Photoelastic scattering stress measurement and analysis device

Abstract

The utility model belongs to the technical field of glass stress measurement devices, and particularly relates to a photoelastic scattering stress measurement and analysis device which comprises a laser, an adjustable diaphragm mechanism, a polarization mechanism, a photoelastic modulation mechanism, a prism and a shooting mechanism. The imaging means captures a plurality of images of scattered light generated by incidence of the laser light having changed polarization phase difference on the tempered glass at predetermined time intervals, acquires a plurality of images, measures a periodic brightness change in the scattered light using the plurality of images, calculates a phase change in the brightness change, and calculates a phase change in the phase change. And a stress distribution in the depth direction from the surface of the tempered glass and a stress value at each stress layer point of the tempered glass are calculated on the basis of the phase change.

Description

Technical Field

[0001] The utility model belongs to the technical field of glass stress measurement devices, and in particular relates to a photoelastic scattering stress measurement and analysis device. Background Art

[0002] Electronic devices such as mobile phones and smartphones often use glass for their displays and housings. To enhance strength, chemically strengthened glass is used, which is reinforced by forming a surface layer (ion exchange layer) on the glass surface. This surface layer includes at least a compressive stress layer on the glass surface that generates compressive stress due to ion exchange, and may also include a tensile stress layer on the glass interior adjacent to the compressive stress layer that generates tensile stress.

[0003] For example, one technique for measuring stress in the surface layer of tempered glass is to non-destructively measure the compressive stress of the surface layer by utilizing the optical waveguide effect and the photoelastic effect, when the refractive index of the surface layer of the tempered glass is higher than that of the interior (hereinafter referred to as non-destructive measurement technology). In this non-destructive measurement technology, monochromatic light is incident on the surface layer of the tempered glass, generating multiple modes due to the optical waveguide effect. Light with a defined ray path for each mode is extracted, and a convex lens is used to form an image of a bright line corresponding to each mode. Furthermore, the imaged bright line is proportional to the number of modes.

[0004] In recent years, lithium-aluminosilicate-based glass has attracted attention as a glass that is easily ion-exchanged and can increase the surface stress value and deepen the stress layer in a short period of time through a chemical strengthening process.

[0005] The glass is chemically strengthened by immersing it in a hot molten salt mixture of sodium nitrate and potassium nitrate. The concentrations of sodium and potassium ions in the molten salt are both high, so they exchange with the lithium ions in the glass. However, since sodium ions diffuse more easily into the glass, the lithium ions in the glass are first exchanged with the sodium ions in the molten salt.

[0006] Here, the refractive index of the glass decreases when sodium ions are ion-exchanged with lithium ions, and increases when potassium ions are ion-exchanged with lithium ions or sodium ions. In other words, the potassium ion concentration is higher in ion-exchanged regions near the surface of the glass than in non-ion-exchanged regions, while the sodium ion concentration increases in deeper ion-exchanged regions. Therefore, the refractive index decreases with depth near the outermost surface of the ion-exchanged glass, but increases with depth from a certain depth toward the non-ion-exchanged region.

[0007] Furthermore, when aluminosilicate glass or soda glass is air-tempered and then chemically strengthened, the stress distribution and stress values ​​of the chemically strengthened portion can be measured using the surface-guided light stress measurement device described in the background art. However, the refractive index change in the air-tempered portion, which has not been chemically strengthened, is small, making it impossible to measure using the surface-guided light stress measurement device described in the background art. As a result, it is impossible to understand the stress values ​​and stress distribution at each point in the stress layer, making it difficult to develop optimal chemical strengthening conditions or to conduct quality control during manufacturing. Utility Model Content

[0008] The purpose of the utility model is to provide a photoelastic scattering stress measurement and analysis device, aiming to solve one of the technical problems existing in the prior art.

[0009] To achieve the above-mentioned objectives, the present invention provides a device for measuring and analyzing photoelastic scattering stress, comprising:

[0010] A laser, for emitting laser light;

[0011] The prism is placed in optical contact with the surface of the tempered glass to be measured;

[0012] An adjustable aperture mechanism, provided between the laser and the prism, for adjusting the light throughput and beam quality of the laser emitted by the laser;

[0013] a polarization mechanism, provided between the adjustable aperture mechanism and the prism, for modulating the polarization state of the laser;

[0014] a photoelastic modulation mechanism disposed between the polarization mechanism and the prism, configured to change the polarization phase difference of the laser light by one wavelength or more relative to the wavelength of the laser light, so that the laser light having the changed polarization phase difference passes through the prism and is incident obliquely relative to the glass surface into the tempered glass to be measured; and

[0015] The imaging means captures scattered light generated by the laser light with the changed polarization phase difference incident on the tempered glass a plurality of times at predetermined time intervals, thereby acquiring a plurality of images.

[0016] Optionally, an angle between an incident plane of the laser incident on the tempered glass and a surface of the tempered glass is 36°.

[0017] Optionally, the refractive index of the prism is the same as the refractive index of the strengthened glass.

[0018] Optionally, a light source modulator is provided between the adjustable aperture mechanism and the polarization mechanism, and the coherent light source modulator is used to increase the energy of the laser beam, that is, the coherent light source modulator is used to optimize the directionality and parallelism of the laser to increase the energy of the laser.

[0019] Optionally, the adjustable iris mechanism is an adjustable iris.

[0020] Optionally, the polarization mechanism is a Glan-Taylor prism.

[0021] Optionally, the photoelastic modulation mechanism is a photoelastic modulator.

[0022] Optionally, a filter is provided between the shooting mechanism and the prism.

[0023] Optionally, the shooting mechanism is a CCD camera, and the shooting mechanism is arranged at a direction of 45° relative to the surface of the tempered glass.

[0024] Optionally, the prism is a triangular prism.

[0025] Compared with the prior art, the one or more technical solutions in the photoelastic scattering stress measurement and analysis device provided by the embodiment of the present invention have at least one of the following technical effects:

[0026] By arranging a laser, an adjustable aperture mechanism, a coherent light source modulator, a polarization mechanism, a photoelastic modulation mechanism, a prism, a filter and a shooting mechanism, the shooting mechanism shoots scattered light generated by the laser light with a changed polarization phase difference incident on the tempered glass multiple times at a prescribed time interval and obtains multiple images. The periodic brightness changes of the scattered light are measured using the multiple images, the phase changes of the brightness changes are calculated, and the stress distribution of the tempered glass in the depth direction from the surface and the stress values ​​of each point in the stress layer of the tempered glass are calculated based on the phase changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0028] Figure 1 This is a structural schematic diagram of a photoelastic scattering stress measurement and analysis device provided in an embodiment of the present utility model.

[0029] Among them, the reference numerals in the figures are:

[0030] 110. Laser; 120. Adjustable aperture mechanism; 130. Coherent light source modulator; 140. Polarization mechanism; 150. Photoelastic modulation mechanism; 160. Prism; 170. Filter; 180. Shooting mechanism; 190. Strengthened glass; 191. Surface. DETAILED DESCRIPTION

[0031] The following describes in detail embodiments of the present invention, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the embodiments of the present invention, and should not be construed as limiting the present invention.

[0032] In the description of the embodiments of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0034] In the embodiments of the present invention, unless otherwise expressly specified or limited, the terms "installed," "connected," "connected," "fixed," etc. should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, indirect connection through an intermediate medium; internal communication between two components, or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of the present invention based on specific circumstances.

[0035] In this embodiment, referring to Figure 1 , provides a photoelastic scattering stress measurement and analysis device, including a laser 110, a prism 160, an adjustable aperture mechanism 120, a polarization mechanism 140 and a shooting mechanism 180.

[0036] Reference Figure 1The laser 110 is a device capable of emitting laser light L, and is used to emit laser light L. For example, the laser 110 can be a semiconductor laser 110, a helium-neon laser 110, or an argon laser 110. The semiconductor laser 110 generally has polarized light, and semiconductor lasers 110 with wavelengths such as 405 nm, 520 nm, and 630 nm are practically used. The shorter the wavelength of the laser light L, the smaller the beam diameter, and the higher the spatial resolution.

[0037] Reference Figure 1 The prism 160 is placed in optical contact with the surface 191 of the tempered glass 190, which is the object to be measured. The prism 160 has the function of allowing the light from the laser 110 to be incident on the tempered glass 190. In this case, in order for the laser light L to be optically incident on the surface 191 of the tempered glass 190 through the prism 160, the refractive index of the prism 160 needs to be substantially the same as the refractive index of the tempered glass 190 (within ±0.2).

[0038] Reference Figure 1 The adjustable aperture mechanism 120 is disposed between the laser 110 and the prism 160 and is used to adjust the light throughput and beam quality of the laser light L emitted by the laser 110 to improve the quality of the light beam. To improve the depth resolution of the tempered glass 190, the minimum beam diameter of the laser light L is preferably located within the ion exchange layer of the tempered glass 190, with the minimum beam diameter being 20 μm or less. More preferably, the minimum beam diameter of the laser light L is located on the surface 191 of the tempered glass 190. Since the beam diameter of the laser light L determines the depth resolution, it is necessary to set the beam diameter to a value less than the desired depth resolution. Therefore, the adjustable aperture mechanism 120 can change the beam diameter of the laser light L. By adjusting the diameter of the adjustable aperture mechanism 120, the beam diameter of the laser light L emitted by the laser 110 passing through the adjustable aperture mechanism 120 can be adjusted, thereby improving the depth resolution of the tempered glass 190.

[0039] Reference Figure 1 The polarization mechanism 140 is disposed between the adjustable aperture mechanism 120 and the prism 160 and is used to modulate the polarization state of the laser light L. If the laser light L emitted by the laser 110 is not polarized, the polarization mechanism 140 modulates the non-polarized light into a polarized state. Furthermore, the laser 110 and the polarization mechanism 140 are configured so that the polarization plane of the laser light L forms an angle of 45° with respect to the surface 191 of the tempered glass 190.

[0040] Reference Figure 1The photoelastic modulation mechanism 150 is disposed between the polarization mechanism 140 and the prism 160 and is used to shift the polarization phase difference of the laser light L by at least one wavelength relative to the wavelength of the laser light L. The laser light L, after undergoing the shifted polarization phase difference, passes through the prism 160 and is incident obliquely with respect to the glass surface 191 upon entering the tempered glass 190, serving as the object to be measured. Specifically, the laser light L undergoes birefringence due to the photoelastic effect upon passing through the photoelastic modulation mechanism 150, causing a phase shift in the light. The phase shift resulting from the birefringence forms a polarization phase difference. As the laser light L travels through the tempered glass 190, the polarization phase difference also shifts, and this shift in the brightness of the scattered light LS also changes.

[0041] Reference Figure 1 The imaging mechanism 180 captures scattered light LS generated by laser light L, whose polarization phase difference is changed, entering the tempered glass 190 multiple times at predetermined time intervals, thereby acquiring multiple images. Specifically, the imaging mechanism 180 can be connected to a computer. The computer includes a control circuit that controls the imaging mechanism 180 and extracts electrical signals for images from the imaging mechanism 180, a digital image data generation circuit that converts the electrical signals into digital image data, and a digital recording device that records multiple digital image data. Furthermore, the digital image data generation circuit and the digital recording device are electrically connected to the computer. The computer has the function of acquiring image data from the imaging mechanism 180 or the digital image data generation circuit and digital recording device connected to the imaging mechanism 180, and performing image processing and numerical calculations.

[0042] Reference Figure 1 Because strong compressive stress is applied to the surface 191 of the tempered glass 190, the polarization phase difference of the laser light L varies with depth due to birefringence caused by the photoelastic effect. Consequently, the brightness of the scattered light LS of the laser light L also varies with depth. Furthermore, the brightness of the scattered light LS of the laser light L varies according to the internal stress of the tempered glass 190. The photoelastic modulation mechanism 150 enables the polarization phase difference of the laser light L before it enters the tempered glass 190 to be continuously varied over time. The brightness of the scattered light LS varies according to the polarization phase difference caused by the photoelastic modulation mechanism 150.

[0043] Among them, the photoelastic modulation mechanism 150 applies different mechanical forces on an isotropic optical material (such as fused quartz) by using a voltage-driven piezoelectric material (such as piezoelectric ceramics), which changes the birefringence properties of the optical material. When the laser L passes through the photoelastic modulation mechanism 150, the phase difference between the o-light and the e-light passing through the photoelastic modulator can be modulated.

[0044] It is important to note that regardless of the angle of incidence (but not zero), the vibration direction of the e-ray is always parallel to the stress axis, while the vibration direction of the o-ray is always perpendicular to the stress axis. Only when the polarization plane of the incident light is parallel to the stress direction in the glass will the plane polarized light remain unchanged when passing through the glass, and no birefringence will occur.

[0045] The propagation distance of light in glass is called optical path. When the o-light and the e-light propagate in the same stressed glass, the distance difference per unit length is called optical path difference. When parallel light passes through the wafer perpendicular to the optical axis, the birefringence optical path difference Δ is the largest, that is, the direction of the light beam corresponds to the maximum birefringence (n e -n o )max direction. For glass, the direction perpendicular to the optical axis is perpendicular to the principal stress direction of the glass. We stipulate that the Δ value measured perpendicular to the principal stress direction is used to represent the magnitude of stress. The birefringence optical path difference is calculated by the following formula:

[0046] Δ=d(n e -n o )

[0047] Where d is the thickness of the wafer or glass plate. It is generally difficult to directly measure the optical path difference Δ, but the optical path difference is determined by measuring the phase difference δ. The relationship between the optical path difference and phase difference of stress birefringence is:

[0048] Δ=δλ / 2π

[0049] Where λ is the measurement wavelength. Usually the birefringence optical path difference per unit thickness is δ n (stress birefringence nm / cm) is used to express the magnitude of stress, where

[0050] δ n =Δ / d=δλ / (2πd)

[0051] In this way, the phase difference between o-light and e-light passing through the sample to be measured can be used to obtain the optical path difference between the two, and the stress birefringence of the glass can be obtained.

[0052] Furthermore, the angle between the incident plane of the laser light L incident on the tempered glass 190 and the surface 191 of the tempered glass 190 is 36°.

[0053] Furthermore, the refractive index of the prism 160 is the same or almost the same (within ±0.3) as that of the tempered glass 190 , so that the laser light L is incident into the tempered glass 190 through the prism 160 at an optical inclination relative to the glass surface 191 .

[0054] Furthermore, a coherent light source modulator 130 is provided between the adjustable aperture mechanism 120 and the polarization mechanism 140. The coherent light source modulator 130 is used to improve the parallelism of the light beam and change the beam penetration intensity to increase the laser beam energy, thereby facilitating the shooting mechanism 180 to perform high-speed shooting with a shorter exposure time. The coherent light source modulator 130 mainly applies a modulation signal directly to the light source, so that the light source completes light parameter modulation during the light emission process. That is, by directly applying a signal to the light source, the light source's light emission parameters (such as intensity, frequency, phase, etc.) are changed, thereby realizing information loading. This modulation method is suitable for semiconductor lasers 110, and changes in light parameters are achieved by changing current or voltage.

[0055] Furthermore, the polarization mechanism 140 is a Glan-Taylor prism 160, a birefringent polarizing device made of natural calcite crystals, primarily composed of rhombohedral CaCO3 crystals. An unpolarized light beam is input via the laser 110, and after passing through the Glan-Taylor prism 160, a linearly polarized light beam is obtained. Compared to other polarizing plates (such as polarizers), the Glan-Taylor prism 160 has higher transmittance and polarization purity.

[0056] Furthermore, the adjustable iris mechanism 120 is an adjustable iris. The principle of an adjustable iris is based on the control of the amount of light passing through the iris aperture. A larger iris aperture allows more light to pass through; a smaller iris aperture allows less light to pass through. By rotating or sliding the iris blades, the iris aperture can be continuously adjusted, thereby achieving precise control of the amount of light. Therefore, the adjustable iris can adjust the beam diameter of the laser light L emitted by the laser 110 that passes through the adjustable iris, thereby improving the depth resolution of the tempered glass 190.

[0057] Furthermore, the photoelastic modulation mechanism 150 is a photoelastic modulator (PEM), which causes the polarization phase difference of the incident light on the tempered glass 190 to vary over time, with the varying polarization phase difference being at least one time the wavelength λ of the laser light L. The photoelastic modulator (PEM) utilizes a voltage-driven piezoelectric material to exert varying mechanical forces on an isotropic optical material, thereby altering the birefringence of the optical material and modulating the phase difference of the light wave. Through the interaction of optics and elastic forces, the phase difference of the light wave is modulated.

[0058] Furthermore, a filter 170 is provided between the shooting mechanism 180 and the prism 160. The filter 170 can select the wavelength of the laser L. The filter 170 absorbs certain wavelengths, can remove the fluorescence and external light generated by the laser L, and only concentrate the scattered light LS on the shooting mechanism 180.

[0059] Furthermore, the photographing mechanism 180 is a CCD camera, which is a mature existing technology. The photographing mechanism 180 is set at a direction of 45 degrees relative to the surface 191 of the tempered glass 190.

[0060] Furthermore, the prism 160 is a triangular prism 160, which is a transparent object with a triangular cross-section in optical terms. It is an optical instrument made of transparent material with a triangular cross-section and is a type of dispersion prism 160. Light enters from one side of the prism 160 and exits from the other side. The outgoing light is deflected toward the bottom surface (the third side). The magnitude of the deflection angle is related to the refractive index of the prism 160, the vertex angle of the prism 160, and the angle of incidence.

[0061] The rest of this embodiment is the same as that of the first embodiment. The features not explained in this embodiment are all based on the explanations of the first embodiment and will not be described in detail here.

[0062] The above description further details the present invention in conjunction with specific preferred embodiments, and should not be construed as limiting the specific implementation of the present invention to these descriptions. A person skilled in the art of the present invention will appreciate that its architecture is flexible and adaptable, allowing for the development of a series of products without departing from the present invention's concept. Simple deductions or substitutions should be considered within the scope of patent protection for the present invention as defined by the submitted claims.

Claims

1. A photoelastic scattering stress measurement and analysis device, characterized in that: include: A laser (110) for emitting laser light; The prism (160) is placed in optical contact with a surface (191) of a tempered glass (190) serving as a measured object. an adjustable aperture mechanism (120), disposed between the laser (110) and the prism (160), for adjusting the light throughput and beam quality of the laser light emitted by the laser (110); a polarization mechanism (140), disposed between the adjustable aperture mechanism (120) and the prism (160), and configured to modulate the polarization state of the laser light; a photoelastic modulation mechanism (150) disposed between the polarization mechanism (140) and the prism (160) and configured to change the polarization phase difference of the laser light by more than one wavelength relative to the wavelength of the laser light, wherein the laser light after the polarization phase difference is changed passes through the prism (160) and is incident obliquely relative to the glass surface (191) into the tempered glass (190) serving as a measured object; and The imaging mechanism (180) captures scattered light generated by the laser light with the polarization phase difference changed incident on the tempered glass (190) a plurality of times at predetermined time intervals, and acquires a plurality of images.

2. The photoelastic scattering stress measurement and analysis device according to claim 1, characterized in that: The angle between the incident surface of the laser incident on the strengthened glass (190) and the surface (191) of the strengthened glass (190) is 36 degrees.

3. The photoelastic scattering stress measurement and analysis device according to claim 1, characterized in that: The refractive index of the prism (160) is the same as the refractive index of the strengthened glass (190).

4. The photoelastic scattering stress measurement and analysis device according to claim 1, characterized in that: A coherent light source modulator (130) is provided between the adjustable aperture mechanism (120) and the polarization mechanism (140), and the coherent light source modulator (130) is used to increase the energy of the laser beam.

5. The photoelastic scattering stress measurement and analysis device according to claim 1, wherein: The adjustable iris mechanism (120) is an adjustable iris.

6. The photoelastic scattering stress measurement and analysis device according to claim 1, characterized in that: The polarization mechanism (140) is a Glan Taylor prism (160).

7. The photoelastic scattering stress measurement and analysis device according to claim 1, characterized in that: The photoelastic modulation mechanism (150) is a photoelastic modulator.

8. The photoelastic scattering stress measurement and analysis device according to claim 1, characterized in that: A filter (170) is provided between the shooting mechanism (180) and the prism (160).

9. The photoelastic scattering stress measurement and analysis device according to claim 1, characterized in that: The photographing mechanism (180) is a CCD camera, and the photographing mechanism (180) is arranged in a direction of 45 degrees relative to the surface (191) of the tempered glass (190).

10. The photoelastic scattering stress measurement and analysis device according to claim 1, characterized in that: The prism (160) is a triangular prism (160).

Images