A method for imaging measurement of the stress birefringence surface of large-diameter flat glass

Abstract

The present invention discloses a method for imaging measurement of the stress birefringence surface of large-caliber flat glass, belonging to the technical field of optical measurement, and aiming to solve the technical problem of low measurement efficiency of glass stress birefringence in the prior art. The method includes: moving the sample to be measured and a quarter-wave plate out of the measurement optical path, rotating the polarizer to find the extinction position and rotating the polarizer by N angles near the extinction position to obtain angles; keeping the polarizer and the analyzer unchanged, moving the quarter-wave plate into the measurement optical path, and rotating the quarter-wave plate to find the extinction position; rotating the polarizer by N angles near the extinction position to obtain angles; keeping the position and direction of the quarter-wave plate and the analyzer unchanged, moving the sample to be measured into the measurement optical path between the polarizer and the quarter-wave plate; rotating the polarizer through a polarizer rotation mechanism, when the angles between the polarizer and the x-axis of the reference coordinate system are 0°, 60°, and 120° respectively, obtaining the light intensities of three images through a CCD camera, and obtaining the stress birefringence of the sample to be measured according to the three light intensities.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement, relates to the measurement of large-aperture flat glass, and particularly relates to a method for imaging measurement of the stress birefringence surface of large-aperture flat glass. Background Art

[0002] During the annealing and cooling process, there is a temperature gradient in the thickness direction of the flat glass, which will generate central stress. Along the thickness direction, the magnitudes of the central stresses at different positions of the flat glass are different, but the directions are parallel to the glass surface, and it shows compressive stress on the glass surface and tensile stress inside the glass. Due to the existence of stress, the internal structure of the glass changes into an anisotropic body, and double refraction occurs when light passes through the glass. Therefore, the stress condition of the glass can be measured by measuring the stress birefringence of the glass.

[0003] The invention patent application with the application number 202410028352.1 discloses a high-precision birefringence phase difference measurement device with a wide spectrum and a large range, which includes: an LED light source with adjustable output wavelength, a converging lens, a polarizer, an achromatic 1 / 4 wave plate, an imaging lens, a detector, an electric rotating table, and a control unit; by using the LED light source with adjustable output wavelength in combination with the achromatic 1 / 4 wave plate, it can be measured within a wide spectral range; by adjusting the relative angles of the fast and slow axes of the achromatic 1 / 4 wave plate with the polarization direction of the linear polarizer and the fast and slow axes of the sample to be measured, as well as the angles of each polarization device rotating around the light transmission axis, the working mode can be switched between the circular polarization mode, the dark field / bright field mode, and the compensation mode, and the corresponding algorithms for the 3 measurement modes are given. By switching the 3 modes, large-range and high-precision measurement can be achieved.

[0004] The invention patent application with the application number 202411081547.9 also discloses an optical glass stress testing device and a digital testing method. The testing device includes a light source, a diffusing filter, a polarizer, a quarter-wave plate, an analyzer, a circular grating, a CCD imaging catcher, a glass strip to be tested, and a host computer. The light source, the diffusing filter, the polarizer, the quarter-wave plate, the analyzer, the circular grating, and the CCD imaging catcher are arranged at intervals in sequence along the horizontal direction; the circular grating and the analyzer are configured to rotate synchronously along the axial direction, and the minimum rotation angle of the circular grating is less than the minimum rotation angle of the analyzer; the glass strip to be tested is arranged between the polarizer and the quarter-wave plate, and the host computer is used to calculate the stress of the glass strip to be tested based on the rotation angle of the circular grating and the image obtained by the CCD imaging catcher. The measuring method includes: arranging the glass strip to be tested between the polarizer and the quarter-wave plate, and using the CCD imaging catcher to obtain an image of the glass strip to be tested; based on the light-transmitting width and light-transmitting thickness of the glass strip to be tested, using computer testing software to generate a virtual straight strip mark on the image of the glass strip to be tested; using the light source to emit light to the light-transmitting surface of the glass strip to be tested to form a test optical path, forming polarized light through the diffusing filter and the polarizer, using the CCD imaging catcher to obtain the image information of the light-transmitting dark band on the glass strip to be tested, and generating the light-transmitting dark band and feeding it back to the image of the glass strip to be tested; synchronously rotating the analyzer and the circular grating, and synchronously sampling through the CCD imaging catcher until the light-transmitting dark band coincides with the virtual straight strip mark, and using the host computer to calculate the stress data of the glass strip to be tested based on the rotation angle of the circular grating.

[0005] Similar to the above-mentioned invention patent application, in the prior art when performing stress birefringence measurement, not only the polarizer needs to be rotated, but also the quarter-wave plate and / or the analyzer need to be rotated simultaneously. The rotation mechanism has high requirements, and at the same time, a phase-shifting step is required, which greatly reduces the measurement efficiency. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for imaging measurement of the stress birefringence surface of large-caliber flat glass in order to solve the technical problem of low measurement efficiency of glass stress birefringence in the prior art.

[0007] In order to achieve the above purpose, the present invention specifically adopts the following technical solutions:

[0008] A method for imaging measurement of the stress birefringence surface of large-caliber flat glass, the measurement optical path includes a parallel light source, a polarizer, a quarter-wave plate, an analyzer, an imaging lens, and a CCD camera arranged in sequence; the polarizer is installed on a polarizer rotation mechanism, the quarter-wave plate is installed on a wave plate rotation and displacement mechanism, and the sample to be tested is installed between the polarizer and the quarter-wave plate through a horizontal displacement mechanism; the measurement steps are specifically as follows:

[0009] Step 1: Move the sample to be measured and the quarter-wave plate out of the measurement optical path. Keep the direction of the analyzer unchanged. Rotate the polarizer counterclockwise through the polarizer rotation mechanism to find the extinction position.

[0010] Near the extinction position, rotate the polarizer through the polarizer rotation mechanism by N angles, and obtain the angle through the least-squares fitting function. ;

[0011] Step 2: Keep the polarizer and the analyzer in an orthogonal state and with unchanged directions. Move the quarter-wave plate into the measurement optical path between the polarizer and the analyzer. Rotate the quarter-wave plate counterclockwise through the wave plate rotation and displacement mechanism to find the extinction position.

[0012] Near the extinction position, rotate the polarizer through the polarizer rotation mechanism by N angles, and obtain the angle through the least-squares fitting function. ;

[0013] Step 3: Keep the position and direction of the quarter-wave plate and the analyzer unchanged. Move the sample to be measured into the measurement optical path between the polarizer and the quarter-wave plate.

[0014] Rotate the polarizer through the polarizer rotation mechanism. When the angles between the polarizer and the x-axis of the reference coordinate system are 0°, 60°, and 120° respectively, obtain the light intensities of three images through the CCD camera. , , , and obtain the stress birefringence of the sample to be measured according to the light intensities , , .

[0015] Step 4: Move the sample to be measured and repeat Step 3 to measure the stress birefringence distribution at different positions of the sample to be measured.

[0016] Furthermore, in Step 1, when obtaining the angle through the least-squares fitting function, the calculation formula is:

[0017] ;

[0018] where represents the light intensity signal measured by the CCD camera, represents the initial light intensity of the light source, represents the rotation angle of the polarizer.

[0019] Furthermore, in Step 2, when obtaining the angle through the least-squares fitting function, the calculation formula is:

[0020] ;

[0021] Among them, represents the light intensity signal measured by the CCD camera, represents the initial light intensity of the light source, represents the angle of rotation of the quarter-wave plate.

[0022] Furthermore, in step 3, when obtaining the stress birefringence of, and of the sample to be measured according to the light intensity, the specific algorithm is as follows:

[0023] ;

[0024] ;

[0025] Among them, represents the wavelength, , , represent the light intensity signals incident on the CCD camera at 0°, 60°, and 120° respectively when the polarizer is rotated, represents the birefringence phase difference.

[0026] Furthermore, it also includes a gantry dual-drive platform. The gantry dual-drive platform includes a base. A left vertical guide rail and a right vertical guide rail are respectively arranged on the left side and the right side of the base. A left mounting seat and a right mounting seat are respectively arranged on the left vertical guide rail and the right vertical guide rail. A parallel light source and a polarizer are mounted on the left mounting seat, and a quarter-wave plate, an analyzer, an imaging lens, and a CCD camera are mounted on the right mounting seat; the sample to be measured is arranged between the left mounting seat and the right mounting seat through a horizontal displacement mechanism.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. In the present invention, an innovative stress measurement method of three-step rotation phase shift of the polarizer is adopted. While ensuring the phase shift accuracy, only the polarizer needs to be rotated, without the need to rotate the quarter-wave plate and the analyzer simultaneously. This greatly reduces the configuration requirements and control requirements for the rotation mechanism, reduces the phase shift steps, and effectively improves the measurement efficiency of glass stress birefringence.

[0029] 2. In the present invention, in order to realize the positioning of the polarization direction of the polarizer and the fast axis direction of the quarter-wave plate, a least-squares fitting method is proposed, which improves the positioning accuracy of the polarization direction of the polarizer and the fast axis direction of the quarter-wave plate, realizes rapid positioning, and improves the measurement efficiency.

[0030] 3. In the present invention, for the splicing detection of large-diameter components, a gantry dual-drive structure is proposed to realize the vertical movement of the detection system and the horizontal movement of the component to be measured. This solution ensures the structural stability while significantly improving the system's load-bearing capacity, enabling the stress birefringence test of large-scale and heavy samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic structural diagram of the measurement system of the present invention;

[0032] Figure 2 is a schematic diagram of the measurement principle of the present invention; wherein, x and y in the coordinate diagrams below each component represent the horizontal and vertical coordinates respectively;

[0033] Figure 3 is a schematic structural diagram of the gantry dual-drive platform in the present invention for driving the measurement system to move up and down;

[0034] Figure 4 is a schematic diagram of the present invention for achieving full coverage measurement of the sample to be measured by moving the measurement system and the sample to be measured. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention.

[0036] Therefore, based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0037] Embodiment 1

[0038] This embodiment provides a stress birefringence surface imaging measurement system for large-diameter flat glass, as Figure 3 shown. It includes a gantry dual-drive platform, which includes a base. On the left and right sides of the base, a left vertical guide rail and a right vertical guide rail are respectively provided. On the left vertical guide rail and the right vertical guide rail, a left mounting seat and a right mounting seat are respectively provided. The left mounting seat and the right mounting seat can move up and down along the height directions of the left vertical guide rail and the right vertical guide rail respectively. A parallel light source and a polarizer are installed on the left mounting seat, and a quarter-wave plate, an analyzer, an imaging lens, and a CCD camera are installed on the right mounting seat; the sample to be measured is arranged between the left mounting seat and the right mounting seat through a horizontal displacement mechanism.

[0039] Furthermore, the polarizer is mounted on the left mounting base through a polarizer rotation mechanism, and the polarizer can be driven to rotate by the polarizer rotation mechanism. The quarter-wave plate is mounted on the right mounting base through a wave plate rotation and displacement mechanism, and the quarter-wave plate can be driven to rotate and move by the wave plate rotation and displacement mechanism. The sample to be measured is mounted on the base through a horizontal displacement mechanism, and the sample to be measured is driven to move by the horizontal displacement mechanism. Under the combined action of the up-and-down movement of the mounting base and the horizontal movement of the sample to be measured, full-coverage measurement of the sample to be measured is achieved, as Figure 4 shown.

[0040] As Figure 1 shown, the measurement optical path of this measurement system is as follows:

[0041] The parallel light source emits parallel light beams, and the parallel light beams are imaged onto the CCD camera after passing through the polarizer, the sample to be measured, the quarter-wave plate, the analyzer, and the imaging lens in sequence.

[0042] Embodiment 2

[0043] This embodiment provides a method for imaging and measuring the stress birefringence surface of large-aperture flat glass. This measurement method uses the Figure 1 measurement optical path of the measurement system shown.

[0044] When using this measurement system for measurement, the specific measurement steps are as follows:

[0045] Step 1: Move the sample to be measured and the quarter-wave plate out of the measurement optical path, keep the direction of the analyzer unchanged, and rotate the polarizer counterclockwise through the polarizer rotation mechanism to find the extinction position;

[0046] Near the extinction position, rotate the polarizer through the polarizer rotation mechanism by N angles, and obtain the angle through the least-squares fitting function; the angle The calculation formula is:

[0047] (1);

[0048] where represents the light intensity signal measured by the CCD camera, represents the initial light intensity of the light source, represents the rotation angle of the polarizer.

[0049] Step 2: Keep the polarizer and the analyzer in an orthogonal state and the direction unchanged, move the quarter-wave plate into the measurement optical path between the polarizer and the analyzer, and rotate the quarter-wave plate counterclockwise through the wave plate rotation and displacement mechanism to find the extinction position;

[0050] Near the extinction position, rotate the polarizer through the polarizer rotation mechanism by N angles, and obtain the angle through the least-squares fitting function; the angle The calculation formula is:

[0051] (2);

[0052] Wherein, represents the light intensity signal measured by the CCD camera, represents the initial light intensity of the light source, represents the rotation angle of the quarter-wave plate.

[0053] Step 3: Keep the positions and directions of the quarter-wave plate and the analyzer unchanged, and move the sample to be measured into the measurement optical path between the polarizer and the quarter-wave plate;

[0054] Rotate the polarizer through the polarizer rotation mechanism. When the angles between the polarizer and the x-axis of the reference coordinate system are 0°, 60°, and 120° respectively, three images of light intensity are obtained through the CCD camera , , , and according to the light intensity , , the stress birefringence of the sample to be measured is obtained ; The stress birefringence The specific algorithm is:

[0055] (3);

[0056] (4);

[0057] Wherein, represents the wavelength, , , represent the light intensity signals incident on the CCD camera at 0°, 60°, and 120° respectively when the polarizer is rotated, represents the birefringence phase difference.

[0058] Step 4: Move the sample to be measured, repeat Step 3, and measure the stress birefringence distribution at different positions of the sample to be measured.

[0059] As Figure 2 shown, the measurement principle of this method is:

[0060] Based on the polarization light measurement principle of the Senarmont method (also known as the single quarter-wave plate method), linearly polarized light passes through the sample to be measured, the quarter-wave plate, and the analyzer and then is imaged and observed by the CCD camera. The measurement optical path is as Figure 2 shown. In the Figure 2 shown optical path, the angle between the polarizer P and the x-axis of the reference coordinate system is , the angle between the analyzer A and the x-axis of the reference coordinate system is , the angle between the fast axis F of the quarter-wave plate and the x-axis of the reference coordinate system is , the birefringence phase difference introduced by the sample to be measured is δ, and the principal stress direction of the sample to be measured makes an angle θ with the x-axis of the reference coordinate system. When the fast axis F of the quarter-wave plate and the analyzer direction are kept at 45°, the polarizer is rotated so that the angles between the polarizer direction and the x-axis of the reference coordinate system are 0°, 60° and 120° respectively, and the three light intensity signals obtained by the detector are respectively , , . Finally, the stress birefringence of the sample to be measured is calculated by formulas (3) and (4).

Claims

1. A method for measuring the stress birefringence surface imaging of large-diameter flat glass, characterized in that: The measuring optical path includes a parallel light source, a polarizer, a quarter wave plate, an analyzer, an imaging lens and a CCD camera arranged in sequence; the polarizer is installed on the polarization rotation mechanism, the quarter wave plate is installed on the wave plate rotation and displacement mechanism, and the sample to be measured is installed between the polarizer and the quarter wave plate through the horizontal displacement mechanism; the measuring steps are as follows: Step 1, move the sample to be tested and the 1 / 4 wave plate out of the measuring light path, keep the direction of the polarizer unchanged, and rotate the polarizer counterclockwise through the polarization rotation mechanism to find the extinction position; The polarizer is rotated by N angles near the extinction position through the polarization rotation mechanism, and the angle is obtained through the least squares fitting function. ; Step 2, keeping the polarizer and the analyzer in an orthogonal state and in an unchanged direction, move the 1 / 4 wave plate into the measuring optical path between the polarizer and the analyzer, and rotate the 1 / 4 wave plate counterclockwise through the wave plate rotation and displacement mechanism to find the extinction position; The polarizer is rotated N angles by the polarization rotation mechanism near the extinction position, and the angle is obtained by the least squares fitting function. ; Step 3, keeping the position and direction of the 1 / 4 wave plate and the analyzer unchanged, move the sample to be measured into the measurement light path between the polarizer and the 1 / 4 wave plate; The polarizer is rotated by the polarizing rotating mechanism. When the angles between the polarizer and the x-axis of the reference coordinate system are 0°, 60°, and 120° respectively, the light intensity of three images is obtained by the CCD camera. , , , and according to the light intensity , , Obtaining the stress birefringence of the sample to be tested; Step 4, move the sample to be tested, repeat step 3, and measure the stress birefringence distribution at different positions of the sample to be tested.

2. A method for measuring stress birefringence surface imaging of large-diameter flat glass according to claim 1, characterized in that: In step 1, the angle is obtained by the least squares fitting function When , the calculation formula is: ； in, Represents the light intensity signal measured by the CCD camera, represents the initial light intensity of the light source, Indicates the rotation angle of the polarizer.

3. A method for measuring stress birefringence surface imaging of large-diameter flat glass as claimed in claim 1, characterized in that: In step 2, the angle is obtained by the least squares fitting function. When , the calculation formula is: ； in, Represents the light intensity signal measured by the CCD camera, represents the initial light intensity of the light source, Indicates the angle of rotation of the quarter wave plate.

4. A method for measuring stress birefringence surface imaging of large-diameter flat glass as claimed in claim 1, characterized in that: In step 3, according to the light intensity , , Get the stress birefringence of the sample to be tested The specific algorithm is: ； ； in, represents the wavelength, , , It represents the light intensity signal incident on the CCD camera at 0°, 60°, and 120° when the polarizer is rotated. Represents the birefringence phase difference.

5. A method for measuring stress birefringence surface imaging of large-diameter flat glass as claimed in claim 1, characterized in that: It also includes a gantry dual-drive platform, which includes a base. A left vertical guide rail and a right vertical guide rail are respectively arranged on the left and right sides of the base. A left mounting seat and a right mounting seat are respectively arranged on the left vertical guide rail and the right vertical guide rail. A parallel light source and a polarizer are mounted on the left mounting seat, and a 1 / 4 wave plate, an analyzer, an imaging lens and a CCD camera are mounted on the right mounting seat; a sample to be tested is arranged between the left mounting seat and the right mounting seat through a horizontal displacement mechanism.

Images