexible forming, and the light module is used to improve the brightness of the plate shooting area.

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

[0024] As a further preferred, it further comprises a surface cleaning module for polishing the surface of the plate around the marking hole.

[0025] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0026] 1. The present application is aimed at the processing scene of high temperature and mechanical contact during flexible forming. By setting corresponding marking holes on the upper and lower surfaces of the plate, non-contact measurement of local deformation of the plate is realized before and after flexible forming, which is not affected by the processing environment, has the advantages of simplicity, easy implementation and strong adaptability to working environment.

[0027] 2. The method proposed in the present application belongs to non-contact measurement. The measurement process does not need to install 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 relatively low. The measurement process does not need to attach additional marking materials, which avoids the failure of measurement caused by the disappearance of the attached materials. Moreover, the measurement method has high universality and can adapt to the result measurement of different forming methods.

[0028] 3. The local deformation of the plate is usually in the order of 10-100 μm. General measurement methods cannot be used, but local photography measurement can achieve high-precision measurement by using a lens with high enough resolution, and the result is stable. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a structure schematic view of the local deformation measurement device of the plate after flexible forming of the embodiment of the present application.

[0030] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein: 1-plate, 2-surface cleaning module, 3-punching module, 4-photographing module, 5-light module, 6-camera clamp, 7-light module clamp, 8-calibration module, 9-computer, 10-marking hole. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0032] The method for measuring local deformation of a plate after flexible forming provided by the embodiment of the present application comprises the following steps:

[0033] S1, array-shaped mark holes are machined on the upper and lower surfaces of the plate, the mark holes are all non-through holes, and the mark hole positions on the upper and lower surfaces correspond; then the material near each mark hole on the upper and lower surfaces of the plate is polished.

[0034] Specifically, the process of machining the mark holes is as follows: the local deformation distribution area of the plate after forming machining is estimated by using an analytical or numerical calculation method; the plate is placed on the ground or a special platform, and m×n matrix distributed mark holes are machined in the local deformation distribution area; after the plate is turned over, m×n matrix distributed mark holes are machined at the same position; and each mark hole is numbered.

[0035] Further, the diameter of the mark hole is not more than 3 mm, and is preferably 2 mm to 3 mm; the depth of the mark hole is not more than 1% of the thickness of the plate, and is preferably 0.5% to 1%; the design of the diameter and depth of the mark hole can ensure that the influence of material damage on the forming machining process is minimized, and at the same time, it can be completed using a common camera lens without using a special lens.

[0036] Further, the maximum distance between the centers of adjacent mark holes is not more than 30 mm, and is preferably 30 mm; the design of the distance between the centers of adjacent mark holes can reduce the difference in object distance of each mark hole and the lens caused by the bending of the plate, thereby ensuring the measurement accuracy.

[0037] Further, the process of polishing the mark holes is as follows: the material within a radius of at least 10 mm near each mark hole is polished until a clear bright surface appears under naked eye observation; the polishing process uses sandpaper or a special tool, and industrial gauze or industrial wiping paper is used to wipe clean in the same direction after being dipped in a small amount of solution (such as acetone). Thus, the dirt and rust on the surface of the plate are cleaned, and the light and dark areas of the to-be-measured area and the remaining area are distinguished.

[0038] S2, images of the upper and lower surfaces of the plate before flexible forming are respectively acquired; the plate is subjected to flexible forming, and after the forming machining is completed, the material near each mark hole on the upper and lower surfaces of the plate is polished again, and images of the upper and lower surfaces of the plate after flexible forming are respectively acquired.

[0039] Further, before and after flexible forming, when the image is acquired by the camera, the conversion relationship between the world coordinate system and the camera pixel coordinate system is acquired according to the Zhang Zhengyou calibration method. When the image is shot, the camera lens and the surface to be shot are basically perpendicular, the focal length of the lens is adjusted to ensure that the picture is clear, and the picture amplitude of the lens is adjusted to ensure that there are at least two adjacent mark holes in the picture. The shooting of the mark holes in the large area to be measured can be realized by the way of local sequential shooting and splicing of a single camera. The shooting of the mark holes in the large area to be measured can also be realized by the way of simultaneous shooting of different parts and splicing of multiple cameras.

[0040] S3, according to the images of the upper and lower surfaces of the plate before and after flexible forming, the distance change of the adjacent mark holes before and after flexible forming is acquired, and then the local deformation of the plate after flexible forming is obtained, including the local shrinkage and the angular deformation.

[0041] Further, the mark holes in the digital image are automatically identified based on the neural network and other artificial intelligence technologies on the computer to obtain the pixel position of the mark holes, then the pixel position of the mark holes is converted into the coordinates of the physical world according to the coordinate conversion relationship obtained by calibration, then the distance change of the centers of the adjacent mark holes before and after the forming processing is calculated on the computer, and finally the distance change is converted into the local deformation.

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

[0043]

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

[0045]

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

[0047] The local deformation measuring device provided by the embodiment of the application after the flexible forming of the plate, as shown in Figure 1 , comprises a surface cleaning module 2, a punching module 3, a photographing module 4, an illumination module 5, a camera clamp 6, an illumination module clamp 7, a calibration module 8 and a computer 9.

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

[0049] The punching module 3 is used for processing the mark holes 10 on the plate to be measured.

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

[0051] The light module 5 is used for irradiating the surface of the plate, compensating for the natural light, and enhancing the light-dark distinction of the surface of the plate and the mark hole;

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

[0053] The light module clamp 7 is used for clamping the light module 5, and the light module clamp 7 has a total of 6 degrees of freedom of translation and rotation;

[0054] The calibration module 8 is used for calibrating the photographing module 4, so as to realize the conversion between the digital image coordinate system and the physical world coordinate; as long as the photographing module and the region to be measured on the plate move relatively, the calibration module needs to be calibrated again;

[0055] The computer 9 is used for receiving the digital image generated by the photographing module 4, and then converting the pixel position of the mark hole into the coordinate of the physical world according to the information provided by the calibration module 8; and further calculating the local deformation according to the distance change of the adjacent mark holes before and after the forming process.

[0056] Further, the surface cleaning module 2, the punching module 3, the photographing module 4, the light module 5, the camera clamp 6, the light module clamp 7 and the calibration module 8 can be carried on the industrial robot arm, and the full-automatic control of the measurement process is realized by means of the communication technology and the automation technology.

[0057] Before the forming process, the mark hole 10 is processed at the same position on the upper and lower surfaces of the plate 1 by using the punching module 3; after the mark hole is processed, the surface cleaning module 2 is used for polishing around the mark hole 10. After the polishing is completed, the photographing module 4 and the camera clamp 6 are combined and installed on the surface of the plate 1, and the light module 5 and the light module clamp 7 are combined and installed on the surface of the plate 1; the camera clamp 6 is adjusted to ensure that the lens of the photographing module 5 and the surface of the plate to be photographed are basically perpendicular; the light module clamp 7 is adjusted to ensure that the light in the photographed region is sufficient. The calibration module 8 is placed in the photographing module picture, the photographing 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 photographing module 5 is used for photographing the mark hole 10 in sequence. The digital image is transmitted to the computer 9, and the local deformation of the plate is calculated.

[0058] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for measuring local deformation of sheet metal after flexible forming, characterized in that, Includes the following steps: Before flexible forming, array-shaped marking holes are machined on the upper and lower surfaces of the sheet material. All marking holes are non-through holes, and the positions of the marking holes on the upper and lower surfaces correspond. Images of the upper and lower surfaces of the sheet before and after flexible forming were acquired respectively. Based on images of the upper and lower surfaces of the sheet before and after flexible forming, the change in distance between adjacent marked holes before and after flexible forming is obtained, thereby determining the local shrinkage amount of the sheet during flexible forming. δ and angular deformation θ ; The local contraction δ The formula for calculation is: The angular deformation θ The formula for calculation is: in, L b This refers to the distance between the centers of adjacent marked holes on the upper or lower surface of the sheet material before flexible forming. L ta This is the distance between the centers of adjacent marked holes on the upper surface of the sheet after flexible forming. L ba This is the distance between the centers of adjacent marked holes on the lower surface of the sheet after flexible forming. h This refers to the thickness of the sheet material.

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

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

4. The method for measuring local deformation of sheet metal after flexible forming as described in claim 1, characterized in that, Multiple images of different parts of the board are taken using a single camera, and then the images are stitched together to obtain images of the upper and lower surfaces of the board; each time an image is taken, at least two marked holes are ensured to be visible in the frame.

5. The method for measuring local deformation of sheet metal after flexible forming as described in claim 1, characterized in that, Multiple cameras are used to simultaneously capture images of different parts of the board, and then the images are stitched together to obtain images of the upper and lower surfaces of the board; each time an image is captured, at least two marked holes are ensured to be visible in the frame.

6. The method for measuring local deformation of sheet metal after flexible forming as described in claim 4 or 5, characterized in that, Before shooting, the camera was calibrated using the Zhang Zhengyou calibration method to obtain the transformation 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 flexible forming plate before and after the flexible forming, the distance between adjacent marking holes before and after the flexible forming was obtained through this transformation relationship.

7. The method for measuring local deformation of sheet metal after flexible forming as described in any one of claims 1-5, characterized in that, After machining an array of marking holes on the top and bottom surfaces of the board, the board surface around each marking hole is polished until a distinct glossy surface appears.

8. An apparatus for implementing the method for measuring local deformation after flexible forming of sheet metal as described in any one of claims 1-7, characterized in that, It includes a punching module (3), a photographing module (4), a lighting module (5), and a computer (9), wherein: The punching module (3) is used to process an array of marking holes (10) on the upper and lower surfaces of the plate (1). The camera module (4) is mounted on the surface of the board (1) via a camera clamp (6), and the lighting module (5) is mounted on the surface of the board (1) via a lighting module clamp (7); the camera module (4) is used to capture images of the upper and lower surfaces of the board before and after flexible forming, and the lighting module (5) is used to increase the brightness of the area of ​​the board being photographed. The computer (9) is used to determine the local shrinkage and angular deformation of the flexible forming of the sheet material based on the images of the upper and lower surfaces of the sheet material before and after flexible forming.

9. The apparatus as claimed in claim 8, characterized in that, It also includes a surface cleaning module (2) for polishing the plate surface around the marking holes.

Images